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- Backéus, Ingvar, 1945-, et al.
(författare)
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Diameter growth of trees in miombo and acacia woodland in an eroded landscape in NE Tanzania
- 2022
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Ingår i: African Journal of Ecology. - : John Wiley & Sons. - 0141-6707 .- 1365-2028. ; 60:3, s. 714-722
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Tidskriftsartikel (refereegranskat)abstract
- Diameter increment of trees typical of miombo and acacia woodland was studied dur- ing a period of 20 years in Kondoa district, Tanzania. The study was performed in permanent plots in a severely degraded area subjected to considerable restoration efforts. A total of 15 species were selected from a database collected within a pro- ject for monitoring the landscape recovery. Growth performance of African woodland species was searched for in the literature for comparison, and a comprehensive list of citations was compiled. We found growth to fall within the range reported in earlier studies, although growth varied both between and within species. There are reports that the radial increments of trees are unimodal over their lifespan, but we found no clear support. In several species, the annual growth increased with stem diameter. Growth during the rainy ENSO year 1997/98 was pairwise compared with the preced- ing two years and was found to be significantly higher during the wet year, pointing to soil water as a limiting factor. We conclude that free development is an alternative to tree planting on marginal land.
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- Backéus, Ingvar, et al.
(författare)
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Vegetation changes on formerly overgrazed hill slopes in semi-arid central Tanzania
- 1994
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Ingår i: Journal of Vegetation Science. - 1100-9233 .- 1654-1103. ; 5, s. 327-336
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Tidskriftsartikel (refereegranskat)abstract
- Composition of hill slope vegetation was studied in a semi-arid part of upland Tanzania where all grazing had been banned for 12 yr. The hills had been severely overgrazed previously and suffered from heavy gully and sheet erosion. Eight vegetation types are described. Floristic gradients revealed by numerical ordination techniques were found to be related mainly to degree of erosion, soil type and succession. The more or less bare soil that prevailed after grazing had ceased is now covered by grassland, woodland and immature secondary forest. The grasslands are still characterized by early successional species and they will probably remain open grassland as long as frequent burning continues. Brachystegia woodlands may have developed during earlier periods when the field layer was sparse due to grazing. The grazing had reduced the frequency of fire which in turn promoted the establishment of Brachystegia spp. Secondary forests are believed to have developed mainly where fires were not frequent, particularly at higher altitudes.
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- Esbjörnsson, Eva, et al.
(författare)
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Cognitive impact of traumatic axonal injury (TAI) and return to work
- 2013
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Ingår i: Brain Injury. - : Informa UK Limited. - 0269-9052 .- 1362-301X. ; 27:5, s. 521-528
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Tidskriftsartikel (refereegranskat)abstract
- Objective: Axonal injury (AI) after traumatic brain injury (TBI) is often overlooked as an explanation Methods: The sample included 17 patients younger than 65 years old, however one died. In the acute Results: After 1 year, all patients still showed cognitive dysfunction. A recovery had been noted at 6
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| 9. |
- Hedwall, Per-Ola, et al.
(författare)
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Interactions with successional stage and nutrient status determines the life-form-specific effects of increased soil temperature on boreal forest floor vegetation
- 2015
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Ingår i: Ecology and Evolution. - : Wiley. - 2045-7758. ; 5, s. 948-960
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Tidskriftsartikel (refereegranskat)abstract
- The boreal forest is one of the largest terrestrial biomes and plays a key role for the global carbon balance and climate. The forest floor vegetation has a strong influence on the carbon and nitrogen cycles of the forests and is sensitive to changes in temperature conditions and nutrient availability. Additionally, the effects of climate warming on forest floor vegetation have been suggested to be moderated by the tree layer. Data on the effects of soil warming on forest floor vegetation from the boreal forest are, however, very scarce. We studied the effects on the forest floor vegetation in a long-term (18years) soil warming and fertilization experiment in a Norway spruce stand in northern Sweden. During the first 9years, warming favored early successional species such as grasses and forbs at the expense of dwarf shrubs and bryophytes in unfertilized stands, while the effects were smaller after fertilization. Hence, warming led to significant changes in species composition and an increase in species richness in the open canopy nutrient limited forest. After another 9years of warming and increasing tree canopy closure, most of the initial effects had ceased, indicating an interaction between forest succession and warming. The only remaining effect of warming was on the abundance of bryophytes, which contrary to the initial phase was strongly favored by warming. We propose that the suggested moderating effects of the tree layer are specific to plant life-form and conclude that the successional phase of the forest may have a considerable impact on the effects of climate change on forest floor vegetation and its feedback effects on the carbon and nitrogen cycles, and thus on the climate.
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| 10. |
- Lyaruu, Herbert V. M.
(författare)
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Seed dynamics and the ecological restoration of hill slopes of Kondoa Irangi, Central Tanzania
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Improper agricultural practices such as bill slope cultivation, extensive clearing of vegetation using fire over a long period, and to some extent overgrazing have converted the once fertile hill slopes of Kondoa Irangi in central Tanzania into unproductive marginal land. It is 25 years now since reclamation measures were introduced to save the hills from further degradation, but the regeneration process, has been rather slow. The present study was initiated with the objective to explore alternative approaches to facilitate vegetation recovery in the hills. It consisted of a description of an Afromontane dry forest, soil seed bank, seed rain and seed longevity studies, and experiments on the influence of different soil treatments on regeneration.There was significant seasonal variation in the seed bank (p < 0.001), with dry-season samples having higher densities than wet-season samples. Annual species dominated the seed bank samples in most of Kondoa Irangi Hills, but perennial species were dominant in the soil seed bank of the Afromontane dry forest. In the seed rain, both density and species richness were negatively correlated with vegetation cover. This points to the important role of anemochory and active seed rain in disturbed sites.The intermittent and extended germination of buried seeds shown by i.e., Acacia tortilis, is an adaptation to prevent synchronous germination in unpredictable, harsh environments, whereas prompt germination after rains of e.g., Acacia seyal, is a strategy to avoid seed predation.Inorganic fertilisation is not an efficient means of improving short-term productivity in poor savanna soils. Nutrient-deficiency should be corrected by moderate grazing and controlled fires.Permanent and speedy vegetation recovery of degraded savannas such as in the Kondoa IrangiHills, may require (1) enhanced nitrogen mineralization and seed dispersal by grazing livestock, (2)selective soil seed bank enrichment, and (3) transplanting seedlings with desired traits.
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