TY - JOUR
T1 - Tree morphologic plasticity explains deviation from Metabolic Scaling Theory in semi-arid conifer forests, Southwestern USA
AU - Swetnam, Tyson L.
AU - O'Connor, Christopher D.
AU - Lynch, Ann M.
N1 - Funding Information:
The research, analysis and other work documented in this publication was partially funded by the USDA Forest Service, Rocky Mountain Research Station, through Agreement # 07-JV-11221615-317 in cooperation with the U.S. Forest Service, Coronado National Forest, and the United States National Park Service, Valles Caldera National Preserve; however the findings, conclusions, and views expressed are those of the authors and do not necessarily represent the views of the U.S. Forest Service or National Park Service. Additional funding and support was provided by the USFS Region 3 Office, the Coronado National Forest, and the Critical Zone Observatory (NSF Award #0724958). Pinaleño lidar data were analyzed by the USFS Remote Sensing and Application Center (RSAC): Tom Mellin, Denise Laes, and Brent Mitchell. Pinaleño plot data were collected by USFS Personnel: Craig Wilcox, and Matt Littrell; University of Arizona personnel: Don Falk, Jesse Minor, Rebecca Minor, Laura Marshall, Alex Arizpe, Josh Farella, Jacquie Dewar, Ben Schippers, Anastasia Rabin, Kyle Miller, Alicia Durnin and Andrew McIntyre. Valles Caldera plot data were collected by Scott Compton of the Valles Caldera Preserve; Jon Pelletier, Shirley Papuga, Joshua Conver, and Kristine Nelson of the University of Arizona CZO. The Santa Catalina plot data were collected by Alicia Durnham, Anastasia Rabin, Benjamin Schippers, Jacquie Dewar, Jesse Minor, Joshua Conver, Kyle Miller, and Shane Cook.
PY - 2016/7
Y1 - 2016/7
N2 - A significant concern about Metabolic Scaling Theory (MST) in real forests relates to consistent differences between the values of power law scaling exponents of tree primary size measures used to estimate mass and those predicted by MST. Here we consider why observed scaling exponents for diameter and height relationships deviate from MST predictions across three semi-arid conifer forests in relation to: (1) tree condition and physical form, (2) the level of inter-tree competition (e.g. open vs closed stand structure), (3) increasing tree age, and (4) differences in site productivity. Scaling exponent values derived from non-linear least-squares regression for trees in excellent condition (n = 381) were above the MST prediction at the 95% confidence level, while the exponent for trees in good condition were no different than MST (n = 926). Trees that were in fair or poor condition, characterized as diseased, leaning, or sparsely crowned had exponent values below MST predictions (n = 2,058), as did recently dead standing trees (n = 375). Exponent value of the mean-tree model that disregarded tree condition (n = 3,740) was consistent with other studies that reject MST scaling. Ostensibly, as stand density and competition increase trees exhibited greater morphological plasticity whereby the majority had characteristically fair or poor growth forms. Fitting by least-squares regression biases the mean-tree model scaling exponent toward values that are below MST idealized predictions. For 368 trees from Arizona with known establishment dates, increasing age had no significant impact on expected scaling. We further suggest height to diameter ratios below MST relate to vertical truncation caused by limitation in plant water availability. Even with environmentally imposed height limitation, proportionality between height and diameter scaling exponents were consistent with the predictions of MST.
AB - A significant concern about Metabolic Scaling Theory (MST) in real forests relates to consistent differences between the values of power law scaling exponents of tree primary size measures used to estimate mass and those predicted by MST. Here we consider why observed scaling exponents for diameter and height relationships deviate from MST predictions across three semi-arid conifer forests in relation to: (1) tree condition and physical form, (2) the level of inter-tree competition (e.g. open vs closed stand structure), (3) increasing tree age, and (4) differences in site productivity. Scaling exponent values derived from non-linear least-squares regression for trees in excellent condition (n = 381) were above the MST prediction at the 95% confidence level, while the exponent for trees in good condition were no different than MST (n = 926). Trees that were in fair or poor condition, characterized as diseased, leaning, or sparsely crowned had exponent values below MST predictions (n = 2,058), as did recently dead standing trees (n = 375). Exponent value of the mean-tree model that disregarded tree condition (n = 3,740) was consistent with other studies that reject MST scaling. Ostensibly, as stand density and competition increase trees exhibited greater morphological plasticity whereby the majority had characteristically fair or poor growth forms. Fitting by least-squares regression biases the mean-tree model scaling exponent toward values that are below MST idealized predictions. For 368 trees from Arizona with known establishment dates, increasing age had no significant impact on expected scaling. We further suggest height to diameter ratios below MST relate to vertical truncation caused by limitation in plant water availability. Even with environmentally imposed height limitation, proportionality between height and diameter scaling exponents were consistent with the predictions of MST.
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U2 - 10.1371/journal.pone.0157582
DO - 10.1371/journal.pone.0157582
M3 - Article
C2 - 27391084
AN - SCOPUS:84978822657
SN - 1932-6203
VL - 11
JO - PloS one
JF - PloS one
IS - 7
M1 - e0157582
ER -