The complexity of forest borders determines the understorey vegetation

Abstract

Questions:What are the most important drivers of plant species richness (gammadiversity) and species turnover (beta-diversity) in the field layer of a forest edge? Does the tree and shrub species richness structure and complexity affect the richness of forest and grassland specialist species?Location: Southeast Sweden. Methods:We sampled 50 forest edges with different levels of structural complexity in agricultural landscapes. In each border we recorded trees, shrubs and herb layer species in a 50-m transect parallel with the forest. We investigated species composition and species turnover in relation to the proportions of gaps in the border and the diversity of trees and shrubs.Results: Total plant species richness in the field layer was mainly explained by the proportion of gaps to areas with full canopy cover and tree diversity. Increasing number of gaps promoted higher diversity of grassland specialist species within the field layer, resulting in open forest borders with the highest overall species richness. Gaps did however have a negative impact on forest species richness. Conversely, increasing forest species richness was positively related to tree diversity, but the number of grassland specialist species was negatively affected by tree diversity. Conclusions:Managing forest borders, and therefore increasing the area of semi-open habitats in fragmented agricultural landscapes, provides future opportunities to create a network of suitable habitats for both grassland and deciduous forest specialist species. Such measures therefore have the potential to increase functional connectivity and support dispersal of species in homogeneous forest/agricultural landscapes. K E Y W O R D Salpha-diversity, beta-diversity, gamma-diversity, canopy cover, forest border, forest management, forest specialist species, grassland specialist species, plant diversity, remnant habitat, species richness, structural heterogeneity,

Functional rather than structural connectivity explains grassland plant diversity patterns following landscape scale habitat loss

“…No semi-open grazed forest remained in contemporary landscapes, so this category was not present in the contemporary landscape digitization. We also digitised road verges, hedges, railway banks and complex forest borders (forest borders where the transition from open to forest habitat is gradual, resulting in heterogeneous conditions with some more open areas (Lindgren et al 2018)), for both time points.…”

“…We considered semi-natural grassland, open forest, midfield islets, forest borders and road verges as potential ''green infrastructure'' (GI) habitats for grassland plant species, in relation to our focal habitats (Cousins 2006;Poschlod and Braun-Reichert 2017;Lindgren et al 2018). We created two metrics of connectivity following Hanski (1994), which we adapted to represent structural and inferred functional connectivity.…”

“…As such, the definition of these green infrastructure habitats relevant to semi-natural grassland connectivity includes restored grasslands, forest borders, midfield islets (small, often rocky areas with a thin topsoil layer within crop fields), managed hedgerows and road verges. Although these landscape features do not have all the environmental attributes of ancient semi-natural grassland, they may support at least some populations of semi-natural grassland species (Cousins 2006;Auffret and Cousins 2013;Jakobsson et al 2016;Hunter et al 2017;Poschlod and Braun-Reichert 2017;Lindgren et al 2018;Thiele et al 2018). Hence, green infrastructure habitats may enhance both structural and functional connectivity by increasing available habitat and linking otherwise isolated grasslands through supporting dispersal processes or the movement of dispersal vectors through the landscape (Auffret and Cousins 2013;Hunter et al 2017;Poschlod and Braun-Reichert 2017;Bullock et al 2018;Damschen et al 2019).…”

Unbalanced species losses and gains lead to non‐linear trajectories as grasslands become forests

“…Although some plants are able to remain for some time following grassland fragmentation or abandonment (Lindborg & Eriksson, ; Vandewalle et al., ), substantial grassland specialist extinctions have been detected over periods of less than 30 years (Deák, Valkó, Török, & Tóthmérész, ; Neuenkamp et al., ; Pykälä, Luoto, Heikkinen, & Kontula, ). While the presence of nearby intact grasslands may help slow population declines of grassland species (Evju, Blumentrath, Skarpaas, Stabbetorp, & Sverdrup‐Thygeson, ; Hooftman, Edwards, & Bullock, ), this may only be the case in very recently abandoned areas, where light availability remains high enough for grassland species establishment (Bagaria et al., ; Lindgren, Kimberley, & Cousins, ). Conversely, poorly dispersing forest specialist species are slow to colonize new habitat, particularly where it is isolated from source populations (Brunet, De Frenne, Holmström, & Mayr, ; Brunet et al., ; De Frenne et al., ; Kimberley, Blackburn, Whyatt, & Smart, ; Naaf & Kolk, ).…”

“…While the presence of nearby intact grasslands may help slow population declines of grassland species (Evju, Blumentrath, Skarpaas, Stabbetorp, & Sverdrup-Thygeson, 2015;Hooftman, Edwards, & Bullock, 2016), this may only be the case in very recently abandoned areas, where light availability remains high enough for grassland species establishment (Bagaria et al, 2015;Lindgren, Kimberley, & Cousins, 2018). Conversely, poorly dispersing forest specialist species are slow to colonize new habitat, particularly where it is isolated from source populations (Brunet, De Frenne, Holmström, & Mayr, 2012;Brunet et al, 2011;De Frenne et al, 2011;Kimberley, Blackburn, Whyatt, & Smart, 2016;Naaf & Kolk, 2015).…”