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Characterization of forest structure is important for management-related decision making, monitoring, and adaptive management. Increasingly, observations of forest structure are needed at both finer resolutions and across greater extents to support spatially explicit management planning. Unmanned aerial system (UAS) based photogrammetry provides an airborne method of forest structure data acquisition at a significantly lower cost and time commitment than existing methods such as airborne laser scanning (LiDAR). This study utilizes nearly 5000 stem-mapped trees in ponderosa pine (Pinus ponderosa Lawson & C. Lawson) dominated forests to evaluate several algorithms for detecting individual tree locations and characterizing crown area across tree sizes. Our results indicate that adaptive variable window detection methods with UAS-based canopy height models have greater tree detection rates compared with fixed window analysis across a range of tree sizes. Using the UAS approach, probability of detecting individual trees decreases from 97% for dominant overstory to 67% for suppressed understory trees. Additionally, crown radii were correctly determined within 0.5 m for approximately two-thirds of sampled trees. These findings highlight the potential for UAS photogrammetry to characterize forest structure through the detection of trees and tree groups in open-canopy ponderosa pine forests. Further work should investigate how these methods transfer to more diverse species compositions and forest structures. Key words: detection, canopy height model, crown delineation, drone, forest structure. Il est important de caracteriser la structure forestiere pour eclairer les decisions de gestion, le suivi et la gestion adaptative. De plus en plus, des observations de la structure forestiere sont necessaires, tant a des resolutions plus fines que sur de plus vastes etendues, pour soutenir une planification de gestion spatialement explicite. La photogrammetrie basee sur des systemes aeriens sans pilote (SASP) fournit une methode aeroportee d'acquisition de donnees sur la structure forestiere a un cout et un investissement en temps nettement inferieurs a ceux des methodes existantes telles que le balayage laser aeroporte. Cette etude utilise pres de 5 000 tiges d'arbre cartographiees, dans des forets dominees par le pin ponderosa (Pinus ponderosa Lawson & C. Lawson), pour evaluer plusieurs algorithmes de detection de l'emplacement des arbres individuels et de caracterisation de la surface de la couronne des arbres de differentes tailles. Nos resultats indiquent que les methodes adaptatives de detection a fenetre variable avec des modeles de hauteur du couvert forestier sur la base des donnees de SASP ont des taux de detection d'arbres plus eleves que l'analyse a fenetre fixe pour un assortiment de tailles d'arbres. Avec l'utilisation des SASP, la probabilite de detecter des arbres individuels passe de 97 % pour l'etage dominant a 67 % pour les arbres opprimes du sous-etage. De plus, les rayons de la couronne ont ete correctement determines, a moins de 0,5 m, pour environ les deux tiers des arbres echantillonnes. Ces resultats mettent en evidence le potentiel de la photogrammetrie basee sur les SASP pour caracteriser la structure forestiere grace a la detection d'arbres et de groupes d'arbres dans les forets de pins ponderosa dont le couvert n'est pas ferme. Des travaux supplementaires devraient etudier comment ces methodes peuvent s'appliquer a des compositions d'especes et des structures forestieres plus diverses. [Traduit par la Redaction] Mots-cles : detection, modele de hauteur du couvert forestier, delimitation des couronnes, drone, structure forestiere., Introduction Since the early 2000s, ecological management of dry, lower montane forest systems has increasingly focused on variability and spatial arrangement of horizontal and vertical forest structure (Lydersen et al. [...]

Wildland fire management has reached a crossroads. Current perspectives are not capable of answering interdisciplinary adaptation and mitigation challenges posed by increases in wildfire risk to human populations and the need to reintegrate fire as a vital landscape process. Fire science has been, and continues to be, performed in isolated "silos," including institutions (e.g., agencies versus universities), organizational structures (e.g., federal agency mandates versus local and state procedures for responding to fire), and research foci (e.g., physical science, natural science, and social science). These silos tend to promote research, management, and policy that focus only on targeted aspects of the "wicked" wildfire problem. In this article, we provide guiding principles to bridge diverse fire science efforts to advance an integrated agenda of wildfire research that can help overcome disciplinary silos and provide insight on how to build fire-resilient communities.

Abstract: individual host plants. Lodgepole pine dwarf mistletoe is an important parasite in forests of the western USA that causes reductions to productivity and is thought to alter wildland fuel [...]

Tree spatial patterns in dry coniferous forests of the western United States, and analogous ecosystems globally, were historically aggregated, comprising a mixture of single trees and groups of trees. Modern forests, in contrast, are generally more homogeneous and overstocked than their historical counterparts. As these modern forests lack regular fire, pattern formation and maintenance is generally attributed to fire. Accordingly, fires in modern forests may not yield historically analogous patterns. However, direct observations on how selective tree mortality among pre‐existing forest structure shapes tree spatial patterns is limited. In this study, we (a) simulated fires in historical and contemporary counterpart plots in a Sierra Nevadan mixed‐conifer forest, (b) estimated tree mortality, and (c) examined tree spatial patterns of live trees before and after fire, and of fire‐killed trees. Tree mortality in the historical period was clustered and density‐dependent, because trees were aggregated and segregated by tree size before fire. Thus, fires maintained an aggregated distribution of tree groups. Tree mortality in the contemporary period was widespread, except for dispersed large trees, because most trees were a part of large, interconnected tree groups. Thus, postfire tree patterns were more uniform and devoid of moderately sized tree groups. Postfire tree patterns in the historical period, unlike the contemporary period, were within the historical range of variability identified for the western United States. This divergence suggests that decades of forest dynamics without significant disturbances have altered the historical means of pyric pattern formation. Our results suggest that ecological silvicultural treatments, such as forest restoration thinnings, which emulate qualities of historical forests may facilitate the reintroduction of fire as a means to reinforce forest structural heterogeneity. [ABSTRACT FROM AUTHOR]

Shifting fire regimes alter forest structure assembly in ponderosa pine forests and may produce structural heterogeneity following stand-replacing fire due, in part, to fine-scale variability in growing environments. We mapped tree regeneration in eighteen plots 11 to 15 years after stand-replacing fire in Colorado and South Dakota, USA. We used point pattern analyses to examine the spatial pattern of tree locations and heights as well as the influence of tree interactions and topography on tree patterns. In these sparse, early-seral forests, we found that all species were spatially aggregated, partly attributable to the influence of (1) aspect and slope on conifers; (2) topographic position on quaking aspen; and (3) interspecific attraction between ponderosa pine and other species. Specifically, tree interactions were related to finer-scale patterns whereas topographic effects influenced coarse-scale patterns. Spatial structures of heights revealed conspecific size hierarchies with taller trees in denser neighborhoods. Topography and heterospecific tree interactions had nominal effect on tree height spatial structure. Our results demonstrate how stand-replacing fires create heterogeneous forest structures and suggest that scale-dependent, and often facilitatory, rather than competitive, processes act on regenerating trees. These early-seral processes will establish potential pathways of stand development, affecting future forest dynamics and management options. [ABSTRACT FROM AUTHOR]