This study investigates the structure, species composition, and diversity of a section of the Kilengwe Forest in Tanzania. In order to accomplish the proposed objectives, 18 plots of 20 m × 20 m were randomly established in the forest and the number of tree species in each plot was identified and counted. The most important families and species were determined using importance value indices at the respective taxonomic levels. Diversity was measured using the Shannon-Wiener and Fisher alpha diversity indices. A total of 276 stems/ha representing 93 species/ha within 26 families were documented from 0.72 ha. Fabaceae and
Globally, 52% of the total forests are in tropical regions and they are known to be the most important areas in terms of biodiversity [
The Kilengwe Forest Reserve is found in Kisaki Ward, Bwakira Chini Division, in the Morogoro Rural District. It is owned by local government and surrounded by the villages of Kilengwe and Zongomero. The forest is situated at latitude 7′29° South and longitude 37′32° East at an elevation of 182 to 228 m above mean sea level covering an area of 995 ha. A number of seasonal streams that provide water to the local community for domestic purpose originate from the forest reserve. The climate of the region is oceanic due to proximity (about 200 km) to the Indian Ocean and the rainfall regime is bimodal. The long rains last from March to May peaking in April while the short rains last from October to December. The mean annual rainfall and temperature in the Morogoro region are about 740 mm and 25.1°C, respectively (10 years data up to 2010 were provided by the Morogoro Meteorological Station). Agriculture is the major socioeconomic activity carried out by locals living in the two neighboring villages.
The tree sampling for the collection of data was performed in a random fashion in 18 plots of 20 m × 20 m each placed from the forest edge (100 m from forest margin) to the interior. In each plot, all trees with diameter at breast height (DBH) ≥10 cm measured at 1.3 m above the ground were counted, identified, and DBH-recorded. Trees with multiple stems at 1.3 m height were treated as a single individual and the diameters of all stems were obtained and averaged. If a tree had buttresses or abnormalities at 1.3 m height, the diameter was measured just above the buttress and the stem was assumed to have a cylindrical shape.
The forest structure was described in terms of tree density (stems/ha), basal area (m2/ha), and size class distributions (SCDs). The tree density was calculated using the number of individuals divided by sample area while the basal area was equal to 0.00007854 ×
A total of 199 trees (276 stems/ha) representing 67 species (93 species/ha) belonging to 54 genera and 26 families were identified from 0.72 ha. Fabaceae was the dominant family in the forest with 21 species, followed by Moraceae (five species) and Sterculiaceae (four species). Within the family Fabaceae, the genera
Family Importance Index Values for the studied plots in the Kilengwe Forest (RDi: relative diversity, RDe: relative density, RDo: relative dominance, and FIV: Family Importance Value).
Family | RDi | RDe | RDo | FIV |
---|---|---|---|---|
Fabaceae | 31.3 | 37.2 | 47.2 | 115.7 |
Moraceae | 7.5 | 6.0 | 7.5 | 21.0 |
Sterculiaceae | 6.0 | 6.5 | 5.8 | 18.3 |
Bignoniaceae | 4.5 | 5.5 | 3.5 | 13.5 |
Sapotaceae | 4.5 | 5.0 | 3.8 | 13.3 |
Combretaceae | 4.5 | 3.5 | 2.9 | 10.9 |
Loganiaceae | 3.0 | 3.5 | 2.9 | 9.4 |
Annonaceae | 3.0 | 3.5 | 2.7 | 9.2 |
Euphorbiaceae | 3.0 | 2.0 | 3.1 | 8.1 |
Clusiaceae | 3.0 | 1.5 | 3.2 | 7.7 |
Araliaceae | 3.0 | 2.0 | 1.8 | 6.8 |
Boraginaceae | 1.5 | 2.5 | 2.8 | 6.8 |
Burseraceae | 3.0 | 1.5 | 1.2 | 5.7 |
Rubiaceae | 3.0 | 1.5 | 0.9 | 5.4 |
Verbenaceae | 1.5 | 2.5 | 1.3 | 5.3 |
Anacardiaceae | 1.5 | 2.5 | 1.1 | 5.1 |
Ebenaceae | 1.5 | 2.5 | 1.1 | 5.1 |
Sapindaceae | 1.5 | 2.0 | 1.4 | 4.9 |
Ulmaceae | 1.5 | 2.0 | 1.2 | 4.7 |
Apocynaceae | 3.0 | 1.0 | 0.4 | 4.4 |
Meliaceae | 1.5 | 1.0 | 1.6 | 4.1 |
Salicaceae | 1.5 | 1.5 | 1.0 | 4.0 |
Tiliaceae | 1.5 | 1.0 | 0.7 | 3.2 |
Rhizophoraceae | 1.5 | 1.0 | 0.4 | 2.9 |
Simaroubaceae | 1.5 | 0.5 | 0.3 | 2.3 |
Phyllanthaceae | 1.5 | 0.5 | 0.2 | 2.2 |
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Total | 100 | 100 | 100 | 300 |
Species Importance Index Values for the studied plots in the Kilengwe Forest (Rf: relative frequency, RDe: relative density, RDo: relative dominance, and IVI: Species Importance Value).
Species name | Rf | RDe | RDo | IVI |
---|---|---|---|---|
|
3.7 | 3.5 | 6.0 | 13.3 |
|
1.9 | 1.5 | 8.1 | 11.5 |
|
3.7 | 4.0 | 3.2 | 11.0 |
|
3.1 | 3.5 | 3.6 | 10.2 |
|
3.1 | 3.5 | 3.2 | 9.8 |
|
2.5 | 2.5 | 3.2 | 8.2 |
|
2.5 | 3.0 | 2.4 | 7.9 |
|
2.5 | 3.0 | 2.0 | 7.5 |
|
1.9 | 2.5 | 2.8 | 7.1 |
|
2.5 | 2.5 | 1.9 | 6.9 |
|
3.1 | 2.5 | 1.3 | 6.9 |
|
1.9 | 2.5 | 2.4 | 6.8 |
|
1.9 | 3.0 | 1.7 | 6.6 |
|
2.5 | 2.5 | 1.6 | 6.6 |
|
1.9 | 3.0 | 1.7 | 6.6 |
|
2.5 | 2.5 | 1.4 | 6.4 |
|
2.5 | 2.5 | 1.1 | 6.1 |
|
1.9 | 2.0 | 2.2 | 6.1 |
|
2.5 | 2.5 | 1.1 | 6.1 |
|
2.5 | 2.0 | 1.4 | 5.9 |
|
1.2 | 1.5 | 3.1 | 5.9 |
|
2.5 | 2.0 | 1.2 | 5.7 |
|
1.9 | 1.5 | 2.0 | 5.4 |
|
1.2 | 2.0 | 2.0 | 5.3 |
|
1.2 | 1.5 | 2.5 | 5.2 |
|
1.2 | 2.0 | 1.8 | 5.0 |
|
1.2 | 1.5 | 2.2 | 5.0 |
|
1.2 | 1.0 | 2.6 | 4.8 |
|
1.9 | 1.5 | 1.3 | 4.7 |
|
1.9 | 1.5 | 1.1 | 4.5 |
|
0.6 | 0.5 | 3.3 | 4.4 |
|
1.2 | 1.5 | 1.5 | 4.3 |
|
1.2 | 1.0 | 2.0 | 4.2 |
|
1.9 | 1.5 | 0.7 | 4.1 |
|
1.2 | 1.0 | 1.6 | 3.8 |
|
1.2 | 1.5 | 1.0 | 3.8 |
|
0.6 | 0.5 | 2.4 | 3.6 |
|
1.2 | 1.0 | 1.2 | 3.5 |
|
1.2 | 1.0 | 1.0 | 3.3 |
|
1.2 | 1.0 | 1.0 | 3.2 |
|
1.2 | 1.0 | 0.9 | 3.1 |
|
1.2 | 1.0 | 0.7 | 3.0 |
|
1.2 | 1.0 | 0.7 | 2.9 |
|
1.2 | 1.0 | 0.6 | 2.8 |
|
1.2 | 1.0 | 0.5 | 2.8 |
|
1.2 | 1.0 | 0.5 | 2.7 |
|
1.2 | 1.0 | 0.4 | 2.7 |
|
1.2 | 1.0 | 0.4 | 2.6 |
|
1.2 | 1.0 | 0.4 | 2.6 |
|
0.6 | 0.5 | 1.1 | 2.2 |
|
0.6 | 0.5 | 0.9 | 2.0 |
|
0.6 | 1.0 | 0.4 | 2.0 |
|
0.6 | 0.5 | 0.7 | 1.8 |
|
0.6 | 0.5 | 0.5 | 1.6 |
|
0.6 | 0.5 | 0.5 | 1.6 |
|
0.6 | 0.5 | 0.4 | 1.5 |
|
0.6 | 0.5 | 0.3 | 1.5 |
|
0.6 | 0.5 | 0.3 | 1.4 |
|
0.6 | 0.5 | 0.3 | 1.4 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
|
0.6 | 0.5 | 0.2 | 1.3 |
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Total | 100 | 100 | 100 | 300 |
Frequency distribution of the tree species recorded in the present study.
A total of 199 individuals (276 stems/ha) were recorded in the 0.72 ha study area. The family Fabaceae accounted for 37.2% of the total individuals, followed by Sterculiaceae (6.5%) and Moraceae (6.0%). Among the members of the family Fabaceae,
Structure and diversity indices of Kilengwe Forest.
Parameter | Value |
---|---|
Number of individuals/ha ( |
|
Number of species/ha ( |
|
|
2.97 |
Shannon-Wiener’s index (±SD) |
|
Fisher’s alpha (±SD) |
|
Evenness (±SE) |
|
MMMeans | 124 |
Jackknife 1 (±SD) |
|
Mean basal area (±SE) m2/ha |
|
The species richness of 67 species was observed in 0.72 ha of the Kilengwe Forest, whereas, the MMMeans and Jackknife 1 richness estimators provided the estimate of 124 and 86 species, respectively. The Fisher’s alpha, Shannon-Wiener diversity, and evenness index values of 35.50, 4.02, and 0.95 were recorded, respectively. The ratio of the number of individuals to the number species (N/S) in the studied plots was 2.97 (see Table
The tree size class distribution in the forest (Figure
The species richness of 93 species/ha is considerably higher compared to the range of 8–66 species/ha recorded by Malimbwi et al. [
The IVI is commonly used in ecological studies as it shows ecological importance of a species in a given ecosystem. The IVI is also used for prioritizing species conservation whereby species with low IVI value need high conservation priority compared to the ones with high IVI [
Species accumulation curves based on (a) numbers of individual trees and (b) cumulative sample area in the forest.
Size class distribution of the trees species recorded in the present study.
Both species-area and species-individual curves displayed an escalating trend, which suggest that increasing the sampling effort (i.e., area and individuals) would increase the observed species richness. This is due to the fact that the larger the forest area sampled is, the more environmentally heterogeneous the sampling area becomes. The observed trend in both curves coincide with the two used species richness estimators (Jackknife 1 and MMMeans) in Table
Density, basal area, frequency distribution, and size or DBH class distributions of trees contribute to the structure of the forest. The forest density and basal area were lower by 7% and 37%, respectively, compared to the values obtained by Malimbwi et al. [
The frequency class distributions showed that 78% of the total species fell in the 0%–10% and 10.0%–19.9% frequency classes whereas the higher frequency classes >40% were not represented. Such a result suggests that most of the species had low occurrence as would be expected in a typical species-abundance distribution. Normally, a tree species is considered homogeneously distributed when the numbers of individuals are equal in all parts of the community. Thus, the frequency distribution analysis indicates the presence of high degree of floristic heterogeneity in the forest. Usually, frequency reflects the pattern of distribution and provides an approximate indication of the heterogeneity of the forest [
Understanding tree species composition, diversity, and structure is a vital instrument in assessing sustainability of any forest, conservation of species, and management of the ecosystems at large [
The author declares that there is no conflict of interests regarding the publication of this paper.
The author is thankful to the Department of Forest in Morogoro Department for permission to access the forest transport logistics and advice when needed. Also, appreciation is extended to the Deutscher Akademischer Austausch Dienst (DAAD) for funding the project.