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ABSTRACT. Farmers' practices in the management of agricultural landscapes influence biodiversity with implications for livelihoods, ecosystem service provision, and biodiversity conservation. In this study, we examined how smallholding farmers in an agricultureforest mosaic landscape in southwestern Ethiopia manage trees and forests with regard to a few selected ecosystem services and disservices that they highlighted as "beneficial" or "problematic." Qualitative and quantitative data were collected from six villages, located both near and far from forest, using participatory field mapping and semistructured interviews, tree species inventory, focus group discussions, and observation. The study showed that farmers' management practices, i.e., the planting of trees on field boundaries amid their removal from inside arable fields, preservation of trees in semimanaged forest coffee, maintenance of patches of shade coffee fields in the agricultural landscape, and establishment of woodlots with exotic trees result in a restructuring of the forest-agriculture mosaic. In addition, the strategies farmers employed to mitigate crop damage by wild mammals such as baboons and bush pigs, e.g., migration and allocation of migrants on lands along forests, have contributed to a reduction in forest and tree cover in the agricultural landscape. Because farmers' management practices were overall geared toward mitigating the negative impact of disservices and to augment positive services, we conclude that it is important to operationalize ecosystem processes as both services and disservices in studies related to agricultural landscapes.

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It is a widely held view that plantations of exotic tree species in the tropics are harmful to the environment. Arguments are collected here from experience in tropical countries, showing that the canopies of exotic trees can exert protective functions and have a nurse effect for the regeneration of natural forest. This counterbalances the opinion that exotic tree plantations generally are detrimental.Keywords Eucalyptus · Exotic tree plantations · Nurse effect · Regeneration · Tropical forest Figure 1 shows the increase in the area covered by plantations of Eucalyptus spp. in Brazil since 1965. It is a widely held view among ecologists that such plantations of exotic trees are harmful to the environment. This short paper aims to support the opinion that exotic tree plantations are not necessarily harmful. We do not aim to review reforestation of pasture and range lands by various approaches (Aide et al. 2000;Cavelier and Santos 1999;Lamb 1998;Parrotta et al. 1997) including promotion of pasture trees (Ortero-Arnaiz et al. 1999) and intensive seedling plantation versus direct seeding (Engel and Parrotta 2001;Hardwick et al. 1997). Throughout the tropical countries of the world natural forests are declining rapidly due to their conversion to arable lands coupled with overexploitation under the increasing pressure of population growth. This has serious consequences on ecosystems. Major tasks of management include conservation and sustainable utilization of the remaining natural forests, expansion of forest plantations and thereby restoration of abandoned degraded areas. Here we restrict ourselves to regeneration of native forest under the canopy of exotic tree plantations. Experience increasingly accumulating in tropical countries counterbalances the argument that exotic tree plantations are always detrimental.With the objectives of meeting the increasing demand for wood, relieving the pressure from the natural forests and revitalizing degraded lands, forest tree plantations were initiated in the early 20th century in many tropical countries. Although indigenous tree species have been tried for afforestation of degraded lands, mainly introduced (exotic) species of Eucalyptus, Cupressus, Acacia, Pinus and Casuarina have been and are still used for that purpose (see Table 1). Forest plantations have increased at a high rate in the tropics (Cohn 1995). For instance,