DOI: 10.5061/dryad.bk3j9kdg0
title: Ecoregion and community structure influences on the foliar elemental niche of balsam fir (Abies balsamea (L.) Mill.) and white birch (Betula papyrifera Marshall)

description: Context: Changes in foliar elemental niche properties, defined by axes of
 carbon (C), nitrogen (N), and phosphorus (P) concentrations, reflect how
 species allocate resources under different environmental conditions. For
 instance, elemental niches may differ in response to large-scale
 latitudinal temperature and precipitation regimes that occur between
 ecoregions and small-scale differences in nutrient dynamics based on
 species co-occurrences at a community level. Methods: at a species level,
 we compared foliar elemental niche hypervolumes for balsam fir (Abies
 balsamea (L.) Mill.) and white birch (Betula papyrifera Marshall) between
 a northern and southern ecoregion. At a community level, we grouped our
 focal species using plot data into conspecific (i.e., only one focal
 species is present) and heterospecific groups (i.e., both focal species
 are present) and compared their foliar elemental concentrations under
 these community conditions across, within, and between these ecoregions.
 Between ecoregions at the species and community level, we expected niche
 hypervolumes to be different and driven by regional biophysical effects on
 foliar N and P concentrations. At the community level, we expected niche
 hypervolume displacement and expansion patterns for fir and birch,
 respectively – patterns that reflect their resource strategy. Results: at
 the species level, foliar elemental niche hypervolumes between ecoregions
 differed significantly for fir (F = 14.591, p-value = 0.001) and birch (F
 = 75.998, p-value = 0.001) with higher foliar N and P in the northern
 ecoregion. At the community level, across ecoregions, the foliar elemental
 niche hypervolume of birch differed significantly between heterospecific
 and conspecific groups (F = 4.075, p-value = 0.021) but not for fir.
 However, both species displayed niche expansion patterns, indicated by
 niche hypervolume increases of 35.49% for fir and 68.92% for birch. Within
 the northern ecoregion, heterospecific conditions elicited niche expansion
 responses, indicated by niche hypervolume increases for fir of 29.04% and
 birch of 66.48%. In the southern ecoregion we observed a contraction
 response for birch (niche hypervolume decreased by 3.66%), and no changes
 for fir niche hypervolume. Conspecific niche hypervolume comparisons
 between ecoregions yielded significant differences for fir and birch (F =
 7.581, p-value = 0.005 and F = 8.038, p-value = 0.001) as did
 heterospecific comparisons (F = 6.943, p-value = 0.004, and F = 68.702,
 p-value = 0.001, respectively). Conclusions: our results suggest species
 may exhibit biogeographical specific elemental niches – driven by
 biophysical differences such as those used to describe ecoregion
 characteristics. We also demonstrate how a species resource strategy may
 inform niche shift patterns in response to different community settings.
 Our study highlights how biogeographical differences may influence foliar
 elemental traits and how this may link to concepts of ecosystem and
 landscape functionality.