The Role of Complex Agroforestry Systems in the Conservation of Forest Tree Diversity and Structure in Southeastern Ghana
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Agroforest Syst (2010) 79:355–368 DOI 10.1007/s10457-010-9311-1 The role of complex agroforestry systems in the conservation of forest tree diversity and structure in southeastern Ghana Alex Asase • Daniel A. Tetteh Received: 16 June 2009 / Accepted: 29 April 2010 / Published online: 20 May 2010 Ó Springer Science+Business Media B.V. 2010 Abstract The role of different agroforestry systems in relative to the agroforest systems. Eighteen native the conservation of plant diversity and forest structure forest/non-crop trees species in the agroforestry systems has not been directly compared in many agricultural were commonly recorded as being used; 100% of them dominated landscapes. In this study, we investigated being used as fuel wood with 83.3 and 77.8%, respec- tree diversity and forest structure in a complex agrofor- tively, used as medicines and materials. The findings of estry landscape traditionally grown for cocoa and mixed this study suggests that although complex agroforestry food crops and compared these to the natural forest in systems are a poor substitute for the natural forest the southeastern Ghana. The study was carried out using 36 heterogeneous mosaic landscape in which complex 25 m 9 25 m plots. There was significant difference agroforestry forms part can be strategically managed to [95% Confidence Interval (95% CI)] in the native forest/ maximize the benefits of both sustainable agriculture non-crop tree species richness between the natural forest production and conservation of plant diversity by acting and the agroforest farmlands but species richness was as buffer between protected areas and intensively similar between the cocoa and mixed food crops managed areas. agroforests. The density of native forest/non-crop trees was significantly higher (P \ 0.05) in the natural forest Keywords Tropical forest Á Deforestation Á but similar between cocoa and mixed food crops Agroforestry Á Management Á Ghana agroforest. Similarly, the basal area of native forest/ non-crop trees was significantly higher (P \ 0.05) in the natural forest but comparable between cocoa and food Introduction crops agroforest. Of the 20 most abundant native forest/ non-crop trees recorded, 12 of them showed significant Human interference into primary forests that were responses (P \ 0.05) to land use change with nine of the previously free of anthropogenic disturbance is becom- species significantly abundant in the natural forest ing common in all major blocks of remaining tropical forest (Witte 1992; Verissimo et al. 1995; Coomes et al. 2000; Kammesheidt 2002). The combined effects of A. Asase (&) Department of Botany, University of Ghana, selective logging and unsustainable farming practices P.O. Box LG 55, Legon, Ghana in agricultural frontiers are expected to result in e-mail: [email protected] considerable loss of biodiversity. Conversion of trop- ical primary forest into various land use systems has D. A. Tetteh Environmental Science Programme, University of Ghana, serious impacts on distribution, community structure P.O. Box LG 71, Legon, Ghana and population characteristics of flora (van Gemerden 123 356 Agroforest Syst (2010) 79:355–368 et al. 2003). Following centuries of deforestation, showed that cocoa agroforestry systems has less many tropical rainforest ecosystems are severely impact on plant diversity and vegetative structure threatened and exist only as forest fragments. Conse- compared to unshaded intensive cocoa farming quently, there is a growing interest in quantifying although how the cocoa agroforest compare with the habitat characteristics such as forest structure, floristic other agroforestry systems is largely unknown. This composition and species diversity in natural forest and information though is very important in managing human dominated landscapes (Myers et al. 2000). agricultural landscapes for the conservation of biodi- Some of the important tools used for mitigating versity and sustainable agricultural production. tropical deforestation are the establishment of tropical In this study, we investigated the role of two protected parks and agroforest areas. Parks are effec- complex agroforestry systems in the conservation of tive for preventing deforestation and thereby protect- tree diversity and forest structure in an agricultural ing biodiversity although they are largely unfunded dominated landscape traditionally grown for cocoa and and associated with substantial land use pressure mixed food crops and compared these to the natural (Bruner et al. 2001). Agroforestry has the advantage forest in southeastern Ghana. Specifically, the objec- of being an integrated approach combining sustainable tives of this study were (1) to quantify the role of agricultural production and biodiversity conservation. traditional cocoa and mixed food crops agroforests in Agroforestry systems can be used to protect biodiver- the conservation of forest tree diversity compared to sity and assist alleviate the negative effects of defor- the natural forest; (2) to determine the structural estation by stimulating natural forest cover through characteristics of the natural forest and that of the cultivation of trees with agricultural crops and may two agroforest systems; (3) to analyse tree species serve as biological corridors between protected areas responses to the land use changes; and (4) to document and non-protected areas (Schroth et al. 2004). Thus, the uses of native forest/non-crop trees retained in the agroforestry ecosystems have attracted the interest of two agroforestry systems. It is hoped that the findings conservation biologists working on the interface of this study will have important implications for between integrated natural resource management and sustainable management of agroforestry landscapes biodiversity conservation (Gajaseni et al. 1996; Per- particularly for the conservation of plant diversity. fecto et al. 1996; Rice and Greenberg 2000). Complex agroforests are special type of agrofor- estry system characterized by a forest-like structure Materials and methods and significant plant diversity in which useful trees and tree crops species attain substantial greater density, Study sites compared to natural forest, through planting, selection, and management of useful species from spontaneous This study was conducted at two sites in the Eastern regeneration (Schroth et al. 2004). The principal tree Region of Ghana between March 2007 and October crops in complex agroforest are either shade tolerant 2008 (Fig. 1). Historically, the area was tropical trees such as cocoa (Theobroma cacao) and coffee forest, but has been extensively cleared to form a (Coffea arabica) or canopy trees such as rubber (Hevea strongly agricultural landscape populated by commu- brasilensis). In West Africa a special type of complex nities of smallholder farmers. This follows a common agroforest exist where mixed food crops are cultivated pattern in Ghana, which now has only 7% forest in the shade of native trees. It can be rightly argued that cover reduced from 35% at the turn of the nineteenth all agroforestry systems no matter how forest-like they century (FAO 2003). Mean annual rainfall is between may appear to be displace natural ecosystems through 1200 and 1800 mm and the study area is character- either clearing or replanting with crops and trees or ized by a two-peak rainy season in April–June and variable levels of domestication of the original land- October. A mild harmattan season occurs from scape and ecosystems. However, the relative impact of November to March. converting natural forest to different agroforestry The first site was at Adjeikrom where traditional systems has not been directly compared in many agroforestry systems are being practiced. The area is agricultural landscapes (Fitzherbert et al. 2008). For located between latitudes 6° and 6°300N and longi- example, in our previous study (Asase et al. 2009), we tudes 0° and 0°300W. Two broad agroforestry land 123 Agroforest Syst (2010) 79:355–368 357 Fig. 1 Map of Ghana showing the locations of the study sites use systems, namely, traditional cocoa (T. cacao) that found in the cocoa agroforestry. The mixed food agroforest and mixed food crops agroforest were crops agroforests were between 3 and 4 years and studied. The crops are traditionally cultivated in the fairly well maintained in terms of weeding and shade of native forest trees by smallholder farmers; harvesting of produce. It is important to note that the most of the farms are less than a hectare in size. Food mixed food crops farms are usually abandoned after 5 crops being cultivated included plantain (Musa years of continuous cultivation as the farmers’ paradisiaca), banana (Musa sapientum), cassava practice essentially shifting cultivation. (Manihot esculenta), maize (Zea mays) and cocoyam The second site was at the Atewa Range Forest (Colocasia esculenta). The food crops are tradition- Reserve in the East Akim District which represented ally cultivated together on the same piece of land but the natural forest. This reserve was used as the without cocoa. Although cocoa agroforest farms are control in this study. There is very little primary purposely grown for cocoa, the farms also contain forest left in Ghana and the Atewa Range Forest other food crops such as banana, plantain and Reserve is representative of remaining natural forest cocoyam. The cocoa agroforest farmlands were in the study area (Hawthorne and Abu-Juam 1995). cultivated with a mixture of Amelonado (30– The reserve is located between latitudes 6°