The effects of biophysical and anthropogenic factors on the recent upper forest‐cover upward shift in the Romanian Carpathians

Abstract

AbstractAimTo estimate the effects of environmental and human drivers on upper forest‐cover upward shift over the period 1945–2018.LocationRomanian Carpathians.MethodsUsing historical topographic maps and high‐resolution Sentinel‐2A satellite images, we delineated the location of the upper forest‐cover limit in 1945 and 2018 to obtain a binary raster with the “forest gains” and “no‐forest gains” for 1945–2018. The maps were overlapped over 12 independent variables to estimate how they affected the recent upper forest‐cover upward shift, and to predict its probability of expansion in the near future. To achieve this, logistic regression models were applied and then integrated into the GIS spatial analysis.ResultsForest gains of almost 35,000 ha have been detected at the upper forest limit in the study sites, leading to an average upward movement of 30 m (0.5 m per year), mainly at the altitudinal bands between 1,400 and 1,800 m a.s.l. (72%); only 9.7% of the gain was detected above the estimated potential climatic limit. The process was significantly inversely related to elevation (−17.3 ≤ β ≤ −5.7, p < 0.01), slope aspect (−1.5 ≤ β ≤ −0.4, p < 0.01), sheepfold numbers (−18.1 ≤ β ≤ −0.7, p < 0.01), and sheep (−18.3 ≤ β ≤ −0.6, p < 0.01) and cattle (−16.4 ≤ β ≤ −0.8, p < 0.01) populations. Strong direct effects were found for the slope angle (1.3 ≤ β ≤ 10.6, p < 0.01) and distance to sheepfolds (0.5 ≤ β ≤ 12.8, p < 0.01). A low contribution was indicated for the trend in mean air temperature (−1.1 ≤ β ≤ 4.3, p < 0.01), growing season length (−2.1 ≤ β ≤ 5.1, p < 0.01) and protective measures (−1.1 ≤ β ≤ 2.4, p < 0.01, for national parks; −1.8 ≤ β ≤ 1.2, p < 0.01, for natural parks).ConclusionsThe analysis demonstrated that decreased land‐use intensity and, in particular, declining traditional practices were the foremost mechanisms of the recent upper forest‐cover upward shift, whereas the effect of climate warming remains not so obvious.