Microclimate edge effect in small fragments of temperate forests in the context of climate change

A long-distance edge effect influences structure of species-rich plant communities in temperate forest fragments surrounded by an agricultural landscape in Central Europe. Though the edge effect may be an aggregate of many environmental conditions, the thermal gradient from the forest edge to the forest interior deserves particular attention due to increasing ambient air temperature over the past decades. With regard to ongoing climate change, any reliable information about magnitude and distance of thermal gradients in these forest fragments has become of great importance. Therefore, we carried out seasonal measurements of forest air and soil temperature at a total 40 sites in 14 forest fragments in central Bohemia with areas ranging between 0.3 and 255 ha. In addition, we assessed spatial and vertical air temperature variability at two sites, on both south and north facing slopes. We found that differences in daily mean air temperature in these forest fragments is significantly modified by slope aspect (and/or slope inclination) and distance to the forest edge. A negative monotonic edge-related thermal gradient was apparent up to 100 m towards the forest interior with differences in daily mean air temperatures of about 0.3 °C. The magnitude of this edge thermal gradient is comparable to the effect of slope aspect. In addition to mean air temperature, maximum and minimum daily temperatures as well as mean soil temperature inside forest fragments also showed impacts caused by the edge effect and other environmental conditions (e.g. forest structure, elevation). The edge-related area closer than 100 m from the forest edge represents the majority (78%) of forested land in the study area as well as a considerable part of temperate forests in Central Europe (40%), including less fragmented mountain forests. Hence, the edge alteration of forest microclimate should be taken into serious consideration when planning adaptation measures against the consequences of climate change in Central Europe. The edge influence could be partially mitigated by preventing further forest fragmentation and the adoption of timber harvesting methods that avoid creation of clearings, such as single-tree selection. Even if such forest management measures are implemented in the study area, spatial patterns and gradients of environmental heterogeneity may be gradually reduced in the forest fragments as a result of further exposure to the combined effects of climate change and edge influence.