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As a tropical nation with ~40% forested land area and 290 protected areas in the Indo-Burma Biodiversity Hotspot, Vietnam holds an important part of global forests. Despite a complex history of multiple colonial rules, war, rapid economic development and societal growth, Vietnam was one of a few Southeast Asian countries to reverse deforestation trends and sustain net forest cover gain since the 1990s. However, a considerable amount of Vietnam's forest gain has been from plantation forestry, as Vietnam's policies have promoted economic development. In the Central Highlands region of Vietnam, widespread forest degradation and deforestation has occurred recently in some areas due to plantation forestry and other factors, including fire-linked deforestation, but protected areas here have been largely effective in their conservation goals. We studied deforestation, wildfires, and the contribution of fire-linked deforestation from 2001 to 2020 in an area near the Da Lat Plateau of the Central Highlands of Vietnam. We stratified our study area to distinguish legally protected areas and those in the surrounding landscape matrix without formal protection. Using satellite-derived data, we investigated four questions: (1) Have regional deforestation trends continued in parts of the Central Highlands from 2001 to 2020? (2) Based on remotely sensed fire detections, how has fire affected the Central Highlands and what proportion of deforestation is spatiotemporally linked to fire? (3) Were annual deforestation and burned area lower in protected areas relative to the surrounding land matrix? (4) Was the proportion of fire-linked deforestation lower in protected areas than in the matrix? To answer these questions, we integrated the Global Forest Change and FIRED VIETNAM datasets. We found that 3794 fires burned 8.7% of the total study area and 13.6% of the area became deforested between 2001 and 2020. While nearly half of fires were linked to deforestation, fire-linked deforestation accounted for only a small part of forest loss. Across the entire study area, 54% of fire-linked deforestation occurred in natural forests and 46% was in plantation forests. Fire ignitions in the study area were strongly linked to the regional dry season, November to March, and instrumental climate data from 1971 to 2020 showed statistically significant increasing trends in minimum, mean, and maximum temperatures. However, the total area burned did not have a significant increasing trend. Regional trends in deforestation continued in Vietnam's Central Highlands from 2001 to 2020, and nearly half of all detected fires can be spatially and temporally linked to forest loss. However, protected areas in the region effectively conserved forests relative to the surrounding landscape. [ABSTRACT FROM AUTHOR]

Highlights • Douglas-fir trees teepee poles are a culturally important resource for the Mescalero Apache tribe. • Stands consist of dense, relatively old trees. • Climate-sensitive simulation modeling predicted loss of most Douglas-fir. • Assisted migration or other innovative strategies may be needed. Abstract Integrating traditional ecological knowledge (TEK) with western science and modeling tools can enhance not only the delivery of culturally important species, but also community support and overall effectiveness of management. This paper presents a case study of co-producing usable science integrating TEK on a culturally important species with a modeling tool, Climate-Forest Vegetation Simulator (C-FVS). The Mescalero Apache tribe (southwestern USA) conduct a coming of age ceremony for young women who follow a traditional way of life. In order to conduct this ceremony, tall, thin teepee poles made from Douglas-fir trees are needed. Douglas-fir trees capable of producing teepee poles are a culturally important resource for the Mescalero Apache tribe. We interacted with medicine people, tribal members, and forest managers to gain insight on characteristics of teepee pole stands. We established thirty, 400 m2 circular plots with nested 100 m2 regeneration plots in teepee pole producing stands to characterize composition, structure, age, growth rates, and fuels. Teepee pole producing stands occupy an elevation range from 2012 to 2561 m, slopes of 3–43%, and aspects from NW to NE. The stands consist of dense, relatively old trees dominated by Douglas-fir, with other species of trees usually present as a minor component. Douglas-firs in teepee pole producing stands averaged 1255 ± 99 trees per ha (TPH), basal area 31.7 ± 1.5 m2/ha, and 18.5 ± 0.5 cm quadratic mean diameters (QMD). Douglas-fir trees in teepee pole producing stands were most commonly 75–100 years old with diameters at breast height (DBH) ranging from 5.1 to 25.4 cm. In order to assess future trajectories of teepee pole stands, we applied C-FVS which incorporates the effects of climate change scenarios over the next 100 years. We compared three standard scenarios ranging from moderate to severe climate change: Representative Concentration Pathways (RCP) 4.5, 6.0, and 8.5. Simulated future forests at the current plot locations even under the most mild climate change scenario (RCP 4.5) did not contain Douglas-fir after a century of modeling. Complete forest mortality was predicted under RCP 6.0 and RCP 8.5. Comparing bioclimatic niche modeling of Douglas-fir with downscaled future climate scenarios indicated that the species would have to be planted at least 305 m higher to maintain 21st century viability under RCP 4.5 and 6.0, or at least 610 m higher under RCP 8.0. The characterization of current teepee pole producing stands and simulations of future effects of climate change provide useful information to the Mescalero Apache Tribe to support management decisions on how they would like to preserve this cultural important resource. [ABSTRACT FROM AUTHOR]

Statistical descriptions of reconstructed fire regimes are often extrapolated from a composite of small forest stands to represent extensive geographical areas. However, statistical properties of fire regimes are scale-dependent, thus causing some extrapolations from fine scale to coarse scale and comparisons between fire-scar-based reconstructions to be inappropriate. We assessed landscape fire regimes of the Sacramento Mountains, in southern New Mexico, using dendrochronological methods and a variety of fire statistics and analysis filters. We reconstructed historical and recent fire regimes for the Mescalero Apache Tribal Lands (MATL) at tree and site scale (25 ha). We then estimated the Sacramento Mountains historical and recent fire regimes by combining paleo fire data from this study with published data from the adjacent Lincoln National Forest (LNF). We applied filters to provide fire statistics that are relatively unbiased to the different spatial measurement extent of the studies. This is the first study to assess fire regime in the MATL over multiple spatial and temporal scales. The results show that frequent surface fires occurred at all scales in the Sacramento Mountains until fire was excluded from the landscape in the early 1900s. Historical fires were found to be synchronous with drought years, typically La Ni~na events, and often preceded by wet years. We did not find evidence supporting differences in fire regimes between the MATL and the LNF, suggesting that fire cessation following intensive Euro-American settlement was widespread. The interruption of frequent surface fires, together with other changes in forest structure and climate, pose a significant threat to sustainability of forest ecosystems on Native American tribal lands. [ABSTRACT FROM AUTHOR]

Increasing tree density that followed fire exclusion after the 1880s in the southwestern United States may have also altered nutrient cycles and led to a carbon (C) sink that constitutes a significant component of the U.S. C budget. Yet, empirical data quantifying century-scale changes in C or nutrients due to fire exclusion are rare. We used tree-ring reconstructions of stand structure from five ponderosa pine-dominated sites from across northern Arizona to compare live tree C, nitrogen (N), and phosphorus (P) storage between the 1880s and 1990s. Live tree biomass in the 1990s contained up to three times more C, N, and P than in 1880s. However, the increase in C storage was smaller than values used in recent U.S. C budgets. Furthermore, trees that had established prior to the 1880s accounted for a large fraction (28-66%) of the C, N, and P stored in contemporary stands. Overall, our century-scale analysis revealed that forests of the 1880s were on a trajectory to accumulate C and nutrients in trees even in the absence of fire exclusion, either because growing conditions became more favorable after the 1880s or because forests in the 1880s included age or size cohorts poised for accelerated growth. These results may lead to a reduction in the C sink attributed to fire exclusion, and they refine our understanding of reference conditions for restoration management of fire-prone forests. [ABSTRACT FROM AUTHOR]

The article discusses how wildfire and climate change are interacting to drive change in vegetation and reduce quality and quantity of water and mentions that the forest restoration helps to mitigate negative outcomes.

Fine-scale forest patterns are an important component of forest ecosystem complexity and spatial pattern objectives are an increasingly common component of contemporary silviculture prescriptions in dry fire-adapted forests of North America. Despite their importance, questions remain regarding the assessment of silvicultural treatments designed to meet spatial objectives. We initiated a replicated silvicultural assessment of two forest management approaches commonly applied in dense ponderosa pine forests of the Southwest United States: historical evidence-based ecological restoration guidelines (ERG) and northern goshawk ( Accipiter gentilis ) foraging area management recommendations (GMR). We compared stand-level characteristics, global tree location point patterns and tree group-level attributes resulting from the marking of these approaches to current forest conditions and patterns of historical forest remnants in six, 2.02 ha stem mapped plots. We also assessed group-level Vegetative Structural Stage (VSS; a classification of fine-scale forest structural development used to regulate fine-scale spatial patterns in these forests). ERG and GMR-based treatments significantly reduced densities and basal area from the current condition, but did not significantly differ in density from historical forest remnant estimates. GMR-based treatments retained greater stand level basal area than ERG-based treatments, primarily in large, 28–48 cm tree diameter classes. GMR-based treatments approximated global tree location point patterns of forest remnants better than ERG-based treatments, primarily due to a 5–6 m minimum spacing of residual trees, but also likely due to specific aspects of ERG-based marking techniques. Despite this difference, both treatments resulted in group-level characteristics similar to those exhibited by historical forest remnants. Both treatments significantly altered group-level VSS area and reduced variation of tree diameters within classified VSS groups. Our study provides insight how tree marking techniques using historical forest remnants may have important effects on resulting fine-scale forest structure patterns. We also demonstrate how the use of global point or group-level pattern assessment methods can affect the evaluation of fine-scale spatial pattern objectives. Our analysis of VSS group characteristics highlights implementation and assessment issues associated with group-level spatial pattern identification, classification and regulation. We conclude that group-level classification and regulation is not necessary for maintaining fine-scale spatial patterns in complex ponderosa pine ecosystems subject to frequent fire disturbances and changing future climate conditions and societal demands. Both ERG and GMR-based approaches applied in this study may have utility in maintaining fine-scale spatial heterogeneity and promoting resiliency in Southwest ponderosa pine forests. [ABSTRACT FROM AUTHOR]

Forests on tribal lands in the western United States have seen the return of low-intensity surface fires for several decades longer than forests on non-tribal lands. We examined the surface fire regime in a ponderosa pine-dominated (Pinus ponderosa) forest on the Hualapai tribal lands in the south-western United States. Using fire-scarred trees, we inferred temporal (frequency and seasonality) and spatial (synchrony) attributes and regulators of the fire regime over three land-use periods (historical, suppression, modern) between 1702 and 2007. Patterns of fire frequency and synchrony were similar, but fire seasonality was dissimilar, between the historical and modern periods. Logistic regression and generalised linear mixed models identified a suite of variables representing fuels, climate and human land uses that were associated with the probability of a site burning. Combined, these results allow for valuable insights regarding past fire spread and variability in fire frequency throughout our study area. In some respects, the current distinct fire regime in our study area, which predominately consists of prescribed fires implemented since the 1960s, resembles the past frequent surface fire regime that occurred here and in similar forest types on non-tribal lands in the south-western United States. Our results will be useful for informing adaptive management throughout the region as climate warms. We studied the surface fire regime in a forest on tribal lands where prescribed burning has occurred since the 1960s. Fire frequency and synchrony were similar, but fire seasonality was dissimilar, between the historical and modern land-use periods. Fuels, climate and human land uses regulated the fire regime over time. [ABSTRACT FROM AUTHOR]

Copyright of Fire Ecology is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Highlights: [•] Southwestern warm/dry mixed conifer structure and fire regimes are poorly understood. [•] Three sites were established to determine historical fire regime and forest structure. [•] Our sites exhibited different fire histories shaping forests with distinct age structures. [•] Our sites had diversity in overall and individual species forest structure attributes. [•] Site-specific reference conditions are needed for warm/dry mixed conifer restoration. [Copyright &y& Elsevier]

Abstract: Increases in stand-replacing wildfires in the western USA have widespread implications for ecosystem carbon (C) cycling, in part because the decomposition of trees killed by fire can be a long-term source of CO2 to the atmosphere. Knowledge of the composition and function of decay fungi communities may be important to understanding how wildfire alters C cycles. We assessed the effects of stand-replacing wildfires on the community structure of wood-inhabiting fungi along a 32-yr wildfire chronosequence. Fire was associated with low species richness for up to 4 yr and altered species composition relative to unburned forest for the length of the chronosequence. A laboratory incubation demonstrated that species varied in their capacity to decompose wood; Hypocrea lixii, an indicator of the most recent burn, caused the lowest decomposition rate. Our results show that stand-replacing wildfires have long-term effects on fungal communities, which may have consequences for wood decomposition and C cycling. [Copyright &y& Elsevier]

The purpose of this study was to reconstruct the precipitation at Basaseachi National Park (BNP) in Chihuahua, Mexico. Tree-ring samples from pine species including Pinus durangensis, P. lumholtzii and P.engelmannii were collected in and near BNP and they were cross-dated with existing chronologies. Ring widths of each sample were measured and models to remove non-climatic trends from the data were applied. The relationship between precipitation from the weather station in Yécora, Sonora, and the ring width indices were modeled using a bivariate linear regression (r² = 0,59, p<0.01). It was found that precipitation from the months of October, December, February and April was most highly correlated with tree ring growth. The reconstruction extends 225 years from 2007-1782. During this time period there were thirteen severe droughts, ten of which affected large areas in northern and central Mexico. [ABSTRACT FROM AUTHOR]

Surface fire has increasingly been regarded as a critical threat to tropical forests, but much of the research documenting degradation of tropical forests by fire comes from the low-elevation humid tropics. Fire in high-elevation tropical forests has received less research attention, but these forests are of high conservation value because they support unique ecosystems, which are often isolated due to their restriction to widely separated peaks., We investigated the frequency and ecological impact of fire on a high-elevation tropical forest of Pinus hartwegii in Pico de Orizaba National Park in central Mexico. This forest was previously thought to have been degraded by excessive human-caused fires. We assessed human-caused changes to the fire regime as well as the impact of climate on fire occurrence, both previously undocumented in this region., We found no increase in fire frequency or evidence of degradation of the forest. We found that the forest was uneven-aged and contained many large and old trees (maximum age 483 years). In the twentieth century, the forest experienced a frequent surface fire regime, with fires scarring trees in 90 of 100 years. However, most fires were small and asynchronous among sites. Inter-annual climatic variability was not an influential driver of fire, and El Niño- Southern Oscillation was not significantly related to the occurrence of widespread fire., Synthesis and applications. Our results show that this high-elevation tropical forest has not been degraded but has existed with frequent fires for at least a century. A trend in the 21st century towards less-frequent fire could be cause for concern, as a decrease in fire frequency could lead to an increase in tree density and a loss of resilience in the face of climate change and other future disturbance. We recommend that managers take into account historical fire regimes in their local areas: frequent surface fires in the case of Pico de Orizaba. It is important to recognize that although fire can be detrimental in many low-elevation tropical forests, it is an integral part of this high-elevation tropical forest ecosystem, and other high-elevation forests may show similar patterns. [ABSTRACT FROM AUTHOR]

Abstract: Although development of pinyon–juniper woodlands is understood to require decades after stand-replacing fire, data describing relationships between many key structural elements and time since fire (TSF) are lacking. In this study, we sampled live trees, seedlings, shrubs, snags, and downed logs on 13 sites that together comprised a 370-year fire chronosequence. We analyzed individual relationships between structural attributes and TSF. We also developed an additive index of structural complexity and analyzed its relationship with TSF. Live juniper and total tree density were positively and linearly related to TSF (R 2 =0.76 and 0.49, respectively). Pinyon tree density and TSF were not significantly related. No live trees (⩾1.37m height) were found on sites burned less than 30years before sampling, although seedlings were found as early as 6years TSF. Live pinyon tree biomass, live juniper biomass, and total tree biomass followed “s-shaped” functions (4-parameter Weibull; R 2 =0.32, 0.62, and 0.96, respectively), with total biomass maximizing at 65Mgha−1 around 250years since fire. Seedling densities and shrub cover were not significantly related to TSF. Juniper snag density showed a significant negative relationship with TSF (R 2 =0.54) and total snag density followed a “u-shaped” function depending on TSF (2nd-order polynomial; R 2 =0.47). Pinyon snag density and TSF were not significantly related. Density of rotten logs was positively and linearly related to TSF (R 2 =0.46) whereas sound logs and TSF were not statistically related. Structural complexity showed a positive linear relationship with TSF (R 2 =0.46). These results indicate that although individual structural elements show various relationships with TSF, structural complexity increases as sites approach persistent woodland conditions. Findings from this study provide resource professionals with information that can help in developing and assessing management approaches intended to emulate natural structural patterns. [Copyright &y& Elsevier]

Abstract: Over a century of fire suppression in warm/dry mixed conifer forests of southwestern Colorado, USA has resulted in changes that have disrupted feedback interactions between vegetation composition and structure and the accompanying natural fire regime. The ecosystem is now more susceptible to high intensity crown fires that were previously rare or absent in this forest type, which can lead to novel ecosystems. We established four replicated blocks of (1) thin/burn, (2) burn alone and (3) control treatments, each approximately 16-ha, to quantify the effects of restoration treatments on forest structure. We sampled in 2003 (pre-treatment) and in 2009 (post-treatment). There were no significant changes in the control and burn alone treatments for tree density, basal area, canopy cover and tree regeneration between pre- and post-treatment. Significant changes in the thin/burn treatments included: tree density declining 82% (582.7treesha−1), principally white fir and Douglas-fir; tree canopy cover decreasing 36%; basal area declining 49% (12.5m2 ha−1), primarily from white fir; aspen tree regeneration increasing by 362% (582.7treesha−1), and white fir regeneration decreasing by 94% (249.1treesha−1). Overstory trees that died tended to be younger, shorter, and/or smaller in diameter. Multivariate analysis of tree basal area by species in the thin/burn treatments in 2009 showed a strong directional shift away from 2003 pre-treatment data towards the reconstructed historical (1870) forest structure. Burn alone treatments were distinct from controls after treatment in 2009 but did not resemble reconstructed 1870 forest structure. Thin/burn treatments moved warm/dry mixed conifer forests in southwestern Colorado rapidly along the trajectory toward historical reference conditions by altering forest composition and structure. Burn alone treatments were less effective but also less costly. Forest restoration will make forests more resilient to stand-replacing fires and subsequent transitions to novel ecosystems under a warmer, drier climate. [Copyright &y& Elsevier]

Severe forest fires worldwide leave behind large quantities of dead woody debris and regenerating trees that can affect future ecosystem trajectories. We studied a chronosequence of severe fires in Arizona, USA, spanning 1 to 18 years after burning to investigate postfire woody debris and regeneration dynamics. Snag densities varied over time, with predominantly recent snags in recent fires and broken or fallen snags in older fires. Coarse woody debris peaked at > 60 Mg/ha in the time period 6-12 years after fire, a value higher than previously reported in postfire fuel assessments in this region. However, debris loadings on fires older than 12 years were within the range of recommended management values (11.2-44.8 Mg/ha). Overstory and regeneration were most commonly dominated by sprouting deciduous species. Ponderosa pine ( C. Lawson var. Engelm.) overstory and regeneration were completely lacking in 50% and 57% of the sites, respectively, indicating that many sites were likely to experience extended periods as shrublands or grasslands rather than returning rapidly to pine forest. More time is needed to see whether these patterns will remain stable, but there are substantial obstacles to pine forest recovery: competition with sprouting species and (or) grasses, lack of seed sources, and the forecast of warmer, drier climatic conditions for coming decades. [ABSTRACT FROM AUTHOR]

ABSTRACT.-Climate change is predicted to increase the frequency of severe drought, yet little information exists on the impacts of drought on dominant trees of Mexican pine forests, which are among the most biologically diverse forests in the world. We conducted the first comparison of growth sensitivity to drought of two co-occurring Pinus species in Mexico to understand whether growth of dominant pines of the Sierra Madre Occidental in northern Mexico is sensitive to drought and temperature variation and to understand how sensitivity differs between tree species and elevations. We sampled and analyzed tree-ring data across a 400-m elevation gradient for the years 1945-2004 for co-occurring Pinus engelmannii and Pinus lumholtzii at Basaseachi National Park, Chihuahua, Mexico. We hypothesized that growth sensitivity to drought would be highest at low elevations, annual basal area increment (BAI) would be lowest at low elevations, and winter precipitation would covary positively with BAI at all elevations. Growth sensitivity to drought, as measured by a wet-dry ring-width index ratio (W:D), was significantly higher for both species at low elevations (W:D range 2.2-2.8) than at intermediate and high elevations (W:D range 1.5-1.9). Pinus engelmannii had significantly higher W:D (2.2) than P. lumholtzii (1.8). Annual BAI did not differ between elevations or species. Annual ring-width index was positively and significantly associated with winter (December-April) precipitation. This association was stronger at low elevations than at high elevations. Other seasons of precipitation and other climatic variables were not significantly associated with annual growth. Our results suggest that the increasing frequency and severity of drought predicted for this region in the coming decades will reduce growth of P. engelmannii and P. lumholtzii, with greater impacts on low-elevation populations and on P. engelmannii. [ABSTRACT FROM AUTHOR]

Copyright of Western North American Naturalist is the property of Monte L. Bean Life Science Museum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We analyzed one of the longest-term ecological data sets to evaluate how forest overstory structure is related to herbaceous understory plant strategies in a ponderosa pine forest. Eighty-two permanent 1-m² chart quadrats that were established as early as 1912 were remeasured in 2007. We reconstructed historical forest structure using dendrochronological techniques. Ponderosa pine basal area increased from an average of 4 m²/ha in the early 1900s to 29 m²/ha in 2007. Understory plant foliar cover declined by 21%, species richness declined by two species per square meter, and functional diversity also declined. The relative cover of C4 graminoids decreased by 18% and C3 graminoids increased by 19%. Herbaceous plant species with low leaf and fine root nitrogen concentrations, low specific leaf area, high leaf dry matter content, large seed mass, low specific root length, short maximum height, and early flowering date increased in relative abundance in sites where pine basal area increased the most. Overall, we observed a long-term shift in composition toward more conservative shade- and stress-tolerant herbaceous species. Our analysis of temporal changes in plant strategies provides a general framework for evaluating compositional and functional changes in terrestrial plant communities. [ABSTRACT FROM AUTHOR]

Abstract: Broadcast seeding is one of the most widely used post-wildfire emergency response treatments intended to reduce soil erosion, increase vegetative ground cover, and minimize establishment and spread of non-native plant species. We conducted an evidence-based review to examine the effectiveness and effects of post-wildfire seeding treatments on soil stabilization, non-native species invasion, and plant community recovery in the western U.S. We reviewed 94 scientific papers and agency monitoring reports identified using a systematic search protocol. As sampling designs have become more rigorous in recent years, evidence that seeding is effective in reducing erosion has decreased. Of highest and high quality studies evaluating soil erosion, 92% (11 of 12) were published since 2000, none of which showed an effective result. Before 2000, the majority of the studies (71%) fell into the lowest quality categories, of which 72% showed seeding to be effective. The majority of studies (20 of 27, 74%) evaluating soil erosion in seeded versus unseeded controls showed that seeding did not reduce erosion relative to unseeded controls. Even when seeding significantly increased vegetative cover, seeded sites rarely supported plant cover levels considered sufficient to stabilize soils within the first and second year post-wildfire. Of the 11 studies evaluating seeding effectiveness for curtailing invasions of non-native plant species, an almost equal percentage found seeding treatments to be either effective (54%, 6 studies) or ineffective (45%, 5 studies). However, the majority of effective and ineffective treatments (83% and 80%, respectively) used non-native species. Sixteen of 26 studies (62%) evaluating seeding effects on plant communities reported that seeding suppressed recovery of native plants, although data on long-term impacts of this reduction are limited. The literature suggests that post-wildfire seeding does little to protect soil in the short-term, has equivocal effect on invasion of non-native species, and can have negative effects on native vegetation recovery, although long-term studies are needed to assess lasting impacts of seeded species. [Copyright &y& Elsevier]

Forest restoration guided by historical reference conditions of fire regime, forest structure, and composition has been increasingly and successfully applied in fire-adapted forests of western North America. But because climate change is expected to alter vegetation distributions and foster severe disturbances, does it make sense to restore the ecological role of wildland fire through management burning and related activities such as tree thinning? I suggest that some site- and date-specific historical conditions may be less relevant, but reference conditions in the broad sense are still useful. Reference conditions encompass not only the recent past but also evolutionary history, reflecting the role of fire as a selective force over millennia. Taking a long-term functional view of historical reference conditions as the result of evolutionary processes can provide insights into past forest adaptations and migrations under various climates. As future climates change, historical reference data from lower, southerly, and drier sites may be useful in places that are higher, northerly, and currently wetter. Almost all models suggest that the future will have substantial increases in wildfire occurrence, but prior to recent human-caused fire exclusion, fire-adapted pine forests of western North America were among the most frequently burned in the world. Restoration of patterns of burning and fuels/forest structure that reasonably emulate historical conditions prior to fire exclusion is consistent with reducing the susceptibility of these ecosystems to catastrophic loss. Priorities may include fire and thinning treatments of upper elevation ecotones to facilitate forest migration, whereas vulnerable low-elevation forests may merit less management investment. [ABSTRACT FROM AUTHOR]

We used maps of fire evidence, fire scar dendrochronology, forest age-structure analysis, and landscape analysis to investigate fire history at pinyon pine (Pinus edulis Engelm.) – juniper (Juniperus osteosperma (Torr.) Little, Juniperus scopulorum Sarg.) woodland – ponderosa pine (Pinus ponderosa P. & C. Lawson) forest ecotones in Arizona (Tusayan) and in New Mexico (Canjilon). Results showed that charred trees were not evenly distributed across vegetative communities but were significantly (p < 0.001) more abundant than expected in ponderosa pine communities. Composite fire scar analysis indicated that surface fires occurred in ponderosa pine stands at both sites and burned at intervals of 7.2–11.1 years (WMPI; Weibull median probability interval). At Tusayan, landscape structure was fine grained, and maximum pinyon age was >200 years across 80% of the site. At Canjilon, landscape pattern was relatively coarse, and most pinyon patches were 200–300 years old. Cumulative standing age distributions suggested pinyon–juniper fire rotations of 340 and 290 years at Tusayan and Canjilon, respectively. We concluded the following: (i) surface fires in ponderosa pine stands did not spread through pinyon–juniper communities at either site, (ii) fire evidence was prevalent across both sites, but old pinyon trees indicated that no widespread lethal fires had occurred in the last 300–400 years, and (iii) structurally heterogeneous landscapes suggested that historical pinyon–juniper fires were of limited extent but lethal in patches. [ABSTRACT FROM AUTHOR]

We evaluated canopy fuels and potential fire behaviour changes following landscape-scale restoration treatments in a ponderosa pine forest at Mt Trumbull, Arizona, USA. The goal of the project was to restore historical forest structure by thinning and burning, thereby reducing canopy fuels and minimising active crown fire potential. We measured 117 permanent plots before (1996-97) and after (2003) treatments. The plots were evenly distributed across the landscape and represented an area of ~1200 ha, about half of which was an untreated control. We compared canopy fuel estimates using three different methods to assess whether fire behaviour modelling outputs were sensitive to the choice of canopy fuel equation. Treatments decreased canopy fuel load by 43-50% from 0.77-1.83 kg m-2 to 0.44-0.91 kg m-2 (the range of values reflects the different canopy fuel equations) and decreased canopy bulk density by 42-61% from 0.038-0.172 kg m-3 to 0.022-0.067 kg m-3 in the treated area, while slight increases occurred in the control. We applied two fire models to estimate potential fire behaviour: FlamMap and NEXUS. These models differ in several important features but predicted outcomes were consistent: under extreme drought and wind conditions, the proportion of the landscape susceptible to active crown fire decreased in the treated area while little change occurred in the control. [ABSTRACT FROM AUTHOR]

Forest restoration in southwestern ponderosa pine forests often consists of tree thinning and prescribed fire. Understanding the effects of thinning treatments on soil integrity is important due to the potential negative effects on soil properties and plant composition and abundance. We investigated the effects of harvest severity levels (control, low, intermediate, high) and harvest systems (machine, hand, whole-tree) on soil profile disturbance, soil bulk density, and dead woody biomass. There were no significant differences in soil profile disturbance, soil bulk density, or dead woody biomass among harvest severity levels. The whole-tree harvest system produced significantly larger areas with high levels of soil profile disturbance and significantly smaller areas with no soil disturbance than either the machine- or hand-harvest systems. There were no significant differences in soil bulk density due to insufficient sampling design. Dead woody biomass was significantly lower in the whole-tree harvested areas than the hand- or machine-harvested areas. Dead woody biomass can play an important role in providing microsites for plant reestablishment following disturbance. Our results illustrate that the type of harvest system used in forest restoration treatments is an important factor that needs to be incorporated into forest restoration design to insure compatibility with overall restoration goals. [ABSTRACT FROM AUTHOR]

The 2002 Rodeo-Chediski fire, the largest wildfire in south-western USA history, burned over treated stands and adjacent untreated stands in the Apache-Sitgreaves National Forest, setting the stage for a natural experiment testing the effectiveness of fuel reduction treatments under conditions of extraordinary fire severity. In seven pairs of treated-untreated study sites measured 2 years after the fire, thinning was strongly associated with reduced burn severity. Treated areas had more live trees, greater survival, and reduced fire intensity as indicated by crown base height and bole char. Ponderosa pine regeneration was patchy but more dense in treated areas. We assessed decade- to century-long effects of the pre-wildfire fuel treatments using the Forest Vegetation Simulator (FVS). Differences between treated and untreated areas were projected to persist for several decades after the fire in terms of stand structure characteristics and for at least 100 years in terms of species composition, with ponderosa pine making up ~60% of basal area in treated areas but only 35% in untreated areas. Future ecosystem development may take the trajectory of recovery to a ponderosa pine/Gambel oak forest or of a shift to an alternative stable state such as an oak-dominated shrubfield, with untreated areas more apt to undergo a shift to a shrubfield state. Current management decisions about fuel treatments have multi-century legacies. [ABSTRACT FROM AUTHOR]

The article discusses the experts's viewpoints on the effects and tradeoffs of diameter caps for thinning southwestern Ponderosa pine forests in the United States. Greater size limits of pine trees that are allowed to be cut and termed diameter caps, resulted in polarization, litigation and delays, and alterations to thinning projects in many western forests. Southwestern Ponderosa pine forests stand as the epitome of viewpoints on caps. Simulation of the effects of caps on thinning prohibitions are provided. The discussion concludes that diameter caps may enhance some ecosystem components, but they have a negative impact on nontree components.

Aim Our objectives were to compare understorey plant community structure among forest types, and to test hypotheses relating understorey community structure within lower montane and subalpine forests to fire history, forest structure, fuel loads and topography. Location Forests on the North Rim of Grand Canyon National Park, Arizona, USA. Methods We measured understorey (< 1.4 m) plant community structure in 0.1-ha plots. We examined differences in univariate response variables among forest types, used permutational manova to assess compositional differences between forest types, and used indicator species analysis to identify species driving the differences between forest types. We then compiled sets of proposed models for predicting plant community structure, and used Akaike's information criterion (AICC) to determine the support for each model. Model averaging was used to make multi-model inferences if no single model was supported. Results Within the lower montane zone, pine–oak forests had greater understorey plant cover, richness and diversity than pure stands of ponderosa pine ( Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.). Plant cover was negatively related to time since fire and to ponderosa pine basal area, and was highest on northern slopes and where Gambel oak ( Quercus gambelii Nutt.) was present. Species richness was negatively related to time since fire and to ponderosa pine basal area, and was highest on southern slopes and where Gambel oak was present. Annual forb species richness was negatively related to time since fire. Community composition was related to time since fire, pine and oak basal area, and topography. Within subalpine forests, plant cover was negatively related to subalpine fir basal area and amounts of coarse woody debris (CWD), and positively related to Engelmann spruce basal area. Species richness was negatively related to subalpine fir basal area and amounts of CWD, was positively related to Engelmann spruce basal area, and was highest on southern slopes. Community composition was related to spruce, fir and aspen basal areas, amounts of CWD, and topography. Main conclusions In montane forests, low-intensity surface fire is an important ecological process that maintains understorey communities within the range of natural variability and appears to promote landscape heterogeneity. The presence of Gambel oak was positively associated with high floristic diversity. Therefore management that encourages lightning-initiated wildfires and Gambel oak production may promote floristic diversity. In subalpine forests, warm southern slopes and areas with low amounts of subalpine fir and CWD were positively associated with high floristic diversity. Therefore the reduction of CWD and forest densities through managed wildfire may promote floristic diversity, although fire use in subalpine forests is inherently more difficult due to intense fire behaviour in dense spruce–fir forests. [ABSTRACT FROM AUTHOR]

This article studies initial carbon, nitrogen, and phosphorus fluxes following ponderosa pine restoration treatments. Humans affect all terrestrial ecosystems, but some ecosystems are not resilient to human-induced disturbances, and large changes in structure and function follow perturbation. Prior to Euro-American settlement, frequent fires, herbaceous competition, and drought limited southwestern ponderosa pine regeneration but rarely killed large trees. This new forest structure supports a stand-replacing fire regime and expansive herbivorous insect outbreaks. Ecological restoration is being used throughout the Southwest to return ponderosa pine forests to pre-settlement conditions by thinning post- settlement trees and introducing prescribed fires. These treatments clearly restore the tree density, fuel, and fire characteristics of the pre-settlement forest. The thinning restoration treatment removed most of the aboveground post-settlement tree biomass from the site. The composite restoration included post-settlement tree removal, manual forest floor fuel reduction, and a prescribed burn.

The article summarizes information on pine-dominated forests in south-western North America that have relatively intact disturbance regimes. This information could be used by forest managers interested in restoring similar forests in the region, particularly in western forests that have experienced a significant increase in area burned over the last 60 years. Reference or "relict" sites are rare because most landscapes have been impacted heavily by industrial human society. In the United States, true relicts include physically inaccessible areas, such as steep mesas at Zion National Park or forest patches isolated by sharp lava flows at El Malpais, New Mexico. These unusual sites may be inherently different from larger forestlands. In many areas of the western United States with ponderosa pine, jeffrey pine and mixed conifer forests, past harvesting has removed the largest trees and fire suppression and livestock grazing have increased understory tree density and fuel loads. Information from forests with relatively intact disturbance regimes can assist in the development of desired conditions in some forests of the U.S.

Ecological restoration of ponderosa pine (Pinus ponderosa) forests in the southwestern United States is a relatively new, adaptive management practice that potentially alters wildlife habitat during and immediately after restoration treatments. To determine whether restoration treatments affected Merriam's wild turkey (Meleagris gallopavo merriami) use of roost sites, we relocated 91 of 120 turkey roost sites that originally had been mapped in 1985 in the Uinkaret Mountains of northern Arizona. We compared current turkey use of historical roost sites in stands that had been thinned and burned between 1995 and 2002 to adjacent (<800 m away) and distant (>800 m) stands. In 2002, 23 historical roosts were still in use, and in 2003, 13 were still in use, 5 of which had not been used in 2002. The number of historical roost sites still in use among treated, adjacent, and distant stands did not differ from that expected based on the total number of historical roosts in each stand type. We also searched for new roosts while traveling between historical roost sites and found 2.2 new roosts per hour searched in treated stands, 1.5 in adjacent stands, and 1 .0 in distant stands. As expected, active roost sites in treated stands had significantly lower basal area, fewer stems, and less canopy cover compared to roost sites in untreated areas. However, roost trees in treated and untreated stands did not differ in diameter at breast height, height, or distance to the lower limb, indicating that treatment did not affect these characteristics. Several factors unique to our study site may have influenced our results: treated areas represented only 5% of total habitat available, treatments occurred primarily on flat areas and not on ridges or slopes, and treatments were implemented over several years. [ABSTRACT FROM AUTHOR]

Relatively intense burning has been suggested as a possible alternative to the restoration of pre-European settlement forest conditions and fire regime in mixed conifer forests, in contrast to thinning of trees and light prescribed burning. In 1993 a management-ignited fire in a dense, never-harvested forest in Grand Canyon National Park escaped prescription and burned with greater intensity and severity than anticipated. We sampled the burned site and an adjacent unburned site (270 ha each) 6 years after the fire to assess burn effects on tree structure (species composition, size and age distributions, regeneration, and snags), forest floor fuels, and coarse woody debris. Tree structure before fire-regime disruption (1879 CE) was reconstructed with dendroecological techniques. By 6 years after burn the fire reduced average tree density (331 trees/ha) and basal area (28.5 m2/ha) to levels similar to pre-European reference conditions (approximately 246 trees/ha and 28.5 m2/ha). Mortality was concentrated in fire-susceptible species, especially white fir, restoring dominance by fire-resistant ponderosa pine. Forest floor fuels were reduced, and regeneration by aspen and understory plants was vigorous. Densities of large snags and logs were high. However the fire also killed a high proportion of old-growth trees, especially aspen. Burning created more spatial variability in forest structure than was present before fire-regime disruption by killing many trees in some areas of the site but few in other areas. The intentional use of severe burning would be challenging to managers because of the increased risk of escaped fires, but the ecological outcome of this particular wildfire was not inconsistent with ecological restoration goals for this ecosystem type. [ABSTRACT FROM AUTHOR]

Focuses on fire regime characteristics of high-elevation forests on the North Rim of the Grand Canyon, Arizona. Factors, taken into account for determining the characteristics; Tree densities and fire-/non-fire-initiated groups, found in the region; Factors used to classify sampling points into fire-initiated and non-fire-initiated groups.

Aim Compare contemporary with pre-fire-disruption forest structures, assessing the influence of factors that caused ecological change and evaluating remote sites as relatively natural areas. Location Grand Canyon National Park contains the largest never-harvested and long-term ungrazed forest ecosystem in Arizona, providing valuable sites for measuring natural variability. However, anthropogenic disruption of natural fire regimes since Euro-American settlement c. 1880 has led to changes in forest structure. Methods We compared species composition, tree structure, regeneration, and canopy cover on large (135–603 ha) ponderosa pine-dominated study sites: (1) isolated points on the North Rim where some surface fires continued after 1880, (2) a higher-elevation North Rim site where fire has been excluded and (3) a South Rim site, also without recent fire, with a paired Kaibab National Forest site. Forest tree structure prior to fire-regime disruption was reconstructed with dendroecological techniques. Results Before fire exclusion, all sites had relatively low tree density (140–246 trees ha-1 ) dominated by large trees (basal area 9.1–28.5 m2 ha-1 ), primarily ponderosa pine or pine/Gambel oak on the South Rim. Currently all sites are relatively dense (389–955 trees ha-1 , 14.1–41.3 m2 ha-1 ) but patterns of species composition and regeneration differed substantially with fire regime and elevation. Regeneration at continued-fire sites was primarily through sprouting species, Gambel oak and New Mexican locust, forming a shrubby midstorey under a relatively open pine canopy. In contrast, all fire-excluded sites were dense with seed-reproducing conifer species. Main conclusions Comparison of change caused by climate fluctuation, tree cutting, fire exclusion, livestock herbivory, and wildlife herbivory, suggests that fire regime alteration appears to have played the... [ABSTRACT FROM AUTHOR]

Old growth in the frequent-fire conifer forests of the western United States, such as those containing ponderosa pine (Pinus ponderosa), Jeffrey pine (P. jeffreyi), giant sequoia (Sequioa giganteum) and other species, has undergone major changes since Euro-American settlement. Understanding past changes and anticipating future changes under different potential management scenarios are fundamental to developing ecologically based fuel reduction or ecological restoration treatments. Some of the many changes that have occurred in these forests include shifts from historically frequent surface fire to no fire or to stand-replacing fire regimes, increases in tree density, increased abundance of fire-intolerant trees, decreases in understory productivity, hydrological alterations, and accelerated mortality of old trees. Although these changes are widespread, the magnitude and causes of changes may vary within and among landscapes. Agents of change, such as fire exclusion or livestock grazing, likely interacted and had multiple effects. For example, historical ranching operations may have altered both fire regimes and understory vegetation, and facilitated institutional fire exclusion through fragmentation and settlement. Evidence exists for large variation in presettlement characteristics and current condition of old growth across this broad forest region, although there are many examples of striking similarities on widely distant landscapes. Exotic species, climate change, unnatural stand-replacing wildfires, and other factors will likely continue to degrade or eradicate old growth in many areas. As a policy of fire exclusion is proving to be unsustainable, mechanical tree thinning, prescribed fire, or wildland fire use will likely be key options for forestalling continued eradication of old growth by severe crown fires. For many practical and societal reasons, the wildland—urban interface may afford some of the most immediate opportunities for re-establishing old growth typical of presettlement forests resistant to crown fires. [ABSTRACT FROM AUTHOR]

There are varying definitions of old-growth forests because of differences in environment and differing fire influence across the Intermountain West. Two general types of forests reflect the role of fire: 1) forests shaped by natural changes in structure and species makeup—plant succession—that are driven by competitive differences among species and individual trees and by small-scale disturbances, and 2) forests where plant succession processes are disrupted by major biological disturbances (fire, insects, wind, or drought) extending across larger areas. Some case examples of old-growth forests where fire was historically frequent are used. The examples sketch out the typical biophysical settings, fire regime, natural disturbance factors, spatial features of patches, and the processes and conditions that produce spatial changes of the landscape over time. These examples confirm the complexity of describing or defining old growth in frequent-fire forests. We define fire-adapted forests at three spatial scales, whereas the standard definition of old growth refers to a patch or stand condition. Our definition is based on ecological principles rather than on the cultural aspects of old growth. It focuses on central tendencies, given all the possible combinations of conditions and processes, that move forests toward old growth in the fire-adapted forests of the Intermountain West. [ABSTRACT FROM AUTHOR]

Persistent changes in tree mortality rates can alter forest structure, composition, and ecosystem services such as carbon sequestration. Our analyses of longitudinal data from unmanaged old forests in the western United States showed that background (noncatastrophic) mortality rates have increased rapidly in recent decades, with doubling periods ranging from 17 to 29 years among regions. Increases were also pervasive across elevations, tree sizes, dominant genera, and past fire histories. Forest density and basal area declined slightly, which suggests that increasing mortality was not caused by endogenous increases in competition. Because mortality increased in small trees, the overall increase in mortality rates cannot be attributed solely to aging of large trees. Regional warming and consequent increases in water deficits are likely contributors to the increases in tree mortality rates. [ABSTRACT FROM AUTHOR]