Alien plant invasion in the Indian Himalayan Region: state of knowledge and research priorities.
Invasion by alien species is a global problem and forms one of the major drivers of global change. The researches on plant invasion have grown rapidly across the globe since the mid-twentieth century. However, in the Indian Himalayan Region (IHR) such studies are inadequate and have not been systematically conducted. Lack of empirical evidences on various described aspects of plant invasion in IHR are likely to aggravate the issue of invasion management in the region. This scenario would become more worst under changing climate. This study analyzed the results of an extensive review of the available information generated through Web of Science and Google scholar. A total of 297 naturalized alien plant species belongs to 65 families in the IHR are reported. Of the total 297 naturalized alien plant species in IHR, maximum species occur in Himachal Pradesh (232; 78.1%) followed by Jammu & Kashmir (192; 64.6%) and Uttarakhand (181; 60.90%). Among various invasive species, Lantana camara, Ageratina adenophora, Parthenium hysterophorus and Ageratum conyzoides have been reported from most of the IHR states and proliferated over larger area. Evidences available in the published studies are indicative that with tourism promotion and increasing roads networks, that passes through forests, many of the alien species in the IHR have started invading forests and even in alpine ecosystems. This study observed expansion of Ageratina adenophora up to 2900 m, which is higher than its reported elevation range (300-2800 m) in west Himalaya. These evidences suggest possible encroachment by alien species in hitherto invasion resilient higher Himalaya, particularly with emerging trends of increasing temperature and human disturbances. The present study also provides a multistage framework for investment on invasion researches in IHR. This will allow developing appropriate management strategies and policy planning for addressing issues pertaining to plant invasions across the IHR states.