Changing Climate, Atmospheric Composition, and Radial Tree Growth in a Spruce-Fir Ecosystem on Grandfather Mountain, North Carolina

Abstract

Grandfather Mountain (GFM) in western North Carolina has been an International Biosphere Reserve since 1992 and is recognized for its natural beauty and ecological diversity. Sixteen unique ecosystems occur on GFM, including a high elevation forest dominated by red spruce (Picea rubens Sarg.) and Fraser fir [Abies Fraseri (Pursh) Poir]. Changing climatic and atmospheric conditions, especially acidic deposition, can harm spruce-fir forests, and heavily impacted ecosystems can be found in nearby locales (e.g., Mount Mitchell, North Carolina) in the southern Appalachian Mountains. Given the ecological significance of the spruce-fir ecosystem on GFM, the primary objectives of this study were to determine: (1) whether radial growth rates of red spruce have changed in recent decades in response to environmental or climatic stimuli; (2) the driving forces behind radial tree growth; and (3) the degree of climate change experienced on GFM. I sampled 47 red spruce trees and developed a tree-ring chronology using standard dendroecological techniques. I examined the relationships between radial growth, climate variables, atmospheric composition variables, and time using simple correlation and regression. Radial growth rates of red spruce increased through time, and growth rates were significantly related to temperature (positively), days with precipitation (negatively), atmospheric carbon dioxide (positively), and emissions of sulfur dioxides and nitrogen oxides (negatively). In addition, significant climate changes on GFM are evident, with the most dramatic change being an increase in mean summer temperatures in excess of 1.4 °C since 1956.