Changes in dispersal and light capturing traits explain post‐abandonment community change in semi‐natural grasslands

Abstract

Question Does the role of dispersal and light limitation for community assembly change in temperate semi‐natural dry grasslands (SNDGs) post‐abandonment? Location Temperate calcareous semi‐natural dry grasslands, western Estonia (58.642 N, 23.516 E). Methods We compared taxonomic and functional community structure of semi‐natural dry grasslands in Estonia at two time periods: first in 1975 when traditional grazing prevailed, and again in 2013 when management had ceased for at least 30 yr. In order to assess functional community structure, we used community‐weighted mean trait values and mean pair‐wise distance as metrics of functional diversity for traits related to plant dispersal and adaptations to reduced light availability. Successional shifts in functional community structure were examined using regression and multivariate analysis. Results Changes in community assembly of SNDGs post‐abandonment were largely driven by more closed vegetation structure and subsequently reduced light availability, as well as altered availability of dispersal vectors. Importance of long‐distance dispersal via grazing animals decreased while importance of bird dispersal increased under abandonment. At the same time, the importance of competition for light increased under abandonment. Results indicate that typical SNDG species are especially susceptible to abandonment because they are light‐demanding and depend on dispersal by wind or epizoochory (i.e. on the fur of animals), and their decline likely leads to reduced small‐scale species richness. Conclusions Vegetation changes in abandoned SNDGs show that regular management, by creating characteristic light and dispersal conditions, is highly important for maintaining both taxonomic and functional diversity. In particular, typical grassland species might be prone to local extinction as taller vegetation develops post‐abandonment. The importance of dispersal processes for community assembly observed in grazed SNDGs thus highlights that successful grassland conservation should include maintenance of dispersal conditions. Grassland conservation should aim to preserve the whole ecosystem and account for the multiple ecosystem processes (e.g. light availability, dispersal), which simultaneously structure plant community composition.

The role of plant mycorrhizal type and status in modulating the relationship between plant and arbuscular mycorrhizal fungal communities

“…The three successional stages (GR, TR, FO) form a temporal sequence of regeneration succession covering c . 60 yr, and are characterised by a gradual overgrowth of open grasslands by shrubs and trees, which is typical for abandoned calcareous grasslands in the study region (Neuenkamp et al ., ; Supporting Information Fig. S1).…”

Woody structure facilitates invasion of woody plants by providing perches for birds

“…Animals, especially birds, may be an important dispersal agent of many woody plants as they can effectively transport seeds long distances from areas containing woody plants into areas lacking them (Neuenkamp, Lewis, Koorem, Zobel, & Zobel, 2016;Proctor, 1968;Sritongchuay, Gale, Stewart, Kerdkaew, & Bumrungsri, 2014). The number of stable structures for perching can limit bird use (Ferguson & Drake, 1999;Graves, Rodewald, & Hull, 2010; but see Vickery & Hunter, 1995), and as a result, increases in woody structure may enhance seed deposition as well as plant diversity by providing structure that birds use for perches (McClanahan & Wolfe, 1993;Graham & Page, 2012).…”

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

“…The likelihood of threatened species being rescued by immigration from neighbouring populations declines with increasing isolation and decreasing habitat amount (Evju et al., ; Hooftman et al., ), and grassland species are often heavily reliant on grazing livestock to disperse seeds (Plue & Cousins, ). Hence the complete loss of landscape‐scale grazing and grassland management in the study area used here is likely to have drastically reduced species’ resilience to changes in habitat availability (Eriksson & Cousins, ; Kuussaari et al., ; Neuenkamp et al., ). This may have contributed to a more rapid loss of vulnerable species and a relatively brief period before extinction debts were fully paid.…”

“…In semi‐natural grasslands the removal of regular, non‐intensive disturbance with the abandonment of traditional management methods results in substantial changes in plant communities. Frequently succession to forest occurs, along with a shift towards species able to compete for light or tolerate shade, and away from those adapted to disturbance (Neuenkamp, Lewis, Koorem, Zobel, & Zobel, ; Poschlod, Bakker, & Kahmen, ; Vandewalle et al., ). Together with pressures of agricultural intensification and habitat loss within the wider landscape, management abandonment has contributed to a loss of vulnerable species across multiple taxa (Öckinger, Eriksson, & Smith, ; Uchida & Ushimaru, ).…”

“…However, the extent to which this process applies generally and how it might be influenced by different local‐ and landscape‐scale factors is unclear. 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, ).…”