TY - JOUR
T1 - Demographic trends in community functional tolerance reflect tree responses to climate and altered fire regimes
AU - Marshall, L. A.
AU - Falk, D. A.
N1 - Funding Information:
This project was funded by the US Forest Service, Rocky Mountain Research Station, RJVA 08-JV-11221632-279 and the U.S. Forest Service, Collaborative Forest Restoration Program, 06-DG-11031000-034. Additional support was provided by the University of Arizona Institute of the Environment, Faculty Exploratory Research Grant to D. A. Falk and the University of Arizona Graduate College Fellowship to L. A. Marshall. Many thanks to Steven Leavitt, Nathan McDowell, David Moore, and Valerie Trouet for comments and critiques, and Margaret Evans for help with FIA interpretation.
Funding Information:
This project was funded by the US Forest Service, Rocky Mountain Research Station, RJVA 08‐JV‐11221632‐279 and the U.S. Forest Service, Collaborative Forest Restoration Program, 06‐DG‐11031000‐034. Additional support was provided by the University of Arizona Institute of the Environment, Faculty Exploratory Research Grant to D. A. Falk and the University of Arizona Graduate College Fellowship to L. A. Marshall. Many thanks to Steven Leavitt, Nathan McDowell, David Moore, and Valerie Trouet for comments and critiques, and Margaret Evans for help with FIA interpretation.
Publisher Copyright:
© 2020 by the Ecological Society of America
PY - 2020/12
Y1 - 2020/12
N2 - Forests of the western United States are undergoing substantial stress from fire exclusion and increasing effects of climate change, altering ecosystem functions and processes. Changes in broad-scale drivers of forest community composition become apparent in their effect on survivorship and regeneration, driving demographic shifts. Here we take a community functional approach to forest demography, by investigating mean drought or shade functional tolerance in community assemblages. We created the Community Mean Tolerance Index (CMTI), a response metric utilizing drought/shade tolerance trade-offs to identify communities undergoing demographic change from a functional trait perspective. We applied the CMTI to Forest Inventory and Analysis data to investigate demographic trends in drought and shade tolerance across the southern Rocky Mountains. To find the major drivers of change in community tolerance within and across forest types, we compared index trends to climate and fire-exclusion-driven disturbance, and identified areas where demographic change was most pronounced. We predicted that greater shifts in drought tolerance would occur at lower forest type ecotones where climate stress is limiting and that shifts in shade tolerance would correspond to excursions from the historic fire regime leading to greater changes in forest types adapted to frequent, low-intensity fire. The CMTI was applied spatially to identify sites likely to transition to oak shrubfield, where disturbance history combined with a species-driven demographic shift toward drought tolerance. Within forest types, lower elevations are trending toward increased drought tolerance, while higher elevations are trending toward increased shade tolerance. Across forest types, CMTI difference peaked in mid-elevation ponderosa pine and mixed-conifer forests, where fire exclusion and autecology drive demographic changes. Peak CMTI difference was associated with fire exclusion in forest types adapted to frequent fire. At higher elevations, site-level stand dynamics appear to be influencing demographic tolerance trends more than broad climate drivers. Through a community demographic approach to functional traits, the CMTI highlights areas and forest types where ecosystem function is in the process of changing, before persistent vegetation type change occurs. Applied to regional plot networks, the CMTI provides an early warning of shifts in community functional processes as climate change pressures continue.
AB - Forests of the western United States are undergoing substantial stress from fire exclusion and increasing effects of climate change, altering ecosystem functions and processes. Changes in broad-scale drivers of forest community composition become apparent in their effect on survivorship and regeneration, driving demographic shifts. Here we take a community functional approach to forest demography, by investigating mean drought or shade functional tolerance in community assemblages. We created the Community Mean Tolerance Index (CMTI), a response metric utilizing drought/shade tolerance trade-offs to identify communities undergoing demographic change from a functional trait perspective. We applied the CMTI to Forest Inventory and Analysis data to investigate demographic trends in drought and shade tolerance across the southern Rocky Mountains. To find the major drivers of change in community tolerance within and across forest types, we compared index trends to climate and fire-exclusion-driven disturbance, and identified areas where demographic change was most pronounced. We predicted that greater shifts in drought tolerance would occur at lower forest type ecotones where climate stress is limiting and that shifts in shade tolerance would correspond to excursions from the historic fire regime leading to greater changes in forest types adapted to frequent, low-intensity fire. The CMTI was applied spatially to identify sites likely to transition to oak shrubfield, where disturbance history combined with a species-driven demographic shift toward drought tolerance. Within forest types, lower elevations are trending toward increased drought tolerance, while higher elevations are trending toward increased shade tolerance. Across forest types, CMTI difference peaked in mid-elevation ponderosa pine and mixed-conifer forests, where fire exclusion and autecology drive demographic changes. Peak CMTI difference was associated with fire exclusion in forest types adapted to frequent fire. At higher elevations, site-level stand dynamics appear to be influencing demographic tolerance trends more than broad climate drivers. Through a community demographic approach to functional traits, the CMTI highlights areas and forest types where ecosystem function is in the process of changing, before persistent vegetation type change occurs. Applied to regional plot networks, the CMTI provides an early warning of shifts in community functional processes as climate change pressures continue.
KW - Southern Rocky Mountains ecoregion
KW - community mean index
KW - drought tolerance
KW - forest inventory analysis
KW - functional traits
KW - shade tolerance
KW - vegetation type change
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U2 - 10.1002/eap.2197
DO - 10.1002/eap.2197
M3 - Article
C2 - 32524676
AN - SCOPUS:85088272695
SN - 1051-0761
VL - 30
JO - Ecological Appplications
JF - Ecological Appplications
IS - 8
M1 - e02197
ER -