Brown K.A.

Multi-scale analysis of species introductions: combining landscape and demographic models to improve management decisions about non-native species

Brown, K.A., Spector, S.& Wu, W. (2008)Multi-scale analysis of species introductions:
combining landscape and demographic models to improve management
decisions about non-native species. Journal of Applied Ecology, 45,
1639–1648.

Abstract: 
1. Non-native, invasive species can affect biological patterns and processes at multiple ecological scales. The multi-scalar effects of invasions can influence community structure, ecosystem processes and function, and the nature and intensity of ecological interactions. Consequently, efforts to assess the spread of invasive species may benefit from a multi-scale analytic approach. 2. We analysed results from landscape- and population-scale models for Syzygium jambos , a nonnative tree in the Luquillo Mountains of Puerto Rico, to demonstrate a multi-scale approach that can be used to inform management decisions about invasive plants. At the landscape-level, we used an Ecological Niche Modelling approach to predict environmentally suitable habitats for the target plant. At the population-level, we constructed matrix projection models to determine the finite rate of population increase ( λ ) for S. jambos . We then extrapolated λ values to the landscape-scale to obtain a distribution map of λ values for the Luquillo forest. 3. The landscape analyses suggested that the most environmentally suitable habitats were those most similar to where S. jambos had already been observed. The population-level analyses showed that four of the seven populations had λ values less than 1, indicating that they were projected to be below replacement. The λ distribution map showed that S. jambos growth was highest in areas where it was most common and lowest in areas where it was most rare. 4. Our analyses further suggested that the importance of different drivers of invasion and the environmental variables that mediate them appear to be strongly scale-dependent. Past disturbances seemed most important for controlling invasions at fine-spatial scales; while abiotic environmental variables modulated coarse-scale invasion dynamics. 5. Synthesis and applications. We have shown that a multi-scale analytic approach can be used to manage invasive species by simultaneously targeting susceptible life stages and rapidly growing populations in a landscape. The utility of this approach stems from an ability to: (i) map the distribution of habitats that can potentially sustain λ values above replacement; (ii) identify populations to manage or monitor during selected stages of an invasion; (iii) forecast the probability for a target species to increase above a critical threshold abundance; and (iv) set priorities for control and monitoring actions.

Effects of an invasive tree on community structure and diversity in a tropical forest in Puerto Rico

Brown, K. A. ; Scatena, F. N., and Gurevitch, J. 2006. Effects of an invasive tree on community structure and diversity in a tropical forest in Puerto Rico. . Forest Ecology and Management . 2006; 226:145-152.

Abstract: 
We report the effects of an invasive tree (Syzygium jambos, Myrtaceace) on species composition, plant diversity patterns, and forest regeneration in primary and secondary forest in the Luquillo Mountains of northeastern Puerto Rico, including the area in and around the Caribbean National Forest (CNF) and the Luquillo Long Term Ecological Research site (Luquillo LTER). Land use history was reconstructed using aerial photographs from 1936 to 1989 and study sites were categorized into four groups that corresponded to their status in 1936: unforested, young secondary, mature secondary, and primary forests. In randomly selected forest stands in each forest type, we measured the abundance of invasive and native tree species, seedling recruitment for S. jambos as well as soil nutrient pools and tested for the effects of land use history on S. jambos density and diversity. A partial Mantel test was used to control for historical and elevational differences across study sites. The results indicate that S. jambos density was highest in habitats classified in 1936 as unforested, young, or mature secondary forests. Compared to all other forest classes, species diversity was significantly higher in primary forests. However, there was no statistically significant difference between observed and estimated species richness across the four forest types. S. jambos density and species diversity were strongly negatively correlated, even after controlling for land use history and elevation. There was significantly higher S. jambos seedling recruitment in areas that were either unforested or had young secondary forests in 1936. The results also indicate that S. jambos is able to establish viable populations in habitats with different soil nutrient status. S. jambos has also altered vegetation composition and diversity patterns in habitats where it is the dominant tree species. After nearly 185 years since its introduction to the island, S. jambos is not only well established within 30 m of stream channels, its presence does not appear to be limited by topographic, soil nutrient, or elevational conditions. This study suggests that land use change and subsequent plant invasions have produced a new vegetation assemblage that has led to potentially long-term changes in community structure, species composition, and successional trajectory in regenerating secondary forests in the Luquillo Mountains.
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