Competition, Climate, and Size Effects on Radial Growth in an Old-Growth Hemlock Forest

Seth W Bigelow,Evan M Oswald,James R Runkle

doi:10.3390/f11010052

Seth W Bigelow, Evan M Oswald + Show 1 more

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https://doi.org/10.3390/f11010052

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Abstract

Research Highlights: We applied neighborhood and dendro-ecological methods in a stand with a 33-year record of forest dynamics, finding that growth will decrease for several species under predicted climate trends. Background and Objectives: Conventional tree-ring analysis removes the influence of competition and size on growth, precluding assessment of the relative influence of these factors. An old-growth eastern hemlock forest in east–central New York was mapped in 1978 and was measured at eight-year intervals since then. Our objective was to use these data to examine the influence of climate, neighborhood, and tree size on radial growth. Materials and Methods: We evaluated an array of climatic indices to find which ones had the strongest influence on radial growth from increment cores of eastern hemlock (Tsuga canadensis L.), yellow birch (Betula alleghaniensis Britton), and sugar maple (Acer saccharum Marsh.). We used the strongest climatic indices in combination with neighborhood and target-tree size information to create growth models for the three tree species. Results: Size accounted for 2% to 21% of observed growth; the shade-tolerant sugar maple and eastern hemlock grew fastest when large, but the mid-tolerant yellow birch grew fastest when small. Competition accounted for 9% to 21% of growth; conifers had a weaker competitive effect than deciduous trees, and eastern hemlock was less sensitive to competition than sugar maple and yellow birch. Climate accounted for only 2% of growth variation; eastern hemlock showed a positive response to warming climate trends, but yellow birch and sugar maple showed negative responses. Conclusions: Predicted climate trends are likely to result in decreased growth of sugar maple and yellow birch, and the sensitivity of these species to competition suggests the effect will be exacerbated when they grow in crowded conditions.

Highlights

Old-growth forests are often characterized by intense competition for growing space among trees [1]
Competition accounted for 9% to 21% of growth; conifers had a weaker competitive effect than deciduous trees, and eastern hemlock was less sensitive to competition than sugar maple and yellow birch
Climate accounted for only 2% of growth variation; eastern hemlock showed a positive response to warming climate trends, but yellow birch and sugar maple showed negative responses

Summary

Introduction

Old-growth forests are often characterized by intense competition for growing space among trees [1]. Competition may be high in old-growth forests because available space may become utilized more completely than in younger stands where trees may not have grown large enough to exploit all available resources [2,3]. Competition may suppress or alter climatic response [4,5], creating the potential for a different relationship between competition and climate in old-growth forests than in early and mid-successional forests. Studies that simultaneously address competitive interactions and climate response in a range of forest types showed that competition from neighboring trees exerts stronger effects than climate on tree growth [6,7]. The nature of the interaction between competition and climate may depend on whether or not the factors are consumed (e.g., soil water vs. air temperature, heat)

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