Data from: Influence of land use and climate on recent forest expansion: a case study in the Eurosiberian-Mediterranean limit of northwest Spain

1. In Mediterranean mountainous areas, forests have expanded in recent decades because traditional management practices have been abandoned or reduced. However, understanding the ecological mechanism behind landscape change is a complex undertaking as the effects of land use may be influenced (reinforced or constrained) by other factors such as climate. 2. We used orthorectified aerial photographs to monitor changes in forest distribution in a set of 20 head-water basins (located in the Cantabrian Mountains of northwest Spain, at the Eurosiberian-Mediterranean limit) during the second half of the 20th century (1956, 1974, 1983, 1990 and 2004). In particular, we evaluated the combined effects of both land use history (comparing natural vs. anthropic basins) and microclimate (comparing shaded vs. sunny aspects) for assessing gain/loss rates and spatial distribution shifts of forests. Finally, in the stated scenarios of land use history and microclimate, we applied Species Distribution Modeling techniques (MaxEnt and BIOMOD) for defining forest expansion both spatially and statistically on the basis of topography, soil properties and mesoclimatic variables. 3. On average, forest cover increased from 10.72% in 1956 to 27.67% in 2004. The rate of expansion was significantly higher in natural basins and, particularly, on shaded slopes in recent decades. In all cases, the mean elevation of new forest patches increased during the study period, this trend being more evident on natural sunny slopes. The performance of the models and the magnitude of the effects varied across land use history, microclimatic conditions and biogeographic origin of forests. The main drivers of forest expansion were temperature and precipitation in late spring and early summer and soil properties, although land use history and plant diversity primarily controlled forest expansion rates and upward altitudinal shifts. 4. Synthesis. The combination of monitoring and modeling used in this work contributes to the understanding of forest dynamics in cultural systems, indicating that ecological succession is not a homogeneous process, but varies spatially due to human and abiotic constraints since historical times.

1. 近数十年来，地中海山地林区的森林面积持续扩张，这源于传统营林管理措施被废弃或缩减。然而，厘清景观变化背后的生态机制是一项复杂的工作：土地利用的影响可能会受到气候等其他因素的调控（强化或约束）。2. 本研究采用正射校正航空照片（orthorectified aerial photographs），对20处源头流域（head-water basins，位于西班牙西北部坎塔布连山脉、地处欧洲西伯利亚-地中海过渡带）在20世纪下半叶（1956年、1974年、1983年、1990年及2004年）的森林分布变化进行监测。具体而言，我们通过对比天然流域与人工流域以评估土地利用历史的影响，对比阴坡与阳坡以评估微气候的影响，进而综合分析二者的联合效应，以此量化森林的面积增减速率与空间分布迁移特征。最后，基于地形、土壤属性和中气候变量，在预设的土地利用历史与微气候场景下，本研究运用物种分布模型（Species Distribution Modeling）技术（MaxEnt与BIOMOD）从空间与统计层面界定森林扩张的范围与规律。3. 整体而言，研究区森林覆盖率从1956年的10.72%提升至2004年的27.67%。近数十年来，天然流域的森林扩张速率显著更高，其中阴坡的扩张效果尤为突出。研究期间，所有样地的新生林斑块平均海拔均呈上升趋势，这一趋势在天然阳坡上表现得更为明显。模型的拟合效果与各因子的影响强度，会因土地利用历史、微气候条件以及森林的生物地理起源不同而存在差异。森林扩张的主要驱动因子为晚春与初夏的气温、降水量以及土壤属性，而土地利用历史与植物多样性则主要调控森林扩张速率与海拔向上迁移的幅度。4. 综合分析：本研究结合监测与建模手段，有助于理解人文生态系统中的森林动态变化，研究表明生态演替并非均质化过程，而是自历史时期以来便受人类活动与非生物因子的双重约束，进而呈现出空间异质性。