On the spatial properties of foliar chemical traits for some commonly occurring eastern boreal forest species

Heckford, Travis Robert (2022) On the spatial properties of foliar chemical traits for some commonly occurring eastern boreal forest species. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

A central focus of trait-based ecology is investigating trait-species-environment relationships. Across landscapes, foliar traits of forest species are influenced by environmental conditions that result in spatial patterns of trait variability. In this thesis, using commonly occurring boreal plant species, I infer ecological processes from the empirical spatial patterns of foliar elemental (i.e., carbon (C), nitrogen (N), and phosphorus (P)), stoichiometric (i.e., C:N, C:P, and N:P), and phytochemical traits (i.e., terpenoid concentrations of coniferous species); herein referred to as foliar ESP traits. In this thesis, I first investigated how the elemental niche of a conifer and deciduous species differ at a species level between ecoregions and at a community level across, within, and between ecoregions. Notably, I found that a species foliar elemental niche is specific to their biogeographic location, suggesting that regional environmental factors constrain eco-physiological processes that influence how species acquire and use elemental resources. Secondly, I compared multiple models to determine parsimonious predictors of foliar ESP traits using combinations of spatial covariates which include land cover (i.e., coniferous, deciduous, mixedwood), productivity (Enhanced Vegetation Index), biotic (stand height, canopy closure, age), and abiotic (elevation, aspect, slope) factors. I found that spatial-trait relationships occurred at the species level. These results suggest that the spatial patterns of foliar ESP traits are largely species-specific at the landscape extent. Thirdly, at the forest stand extent, I examined the spatial co-variance of foliar ESP traits between species. I found that in most cases, spatial correlations of foliar ESP traits differed between forest stands and that spatial aggregation/segregation patterns of foliar ESP traits varied with distance/direction. Notably, most foliar phytochemical traits of conifers exhibit strong aggregation at a close distance (0-50 metres). Finally, I summarized the main thesis takeaways that (1) foliar traits differ by biogeographical locations and in response to common community-level configurations, (2) the spatial predictors of foliar traits are species-specific, and (3) the spatial co-variance patterns of foliar traits are scale, site and species-dependent. My thesis contributes to our understanding of how traits can be used to inform different aspects of landscape functionality by bridging community, ecosystem, and landscape ecology disciplines.

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