Fragmentation and Connectivity of Island Forests in Agricultural Mediterranean Environments: A Comparative Study between the Guadalquivir Valley (Spain) and the Apulia Region (Italy)

Abstract

Habitat loss and fragmentation are considered some the main threats to biodiversity. Original forests have suffered an accentuated fragmentation and agricultural homogenization, leaving only some areas of natural vegetation, relegated to strongly anthropized disconnected patches (island forests, IFs) in a hostile matrix. These patches of original vegetation could be the key for the design and management of ecological corridors to promote species migration, an essential strategy for meeting the consequences of Global Change. This study proposes a comparative analysis of the fragmentation and connectivity of IFs of Quercus in two typically Mediterranean areas of predominantly agricultural use: the Guadalquivir valley (Spain) and the Apulia region (Italy). A retrospective comparison is also carried out in the Guadalquivir valley. The aim is to develop an objective new methodology to locate the patches of most interest using quantitative and qualitative data. Reference cartography of current island forests of Quercus species was developed from several digital sources and validated with orthoimages and field observations. Fragmentation analysis was based on graph structures using the software Conefor 2.6, a reliable tool for assessment of the role of patches in the landscape. Area and distance were used as node and connector values. Dispersion distance was established as 500 m, based on the maximum dispersion of acorns. Results indicate that the Guadalquivir valley has suffered an intensive fragmentation in recent decades. Both the Guadalquivir and Apulia regions host some IFs with the relevant potential to contribute as core habitats in the creation of connections to other natural protected sites. Many residual IFs in the landscape could contribute as stepping stones in the design and management of ecological corridors. Our methodology highlights the value of IFs to develop assessment strategies using homogenized available digital cartography and common criteria for the dispersion distances in graph theory analysis. The application of this new methodology could help in the management of protected sites using highly fragmented areas to allow the species movement through inhospitable landscapes in a unique opportunity to connect the different protected areas.

The Role of Trees Outside Forests in the Cultural Landscape of the Colline del Prosecco UNESCO Site

“…According to Sallustio et al [49], TOF represent essential elements of the green infrastructure network in many Italian landscapes, but the expansion of big and continuous forest patches on marginal lands and, on the other side, the agricultural intensification, can lead to a decrease in TOF and in the historical landscape mosaic structures. Similar findings have been reported for southern Spain and Italy by Hidalgo et al [50], where residual "island forests" could act as "stepping stones" in the local ecological network. TOF are also important for landscape perception, especially in intensive agricultural landscapes, as they contribute to increase the landscape heterogeneity and to the visual interruption of large extensions of monocultures [51].…”

Strengthening a Regional Green Infrastructure through Improved Multifunctionality and Connectedness: Policy Suggestions from Sardinia, Italy

“…On the contrary, connectivity is positively influenced by forests and woodlands, as shown by lower CWD in wooded land covers. Following Santos et al [74], land cover changes in forest areas are prominent drivers of habitat loss for a number of species due to reduction in patch sizes and increase in landscape fragmentation, which result in lower variety and population numbers of species that can survive [75]. Moreover, small forestcovered patches may seem irrelevant in terms of connectivity; however, they do play a key role in connecting remote and isolated patches [76], and additionally, small forest-covered patches can work as stepping stones to foster species movement [77] and as fundamental habitats for some species [76], as shown in the case of the Stołowe Mountains National Park, where a staggering 40% of epiphytic bryophytes are hosted by broadleaved forest-covered patches, although these account for less than 5% of the area [78].…”

Islandization and species diversity of semi-humid evergreen broad-leaved forests in the Central Yunnan Plateau

“…彼此隔离的不同大小斑块分布的状态, 或者由于自 然干扰或人为活动(如砍伐等)的影响, 连续森林被 分 割 成 彼 此孤 立 林 斑 的生 态 过 程 (Haddad et al, 2015)。 干扰作用下的森林破碎化导致森林斑块之间 的物种流和物质能量交换在不同程度上被截断, 形 成彼此隔离、孤立的森林岛屿 (Turner & Corlett, 1996;Hidalgo et al, 2021), 并导致森 林内部生境缩小、 生境质量下降 (D'Eon, 2002; 李瑶 等, 2017)。 研究表明, 全球现存森林面积的70%位于 离森林边缘1 km以内 (Haddad et al, 2015), 仅40%的 森 林 保 持 了 生 态 系 统 的 完 整 性 (Grantham et al, 2020); 热带森林中84%的边缘生境由人类活动所 产生 (Brinck et al, 2017)。在中国, 森林密度和连接 度为1的内部森林比例仅占3.4% (李瑶等, 2017)。因 此, 森林破碎化是森林生态系统普遍面临的严重问 题 (Fahrig, 2003)。 生境破碎化是导致全球生物多样性丧失的一 个重要因素 (Gibson et al, 2011;Saravia et al, 2018) 洲, 1979;姜汉侨, 1980;宋永昌, 2004;Tang, 2015), 和吴兆录, 1994a, b; 党承林等, 1994a, b)…”