Soil seed banks of remnant and degraded Swartland Shale Renosterveld

Questions: What are the characteristics of soil seed banks in highly endangered renosterveld vegetation and adjacent degraded sites? What is the contribution of the soil seed bank to restoring renosterveld vegetation after degradation through agriculture or afforestation? Location: Tygerberg Nature Reserve – one of the largest remaining fragments of Swartland Shale Renosterveld, Cape Floristic Region, South Africa. Methods: Assessment of vegetation, soil parameters and soil seed banks in three renosterveld sites, two adjacent abandoned fields, one pine plantation and one pine plantation clear-cut site. Smoke primer (i.e. fire surrogate) was applied to soil seed bank samples to evaluate fire as a possible management and restoration tool. Results: Abandoned agricultural fields adjacent to renosterveld remnants are characterized by alien grass cover, nutrient enrichment of the soil and depletion of the indigenous soil seed bank. In contrast, pine plantations show less alien species infestation, soil nutrient alteration and have a viable soil seed bank as well as re-development of indigenous renosterveld vegetation after clearance. Seedling recruitment was not significantly influenced by application of a smoke primer compared to the magnitude of fire response in fynbos. Conclusion: Abandoned agricultural fields (previously renosterveld) at Tygerberg have a very low restoration potential. In contrast, pine plantation sites should be given priority in restoration, because soil chemistry is less significantly altered and a viable indigenous soil seed bank is still present, which can be successfully activated through clearance management

Genetic variation of two species with different life-history traits in the endangered renosterveld of South Africa – a comparative analysis of Eriocephalus africanus and Hemimeris racemosa

We tested the effects of life-history traits on genetic variation and conducted a comparative analysis of two plant species with differing life-history traits co-occurring in the highly endangered renosterveld of South Africa. We selected eighteen renosterveld remnants with varying degrees of size and isolation where populations of the herbaceous, annual and insect-pollinated Hemimeris racemosa and the shrubby perennial and both wind- and insect-pollinated Eriocephalus africanus occurred. We postulated a lower genetic variation within populations and increased genetic variation between populations in the annual than in the perennial species. Genetic variation was lower within populations of H. racemosa than within E. africanus, as is typical for annual compared to perennial species. Variation within populations was, however, not correlated with fragment size or distance in either of the two species and genetic variation between populations of the two species was comparable (ΦST = 0.10, 0.09)

Pioneers and perches-promising restoration methods for degraded renosterveld habitats?

Areas of abandoned agricultural fields are globally increasing and are also common features in the Cape Lowlands of South Africa. Previous restoration attempts in degraded West Coast renosterveld, a Mediterranean-climate shrubland, have attained limited success and therefore novel approaches are needed for this area. The study reports on two restoration experiments, designed to re-introduce key plant functional types back into this critically endangered habitat. The first experiment concentrated on a common pioneer species in renosterveld vegetation, Otholobium hirtum. Although in vitro experiments showed a significantly elevated germination response after scarification, in vivo experiments failed to produce establishment in an abandoned field. The second restoration experiment focused on bush clumps, a sub-type of renosterveld vegetation that is characterized by broad-leaved shrubs with fleshy bird-dispersed diaspores. The effect of artificial bird perches and their potential to enhance diaspore dispersal by frugivorous birds in two abandoned field communities was tested. Results showed a significant increase in seed dispersal at artificial perch sites. However, in the next fruiting season, and after perch removal, seed germination and establishment in abandoned fields was not successful. The experiments revealed that restoration using early-succession species and natural dispersal vectors appear not to produce demonstrable benefits, despite their promising potential and pre-testing of effectiveness. Before launching large-scale restoration programs in abandoned fields of renosterveld, preliminary studies in-field are strongly recommended. © 2011 Society for Ecological Restoration International

Soil seed banks of remnant and degraded Swartland Shale Renosterveld

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Low impact of fragmentation on genetic variation within and between remnant populations of the typical renosterveld species Nemesia barbata in South Africa

Renosterveld is a Mediterranean-type shrubland in the south-western Cape of South Africa. It is an exceptionally species-rich habitat and a local biodiversity hotspot. However, it has been strongly fragmented due to land use intensification during the last centuries. We analysed the impact of fragmentation on the genetic variation of a typical renosterveld species, the annual herb Nemesia barbata. For our investigation we selected populations of the species in 20 renosterveld fragments of different sizes in the Cape lowlands and determined genetic variation within and between populations using amplified fragment polymorphsims (AFLPs). We expected genetic pauperisation within small and isolated fragments and a lack of gene flow between these fragments. We observed considerable genetic variation within but only a low level of variation between populations. Genetic variation within populations was not correlated with the size of the fragment or the distance to the nearest adjacent fragment. However, genetic variation between populations was positively correlated with geographic distance between fragments, indicating historical and/or actual gene flow. Based upon our results, we conclude that habitat fragmentation does not yet influence the genetic variation of N. barbata. Historical and possibly actual gene flow, combined with buffering effects of the soil seed bank, appear to have minimized the negative impacts of habitat fragmentation on genetic variation of this renosterveld species

Fire season effects on the recruitment of non-sprouting serotinous Proteaceae in the eastern (bimodal rainfall) fynbos biome, South Africa

Research in Mediterranean-climate shrublands in both South Africa and Australia shows that recruitment of proteoid shrubs (non-sprouting, serotinous Proteaceae) is best after warm-season (summer and autumn) fires and worst after cool-season (winter and spring) ones. This pattern has been attributed to post-dispersal seed attrition as well as size of pre-dispersal seed reserves. Here we investigate patterns of post-fire recruitment for four proteoid species in the eastern part of South Africa’s fynbos biome, which has a bimodal (spring and autumn) rainfall regime. Despite the lack of significant differences in recruitment between cool- and warm-season burns, we find some evidence for favourable recruitment periods following fires in spring and autumn, immediately before, and coinciding with, the bimodal rainfall peaks. This suggests that enhanced recruitment is associated with conditions of high soil moisture immediately after the fire, and that rapid germination may minimize post-dispersal seed attrition. In two of the species, we also find a shift from peak flowering in winter and spring in the Mediterranean-climate part of the fynbos biome, to summer and autumn flowering in the eastern part. Because these two species are only weakly serotinous, warm-season flowering would result in maximal seed banks in spring, which could explain the spring recruitment peak, but not the autumn one.We conclude that eastern recruitment patterns differ significantly from those observed in the western and central parts of the biome, and that fire management protocols for the east, which are currently based on data and experience from the winter-rainfall fynbos biome, need to be adjusted accordingly. Fire managers in the eastern fynbos biome should be less constrained by requirements to burn within a narrow seasonal range, and should therefore be in a better position to apply the required management burns.Centre of Excellence for Invasion Biolog

Keeping the Cape Lowland archipelago afloat

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