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Fig. A2. Landscape representation of reference period forest structure types from the 1860s General Land Office survey in the LTB. See Methods for naming convention.
Source publication
Forest conditions prior to extensive land clearing are often used as a point-of-reference by ecologists and resource managers for characterizing the historical range of variability in forest conditions shaped by intact disturbance regimes. Quantitative data on forest reference conditions can be developed from forest surveys and reconstructions usin...
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Dendroecological methods were used to select and analyze fire scarred trees in central Idaho. Twenty four trees and stumps with multiple fire scars were cross-dated to identify the year and season of fire occurrence, referenced to a master chronology developed from increment cores from live trees in the area. Fires were frequent in the area, with W...
Changes in climate, land use and management have led to an increase in woody species encroachment into grasslands, threatening key ecosystem services and resilience. This study uses dendroecological techniques to investigate acclimation strategies of two native woody species, Juniperus virginiana and Pinus ponderosa, to spatial and temporal variabi...
Citations
... We modeled a 100-year period to explore trends and variability within and among management scenarios because many landscape-level dynamics emerge over long time horizons (e.g., carbon flux, effects of a changing climate). Although previous work in the LTW region focused on understanding forest composition and structure under the historical range of variation (Maxwell et al. 2014, McGarigal et al. 2018, we sought to expand upon past work by also considering disturbances under future climate conditions. That said, we acknowledge the substantial uncertainty in projecting future vegetation conditions and fire dynamics; it is certainly possible, as a result, for complex shifts in forest composition to occur (for example, we observe a modeled reduction in Abies magnifica). ...
Rapid environmental changes challenge the resilience of wildlands. The western portion of the Lake Tahoe Basin in California is an important ecological and cultural hotspot that is at risk of degradation from current and future environmental pressures. Historical uses, fire suppression, and a changing climate have created forest landscape conditions at risk of drought stress, destructive fire, and loss of habitat diversity. We prospectively modeled forest landscape conditions for a period of 100 years to evaluate the efficacy of 5 unique management scenarios in achieving desired landscape conditions. Management scenarios ranged from no management other than fire suppression to applying treatments consistent with historical fire frequencies and extent (i.e., regular and broadscale biomass reduction). We developed a decision support tool to evaluate environmental and social outcomes within a single framework to provide a transparent set of costs and benefits. Results illuminated underlying mechanisms of forest resilience and provided actionable guidance to decision makers. Sixteen attributes were assessed in the model after assigning weights to each. We found that removing forest biomass across the landscape, particularly when accomplished using extensive fire-based removal techniques, led to highly favorable conditions for environmental quality and promoted overall landscape resilience. Environmental conditions resulting from extensive fire-based biomass removal also had nominal variation over time, in contrast with strategies that had less extensive and/or used physical removal techniques (e.g., mechanical thinning). Our analysis provides a transparent approach to assess large datasets with complex and interacting variables. Ultimately, we aim to provide insights into the complexities of maintaining optimal conditions and managing landscapes to promote ecosystem resilience in a changing world.
... An important question, even for well-sampled ecoregions, is what is an appropriate spatial scale of inference beyond the immediate stand or vegetation patch where trees were sampled? This can be tested through combinations of fire history, stand reconstructions, and modeling (e.g., Kennedy & McKenzie, 2010;Maxwell et al., 2014). The answer to this question undoubtedly depends on fire size and frequency and varies among landscapes within the continent, with important implications for ongoing debates in fire science and management (e.g., Fulé et al., 2014;Lafon et al., 2017;Matlack, 2013;Oswald et al., 2020). ...
Fire regimes in North American forests are diverse and modern fire records are often too short to capture important patterns, trends, feedbacks, and drivers of variability. Tree‐ring fire scars provide valuable perspectives on fire regimes, including centuries‐long records of fire year, season, frequency, severity, and size. Here, we introduce the newly compiled North American tree‐ring fire‐scar network (NAFSN), which contains 2562 sites, >37,000 fire‐scarred trees, and covers large parts of North America. We investigate the NAFSN in terms of geography, sample depth, vegetation, topography, climate, and human land use. Fire scars are found in most ecoregions, from boreal forests in northern Alaska and Canada to subtropical forests in southern Florida and Mexico. The network includes 91 tree species, but is dominated by gymnosperms in the genus Pinus. Fire scars are found from sea level to >4000‐m elevation and across a range of topographic settings that vary by ecoregion. Multiple regions are densely sampled (e.g., >1000 fire‐scarred trees), enabling new spatial analyses such as reconstructions of area burned. To demonstrate the potential of the network, we compared the climate space of the NAFSN to those of modern fires and forests; the NAFSN spans a climate space largely representative of the forested areas in North America, with notable gaps in warmer tropical climates. Modern fires are burning in similar climate spaces as historical fires, but disproportionately in warmer regions compared to the historical record, possibly related to under‐sampling of warm subtropical forests or supporting observations of changing fire regimes. The historical influence of Indigenous and non‐Indigenous human land use on fire regimes varies in space and time. A 20th century fire deficit associated with human activities is evident in many regions, yet fire regimes characterized by frequent surface fires are still active in some areas (e.g., Mexico and the southeastern United States). These analyses provide a foundation and framework for future studies using the hundreds of thousands of annually‐ to sub‐annually‐resolved tree‐ring records of fire spanning centuries, which will further advance our understanding of the interactions among fire, climate, topography, vegetation, and humans across North America.
... They found that burned plots had 3.5 times lower tree densities (mean = 252 trees/ ha; ± 159 standard deviation [SD]) than unburned plots (mean = 873; ± 498 SD). Taylor et al. (2004Taylor et al. ( , 2014 found similar results in the Lake Tahoe Basin where presettlement (pre-1870) tree densities in historical red fir-western white pine forests (average = 162; range: 118 to 208 trees/ha) were substantially lower than modern forests that were intensively logged in the late 19 th century (average = 538; ...
... A similar pattern was documented in reconstructed presettlement red fir and western white pine forests of the Lake Tahoe Basin, where the distribution of size classes followed a hump-shape pattern and very few presettlement trees were <30 cm d.b.h. (Taylor 2004, Taylor et al. 2014. In contrast, contemporary stands in the same study that were logged in This pattern has also been documented in unlogged contemporary red fir forests after a century of fire exclusion in Crater Lake National Park (Chappell 1991), Thousand Lakes Wilderness (Bekker and Taylor 2010), and Lassen Volcanic National Park (Taylor 2000) in the southern Cascades, as well as in stands in the Sierra Nevada (Potter 1998). ...
... In contrast, a comparison of unlogged red fir stands in both active-fire and long-unburned landscapes found no significant difference in basal area, even with significant increases in overall tree density . Taylor et al. (2004Taylor et al. ( , 2014 found no difference in basal area in their study of presettlement and contemporary red fir-western white pine stands in the Lake Tahoe Basin. They attributed this finding to the longer FRIs found in red fir forests, as well as potential limitations in forest reconstruction methods (i.e., the removal of evidence by decay, logging, or fire) (Taylor 2004, Taylor et al. 2014). ...
This assessment uses historical observations and datasets, as well as studies conducted in contemporary reference landscapes (i.e., those with active fire regimes and minimal management impacts) to define the natural range of variation (NRV) for red fir (Abies magnifica) and subalpine forests in northwestern California and southwestern Oregon.
... However, wildfires could also be restorative to the extent that they return forest structure and distribution closer to reference conditions prior to Euro-American settlement. Restoring dry forests to historical patterns of forest extent and structure is a high management priority, especially because reducing tree density decreases the risk of future tree mortality from fire, drought and insect outbreaks (Maxwell et al. 2014;Addington et al. 2018;Restaino et al. 2019). Furthermore, counteracting tree encroachment into steppe is of high priority to restore steppe ecosystems (Romme et al. 2009;Davies et al. 2011). ...
Context
Increases in tree cover at dry forest margins are a global phenomenon. Yet, how pre-existing tree cover interacts with terrain and water balance to influence tree cover change is not well-understood, nor whether subsequent disturbances restore prior tree cover patterns or create novel patterns.
Objectives
To assess how terrain, water balance and pre-existing patterns of tree cover influenced late twentieth century tree cover change, and how subsequent wildfires altered tree cover patterns.
Methods
We analyzed tree canopy cover at four sites at the forest-steppe ecotone on the eastern side of the Sierra Nevada, California, U.S.A., using aerial photographs from 1953/1955, 1999/2002 and 2016. Influences on tree cover change were assessed using statistical modeling, and tree cover in 1953/1955 was compared with post-wildfire tree cover in 2016.
Results
From 1953 to 2002, area with > 25% canopy cover increased by 1.5 to 5-fold and treeless area decreased by 17–111%. Mesic areas and areas of sparse tree cover close to existing forest tended to gain more canopy cover. Subsequent wildfires caused a mix of net tree cover loss, little change and gain relative to 1953/1955, but at all sites areas with > 25% cover and < 10% cover in 1953/55 experienced net losses and gains respectively by 2016.
Conclusions
Accounting for initial tree cover and its configuration are crucial to assessing water balance and terrain effects on tree cover change. Our work highlights how wildfires can generate novel patterns of tree cover relative to historical baselines, especially following decades of fire exclusion.
... Historical studies indicate that montane forests of the LTB supported frequent fires before the arrival of Euro-Americans (Taylor 2004;Maxwell et al. 2014), with hundreds to thousands of hectares burning per year (Manley et al. 2000). This fire frequency and extent are proportionate to forest fire regimes throughout much of the Sierra Nevada. ...
Background
In fire-adapted ecosystems of the western USA, prescribed fire is an essential restoration and fuel reduction tool. There is general concern that, as the fire season lengthens, the window for conducting prescribed burns will contract unless management changes are made. This could occur because a number of conditions must be met before prescribed fire can be used in the field, and those are most common during the spring and autumn when the need for fire suppression response has been historically less. To assess patterns of potential prescribed burning feasibility, this study evaluated three conditions: (1) permission to burn as granted by air quality regulators; (2) weather within burn plan prescription; and (3) availability of operational and contingency resources. Our 21-year analysis (1999 to 2019) combines three independent datasets for a daily comparison of when prescribed fires could have been implemented (henceforth, burn windows) in the Lake Tahoe Basin (LTB) and analyzes seasonality, interannual variability, and trends.
Results
Burn windows were most frequent during spring, followed by autumn, with the fewest burn windows during the summer and winter. Burn windows lasting multiple days occurred infrequently. Two- to three-day burn windows did not often occur more than twice per month over the study period, and longer burn windows were very rare. Interannual variation was considerable. Finally, an abrupt increase in burn windows was detected in 2008. This was determined to be related to a methodological change by air quality regulators and not to any changes in climate or resource availability.
Conclusions
While this case study focuses on the LTB, the analysis was performed with readily available data and could be applied easily to other land management units, demonstrating a valuable method for planning and prioritizing fire and fuels management activities. This type of tool can also identify areas for research. For example, if there were unused burn windows during the winter and early spring—or they were projected to increase—research into the ecological impacts of winter and spring burning may allow managers to more confidently adapt to changing climate. Moreover, this analysis demonstrated that modest and reasonable regulatory changes can increase opportunities for prescribed burning.
... Dukpa et al., 2018;Hart et al., 2012;Helama, Salminen, Timonen, & Varmola, 2008;Metslaid et al., 2016;Misson, Vincke, & Devillez, 2003;Muñoz et al., 2010;Pérez-de-Lis et al., 2011;Rozas, 2004; Stan & Daniels, 2010;Stojanović et al., 2017;Vernon et al., 2018; Winck et al.al., 2012;Powers, Pregitzer, Palik, & Webster, 2010; Trotsiuk et al., 2018; Trujillo-Martínez et al.al., 2019; April Sahara, Sarr, Van Kirk, & Jules, 2015;Babst et al., 2014;Chauchard & Sbrancia, 2003;Chidumayo, 2019;Maxwell et al., 2014;Mbow, Chhin, Sambou, & Skole, 2013;Olano, Rozas, Bartolomé, & Sanz, 2008;Pretzsch et al., 2014;Rozas & Olano, 2013; Xu et al., 2019 Evaluación de plantación (4)Boyden et al., 2009;De Ridder et al., 2013;Jäghagen & Albrektson, 1996;Nock et al. ...
Los anillos de crecimiento son un registro histórico natural de procesos ecológicos, que incluye las respuestas fisiológicas y estructurales del xilema, a factores abióticos, interacciones bióticas y prácticas de manejo forestal. El objetivo general del presente trabajo fue evaluar los impactos multiescalares de las prácticas de manejo forestal sobre el crecimiento radial de bosques de coníferas del Estado de México al interior de la ecorregión del Eje Volcánico Transmexicano. El crecimiento de un árbol puede abordarse desde diferentes escalas que involucran los niveles rodal—árbol individual—anillo de crecimiento—célula del xilema. Las técnicas dendroecológicas permiten evaluar el crecimiento de los árboles remanentes después de intervenciones de manejo en escalas de tiempo amplias. Se analizó el efecto de una corta de saneamiento sobre el crecimiento radial del arbolado residual de Pinus hartwegii, y se encontró una respuesta favorable a la intervención con un aumento estadísticamente significativo del incremento de área basal explicado por una disminución de la competencia. Adicionalmente, se evaluó el efecto de un aprovechamiento forestal sobre la formación de madera en árboles remanentes de Abies religiosa, se encontró que las anchuras de anillo aumentaron significativamente después de la corta. La madera tardía después de la intervención presentó traqueidas con lúmenes de mayor diámetro y paredes celulares de menor grosor, estos cambios suscitaron variaciones en la microdensidad de la madera, con un aumento en la densidad mínima y una disminución de la densidad máxima. El conocimiento dendroecológico de un bosque contribuye a optimizar la producción maderable y favorecer la conservación de los ecosistemas forestales.
... Importantly, the application of the FRS concept to landscape biogeographical models is highly sensitive to the processes underlying the biogeographical models; contemporary distribution models, such as those we analysed here (Wilson et al., 2013), reflect a long legacy of change in land use and fire exclusion and do not necessarily reflect the potential type of vegetation under a historical fire regime or a past climate. Future research could apply the FRS concept, and functional trait biogeography more broadly, to reconstructed forest stands such as those generated by predictive vegetation mapping (Maxwell et al., 2014) or other reconstruction methods (Yocom-Kent et al., 2015). ...
Aim
Functional traits are a crucial link between species distributions and the ecosystem processes that structure those species’ niches. Concurrent increases in the availability of functional trait data and our ability to model species distributions present an opportunity to develop functional trait biogeography (i.e., the mapping of functional traits across space). Functional trait biogeography can improve process‐based predictions about the resistance of certain species assemblages to changing environmental conditions across landscape scales. We illustrate this concept by developing the first trait‐based, quantitative ranking of fire resistance (adult tree survival) in North American conifer species and mapping that fire resistance across space.
Location and time period
Western continental USA, present day.
Major taxa studied
Twenty‐nine common conifer tree species.
Methods
We compiled six traits for each species: three relating to tree morphology and three relating to litter flammability. We combined these traits into a single fire resistance score and used community‐weighted averaging to estimate the fire resistance scores of different forest communities, using interpolated species distribution and relative abundance data.
Results
Species associated historically with frequent fire have high fire resistance scores (e.g., Pinus ponderosa ), reflected by thick bark, tall crowns and flammable litter. Species associated with subalpine or arid conditions have low fire resistance scores (e.g., Picea engelmannii and Pinus edulis ), reflected by thin bark, short stature, poor self‐pruning and low litter flammability. A map of forest community fire resistance across the western USA reveals agreement with independent assessments of historical fire regimes, while also identifying areas where community‐wide species traits might be mismatched with historical fire regimes.
Main conclusions
Quantifying the functional traits that confer resistance to tree‐killing fire provides a direct link between ecosystem disturbance and community resistance. Understanding this link is crucial to evaluation of the long‐term resilience of different forest types under dynamic fire regimes. Our work represents the first known spatial representation of fire resistance traits at a regional scale and, as such, provides a link between functional traits and biogeography relevant to a critical ecosystem process.
... Levine et al. (2017) tested the accuracy and precision of four plotless density estimators that can be applied to GLO survey sample data, including the Cottam (Cottam and Curtis 1956), Pollard (Pollard 1971), Morisita (Morisita 1957), and mean harmonic Voronoi density (MHVD; Williams and Baker 2011) estimators. The Cottam, Pollard, and Morisita are count-based plotless density estimators (PDE) and have a history of being applied to GLO data (e.g., Kronenfeld and Wang 2007, Rhemtulla et al. 2009, Hanberry et al. 2012, Maxwell et al. 2014, Goring et al. 2016. The MHVD estimator is an area-based PDE that has been applied by the study's authors to sites in the western United States (Baker 2012(Baker , 2014), but had not been independently evaluated. ...
In the Western United States, historical forest conditions are used to inform land management and ecosystem restoration goals (North et al. 2009, Stephens et al. 2016). This interest is based on the premise that historical forests were resilient to ecological disturbances (Keane et al. 2018). Researchers throughout the US have used the General Land Office (GLO) surveys of the late 19th and early 20th centuries to estimate historical forest conditions (Bourdo 1956, Schulte and Mladenoff 2001, Cogbill et al. 2002, Paciorek et al. 2016). These surveys were conducted throughout the US and represent a systematic, historical sample of trees across a broad geographic area. This article is protected by copyright. All rights reserved.
... Hierarchical clustering techniques are used more frequently than non-hierarchical ones (e.g., k-means), as these techniques are better suited for examining ecological relationships within and between resulting classes (McGarigal et al. 2000). Ward's method in particular is used for ecosystem classification research in natural landscapes (McNab et al. 1999;Mora and Iverson 2002;Hargrove and Hoffman 2005;Maxwell et al. 2014) and more recently in urban landscapes . The hierarchical nature of the cluster analysis approach enabled the classification of both prominent tree species assemblages and the sub-classes within these assemblages. ...
Urban forests have garnered increasing attention as providers of an array of beneficial ecosystem services. However, urban forest ecosystems are highly complex and heterogeneous systems whose structure are shaped by interacting social and ecological processes. Approaches to reliably identify and differentiate these processes could be valuable for addressing complexity and reducing uncertainty in decision-making in urban forestry. The purpose of this study is to identify and quantify a range of social and ecological drivers of urban forest species composition, distribution, and diversity. This was done using hierarchical cluster analysis and discriminant analysis with empirical plot data describing the tree species composition in Toronto, Canada. Tree density and imperviousness were by far the most influential drivers of species composition. Increasing imperviousness saw not just reduced tree density but a decline in native species abundance. Additionally, single-detached housing, homeownership, and income were closely associated and explained higher tree densities and abundances of native species. However, income had a lower than expected influence on urban forest species composition given its importance in canopy cover research. Continuous forest patches were highly distinct compared to the remainder of the urban landscape, which highlights the ecological distinctiveness of residual forests within cities and lends support to their conservation. Increasing the understanding of social and ecological drivers of tree species composition, distribution, and diversity within cities is an integral part of urban forest ecosystem classification, which can be a valuable decision-support tool for ecosystem-based management in urban forestry.
... These studies have demonstrated that there was a high degree of spatial complexity driven by the interaction between vegetation, fuels, and topography (Nagel and Taylor 2005, Beaty and Taylor 2008, Lauvaux et al. 2016). These interpretations drawn from tree rings have been corroborated with independent historical data (Maxwell et al. 2014. ...
... These datasets provide detailed information on forest structure and composition prior to the widespread changes associated with fi re suppression and timber harvesting (Table 6.1). These datasets have been used to document change in contemporary forest structure and composition, which generally corroborate fi ndings from tree ringbased studies (Scholl and Taylor 2010, Collins et al. 2011, Maxwell et al. 2014). These datasets have also been used to infer historical fi re-severity patterns , Hanson and Odion 2016. ...
... May not be reproduced in any form without permission from the publisher, except fair uses permitted under U.S. or applicable copyright law. (Maxwell et al. 2014, Steel et al. 2015. The primary assumption is that these fi re patterns are indicative of a healthy, functional, and resilient ecosystem. ...
