| 1. |
- Mantlana, K. B., et al.
(författare)
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Biomass and leaf-level gas exchange characteristics of three African savanna C-4 grass species under optimum growth conditions
- 2009
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Ingår i: African Journal of Ecology. - : Wiley. - 1365-2028 .- 0141-6707. ; 47:4, s. 482-489
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Tidskriftsartikel (refereegranskat)abstract
- C-4 savanna grass species, Digitaria eriantha, Eragrostis lehmanniana and Panicum repens, were grown under optimum growth conditions with the aim of characterizing their above- and below-ground biomass allocation and the response of their gas exchange to changes in light intensity, CO2 concentration and leaf-to-air vapour pressure deficit gradient (D-l). Digitaria eriantha showed the largest above- and below-ground biomass, high efficiency in carbon gain under light-limiting conditions, high water use efficiency (WUE) and strong stomatal sensitivity to D-l (P = 0.002; r2 = 0.5). Panicum repens had a high aboveground biomass and attained high light saturated photosynthetic rates (A(sat), 47 mu mol m-2 s-1), stomatal conductance, (g(sat), 0.25 mol m-2 s-1) at relatively high WUE. Eragrostis lehmanniana had almost half the biomass of other species, and had similar A(sat) and g(sat) but were attained at lower WUE than the other species. This species also showed the weakest stomatal response to D-l (P = 0.19, r2 = 0. 1). The potential ecological significance of the contrasting patterns of biomass allocation and variations in gas exchange parameters among the species are discussed.Resume On a fait pousser des especes herbeuses de savane de type C4, Digitaria eriantha, Eragrostis lehmanniana et Panicum repens, dans des conditions optimales dans le but de caracteriser l'allocation de leur biomasse aerienne et racinaire et la reponse de leur echange gazeux des changements d'intensite de la lumiere, de concentrations de CO2, et un gradient deficitaire (D-l) de pression de vapeur feuille-air. D. eriantha montrait la plus grande biomasse aerienne et racinaire, une grande efficience de l'assimilation de carbone dans des conditions de luminosite limitee, une grande efficience d'utilisation de l'eau (WUE) et une forte sensibilite des stomates D-l (P = 0,002; r2 = 0,5). P. repens avait une grande biomasse aerienne et atteignait des taux photosynthetiques eleves en lumiere saturee (A(sat), 47 mu mol m-2 s-1), et une conductance stomatique (g(sat) 0.25 mol m-2 s-1) une WUE relativement elevee. E. lehmanniana avait une biomasse qui etait presque la moitie de celle des autres especes et avait un A(sat) et un g(sat) similaires mais qui etaient atteints une WUE plus basse que les autres especes. Cette espece montrait aussi la plus faible reponse stomatique D-l (P = 0,19, r2 = 0,1). L'on discute de la signification ecologique potentielle de ces schemas contrastes d'allocations de biomasse et des variations des parametres des echanges gazeux entre les especes.
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| 2. |
- Mhlanga, L, et al.
(författare)
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Observations on limnological conditions associated with a fish kill of Oreochromis niloticus in Lake Chivero following collapse of an algal bloom
- 2006
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Ingår i: African Journal of Ecology. - : Wiley. - 1365-2028 .- 0141-6707. ; 44:2, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- Possible causes of deaths of Oreochromis niloticus in Lake Chivero were examined in relation to changes in limnological conditions monitored over a 25-month period. The fish deaths coincided with the collapse of an algal bloom that had developed and builtup in the lake for 8 months. Chlorophyll a and dissolved oxygen increased to average concentrations of 42.4 mu g l(-1) and 10.9 mg l(-1) respectively prior to the collapse of the bloom. Dissolved oxygen decreased when the bloom started to die off and coincided with the fish deaths when the average surface dissolved oxygen concentration in the lake was 3.9 mg l(-1) and was at a depth of 5 m < 2 mg l(-1). Mortality probably resulted from depressed oxygen levels caused by the high oxygen demand from the massive algal die-off and released algal toxins. This is the first time that die-off of algae has been linked to fish-kills in Lake Chivero as occurs in other hypereutrophic systems.
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| 3. |
- Monadjem, Ara, et al.
(författare)
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The activity of an insectivorous bat Neoromicia nana on tracks in logged and unlogged forest in tropical Africa
- 2010
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Ingår i: African Journal of Ecology. - : Wiley. - 1365-2028 .- 0141-6707. ; 48:4, s. 1083-1091
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Tidskriftsartikel (refereegranskat)abstract
- Logging activities and the associated creation of roads and tracks can disturb and fragment forests, which may lead to a loss of forest-dependent species and possibly favour nonforest generalists and edge species. The effects of such disturbance are poorly known for African insectivorous bats. We studied the activity patterns of insectivorous bats in a tropical African forest at Kibale National Park, Uganda, using an Anabat bat detector. The echolocation calls of the vespertilionid bat Neoromicia nana were the most frequently detected. This species was most active in the first 5 h after sunset with activity declining rapidly after midnight until sampling finished at 01:00 h. There was no difference in activity of N. nana levels between logged or undisturbed forest; however, this species exhibited higher levels of activity along the wide tracks running through the two forests than either 30 m off these tracks or along the narrow forest trails. The wing morphology and echolocation call of N. nana may be constraining it to flying in uncluttered space on the edge of the forest, penetrating mostly along wider tracks and roads. Further research (in particular radio-telemetry) is required to test and validate these data.Resume
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| 4. |
- Tende, Talatu, et al.
(författare)
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Population size of lions in Yankari Game Reserve as revealed by faecal DNA sampling
- 2010
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Ingår i: African Journal of Ecology. - : Wiley. - 1365-2028 .- 0141-6707. ; 48:4, s. 949-952
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Tidskriftsartikel (refereegranskat)abstract
- Studies have shown that lion (Panthera leo) populations in West Africa are small, isolated and fragmented. In Nigeria, lions have disappeared from unprotected areas and are nowadays found only in parks and reserves where these populations may still decline. It is therefore urgent to obtain reliable estimates of population sizes at different localities. Direct observational surveys may either fail to count all individuals or count some individuals repeatedly and are therefore associated with unknown levels of estimation errors. More accurate estimates can be obtained if direct counting is combined with DNA-based individual identification. As lions are difficult to identify individually, presented here is a method that can be a valuable addition to the existing census methods.Resume Des etudes ont montre que les populations de lions Panthera leo d'Afrique de l'Ouest sont petites, isolees et fragmentees. Au Nigeria, les lions ont disparu des zones non protegees et ne se trouvent plus aujourd'hui que dans des parcs et des reserves ou leurs populations peuvent d'ailleurs encore decliner. Il est donc urgent d'avoir des estimations fiables de la taille des populations en differents endroits. Les etudes par observations directes risquent de ne pas reussir a compter tous les individus ou, a l'oppose, d'en compter certains plusieurs fois, et on les associe des lors de niveaux d'erreur d'estimation inconnus. On peut obtenir des estimations plus precises si les comptages directs sont combines avec des identifications individuelles basees sur des analyses d'ADN. Comme les lions sont difficiles a identifier individuellement, voici presentee ici une methode qui peut etre un ajout interessant aux methodes de recensement existantes.
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| 5. |
- Börjeson, Lowe, 1968-
(författare)
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Using a historical map as a baseline in a land-cover change study of northeast Tanzania
- 2009
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Ingår i: African Journal of Ecology. - Chichester : Wiley-Blackwell. - 0141-6707 .- 1365-2028. ; 47:s1, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- Vegetation data in an early 20th century map from northern Tanzania are presented and discussed for its potential of expanding the analytical time-frame in studies of land-use and land-cover change. The starting point is that much research on land-use and land-cover change suffers from a time-frame bias, caused by limitations in remote sensing data. At the same time, the use of historical maps as a complementary data-set is rather insignificant. Can information in historical maps be used to extend the baseline in land-use and land-cover change studies? The historical context of the vegetation data is evaluated, and as an illustration of its potential for interdisciplinary research on land-cover and ecosystems change, a section of the map is juxtaposed with a recent pollen record specifically addressing the impact of a 'large infrequent disturbance' (LID) event at the end of the 19th century. It is concluded that the vegetation data in the map are not likely to be reflecting an extreme situation due to the LID event. Finally, the historical vegetation data were visually compared with a national 1995 land-cover data set, illustrating the possibility of using the map data as a baseline in land-cover change studies.
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| 6. |
- Gerhardt, Karin
(författare)
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Natural regeneration and population dynamics of the tree Afzelia quanzensis in woodlands in Southern Africa
- 2009
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Ingår i: African Journal of Ecology. - : Wiley. - 0141-6707 .- 1365-2028. ; 47, s. 583-591
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Tidskriftsartikel (refereegranskat)abstract
- The logging of tree species of high commercial value is increasing throughout the African continent, yet the ecology of these species is generally poorly known. We studied the regeneration pattern and size class distribution of Afzelia quanzensis populations in northern South Africa over a 5-year period. Recruitment was low as the annual seedling mortality was > 65%. Seedlings were located under the canopy and were affected by drought and browsing. The adults were scattered or were in a clump-dispersed pattern, which would result in higher recruitment of offspring near parents. Individuals of 0-10 cm diameter at breast height (DBH) were few, while there were 32 trees ha-1 at > 10 cm DBH with an annual mortality of 0.8%. Annual diameter increments varied between 0.06 and 0.28 cm. It appears that the transition from the sapling into the juvenile stage could be a bottleneck in the regeneration of the species. A longer study, including more rainfall cycles, may reveal other patterns as dry and wet years have different impacts on dynamics.
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| 7. |
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| 8. |
- Olsson, Mats
(författare)
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Scattered trees as modifiers of agricultural landscapes: the role of waddeessa (Cordia africana Lam.) trees in Bako area, Oromia, Ethiopia
- 2009
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Ingår i: African Journal of Ecology. - : Wiley. - 0141-6707 .- 1365-2028. ; 47, s. 78-83
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Tidskriftsartikel (refereegranskat)abstract
- Scattered trees in general and scattered waddeessa (Cordia africana Lam.) trees in particular are very common across the agricultural landscapes in Oromia, Ethiopia. A study on this scattered waddeessa trees commonly growing on farmers' agricultural fields was conducted at Bako in western Oromia, Ethiopia with the objective of assessing their role in modifying the soil properties in the agricultural landscape. Soil samples from surface layers (0-10 cm) were taken at three concentric transects (0.5, 2 and 4 m) around the tree and compared with soil samples from the adjacent open areas (15 m distance from the tree), and then analysed following the standard procedures. Results showed that scattered waddeessa trees significantly modified the overall properties of the soil in the agricultural landscape of Bako area. But soil texture was not affected, indicating that it is more related to parent material than the tree influence. Hence, the soil patches observed under these waddeessa trees can be important local nutrient reserves that may influence the rural agricultural landscape. They also play an important role in generating local household income from the sale of products and conserving biodiversity by providing habitats and resources that are otherwise absent or scarce in agricultural landscape.
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| 9. |
- Savadogo, Patrice, et al.
(författare)
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Herbaceous phytomass and nutrient concentrations of four grass species in Sudanian savanna woodland subjected to recurrent early fire
- 2009
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Ingår i: African Journal of Ecology. - : Wiley. - 0141-6707 .- 1365-2028. ; 47, s. 699-710
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Tidskriftsartikel (refereegranskat)abstract
- Fire is an integral ecological factor in African savanna ecosystems, but its effects on savanna productivity are highly variable and less understood. We conducted a field experiment to quantify changes in herbaceous phytomass and nutrient composition in a Sudanian savanna woodland subjected to annual early fire from 1993 to 2004. Fire effects were also assessed on two perennial and two annual grass species during the following growing season. Early fire significantly reduced above-ground phytomass of the studied species (P = 0.03), their crude protein (P = 0.022), neutral detergent insoluble crude protein (P = 0.016) and concentrations of Ca, Fe and Mn (P < 0.05). Perennial grasses had higher above-ground phytomass but lower total crude protein and fat than annual grasses. Nonstructural carbohydrates tended to be higher for annuals, while fibre and lignin contents were high for perennials. Except Na and Fe, the concentration of mineral elements varied between species. Fire did not affect measures of digestibility and metabolizable energy, but its effect differed significantly among species. In conclusion, the results illustrate that long-term frequent fire will counterbalance the short-term increase in soil fertility and plant nutrient concentrations claimed to be accrued from single or less frequent fire.
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| 10. |
- Tigabu, Mulualem, et al.
(författare)
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Does designation of protected areas ensure conservation of tree diversity in the Sudanian dry forests of Burkina Faso?
- 2010
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Ingår i: African Journal of Ecology. - : Wiley. - 0141-6707 .- 1365-2028. ; 48, s. 347-360
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Tidskriftsartikel (refereegranskat)abstract
- The importance of conservation status of the forest (protected versus unprotected) at two sites with differing human population density (high versus low) on the tree diversity of a Sudanian dry forest in Burkina Faso was studied. All woody species were recorded in 127 circular plots (area = 456.16 m2), and density, dominance, frequency, importance value indices and a variety of diversity measures were calculated to assess the species composition, structure and heterogeneity. A total of 69 species, representing 26 families and 52 genera, were found. Combretaceae, Leguminosae subfamily Caesalpinioideae and Rubiaceae were the dominant families. Neither human pressure nor forest conservation status significantly influenced the tree species richness. Stem density and basal area were significantly higher at the site with high population density than otherwise. Fisher's diversity index revealed the unprotected forest at the site with low population density as the most diverse. We identified species with high conservation importance that should be enriched to maintain a viable population size. In conclusion, the current designation of protected areas seems inefficient at ensuring the conservation of tree diversity in the forest reserve. Thus, participatory conservation programme should be initiated.
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