Consistent Effects of Disturbance and Forest Edges on the Invasion of a Continental Rain Forest by Alien Plants

Predicting spatially heterogeneous invasive spread: Pyracantha angustifolia invading a dry Andean valley in northern Argentina

Understanding the drivers of invasive species spread is key to designing optimal management programmes for controlling them. Population models, parameterized from demographic and dispersal data, are useful for simulating invasion when long-term observations are lacking, which is particularly important when invasions are occurring rapidly. We aimed to understand how the spread of Pyracantha angustifolia (an invasive ornamental shrub) is influenced by heterogeneity in local conditions within a dry inter-montane valley in northwestern Argentina that is currently experiencing rapid urban expansion and concomitant reduction in cattle farming. Field surveys demonstrated that individuals growing in shrublands have a higher fecundity than those in grassland and rocky habitats. Furthermore, grazing pressure of cattle and horses substantially reduces fecundity and impacts the relationship between age and fecundity. We incorporated our field-estimated habitat and age-specific fecundities into both analytical integro-difference equation models and individual-based models to predict rates of spread across each habitat type in the presence or absence of grazing pressure. Results indicate that the rate of spread would be substantially higher in shrublands (by up to 33%) and highlight that grazing pressure can, through direct consumption of seeds by livestock, substantially depress the rate of spread (by up to 53%). These results suggest that shrubland areas in the valley are most vulnerable to invasion and that grazing may help to reduce the impact of Pyracantha. This suggests that a synergism between urban expansion and reduction in domestic livestock density contributes to the spread of an invasive species in this environment.

Species composition and diversity of ground bryophytes across a forest edge-to-interior gradient

Understanding diversity patterns and community structure of bryophytes will help integrate nature conservation at multiple biotic-group levels. We conducted a survey of ground bryophytes in a subtropical forest along an edge-to-interior gradient in South China. We recorded 11 liverwort species from 10 genera of seven families, and 26 moss species from 23 genera of 16 families in three transects. A two-way cluster analysis detected the environmental gradient between the forest edge and forest interior for bryophytes with habitat specificity. Functional diversity of bryophytes differed significantly across an edge-to-interior gradient. The range and median in both structural and functional diversity decreased remarkably from the forest edge to the interior. Multi-response permutation procedures showed significant differences in species composition between the forest-edge and forest-interior, and between the intermediate and forest-interior transects. Seven species were detected with a significant indicator value for indicating environmental conditions in the forest edge, while only one such species was found indicative of the intermediate transect. Our results demonstrate that remarkable edge effects exist for species composition and functional diversity patterns, and the forest edge is a marginal habitat with high biotic heterogeneity. Furthermore, functional diversity metrics are more sensitive to the edge effect than species diversity.

Alien plant invasions of protected areas in Java, Indonesia

Alien plants are invading protected areas worldwide, but there is little information from tropical Asia. Java has the longest record of human occupation in Asia and today supports 145 m people. Remnants of natural ecosystems survive in 12 small National Parks surrounded by dense human populations, making them highly vulnerable to invasions. We surveyed eight of these, along a rainfall gradient from lowland rainforest with >3000 mm annual rainfall to savanna with <1500 mm, and a 0-3158 m altitudinal gradient, using 403 10 × 5 m plots along trails. We found 67 invasive alien plant species, of which 33 occurred in only one park and two (Chromolaena odorata and Lantana camara) in all. Historical factors relating to plant introduction appeared to be as important as environmental factors in determining which species occurred in which park, while within parks canopy cover and altitude were generally most influential. Spread away from trails was only evident in open habitats, including natural savannas in Baluran National Park, threatened by invasion of Acacia nilotica. Existing control attempts for invasive aliens are reactive, localized, and intermittent, and insufficient resources are currently available for the early detection, prompt action, and continued monitoring that are needed.