Exclosure

Herbivory is a fundamental process that controls primary producer abundance and regulates energy and nutrient flows to higher trophic levels. Despite the recent proliferation of small-scale studies on herbivore effects on aquatic plants, there remains limited understanding of the factors that control consumer regulation of vascular plants in aquatic ecosystems. Our current knowledge of the regulation of primary producers has hindered efforts to understand the structure and functioning of aquatic ecosystems, and to manage such ecosystems effectively. We conducted a global meta-analysis of the outcomes of plant–herbivore interactions using a data set comprised of 326 values from 163 studies, in order to test two mechanistic hypotheses: first, that greater negative changes in plant abundance would be associated with higher herbivore biomass densities; second, that the magnitude of changes in plant abundance would vary with herbivore taxonomic identity. We found evidence that plant abundance declined with increased herbivore density, with plants eliminated at high densities. Significant between-taxa differences in impact were detected, with insects associated with smaller reductions in plant abundance than all other taxa. Similarly, birds caused smaller reductions in plant abundance than echinoderms, fish, or molluscs. Furthermore, larger reductions in plant abundance were detected for fish relative to crustaceans. We found a positive relationship between herbivore species richness and change in plant abundance, with the strongest reductions in plant abundance reported for low herbivore species richness, suggesting that greater herbivore diversity may protect against large reductions in plant abundance. Finally, we found that herbivore–plant nativeness was a key factor affecting the magnitude of herbivore impacts on plant abundance across a wide range of species assemblages. Assemblages comprised of invasive herbivores and native plant assemblages were associated with greater reductions in plant abundance compared with invasive herbivores and invasive plants, native herbivores and invasive plants, native herbivores and mixed-nativeness plants, and native herbivores and native plants. By contrast, assemblages comprised of native herbivores and invasive plants were associated with lower reductions in plant abundance compared with both mixed-nativeness herbivores and native plants, and native herbivores and native plants. However, the effects of herbivore–plant nativeness on changes in plant abundance were reduced at high herbivore densities. Our mean reductions in aquatic plant abundance are greater than those reported in the literature for terrestrial plants, but lower than aquatic algae. Our findings highlight the need for a substantial shift in how biologists incorporate plant–herbivore interactions into theories of aquatic ecosystem structure and functioning. Currently, the failure to incorporate top-down effects continues to hinder our capacity to understand and manage the ecological dynamics of habitats that contain aquatic plants.

This study conducted in the south slope of the Al-Jabal Al-Akhdar (the Green Mountain) rangelands, northeast Libya to investigate changes in perennial plant species richness, landscape function and soil surface condition in order to determine whether exclosures are effected strategy for the improvement and rehabilitation of rangeland ecosystem at the regional level. Four exclosures are positioned along a strong north-south rainfall gradient encompassing a range of soil and vegetation types. A total of 28 monitoring sites were reinstalled and assessed between May and December 2014, the sites were then initially installed and assessed between the period of May and December 2006. The monitoring site layout is based on the Western Australia Rangeland Monitoring System (WARMS). In order to achieve the research objective, we employed LFA technique. LFA field data collection protocols also follow the WARMS. Based on the results, LFA indices are in the low and medium scales in all of the monitoring sites within the fenced areas. Notably, it is considered a good comparison tool for what it is currently occurring at the target grazing areas. No changes in perennial plant species richness amid the study areas, with the exception of the TT area. Overall, in estimation, at least 10 years of protection from grazing is required in the highest rainfall area (MZ), and a considerably longer period in the lower rainfall areas to the south before vegetation cover and soil surface conditions recover sufficiently to be re-exposed to grazing. Consequently, grazing should be controlled to conserve national forage resources.

In the Sahelian region, different approaches are being used to halt environmental degradation and restore tree cover, with varying degrees of success. Initiatives vary according to projects' objectives, type of land to restore, and technical practices used (natural regeneration, farmer-managed assisted regeneration, enrichment planting, etc.). This study investigates tree planting choices and selection of tree seed sources in some villages of the Central region of Burkina Faso. The study targeted 96 farmers and compared planting practices adopted by farmers involved in small-scale forest restoration using fences, with those not involved in this initiative. The objective was to understand what portfolio of tree species were planted, what factors influenced tree species selection, what tree seed sources were used, what collection practices were generally adopted, and whether there were significant differences between types of farmers. The results showed that the use of fencing to promote forest restoration support the planting of a more diverse portfolio of tree species than other small scale efforts and includes a greater representation of indigenous trees. Fenced plots have therefore a conservation value in landscapes where the diversity of tree species is progressively declining. In addition to the use of fences, some other key factors affect tree planting, mainly land tenure, availability of diverse tree seed sources, and availability of land. Farmers tend to collect directly most of the planting material they need, but in the majority of cases they do not follow recommended best practices. In light of the ambitious forest restoration targets of Burkina Faso and the need to provide diverse options to rural communities to enhance their resilience vis-à-vis increasing environmental challenges, strengthening the capacity of farmers in tree planting and establishing a robust tree seed systems are crucial targets.