Natural Seed Limitation and Effectiveness of Forest Plantations to Restore Semiarid Abandoned Metal Mining Areas in SE Spain

The natural regeneration of forests in mining areas is typically hampered by edaphic stress. Semiarid conditions add a climatic stress that challenges the restoration of these harsh ecosystems. This is the case of Tetraclinisarticulata (Vahl) Masters mixed forests in the Western Mediterranean region colonizing mining structures abandoned three decades ago. We studied the factors controlling the natural establishment of nine shrub and tree species key in these forests in eight metal mine tailings in SE Spain. In addition, we assessed the success of reintroducing 1480 individuals of the nine species 15 months after planting in one of the tailings. Specifically, we analyzed the effect of (i) species identity in terms of sapling survival, growth, nutritional status and metal bioaccumulation, and (ii) adding organic amendments into the planting holes on the same parameters. Our results indicated that natural colonization is a recent process, with seedling cohorts that vary up to two orders of magnitude among species and a practical absence of adult plants in most species excepting T. articulata. We identified seed limitation as a key factor controlling seedling density, which was significantly explained by the distance from the border of the tailing to the closest adult out of the tailing. Soil metal concentration did not have any explanatory power on the density of naturally-established seedlings, whereas soil fertility was relevant only for Rhamnus lycioides L. Overall survival of planted individuals was over 80%, survival and growth remarkably differing among species. Organic amendments had neutral or negative effects on plant survival, but significantly increased the growth of survivors despite their modest effects on leaf nutrient contents. Most species showed high metal bioaccumulation, which was exacerbated by organic amendments. We discuss how biodiversity conservation programs can benefit from the affordable and successful plantation of stress-tolerant local species, but come at the expense of potential metal transfer through trophic webs.

Limited seed dispersability in a megadiverse OCBIL grassland

Species from OCBILs (old, climatically buffered, infertile landscapes) are expected to exhibit reduced dispersability, linked to long-term stable environmental conditions. We tested the prediction of limited dispersability in plant communities in campo rupestre, a megadiverse OCBIL grassland. In a field experiment, we sampled sticky and funnel traps for 12 months along paired preserved and disturbed plots to estimate and compare annual seed density and richness. Our community-level seed rain assessment suggested widespread seed limitation in both preserved and disturbed areas, expressed by the low seed density in traps (average of 2.6 seeds/m2/day) and remarkably low seed density found for 90% of the morphospecies. Although seed density in campo rupestre was much lower than for other grasslands, species richness (92 seed morphospecies) was the highest reported in the literature. Higher seed density and species richness were captured in funnel traps, especially during the rainy season. Approximately 32% of morphospecies were registered exclusively in disturbed plots and 25% exclusively in preserved plots. This limited seed dispersability is of particular relevance for a better understanding of seed ecology and resilience in campo rupestre and may partially explain the poor recovery of these disturbed areas after soil removal.

Reproductive biology of the sausage tree (Kigelia africana) in Kruger National Park, South Africa

Kigelia africana has large flowers that are vertebrate pollinated and very large fruits that are likely to be vertebrate dispersed. Our field surveys of size–class distributions of K. africana in the southern Kruger National Park (KNP) suggest a lack of recruitment. This is possibly the result of a failure of mutualistic relationships with vertebrate dispersers and/or pollinators. Breeding system experiments indicated that K. africana is an obligate out-crosser. Despite being primarily adapted for bat pollination, in KNP that K. africana is presently mainly pollinated by a diversity of largely facultatively nectarivorous bird species. Fruit-set is high, although trees isolated by > 50 m were found to suffer depressed seed output. Our preliminary investigation of dispersal suggests that fruits are largely ignored and are thus weakly attractive to potential dispersers. Seedlings placed out in the field in KNP suffered high levels (> 50%) of mortality compared to 17.5% in control plots. This threefold difference is the result of herbivory over a 2-month period. In summary, the adult centric population structure is probably not because of pollen or seed limitation but may result from dispersal limitation or excessive herbivory.

Frugivory and seed dispersal effectiveness in two Miconia (Melastomataceae) species from ferruginous campo rupestre

Seed dispersal effectiveness (SDE) is a useful framework to explore the evolutionary and ecological consequences of seed dispersal to plant fitness. However, SDE is poorly studied in tropical open grasslands. Here, we studied both quantitative and qualitative components of SDE in two species of Miconia (Melastomataceae) from ferruginous campo rupestre, a vegetation highly threatened by mining activities. We determined fruit traits and fruit availability and found that fruits of both species are produced in times of resource scarcity at the study site. Based on the number of visits and the number of fruits removed per visit, we calculated the quantitative component of SDE for both species. Finally, we explored the qualitative component of SDE by means of a controlled experiment that simulated the effects of gut passage on seed germination. Bird species differed strongly in the quantitative component of SDE. Gut passage did not affect germination compared with hand-extracted seeds, except for a minor negative effect on germination time in M. pepericarpa. However, seeds within intact fruits showed lower germination percentages compared with hand-extracted seeds. Our data indicate that Miconia species from ferruginous campo rupestre are visited by a diverse assemblage of generalist birds that differ in quantitative, but not qualitative, seed dispersal effectiveness. We argue that planting Miconia species can overcome seed limitation in degraded areas and thus assist ecological restoration after mining abandonment.