Forest structure and pattern vary by climate and landform across active-fire landscapes in the montane Sierra Nevada

Jeronimo, Sean M.A.; Kane, Van R.; Churchill, Derek J.; Lutz, James A.; North, Malcolm P.; Asner, Gregory P.; Franklin, Jerry F.

doi:10.1016/j.foreco.2019.01.033

Cited by 54 publications

(33 citation statements)

References 86 publications

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“…Though clustered tree regeneration may recover aspects of spatial heterogeneity at some time after fire (Ziegler, Hoffman, Fornwalt, et al., 2017), the overall stocking would likely be well under the natural range of variation for these forests (Safford & Stevens, 2017). This is somewhat counter to findings from studies that reported restorative effects from actual wildfires in long fire‐excluded forests (Jeronimo et al., 2019; Kane et al., 2019; Larson et al., 2013). However, these differences are likely explained by the variation in fire weather in actual wildfires and prefire fuel structures, which are likely more variable than fuel models indicate.…”

Section: Discussioncontrasting

confidence: 76%

Pyric tree spatial patterning interactions in historical and contemporary mixed conifer forests, California, USA

Ziegler

Hoffman

Collins

et al. 2020

Ecology and Evolution

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Section: Discussioncontrasting

confidence: 76%

Pyric tree spatial patterning interactions in historical and contemporary mixed conifer forests, California, USA

Ziegler

Hoffman

Collins

et al. 2020

Ecology and Evolution

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“…2, 6). Furthermore, Sierra Nevada forests have a heterogeneous structure in terms of the presence of small-and large-diameter trees, snags, and deadwood at multiple scales, which is at least partly due to spatial and temporal heterogeneity in fire behavior and effects (Jeronimo et al 2019(Jeronimo et al , 2020. This fire-induced heterogeneity depends on the structural heterogeneity associated with spatial variation in large-diameter trees (Furniss et al 2020b) and largediameter deadwood (Lutz et al 2009a, Kane et al 2014.…”

Section: Discussionmentioning

confidence: 99%

Large-diameter trees dominate snag and surface biomass following reintroduced fire

et al. 2020

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The reintroduction of fire to landscapes where it was once common is considered a priority to restore historical forest dynamics, including reducing tree density and decreasing levels of woody biomass on the forest floor. However, reintroducing fire causes tree mortality that can have unintended ecological outcomes related to woody biomass, with potential impacts to fuel accumulation, carbon sequestration, subsequent fire severity, and forest management. In this study, we examine the interplay between fire and carbon dynamics by asking how reintroduced fire impacts fuel accumulation, carbon sequestration, and subsequent fire severity potential. Beginning pre-fire, and continuing 6 years post-fire, we tracked all live, dead, and fallen trees ≥ 1 cm in diameter and mapped all pieces of deadwood (downed woody debris) originating from tree boles ≥ 10 cm diameter and ≥ 1 m in length in 25.6 ha of an Abies concolor/Pinus lambertiana forest in the central Sierra Nevada, California, USA. We also tracked surface fuels along 2240 m of planar transects pre-fire, immediately post-fire, and 6 years post-fire. Six years after moderate-severity fire, deadwood ≥ 10 cm diameter was 73 Mg ha −1 , comprised of 32 Mg ha −1 that persisted through fire and 41 Mg ha −1 of newly fallen wood (compared to 72 Mg ha −1 pre-fire). Woody surface fuel loading was spatially heterogeneous, with mass varying almost four orders of magnitude at the scale of 20 m × 20 m quadrats (minimum, 0.1 Mg ha −1 ; mean, 73 Mg ha −1 ; maximum, 497 Mg ha −1). Wood from large-diameter trees (≥ 60 cm diameter) comprised 57% of surface fuel in 2019, but was 75% of snag biomass, indicating high contributions to current and future fuel loading. Reintroduction of fire does not consume all large-diameter fuel and generates high levels of surface fuels ≥ 10 cm diameter within 6 years. Repeated fires are needed to reduce surface fuel loading.

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“…Forest structure regulates fire behavior at both fine (Thaxton and Platt 2006, Hiers et al 2009, Loudermilk et al 2012) and broad scales (Rothermel 1972, Miller and Urban 1999 a , b , 2000 a , Harris and Taylor 2015), and it contributes to temporal patterns by moderating fuel connectivity and regulating spread rate (Caprio and Swetnam 1995, Miller and Urban 2000 b , Taylor and Skinner 2003). Conversely, repeated fire events influence the spatial pattern dynamics of trees and fuels within stands (scales <10 ha; Youngblood et al 2004, North et al 2007, Larson and Churchill 2012), and broad‐scale patterns in fire behavior (>10 ha) create, rearrange, and refine patches of forest, unburned islands, and early‐seral habitat among stands and across broad landscapes (>1000 ha; Turner et al 1997, Hessburg et al 1999, Taylor and Skinner 2003, Kane et al 2014, Meddens et al 2018 a , b , Jeronimo et al 2019). In short, heterogeneity in forest spatial structure contributes to variability in fire intensity, and variability in fire intensity perpetuates heterogeneity in forest structure.…”

Section: Introductionmentioning

confidence: 99%

Wildfire and drought moderate the spatial elements of tree mortality

et al. 2020

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Background tree mortality is a complex process that requires large sample sizes and long timescales to disentangle the suite of ecological factors that collectively contribute to tree stress, decline, and eventual mortality. Tree mortality associated with acute disturbance events, in contrast, is conspicuous and frequently studied, but there remains a lack of research regarding the role of background mortality processes in mediating the severity and delayed effects of disturbance. We conducted an empirical study by measuring the rates, causes, and spatial pattern of mortality annually among 32,989 individual trees within a large forest demography plot in the Sierra Nevada. We characterized the relationships between background mortality, compound disturbances (fire and drought), and forest spatial structure, and we integrated our findings with a synthesis of the existing literature from around the world to develop a conceptual framework describing the spatio‐temporal signatures of background and disturbance‐related tree mortality. The interactive effects of fire, drought, and background mortality processes altered the rate, spatial structuring, and ecological consequences of mortality. Before fire, spatially non‐random mortality was only evident among small (1 < cm DBH ≤ 10)‐ and medium (10 < cm DBH ≤ 60)‐diameter classes; mortality rates were low (1.7% per yr), and mortality was density‐dependent among small‐diameter trees. Direct fire damage caused the greatest number of moralities (70% of stems ≥1 cm DBH), but the more enduring effects of this disturbance on the demography and spatial pattern of large‐diameter trees occurred during the post‐fire mortality regime. The combined effects of disturbance and biotic mortality agents provoked density‐dependent mortality among large‐diameter (≥60 cm DBH) trees, eliciting a distinct post‐disturbance mortality regime that did not resemble the pattern of either pre‐fire mortality or direct fire effects. The disproportionate ecological significance of the largest trees renders this mortality regime acutely consequential to the long‐term structure and function of forests.

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Forest structure and pattern vary by climate and landform across active-fire landscapes in the montane Sierra Nevada

Cited by 54 publications

References 86 publications

Pyric tree spatial patterning interactions in historical and contemporary mixed conifer forests, California, USA

Pyric tree spatial patterning interactions in historical and contemporary mixed conifer forests, California, USA

Large-diameter trees dominate snag and surface biomass following reintroduced fire

Wildfire and drought moderate the spatial elements of tree mortality

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