Anneli Ekblom

Resilience and Thresholds in Savannas: Nitrogen and Fire as Drivers and Responders of Vegetation Transition

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 quasi-stable 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 δ15N 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.

Trade and society on the south-east African coast in the later first millennium AD : the case of Chibuene

The south-east coast of Africa in the later first millennium was busy with boats and the movement of goods from across the Indian Ocean to the interior. The landing places were crucial mediators in this process, in Africa as elsewhere. Investigations at the beach site of Chibuene show that a local community was supplying imported beads to such interior sites as Schroda, with the consequent emergence there of hierarchical power structures.

Anthropological contributions to historical ecology: 50 questions, infinite prospects

This paper presents the results of a consensus-driven process identifying 50 priority research questions for historical ecology obtained through crowdsourcing, literature reviews, and in-person workshopping. A deliberative approach was designed to maximize discussion and debate with defined outcomes. Two in-person workshops (in Sweden and Canada) over the course of two years and online discussions were peer facilitated to define specific key questions for historical ecology from anthropological and archaeological perspectives. The aim of this research is to showcase the variety of questions that reflect the broad scope for historical-ecological research trajectories across scientific disciplines. Historical ecology encompasses research concerned with decadal, centennial, and millennial human-environmental interactions, and the consequences that those relationships have in the formation of contemporary landscapes. Six interrelated themes arose from our consensus-building workshop model: (1) climate and environmental change and variability; (2) multi-scalar, multi-disciplinary; (3) biodiversity and community ecology; (4) resource and environmental management and governance; (5) methods and applications; and (6) communication and policy. The 50 questions represented by these themes highlight meaningful trends in historical ecology that distill the field down to three explicit findings. First, historical ecology is fundamentally an applied research program. Second, this program seeks to understand long-term human-environment interactions with a focus on avoiding, mitigating, and reversing adverse ecological effects. Third, historical ecology is part of convergent trends toward transdisciplinary research science, which erodes scientific boundaries between the cultural and natural.

Holocene palaeo-invasions: the link between pattern, process and scale in invasion ecology?

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.

Fire history and fire ecology of Northern Kruger (KNP) and Limpopo National Park (PNL), southern Africa

This paper explores the general correlations between fire and grass/tree relationships, as represented by fossil charcoal and pollen, from different vegetation types in the savanna ecosystems of the neighbouring Kruger (KNP) and Limpopo (PNL) national parks. Our analysis suggests that the basic presumption that fire is a main driver of vegetation dynamics in the savanna ecosystem by suppressing tree seedlings and encouraging grasses needs to be re-examined. An improved approach is to understand how fire may act both as a negative and positive feedback in different vegetational phases and both as a driver and responder in transitions between phases. The correlation between arboreal pollen (AP) percentages and charcoal influx suggests that in the grassland phase (< 5% AP), fire acts as a driver of woody recruitment and as a positive feedback, i.e. potentially driving the system to shift into a savanna phase. In the savanna phase (5—10% AP) fire limits woody recruitment and acts as a negative feedback in maintaining the savanna. Thus, in the savanna phase other factors than fire alone drive the transition from savanna to woodland-forest. In the riparian phase, where evidence of farming is present particularly from AD 1600 onwards, fire appears to facilitate tree recruitment where AP ranges between c. 10 and 20% AP. Though a decline in AP abundance can be seen contemporaneously with charcoal peaks, our analysis suggests that overall, human-induced fires do not seem to have a negative impact on woody cover. Our results have implications for fire management as riparian-dominated phases and savannas with a sufficient woody cover are less sensitive to changes in fire policies than open grasslands that may, with a change in fire frequency, change into another state.

Livelihood Security, Vulnerability and Resilience: A Historical Analysis of Chibuene, Southern Mozambique

A sustainable livelihood framework is used to analyse livelihood security, vulnerability and resilience in the village of Chibuene, Vilanculos, southern Mozambique from a historical and contemporary perspective. Interviews, assessments, archaeology, palaeoecology and written sources are used to address tangible and intangible aspects of livelihood security. The analysis shows that livelihood strategies for building resilience, diversification of resource use, social networks and trade, have long historical continuities. Vulnerability is contingent on historical processes as long-term socio-environmental insecurity and resultant biodiversity loss. These contingencies affect the social capacity to cope with vulnerability in the present. The study concludes that contingency and the extent and strength of social networks should be added as a factor in livelihood assessments. Furthermore, policies for mitigating vulnerability must build on the reality of environmental insecurity, and strengthen local structures that diversify and spread risk.

Land use history and resource utilisation from a.d. 400 to the present, at Chibuene, southern Mozambique

This paper discusses changing patterns of resource utilisation over time in the locality of Chibuene, Vilankulos, situated on the coastal plain of southern Mozambique. The macroscopic charcoal, bone and shell assemblages from archaeological excavations are presented and discussed against the off-site palaeoecological records from pollen, fungal spores and microscopic charcoal. The Chibuene landscape has experienced four phases of land use and resource utilisation that have interacted with changes in the environment. Phase 1 (a.d. 400–900), forest savanna mosaic, low intensity cattle herding and cultivation, trade of resources for domestic use. Phase 2 (a.d. 900–1400), forest savanna mosaic, high intensity/extensive cultivation and cattle herding. Phase 3 (a.d. 1400–1800), savanna woodland and progressive decrease in forests owing to droughts. Decline of agricultural activities and higher reliance on marine resources. Possible trade of resources with the interior. Phase 4 (a.d. 1800–1900), open savanna with few forest patches. Warfare and social unrest. Collapse of trade with the interior. Decline in marine resources and wildlife. Loss of cattle herds. Expansion of agriculture locally and introduction of New World crops and clearing of Brachystegia trees. The study shows the importance of combining different environmental resources for elucidating how land use and natural variability have changed over time.

Coastal forest and Miombo woodland history of the Vilankulo region, Mozambique

The present day distribution of Miombo savanna-woodland in Mozambique has been attributed to an expansion due to the clearing of original coastal forests through agriculture and use of fire. Here, we test this hypothesis using palaeoecological data from Lake Nhauhache, situated in the Vilankulo region. Our analysis shows that Brachystegia, one of the main constituents of the Miombo, has varied over time, and its variability seems to be driven by hydrological changes related to climatic variability rather than by land-use changes. The analyses show that Brachystegia was most common during ad 200–700 when a marshy forest/shrub community was dominant. After ad 700, this community changes to a dominance of Syzygium and Fagara linked to gradually rising water levels. Brachystegia remains in low abundance and fluctuating over time. From ad 1000, a general decline in trees/shrubs in favour of grasses concurs with an increase in grass pollen (possibly cereal) and charcoal, most probably as a result of farming activities. The decline in tree taxa was probably exacerbated by periodic droughts after c. ad 1200 as indicated by the diatom assemblage. In the period ad 1700 to late 1800, arboreal pollen is well represented, and this is concurrent with the diatom record suggesting high lake levels.

Vegetation dynamics within the savanna biome in southern Mozambique during the late Holocene

This study explores temporal dynamics within grassland and Miombo woodland ecosystems in southern Mozambique and their potential coupling to hydro-climate change during the late-Holocene period. Palaeo-reconstructions are based on phytolith and diatom assemblages and mineral magnetic properties in fossil sediments from Lake Chilau, southern Mozambique. Phytolith interpretation was aided by previous ecological studies on modern plants and soils. The Lake Chilau record suggests high abundance of Panicoideae and other mesophytic grasses during the AD 1200s and 1300s, followed by an increase in Chloridoideae and grasses of more xerophytic affinity between ca. AD 1400 and 1550. This vegetation transition takes place during the early phase of the so-called ‘Little Ice Age’ (LIA), when regional palaeoclimate records report a shift from warmer and wetter towards drier and cooler conditions in southern Africa. Concurrent to these shifts within the grassland biome, the Chilau record reports an increase in phytoliths associated with arboreal vegetation (ca. AD 1400–1550), probably associated with the woody component of the Miombo savanna ecosystem. This supports previous studies hypothesizing that the forest component of the Miombo savanna was favoured by LIA dryness, although at Chilau, this expansion may have been amplified by a decline in fire disturbance. These tentative responses in the woody components of the savanna biome to shifts in moisture availability in the past have implications for future management and sustainability of the Miombo ecosystem in southern Mozambique under a changing climate.

Negotiating identity and heritage through authorised vernacular history, Limpopo National Park:

In this paper, we assess vernacular history, traditional authority and the use of heritage places as mediums for negotiating ancestry, identity, territory and belonging based on conversations, interviews and visitations to heritage places together with residents in Limpopo National Park. We explore how particular vernacular histories become dominant village history through the authorisation of traditional leaders and their lineage histories and how traditional leaders use heritage places to mediate narratives. Authorised vernacular histories are narratives about mobility and identity, but they are also localised narratives about ‘home’ in terms of access to resources and heritage places. We discuss how lineage histories and traditional authority are mobilised or questioned in the context of the ongoing displacement of local residents through resettlement programmes and make comparisons with the historical experiences of evictions in the neighbouring Kruger and Gonarezhou National Parks. We emphasise the need for residents to remain connected to and in control of heritage places; otherwise, the linkages between these places, ancestral authority, and present-day authority risk being severed.