Human impact on forest fragmentation in the Comoé National Park region, NE Côte d'Ivoire

1. A B Fig. 1. A) Landsat 7 image of the study area in the utilized regions outside of the CNP (lower part). Forest islands (dark red); savanna (green colouring); agriculture outside the park (pink tints); park border (black line); villages (Kakpin, Banvayo, Zamou, Solokahi). B) Location of transects (black bars) and fallow-plots (squares; 2-4 plots per location). Kakpin Banvayo Study area Zamou Solokahi Fig. 2: floristic composition of differents position along transect: forest (A); boundary (C); savanna (E) and of the fallow Comoé N.P. Human impact on forest fragmentation in the Comoé National Park region, NE Côte d'Ivoire West Africa 04 1Annick Koulibaly, 2Dethardt Goetze, 1Dossahoua Traoré, 2Stefan Porembski 1 University of Cocody, UFR Biosciences, Laboratory of Botany, 22 B.P. 582, Abidjan 22, Côte d’Ivoire 2 University of Rostock, Institute of Biodiversity Research, Department of Botany, Wismarsche Str. 8, D-18051 Rostock, Germany Introduction The Comoé National Park (CNP) is located in the transition zone between Guinean and Sudanian woodland (Fig. 1A). The southern park area is characterized by a mosaic of savannas and forests that is typical for a wide range of West African landscapes. Human activities are responsible for the recent increase of habitat fragmentation and loss of biodiversity. In Côte d’Ivoire, habitat fragmentation is accelerated by intensified forest exploitation, agriculture, and traffic infrastructure because of demographic growth and climate changes in the course of global change. The proximity of semi-natural vegetation inside the CNP and anthropogenic vegetation outside of the park (Fig. 1A) offers the possibility to point out the human impact on vegetation. In our study we focus on the former and the present system of use and ethnobotanical aspects. In this context we ask the following questions: (1) Which floristic composition and vegetation structure occur in different vegetation types? (2) What is the impact of the agricultural system? Results Methods In the study area (Fig. 1A) forest-savanna transects were installed in forest fragments (Fig. 1B). Transect are divided in five sub-plots (a, b, c, d, e) of 20 x 20m² each. In addition, near the forest border 14 fallow plots 10 x 10m² of size have been established. In the context of this study the term fallow is used for agricultural fields that are left open after cultivation of Injam (harvest in the first year) and Maniok (harvest in the second year). Seeds of cashew are planted into the plantation mounds of these crops in the first year. This extensive plantation is influenced by moderate weeding. At each plot tree composition and structural data have been investigated. All tree individuals (fallow) and all trees lager than 2m (transect plots) have been mapped. Total height and diameter at breast height (DBH) were measured. Structural data along three transects are shown in Fig. 2. The younger size classes (DC1 and DC2, HC1 and HC2) do not show significant differences between transect positions. Only for the lager size classes (DC3 and HC3) significant results could be computed (ANOVA: p = 0.001 (DC3); p = 0.004 (HC3)). Thus, structural differences along the transects are mainly influenced by lager tree individuals. Tree composition data along the transects show that Caesalpiniaceae, Combretaceae et Annonaceae provide 38, 48 and 53% for forest, boundary and savanna plots, respectively (Fig. 3). Typical representatives of these families are Dialium guineense (Willd.; forest plots), Cola millenii (Schum.; forest plots), Anogeissus leiocarpus (Guill. & Perr.; forest and boundary), Daniellia oliveri ((Rolfe) Hutch. & Dalziel, savanna plots) and Isoberlinia doka (savanna plots). In addition, in the forest plots Sterculiaceae represent 13% of all measured trees. Rubiaceae (11%) and Sapotaceae (11%) are other frequent families in the border plots. In savanna plots Rubiaceae (13%) and Euphorbiaceae (13%) play a role. Comprising, in forest, boundary and savanna plots 11, 11 and 8 families were found with 15, 19 and 15 species, respectively. Fallow plots were composed of 7 families within 9 species obtained for trees lager than 2m, within Anacardiacea (59%, mainly Cashew individuals) and Combretaceae (19%) dominating the plots (not shown). Typical components are Anogeissus leiocarpus, Pseudocedrela kotschiii ((Schweinf.) Harms) and Crossopteryx febrifuga. Compared to the transect plots, fallow plots are most similar to savanna and boundary plots. Considering all tree individuals – from seedlings up to old trees (Fig. 3, fallow) – 21 families occur in the fallow plots. 52 were found, thus, 43 additional species compared to the older trees. The species composition is a mixture of forest, boundary and savanna species. Families that do not occur within the lager trees are e.g. Cesalpinaceae (11%) Fabaceae (6%) and Sapotaceae (6%, Fig. 3). This and the high number species stresses the high potential of the fallow plots for the regeneration of both, forest and savanna. Conclusions Along forest borders we found continuous changes from savanna to forest interior. Concerning the structure, this change is only characterized by larger trees. Also tree composition changes along this gradient with a clear change in species composition and on family level. After agricultural disturbance, fallows show a high potential for the regeneration of the original vegetation. Both, tree species and family composition of off-spring, do not indicate a successional direction to forest, boundary or savanna. We can assume that environmental factors determine the succession process not on the level of seedlings and young saplings but on older live stages. Extensive plantations of cashew repress the described regeneration potential of fallows. On the landscape level the increasing world price of cashew results in a loss of agricultural lands. A future study of more transects in the CNP region shall permit a comparison with human impact on forest islands in the Southwest of Ghana. In the latter region, the Guineo-Congolian forest cover has been divided into many artificial fragments by human impact. The ecological consequences of the highly man-made fragmentation and their floristic diversity shall be studied with respect to different land use regimes.