Do alien plant invasions cause biotic homogenization of terrestrial ecosystems in the Kashmir Valley, India?

Habitat characteristics and the species attributes that determine the rate of spread of alien plant species are likely to be pivotal in determining the extent of homogenization, particularly at regional level. In order to determine which habitats are more likely to be homogenized and which groups of alien plant species promote homogenization, we sampled seven sites of each of the three habitats namely forests, grasslands, and roadsides for presence-absence of plant species. We calculated a Jaccard similarity index separately for native, alien, and native + alien species. We used the average of Jaccard dissimilarity index (1- Jaccard index) of all paired localities as a measure of the mean overall beta diversity and mean beta diversity of alien and native species for each set of localities examined in an analysis. We used a homogenization index to quantify the homogenization or differentiation effect. For habitats, we found that biotic homogenization followed the order: roadsides > grasslands > forests. The various categories of plants varied in bringing about homogenization and the following order in respect of homogenization was recorded: invasive > naturalized > casual; perennial > annual/biennial; herbs > shrubs/subshrubs/lianas > trees. Beta diversity, based on alien species, was lower for roadsides; invasive, perennial and herbaceous alien plants, than their counterparts (i.e. grasslands, forests; casual, naturalized; annual/biennial and shrubs/sub- shrubs/lianas and trees alien plants, respectively). Our study clearly shows that extent of biotic homogenization depends upon habitat type, and alien plant species differ in their homogenization potential depending upon stage of invasion of alien species, life span and growth form. These observations assume significance in conservation biology to predict the impact of alien plant species on ecosystems. Resumen: Las caracteristicas del habitat y los atributos de las especies que determinan la velocidad de propagacion de las especies de plantas exoticas probablemente sonfundamentales en la determinacion del grado de homogeneizacion, especialmente a nivel regional. Para determinar cuales habitats son mas propensos a la homogeneizacion y que grupos de especies de plantas exoticas promueven la homogeneizacion, muestreamos siete sitios de cada uno de tres habitats (bosques, pastizales y bordes de camino)para determinar la presencia-ausencia de las especies de plantas. Calculamosun indice de similitud de Jaccard por separado para las especies nativas, las exoticas y el conjunto de nativas + exoticas. Utilizamos el indice promedio de disimilitud de Jaccard (1 - indice de Jaccard) de todas las localidades pareadas como una medida de la diversidad beta global promedio y de la diversidad beta promedio de las especies exoticas y nativas para cada conjunto de localidades examinadas en el analisis. Utilizamos un indice de homogeneizacion para cuantificar el efecto de homogeneizacion o diferenciacion. Para los habitats, encontramos que la homogeneizacion biotica siguio el siguiente orden: bordes de caminos > pastizales > bosques. Las diversas categorias de plantas variaron en lageneracion de homogenizacion, habiendose registrado el siguiente orden con respecto a la homogeneizacion: invasoras > naturalizadas > ocasionales; perennes > anuales/bienales; hierbas > arbustos/subarbustos / lianas > arboles. La diversidad beta, con baseen las especies exoticas, fue