Ecology and Development Series No. 10, 2003 - ZEF

Impacts of human use on the forest vegetation5.4.1 Differences in species diversity and compositionThis study shows that, based on species composition, a clear distinction can be madebetween the undisturbed forests and the forests managed for coffee production (Figure 5.1;5.3.). Species richness decreased on average by nearly 40% in the semi-forest-plantations(SEMIFOR-PLAN) as compared to undisturbed natural forest (NATFOR and SECFOR;Tables 5.1; 5.3). The decrease in the mean number of species per sample plot is even higher(Table 5.4). In the older managed forests (SEMIFOR-OLD and SEMIFOR-PLAN), thenumber of woody plant species per plot declined by about 50%, compared to that of theundisturbed forests (16 vs. 31; Table 5.4). The impact of frequent disturbance for coffeeproduction on the diversity of plant species in the managed forests is very high compared toother types of managed forests in the tropics. For instance, Parthasarathy (1999) observedno difference in species diversity except changes in species composition in a wet evergreenforest frequently disturbed for cardamom production in India. Similarly, Webb and Peralta(1998) also reported only minor changes in species diversity in a forest in which controlledselective logging is practiced in the neotropics. The traditional system of coffee productionis quite intensive and far beyond the extractive use system practiced elsewhere in thetropics.Species diversity tends to decrease with the increase in the length of managementperiod. There are three possible reasons for the higher species diversity in the youngestmanaged forest category, the SEMIFOR-NEW, as compared to other managed forestcategories: (a) presence of seedlings of many species in the seedling bank; (b) regenerationof some pioneer species from the soil seed bank; and (c) re-growth of coppice stands fromthe stumps of recently cut stems. Most woody plants in mature forests (e.g. undisturbedforests like NATFOR in this case) have multiples of suppressed seedlings awaiting thecreation of gaps (Kitajima and Fenner 2000). At the early stage of gap formation, theexisting seedlings of mature forest species serve as sources of regeneration, while gapformation also creates favorable conditions for the germination of the seeds of pioneerspecies from the soil seed bank and the seed rain from the surrounding vegetation (Demeland Tamrat 1995). Coppice regeneration is also a widespread phenomenon in tropicalforests (Swaine et al. 1990; Whitemore 1991; Demel and Tamrat 1995). Regeneration of91