Abstract
Microclimate and vegetation architecture are interdependent. Little information is available, however, about the fine-scale spatio-temporal relationship between the microclimate and herb layer of forest-steppe mosaics. In 2018 a three-season-long vegetation sampling and measurements of air temperature and air humidity were performed along 4 transects (44 m long each) in the herb layer with 89 dataloggers in the sandy region of Central Hungary, in a poplar grove and the surrounding open grassland. In order to improve data analysis, we introduced the use of a duration curve widely used in hydrology and proved to be useful in the processing of intensive climatic data. We analysed the effect of the direction and altitude of the solar irradiation and the edge effect on the microclimatic pattern. We also surveyed, seasonally, the spatial pattern of the exceedance rate for the vapour pressure deficit (VPD) in relation to the transect direction and to the edge of the grove. The exceedance rate for the VPD indicated considerable seasonal differences. The VPD exceedance rate indicates the stress effect for the vegetation. The moderating effect of the grove was small at 1.2 kPa VPD, but at 3.0 kPa—stronger stress—it was considerable. On the warmer side of the transects, mostly exposed at the south-eastern edge, the exceedance rate rose abruptly with distance from the edge compared to the gradual increase on the colder side. The cardinal and intercardinal directions as well as the altitude of the Sun all had influences on the moderating and shading effects of the grove. The southern edge was not always consistently the warmest. The distribution of the VPD values above the 3.0 kPa threshold varied within a seemingly homogeneous grassland, which highlights the importance of fine-scale sampling and analysis. This knowledge is valuable for assessing the dynamics and spatio-temporal patterns of abiotic factors and physiognomy in this type of ecosystem.
Highlights
Climate change is expected to have a major impact on long-term community dynamics worldwide.Among other things, the global temperature increase and extreme weather events have a significant impact on the structure of forest ecosystems and on the dynamics of environmental factors in forest patches and nearby open areas [1,2,3]
Our study focused primarily on the derived data, such as the percentage of the vapour pressure deficit (VPD) values above an appropriate threshold (1.2 or 3.0 kPa) over a 24-h period that can indicate the microclimatic conditions of the vegetation
The distribution of the VPD values originating from 89 locations (4 × 22 positions in the four transects and the centre position) representing three seasons is illustrated by boxplots (Figure 2)
Summary
Climate change is expected to have a major impact on long-term community dynamics worldwide.Among other things, the global temperature increase and extreme weather events have a significant impact on the structure of forest ecosystems and on the dynamics of environmental factors in forest patches and nearby open areas [1,2,3]. In the case of this sandy forest-steppe vegetation, the fragmented structure has a natural origin In this habitat, natural drying processes have been observed for decades [9,10], inhibiting the growth of woody vegetation. Natural drying processes have been observed for decades [9,10], inhibiting the growth of woody vegetation In addition to these processes, the seeds of tree species in this habitat can only germinate in depressions with ideal topographic conditions where a sufficient amount of water can accumulate. The succession dynamics in a sandy-forest-steppe habitat are rather slow due to the vegetation edges, where the strong abiotic differences between the grassland and the fragment prevent forest expansion and development [10]. It is important to examine the effect of smaller groups of trees and larger forest patches on the surrounding grassland matrix where an edge effect is observed [12,13,14]
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