The application of a filter‐based assembly model to develop best practices for Pannonian sand grassland restoration

Abstract

1. The application of a filter-based assembly model is a promising concept to support ecological restoration. The filters illustrate dispersal, abiotic and biotic constraints that narrow down the species pool and determine the realized species composition. The aim of restoration interventions is the manipulation of filters to achieve a restoration target. 2. We tested the applicability of a filter-based assembly model in the restoration of endemic Pannonian sandy grassland on old-fields. We report the results of a six-year experiment to identify key filters and find possible interactions. Treatments included the following: (i) seeding (dispersal filter), (ii) carbon amendment to lower nitrogen availability (abiotic filter) and (iii) mowing (biotic filter). Treatments were carried out in 1 m 2 plots following the same Latin square design in three old-fields. 3. Seeding was the most important treatment increasing species richness, vascular cover and enhancing target species composition. Mowing played a secondary role, acting primarily in interaction with the other treatments. Carbon amendment significantly reduced soil mineral nitrogen, but played a subordinate role in determining vegetation composition. Significant interactions were found between the biotic and dispersal and the biotic and abiotic filters determining primarily the structural characteristics of the vegetation in terms of vascular cover, moss cover, litter and bare ground. Regarding species composition, synergistic links between the dispersal and biotic filters for seeded species and long-lived forbs, and antagonistic interaction between the dispersal and abiotic filters for seeded species were found. 4. Synthesis and applications. Based on the impact and interactions of filters uncovered in this experiment, we propose a scheme for Pannonian grassland restoration, which can be validated and also used for other oligotrophic systems. In the proposed conceptual model, the dispersal filter plays a key role in determining the outcome of restoration measures followed by the biotic filter if manipulated by mowing, while the abiotic filter altered by nitrogen immobilization proved to have a weak effect. Based on our results, targeting several filters in parallel would improve restoration outcome. We propose that filter interactions should form an integral part of filter-based assembly models and should be taken into account in restoration decisions.

Trait‐based approach confirms the importance of propagule limitation and assembly rules in old‐field restoration

“…Three abandoned arable fields were selected for the experiment with similar climate, soil characteristics, and earlier management (Halassy et al ). Although the time of abandonment was different for the three sites (2002, 1999, and 1987), this had negligible impact on our treatments.…”

“…(2) Carbon amendment with a dosage of 45 g sucrose/m 2 based on earlier experimental results (Török et al ) was applied every 3 weeks in the vegetation period from April till October (2003–2008). Carbon amendment lowered soil available nitrogen (Halassy et al ) that supposedly increased abiotic stress. (3) Mowing with hay removal was applied once a year in September to control interspecific competition for light (2003–2008).…”

“…Cover data were pooled based on the yearly maximum per species. The study area and experimental design are described in detail in Halassy et al ().…”

“…In the present article, we study propagule limitation, environmental filtering, and limiting similarity in a microscale restoration field experiment (2003–2008). Treatments include the introduction of a low‐diversity seed mixture, and carbon amendment to lower soil available nitrogen and thus increase environmental stress and mowing to decrease competition (see also Halassy et al ). We analyze traits separately and use the null model approach to reveal assembly rules, where we interpret negative effect sizes (functional diversity lower than expected by the randomization) as indication of environmental filtering, and positive effect sizes (functional diversity higher than expected by the randomization) as indication of competitive exclusion.…”

Species transfer via topsoil translocation: lessons from two large Mediterranean restoration projects

“…The restoration of species‐rich grasslands is often limited by low seed dispersal (Buisson et al ; Grman et al ; Halassy et al ), both in space and time (e.g. Römermann et al ).…”