Edge effects disrupt vertical stratification of microclimate in a temperate forest canopy

© 2014 by University of Hawai'i Press. Forest edge structure plays a key role in modulating microclimatic edge responses. However, empirical evidence for this is derived almost entirely from ground-based measurements, rather than measurements across the vertical canopy profile. Intuitively, canopy organisms are not only exposed to altered lateral-edge processes but also vertical influences from the hot, dry canopy edge above. The question then is "what is the influence of edge formation on vertical stratification of edge microclimate?" Here, we undertake a novel test of edge influence on vertical stratification of microclimate across the full vertical profile from ground level to upper canopy in a New Zealand temperate rain forest. We hypothesized that there would be a breakdown of vertical stratification at the edge and "compression" of the abiotic envelope experienced by organisms. We deployed 25 data loggers at five heights from canopy down to ground level (0, -2, -4, -8, -16 m) at each of five distances from edge (0, -2, -4, -8, -16 m) and quantified incident light, air temperature, and vapor pressure deficit relative to an external control. As predicted, we found strong evidence of a breakdown of vertical stratification at the edge for all microclimate variables. In generalized linear mixed models there was a significant interaction between vertical height and distance from edge, with microclimate differentials increasing in magnitude from edge to interior at ground level but decreasing in magnitude from edge to interior at canopy level. Attenuation of edge effects was lower above ground level, suggesting that past evidence of microclimatic edge effects based on ground-level measurements may underestimate the full extent of edge influence on vertical stratification of microclimate in forest remnants.