Abstract
In the current alteration of temperature and snow cover regimes, the impacts of winter climate have received considerably less attention than those of the vegetation period. In this study, we present the results demonstrating the influence of the winter climate conditions on the Mountain pine (Pinus mugo Turra) communities in High Tatra Mts (Western Carpathians). The changes in greenness in 2000–2020 were represented by the inter-annual differences of satellite-derived Normalized Difference Vegetation Index (NDVI). The winter climate conditions were characterized by climate indices calculated from the temperature and snow cover data measured at Skalnaté Pleso Observatory (1778 m a.s.l.) over the period between 1941–2020. Areas with P. mugo were classified into two density classes and five altitudinal zones of occurrence. The partial correlation analyses, which controlled the influence of summer climate, indicated that winter warm spells (WWS) caused a significant decrease in the greenness of the P. mugo thickets growing in the dense class D2 (R = −0.47) and in the altitudinal zones A2 (1600–1700 m a.s.l.) and A3 (1700–1800 m a.s.l.) with R = −0.54 for each zone. The changes in greenness were related to the average snow depth (ASD) as well, particularly in the dense class D2 (R = 0.45) and in the altitudinal zone A2 (R = 0.50). Here, in the summers following winters with the incidence of WWS or low ASD, we found decreased greenness following the injury of P. mugo shrubs, but NDVI after winters with higher ASD indicated more greenness. At lower altitudes, injuries may result in the loss of competition capacity of P. mugo near the timberline, where taller mountain tree species can utilize the conditions of warmer climate for expansion. We also found a significant positive effect of warmer winter seasons in the sparse P. mugo thickets (D1) with R = 0.50 and at higher altitudes (R = 0.49 in A4—1800–1900 m a.s.l.; R = 0.53 in A5—1900–2000 m a.s.l.). The increased temperatures in December correlated significantly with the increase of the greenness in all P. mugo pixels (R = 0.47), with the most pronounced effect in the sparse class D1 (R = 0.57) and in altitudinal zones A4 (R = 0.63) and A5 (R = 0.44), creating advantageous conditions for the thermophilisation of the alpine zone by P. mugo.
Highlights
Mountain and alpine ecosystems cover more than 20% of the Earth’s land surface spanning over areas from the equator to just near the poles [1,2]
Our results show negative inter-annual changes in P. mugo greenness occurring in the dense thickets D2 (R = 0.45), which were indicated in the partial correlation analyses as close-to-significant
Across the studied subalpine area in High Tatra Mts, we found a considerable effect of stand factors—altitude and density, on the NDVIdif,5y between the beginning
Summary
Mountain and alpine ecosystems cover more than 20% of the Earth’s land surface spanning over areas from the equator to just near the poles [1,2]. P. mugo is native to central and southeast Europe, ranging from the Swiss-Austrian border in the Alps to the. In most of these mountains, the P. mugo shrubs form a coherent, climatically conditioned vegetation belt, mostly known as a subalpine belt near the timberline [4]. The subalpine belt refers to an intermediate zone between the mountain and alpine vegetation with an ecotone character [5]. P. mugo reaches higher altitudes than any other conifers (up to 2400 m). In Holocene, in the Western Carpathians and Hercynian region, it was pushed by spruce and beech to higher altitudes (above 1250–1500 m a.s.l.), and eventually to peatlands and rocky mountains. The presence of symbiotic fungi on the pine roots enables this scrub to procure the nitrogen component of nutrients and thereby enables
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