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

Abstract

Context Functional connectivity is vital for plant species dispersal, but little is known about how habitat loss and the presence of green infrastructure interact to affect both functional and structural connectivity, and the impacts of each on species groups. Objectives We investigate how changes in the spatial configuration of species-rich grasslands and related green infrastructure such as road verges, hedgerows and forest borders in three European countries have influenced landscape connectivity, and the effects on grassland plant biodiversity. Methods We mapped past and present land use for 36 landscapes in Belgium, Germany and Sweden, to estimate connectivity based on simple habitat spatial configuration (structural connectivity) and accounting for effective dispersal and establishment (functional connectivity) around focal grasslands. We used the resulting measures of landscape change to interpret patterns in plant communities. Results Increased presence of landscape connecting elements could not compensate for large scale losses of grassland area resulting in substantial declines in structural and functional connectivity. Generalist species were negatively affected by connectivity, and responded most strongly to structural connectivity, while functional connectivity determined the occurrence of grassland specialists in focal grasslands. Restored patches had more generalist species, and a lower density of grassland specialist species than ancient patches. Conclusions Protecting both species rich grasslands and dispersal pathways within landscapes is essential for maintaining grassland biodiversity. Our results show that increases in green infrastructure have not been sufficient to offset loss of semi-natural habitat, and that landscape links must be functionally effective in order to contribute to grassland diversity.

Combatting global grassland degradation

“…In regions where semi-natural grassland remnants are fragmented and persist within a matrix of forested or intensive agriculture land uses, new research could facilitate landscape and regional scale restoration of inter-connected grasslands. There is increasing evidence that grassland dynamics and function are enhanced by connectivity that encourages flows of species and biogeochemical processes 111,112 . In theory, such spatial networks have improved resilience to perturbations, such as climate extremes, and the ability to adapt to a changing environment 113 .…”

Soil phosphorus availability determines the contribution of small, individual grassland remnants to the conservation of landscape‐scale biodiversity

“…Consequently, dispersal and recruitment opportunities between high‐quality remnant grasslands and semi‐natural grasslands are reduced further in a species group with trait syndromes typically already indicative of poor dispersal capabilities (Saar et al, 2012; Auffret et al, 2017a; Thiele et al, 2018). This is particularly problematic, as increasing levels of green infrastructure which supposedly enhance the landscape's permeability are still failing to offset continued losses of semi‐natural grasslands (Kimberley et al, 2020).…”

“…First, remnant grassland fragments form a vital part of a landscape's green infrastructure, i.e. the assemblage of structural elements of (remnant) semi‐natural habitats, structurally connecting large, remaining semi‐natural habitats (Kimberley et al, 2020). However, their mere presence does not guarantee that plant species migrations are effectively happening along these remnant grasslands, supporting so‐called functional connectivity (Auffret et al, 2017b).…”

“…Measures rehabilitating soil quality following chronic P eutrophication are a prerequisite for the recovery of grassland communities, but they demand a substantial and sustained effort which is often not feasible nor practical to implement (Schelfhout et al, 2015), particularly in small, isolated remnant grasslands. At the same time, P fertiliser applications continue at levels detrimental to biodiversity (Ceulemans et al, 2014) and large, intact semi‐natural grasslands continue to be lost at alarming rates (Watson et al, 2016; Auffret et al, 2018; Kimberley et al, 2020; Ridding et al, 2020). Consequently, the protection and integrated landscape‐scale management of semi‐natural grasslands in agricultural landscapes must remain a top priority, in conservation management and policy actions (Hodgson et al, 2011; Watson et al, 2016).…”

“…First, remnant grassland fragments form a vital part of a landscape's green infrastructure, i.e. the assemblage of structural elements of (remnant) semi-natural habitats, structurally connecting large, remaining semi-natural habitats (Kimberley et al, 2020).…”