Phenology at the Bear Brook Watershed in Maine, USA: Foliar Chemistry and Morphology

Abstract

Annual developmental events in biological systems are dependent, in part, on environmental conditions and can be valuable bio-indicators of environmental change. Many studies have been done on the effects of temperature and pho toperiod on phenophases, but fewer have explored the consequences of nutrient availability in terrestrial ecosystems on forest phenology. Here we examined phenological phenomena at a long-term experimental forested watershed subjected to decadal-scale ecosystem acidification and nitrogen (N) enrichment. Phenophases of Acer rubrum , Acer saccharum , and Picea rubens in both watersheds were observed throughout the 2010 growing season and included bud burst, flow ering ( A. rubrum ), leaf or needle emergence and unfolding, leaf senescence ( Acer spp . ), and leaf fall ( Acer spp). Clear species-specific phenological patterns were observed, but no treatment effects were evident. Chemical phenology of canopy tree foliage was also examined on a monthly basis from May through October 2010. Nitrogen was the only element that was significantly higher in the WB watershed for all species, although not all months showed significant differences. Other treatment differences in elemental composition of foliage are discussed. Foliar N and P concentra tions decreased in all species throughout the growing season, while foliar Ca, K, and Al concentrations increased or were constant. This study found clear species-specific patterns of morphological and chemical phenology with time, but did not show evidence for visible alterations in seasonal development as a result of ecosystem acidification and N en richment. Treatment effects on chemical phenology, as applied here, showed some responses and warrant further con sideration for application to coupled chemical-biological indicators of a changing chemical and physical climate.