Fisheries in the Southern Border Zone of Takamanda - Impact ...

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32 Sunderland et al. Table 3. Comparison of structure and diversity of Takamanda Forest Reserve biodiversity plots with other biodiversity plots in Cameroon and Nigeria. Plot # 6 7 8 9 10 11 12 13 14 15 # of trees 491 498 527 523 414 428 426 477 406 438 # of species 103 98 64 74 90 113 93 118 83 91 Mean dbh (cm) 30.0 32.2 24.4 21.3 29.7 25.4 30.9 29.3 35.6 31.1 Total BA (m 2 Takamanda /ha) 34.7 42.1 24.6 18.6 28.7 21.7 32.0 32.1 40.5 33.2 Plot # 1 2 3 4 5 # of trees 397 402 394 525 526 # of species 74 81 74 71 80 Mean dbh (cm) 28.8 30.6 26.0 28.5 27.8 Total BA (m 2 /ha) 30.8 30.0 35.0 33.2 34.0 elsewhere in West Africa’s montane forests (Morton 1986). The lower montane forest occurs at higher elevations elsewhere in the region than was observed in Takamanda. Nevertheless, the proximity of the Okwangwo region of Nigeria and the Obudu Plateau means that the two areas are similar in relation to altitudinal zonation of vegetation types (Hall and Medler 1975, Keay 1979). 5.2 Species Richness and Diversity The forests of southwestern Cameroon are generally known to contain a rich species diversity because of their location in an area of high rainfall. It is also believed that the area formed a Pleistocene refugium during the last glacial advance, becoming isolated and allowing for the development of regional endemic species (Lawson 1996). The forests of Takamanda appear to be even more diverse than those of surrounding areas. The number of species in the lowland forest plots ranged from 83 to 113 species/ha, with the riverine plots containing between 93 and 118 species/ha, and the ridge forests between 98 and 103 species/ha (Table 3). To the south of Takamanda lies the Ejagham Forest Reserve, where richness in biodiversity plots reached 80 species/ha. The 50-ha Smithsonian forest dynamics plot at Korup averaged 86 species greater than 10 cm dbh per ha (Songwe et al. in press, Thomas et al. 2003). The Nigerian plots had lower Takamanda: the Biodiversity of an African Rainforest Campo Ejagham Akampka N2 471 128 21.2 16.8 Okwangwo N3 467 82 26.9 26.5 species richness values in the Okwangwo region, while the highest species richness of all plots compared to the study area was the Akampka site in the Oban region (128 species/ha). TFR’s relatively high levels of diversity are undoubtedly due to the intricate mosaic of vegetation types and forest formations found along the Reserve’s altitudinal gradients. While it is agreed that species richness generally decreases with increasing altitude, this correlation is not significant at TFR and only becomes marked in the transition between the lowland forests (including the ridge forest) and the mid-elevation and montane forest. Species diversity does show a slight but significant decline with altitude (r 2 = 0.436, P = 0.038). Likewise, tree density shows a significant increase with elevation (r 2 = 0.618, P = 0.07; Figure 6). These trends are in line with what has been observed at other sites. 5.3 Vegetation Similarities Based on Sorensen’s coefficient, TFR’s montane and mid-altitude vegetation share more species than montane/lowland and lowland/mid-altitude vegetation. Comparable results were obtained from Jaccard’s coefficient of similarity. The shared taxa might be due to continuous vegetation belts that these habitats share. Interestingly, despite the unique composition of TFR
Vegetation Assessment Table 4. Similarity of Takamanda plots to other plots in Cameroon. habitats, some taxa were recorded at every assessment site, ranging from lowland forest to montane forest. These include Protomegabaria stapfiana, Santiria tremira, Hypnodaphnis zenkeri, Xylopia staudtii, Tabernaemontana crassa, Strombosia grandifolia, Strombosia pustulata, Strombosiopsis tetandra, and Treculia oboviodea. 5.4 Floristic Affinities The Reserve encompasses a unique region that includes the full altitudinal vegetation range found in this part of Cameroon. From our surveys, it is clear that vegetation of the area is somewhat distinctive and concurs with studies from the Nigerian side of the border (Hall and Medler 1975, Keay 1979). As evidence of this uniqueness, the Number of trees per hectare Takamanda/ Campo Takamanda / Ejagham Campo / Ejagham 560 540 520 500 480 460 440 420 400 Sorensen©s Coefficient Jaccard©s Coefficient 0.277 0.161 0.308 0.182 0.491 0.325 380 0 200 400 600 800 1000 1200 1400 Altitude (m) r2 = 0.618 Figure 6. Relationship between altitude and tree density in the biodiversity plots of Takamanda Forest Reserve, Camerooon. Caesalpinaceae are relatively poorly represented in TFR lowland forests, unlike the Ejagham and Korup forests to the south and the majority of forested areas in Southwest Province. Rather, TFR lowland forests possess a far richer tree flora than these other forests. Indeed, diversity decreases significantly as one moves from Takamanda (H′=4.61) to Ejagham (H′=3.69). This uniqueness is also evident when floristic similarities and evenness at TFR are compared to the Ejagham forest, also in the Southwest Province, and the Campo region in southern Cameroon. It came as a surprise that the geographically disjunct Campo/Ejagham shared more species than Takamanda/Ejagham and Takamanda/Campo (Table 4). For the montane forest and high-altitude grassland, however, the floristic affinities are more complex, resulting from climatic change and phytogeographical variance. Hall (1981) suggests that the montane forest flora of the Obudu area represents “an impoverished variant of the flora of the lowland forest of the Oban hills,” a known Pleistocene refuge, with the addition of an Afromontane element. The presence (if not dominance) of many lowland species in TFR montane forest, along with Afromontane taxa, supports this hypothesis and suggests that: • The “montane” forest is influenced by anthropogenic interventions such as burning of highaltitude grassland that is reducing its altitudinal extent and ability to regenerate; hence, the tree line is gradually reducing. This accounts for the significant numbers of lowland forest species in this forest formation. • At lower altitudes (
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82 Family / Species Notes Locations
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84 LeBreton et al. 3 Methods A team
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148 Mdaihli et al. Mochokidae Barbu
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150 Monthly yield (t) 200 160 120 8
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No. of individuals (n = 315) 200 15
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No. of individuals (n = 1065) 1000
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Gnetum spp. Piper guineensis Site T
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Resource Impacts of seasonality Ava
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