| 1. |
- Cromsigt, Joris
(författare)
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A sharp floristic discontinuity revealed by the biogeographic regionalization of African savannas
- 2019
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Ingår i: Journal of Biogeography. - : Wiley. - 0305-0270 .- 1365-2699. ; 46, s. 454-465
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Tidskriftsartikel (refereegranskat)abstract
- Aim In tropical Africa, savannas cover huge areas, have high plant species richness and are considered as a major natural resource for most countries. There is, however, little information available on their floristics and biogeography at the continental scale, despite the importance of such information for our understanding of the drivers of species diversity at various scales and for effective conservation and management. Here, we collated and analysed floristic data from across the continent in order to propose a biogeographical regionalization for African savannas. Location We collated floristic information (specifically woody species lists) for 298 samples of savanna vegetation across Africa, extending from 18 degrees N to 33 degrees S and from 17 degrees W to 48 degrees E. Taxa We focused on native woody species. Methods We used ordination and clustering to identify the floristic discontinuities and gradual transitions across African savannas. Floristic relationships, specificity and turnover, within and between floristic clusters, were analysed using a (dis-)similarity-based approach. Results We identified eight floristic clusters across African savannas which in turn were grouped into two larger macro-units. Ordinations at species and genus levels showed a clear differentiation in woody species composition between the North/West macro-unit and the South/East macro-unit. This floristic discontinuity matches to the High (i.e. N&W) and Low (S&E) division of Africa previously proposed by White () and which tracks climatic and topographical variation. In the N&W savannas, the floristic gradient determined by rainfall was partitioned into the Sudanian (drier) and Guinean (wetter) clusters. Within the highly heterogeneous S&E savannas and woodlands, six clusters were identified: Ugandan, Ethiopian, Mozambican, Zambezian, Namibian and South African. Main conclusions The proposed pan-African classification of savannas and woodlands might assist the development of coordinated management and conservation policies.
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| 2. |
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| 3. |
- Cromsigt, Joris
(författare)
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Brown world forests: increased ungulate browsing keeps temperate trees in recruitment bottlenecks in resource hotspots.
- 2017
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Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 214, s. 158-168
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Tidskriftsartikel (refereegranskat)abstract
- * Plant biomass consumers (mammalian herbivory and fire) are increasingly seen as major drivers of ecosystem structure and function but the prevailing paradigm in temperate forest ecology is still that their dynamics are mainly bottom-up resource-controlled. Using conceptual advances from savanna ecology, particularly the demographic bottleneck model, we present a novel view on temperate forest dynamics that integrates consumer and resource control. * We used a fully factorial experiment, with varying levels of ungulate herbivory and resource (light) availability, to investigate how these factors shape recruitment of five temperate tree species. We ran simulations to project how inter- and intraspecific differences in height increment under the different experimental scenarios influence long-term recruitment of tree species. * Strong herbivore-driven demographic bottlenecks occurred in our temperate forest system, and bottlenecks were as strong under resource-rich as under resource-poor conditions. Increased browsing by herbivores in resource-rich patches strongly counteracted the increased escape strength of saplings in these patches. * This finding is a crucial extension of the demographic bottleneck model which assumes that increased resource availability allows plants to more easily escape consumer-driven bottlenecks. Our study demonstrates that a more dynamic understanding of consumer-resource interactions is necessary, where consumers and plants both respond to resource availability.
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| 4. |
- Cromsigt, Joris
(författare)
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Comparing the impact of a grazing regime with European bison versus one with free-ranging cattle on coastal dune vegetation in the Netherlands
- 2018
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Ingår i: Mammal Research. - : Springer Science and Business Media LLC. - 2199-2401 .- 2199-241X. ; 63, s. 455-466
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Tidskriftsartikel (refereegranskat)abstract
- Woody plant encroachment has increased across the globe and threatens biodiversity associated with open habitats. In order to prevent or reduce woody encroachment, conservation managers across Europe introduce large mammalian herbivores. While up to recently, managers were mostly using free-ranging domestic cattle and horses for this, there is an increasing interest in the use of European bison for nature management. However, we lack studies that compare the impact of these different grazers on vegetation. We report results from a unique grazing pilot in the National Park Zuid-Kennemerland, a heterogeneous coastal dune landscape in the Netherlands, where European bison, horses, and cattle were introduced to reverse the encroachment of grass and shrub species. We present results of an 8-year study on the development of woody and grassy vegetation on fixed transects in three different grazing areas within the national park; one area with European bison and horses, one area with cattle and horses, and one area where these large grazers were excluded. In all three areas, rabbit, fallow deer, and roe deer were present. Over time, we observed strong reductions in the vitality of several woody species, such as spindle tree, and this decline was similar across all areas. Grass height and cover also declined and the proportion of herbs increased in all three grazing areas in similar ways. However, the type of herbivore use (debarking, foraging on buds, branches) of several woody species differed significantly among areas. For instance, maple tree was only debarked in the E. bison area, while hawthorn branches were eaten significantly more in the cattle than in the bison area. Due to differences in herbivore densities among areas, it was difficult to draw strong conclusions on how the different herbivore species differed in their impact, but, importantly, we found that grazing regimes with bison can lead to as strong effects on vegetation structure and composition as grazing regimes with cattle. This is an important result since certain conditions, such as legal aspects, may motivate managers to introduce a wild large grazer rather than a domesticated one.
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| 5. |
- Cromsigt, Joris
(författare)
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Different-sized grazers have distinctive effects on plant functional composition of an African savannah
- 2016
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 104, s. 864-875
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Tidskriftsartikel (refereegranskat)abstract
- 1. Grazing ungulates play a key role in many ecosystems worldwide and can form diverse assemblages, such as in African savannahs. In many of these ecosystems, present-day ungulate communities are impoverished subsets of once diverse assemblages. While we know that excluding all ungulates from grasslands can exert major effects on both the structure and composition of the vegetation, how different individual ungulate species may have contrasting effects on grassland communities remains poorly understood.2. Here, we performed a long-term 'Russian doll' grazing exclosure experiment in an African savannah to test for the effects of different size classes of grazers on grassland structure and composition. At five sites, grazer species of decreasing size class (ranging from white rhino to scrub hare) were excluded using four fence types, to experimentally create different realized grazer assemblages. The vegetation structure and the grass functional community composition were characterized in 6 different years over a 10-year period. Additionally, animal footprints were counted to quantify the abundance of different ungulate species in each treatment.3. We found that while vegetation height was mostly driven by total grazing pressure of all species together, ungulate community composition best explained the functional community composition of grasses. In the short term, smaller ungulate species ('6mesoherbivores') had strongest effects on vegetation composition, by shifting communities towards dominance by species with low specific leaf area and low nutritional value. In the long term, large grazers had stronger but similar effects on the functional composition of the system. Surprisingly, the largest 'mega-herbivore', the white rhinoceros, did not have strong effects on the vegetation structure or composition.4. Synthesis. Our results support the idea that different size classes of grazers have varying effects on the functional composition of grassland plant communities. Therefore, the worldwide decline in the diversity of ungulate species is expected to have (had) major impacts on community composition and functioning of grassland ecosystems, even if total grazing pressure has remained constant, for example, due to replacement by livestock.
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| 6. |
- Cromsigt, Joris
(författare)
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Elephant effects on treefall and logfall highlight the absence of megaherbivores in coarse woody debris conceptual frameworks
- 2019
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 438, s. 57-62
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Tidskriftsartikel (refereegranskat)abstract
- Despite the importance of coarse woody debris (CWD) in woody ecosystems, conceptual frameworks of its dynamics currently exclude the role of the megaherbivores, focusing instead on the role of insects, disease, fire, wind and droughts. However, recognizing the ecological roles of the megaherbivores is one of the most urgent contemporary issues, particularly as their decline will likely have unanticipated outcomes at the ecosystem-level. Here we used sites with and without elephants in a semi-arid woodland ecosystem in South Africa to test whether elephants changed the quantitative and qualitative features of the CWD profile in relation to other wood producers. We show that elephants increased the abundance of CWD, influenced its quality by toppling mostly maturing trees, and changed the distribution of large woody items along gentle hillslopes. Surprisingly, and despite the recognized importance of both CWD and elephants for biodiversity, there is almost no published data on the role of elephants in shaping wood-living communities by changing fallen woody debris dynamics. Our study contributes towards developing a broader conceptual framework of CWD dynamics that includes the role of megaherbivores and provides a novel view of the ecological consequences of the loss of the Pleistocene megaherbivores. Our findings have important implications for CWD restoration efforts in transformed systems that previously supported megaherbivores.
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| 7. |
- Cromsigt, Joris
(författare)
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Keep the wolf from the door: How to conserve wolves in Europe's human-dominated landscapes?
- 2019
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Ingår i: Biological Conservation. - : Elsevier BV. - 0006-3207 .- 1873-2917. ; 235, s. 102-111
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Tidskriftsartikel (refereegranskat)abstract
- The recolonization of wolves in European human-dominated landscapes poses a conservation challenge to protect this species and manage conflicts. The question of how humans can co-exist with large carnivores often triggers strong emotions. Here we provide an objective, science-based discussion on possible management approaches. Using existing knowledge on large carnivore management from Europe and other parts of the globe, we develop four potential wolf management scenarios; 1) population control, 2) protection and compensation, 3) fencing, 4) managing behaviour of wolf and man. For each scenario, we discuss its impact on wolf ecology, its prospects of reducing wolf-human conflicts and how it relates to current European legislation. Population control and fencing of local wolf populations are problematic because of their ecological impacts and conflicts with European legislation. In contrast, a no-interference approach does not have these problems but will likely increase human-wolf conflicts. Despite the large challenges in European, human-dominated landscapes, we argue that wolf management must focus on strengthening the separation between humans and wolves by influencing behaviour of wolves and humans on a fine spatio-temporal scale to prevent and reduce conflicts. As separation also demands a sufficiently large wild prey base, we urge restoring natural ungulate populations, to reduce human-wolf conflicts. Mutual avoidance provides the key to success, and is critical to avoid creating the conditions for reinstating wolf persecution as the default policy in Europe.
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| 8. |
- Cromsigt, Joris
(författare)
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Large herbivore assemblages in a changing climate: incorporating water dependence and thermoregulation
- 2019
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248.
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Tidskriftsartikel (refereegranskat)abstract
- The coexistence of different species of large herbivores (ungulates) in grasslands and savannas has fascinated ecologists for decades. However, changes in climate, land-use and trophic structure of ecosystems increasingly jeopardise the persistence of such diverse assemblages. Body size has been used successfully to explain ungulate niche differentiation with regard to food requirements and predation sensitivity. But this single trait axis insufficiently captures interspecific differences in water requirements and thermoregulatory capacity and thus sensitivity to climate change. Here, we develop a two-dimensional trait space of body size and minimum dung moisture content that characterises the combined food and water requirements of large herbivores. From this, we predict that increased spatial homogeneity in water availability in drylands reduces the number of ungulate species that will coexist. But we also predict that extreme droughts will cause the larger, water-dependent grazers as wildebeest, zebra and buffalo-dominant species in savanna ecosystems - to be replaced by smaller, less water-dependent species. Subsequently, we explore how other constraints such as predation risk and thermoregulation are connected to this two-dimensional framework. Our novel framework integrates multiple simultaneous stressors for herbivores and yields an extensive set of testable hypotheses about the expected changes in large herbivore community composition following climate change.
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| 9. |
- Cromsigt, Joris
(författare)
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Legacy effects of different land-use histories interact with current grazing patterns to determine grazing lawn soil properties
- 2015
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 18, s. 720-733
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Tidskriftsartikel (refereegranskat)abstract
- Pastoralism and agriculture have affected rangeland ecosystems over the past millennia, including many ecosystems that are currently protected as reserves. However, the legacy of these land-use practices on current ecosystem functioning remains unclear. We studied legacy effects of former human land use on soil physical and chemical properties in a South African savanna. We did this by comparing soil properties in grazing lawns (patches of short grass maintained by the positive feedback between grazing intensity and forage quality) with the surrounding less grazed bunch grasslands within three different human land-use history contexts: (i) Abandoned bomas: permanent stone enclosures where livestock were kept overnight, and dung and urine accumulated for several years or decades. (ii) Old fields: areas where vegetation was cleared, soil tilled, and cultivated, but received little or no fertilization. (iii) Natural grasslands: not cultivated but grazed by livestock before the establishment of the reserve and wildlife thereafter. Former human land use rather than soil texture was the main determinant of grazing lawn location. Moreover, lawn soil properties also varied among land-use histories. In all grazing lawns, soil nutrient concentrations were higher than in adjacent grasslands but abandoned bomas contained three times more phosphorus, and twice as much nitrogen and carbon than old fields and natural grassland lawns. In addition to past land use, soil texture influenced lawn soil nutrients: Concentrations of phosphorus, potassium, calcium, magnesium, total nitrogen, and carbon in lawns were higher on clayey soils than sandy soils, whereas phosphorus, C:N ratio, and pH did not change with soil texture. Our study confirms previous findings on the effect of human land use on savanna heterogeneity, but also highlights how legacy effects may vary among different historic land-use practices.
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| 10. |
- Cromsigt, Joris
(författare)
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Mammalian herbivores, grass height and rainfall drive termite activity at different spatial scales in an African savanna
- 2016
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Ingår i: Biotropica. - : Wiley. - 0006-3606. ; 48, s. 656-666
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Tidskriftsartikel (refereegranskat)abstract
- Termites have a large influence on ecosystem functioning. Understanding what drives termite activity patterns improves understanding of nutrient cycling, productivity, and heterogeneity in savannas. We present a mechanistic framework that relates the interactive effects of rainfall, grassland structure, large herbivore presence, and soil factors to termite activity. To test this framework, we used grass litterbags to monitor termite activity at ten sites across Hluhluwe-iMfolozi Park, South Africa. We assessed the effects of abiotic and biotic factors on termite activity at two scales: the large (landscape) scale, variation in bait removal among 300m2 plots that were distributed across the park and at the small (within-plot) scale (1-300m2). Half of our sites were located inside large herbivore exclosures to test for the effect of mammalian herbivore presence. At the landscape scale, termite grass removal declined towards higher rainfall and in the presence of mammalian herbivores. Removal did not depend on soil factors. At the small scale, removal declined with increasing grass height, particularly in the 1m surrounding the bait bag. Resource quality did not affect bait removal. We suggest that competition for forage drives the negative effect of mammalian herbivores on termites, whereas lower bait removal in taller swards may be due to direct negative effects from rainfall, fire and/or competition with free-living microbes. Ultimately, we suggest that the impact of termites on nutrient cycling is most pronounced when abiotic (rainfall) and biotic conditions (mammalian herbivory) limit grass removal by fire and decomposition by free-living microbes.
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