Summary 1.We expect tree species that regenerate primarily by sprouting to produce fewer seedlings than co-occurring species that regenerate mainly from seedlings, because of the trade-off between allocating resources either to ensuring vegetative reproduction (e.g. protective bark/latent buds) or to sexual reproduction (e.g. seeds). 2. Furthermore, resprouting species, because of their multi-stemmed nature, should be at a relative disadvantage, and therefore relatively infrequent, in tall forests. This is because a resprouting individual allocates resources to a number of basal branches/stems and buds rather than maximizing vertical extension of a single leader, as is the case in a seeder. Also, many tall stems arising from the same multi-stemmed base, as is the case in resprouters, will be relatively poorly supported in comparison to the single stem of a reseeder. 3. To test these two ideas we surveyed a number of plots in a range of South African forests and thicket communities. We noted the numbers of seedlings and resprouts for each species and determined a mean for each site. 4. Short forests and thickets were dominated by multi-stemmed species and there was an almost total absence of seedlings. In contrast, tall forests were dominated by singlestemmed reseeding species and were accompanied by seedlings. Key-words: Forest dynamics, persistence, recruitment, regenerationFunctional Ecology (1997) 11, [101][102][103][104][105] will first develop an argument that resprouters should be rare in tall forests and second that resprouters will only rarely produce seedlings.In tall forests where the ability to grow tall is critical for potential canopy species, a resprouter is likely to be at a disadvantage for both resource allocation and structural reasons. Resprouters divert resources to developing, maintaining and protecting a bud-bank instead of devoting it to vertical growth. Because they are often multi-stemmed they also share their resources amongst several stems. Reseeders, in contrast, can divert resources to maximizing rates of vertical extension of a single stem. Based on this resource allocation argument we suggest that reseeders will be able to grow taller and/or faster than resprouters. Again, because of their multi-stemmed nature, each stem of a resprouter will be more poorly structurally supported than will the single stem of a reseeder. This too will disadvantage resprouters in tall forests. Our first prediction then is that resprouters and multi-stemmedness should be more common in short forests than tall forests.Resprouters should produce fever viable seeds and seedlings than reseeders. First, this is because parent resprouters must devote resources to maintaining and protecting latent buds. Second, this is because seedlings of resprouters will be less competitive because they too must allocate resources to developing and protecting buds rather than growing tall. These differences between resprouters and reseeders are well known for shrublands (e.g. Hansen, Pate & Hansen 1991) but have not been we...
According to the equilibrium theory of island biogeography, insularisation will lead to species loss from habitat remnants. Extinctions will continue untill species number equilibrates at a level appropriate for the size and isolation of the island remnants. We tested whether insularisation leads to species loss by comparing plant species numbers on islands of fynbos shrublands surrounded by Afrotemperate evergreen forest with extensive "mainland" tracts of fynbos. Species area curves for islands and subsamples of mainland had significantly different slopes (z =0.43, z=0.16). Small islands had the fewest species (less than one fifth) relative to mainland samples of similar size. The species area curves intersect at 590 ha so that reserve sizes of this order of magnitude are needed to avoid species losses relative to extensive areas of fynbos.We compared traits of species on islands and mainlands to determine processes most affected by insularisation. Island floras did not differ from the mainland in the mix of dispersal types, pollinator syndromes or proportion of dioecious species. Islands did have significantly fewer species of low stature and significantly more species that survive fire only as seed and not by resprouting. We infer that the main cause of species loss is change in disturbance frequency. Islands have fewer fires and lose species dependent on frequent fires. We predict that island effects could be reduced by judicious fire management of small reserves.
The study described changes in floristic and vegetation structure in relation to livestock grazing intensity in a conservation area in the Succulent Karoo, South Africa. Grazing by goats and sheep is allowed in the Richtersveld National Park ͑a contractual National Park͒ which is also an area of high floristic richness and endemism. We used goat faecal pellet density, degree of trampling and percentage bare-ground at distances from the stock posts as surrogates for a gradient in grazing pressure. A stock post is the place where farmers keep, in most cases in an enclosure called a 'kraal', their animals at night and to which they return every evening after the day's herding. Twenty-seven stock posts were located in the Richtersveld National Park; nine stock posts on flats, footslopes and mountain each. We measured plant species richness and diversity, and mean percentage cover of the various plant growth forms ͑including the number of species falling into each growth form category͒ in each of the five 10 m ϫ 10 m plots ͑each 200 m apart͒ demarcated along a transect of one kilometre length from the centre of each stock post. The results showed that distance from the stock post does reflect grazing intensity use because densities in faecal pellets rapidly declined with increasing distances away from the stock post for all habitats studied. Faecal density was positively correlated with stocking density. Plant species richness and diversity was at a minimum near stock posts. Plants able to endure the effects of heavy grazing occurred near stock posts where declines in palatable plant species, assumingly sensitive to heavy grazing and trampling, were recorded. Grazing increased vegetation patchiness up to 800 m from the stock post for all the habitats. The degree to which this change in species composition occurred did not depend on stocking densities, suggesting that both grazing and landscape variability were responsible for vegetation changes in rangelands of that area of the Succulent Karoo biome.
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