No recovery of campo rupestre grasslands after gravel extraction: implications for conservation and restoration

Abstract

Old‐growth grasslands, including savannas and tropical grasslands, need centuries to assemble; they are therefore expected to have low resilience to anthropogenic activities that disturb the soil (e.g. cultivation, quarrying, mining, etc.). Understanding which parameters restrict the natural recovery of degraded ecosystems is a major prerequisite for planning an effective restoration program. This study was designed to evaluate the recovery of an old‐growth grassland, the campo rupestre, after a major disturbance: gravel extraction. In 2010 (i.e. 8 years after the degradation), we analyzed soil characteristics, seed bank, and vegetation composition in degraded sites consisting of sandy or gravel substrates, as well as in reference sites of sandy and gravel grasslands. At degraded sites, soils contained lower concentrations of the main nutrients, and seed banks consisted mainly of nontarget species. Seed banks of reference grasslands were poor in species and in seeds. Eight years after the degradation, plant communities at degraded sites were still very different from those at the reference sites, with ruderals and almost no target species. Altered soil conditions, low capacity of campo rupestre species to form seed banks, and the probable restriction of seed dispersal from the target species in nearby campo rupestre considerably limited the establishment of campo rupestre plant communities in degraded areas. Time is essential for old‐growth grassland assemblage and, even with the presence of a propagule source in the surroundings, the assembly of campo rupestre plant communities in degraded sites will take centuries. Therefore, human intervention is necessary to rapidly reestablish the main species.

Resilience and restoration of tropical and subtropical grasslands, savannas, and grassy woodlands

“…Cava et al, 2018). Grassland conversion for agriculture, plantation forestry, or mining not only destroys plant and animal communities, but also profoundly changes chemical and physical soil features Le Stradic et al, 2018a). Our review of the restoration literature suggests that such human-induced environmental change often pushes tropical grasslands across ecological thresholds to alternative ecosystem states, from which recovery, where possible, requires huge efforts and many decades to centuries.…”

“…In South Africa, Zaloumis () found, 20 years after cultivation, that secondary grasslands recovered only 25% of the species that occur in old‐growth grasslands. In Brazil, Le Stradic, Fernandes & Buisson () found, 8 years after excavation for gravel, that quarry sites had almost no grassland species, suggesting severe recruitment limitation. In mined heavy‐metal grasslands in central Africa, both Faucon et al .…”

“…copper, cobalt (Leteinturier, Baker & Malaisse, ; Barbosa et al ., ; Faucon et al ., )]; or depletion of soil microbial communities (Bach et al ., ). For all these reasons, the species composition of secondary grasslands that develops following agriculture or mining is very different from that of old‐growth grasslands (Faucon et al ., ; Ilunga wa Ilunga et al ., ; Koch et al ., ; Le Stradic et al ., ); full grassland community recovery in such circumstances will require many decades to several centuries (Veldman et al ., ; Fernandes, ). Consequently, we suggest that in many cases, secondary grasslands that form after abandonment of row crop agriculture, afforestation, or mining operations qualify as novel ecosystems (Fig.…”

“…In South Africa, Zaloumis (2013) found, 20 years after cultivation, that secondary grasslands recovered only 25% of the species that occur in old-growth grasslands. In Brazil, Le Stradic, Fernandes & Buisson (2018a) found, 8 years after excavation for gravel, that quarry sites had almost no grassland species, suggesting severe recruitment limitation. In mined heavy-metal grasslands in central Africa, both Faucon et al (2011) and Ilunga wa Ilunga et al (2015) found, 60 years after mining for heavy metals, that despite the proximity of seed sources, vegetation on mining sites remained very different, both compositionally and functionally from old-growth grasslands.…”

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

“…Thus, in stable communities, due to the lack of disturbances creating gaps for germination and establishment most species do not have persistent seed banks (Bossuyt & Honnay ; Schwab & Kiehl ). But also in ancient grassland habitats regularly disturbed by fire, such as old‐growth campo rupestre grasslands, the seed bank was found to be insufficient for community recovery after severe anthropogenic disturbance (Le Stradic et al ). Obviously the bud bank is more important in regularly burnt old‐growth grasslands than the seed bank (Fidelis et al ; Pausas et al ) and resprouting seems to be the major way of plant regeneration (see also Kiss et al ).…”