Roadside diversity in relation to age and surrounding source habitat: evidence for long time lags in valuable green infrastructure

Abstract

1. The severe and ongoing decline in semi‐natural grassland habitat during the past two centuries means that it is important to consider how other, marginal grassland habitat elements can contribute to landscape‐level biodiversity, and under what circumstances. 2. To examine how habitat age and the amount of core grassland habitat in the surrounding landscape affect diversity in green infrastructure, we carried out inventories of 36 rural road verges that were either historical (pre‐1901) or modern (established post‐1901 and before 1975), and were surrounded by relatively high (>15%) or low (<5%) levels of grassland habitat. We recorded the number of plant species, grassland specialists, grassland conservation species and the fraction of the landscape's species and specialists found in the road verge. 3. Road verge communities were characterised by high levels of grassland specialist species (35% of the 161 species recorded), with road verge sites supporting 15–20% of the specialist species found in the surrounding 25 km2 landscape. 4. Richness of species and specialists were more closely related to road age than to the amount of surrounding habitat. Higher diversity in historical roads, despite the majority of modern roads being at least 60 years old, suggests a long time lag in the establishment of grassland communities in marginal grassland habitats. We identified no effect of historical surrounding land use on present day diversity in road verges. 5. Road verge richness was not affected by the amount of surrounding grassland. This could be due to the relatively low amounts of grassland remaining in all landscapes, together with dispersal limitation commonly found in grassland plant communities contributing to a potential time lag. 6. We identified road verges as potentially very important habitats for grassland communities. Because of the high levels of grassland specialists present, these and other marginal grasslands and grassland green infrastructure should be explicitly considered in landscape‐scale conservation management. Practitioners looking to identify the most species‐rich road verges should aim to find the oldest possible, while long time lags in community assembly suggests that seed sowing could be appropriate to enhance roadside diversity, even in decades‐old road verges.

Valuing the Role of Time in Urban Ecology

“…This is an important data gap because evidence from non-urban systems demonstrates ecological time lags can determine the success of ecological management and conservation efforts (Watts et al, 2020). For instance, in road verges, multi-decadal time lags have been identified when investigating community assembly, thus posing new challenges when designing appropriate urban restoration and conservation efforts (Auffret and Lindgren, 2020). More detailed knowledge is needed on the effects of time lags and delays on urban biodiversity and ecological functioning, and how they could underpin effective urban planning and management interventions.…”

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

“…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). Numerous environmental factors such as matrix quality, management or habitat age indeed constrain the efficiency of the green infrastructure (Baum et al, 2004;Aavik & Liira, 2010;Thiele et al, 2018;Auffret & Lindgren, 2020), and our results add habitat quality of the remnants prominently to this list. Local habitat quality has repeatedly been pinpointed as a crucial factor explaining the richness and abundance of numerous taxa when compared to other patch-and landscape-scale variation in large, intact semi-natural grasslands (Gonthier et al, 2014;Zulka et al, 2014), but it is clear from our results that this also holds for the grassland remnants.…”

“…In order to attain nature retention goals, conservationists are increasingly turning their attention to small, remnant or even artificial habitats that are scattered in the landscape to assess their potential in conserving biodiversity in human‐dominated landscapes (Wintle et al, 2019). These include, for example, urban lawns (Thompson et al, 2004), small forests (Valdés et al, 2019), burial mounds (Deak et al, 2018), hedgerows (Staley et al, 2013), ditches (Meier et al, 2017), forest edges (Lindgren et al, 2018), road verges (Auffret & Lindgren, 2020) or other linear landscape features (Gardiner et al, 2018). Such small, individual habitat patches tend to support only a limited number of species, yet their combined surface area can substantially contribute to the landscape‐scale habitat amount (Lindgren & Cousins, 2017; Gardiner et al, 2018), potentially increasing the species density in local communities (Watling et al, 2020) and harbouring important portions of landscape‐scale species pools, including habitat specialists (Deak et al, 2018; Gardiner et al, 2018).…”

Mapping the purple menace: spatiotemporal distribution of purple loosestrife (Lythrum salicaria) along roadsides in northern New York State

“…All plant species within 1 m of a purple loosestrife infestation were recorded, and increased species richness was a predictor of higher purple loosestrife density. Species richness and diversity along roadside right of way (ROW) has been studied as it connects to the spread from the ROW to neighboring forests or hedgerows 44 or grasslands 45 , and agriculture landscapes 46 as well as the conservation value of ROWs for avian and small mammal conservation 46 . These studies most often focus on the conservation value or use as habitat for wildlife.…”