in Sri Lanka - Ministry of Environment

Death of trees in the montane forestsThe dying of trees in Totapolakande forest of the montane zone imparting an unhealthyappearance to the forests has been observed by a former Conservator of Forests,Mr. W.R.H. Perera (Perera, 1978). The dying of trees in montane forests has also beenreported by de Rosayro (1946). Perera (1978) reported that over 50% of the dominant Kina(Calophyllum) and Damba (Syzygium) trees on the slopes and summit of Totapolakandewere dead or dying, but trees of Rhododendron arboreum ssp. zeylanicum, common evenin montane grasslands, a large number of Nelu (Strobilanthes.) species and other shrubs inthe lower strata of the forest were found to grow well while the forest tree species failed toregenerate. Several studies have been conducted on the dieback of montane forests in SriLanka (Werner, 1988; Adikaram et al, 1999; Ranasinghe et al., 2009)Widespread forest decline due to die-back is now a severe problem in many parts of the world.Some of these countries include Europe, North America, New Zealand, former Soviet Unionand Pacific Islands. In Germany, it is reported that about 52% of the forest surveyed areaffected by this phenomenon.In some cases the tree-death is due to natural causes. Die-back stands in such areas mayrepresent a senescing stage in the forest life cycle. Drastic changes in the climate such assevere drought or flood can also cause natural die-back in forests (Werner, 1988). However, inmost industrial countries the death of forest trees is mainly due to human induced environmentalchanges such as the pollution of atmosphere.A study conducted by us (Wijesundara and Samarasinghe 1993) to examine floristiccomposition of forest gaps in Horton Plains revealed that Nelu (Stobilanthes) species arefound in almost all gaps created by dieback. Gaps created by fire are different from those asthey are occupied by a fern, Pteridium revolutum. It was also observed that alien invasivespecies such as Ageratina riparia, Austroeupatorium inulifolium and Cestrum aurantiacum areinvading the dieback gaps. Dieback of canopy trees was also observed in the Hakgala SNR,which is a similar montane forest in the same region. Over 50% of the species were affectedby dieback. Observations made during the past two decades in the areas affected by forestdieback reveal that the following changes have been taken place in the dieback stands.a) Regeneration of the montane forestb) Formation of a pigmy forestc) Colonization of gaps by Nelu (Strobilanthes spp.)d) Colonization of gaps by alien invasive speciesRegeneration of montane forest can be seen in certain places where the number of deadtrees is less. New shoots are formed on the defoliated trunks and at the bases of the trees.A formation of a pigmy forest in the gaps can be observed in areas where the wind actionis severely felt. In the area where the gaps are colonized by Nelu, a lesser number of treeseedlings were observed. The dense growth of Nelu may suppress establishment of treeseedlings. These nelu stands, which die en mass after several years, are being invaded bygrasses in some areas (Wijesundara, 1991).183