Changes in forest landscape patterns resulting from recent afforestation in Europe (1990-2012): Defragmentation of pre-existing forest versus new patch proliferation.

The present dataset was construct with the aim of addressing the association between forests cover increase and spatial pattern change in the European landscapes, while considering the landscape land cover composition and the altitudinal and geographical gradients. We hypothesized that forest increase is determining (i) a decrease in the overall landscape diversity, (ii) a forest defragmentation and (iii) an increase in forest connectivity across Europe.

We used the recent set of medium- to high-resolution land use and cover (LC) maps worldwide available: those of the Climate Change Initiative (CCI) by the European Spatial Agency (ESA 2017), and the forest cover change maps of the Global Land Cover Facility (GLCF) from the University of Maryland(Hansen et al. 2013; Kim et al. 2014).

Using LC maps we randomly selected 752 landscapes 5-km radius across Europe with recent (1990-2012) forest increase and we calculate for each landscape for the years 1990 and 2012 the following landscape metrics: forest patch number (n), mean and largest forest patch size (ha), total forest edge (m), forest effective mesh size (ha), percentage of forest like adjacencies (%), Euclidean nearest neighbour distance and Shannon diversity index.

In order to assess the modulating role of environmental context on the association between forest increase and landscape change, we included a set of variables regarding geographical position, topography, and initial composition of the study landscapes: Percentage of each land cover in 1990 (%), longitude (º), latitude (º), average of slope in the plot (º), average of elevation in the plot (m), mean annual temperature between 1970-2000 (ºC), standard deviation of annual temperature between 1970-2000 (ºC), Annual precipitation between 1970-2000 (ºC) and Annual precipitation standard deviation between 1970-2000 (ºC).

Finally we performed a set of GLM on randomly selected 752 landscapes with recent (1990-2012) forest increase to assess the modulating role of environmental context on the association between forest increase and landscape change.

Results showed that the decrease in landscape diversity in the last decades was not associated to forest increase but to high cropland and low scrub-grassland cover. Forest increase promoted the defragmentation of already existing forests and new patch proliferation in forest-dominated and non-dominated landscapes, respectively. These processes also depend on elevation and geographical position, with forest defragmentation concentrated in Northern and Eastern Europe and new patch proliferation in southern and western regions, and in mid-elevation areas.

本数据集旨在探究欧洲景观中森林覆盖率增长与空间格局变化之间的关联，同时考量景观土地覆被组成、海拔与地理梯度。我们提出如下研究假设：森林增长将（i）降低整体景观多样性，（ii）推动森林去碎片化，（iii）提升欧洲全域的森林连通性。

本研究采用当前全球可获取的中高分辨率土地利用与覆被（LC, Land Cover）地图集，包括欧洲空间局（ESA, European Spatial Agency）2017年发布的气候变化倡议（CCI, Climate Change Initiative）数据集，以及马里兰大学全球土地覆被设施（GLCF, Global Land Cover Facility）发布的森林覆被变化地图（Hansen等，2013；Kim等，2014）。

基于上述土地覆被地图，我们在欧洲范围内随机选取了752个半径5公里的景观样地，这些样地在1990-2012年间存在森林增长。针对每个样地，我们分别计算了1990年与2012年的如下景观格局指标：森林斑块数量（n）、森林斑块平均面积与最大斑块面积（单位：公顷）、森林总边缘长度（单位：米）、森林有效网格面积（单位：公顷）、类邻接森林占比（%）、欧氏最近邻距离以及香农多样性指数（Shannon diversity index）。

为评估环境背景对森林增长与景观变化之间关联的调节作用，我们纳入了一系列与研究样地地理位置、地形及初始覆被组成相关的变量：1990年各土地覆被类型占比（%）、经度（°）、纬度（°）、样地平均坡度（°）、样地平均海拔（单位：米）、1970-2000年平均气温（℃）、1970-2000年气温标准差（℃）、1970-2000年年降水量（单位：毫米）、1970-2000年年降水量标准差（单位：毫米）。

最后，我们针对1990-2012年间存在森林增长的752个随机选取样地，开展了一系列广义线性模型（GLM, Generalized Linear Model）分析，以评估环境背景对森林增长与景观变化之间关联的调节作用。

研究结果显示，近数十年间景观多样性的降低与森林增长并无关联，而是与高耕地占比、低灌丛-草地占比相关。森林增长分别推动了森林主导景观与非森林主导景观中现有森林的去碎片化，以及新斑块的增殖。上述过程同时受海拔与地理位置的调控：森林去碎片化主要集中于北欧与东欧地区，而新斑块增殖则出现在南欧、西欧及中海拔区域。