Efficacy of exclusion fencing to protect ephemeral floodplain lagoon habitats from feral pigs (Sus scrofa)

Foraging by feral pigs can strongly affect wetland vegetation assemblages and so too wider ecological processes, although their effects on freshwater ecosystems have seldom been studied. We assessed the ecological effects of pig foraging in replicate fenced and unfenced ephemeral floodplain lagoons in tropical north-eastern Australia. Pig foraging activities in unfenced lagoons caused major changes to aquatic macrophyte communities and as a consequence, to the proportional amounts of open water and bare ground. The destruction of macrophyte communities and upheaval of wetland sediments significantly affected wetland turbidity, and caused prolonged anoxia and pH imbalances in the unfenced treatments. Whilst fencing of floodplain lagoons will protect against feral pig foraging activities, our repeated measures of many biological, physical and chemical parameters inferred that natural seasonal (i. e. temporal) effects had a greater influence on these variables than did pigs. To validate this observation requires measuring how these effects are influenced by the seemingly greater annual disturbance regime of variable flooding and drying in this tropical climate

Short-term response and recovery of bluebells (Hyacinthoides non-scripta) after rooting by wild boar (Sus scrofa)

Species reintroduction programmes should include consideration of potential impacts on key species in the recipient community. Wild boar (Sus scrofa) have been reintroduced into Britain after a 700-year absence. There is an urgent need to understand how this ecosystem engineer will affect plant communities in the habitats that it invades. We investigated the impact of rooting by wild boar on bluebells (Hyacinthoides non-scripta), a species that is highly valued for its impressive floral displays and is an important and legally protected component of the UK forest flora. We monitored bluebell performance over three growing seasons in woodland habitats that are routinely rooted by boar in southern England. H. non-scripta cover and reproductive performance were monitored in small-scale experimental exclosures to exclude boar, compared to open control plots, set up on areas that either had or had not been previously rooted. Immediate effects were that rooting significantly reduced the percentage cover and density of H. non-scripta plants, by up to 95 and 60 %, respectively, and also adversely affected the number of flowering stems. However, there was evidence that cessation of rooting brought about by excluding the boar enabled substantial recovery in percentage cover and the density of flowering stems within 2 years. A positive effect of rooting on germination may have assisted this recovery. Thus, the impact of wild boar rooting on bluebell populations is locally severe, but there is potential for rapid recovery if plants are protected. Long-term effects of sustained or frequently repeated rooting still need to be investigated

California native and exotic perennial grasses differ in their response to soil nitrogen, exotic annual grass density, and order of emergence

Early emergence of plant seedlings can offer strong competitive advantages over later-germinating neighbors through the preemption of limiting resources. This phenomenon may have contributed to the persistent dominance of European annual grasses over native perennial grasses in California grasslands, since the former species typically germinate earlier in the growing season than the latter and grow rapidly after establishing. Recently, European perennial grasses have been spreading into both non-native annual and native perennial coastal grass stands in California. These exotic perennials appear to be less affected by the priority effects arising from earlier germination by European annual grasses. In addition, these species interactions in California grasslands may be mediated by increasing anthropogenic or natural soil nitrogen inputs. We conducted a greenhouse experiment to test the effects of order of emergence and annual grass seedling density on native and exotic perennial grass seedling performance across different levels of nitrogen availability. We manipulated the order of emergence and density of an exotic annual grass (Bromus diandrus) grown with either Nassella pulchra (native perennial grass), Festuca rubra (native perennial grass), or Holcus lanatus (exotic perennial grass), with and without added nitrogen. Earlier B. diandrus emergence and higher B. diandrus density resulted in greater reduction in the aboveground productivity of the perennial grasses. However, B. diandrus suppressed both native perennials to a greater extent than it did H. lanatus. Nitrogen addition had no effect on the productivity of native perennials, but greatly increased the growth of the exotic perennial H. lanatus, grown with B. diandrus. These results suggest that the order of emergence of exotic annual versus native perennial grass seedlings could play an important role in the continued dominance of exotic annual grasses in California. The expansion of the exotic perennial grass H. lanatus in coastal California may be linked to its higher tolerance of earlier-emerging annual grasses and its ability to access soil resources amidst high densities of annual grasses