Disturbance, microclimate and historical habitat connectivity determine the population performance of the threatened grassland specialist Carex caryophyllea in remnant grasslands

Abstract

Many grassland specialist plant populations in Europe have become restricted to remnant habitats. The performance of these populations depends on both species‐specific traits and local and landscape level aspects of habitat quality. Understanding which specific local or landscape level conditions determine the performance of grassland species populations in remnant habitats would help design the restoration of the habitats and to detect the conditions that favour the long‐term persistence of grassland species in them. Such information is especially needed in urbanised landscapes, where remnant habitats engulfed by urban land use types may experience increased erosion, higher temperatures and invasion by alien species. This study investigates the population performance determinants of Carex caryophyllea (VU), a grassland specialist, in 43 remnant grasslands in an urban‐rural gradient in Finland. The population performance was assessed with metrics of persistence, establishment and reproduction, and related to environmental conditions with generalized additive models and redundancy analysis. The most important positive determinants for the performance of C. caryophyllea populations were disturbance through management or ground erosion, a warm microclimate, large habitat area and high historical connectivity to suitable grassland habitats. Present connectivity to other C. caryophyllea populations had a weak and near‐significant positive relationship with population performance. Urbanisation of the surrounding landscape correlated with population performance as well, possibly due to the high historical cover of grasslands in presently urbanised landscapes. The results imply that the most effective restoration method of remnant C. caryophyllea populations would be reinstating disturbance regimes in overgrown habitats with warm microclimates close to suitable habitats and other existing populations, whether urban or rural. This would counteract the species future decline due to possible extinction debts and help the species persist in the study area in the long term.

Contrasting responses of vascular plants and bryophytes to present and past connectivity in unmanaged grasslands

“…These specialist species depend on disturbance to deter the progress of secondary succession, usually in the form of traditional dry grassland management such as grazing (Raatikainen et al 2009). Together with previous studies (Burden and Randerson 1972;Lampinen 2019), our results suggest that trampling may function as a suitable disturbance and benefit grassland specialist vascular plant species in grasslands that are under no other management or disturbance regime. Although we found no evidence of trampling affecting the species richness of bryophytes, they have been shown to respond positively to moderate trampling in other studies.…”

“…Such an approach is seldom applicable in dry grassland conservation, because in most landscapes these habitats exist only as small, fragmented remnants of their previous extent. Despite their small size and isolation, such remnant grasslands may contribute to landscape-scale biodiversity by supporting communities and endangered species not found in other habitats (Albrecht and Haider 2013;Janišová et al 2014;Lampinen 2019). This highlights the importance of acknowledging them in conservation planning (Wintle et al 2019).…”

“…Species communities assemble based on both local and landscape-scale conditions that filter species according to variation in the environment (Löbel et al 2006;Raatikainen et al 2009;Frey et al 2011;Reitalu et al 2012). In dry grasslands, local conditions are central aspects of habitat quality that define whether grassland species persist in a grassland (Pykälä et al 2005;Lampinen 2019). From the perspective of a given plant species, the most important local conditions comprise those related to prevailing microclimate and soil properties.…”