Phenological trends of European beech stands along the Carpathian arc: a 20-year MOD13Q1/MYD13Q1 based analysis

European forests are severely threatened by rapid global climate change. Predicting the effects of climate change on the future performance of tree species can be enhanced by using geographical gradients as space-time proxies. This study focuses on analysing seasonal and inter-annual phenological trends for eight sites of European beech (<i>Fagus sylvatica</i> L.) in the Carpathians along such geographical gradient. Using time series of the Enhanced Vegetation Index (EVI) from 2003 to 2022, derived from 16-day MODIS Terra and Aqua vegetation products, combined with meteorological parameters (temperature and precipitation) interpolated for a grid and Land Surface Temperature (LST) data from Landsat, we compared annual forest development at the study sites and extracted key phenological metrics (start, length, and end of the growing season) using the phenofit software package for R. Our results show varied responses of the studied forest sites to climate change. The end of season extended significantly at Soveja (slope = 0.50, <i>p</i> = 0.023). Spring temperatures had negative correlations with the start of season (<i>r</i> = -0.37) and autumn temperatures positive correlation with the end of season (<i>r</i> = 0.43). Understanding these patterns is crucial for developing adaptive forest management strategies in Carpathians.

欧洲森林正受到全球气候变化的严重威胁。通过将地理梯度作为时空替代指标，可提升对气候变化对树种未来生长表现影响的预测能力。本研究聚焦于分析喀尔巴阡山脉沿该地理梯度分布的8个欧洲山毛榉（<i>Fagus sylvatica</i> L.）站点的季节及年际物候趋势。使用2003-2022年的增强植被指数（EVI）时间序列（源自16天分辨率的MODIS Terra与Aqua植被产品），结合网格化插值的气象参数（温度与降水）及Landsat的地表温度（LST）数据，我们对比了各研究站点的年度森林生长动态，并利用R语言的phenofit软件包提取了关键物候指标（生长季开始、持续时长及结束时间）。研究结果显示，各研究森林站点对气候变化的响应存在差异。Soveja站点的生长季结束时间显著延长（斜率=0.50，<i>p</i>=0.023）。春季温度与生长季开始时间呈负相关（<i>r</i>=-0.37），秋季温度与生长季结束时间呈正相关（<i>r</i>=0.43）。理解这些模式对于制定喀尔巴阡山脉的适应性森林管理策略至关重要。