289 results on '"Weiskittel, Aaron R."'
Search Results
2. Quantifying and correcting geolocation error in spaceborne LiDAR forest canopy observations using high spatial accuracy ALS: A Bayesian model approach
- Author
-
Shannon, Elliot S., Finley, Andrew O., Hayes, Daniel J., Noralez, Sylvia N., Weiskittel, Aaron R., Cook, Bruce D., and Babcock, Chad
- Subjects
Statistics - Applications - Abstract
Geolocation error in spaceborne sampling light detection and ranging (LiDAR) measurements of forest structure can compromise forest attribute estimates and degrade integration with georeferenced field measurements or other remotely sensed data. Data integration is especially problematic when geolocation error is not well quantified. We propose a general model that uses airborne laser scanning (ALS) data to quantify and correct geolocation error in spaceborne sampling LiDAR. To illustrate the model, LiDAR data from NASA Goddard's LiDAR Hyperspectral & Thermal Imager (G-LiHT) was used with a subset of LiDAR data from NASA's Global Ecosystem Dynamics Investigation (GEDI). The model accommodates multiple canopy height metrics derived from a simulated GEDI footprint kernel using spatially coincident G-LiHT, and incorporates both additive and multiplicative mapping between the canopy height metrics generated from both datasets. A Bayesian implementation provides probabilistic uncertainty quantification in both parameter and geolocation error estimates. Results show a systematic geolocation error of 9.62 m in the southwest direction. In addition, estimated geolocation errors within GEDI footprints were highly variable, with results showing a ~0.45 probability the true footprint center is within 20 m. Estimating and correcting geolocation error via the model outlined here can help inform subsequent efforts to integrate spaceborne LiDAR data, like GEDI, with other georeferenced data.
- Published
- 2022
3. Tree-level responses to commercial thinning in spruce-fir forests across northern Maine, USA
- Author
-
Wagle, Bishnu Hari, Weiskittel, Aaron R., Berrill, John-Pascal, Kizha, Anil R., D'Amato, Anthony W., and Marshall, David
- Published
- 2023
- Full Text
- View/download PDF
4. Tree quality and value: results in northern conifer stands after 65 years of silviculture and harvest
- Author
-
Granstrom, Maren, Crandall, Mindy S., Kenefic, Laura S., and Weiskittel, Aaron R.
- Subjects
Logging -- Environmental aspects -- Forecasts and trends -- Methods ,Conifers -- Environmental aspects -- Forecasts and trends ,Arboriculture -- Methods -- Forecasts and trends -- Environmental aspects ,Market trend/market analysis ,Earth sciences - Abstract
Despite the importance of financial outcomes to stand-level forest management decision-making, long-term assessments are rare. We compared the quality and value of mixed, northern conifer (Picea-Abies-Tsuga) stands in Maine, USA, treated with a range of silvicultural systems and exploitive cuttings for 65 years. Ten replicated treatments--single-tree selection and uniform shelterwood systems, commercial clearcutting, fixed and guiding diameter-limit cutting, and no cutting--were assessed for quality and value of standing and harvested trees. Selection systems resulted in good tree quality and high stand value, particularly when applied on a short cutting cycle, but small harvest volumes were not always commercially operable. Shelterwood system resulted in good tree quality, but changes in species values over time influenced financial outcomes. In contrast, commercial clearcutting and fixed diameter-limit cutting resulted in poor tree quality and low residual stand value after multiple harvests. Guiding diameter-limit cutting resulted in high stand value and is more appropriately characterized as a silvicultural system than exploitive harvesting when applied with harvest volume limits and seed tree retention. Overall, treatments focused on short-term financial gain led to degraded stand conditions, while those that sought to grow high-quality trees resulted in desirable outcomes over the long term. Key words: spruce-fir, shelterwood, selection cutting, exploitation, forest management. Malgre l'importance des resultats financiers resultant des prises de decisions en gestion forestiere des peuplements, les evaluations a long terme sont rares. Nous avons compare la qualite et la valeur de coniferes septentrionaux sur pied mixtes (Picea-Abies-Tsuga) dans le Maine, aux Etats-Unis, traites avec un eventail de systemes sylvicoles et de coupes d'exploitation durant 65 annees. Dix traitements reproduits--systemes de coupe progressive uniforme et de jardinage d'arbres individuels, coupes a blanc commerciales, coupes de diametre limite fixes et generales et absence de coupes--ont ete evalues en fonction de la qualite et de la valeur des arbres sur pied et des arbres recoltes. Les systemes de selection ont eu comme resultat une bonne qualite d'arbres et une valeur elevee des arbres sur pied, particulierement lorsqu'ils etaient appliques a un cycle court de coupes, mais les volumes reduits de recoltes n'etaient pas toujours exploitables sur le plan commercial. Le systeme de coupe progressive a eu comme resultat une bonne qualite d'arbres, mais les changements dans les valeurs des especes au fil du temps ont influence les resultats financiers. Par contre, la coupe a blanc commerciale et la coupe limitee a un diametre fixe ont eu comme resultat une mauvaise qualite d'arbres et une faible valeur residuelle des arbres sur pied apres de nombreuses recoltes. La coupe de diametre limite generale a eu comme resultat une valeur elevee des arbres sur pied et elle est caracterisee de maniere plus appropriee comme un systeme sylvicole plutot qu'une recolte d'exploitation lorsqu'elle est appliquee avec des limites du volume des recoltes et une sauvegarde des semenciers. Dans l'ensemble, les traitements axes sur les gains financiers a court terme ont entraine des conditions de degradation des arbres sur pied alors que ceux qui visaient a accroitre une qualite elevee des arbres ont mene a des resultats souhaitables a long terme. [Traduit par la Redaction] Mots-cles: epinette-sapin, coupe progressive, coupe de jardinage, exploitation, gestion forestiere., Introduction Forest landowners and managers make decisions about whether and how to manage forests based on a number of short- and long-term considerations. For commercial landowners, return on investment or [...]
- Published
- 2022
- Full Text
- View/download PDF
5. A national-scale tree volume, biomass, and carbon modeling system for the United States
- Author
-
Westfall, James A., primary, Coulston, John W., additional, Gray, Andrew N., additional, Shaw, John D., additional, Radtke, Philip J., additional, Walker, David M., additional, Weiskittel, Aaron R., additional, MacFarlane, David W., additional, Affleck, David L.R., additional, Zhao, Dehai, additional, Temesgen, Hailemariam, additional, Poudel, Krishna P., additional, Frank, Jereme M., additional, Prisley, Stephen P., additional, Wang, Yingfang, additional, Meador, Andrew J. Sánchez, additional, Auty, David, additional, and Domke, Grant M., additional
- Published
- 2023
- Full Text
- View/download PDF
6. Quantifying and correcting geolocation error in spaceborne LiDAR forest canopy observations using high spatial accuracy data: A Bayesian model approach
- Author
-
Shannon, Elliot S., primary, Finley, Andrew O., additional, Hayes, Daniel J., additional, Noralez, Sylvia N., additional, Weiskittel, Aaron R., additional, Cook, Bruce D., additional, and Babcock, Chad, additional
- Published
- 2024
- Full Text
- View/download PDF
7. Dynamic spatial regression models for space-varying forest stand tables
- Author
-
Finley, Andrew O., Banerjee, Sudipto, Weiskittel, Aaron R., Babcock, Chad, and Cook, Bruce D.
- Subjects
Statistics - Applications - Abstract
Many forest management planning decisions are based on information about the number of trees by species and diameter per unit area. This information is commonly summarized in a stand table, where a stand is defined as a group of forest trees of sufficiently uniform species composition, age, condition, or productivity to be considered a homogeneous unit for planning purposes. Typically information used to construct stand tables is gleaned from observed subsets of the forest selected using a probability-based sampling design. Such sampling campaigns are expensive and hence only a small number of sample units are typically observed. This data paucity means that stand tables can only be estimated for relatively large areal units. Contemporary forest management planning and spatially explicit ecosystem models require stand table input at higher spatial resolution than can be affordably provided using traditional approaches. We propose a dynamic multivariate Poisson spatial regression model that accommodates both spatial correlation between observed diameter distributions and also correlation between tree counts across diameter classes within each location. To improve fit and prediction at unobserved locations, diameter specific intensities can be estimated using auxiliary data such as management history or remotely sensed information. The proposed model is used to analyze a diverse forest inventory dataset collected on the United States Forest Service Penobscot Experimental Forest in Bradley, Maine. Results demonstrate that explicitly modeling the residual spatial structure via a multivariate Gaussian process and incorporating information about forest structure from LiDAR covariates improve model fit and can provide high spatial resolution stand table maps with associated estimates of uncertainty.
- Published
- 2014
8. Linking annual tree growth with eddy-flux measures of net ecosystem productivity across twenty years of observation in a mixed conifer forest
- Author
-
Teets, Aaron, Fraver, Shawn, Hollinger, David Y., Weiskittel, Aaron R., Seymour, Robert S., and Richardson, Andrew D.
- Published
- 2018
- Full Text
- View/download PDF
9. Hierarchical Bayesian models for small area estimation of forest variables using LiDAR
- Author
-
Ver Planck, Neil R., Finley, Andrew O., Kershaw, John A., Jr., Weiskittel, Aaron R., and Kress, Megan C.
- Published
- 2018
- Full Text
- View/download PDF
10. Psychological distance of timber harvesting for private woodland owners
- Author
-
Huff, Emily S., Leahy, Jessica E., Kittredge, David B., Noblet, Caroline L., and Weiskittel, Aaron R.
- Published
- 2017
- Full Text
- View/download PDF
11. An imputation/copula-based stochastic individual tree growth model for mixed species Acadian forests: a case study using the Nova Scotia permanent sample plot network
- Author
-
Kershaw, Jr, John A., Weiskittel, Aaron R., Lavigne, Michael B., and McGarrigle, Elizabeth
- Published
- 2017
- Full Text
- View/download PDF
12. Climate and Socioeconomic Impacts on Maine's Forests Under Alternative Future Pathways
- Author
-
Zhao, Jianheng, primary, Daigneault, Adam, additional, Weiskittel, Aaron R., additional, and Wei, Xinyuan, additional
- Published
- 2023
- Full Text
- View/download PDF
13. Identifying Factors Affecting Regional Patterns of Sugar Maple Regeneration in Northern New England and New York
- Author
-
Rogers, Nicole, primary, D'Amato, Anthony W., additional, Weiskittel, Aaron R., additional, and Kenefic, Laura, additional
- Published
- 2023
- Full Text
- View/download PDF
14. Whoa on the Wobble! Stem Sinuosity in Juvenile Douglas-Fir Across Levels of Genetic Gain, Silvicultural Treatments, Site Conditions, and Climatic Variables in the Pacific Northwest
- Author
-
Premer, Michael, primary, Turnblom, Eric, additional, and Weiskittel, Aaron R., additional
- Published
- 2023
- Full Text
- View/download PDF
15. Forest Growth and Yield Models for Intensively Managed Plantations
- Author
-
Weiskittel, Aaron R., von Gadow, Klaus, Series editor, Pukkala, Timo, Series editor, Tomé, Margarida, Series editor, Borges, José G., editor, Diaz-Balteiro, Luis, editor, McDill, Marc E., editor, and Rodriguez, Luiz C.E., editor
- Published
- 2014
- Full Text
- View/download PDF
16. Maine woodland owner perceptions of long rotation woody biomass harvesting and bioenergy
- Author
-
Silver, Emily J., Leahy, Jessica E., Noblet, Caroline L., and Weiskittel, Aaron R.
- Published
- 2015
- Full Text
- View/download PDF
17. Long-term influence of commercial thinning on stand structure and yield with/without pre-commercial thinning of spruce-fir in northern Maine, USA
- Author
-
Wagle, Bishnu Hari, primary, Weiskittel, Aaron R., additional, Kizha, Anil R., additional, Berrill, John-Pascal, additional, D'Amato, Anthony W., additional, and Marshall, David, additional
- Published
- 2022
- Full Text
- View/download PDF
18. Influence of browsing damage and overstory cover on regeneration of American beech and sugar maple nine years following understory herbicide release in central Maine
- Author
-
Bose, Arun K., Wagner, Robert G., Roth, Brian E., and Weiskittel, Aaron R.
- Published
- 2017
- Full Text
- View/download PDF
19. Long-term influence of alternative forest management treatments on total ecosystem and wood product carbon storage
- Author
-
Puhlick, Joshua J., Weiskittel, Aaron R., Fernandez, Ivan J., Fraver, Shawn, Kenefic, Laura S., Seymour, Robert S., Kolka, Randall K., Rustad, Lindsey E., and Brissette, John C.
- Subjects
Carbon sequestration -- Methods ,Forest products -- Environmental aspects ,Forest management -- Methods ,Earth sciences - Abstract
Developing strategies for reducing atmospheric C[O.sub.2] is one of the foremost challenges facing natural resource professionals today. The goal of this study was to evaluate total ecosystem and harvested wood product carbon (C) stocks among alternative forest management treatments (selection cutting, shelterwood cutting, commercial clearcutting, and no management) in mixed-species stands in central Maine, USA. These treatments were initiated in the 1950s and have been maintained since, and ecosystem C pools were measured in 2012. When compared across managed treatments, the commercial clearcut had the lowest total ecosystem C stocks by 21%, on average (P < 0.05), while the selection and shelterwood treatments had similar total ecosystem C stocks. Including the C stored in harvested wood products did not influence observed differences in C storage among treatments. Total ecosystem C stocks in the reference stand were 247.0 ± 17.7 Mg x [ha.sup.-1] (mean ± SD) compared with 161.7 ± 31.3 Mg x [ha.sup.-1] in the managed stands (171.2 ± 31.7 Mg*[ha.sup.-1] with products C). This study highlights the impacts of long-term forest management treatments on C storage and indicates that the timing of harvests and the species and sizes of trees removed influence C stored in harvested wood products. Key words: carbon stocks, forest products, forest soils, coarse fragments, site quality. Le developpement de strategies visant a reduire le C[O.sub.2] atmospherique est un des principaux defis que doivent relever aujourd'hui les professionnels des ressources naturelles. Le but de cette etude consistait a estimer les stocks totaux de carbone (C) emmagasines dans l'ecosysteme et les produits forestiers recoltes dans des peuplements mixtes soumis a differents traitements d'amenagement forestier (coupe de jardinage, coupe progressive, coupe a blanc commerciale et aucun traitement) dans le centre du Maine, aux Etats-Unis. Ces traitements ont debute dans les annees 1950 et ont ete maintenus depuis. Les reservoirs de C dans l'ecosysteme ont ete mesures en 2012. Parmi les traitements d'amenagement, les stocks de C les plus faibles, de 21 % en moyenne (P < 0,05), etaient associes a la coupe a blanc commerciale tandis que les stocks totaux de C dans l'ecosysteme etaient similaires pour la coupe de jardinage et la coupe progressive. Inclure le C emmagasine dans les produits forestiers recoltes n'a pas influence les differences observees entre les traitements dans le stockage du C. Les stocks totaux de C dans l'ecosysteme atteignaient 247,0 ± 17,7 Mg x [ha.sup.-1] (moyenne ± ecart-type) dans le peuplement temoin comparativement a 161,7 [+ or -] 31,3 Mg x [ha.sup.-1] dans les peuplements amenages (171,2 ± 31,7 Mg x [ha.sup.-1] incluant le C dans les produits forestiers). Cette etude met en evidence les impacts a long terme des traitements d'amenagement forestier sur le stockage du C et indique que le moment de la recolte ainsi que l'espece et la taille des arbres recoltes influencent le C emmagasine dans les produits forestiers recoltes. [Traduit par la Redaction] Mots-cles : stocks de carbone, produits forestiers, sols forestiers, fragments grossiers, qualite de station., Introduction Concerns about climate change have increased interest in developing forest management strategies to produce a net reduction in atmospheric C[O.sub.2] and to make forests more resilient to future climatic [...]
- Published
- 2016
- Full Text
- View/download PDF
20. Effects of uncertainty in upper-stem diameter information on tree volume estimates
- Author
-
Westfall, James A., McRoberts, Ronald E., Radtke, Philip J., and Weiskittel, Aaron R.
- Published
- 2016
- Full Text
- View/download PDF
21. Development and evaluation of aboveground small tree biomass models for naturally regenerated and planted species in eastern Maine, U.S.A.
- Author
-
Nelson, Andrew S., Weiskittel, Aaron R., Wagner, Robert G., and Saunders, Michael R.
- Published
- 2014
- Full Text
- View/download PDF
22. Assessing the role of natural disturbance and forest management on dead wood dynamics in mixed-species stands of central Maine, USA
- Author
-
Puhlick, Joshua J., Weiskittel, Aaron R., Fraver, Shawn, Russell, Matthew B., and Kenefic, Laura S.
- Subjects
Maine -- Natural history ,Forest dynamics -- Observations ,Forest management -- Methods ,Earth sciences - Abstract
Dead wood pools are strongly influenced by natural disturbance events, stand development processes, and forest management activities. However, the relative importance of these influences can vary over time. In this study, we evaluate the role of these factors on dead wood biomass pools across several forest management alternatives after 60 years of treatment on the Penobscot Experimental Forest in central Maine, USA. After accounting for variation in site quality, we found significant differences in observed downed coarse woody material (CWM; ≥ 7.6 cm small-end diameter) and standing dead wood biomass among selection, shelterwood, and commercial clear-cut treatments. Overall, total dead wood biomass was positively correlated with live tree biomass and was negatively correlated with the average wood density of nonharvest mortality. We also developed an index of cumulative harvest severity, which can be used to evaluate forest attributes when multiple harvests have occurred within the same stand over time. Findings of this study highlight the dynamic roles of forest management, stand development, and site quality in influencing dead wood biomass pools at the stand level and underscore the potential for various outcomes from the same forest management treatment applied at different times in contrasting stands. Key words: silviculture, tree mortality, spruce budworm, harvest severity index, woody debris. Les reservoirs de bois mort sont fortement influences par les perturbations, les processus de developpement des peuplements et les activites d'amenagement forestier. Cependant, l'importance relative de ces facteurs peut varier dans le temps. Dans cette etude, nous evaluons le role de ces facteurs sur les reservoirs de biomasse de bois mort en fonction de plusieurs options d'amenagement forestier apres 60 annees de traitement a la foret experimentale de Penobscot, dans le centre du Maine, aux Etats-Unis. Apres avoir tenu compte de la variation dans la qualite de station, nous avons observe des differences significatives dans les debris ligneux grossiers au sol (DLG; diametre au fin bout [greater than or equal to] 7,6 cm) et la biomasse de bois mort sur pied entre la coupe de jardinage, la coupe progressive et la coupe rase commerciale. Globalement, la biomasse totale de bois mort etait correlee positivement avec la biomasse des arbres vivants et negativement avec la densite moyenne du bois mort non recolte. Nous avons aussi developpe un indice d'intensite cumulative de recolte, qui peut etre utilise pour evaluer les attributs de la foret lorsque de multiples recoltes sont survenues avec le temps dans le meme peuplement. Les resultats de cette etude mettent en evidence les roles dynamiques de l'amenagement forestier, du developpement des peuplements et de la qualite de station quant a leur influence sur les reservoirs de biomasse de bois mort a l'echelle du peuplement et souligne la possibilite que le meme traitement d'amenagement forestier applique a differents moments dans differents peuplements produise differents resultats. [Traduit par la Redaction] Mots-cles : sylviculture, mortalite des arbres, tordeuse des bourgeons de l'epinette, indice d'intensite de recolte, debris ligneux., Introduction Dead wood is an important component of ecosystem structure and function (Harmon et al. 1986; McComb and Lindenmayer 1999; Siitonen 2001). Specifically, dead wood plays a key role in [...]
- Published
- 2016
- Full Text
- View/download PDF
23. A new method for capturing stem taper variation for trees of diverse morphological types
- Author
-
MacFarlane, David W. and Weiskittel, Aaron R.
- Subjects
Stems (Botany) -- Physiological aspects -- Models ,Botany -- Morphology ,Trees -- Physiological aspects -- Models ,Earth sciences - Abstract
Understanding variation in tree stem form is fundamental to both ecological and economic assessments of forest ecosystem structure and function. Stem taper models (STMs) are widely used to describe tree form, but it can be challenging to apply them to trees with stems that diverge from an idealized norm, often leading to the exclusion of many trees from stem taper studies. Here, new 'whole-tree' form type classes are advanced as simple and useful groupings for capturing stem form variation of trees of diverse morphological types and tested with a large tree data set without exclusion criteria. New form type classes explained much more of main stem form variation than knowledge of tree species, while 'merchantable' form types explained the most variation between trees and stands. Broad-leaved species were much more likely to have complex stem forms than needle-leaved species, but species 'evergreenness' was a very weak predictor of stem form variation when tree- and stand-level form variation was accounted for. A new, generalized framework for stem taper modeling is demonstrated, using both species and merchantable form types to capture tree-level random effects. New form types and the STM approach are relatively easy to apply and should be relatively simple to integrate into any conventional forest inventory system. Overall, the study demonstrates the importance of including and accounting for the diversity of observed stem forms in developing STMs. Key words: taper, form, branching architecture, mixed-effects modeling, morphology. Il est essentiel de comprendre les variations de forme de la tige des arbres tant pour l'evaluation ecologique qu'economique de la structure et des fonctions des ecosystemes forestiers. Les modeles de defilement des tiges (MDT) sont largement utilises pour decrire la forme des arbres, mais il peut etre difficile de les appliquer a des arbres dont la tige diverge d'une norme idealisee, ce qui entraine souvent l'exclusion de nombreux arbres des etudes de defilement des tiges. Dans cette etude, de nouvelles classes de type de forme d'arbres entiers sont proposees, sous forme de regroupements simples et utiles pour capter les variations de la forme de la tige de divers types morphologiques, et testees sans criteres d'exclusion avec un jeu de donnees comptant un grand nombre d'arbres. Les nouvelles classes de type de forme ont explique une beaucoup plus grande part de variation de la forme de la tige principale que la connaissance des especes d'arbres, tandis que les types de formes << marchandes >> ont explique la plupart des variations entre les arbres et les peuplements. Les especes feuillues etaient beaucoup plus susceptibles d'avoir des formes de tige complexes que les especes resineuses, mais le caractere sempervirent des especes etait un tres mauvais predicteur des variations de la forme de la tige, lorsqu'on tenait compte de la variation de la forme a l'echelle de l'arbre et du peuplement. Utilisant a la fois l'espece et le type de forme marchande, un nouveau cadre generalise permettant de capter les effets aleatoires au niveau des arbres est presente pour la modelisation du defilement des tiges. Les nouveaux types de forme et l'approche de modelisation du defilement des tiges sont relativement faciles a appliquer et devraient etre relativement simples a integrer dans tout systeme d'inventaire forestier classique. Dans l'ensemble, l'etude demontre l'importance d'inclure et de rendre compte de la diversite des formes de tige observees dans le developpement des MDT. [Traduit par la Redaction] Mots-cles: defilement, forme, architecture des branches, modeles a effets mixtes, morphologie., 1. Introduction Stem taper models (STMs) describe the changing shape of the 'main' stem of a tree, from ground to tree top. This enables them to be used to explore [...]
- Published
- 2016
- Full Text
- View/download PDF
24. Measurement and prediction of bark thickness in Picea abies: assessment of accuracy, precision, and sample size requirements
- Author
-
Stangle, Stefan M., Weiskittel, Aaron R., Dormann, Carsten F., and Bruchert, Franka
- Subjects
Bark -- Properties ,Accuracy and precision -- Measurement ,Spruce -- Physiological aspects ,Thickness measurement -- Methods ,Earth sciences - Abstract
Tree and log diameters are usually measured outside bark, but inside-bark diameters are of greater economic interest and are often derived with local or regional bark thickness equations. To date, the influence of measurement method, sampling design, and sample size on bark thickness equation accuracy and precision has received limited attention. The objectives of this study were to use an extensive regional bark thickness dataset for Norway spruce (Picea abies (L.) Karst) in southwestern Germany to (1) quantify the accuracy and precision of bark thickness measurements with a Swedish bark gauge, (2) determine the required number of measurements to assess the within-tree variation, and (3) estimate the required sample sizes per plot and per region to develop an accurate bark thickness prediction equation. Bark gauge readings were validated with measurements derived from X-ray computed tomography (CT) and indicate that Swedish bark gauges generally overestimated bark thickness by 13.6% ± 28.4% (mean ± standard deviation). Results suggested having at least one measurement location every 2 m along a tree bole and at least five bark thickness measurements per each of these locations to achieve an allowable error of Key words: bark factor, measurement error, variance, equivalence, model performance. Le diametre des arbres et des grumes est generalement mesure sur ecorce, mais le diametre sous-ecorce presente un plus grand interet economique et est souvent derive en utilisant des equations d'epaisseur d'ecorce locale ou regionale. A ce jour, l'influence de la methode de mesure, du plan d'echantillonnage et de la taille de l'echantillon sur l'exactitude et la precision des equations d'epaisseur d'ecorce a recu peu d'attention. En utilisant une importante base de donnees regionale d'epaisseur d'ecorce pour l'epicea commun (Picea abies (L.) Karst.) dans le sud-ouest de l'Allemagne, les objectifs de cette etude etaient: (1) de quantifier l'exactitude et la precision des mesures d'epaisseur d'ecorce avec une jauge d'ecorce suedoise, (2) de determiner le nombre requis de mesures pour evaluer la variation intra-arbre et (3) d'estimer la taille de l'echantillon requis par parcelle et par region pour developper une equation precise de prediction de l'epaisseur d'ecorce. Les lectures de la jauge d'ecorce ont ete validees avec des mesures de tomographie aux rayons X informatisee et indiquent que les jauges d'ecorce suedoises ont generalement surestime l'epaisseur d'ecorce de 13,6 % ± 28,4 % (moyenne ± ecart type). Les resultats indiquent qu'on devrait mesurer au moins a tous les deux metres le long d'un tronc d'arbre et prendre au moins cinq mesures d'epaisseur d'ecorce a chacun de ces endroits pour obtenir une marge d'erreur Mots-cles: facteur d'ecorce, erreur de mesure, variance, equivalence, performance du modele., Introduction Although tree and log diameters are usually measured outside bark, wood volume calculations in forest inventories, round-wood markets, and bucking optimization algorithms generally assume inside-bark diameters. To convert outside-bark [...]
- Published
- 2016
- Full Text
- View/download PDF
25. Effects of thinning-induced changes in structural heterogeneity on growth, ingrowth, and mortality in secondary coastal Douglas-fir forests
- Author
-
Kuehne, Christian, Weiskittel, Aaron R., Fraver, Shawn, and Puettmann, Klaus J.
- Subjects
Mortality -- Observations ,Fir -- Environmental aspects -- Health aspects ,Balsam fir -- Environmental aspects -- Health aspects ,Forest thinning -- Environmental aspects -- Health aspects ,Earth sciences - Abstract
Thinning is believed to accelerate the development of late-successional attributes, thereby enhancing stand structural heterogeneity in young, secondary forests. By making use of a large-scale experiment implemented in 40- to 60-year-old coastal Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) forests, we addressed the following objectives: (i) determine the effect of three thinning treatments on the temporal dynamics (first 11 years after thinning) of key forest structure measures, (ii) evaluate the relationships between spatially explicit structural diversity measures and spatially nonexplicit stand metrics, and (iii) test the relationships between stand structure and observed periodic stand volume growth, ingrowth, and mortality. Treatments consisted of high-density, moderate-density, and variable-density thinnings-from-below, as well as a control. Differences in stand structural heterogeneity between treatments were mostly nonsignificant. However, our results suggest that variable- density stands displayed structural enrichment as tree size and tree species diversity increased throughout the study period as a result of continuous ingrowth of species other than Douglas-fir. Simple spatially nonexplicit metrics could not be used to reliably model spatially explicit structural diversity measures. The inclusion of structural and species diversity measures only rarely improved accuracy of sample plot level growth, ingrowth, and mortality prediction models. Despite the short-term nature of this study, we conclude that variable-density thinning shows promise in increasing structural heterogeneity in young even- aged stands. The inclusion of structural diversity measures in growth and mortality models may be beneficial, but further work is needed to clarify the underlying relationships, particularly at the individual-tree level. Key words: variable-density thinning, tree species diversity, tree size diversity, spatial tree arrangement, forest structure. L'eclaircie est censee accelerer le developpement des attributs de fin de succession, ameliorant ainsi l'heterogeneite structurelle des jeunes peuplements de seconde venue. A l'aide d'une experience a grande echelle etablie dans des forets cotieres de douglas de Menzies (Pseudotsuga menziesii (Mirbel) Franco) agees de 40 a 60 ans, nous avons poursuivi les objectifs suivants: (i) determiner l'effet de trois traitements d'eclaircie sur la dynamique temporelle (11 premieres annees apres l'eclaircie) des mesures cles de la structure forestiere, (ii) evaluer les relations entre des mesures spatialement explicites de diversite structurelle et des mesures de peuplements non spatialement explicites, et (iii) tester la relation entre la structure du peuplement et les valeurs observees de croissance periodique du volume, du recrutement et de la mortalite dans le peuplement. Les traitements etaient des eclaircies par le bas a densites forte, moderee et variable ainsi qu'un temoin. Les differences d'heterogeneite structurelle des peuplements entre les traitements etaient generalement non significatives. Cependant, nos resultats indiquent qu'un enrichissement structurel s'est produit dans les peuplements a densite variable puisque la diversite en taille et en espece d'arbre a augmente pendant la periode d'etude a cause du recrutement continu d'especes autres que le douglas de Menzies. Des mesures simples, non spatialement explicites, n'ont pu etre utilisees pour modeliser de facon fiable les mesures de diversite structurelle spatialement explicites. L'inclusion de mesures de diversite structurelle et specifique a rarement ameliore la precision des modeles de prevision de la croissance, du recrutement et de la mortalite a l'echelle de la placette echantillon. Malgre la courte echelle temporelle de cette etude, nous concluons que l'eclaircie a densite variable semble prometteuse pour augmenter l'heterogeneite structurelle dans les jeunes peuplements equiennes. L'inclusion de mesures de diversite structurelle dans les modeles de croissance et de mortalite peut etre benefique, mais d'autres travaux sont necessaires pour clarifier les relations sous-jacentes, particulierement a l'echelle de l'arbre individuel. [Traduit par la Redaction] Mots-cles: eclaircie a densite variable, diversite des especes d'arbre, diversite de la taille des arbres, distribution spatiale des arbres, structure forestiere., 1. Introduction Restoring structural heterogeneity in secondary forests as a means to increasing the provision of ecosystem services has become a major objective in forest management and a much-noticed topic [...]
- Published
- 2015
- Full Text
- View/download PDF
26. Testing a generalized leaf mass estimation method for diverse tree species and climates of the continental United States
- Author
-
Dettmann, Garret T., primary, MacFarlane, David W., additional, Radtke, Philip J., additional, Weiskittel, Aaron R., additional, Affleck, David L. R., additional, Poudel, Krishna P., additional, and Westfall, James, additional
- Published
- 2022
- Full Text
- View/download PDF
27. Carbon conundrums: Do United States' current carbon market baselines represent an undesirable ecological threshold?
- Author
-
D'Amato, Anthony W., primary, Woodall, Christopher W., additional, Weiskittel, Aaron R., additional, Littlefield, Caitlin E., additional, and Murray, Lara T., additional
- Published
- 2022
- Full Text
- View/download PDF
28. Quantifying and correcting geolocation error in sampling LiDAR forest canopy observations using high spatial accuracy ALS: A case study involving GEDI
- Author
-
Shannon, Elliot S., Finley, Andrew O., Hayes, Daniel J., Noralez, Sylvia N., Weiskittel, Aaron R., Cook, Bruce D., and Babcock, Chad
- Subjects
FOS: Computer and information sciences ,Applications (stat.AP) ,Statistics - Applications - Abstract
Geolocation error in sampling LiDAR measurements of forest structure can compromise forest attribute estimates and degrade integration with georeferenced field measurements or other remotely sensed data. Integrating sampling LiDAR with other georeferenced data is especially problematic when geolocation error is not well quantified. Here, we propose and illustrate a model that uses high spatial accuracy airborne laser scanning (ALS) data from NASA Goddard's LiDAR, Hyperspectral & Thermal Imager (G-LiHT) to quantify and correct geolocation error in NASA's Global Ecosystem Dynamics Investigation (GEDI) spaceborne sampling LiDAR. The model accommodates multiple canopy height metrics derived from a simulated GEDI footprint kernel of known functional form using spatially coincident G-LiHT, and incorporates both additive and multiplicative mapping between the canopy height metrics generated from both LiDAR datasets. A Bayesian implementation provides probabilistic uncertainty quantification in both parameter and geolocation error estimates. Results show an estimated maximum a posteriori (MAP) systematic geolocation error (i.e., across all GEDI footprints) of 9.62 m in the southwest direction. In addition, estimated MAP actual geolocation errors (i.e., within GEDI footprints) were highly variable with results showing a ~0.15 probability the true GEDI footprint center is within 10 m and a ~0.45 probability the true GEDI footprint center is within 20 m. Estimating and correcting geolocation error via the modeling approach outlined here can help inform subsequent efforts to integrate sampling LiDAR, like GEDI, with other georeferenced data.
- Published
- 2022
- Full Text
- View/download PDF
29. Forest Carbon Accounting and Modeling Framework Alternatives: An Inventory, Assessment, and Application Guide for Eastern US State Policy Agencies
- Author
-
Daigneault, Adam J, Hayes, Daniel J, Fernandez, Ivan J, and Weiskittel, Aaron R
- Published
- 2022
- Full Text
- View/download PDF
30. Climate- and soil-based models of site productivity in eastern US tree species
- Author
-
Jiang, Huiquan, Radtke, Philip J., Weiskittel, Aaron R., Coulston, John W., and Guertin, Patrick J.
- Subjects
Forest productivity -- Environmental aspects ,Climatic changes -- Environmental aspects ,Plant-soil relationships -- Environmental aspects ,Earth sciences - Abstract
As concerns rise over potential effects of greenhouse gas related climate change on terrestrial ecosystems, forest managers require growth and yield modeling capabilities responsive to changing climate conditions. Our goal was to develop prediction models of site index for eastern US forest tree species with climate and soil properties as predictors for use in predicting potential responses of forest productivity to climate change. Species-specific site index data from the USDA Forest Service Forest Inventory and Analysis (FIA) program were linked to contemporary climate data and soil properties mapped in the USDA Soil Survey Geographic (SSURGO) database. Random forest regression tree based ensemble prediction models of site index were constructed based on 37 climate-related and 15 soil attributes. In addition to a species-specific site index, aggregate models were developed for species grouped into two broad categories: conifer (softwood) and hardwood (broadleaved) species groups. Species-specific models based on climate and soil predictors explained the most variation in site index of any models tested ([R.sup.2] = 62.5%, RMSE = 3.2 m). Comparable results were found when grouping species into conifer and hardwood groups ([R.sup.2] = 63.9%, RMSE = 4.6 m for conifers; R2 = 35.9%, RMSE = 4.2 m for hardwoods). Model predictions based on multiple global circulation models (GCMs) and Intergovernmental Panel on Climate Change (IPCC) development scenarios were tested for statistical significance using bootstrap resampling methods. Results showed significant increases over the 21st century in mean site index for conifers between +0.5 and +2.4 m. Over the same time period, mean hardwood site index showed decreases of as much as -1.7 m for the scenarios tested. The results demonstrate the utility of using climate and soils data in predicting site index across a large geographic region, and the potential of climate change to alter forest productivity in the eastern US. Additional investigation is needed to interpret spatial patterns and ecological relationships related to predictions from this type of model. Key words: bootstrap, climate change, climate envelope models, random forest, regression trees, site index. A cause des preoccupations croissantes au sujet des effets potentiels des changements climatiques lies aux gaz a effet de serre sur les ecosystemes terrestres, les amenagistes forestiers ont besoin de modeles de croissance et de production capables de tenir compte des conditions engendrees par les changements climatiques. Notre but etait de mettre au point des modeles de prevision de l'indice de qualite de station pour les especes d'arbre des forets de l'est des Etats-Unis avec le climat et les proprietes du sol comme variables de prediction pour prevoir les reactions potentielles de la production forestiere face aux changements climatiques. Les donnees d'indice de qualite de station de chaque espece provenant du programme d'analyse et d'inventaire forestier de l'USDA Forest Service ont ete jumelees aux donnees du climat contemporain et aux proprietes du sol cartographiees dans la base de donnees SSURGO de l'inventaire geographique des sols de l'USDA. Des modeles d'ensemble de forets aleatoires fondes sur des arbres de regression ont ete construits a l'aide de 37 attributs relies au climat et 15 attributs relies au sol pour prevoir l'indice de qualite de station. En plus de l'indice de qualite de station pour chaque espece, des modeles globaux ont ete mis au point pour deux grandes categories d'especes, les coniferes et les feuillus. Parmi les modeles testes, les modeles pour chaque espece fondes sur les predicteurs du climat et du sol ont explique la plus grande partie de la variation de l'indice de qualite de station ([R.sup.2] = 62,5 %, EMQ = 3,2 m). Des resultats comparables ont ete obtenus lorsque les especes etaient regroupees en coniferes ou feuillus ([R.sup.2] = 63,9 %, EMQ = 4,6 m pour les coniferes; [R.sup.2] = 35,9 %, EMQ = 4,2 m pour les feuillus). La signification statistique des previsions des modeles bases sur les modeles de circulation globale multiple et les scenarios du Groupe d'experts intergouvememental sur l'evolution du climat a ete testee a l'aide de methodes de reechantillonnage avec autoamorcage. Selon les resultats, l'indice de qualite de station moyen des coniferes connaitrait au cours du 21e siecle des augmentations significatives variant de 0,5 a 2,4 m. Pendant la meme periode, l'indice de qualite de station moyen des feuillus subirait une diminution pouvant aller jusqu'a 1,7 m selon les scenarios testes. Les resultats demontrent l'utilite d'utiliser des donnees sur le climat et le sol pour prevoir l'indice de qualite de station dans une grande region geographique et le potentiel des changements climatiques pour modifier la productivite des forets de l'est des Etats-Unis. Des etudes supplementaires sont necessaires pour interpreter les patrons spatiaux et les relations ecologiques associes aux previsions de ce type de modele. [Traduit par la Redaction] Mots-cles : autoamorcage, changements climatiques, modeles d'enveloppe climatique, foret aleatoire, arbres de regression, indice de qualite de station., Introduction Greenhouse gas related global warming has led to changing patterns of precipitation and temperature over much of North America in the past half-century (Intergovernmental Panel on Climate Change (IPCC) [...]
- Published
- 2015
- Full Text
- View/download PDF
31. Effects of species composition, management intensity, and shade tolerance on vertical distribution of leaf area index in juvenile stands in Maine, USA
- Author
-
Nelson, Andrew S., Wagner, Robert G., Weiskittel, Aaron R., and Saunders, Michael R.
- Published
- 2015
- Full Text
- View/download PDF
32. Evaluation of projected carbon accumulation after implementing different forest management treatments in mixed-species stands in northern Maine
- Author
-
Puhlick, Joshua J., primary, Weiskittel, Aaron R., additional, Fernandez, Ivan J., additional, Solarik, Kevin A., additional, and Sleep, Darren J. H., additional
- Published
- 2022
- Full Text
- View/download PDF
33. Examining approaches for modeling individual tree growth response to thinning in Norway spruce
- Author
-
Kuehne, Christian, primary, Weiskittel, Aaron R., additional, and Granhus, Aksel, additional
- Published
- 2022
- Full Text
- View/download PDF
34. Comparing strategies for modeling individual-tree height and height-to-crown base increment in mixed-species Acadian forests of northeastern North America
- Author
-
Russell, Matthew B., Weiskittel, Aaron R., and Kershaw, Jr., John A.
- Published
- 2014
- Full Text
- View/download PDF
35. Synthesizing Disparate LiDAR and Satellite Datasets through Deep Learning to Generate Wall-to-Wall Regional Inventories for the Complex, Mixed-Species Forests of the Eastern United States
- Author
-
Ayrey, Elias, primary, Hayes, Daniel J., additional, Kilbride, John B., additional, Fraver, Shawn, additional, Kershaw, John A., additional, Cook, Bruce D., additional, and Weiskittel, Aaron R., additional
- Published
- 2021
- Full Text
- View/download PDF
36. Efficiency of alternative forest inventory methods in partially harvested stands
- Author
-
Rice, Ben, Weiskittel, Aaron R., and Wagner, Robert G.
- Published
- 2014
- Full Text
- View/download PDF
37. Development of branch, crown, and vertical distribution leaf area models for contrasting hardwood species in Maine, USA
- Author
-
Nelson, Andrew S., Weiskittel, Aaron R., and Wagner, Robert G.
- Published
- 2014
- Full Text
- View/download PDF
38. Relative influence of stand and site factors on aboveground live-tree carbon sequestration and mortality in managed and unmanaged forests
- Author
-
Kern, Christel C., primary, Kenefic, Laura S., additional, Kuehne, Christian, additional, Weiskittel, Aaron R., additional, Kaschmitter, Sarah J., additional, D'Amato, Anthony W., additional, Dey, Daniel C., additional, Kabrick, John M., additional, Palik, Brian J., additional, and Schuler, Thomas M., additional
- Published
- 2021
- Full Text
- View/download PDF
39. Long-term response of spruce-fir stands to herbicide and precommercial thinning: observed and projected growth, yield, and financial returns in central Maine, USA
- Author
-
Bataineh, Mohammad M., Wagner, Robert G., and Weiskittel, Aaron R.
- Subjects
Herbicides -- Analysis -- Forecasts and trends -- Growth -- Research ,Spruce -- Growth ,Company growth ,Earth sciences - Abstract
Herbicide application and precommercial thinning (PCT) are common silvicultural treatments used across North America and Europe. Despite this widespread use, long-term growth and yield responses from controlled experiments that include both of these treatments are relatively rare. We used 40-year growth and yield responses of spruce-fir stands to various combinations of early herbicide and PCT in a long-term silvicultural experiment in central Maine, USA, to calibrate the Forest Vegetation Simulator (Northeast Variant). Using the calibrated model, we projected rotation-length outcomes for stand development, merchantable wood volumes, and stumpage-based financial returns. Projections indicated gains in total yield (17%-31%) from herbicide treatments at the end of the rotation (~60 years postharvest) relative to untreated stands. Substantial increases in merchantable wood volume also were achieved with PCT. Twenty-four years after PCT, stand stumpage value averaged $907 USD*[ha.sup.-1] higher than that for unthinned stands. Total yield and stumpage gains from PCT were projected to continue through the end of rotation. Highest stumpage values resulted from combined herbicide and PCT treatments, followed by PCT-only and then herbicide-only. At end of rotation, highest net present value (NPV) resulted from PCT, whether alone or in combination with herbicides. PCT and herbicide investments substantially improved the NPV relative to untreated stands when using discount rates of 2% and 4%, but not when using a 6% rate. Our results documented that good financial returns are possible over the long-term from early investments in herbicide and PCT treatments in Maine spruce-fir stands. Resume: L'application d'herbicide et l'eclaircie precommerciale (EPC) sont des traitements sylvicoles couramment utilises en Amerique du Nord et en Europe. Malgre une utilisation repandue, il est plutot rare de trouver des experiences controlees qui ont pour objet les effets a long terme de ces deux traitements sur la croissance et la production. Nous avons utilise la reaction de 40 ans en croissance et en production de peuplements d'epinette et de sapin soumis a l'application hative de diverses combinaisons d'herbicide et d'EPC dans le cadre d'une experience sylvicole de longue duree etablie dans le centre du Maine, aux Etats-Unis, pour etalonner le simulateur de vegetation forestiere (version du nord-est). A l'aide du modele etalonne, nous avons simule les resultats apres une rotation complete en termes de developpement du peuplement, de volume de bois marchand et de rendement financier sous forme de droits de coupe. Dans le cas de l'application d'herbicide, les resultats indiquaient des gains en production totale de 17 a 31 % a la fin de la rotation (environ 60 ans apres la coupe) par rapport aux peuplements non traites. Une augmentation substantielle du volume de bois marchand a aussi ete observee apres l'EPC. Les droits de coupe etaient en moyenne 907 $US a l'hectare plus eleves que dans les peuplements non eclaircis 24 ans apres l'EPC. Les resultats indiquaient que les gains en production totale et en droits de coupe persistaient jusqu'a la fin de la rotation. Les droits de coupe les plus eleves ont ete obtenus par l'application combinee d'herbicide et de l'EPC, suivie de l'EPC seule, puis d'herbicide seul. A la fin de la rotation, la plus forte valeur actualisee nette (VAN) a ete obtenue avec l'EPC seule ou combinee a l'application d'herbicide. Les investissements consentis pour l'application d'herbicide et de l'EPC ont augmente substantiellement la VAN par rapport aux peuplements non traites lorsque des taux d'interet de 2 et 4 % etaient utilises, mais ce n'etait pas le cas avec un taux de 6 %. Nos resultats indiquent que de bons rendements sont possibles a long terme a condition d'investir dans l'application d'herbicide et l'EPC tot dans le developpement des peuplements d'epinette et de sapin du Maine., Introduction Herbicide application and precommercial thinning (PCT) are common silvicultural treatments used in the successful regeneration and early management of conifer forests across North America (Cain 1999; Pothier 2002; Zhang [...]
- Published
- 2013
- Full Text
- View/download PDF
40. Forest Growth and Yield Models for Intensively Managed Plantations
- Author
-
Weiskittel, Aaron R., primary
- Published
- 2014
- Full Text
- View/download PDF
41. Assessing and modeling standing deadwood attributes under alternative silvicultural regimes in the Acadian Forest region of Maine, USA
- Author
-
Russell, Matthew B., Kenefic, Laura S., Weiskittel, Aaron R., Puhlick, Joshua J., and Brissette, John C.
- Subjects
Population ecology -- Observations ,Forest ecology -- Research ,Trees -- Observations ,Earth sciences - Abstract
Estimating the amount of standing deadwood in forests is crucial for assessing wildlife habitat and determining carbon stocks. In this analysis, snags (standing dead trees) in various stages of decay were inventoried across eight silvicultural treatments in eastern spruce-fir forests in central Maine nearly 60 years after treatments were initiated. Several modeling strategies were developed to estimate number of snags per hectare in various stages of decay. An unmanaged reference area displayed the highest basal area and volume of snags (5.4 [+ or -] 3.1 [m.sup.2] * [ha.sup.-1] and 29.4 [+ or -] 23.6 [m.sup.3] * [ha.sup.-1], respectively, (mean [+ or -] standard deviation)), while the lowest basal area and volume (0.9 [+ or -] 1.0 [m.sup.2] * [ha.sup.-1] and 3.1 [+ or -] 5.2 [m.sup.3] * [ha.sup.-1]) were observed in selection system with a 5-year cutting cycle. Models indicated that snag abundance was related to stand density, depth to water table, and the average harvest interval of the treatment. At a fixed stand density, approximately 140% more snags were predicted to occur in treatments with an average harvest interval of 55 compared with 5 years. An index of error reflecting the number of snags found in certain decay classes was reduced by 40% when predictions from count regression models fit with a mixed modeling strategy were used over ordinal regression. Results from these analyses can help to reduce the disparities between observed and modeled snag stocking levels and further our understanding of the relationships between live and standing dead trees inherent to eastern spruce-fir forests. Resume: Il est essentiel d'estimer la quantite de bois mort debout dans les forets pour evaluer l'habitat faunique et determiner les stocks de carbone. Dans cette etude, les chicots (arbres morts debout) a differents stades de decomposition ont ete inventories dans huit traitements sylvicoles dans des peuplements melanges d'epicea et de sapin situes dans le centre du Maine, presque 60 ans apres le debut des traitements. Plusieurs strategies de modelisation ont ete developpees pour estimer le nombre de chicots a l'hectare rendus a differents stades de decomposition. Une zone temoin non amenagee avait la surface terriere et le volume les plus eleves de chicots, soit respectivement (moyenne [+ or -] ecart type) 5,4 [+ or -] 3,1 [m.sup.2]*[ha.sup.-1] et 29,4 [+ or -] 23,6 [m.sup.3]*[ha.sup.-1], tandis que la surface terriere et le volume les plus faibles (0,9 [+ or -] 1,0 [m.sup.2]*[ha.sup.-1] et 3,1 [+ or -] 5,2 [m.sup.3]*[ha.sup.-1]) ont ete observes dans la coupe de jardinage avec une rotation de cinq ans. Les modeles indiquaient que l'abondance de chicots etait reliee a la densite du peuplement, a la profondeur de la nappe phreatique et a la l'intervalle moyen entre les recoltes. Avec une densite de peuplement fixe, les modeles predisaient approximativement 140% plus de chicots dans les traitements dont l'intervalle entre les recoltes etait de 55 ans comparativement a cinq ans. Un indice d'erreur refletant le nombre de chicots observes dans certaines classes de decomposition a ete reduit de 40% lorsqu'on utilisait les predictions des modeles de regression de variables explicatives de denombrement ajustes avec une strategie de modelisation mixte plutot que la regression ordinale. Les resultats de ces analyses peuvent contribuer a reduire les ecarts entre les niveaux observes de densite relative des chicots et ceux qui sont predits par les modeles et ameliorer notre comprehension des relations entre les arbres vivants et les arbres morts sur pied propres aux forets melangees d'epicea et de sapin. [Traduit par la Redaction], Introduction Snags (standing dead trees) play an important role in forest carbon dynamics (Harmon et al. 2011) and are key elements for maintaining forest biodiversity and providing a heterogeneous forest [...]
- Published
- 2012
- Full Text
- View/download PDF
42. Influence of early re-spacing on Sitka spruce branch structure
- Author
-
Auty, David, Weiskittel, Aaron R., Achim, Alexis, Moore, John R., and Gardiner, Barry A.
- Published
- 2012
- Full Text
- View/download PDF
43. Effects of seed source origin on bark thickness of Douglas-fir (Pseudotsuga menziesii) growing in southwestern Germany
- Author
-
Kohnle, Ulrich, Hein, Sebastian, Sorensen, Frank C., and Weiskittel, Aaron R.
- Subjects
Bark -- Physiological aspects ,Fir -- Physiological aspects ,Balsam fir -- Physiological aspects ,Seeds -- Physiological aspects ,Plant physiology -- Research ,Earth sciences - Abstract
Provenance-specific variation in bark thickness in Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) is important for accurate volume calculations and might carry ecological implications as well. To investigate variation, diameter at breast height (dbh) and double bark thickness (dbt) were measured in 10 experiments in southwestern Germany (16 American and six German seed sources), which were approximately 50 years old and ranged in productivity. Provenance-specific mixed models for dbt versus dbh varied considerably with respect to intercept and slope. Likewise, analysis of covariance on bark ratio (range = 8.0% to 13.2%) with dbh as the linear predictor revealed significant differences (p < 0.05 to p < 0.0001) in 70% of the comparisons. Influence of seed origin on bark ratio was analyzed for our 16 American sources plus six provenances reported from New Zealand tests. In linear regressions, single geographic position variables explained only a small proportion of the variation in bark ratio (range of [r.sup.2] = 0.01-0.33), and the same was true for individual climate variables. In contrast, physiographic regions significantly (p = 0.0013) explained considerable variation ([r.sup.2] = 0.66). Likewise, a combination of three climate variables (temperature, frost days, precipitation) proved significant (p < 0.0001; [r.sup.2] = 0.87). As bark ratio was inversely related to precipitation at the seed origin, it is inferred that historic fire regimes may have played a selective role in the process by which Douglas-fir allocates dry matter between bark and wood. Resume: La variation de l'epaisseur de l'ecorce qui est specifique a la provenance chez le douglas de Menzies (Pseudo-tsuga menziesii (Mirb.) Franco) est importante pour calculer avec precision le volume et pourrait aussi avoir des implications ecologiques. Pour etudier cette variation, le diametre a hauteur de poitrine (dhp) et la double epaisseur de l'ecorce (dee) ont ete mesures dans 10 plantations experimentales d'environ 50 ans (six provenances de graines allemandes et 16 americaines) etablies dans le sud-ouest de l'Allemagne et dont la productivite differait. Le point d'intersection et la pente des modeles mixtes de la dee en fonction du dhp specifiques a chaque provenance variaient considerablement. De la meme facon, une analyse de covariance sur le rapport de l'ecorce (etendue: 8,0 a 13,2 %) avec le dhp comme predicteur lineaire a revele des differences significatives (p < 0,05 a p < 0,0001) dans 70 % des comparaisons. L'influence de la provenance des graines sur le rapport de l'ecorce a ete analysee pour nos 16 provenances americaines plus six provenances sur la base de tests menes en Nouvelle-Zelande. Dans les regressions lineaires, les variables associees a la position geographique de chaque provenance expliquaient seulement une faible proportion de la variation du rapport de l'ecorce (etendue de [r.sup.2] = 0,01-0,33) et la meme chose etait vraie pour les variables climatiques associees a chacune des provenances. Au contraire, les regions physiographiques expliquaient significativement (p = 0,0013) une proportion considerable ([r.sup.2] = 0,66) de la variation. De la meme facon, une combinaison de trois variables climatiques (la temperature, les jours de gel, la precipitation) etait significative (p < 0,0001; [r.sup.2] = 0,87). Etant donne que le rapport de l'ecorce etait inversement relie a la precipitation au point d'origine des graines, on suppose que les regimes historiques des feux pourraient avoir joue un role de selection dans le processus d'allocation de matiere seche entre l'ecorce et le bois chez le douglas. [Traduit par la Redaction], Introduction In Germany, the first Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) were planted in 1831 in an arboretum close to Hamburg. The species was introduced into southwestern Germany (Baden-Wuerttemberg) in the [...]
- Published
- 2012
- Full Text
- View/download PDF
44. Estimating and predicting bark thickness for seven conifer species in the Acadian Region of North America using a mixed-effects modeling approach: comparison of model forms and subsampling strategies
- Author
-
Li, Rongxia and Weiskittel, Aaron R.
- Published
- 2011
- Full Text
- View/download PDF
45. Assessing model performance in forecasting long-term individual tree diameter versus basal area increment for the primary Acadian tree species
- Author
-
Russell, Matthew B., Weiskittel, Aaron R., and Kershaw, John A.
- Subjects
Trees -- Physiological aspects -- Growth ,Prediction (Logic) -- Research ,Dimensions -- Research ,Monte Carlo method -- Research ,Growth (Plants) -- Research ,Company growth ,Earth sciences - Abstract
: Tree basal area (ba) or diameter at breast height (dbh) are universally used to represent tree secondary growth in individual tree based growth models. However, the long-term implications of using either ba or dbh for predictions are rarely fully assessed. In this analysis, Dba and Ddbh increment equations were fit to identical datasets gathered from six conifer and four hardwood species grown in central Maine. The performance of Dba and Ddbh predictions from nonlinear mixed-effects models were then compared with observed growth measurements of up to 29 years via a Monte Carlo simulation. Two evaluation statistics indicated substantial improvement in forecasting dbh using Ddbh rather than Dba. Root mean squared error (RMSE) and percentage mean absolute deviation (MAD%) were reduced by 14% and 15% on average, respectively, across all projection length intervals (5-29 years) when Ddbh was used over Dba. Differences were especially noted as projection lengths increased. RMSE and MAD% were reduced by 24% when Ddbh was employed over Dba at longer projection lengths (up to 29 years). Simulations found that simulating random effects rather than using local estimates for random effects performed as well or better at longer interval lengths. These results highlight the implications that selecting a growth model dependent variable can have and the importance of incorporating model uncertainty into the growth projections of individual tree based models. Resume: La surface terriere de l'arbre (G) ou le diametre o hauteur de poitrine (D) sont universellement utilises pour repre-senter la croissance secondaire dans les modeles de croissance d'arbre individuel. Cependant, les implications o long terme de l'emploi de G ou D pour les predictions sont rarement pleinement evaluees. Dans cette analyse, les equations d'accroissement DG et DD ont ete ajustees o des ensembles de donnees identiques recueillies o partir de six coniferes et quatre feuillus dans le centre du Maine. La performance des predictions de DG et DD o l'aide des modeles non lineaires o effets mixtes a ete comparee aux mesures de croissance prises sur une periode de 29 ans en utilisant une simulation de Monte Carlo. Deux statistiques d'evaluation indiquent une amelioration substantielle de la prediction de D en utilisant DD plutot que DG. Lorsque DD a ete utilise o la place de DG, l'ecart type residuel et l'ecart moyen absolu en pourcentage ont ete reduits respectivement de 14 et 15 % en moyenne pour tous les horizons de projection (5-29 ans). Ces differences etaient particulierement marquees lorsque les horizons de projection s'allongeaient. En effet, l'ecart type residuel et l'ecart moyen absolu en pourcentage ont ete reduits de 24 % lorsque DD a ete employe au lieu de DG pour les horizons de projection plus longs (jusqu'o 29 ans). Les simulations ont montre que la simulation des effets aleatoires performe aussi bien sinon mieux que les estimations locales des effets aleatoires lorsque les horizons sont longs. Ces resultats mettent en evidence, d'une part, les impacts causes par la selection de la variable dependante pour un modele de croissance et, d'autre part, l'importance d'inte-grer l'incertitude des modeles dans les projections de croissance par des modeles d'arbre individuel. [Traduit par la Redaction], Introduction Diameter (at breast height, dbh) or basal area (ba) can be used to predict secondary growth of individual trees in forest growth models. The circumference of the tree at [...]
- Published
- 2011
- Full Text
- View/download PDF
46. Modeling annualized occurrence, frequency, and composition of ingrowth using mixed-effects zero-inflated models and permanent plots in the Acadian Forest Region of North America
- Author
-
Li, Rongxia, Weiskittel, Aaron R., and Kershaw, Jr., John A.
- Subjects
Acadia -- Environmental aspects ,Forests and forestry -- Research ,Poisson distribution -- Measurement ,Earth sciences - Abstract
Forest tree ingrowth is a highly variable and largely stochastic process. Consequently, predicting occurrence, frequency, and composition of ingrowth is a challenging task but of great importance in long-term forest growth and yield model projections. However, ingrowth data often require different statistical techniques other than traditional Gaussian regression, because these data are often bounded, skewed, and non-normal and commonly contain a large fraction of zeros. This study presents a set of regression models based on discrete Poisson and negative binomial probability distributions for ingrowth data collected from permanent sample plots in the Acadian Forest Region of North America. Models considered here include regular Poisson, zero-inflated Poisson (ZIP), zero-altered Poisson (ZAP; hurdle Poisson), regular negative binomial (NB), zero-inflated negative binomial (ZINB), and zero-altered negative binomial (ZANB; hurdle NB). Plot-level random effects were incorporated into each of these models. The ZINB model with random effects was found to provide the best fit statistics for modeling annualized occurrence and frequency of ingrowth. The key explanatory variables were stand basal area per hectare, percentage of hardwood basal area, number of trees per hectare, a measure of site quality, and the minimum measured diameter at breast height of each plot. A similar model was developed to predict species composition. All models showed logical behavior despite the high variability observed in the original data. Le recrutement d'arbres en foret est un processus tres variable et fortement stochastique. Par consequent, la prevision de l'occurrence, de la frequence et de la composition du recrutement d'arbres est une tache difficile, mais d'une grande importance pour les projections a long terme des modeles de croissance et de production forestiere. Cependant, les donnees de recrutement necessitent souvent des techniques statistiques autres que la traditionnelle regression gaussienne parce que ces donnees sont generalement delimitees, asymetriques et non normales en plus de contenir couramment une grande proportion de valeurs nulles. Cette etude presente une serie de modeles de regression bases sur des distributions de probabilite discretes de Poisson et binomiales negatives etalonnes a partir de donnees de recrutement provenant de placettes echantillons permanentes etablies dans la region forestiere acadienne de l'Amerique du Nord. Les modeles consideres dans cette etude incluent la distribution de Poisson reguliere, de Poisson a exces de zeros (PEZ), de Poisson tronquee a zero (PTZ; Poisson a obstacle), binomiale negative reguliere (BN), binomiale negative a exces de zeros (BNEZ) et binomiale negative tronquee a zero (BNTZ; BN a obstacle). Les effets aleatoires a l'echelle de la placette ont ete introduits dans chacun de ces modeles. Le modele BNEZ avec effets aleatoires a produit les meilleurs ajustements statistiques pour modeliser l'occurrence et la frequence annualisees du recrutement. Les variables explicatives les plus importantes etaient la surface terriere du peuplement a l'hectare, la proportion de la surface terriere en feuillus, le nombre d'arbres a l'hectare, une mesure de la qualite de la station et le DHP minimal mesure dans chaque placette. Un modele similaire a ete mis au point pour predire la composition en especes. Tous les modeles ont produit un comportement logique malgre la grande variabilite observee dans les donnees originales. [Traduit par la Redaction], Introduction Ingrowth is defined as trees in a sample plot that have grown into a required threshold size (usually measured by tree height or diameter at breast height (dbh)) over [...]
- Published
- 2011
- Full Text
- View/download PDF
47. Linking climate, gross primary productivity, and site index across forests of the western United States
- Author
-
Weiskittel, Aaron R., Crookston, Nicholas L., and Radtke, Philip J.
- Subjects
Global temperature changes -- Environmental aspects ,Sustainable forestry -- Research ,Forest productivity -- Research ,Earth sciences - Abstract
Assessing forest productivity is important for developing effective management regimes and predicting future growth. Despite some important limitations, the most common means for quantifying forest stand-level potential productivity is site index (SI). Another measure of productivity is gross primary production (GPP). In this paper, SI is compared with GPP estimates obtained from 3-PG and NASA's MODIS satellite. Models were constructed that predict SI and both measures of GPP from climate variables. Results indicated that a nonparametric model with two climate-related predictor variables explained over 68% and 76% of the variation in SI and GPP, respectively. The relationship between GPP and SI was limited ([R.sup.2] of 36%-56%), while the relationship between GPP and climate ([R.sup.2] of 76%-91%) was stronger than the one between SI and climate ([R.sup.2] of 68%-78%). The developed SI model was used to predict SI under varying expected climate change scenarios. The predominant trend was an increase of 0-5 m in SI, with some sites experiencing reductions of up to 10 m. The developed model can predict SI across a broad geographic scale and into the future, which statistical growth models can use to represent the expected effects of climate change more effectively. Il est important d'evaluer la productivite forestiere pour elaborer des regimes d'amenagement efficace et predire la croissance future. Malgre certaines limitations importantes, le moyen le plus frequemment utilise pour quantifier la productivite potentielle A l'echelle du peuplement forestier est l'indice de qualite de station (IQS). La production primaire brute (PPB) est une autre mesure de la productivite. Dans cet article, IQS est compare aux estimations de PPB obtenues A l'aide du modele 3-PG et de l'instrument satellitaire MODIS de la NASA. Nous avons bati des modeles qui predisent IQS et les deux mesures de PPB A partir des variables climatiques. Les resultats ont montre qu'un modele non parametrique avec deux variables explicatives reliees au climat expliquait respectivement 68 % et 76 % de la variation de IQS et de PPB. La relation entre PPB et IQS etait faible ([R.sup.2] de 36 % A 56 %) tandis que la relation entre PPB et le climat ([R.sup.2] de 76 % A 91 %) etait plus forte que la relation entre IQS et le climat ([R.sup.2] de 68 % A 78 %). Le modele qui a ete developpe pour IQS a ete utilise pour predire IQS A partir de differents scenarios previsibles de changement climatique. Une augmentation de IQS de 0 A 5 m etait la tendance predominante alors que certaines stations subissaient des reductions allant jusqu'A 10 m. Le modele qui a ete developpe peut predire IQS pour une large gamme d'echelles geographiques ainsi que dans le futur et la valeur de IQS ainsi obtenue peut etre utilisee par les modeles statistiques de croissance pour illustrer plus efficacement les effets anticipes du changement climatique. [Traduit par la Redaction], Introduction Measures of productivity are critical in efforts to understand and maintain forest ecosystems sustainably for a range of products and services, while managing risks related to wildfire, pests, and [...]
- Published
- 2011
- Full Text
- View/download PDF
48. Cutpoint analysis for models with binary outcomes: a case study on branch mortality
- Author
-
Hein, Sebastian and Weiskittel, Aaron R.
- Published
- 2010
- Full Text
- View/download PDF
49. A hybrid model for intensively managed Douglas-fir plantations in the Pacific Northwest, USA
- Author
-
Weiskittel, Aaron R., Maguire, Douglas A., Monserud, Robert A., and Johnson, Gregory P.
- Published
- 2010
- Full Text
- View/download PDF
50. Effect of wide spacing on tree growth, branch and sapwood properties of young Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] in south-western Germany
- Author
-
Hein, Sebastian, Weiskittel, Aaron R., and Kohnle, Ulrich
- Published
- 2008
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.