By investing in relatively tough leaves, evergreen plants exhibit a level of herbivory resistance and nutrient retention that exceeds that of their deciduous counterparts. The trade-off for these persistent leaves, however, is a reduced ability to adjust to changing environmental conditions and consequently reduced growth and competitive ability. This, in turn, may influence how the plants are able to response to spatial (north- and south-facing aspect) and temporal (summer and winter) extremes. Both survey and demography data of natural understory evergreen populations suggest seasonal light, soil moisture and temperature explain a great deal of plant distribution and performance; here I use experimental gardens with light and soil moisture manipulation to test these results. Specifically, three questions were addressed: (1) Can abiotic (environmental) variables account for the observed limited distribution of understory evergreen herbs on south-facing slopes? (2) What environmental variables best explain variation in understory evergreen herb vital rates? (3) Do three phylogenetically distinct understory evergreen herbs respond similarly or uniquely in response to environmental gradients?

Results/Conclusions

Experimental common gardens were established on north- and south-facing slopes in North Carolina and Georgia, and 864 individuals of three understory evergreen species (Hexastylis arifolia, Hepatica nobilis and Goodyera pubescens) were randomly assigned to plots that included nested water augmentation and light suppression treatments. The understory evergreen herbs responded to the environmental variables in a manner consistent with a guild that has limited natural distributions on south-facing slopes. Increased temperatures and light exposure and lower soil moisture generally led to decreased survival and growth, and the responses varied among the three species.