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

Abstract

Community assembly theory is suggested as a guiding principle for ecological restoration to help understand the mechanisms that structure biological communities and identify where restoration interventions are needed. We studied three hypotheses related to propagule limitation, stress-dominance, and limiting similarity concepts in community assembly in a restoration field experiment with a trait-based null model approach. The experiment aimed to assist the recovery of sand grassland on former arable land in the Kiskunság, Pannonian biogeographic region, Europe. Treatments included initial seeding of five grassland species, carbon amendment, low-intensity mowing, and combinations in 1 m by 1 m plots in three old fields from 2003 to 2008. The distribution of 10 individual plant traits was compared to the null model and the effect of time and treatments were tested with linear mixed effect models. Initial seeding had the most visible impact on species and trait composition confirming propagule limitation in grassland recovery. Reducing nutrient availability through carbon amendment strengthened trait convergence for length of flowering as expected based on the stress-dominance hypothesis. Mowing changed trait divergence to convergence for plant height with a strengthening impact with time, supporting our hypothesis of increasing dominance of limiting similarity with time. Our results support the idea that community assembly is simultaneously influenced by propagule limitation and multiple trait-based processes that act through different traits. The limited impact of manipulating environmental filtering and limiting similarity compared to seeding, however, supports the view that only targeting the dispersal and environmental filters in parallel would improve restoration outcome.

Disentangling the Effects of Disturbance from Those of Dominant Tall Grass Features in Driving the Functional Variation of Restored Grassland in a Sub-Mediterranean Context

“…In addition, mowing affected traits related to avoidance strategies. In fact, we found that mowing promoted small-sized species (lower plant height classes, reptant strategy) [10,32] and fast growth strategies (i.e., annual life span) [34] or early flowering strategies, related to spring green and mesomorphic leaves, as stated by Catorci, et al [52] for a sub-Mediterranean climate. It was argued that species with fast growth and only sexual reproduction (absence of vegetative propagation, in the study case) complete their life cycles before the growth of the dominant species [53] and the mowing events [54].…”

“…It is a non-selective disturbance [24] that, increasing light availability, promotes the survival of light-demanding seedlings, low-growth species [25,26] and germination rates of subdominant plants [27,28]. Moreover, it modifies the functional composition of plant communities by enhancing specific avoidance and tolerance strategies [29][30][31][32]. In particular, it was proven that vascular plant species richness was highest with two cuts per year, however the effect may differ in relation to the type of plant community, the timing of cutting and the biogeographic context [33].…”

“…Notwithstanding such scientific advancement, there is still a need to understand better the effect of disturbance activities (i.e., mowing) and disentangle such effects from those related to the processes of plant-plant interaction (dominant vs subordinate species) [36]. Abiotic interactions (i.e., disturbance through mowing) could be an important driver in species coexistence at a small-scale, with different effects depending on the type and intensity of the disturbance regime, the frequency in the disturbance events [37], but also depending on the considered time scale [32]. However, biotic interactions (i.e., plant-plant interactions) are considered the major driver at a small-scale.…”

“…Indeed, dominant species may remove from the community all weaker competitors (i.e., weaker competitor exclusion), acting as a biotic filter, which leads to the coexistence of more functionally similar species. Otherwise, it is possible that in the absence of dominant species, biotic interactions may lead to coexistence of functionally dissimilar species [32,38].…”

N immobilization treatment revisited: A retarded and temporary effect unfolded in old‐field restoration

“…However, the cover of neophytes might not decrease significantly during secondary succession (Csecserits et al, 2011) and some specialist species might not be able to establish (Molnár & Botta‐Dukát, 1998). This implies that generalist species can establish without carbon amendment, but the specialist species cannot arrive at the old‐fields without assisted dispersal (Halassy et al, 2019), and therefore the impact of carbon addition might not be detectable because of the lack of propagules of specialist species.…”