Reductions in plant species richness under stands of alien trees and shrubs in the Fynbos Biome.
TL;DR: A synthesis was made of published and unpublished data on plant species richness in fynbos with different levels of invasion and different histories of control, indicating a marked reduction in richness of indigenous plant species in invaded areas.
Abstract: Synopsis The reduction of species richness of indigenous plants is one of the major problems associated with the presence of dense stands of invasive alien trees and shrubs in the Fynbos Biome of the Cape Province, South Africa. A synthesis was made of published and unpublished data on plant species richness in fynbos with different levels of invasion and different histories of control. Linear regressions of species richness on the log of quadrat size were significant for both uninvaded fynbos and fynbos under dense stands of alien trees and shrubs. The slopes of the regression equations did not differ significantly between invaded and uninvaded sites, but elevations were significantly different, indicating a marked reduction in richness of indigenous plant species in invaded areas. The linear regression of species richness on quadrat size for cleared areas was not significant, but quadrats at most cleared sites showed species richness values intermediate to those of uninvaded fynbos and dense stands of a...
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TL;DR: Assessing the impact of 13 species invasive in the Czech Republic on a wide range of plant communities found Tall invading species capable of forming populations with the cover markedly greater than that of native dominant species exert the most severe effects on species diversity and evenness.
Abstract: Summary 1. Much attention has been paid to negative effects of alien species on resident communities but studies that quantify community-level effects of a number of invasive plants are scarce. We address this issue by assessing the impact of 13 species invasive in the Czech Republic on a wide range of plant communities. 2. Vegetation in invaded and uninvaded plots with similar site conditions was sampled. All species of vascular plants were recorded, their covers were estimated and used as importance values for calculating the Shannon diversity index H\ evenness J and Sorensen index of similarity between invaded and uninvaded vegetation. 3. With the exception of two invasive species, species richness, diversity and evenness were reduced in invaded plots. Species exhibiting the greatest impact reduced species numbers per plot and the total number of species recorded in the communities sampled by almost 90%. A strong reduction of species number at the plot scale resulted in a marked reduction in the total species number at the landscape scale, and in less similarity between invaded and uninvaded vegetation. The decrease in species richness in invaded compared to uninvaded plots is largely driven by the identity of the invading species, whereas the major determinants of the decrease in Shannon diversity and evenness are the cover and height of invading species, and differences between height and cover of invading and dominant native species, independent of species identity. 4. Synthesis. Management decisions based on impact need to distinguish between invasive species, as their effects on diversity and composition of resident vegetation differ largely. Tall invading species capable of forming populations with the cover markedly greater than that of native dominant species exert the most severe effects on species diversity and evenness. Since a strong impact on the community scale is associated with reduction in species diversity at higher scales, invaders with a high impact represent a serious hazard to the landscape.
951 citations
Cites background from "Reductions in plant species richnes..."
...The impact of an invasive species is usually associated with the degree of its dominance (Richardson et al. 1989, Pysek & Pysek 1995) and our results suggest that the advantage of monopolizing relatively more space in the community than occupied by the native dominant is directly associated with…...
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Journal Article•
TL;DR: The ecological evidence for the impacts of invasive alien plants on South African ecosystems is examined and a framework to suggest the main challenges for research is suggested that will address critical gaps in knowledge and that will serve explicit management needs is suggested.
Abstract: .South Africa has a long history of problems with invasive alien species, and of research and management of biological invasions (Table 1). The Working for Water programme 26–28 was started in 1995 to conduct and coordinate alien-plant management throughout South Africa. The programme initially worked only in watersheds and riparian areas, but now leads alien-plant management initiatives in all natural and semi-natural ecosystems. It has grown into one of the world’s biggest programmes dealing with invasive alien species. The enterprise’s success has been attributed to its multi-faceted and cross-disciplinary nature that has enabled it to leverage local and international funding and continuing political support. The programme is driven by multi-disciplinary ecological, hydrological, social and economic goals. In practice it has focused on hydrological and social concerns (as embodied in the name of the programme), and its ecological goals are less clearly defined. The extent to which the aim of improving the ecological integrity of natural ecosystems through the control of invasive alien plants has therefore not always been clear to both programme participants and other stakeholders. In this paper, we examine the ecological evidence for the impacts of invasive alien plants on South African ecosystems. We begin with a brief review of what is known about the extent of invasions and influences of these plants, and then discuss the consequences for the delivery of ecosystem goods and services to people. However, the emerging field of invasion ecology addresses issues beyond the effects of invasive species. The different aspects of invasion ecology can be related to the critical stages of invasion, and these stages also provide a useful framework for classifying the management interventions that are required to deal with the problem (Box 1). Our understanding of many of the broader aspects of invasion ecology needs to improve, and we use this framework to suggest the main challenges for research that will address critical gaps in knowledge and that will serve explicit management needs. Components of impact
504 citations
Cites background from "Reductions in plant species richnes..."
...This research has shown that dense stands of alien trees and shrubs in fynbos can rapidly reduce abundance and diversity of native plants at the scale of small plots.(44,45) As regards mechanisms for this attrition, studies in dense stands of Port Jackson willow (Acacia saligna) have documented the decline of soil-stored seed banks of native plants, leading to the local extinction of native species....
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TL;DR: A meta-analysis of studies in Mediterranean-type ecosystems to examine whether invasion of alien plant species indeed causes a reduction in the number of native plant species at different spatial and temporal scales confirms a significant decline in native species richness attributable to alien invasions.
Abstract: Besides a general consensus regarding the negative impact of invasive alien species in the literature, only recently has the decline of native species attributable to biological invasions begun to be quantifi ed in many parts of the world. The cause-effect relationship between the establishment and proliferation of alien species and the extinction of native species is, however, seldom demonstrated. We conducted a meta-analysis of studies in Mediterranean-type ecosystems (MTEs) to examine: (1) whether invasion of alien plant species indeed causes a reduction in the number of native plant species at different spatial and temporal scales; (2) which growth forms, habitat types and areas are most affected by invasions; and (3) which taxa are most responsible for native species richness declines. Our results confi rm a signifi cant decline in native species richness attributable to alien invasions. Studies conducted at small scales or sampled over long periods reveal stronger impacts of alien invasion than those at large spatial scales and over short periods. Alien species from regions with similar climates have much stronger impacts, with the native species richness in South Africa and Australia declining signifi cantly more post-invasion than for European sites. Australian Acacia species in South Africa accounted for the most signifi cant declines in native species richness. Among the different growth forms of alien plants, annual herbs, trees and creepers had the greatest impact, whereas graminoids generally caused insignifi cant changes to the native community. Native species richness of shrublands, old fi elds and dune vegetation showed signifi cant declines, in contrast to insignifi cant declines for forest habitats.
438 citations
TL;DR: Most of the important invaders share a suite of biological traits that facilitate long-distance dispersal by wind, and allow invading populations to persist in habitats subjected to frequent disturbance, which is used to predict future trends in pine invasions.
Abstract: Many factors interact to determine whether an introduced organism will become invasive. The widespread planting of many Pinus species at various densities and in many habitats at different times in the Southem Hemisphere (well outside their natural range) provides a unique opportunity to identify the determinants of invasive success for a large group of related organisms. At least sixteen pine species have spread from planting sites to invade natural or semi-natural vegetation. Species with adventive populations over fairly large areas are P. contorta Dougl., P. halepensis Mill,, P. nigra Arnold, P. patula Schiede & Deppe, P. pinaster Ait., P. ponderosa Laws., P. radiata D. Don and P. sylvestris L. This paper explores the biological profiles of successful invaders, the inherent and induced susceptibility of different vegetation types to invasion, patterns of invasion, the role of disturbance in initiating and sustaining invasions, the role of time, and the various functions of the resident biota in the receiving habitat in mediating the outcome of an introduction. This information, with evidence from contemporary studies of pine dynamics in the Northem Hemisphere and reconstructions of pine migrations in the early Holocene, shows that: (1) Most of the important invaders share a suite of biological traits that facilitate long-distance dispersal by wind, and allow invading populations to persist in habitats subjected to frequent disturbance. (2) The extent of invasion for widely planted species is positively correlated with the residence period. (3) Ground-cover categories can be ranked according to their vulnerability to invasion as follows: forest < shrubland < grassland << dunes < bare ground. (4) Disturbance regimes and the resident biota have a marked (and complex) influence on invadability. This information is used to predict future trends in pine invasions
420 citations
TL;DR: The question of which factors limit the occurrence of a plant species to a particular site is addressed by considering 53 cases in which the distribution of pines has changed in the last century, and the fundamental role of biotic factors in regulating the distribution is discussed with reference to aspects of land husbandry including the management of biological invasions.
Abstract: The question of which factors limit the occurrence of a plant species to a particular site is addressed by considering 53 cases in which the distribution of pines (Pinus species; Pinaceae) has changed in the last century. We consider expansions of pines in and adjacent to their natural ranges in the Northern Hemisphere and the spread from sites of introduction in the Southern Hemisphere well outside the contemporary range of pines. We first consider a neutral hypothesis (with respect to climate or biological interactions as determinants of invasion): invasion simply requires that a species is present in sufficient numbers, with sufficient propagules over sufficient time to invade. We then explore the relative importance of climatic changes, disturbance, competition (including competition between seedlings and herbaceous plants during early establishment), herbivory, pathogens, and other agents that might influence pine membership in communities. Determinants of susceptibility to invasion often interact in...
386 citations
References
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434 citations
01 Mar 1984
118 citations
TL;DR: Smaller reserves tend to show higher proportions of invasive introduced species in their vascular plant floras, and both freshwater fish and mammalian faunas, than do larger reserves, and the intentional or accidental introduction of species to these reserves should be avoided.
99 citations
TL;DR: In this paper, the authors analysed Fynbos vegetation with three differing fire histories by means of a stratified systematic sample of 100 plots and found that short rotation burning resulted in a reduction in plant cover, height and biomass, as well as in the elimination of longer lived seed regenerating shrubs.
Abstract: SYNOPSIS Fynbos vegetation with three differing fire histories was analysed for floristic composition and structure by means of a stratified systematic sample of 100 plots. The three treatments (fire histories) investigated were short rotation burning (about six years), longer rotation burning (about 15 to 20 years) and protection from fire for 37 years. Short rotation burning resulted in a reduction in plant cover, height and biomass, as well as in the elimination of longer lived seed regenerating shrubs. Species diversity was relatively high and short graminoid and herb species dominated the vegetation. Longer intervals between burning resulted in a high cover and large mean plant height in mature 21-year-old vegetation, but species diversity was relatively low and undergrowth species were of much reduced importance. In vegetation protected for 37 years, large shrubs were reduced in importance due to high mortality and low recruitment; as a result undergrowth species showed some signs of recovery, and s...
77 citations
01 Jan 1983
TL;DR: The Cape floristic region is very rich in species with a high proportion of endemics (Goldblatt 1978; Taylor 1978) and most speculation on the origin of fynbos diversity has had a biogeographic perspective dealing with total floras and the effects on speciation of geomorphic rejuvenation, climatic change, topographic diversity, age of taxa and other broad-scale influences.
Abstract: The Cape floristic region is very rich in species with a high proportion of endemics (Goldblatt 1978; Taylor 1978). Most speculation on the origin of fynbos (and Australian heathland) diversity has had a biogeographic perspective dealing with total floras and the effects on speciation of geomorphic rejuvenation, climatic change, topographic diversity, age of taxa and other broad-scale influences (Levyns 1964; Raven 1973; Axelrod and Raven 1978; Goldblatt 1978; Taylor 1978, 1980; Hopper 1979). Few studies have dealt with lower levels of diversity with the recent and notable exception of Kruger and Taylor’s (1979) comparative study on gamma and delta diversity of fynbosa. Alpha and/or beta diversity patterns have been studied by Werger (1972), Campbell and van der Meulen (1980) and Naveh and Whittaker (1980).
70 citations