DOI: 10.5061/dryad.t4b8gtjbm
title: Tree basal area growth data for fitting allometric equations to 20 species of NE North America

description: A tree’s basal area and wood volume scale exponentially with tree diameter
 in species-specific patterns. Recent observed increases in tree growth
 suggest these allometric relationships are shifting in response to climate
 change, rising CO2 levels, and/or changes in forest management. We
 analyzed 9214 cores from nine conifer and 11 broadleaf species grown in
 managed mixed-species stands in the upper Midwest to quantify how well
 diameter (DBH) serves to predict basal area (BA) growth and above-ground
 wood and carbon (C). These samples include many large trees. We fit mixed
 models to predict BA growth and above-ground biomass/C from diameter, tree
 height, and the BA of nearby trees while controlling for site effects.
 Models account for 55-83% of the variance in (log) recent growth,
 improving predictions over earlier models. Growth-diameter scaling
 exponents covary with certain leaf and stem (but not wood) functional
 traits, reflecting growth strategies. Log BA increment scales linearly
 with log diameter as trees grow bigger in 16/20 species, and growth
 accelerates in Quercus rubra L. Three other species plateau in growth.
 Growth only decelerates in red pine, Pinus resinosa Ait. Growth in
 whole-tree, above-ground biomass, and C accelerates even more strongly
 with diameter (mean exponent: 2.08 vs. 1.30 for BA growth). Sustained BA
 growth and accelerating wood/C growth contradict the common assumption
 that tree growth declines in bigger trees. Yield tables and silvicultural
 guidelines should be updated to reflect these current relationships. Such
 revisions will favor delaying harvests in many managed stands to increase
 wood production and enhance ecosystem values, including C fixation and
 storage. Further research may resolve the relative roles of thinning,
 climatic conditions, nitrogen inputs, and rising CO2 levels on changing
 patterns of tree growth.
description: The data are for 20 species / 9,453 trees reflecting a broad
 range of tree sizes and growth rates in managed public forest (BCPL)
 stands in N Wisconsin. These stands were managed using thinning to release
 faster-growing trees. We analyzed growth in 9 conifer and 11 deciduous
 species. Between 2005 and 2018, the BCPL’s continuous forest inventory
 team extracted increment cores from the first and third trees sampled
 within each forest inventory plot (generally &gt;10cm DBH). This
 ensured sampling trees in proportion to their abundance and avoided
 sampling adjacent trees whose growth might be correlated. Teams measured
 DBH to the nearest 2.6mm using a tape and estimated tree height to the
 nearest foot (31cm) using a clinometer. Tree cores were drilled to a depth
 of 5-6 cm, reflecting growth from roughly 1985 to 2018. A dissecting
 microscope (10x) allowed us to count the number of rings spanning the last
 inch (2.54 cm) of growth (excluding the bark). We estimate DBH at the
 beginning of the growth period as the final DBH (measured when the core
 was collected) minus 5.08cm. We estimate basal area increases from
 differences in cross-sectional area, assuming successive tree disks to be
 circles of area π r<sup>2</sup>. Data include plot and stand
 ID, geographic location, estimated total plot basal area (BA/acre or ha),
 species, initial DBH, height, crown class, and the number of growth rings
 in the outer 2.56 cm of wood. We first modeled growth (mean annual basal
 area increment in the outermost annulus) across all trees as a function of
 species, diameter (DBH at the start of the growth period), height, crown
 class, and competition (plot basal area minus focal tree BA). We then
 fitted species-specific models that included site (Stand ID) as a random
 factor to adjust the models for different local growing
 conditions.
description: # Tree basal area growth data for fitting allometric equations to 20
 species of NE North America
 [https://doi.org/10.5061/dryad.t4b8gtjbm](https://doi.org/10.5061/dryad.t4b8gtjbm) ## Description of the data and file structure We analyzed growth in 9 conifer and 11 deciduous tree species using these data on 9,453 trees. We fit growth equations to each species based on predictor variables including diameter (DBH at the start of the growth period), height, crown class, competition (plot basal area minus focal tree BA), and Stand ID -- a random factor to adjust the models for different local growing conditions. Two files are included -- the data themselves and a Metadata file which includes descriptions and units for all the variables. Note that missing values are represented within cells by the symbol "." These missing values reflect when no data were taken on that variable for that tree. ## Code/software JMP was used for all data analyses and graphics. ## Access information Data was derived from the following sources: * Wisconsin BCPL forestry data