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- Ekblom, Anneli, 1969-
(författare)
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Forest-savanna dynamics in the coastal lowland of southern Mozambique since 400 AD
- 2008
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Ingår i: The Holocene. - 0959-6836 .- 1477-0911. ; 18, s. 1247-1257
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Tidskriftsartikel (refereegranskat)abstract
- In the coastal lowlands of Mozambique, an expansion of savannas at the cost of forests has been attributed to anthropogenic influence. There are few investigations that have studied vegetation dynamics over the long term. Pollen analysis from two sedimentary cores in the Chibuene area, 7 km south of Vilanculos presented in this paper show that the coastal area 1600 years ago consisted of a mosaic of forests, Miombo woodlands and grasslands. The data also show that the area supported extensive forests in the past until AD 1400–1600 when the forests declined dramatically. Changing settlement patterns, as suggested from archaeological excavations, cannot be correlated with the forest decline and the charcoal abundance, in the sedimentary cores does not suggest an intensification of farming. Instead the decline of forests appears to be temporally correlated with a prolonged period of repeated dry spells associated with the ‘Little Ice Age’, which caused a shift in vegetation whereby typical forest species as Trema, Celtis and Moraceae were outcompeted on account of the droughts. This study challenges rooted assumptions about the cause of decline of forests in the coastal region. It also suggests that the forest fragments present on the Mozambique coast today are naturally subject to threat from climatic stress and as such are highly sensitive areas to future climate change.
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| 3. |
- Ekblom, Anneli, 1969-, et al.
(författare)
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Paleohydrology of Lake Nhaucati (southern Mozambique),c. 400 AD to present
- 2008
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Ingår i: Journal of Paleolimnology. - Dordrecht : Kluwer. - 0921-2728 .- 1573-0417. ; 40, s. 1127-1141
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Tidskriftsartikel (refereegranskat)abstract
- This paper investigates the correlations between lake level change, rainfall variability and general atmospheric forcing in southern Africa. The analysis of fossil diatom assemblages in a sediment sequence from the small, rain-fed Lake Nhaucati, southern Mozambique, is presented and discussed in relation to regional palaeoclimate data. The accumulation of organic sediments in Lake Nhaucati began 1,600 years ago when the lake level was rising. Lithology and pollen suggest a low stand at 800 AD, which correlates with other climate proxies from the summer rainfall region of southern Africa. The diatom assemblage suggests that lake levels were high between 900 and 1300 AD, with shorter low stands at c.1100 and 1200 AD. The period after 1400 AD was marked by a slow rate of accumulation and consequently a low temporal resolution. The correlation with other climate proxies in the summer rainfall region, written sources, and pollen data suggests repeated droughts corresponding to the Little Ice Age, though the driest periods may have caused complete desiccation of the lake. Higher lake levels are suggested after 1800 AD, though written sources suggest droughts in the beginning of the twentieth century. The analysis shows a good correlation with palaeoclimate data from the summer rainfall region and confirms the presence of an antiphase relationship between the summer rainfall region of southern Africa and the bi-modal rainfall region of east tropical Africa. It also supports the general hypothesis that variation in the intensity of the Inter Tropical Convergence Zone is the main agent modulating rainfall over southern and eastern Africa on centennial timescales.
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| 5. |
- Gillson, Lindsey, et al.
(författare)
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Holocene palaeo-invasions : the link between pattern,process and scale in invasion ecology?
- 2008
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Ingår i: Landscape Ecology. - : Springer Science and Business Media LLC. - 0921-2973 .- 1572-9761. ; 23:7, s. 757-769
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Tidskriftsartikel (refereegranskat)abstract
- Invasion ecology has made rapid progress in recent years through synergies with landscape ecology, niche theory, evolutionary ecology and the ecology of climate change. The palaeo-record of Holocene invasions provides a rich but presently underexploited resource in exploring the pattern and process of invasions through time. In this paper, examples from the palaeo-literature are used to illustrate the spread of species through time and space, also revealing how interactions between invader and invaded communities change over the course of an invasion. The main issues addressed are adaptation and plant migration, ecological and evolutionary interactions through time, disturbance history and the landscape ecology of invasive spread. We consider invasions as a continuous variable, which may be influenced by different environmental or ecological variables at different stages of the invasion process, and we use palaeoecological examples to describe how ecological interactions change over the course of an invasion. Finally, the use of palaeoecological information to inform the management of invasions for biodiversity conservation is discussed.
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| 6. |
- Gillson, Lindsey, et al.
(författare)
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Resilience and Thresholds in Savannas : Nitrogen and Fireas Drivers and Responders of Vegetation Transition
- 2009
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Ingår i: Ecosystems (New York. Print). - New York, N.Y. : Springer. - 1432-9840 .- 1435-0629. ; 12, s. 1189-1203
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Tidskriftsartikel (refereegranskat)abstract
- Resilience theory suggests that ecosystems can persist for long periods, before changing rapidly to a new vegetation phase. Transition between phases occurs when ecological thresholds have been crossed, and is followed by a reorganization of biotic and environmental interactions, leading to the emergence of a new vegetation phase or quasistable state. Savannas are dynamic, complex systems in which fire, herbivory, water and nutrient availability interact to determine tree abundance. Phase and transition has been observed in savannas, but the role of these different possible drivers is not always clear. In this study, our objectives were to identify phase and transition in the fossil pollen record, and then to explore the role of nitrogen and fire in these transitions using d15N isotopes and charcoal abundance. We present palaeoenvironmental data from the Kruger National Park, South Africa, which show transition between grassland and savanna phases. Our results show transition at the end of the ninth century A.D. from a nutrient and herbivore-limited grazing lawn, in which fire was absent and C4 grasses were the dominant and competitively superior plant form, to a water-, fire and herbivory-limited semi-arid savanna, in which C4 grasses and C3 trees and shrubs co-existed. The data accord with theoretical frameworks that predict that variability in ecosystems clusters in regions of higher probability space, interspersed by rapid transitions between these phases. The data are also consistent with the idea that phase transitions involve switching between different dominant driving processes or limiting factors.
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