Lichens as indicators of environmental conditions

Lichens and Termites Bioindicators and the assessment of sustainable forestry

Lichens as indicators of environmental conditions

The use of lichens as indicators of `old- growth forest’ with long term ecological stability was first developed in Britain from extensive surveys of the lichen flora of woods with independent documentary evidence (Rose 1976, 1992). The increasing need for evaluation of sites has led to the development of the New Index of Ecological Continuity where widespread faithful species form the basic indicator list and specialist or regionally rare species are counted as “bonuses” (Rose 1992). Similar techniques have been used to define species of `old-growth’ forests in the USA and Canada, and further developed to assess habitat diversity in managed forests of the Pacific Northwest by arranging species in functional groups (Rosentreter, 1995). This research has been undertaken in areas where the lichen flora is reasonably well known, and in a continuum of management options from a base-line of undisturbed old-growth forests. Lichens have also been used widely as indicators of atmospheric conditions in particular acid rain deposition, where absence of sensitive species and presence of tolerant species has been used to construct a scale of atmospheric pollution (Hawksworth & Rose, 1970).

Lichens as indicators of environmental conditions in tropical forests

Lichens have been used to interpret the effects of fire history in tropical forests of Thailand where the replacement of fire-sensitive evergreen forest by fire-tolerant deciduous dipterocarp forest could be assessed over time using lichen taxa associated with each forest type (Wolseley et al., 1997b). In lowland dipterocarp forests of Peninsular Malaysia and Danum Valley Sabah lichens and bryophyte taxa were assessed in plots within established 50 ha Forest Dynamic Plots, and in a range of logged, regenerating and planted forest conditions. The highest diversity of lichens and bryophytes was found in the 50 hectare plots where no known extraction had occurred, and plots in logged forests where canopy trees were retained showed a higher diversity and retention of sensitive species than that of heavily logged forest (Wolseley et al., 1998a, 1998b).

The importance of termites in tropical ecosystems

Termites (Insecta: Isoptera) are predominantly tropical in distribution. Their species richness is highest in lowland equatorial rain forests, and generally declines with increasing latitude and altitude (Collins 1983; Eggleton et al., 1994; Jones 2000). Termite survival is limited by low temperatures and high aridity, and very few species occur beyond 45° latitude (Collins 1989) or above 1800m altitude (Collins 1980; Jones 2000). Recent studies (Eggleton 2000) indicate that the forests of West Africa have the highest termite diversity, closely followed by South America. The forests of Southeast Asia and Madagascar are considerably lower in species richness. These regional diversity anomalies are also associated with significant differences in clade and functional diversity (Eggleton 2000; Davies, 2001).

Termites are at the ecological centre of many tropical ecosystems (Wilson 1992). They can achieve very high population densities. For example, in the forests of southern Cameroon, termites are one of the most numerous of all arthropod groups (Watt et al., 1997) with abundances of up to 10,000 m^-2, and live biomass densities up to 100 g m^-2 (Eggleton et al., 1996). Across the Isoptera, a wide range of dietary, foraging and nesting habits occur, but many species show a high degree of resource specialization (Wood 1978; Collins 1989; Sleaford et al., 1996). A few species feed on living plant tissue but most are detritivores, feeding on dead plant material along a humification gradient, from dead wood and leaf-litter to humus in the soil (Donovan et al., in press). As the dominant arthropod detritivores, termites are important in decomposition processes (Wood & Sands 1978; Matsumoto & Abe 1979; Collins 1983) and play a central role as mediators of nutrient and carbon fluxes (Jones 1990; Lawton et al., 1996; Bignell et al., 1997; Tayasu et al., 1997; Eggleton et al., 1999). Termite activity, such as mound-building, subterranean tunnelling and soil-feeding, is thought to have a positive effect upon soil structure and quality (Lee & Wood 1971; Lobry de Bruyn & Conacher 1990; Black & Okwakol 1997; Holt & Lepage 2000; Donovan et al., 2001). To date, about 2,650 species of termites have been described (Kambhampati & Eggleton 2000), and less than 3% of these cause significant economic damage to buildings or related human-made structures (Pearce 1997). A similar proportion are serious pests of crops (Wood 1996). The termite fauna of urban environments is usually depauperate and characterised by wood-feeding species, unlike natural habitats that often support great termite diversity. For example, 136 species have been recorded in a single forest site in Cameroon, 73% of which feed on soil (Jones & Eggleton 2000). The impact of termites on ecosystem processes in natural habitats and in agroforestry systems is likely to be governed by the species composition and abundance of the local termite assemblage. Therefore, to quantify the influence of termites, it is necessary to accurately characterize the structure of that assemblage. In response to the need for standardized methods for sampling insects (Sutton & Collins 1991; Stork & Samways 1995) a termite sampling protocol has been developed. The protocol, described and tested by Jones & Eggleton (2000), produces samples that are representative of the taxonomic and functional diversity of the local termite assemblage. The protocol is based on standardised sampling effort, thus ensuring the samples from different sites are directly comparable.