in Sri Lanka - Ministry of Environment

Although the causal factors are not fully understood, widespread die-back could seriouslydamage the vegetation in these areas (Adikaram et al., 1999). Whether the die-back standsrepresent a senescing stage of the forest life cycle or whether it is due to human inducedenvironmental changes is not known. If it is a cyclic vegetational change where the gaps formedby die-back stands represent only a regenerative phase, it is not harmful to the vegetation.However, if the cycle is interrupted by an outside factor diverting it into a different directionthe existing vegetation will be affected. In other words, if an aggressive species invades thegaps the natural regeneration will not take place. Tussocks of Gawara Mana (Chrysopogonnodulibarbis) were observed in die back stands in the Horton Plains area, (Totapolakande andKirigalpotte) and in Pidurutalagala. On the peak of Hakgala Strict Natural Reserve also, thereis a small patch of grassland in the middle of a die-back stand.Since the montane forests and wet patana grasslands are present side by side, there is alwaysa chance for propagules from each type to cross their boundaries. The stand level die-back inthe upper altitudes of the montane forests in Sri Lanka can lead to a decrease in the biodiversity.Floristic composition and the structure of the affected areas will also be changed as a result. Moreresearch is needed to determine whether the edaphic factors in die-back stands are conduciveto the establishment of grassland species. In some areas in the montane zone, the origin ofgrassland could have been due to the stand level forest die-back (Wijesundara, 1991).In the montane region the boundary between forest and the grassland is sharp; this is true forother countries as well (Richards, 1963; Blasco, 1971). The sharpness of the edge of montaneforests is sometimes attributed to anthropogenic fire. Some speculate that in Sri Lanka thepresent line of demarcation of forest and grassland is not the original line but a result of humandisturbances at a later stage.Invasive speciesThe other serious threat to the montane vegetation is caused by the exotic species that haveescaped mainly from the Hakgala Botanic Gardens (Wijesundara, 1999). When a gap isformed in the forest there is always a possibility of an exotic species with higher reproductivevigour getting established there. This is taking place along the periphery of the Hakgala SNRand already there are populations of such species that have invaded into the reserve. In thesouthern areas there are large patches of Cestrum aurantiacum which sometimes spread intothe forest interior. The flowers of this species are pollinated by the endemic bird, Sri Lankawhite eye (Zosterops ceylonensis) and the seeds are dispersed by another endemic bird,Yellow-eared bulbul (Pycnonotus penicillatus). It will be interesting to study the effect of thechanges of food preferences of these birds on the regeneration of natural forest plant species(Wijesundara, 1991).Almost all the foot paths in open areas and even the streams of some motane forests are linedwith such exotic weeds as Ageratina riparia and Aristea ecklonii. Aristea ecklonii is also foundin more open areas such as hill tops and grassland. More recently several other invasivespecies were observed in the montane region. These include Calliandra calothyrsus, Miconiacalvescens, Psidium litorale, Pennisetum clandestinum, and Austroeupatorium inulifolium. Theeffects of these alien species on the local vegetation should be an important study.184