Time filter

Source Type

Wilson J.R.U.,South African National Biodiversity Institute | Wilson J.R.U.,Stellenbosch University | Gairifo C.,Stellenbosch University | Gairifo C.,University of Lisbon | And 20 more authors.
Diversity and Distributions | Year: 2011

Aim Many Australian Acacia species have been planted around the world, some are highly valued, some are invasive, and some are both highly valued and invasive. We review global efforts to minimize the risk and limit the impact of invasions in this widely used plant group. Location Global. Methods Using information from literature sources, knowledge and experience of the authors, and the responses from a questionnaire sent to experts around the world, we reviewed: (1) a generalized life cycle of Australian acacias and how to control each life stage, (2) different management approaches and (3) what is required to help limit or prevent invasions. Results Relatively few Australian acacias have been introduced in large numbers, but all species with a long and extensive history of planting have become invasive somewhere. Australian acacias, as a group, have a high risk of becoming invasive and causing significant impacts as determined by existing assessment schemes. Moreover, in most situations, long-lived seed banks mean it is very difficult to control established infestations. Control has focused almost exclusively on widespread invaders, and eradication has rarely been attempted. Classical biological control is being used in South Africa with increasing success. Main conclusions A greater emphasis on pro-active rather than reactive management is required given the difficulties managing established invasions of Australian acacias. Adverse effects of proposed new introductions can be minimized by conducting detailed risk assessments in advance, planning for on-going monitoring and management, and ensuring resources are in place for long-term mitigation. Benign alternatives (e.g. sterile hybrids) could be developed to replace existing utilized taxa. Eradication should be set as a management goal more often to reduce the invasion debt. Introducing classical biological control agents that have a successful track-record in South Africa to other regions and identifying new agents (notably vegetative feeders) can help mitigate existing widespread invasions. Trans-boundary sharing of information will assist efforts to limit future invasions, in particular, management strategies need to be better evaluated, monitored, published and publicised so that global best-practice procedures can be developed. © 2011 Blackwell Publishing Ltd.

Gibson M.R.,Stellenbosch University | Richardson D.M.,Stellenbosch University | Marchante E.,University of Coimbra | Marchante H.,University of Coimbra | And 17 more authors.
Diversity and Distributions | Year: 2011

Aim Reproductive traits are important mediators of establishment and spread of introduced species, both directly and through interactions with other life-history traits and extrinsic factors. We identify features of the reproductive biology of Australian acacias associated with invasiveness. Location Global. Methods We reviewed the pollination biology, seed biology and alternative modes of reproduction of Australian acacias using primary literature, online searches and unpublished data. We used comparative analyses incorporating an Acacia phylogeny to test for associations between invasiveness and eight reproductive traits in a group of introduced and invasive (23) and non-invasive (129) species. We also explore the distribution of groups of trait 'syndromes' between invasive and non-invasive species. Results Reproductive trait data were only available for 126 of 152 introduced species in our data set, representing 23/23 invasive and 103/129 non-invasive species. These data suggest that invasives reach reproductive maturity earlier (10/13 within 2years vs. 7/26 for non-invasives) and are more commonly able to resprout (11/21 vs. 13/54), although only time to reproductive maturity was significant when phylogenetic relationships were controlled for. Our qualitative survey of the literature suggests that invasive species in general tend to have generalist pollination systems, prolific seed production, efficient seed dispersal and the accumulation of large and persistent seed banks that often have fire-, heat- or disturbance-triggered germination cues. Conclusions Invasive species respond quicker to disturbance than non-invasive taxa. Traits found to be significant in our study require more in-depth analysis involving data for a broader array of species given how little is known of the reproductive biology of so many taxa in this species-rich genus. Sets of reproductive traits characteristic of invasive species and a general ability to reproduce effectively in new locations are widespread in Australian acacias. Unless there is substantial evidence to the contrary, care should be taken with all introductions. © 2011 Blackwell Publishing Ltd.

Marchante H.,Center for Studies of Natural Resources | Freitas H.,University of Coimbra | Hoffmann J.H.,University of Cape Town
American Journal of Botany | Year: 2010

Premise of the study: Worldwide, invasive plants threaten biodiversity, by disrupting habitats and ecosystem processes, and cause major economic losses. Invasiveness in plants is frequently associated with prolific production of seeds that accumulate in the soil. Knowledge of the extent and persistence of invasive seed banks helps explain invasion processes and enables management planning. A study of Acacia longifolia, an invasive species in Portuguese dune ecosystems, provides an informative example. Methods: Seed rain and dispersal (seed traps), the persistence of seeds in the soil (burial), and the extent of seed banks were measured and analyzed. Key results: Seed rain is concentrated under the canopy with about 12000 seeds · m-2 falling annually. The number of seeds in the soil declined with time, with only 30% surviving after 75 mo. Losses were lowest at greater depths. Seed germinability was low (<12%), but viability was high (>85%) for surviving seeds. The seed bank under the canopy was approximately 1500 and 500 seeds · m-2 in long- and recently invaded stands, respectively. Some seeds were found up to 7 m from the edge of stands, indicating that outside agencies facilitate dispersal. Conclusions: Acacia longifolia produces large numbers of seeds, some of which are lost through germination, decay, and granivory. The remainder form vast and persistent seed banks that serve as a source of replenishment and make it difficult to control the invader once it is established. Control costs escalate as the duration of an invasion increases, highlighting the urgency of initiating and persevering with control efforts. © 2010 Botanical Society of America.

Marchante H.,Center for Studies of Natural Resources | Freitas H.,University of Coimbra | Hoffmann J.H.,University of Cape Town
Biological Control | Year: 2011

Acacia longifolia is a widespread invasive plant species in Portugal. In South Africa, it is controlled by a bud-galling wasp, Trichilogaster acaciaelongifoliae, which could also be used in Portugal. Biological control of invasive alien plants has received little consideration anywhere in Europe and has never been attempted in Portugal. The lack of a suitably-large quarantine facility necessitated the use of a novel approach to test non-target species in Portugal. Mature T. acaciaelongifoliae galls were shipped to Portugal from South Africa to obtain adult female wasps which were confined in Petri dishes each with a bud-bearing branch of one of 40 non-target plant species. The time spent by the wasps exploring and probing the buds was measured after which buds were dissected to detect any egg deposition. The results showed that T. acaciaelongifoliae did not respond to the buds of most (23) species. The females spent time on the buds of the other 17 species but only laid eggs in three species besides A. longifolia. Oviposition on Acacia melanoxylon was expected but was not anticipated on Vitis vinifera, vines, (where eggs were deposited externally in the pubescent coat of the buds) or on Cytisus striatus, broom, (where eggs were inserted into the buds as they are on A. longifolia). Subsequent trials on potted plants showed that galls only developed on A. longifolia. Field surveys in South Africa and Australia showed that galls never occur on either vines or broom. The implications of these findings for the use of T. acaciaelongifoliae for biological control of A. longifolia in Portugal are considered in relation to the wealth of experience and knowledge about the specificity of the wasp and the reliability of conducting host-specificity tests under confined conditions of cages. © 2010 Elsevier Inc.

Marchante H.,Center for Studies of Natural Resources | Marchante H.,University of Coimbra | Freitas H.,University of Coimbra | Hoffmann J.H.,University of Cape Town
Applied Vegetation Science | Year: 2011

Question: How resilient is the seed bank of an invaded dune system? Is that resilience dependent on duration of invasion? How does the accumulated litter layer contribute to the soil seed bank?Location: Coastal sand dunes invaded by Acacia longifolia, Portugal.Methods: Seedling emergence was used to quantify and compare soil seed banks in long-invaded, recently invaded and non-invaded areas. Changes in seed banks were also compared with areas where A. longifolia and the litter layer were removed.Results: Species richness, seedling density and diversity were higher in non-invaded and recently-invaded areas than in long-invaded areas. Although there was an apparent similarity between non-invaded and recently-invaded areas, analyses of species traits revealed differences. Non-invaded areas had a wider array of traits. Exotic/invasive species dominated invaded seed banks while native species dominated non-invaded seed banks. Life forms, growth forms, longevity and dispersal mode showed differences between areas, with cleared plots of long-invaded areas being apparently the most similar to non-invaded plots. Acacia longifolia seeds were most abundant in long-invaded areas, particularly where the litter layer remained. Removal of A. longifolia plus the litter had little effect on the seed bank composition of recently-invaded areas but resulted in noticeable changes in seed banks of long-invaded areas.Conclusions: Long-invaded areas are less resilient and show a higher reinvasion potential, despite severe alteration of the seed banks of both areas. Seed bank studies can be a useful tool to guide management, but can give misleading results when invasion periods are protracted. © 2010 International Association for Vegetation Science.

Tavares A.O.,University of Coimbra | Pato R.L.,Center for Studies of Natural Resources | Magalhaes M.C.,Center for Studies of Natural Resources
Applied Geography | Year: 2012

Understanding the reorganisation of land in order to adapt its use and spatial structure to social demands has become crucial to management and represents a major challenge to land use planning and public policies. This study explores the temporal and spatial land use change transitions in a peri-urban area of a medium-sized city located in the central Portugal and characterised by profound changes in the last half century. The study is supported by a collection of seven years/moments of image analysis (the 1958, 1973, 1979, 1995, 2002 and 2007 maps). Cross-referencing the successive sets of images defines the percentage of land transition and provides the stability grade (SG), which expresses the total proportion of the landscape that has not experienced any transition to a different category of land use. In order to evaluate the intensity of urban expansion, an annual rate of artificialisation of surfaces (AS) indicator was used. The seven cartographic outputs highlight a decrease in the area occupied by permanent crops, an increase in urban areas, especially the continuous urban fabric, a large forest occupation involving different typologies and paths, and an increase in base soil areas. The data also shows a general increase in the number of patches recognised and in pattern complexity. The results show that land use changes are created by systematic transitions, with or without gross variations, and also by casuistic processes associated with an increase in artificialised areas and the growth of the continuous urban fabric. Land use transition reflects the internal and external inputs associated with the approval of Municipal Master Plans and the land regulatory regime, and also the consolidation of the road infrastructure network. The analysis indicates that the transfer takes place in a set of small sequential steps marking the evolution from rural characteristics to a process of peri-urbanisation, ending in urban consolidation. © 2012 Elsevier Ltd.

Loading Center for Studies of Natural Resources collaborators
Loading Center for Studies of Natural Resources collaborators