In situ and Ex situ Conservation of Commercial Tropical Trees - ITTO

494Burning following clear cutting is widely practised to clear land beforetrees are re-planted or forests are converted to plantations such as rubber andoil palm. This method of land clearing is economical, requiring only one third ofthe cost of land clearing by mechanical methods (Saharjo & Watanabe 1999).A good burning can also provide easy access during planting, kill seeds andcoppice shoots of weeds, and make available nutrients such as P, K, Ca andMg in the “A” horizon.When the burning become uncontrolled, however, fire can be a big disaster.In 1997, for example, forest fire destroyed at least 2 million ha of forest inIndonesia. Haze spread into the atmosphere causing air pollution in Indonesiaand the neighbouring countries such as Malaysia, Singapore, Thailand, Philippines,Brunei, and Papua New Guinea. The highest air pollution index (API) of 859was recorded in Malaysia. It has been estimated that this forest fire contributedapproximately 20% of the recent increase in the greenhouse gasses, primarilyby releasing CO 2and CH 4(Saharjo & Watanabe 1999).Effect of forest fire on mycorrhizal fungal populationForest fire has been reported to reduce endomycorrhizal fungal populations(Dhillion et al. 1988, Klopatek et al. 1988, Vilarino & Arines 1990, Wicklow-Howard 1989). Mycorrhizal inoculum potential observed following burning wasextremely low (Anderson & Menges 1997). Severe forest fire can affectendomycorrhizal fungi by changing soil conditions and by directly alteringendomycorrhizal proliferation. Rashid et al. (1997) found a similar number oftotal spores, but a lower number of viable endomycorrhizal fungal propagulesin soil from a burnt forest than from the nearby unburnt control forest at MargallaHills near Islamabad. Their results also indicated that after fire, mycorrhizalactivity was initiated from endomycorrhizal hyphae in the roots of dominantshrubs. This indication was supported by Bellgard et al. (1994) who suggestedthat endomycorrhizal fungi maintained their viability in the underground organsof plants in New South Wales, Australia. After the fire, these re-establishedthe arbuscular mycorrhizal associations.Similarly, populations of ectomycorrhizal fungi can be affected by forestfire. Severe forest fires in the Siskiyou Mountains of southern Oregon USA in1987 reduced inoculum potential of ectomycorrhizal fungi resulting in a slightformation of ectomycorrhiza in Pseudotsuga seedlings grown in the followingseason (Amaranthus & Trappe 1993). Similar low levels of ectomycorrhizalfungal propagules after a forest fire were previously observed by Parke et al.(1984) and Harvey et al. (1980, 1981).Fire also changes mycorrhizal fungal diversity, as shown by Torres and