Strong differences in microclimate among the habitats of a forest-steppe ecosystem

Abstract

Microclimate has a substantial impact on plant composition, survival, and growth, as well as ecosystem processes. Although microclimatic conditions in anthropogenically fragmented ecosystems have received considerable scientific attention, they are understudied in naturally fragmented ecosystems, including forest-steppes. In addition, earlier investigations in these mosaics only measured microclimate parameters for a very short period (i.e., 24 hours on a single summer day). In the present study, the long-term microclimatic conditions were described in multiple habitat types, both woody and non-woody, in a sandy forest-steppe ecosystem in the Kiskunság, central Hungary. The aim of this study was to answer (1) how air humidity and temperature conditions differ among the studied habitats during the growing season and (2) which habitats are more stressed to vegetation growth regarding vapor pressure deficit (VPD). Wireless sensors recording air temperature and humidity values were used to monitor microclimatic parameters. VPD values were calculated based on the obtained air temperature and humidity, and two thresholds at 1.2 and 3.0 kPa were defined. To compare mean air temperature and humidity variables, as well as above-threshold VPD rate among habitat types, general linear models were used. Our results indicated that open grasslands were the warmest and driest habitats. Among woody habitats, south-facing edges had the harshest microclimatic conditions. The current work also found that small forest patches and larger forest patches had similar air temperature and humidity variables. Regarding VPD, open grasslands were the most stressed for vegetation growth from May to October. During the summer season, forest patches had a small moderating effect at the limiting threshold of 1.2 kPa VPD, but a stronger moderating effect at the 3.0 kPa threshold. With ongoing climate change, this role of forest patches is expected to become increasingly important in forest-steppes. Therefore, it is suggested that the remaining near-natural forest stands in sandy forest-grassland ecosystems should be prioritized for protection, and that scattered trees or groups of trees of native species should be established in extensive treeless grasslands.