Plants change their physiologies in response to environmental change. Patterns of plant physiologies result from environmental heterogeneity at different spatial and temporal scales. At the global scale, selection pressures in different environments give rise to heritable differences between populations across generations, as evidenced by the evolution of diverse plant physiologies. Adaptation results in inter-population and ultimately inter-species physiological variation. Within an individual’s lifetime, plants respond to landscape-level environmental change via phenotypic plasticity, a process known as acclimation. Acclimation results in intra-species physiological variation.

Functional traits are an established method of quantifying physiological response. Recent work has identified a suite of key traits that reflect evolutionary tradeoffs between growth and survival across environmental gradients at the global scale. At the landscape level, do co-existing plant species similarly respond to environmental change? I investigated patterns of functional traits of understory herbs to canopy gap creation in a hardwood forest in Wisconsin, USA to answer this question. Specific leaf area (SLA), leaf dry matter content (LDMC), leaf size, and height were measured for nine species during the first (2007) and third (2009) growing seasons following experimental gap creation. Hemispherical photos were taken directly above each plant to measure light transmittance. Using analysis of variance (ANOVA), I examined the effects of gap treatments (medium and large) relative to closed canopy controls on functional trait values among years. Regression analysis and analysis of covariance (ANCOVA) were performed to examine the relationship between trait values and light transmittance for each species, and differences between these relationships among species.  

Results/Conclusions

Few species exhibited predicted patterns of trait variation in response to canopy gaps; nor did trait values respond to treatments differently over time (2007 vs. 2009).  Instead, SLA and LDMC trait values differed mostly between years, which may be attributable to low spring rainfall in 2007. SLA, LDMC, and height did vary along the light gradient as expected, although mostly for Impatiens sp. and Laportea canadensis. These two species grow and reproduce in the late summer after the canopy closes, which explains their strong response to the increased light in canopy gaps. Understory species do not uniformly respond to environmental change; species composition and distribution may therefore be altered under changing environmental conditions.