Effects of Alien Plants on Ecosystem Structure and Functioning and Implications for Restoration: Insights from Three Degraded Sites in South African Fynbos

We investigated the type and extent of degradation at three sites on the Agulhas Plain, South Africa: an old field dominated by the alien grass Pennisetum clandestinum Pers. (kikuyu), an abandoned Eucalyptus plantation, and a natural fynbos community invaded by nitrogen fixing—Australian Acacia species. These forms of degradation are representative of many areas in the region. By identifying the nature and degree of ecosystem degradation we aimed to determine appropriate strategies for restoration in this biodiversity hotspot. Vegetation surveys were conducted at degraded sites and carefully selected reference sites. Soil-stored propagule seed banks and macro- and micro-soil nutrients were determined. Species richness, diversity and native cover under Eucalyptus were extremely low compared to the reference site and alterations of the soil nutrients were the most severe. The cover of indigenous species under Acacia did not differ significantly from that in reference sites, but species richness was lower under Acacia and soils were considerably enriched. Native species richness was much lower in the kikuyu site, but soil nutrient status was similar to the reference site. Removal of the alien species alone may be sufficient to re-initiate ecosystem recovery at the kikuyu site, whereas active restoration is required to restore functioning ecosystems dominated by native species in the Acacia thicket and the Eucalyptus plantation. To restore native plant communities we suggest burning, mulching with sawdust and sowing of native species.     

Spatial structure and habitat associations of demersal assemblages in the Gulf of Lions: a multicompartmental approach

Experimental trawl surveys were performed in the Gulf of Lions. A multicompartmental approach was used to study the spatial distribution of demersal assemblages and to estimate their associations with two other components of the ecosystem: the benthic macrofauna and substratum type. At the Gulf scale, we found that these components explained 38 and 19% of the total variability of the spatial organization of groundfishes, respectively. Our results showed that groundfish and benthic macrofauna species were primarily distributed along a coast–open sea gradient and secondarily along a longitudinal axis. The longitudinal variability of the spatial organisation of species was maximal in the shelf area, whereas the upper-slope and coastal areas were characterized by strong homogeneity. Although no partitioning could be made based on their spatial distribution, the coastal groundfish assemblages were split into two groups. In the first group, groundfishes were strongly associated with both benthic macrofauna and type of substratum; in the second group, they were strongly independent of these two components. Furthermore, in the Gulf of Lions, the presence of productive zones associated with the Rhône river plume or with shelf-break upwelling seemed to attract some groundfishes. This study illustrates how useful such a multicompartmental approach can be for both fisheries management and community ecology.     

Optimisation analysis and integrated models of the enhanced greenhouse effect

The issues surrounding the anticipated impacts of the enhanced greenhouse effect are likely to form a significant part of the research activities in the coming years. In this paper we have adopted a control theoretic approach to the analysis of one of the world's best known integrated models of the enhanced greenhouse effect: the Dutch IMAGE 1.0 (Integrated Model to Assess the Greenhouse Effect) model. The paper demonstrates that optimisation methodologies can be applied to integrated models to enhance their interpretative power. This is accomplished by providing a mechanism whereby optimal emission allocation strategies can be formulated from existing models. One result of particular interest is that the analysis confirms that the earlier human input into the climate system can be stabilised, the higher the levels of CO₂ emissions can be permitted and still achieve specific long-term environmental target.     

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Using spatially explicit,time-dependent analysis to understand how social factors influence conservation outcomes

Conservation across human-dominated landscapes requires an understanding of the social and ecological factors driving outcomes. Studies that link conservation outcomes to social and ecological factors have examined temporally static patterns. However, there may be different social and ecological processes driving increases and decreases in conservation outcomes that can only be revealed through temporal analyses. Through a case study of the invasion of Falcataria moluccana in Hawaii, we examined the association of social factors with increases and decreases in invader distributions over time and space. Over 7 years, rates of invader decrease varied substantially (66–100%) relative to social factors, such as building value, whether land was privately or publically owned, and primary residence by a homeowner, whereas rates of increase varied only slightly (<0.1–3.6%) relative to such factors. These findings suggest that links between social factors and invasion in the study system may be driven more by landowners controlling existing invasive species, rather than by landowners preventing the spread of invasive species. We suggest that spatially explicit, time-dependent analyses provide a more nuanced understanding of the way social factors influence conservation outcomes. Such an understanding can help managers develop outreach programs and policies targeted at different types of landowners in human-dominated landscapes.