Impact of land use and climate changes on expansion of woody species on subalpine meadows in the Eastern Carpathians

Abstract

In the 20th century, woody species expanded on many mountain ridges as grazing and mowing of subalpine grasslands was abandoned. As a result, subalpine meadows started disappearing, affecting entire montane ecosystems. To predict the consequences of changes in land use it is important to identify the ecological mechanisms behind changes in vegetation. This study examined the temporal and spatial variability of woody species succession on abandoned subalpine meadows in the Western Bieszczady Mts. (Eastern Carpathian Biosphere Reserve). We analysed the spatial patterns of Sorbus aucuparia recruitment in relation to topography and temporal changes in weather conditions, and found that the recruitment rate was not continuous. Two phases of rowan expansion were distinguished. In the first (before the 1970s), expansion depended on topography: northern and steep slopes were colonised and the development of thickets progressed from lower to higher elevations. In the second phase, starting in the 1970s, rowans crossed the historical timberline and on both northern and southern slopes was unrelated to topographical conditions. Moreover, in the last 60years, during which meteorological data were recorded, the rate of rowan expansion has been negatively correlated with precipitation and snow cover thickness. The temporal and spatial patterns of rowan recruitment on abandoned subalpine meadows indicate that land use changes were important in initiating the first stage of succession. Contrary to the common view and our own expectation that mildening of weather conditions facilitates colonisation of montane areas by trees, our results suggest that rowan expansion was positively associated with worsening of weather conditions (i.e. thinner snow cover and lower temperatures).