PHENOLOGY AND GROWTH OF 3 TEMPERATE FOREST LIFE FORMS IN RESPONSE TO ARTIFICIAL SOIL WARMING

1 Responses of temperate deciduous forest vegetation to artificial soi l warming (simulating one component of projected global climate change ) were investigated in field plots over two growing seasons, 1992-93. Six replicate plots were established for each of three treatments: hea ting, disturbance-control, and intact control. Growth and phenology of 26 species of three life forms (12 herbaceous understorey species; si x shrub species; eight tree species) were monitored non-destructively in the plots at 20 sampling dates. 2 Phenology of leaf emergence and f lower production in saplings was not affected by soil warming. Mature trees and shrubs leafed out slightly earlier and in larger numbers in heated plots. Trees flowered earlier and in higher proportions in the heated plots in 1993. 3 Mean area per leaf per plant and leaf expansio n rates in 1992 were greatest in control saplings of Acer pensylvanicu m and Fagus grandifolia. Vaccinium corymbosum, a shrub, showed reduced leaf sizes under soil heating. 4 Soil warming significantly enhanced relative diameter growth of woody individuals, especially shrubs, in 1 992. This effect was less pronounced in 1993. 5 Species richness was l ower in heated plots than in intact control plots at all sampling date s in both years. Disturbed but unheated control plots exhibited the lo west species richness overall. Species richness declined in all plots in 1993. 6 Changes in relative abundance of herbaceous species from 19 92 to 1993 were highly variable, and not significantly affected by tre atment. Rank abundances of species changed more from 1992 to 1993 in i ntact control plots than in the other two treatments. 7 Total density (stems m(-2)) of herbaceous species was highest in heated plots during April and May of both years, reflecting accelerated emergence of Maia nthemum canadense and Uvularia sessilifolia. From June through October , however, intact control plots exhibited the highest stem densities, as numbers of the early emergents declined. 8 Photosynthetic rates of the dominant herbs, Maianthemum canadense and Uvularia sessilifolia, w ere not significantly affected by heating. 9 Of all life forms, herbac eous species were most sensitive to soil warming. Their early appearan ce could influence carbon and nutrient acquisition dynamics under chan ged climatic conditions in deciduous forests.