Succession in soil seed banks and its implications for restoration of calcareous sand grasslands

Abstract

Spontaneous succession is increasingly involved in grassland restoration, because it offers a cost‐effective solution compared to technical reclamation methods. This topic is especially important nowadays, as large areas of marginal croplands are being abandoned on poor soils of Central and Eastern Europe, which offers a possibility for the spontaneous recovery of typical target grasslands. Studying the vegetation composition, aboveground biomass, and seed bank in old fields of different age and target calcareous sand grasslands using the chronosequence method, we aimed to answer the following questions: (1) Which species contribute to the seed banks of old fields and reference grasslands? (2) Does the direction of vegetation and seed bank succession trend toward the reference grasslands? (3) How are the vegetation changes in spontaneous succession reflected by the soil seed banks of old fields? In reference grasslands on the dune tops only sporadic seed banks were detected, while several hygrophytes had dense seed banks in reference grasslands in dune slacks. Similarity between the species composition of vegetation and seed banks was low. The development of vegetation and seed banks in old fields progressed toward that of target grasslands and the proportion of weedy species (e.g. indigenous weeds and invasive species) also decreased with time. The cryptogam biomass correlated significantly negatively, while the soil phosphorus significantly positively with the weedy species seed bank density. Our results indicated that the role of persistent seed banks in the regeneration of calcareous sand grasslands from old fields is rather limited and promising vegetation changes are mostly driven by spatial dispersal.

Can we rely on the soil seed bank for restoring xeric sandy calcareous grasslands?

“…These figures are somewhat lower than the 54% similarity found by Hopfensperger () between vegetation and seed bank communities in her review of 55 studies conducted in grassland ecosystems. A weak similarity (<40%) has, however, been generally reported in European grasslands (Bossuyt & Honnay ), in particular in sandy grasslands (Török et al , ) and in calcareous grasslands (Bisteau & Mahy ).…”

Beyond the species pool: modification of species dispersal, establishment, and assembly by habitat restoration

“…In their meta‐analysis, Bossuyt and Honnay () found that in most grassland and forest communities, target species with persistent seed bank are too scarce to effectively support spontaneous recovery. This is especially true, because most of the rare species, and also several characteristic matrix species generally lack persistent seed banks in these communities (Kiss et al ; Klaus et al ; Godefroid et al ; Török et al ). In wetlands, heathlands, and habitats with frequent and unpredictable disturbances, regeneration from the seed bank is more important and thus persistent seed banks can support the spontaneous recovery of these habitats better than in grasslands or forests (Bossuyt & Honnay , Kiss et al ).…”

“…This finding should be considered in restoration prioritization: if resources for restoration are limited, site managers should select less severely degraded sites for spontaneous recovery or assisted restoration. Given the low contribution of soil seed banks to vegetation recovery, enabling the spatial component of seed dispersal is crucial in restoration projects (see Török et al ). Landscape‐scale extent and spatial configuration of reference grasslands should be evaluated and sites where spatial dispersal of target species is more promising and where unwanted invasive species are absent should be prioritized for spontaneous recovery.…”

“…In general, the soil seed bank of degraded sites mainly consists of undesired species (Török et al ; Hess et al ; Klaus et al ; Török et al ). Thus, information about the composition of the seed bank can inform site managers about the most important future threats, such as the encroachment of weeds and invasive species.…”

“…Finally, knowledge on soil seed banks also supports the monitoring of restoration success and helps us estimate the resilience of the restored communities. Török et al () evaluated the success of spontaneous recovery of sandy old‐fields in a chronosequence study and showed that the development of seed banks is also a proper indicator of restoration success. The seed bank informs us about community resilience, which is especially important faced with changing climate as shown by Kiss et al ().…”