Cross-boundary human impacts compromise the Serengeti-Mara ecosystem

Veldhuis, Michiel P.; Ritchie, Mark E.; Ogutu, Joseph O.; Morrison, Thomas A.; Beale, Colin M.; Estes, Anna B.; Mwakilema, William; Ojwang, Gordon O.; Parr, Catherine L.; Probert, James; Wargute, Patrick W.; Hopcraft, J. Grant C.; Olff, Han

doi:10.1126/science.aav0564

Cited by 178 publications

(185 citation statements)

References 69 publications

Supporting

Mentioning

180

Contrasting

Order By: Relevance

“…If anything, the positive association between browser biomass and tree cover suggests that this guild is attracted to areas of high food availability (i.e., trees), rather than causing a lack of trees in open areas. The latter is often the case in savannah ecosystems, where spatial constraints on animal population densities such as water availability, predation risk or human-driven compression can have downstream effects on vegetation (Atkins et al, 2019;Glover, 1963;Valeix, Fritz, Chamaillé-Jammes, Bourgarel, & Murindagomo, 2008;Veldhuis et al, 2019). For example, areas close to permanent water sources can be heavily impacted by elephant browsing, creating a negative relationship between elephant population density and tree cover (Glover, 1963;Mosugelo, Moe, Ringrose, & Nellemann, 2002).…”

Section: Discussionmentioning

confidence: 99%

Spatial transitions in tree cover are associated with soil hydrology, but not with grass biomass, fire frequency, or herbivore biomass in Serengeti savannahs

et al. 2019

View full text Add to dashboard Cite

Although there is a well‐known association between tree cover and soil texture in savannahs, the hydrological drivers of tree cover variation have not been systematically explored, particularly in parallel with factors such as fire, herbivory, and tree–grass interactions. The relationship between hydrological factors and tree cover is important for resolving the relative contribution of bottom‐up versus top‐down factors in structuring savannah vegetation. We quantified soil moisture dynamics across eight 1‐km transects spanning tree cover gradients from open to woody savannah in Serengeti National Park in Tanzania using soil moisture sensors coupled with dataloggers. We mapped tree cover at two spatial scales through supervised classification of high‐resolution satellite imagery. We simultaneously produced water retention curves in open and woody habitats within each transect to compare soil hydrological properties and to convert volumetric water content (θ) from dataloggers to plant‐available water over the course of an annual cycle. We also quantified grass biomass at 100 locations per transect, estimated fire frequency from MODIS satellite data, and quantified herbivore occupancy with paired camera traps situated in open and woody habitats within each transect. We found a positive relationship between tree cover and soil moisture drainage rate, and found that open habitats had more negative water potentials than woody habitats for a given value of θ. In contrast, we found no evidence for a consistent relationship between grass biomass or fire frequency and tree cover. We found evidence for higher browser occupancy in woody than open habitats, but no habitat effects on herbivores as a group (browsers plus grazers), suggesting that herbivory is unlikely to be the dominant factor explaining variation in tree cover. Synthesis. Our results suggest that variation in tree cover is partly driven by hydrological (edaphic) factors unrelated to fire, herbivory, tree–grass interactions or mean annual precipitation at these spatial scales in Serengeti. We contrast our findings with previous work attributing tree cover shifts in Serengeti to precipitation gradients.

show abstract

Section: Discussionmentioning

confidence: 99%

Spatial transitions in tree cover are associated with soil hydrology, but not with grass biomass, fire frequency, or herbivore biomass in Serengeti savannahs

et al. 2019

View full text Add to dashboard Cite

show abstract

“…Pasturelands adjacent to wildlife‐protected areas in tropical savannahs provide an important buffer area that can be occupied by wild herbivores for short durations of the year, as seen in our system (see also Veldhuis et al, ). To ensure these pasturelands sustain herbaceous biomass as forage for both wildlife and livestock herbivores, it is necessary to preserve tall trees (Smit, , ), i.e.…”

Section: Discussionmentioning

confidence: 79%

Section: Methodsmentioning

confidence: 99%

“…Outside the park, intense livestock grazing usually results in reduced fire frequencies due to insufficient fuel loads in the dry season, in contrast to regular burning undertaken by park managers inside the protected areas (Veldhuis et al, ). By selecting sites at the periphery of protected areas we aimed to reduce variation in fire frequency given an increasing retraction of fire from the boundaries of the Serengeti ecosystem (Veldhuis et al, ). However, minimising variation in fire history was not possible and mesic protected areas ranged from 2 to 12 years since the last fire (average six fires over 16 year period from 2000), mesic pastures 6 years (six fires over 16 years), wet protected areas 2 years (seven fires over 16 years).…”

Section: Methodsmentioning

confidence: 99%

“…Across the savannah biome, the highest rates of tree clearance and land conversion from wildlife to livestock-dominated savannah are concentrated at the borders of protected areas, e.g., national parks (Beale et al, 2013;Fynn, Augustine, Peel, & Garine-Wichatitsky, 2016;Veldhuis et al, 2019). Thus, we directed our attention to an increasingly common juxtaposition of wildlife-versus livestock-dominated savannah across the border of the Serengeti National Park, Tanzania, and its impact on tree-herbaceous vegetation interactions.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Savannah trees buffer herbaceous plant biomass against wild and domestic herbivores

Smith

Graae

Bukombe

et al. 2020

Applied Vegetation Science

View full text Add to dashboard Cite

Questions Given the growing abundance and dominance of domestic herbivores in savannah ecosystems, can trees maintain plant herbaceous standing biomass under increasing herbivore pressure? Are there differences in the capacity of leguminous and non‐leguminous trees in sustaining understory herbaceous biomass? And finally, to what extent does plant community composition underneath trees modulate the effects of herbivore assemblage and abundance on herbaceous biomass? Location Pasturelands and protected areas along the borders of the Serengeti National Park, Tanzania, East Africa. Method Monthly herbaceous biomass was monitored non‐destructively using a calibrated pasture disc. Measurements were taken within a network of paired exclosures and open plots, underneath large leguminous and non‐leguminous tree canopies and outside canopies. Herbivore community assemblage compositions and abundances were characterised using monthly dung counts, and herbaceous plant community composition was surveyed annually every wet season over two years. Results Overall, we found that trees promote herbaceous standing biomass, particularly in the presence of moderate herbivory rather than under herbivore exclusion. Greater herbivore abundance and livestock dominance reduced herbaceous plant biomass, but trees, particularly leguminous trees, limited these negative effects. This capacity for trees to limit the effect of herbivores was related to herbaceous plant species composition. Understory plant communities that were compositionally typical of protected areas sustained the highest plant biomass when found in pasturelands with high herbivore pressure. Conclusion Our findings give greater credence to the importance of preserving large trees in savannah landscapes increasingly dominated by high abundances of livestock. Moreover, our results highlight that park managers and pastoralists need to maintain the specialist herbaceous understory community beneath trees in order to benefit from facilitative tree–understory interactions.

show abstract

Non‐local effects of human activity on the spatial distribution of migratory wildlife in Serengeti National Park, Tanzania

Kavwele

Torney

Morrison

et al. 2022

Ecol Sol and Evidence

Self Cite

View full text Add to dashboard Cite

1. Human activities are transforming landscapes and altering the structure and functioning of ecosystems worldwide and often result in sharp contrasts between human-dominated landscapes and adjacent natural habitats that lead to the creation of hard edges and artificial boundaries. The configuration of these boundaries could influence local biotic interactions and animal behaviours.2. Here, we investigate whether boundaries of different degrees of 'hardness' affect space utilization by migratory species in Serengeti National Park, Tanzania. We deployed camera traps along transects perpendicular to the national park boundary at three different locales. The transects were located in areas that consisted of two types of human-wildlife interface: a sudden transition from the national park into agro-pastoral land use (termed a 'hard' boundary) and a more gradual transition mediated by a shared usage area (termed a 'soft' boundary).3. Camera traps were placed at 2 km intervals along each 10 km transect from the edge towards the core of the park and were programmed to collect images hourly between dawn and dusk between June 2016 and March 2019. We used a deep neural network to detect the presence of wildlife within images and then used a Bayesian model with diffuse priors to estimate parameters of a generalized linear model with a Bernoulli likelihood. We explored the binomial probability of either wildebeest or zebra presence as a function of distance to the boundary, the rate of grass greening or drying (dNDVI) and the concentration of grass protein.4. There was a strong negative effect of distance to boundary on the probability of detecting wildebeest or zebra; however, this was only observed where the transition from human-dominated landscape to protected areas was sudden. Conversely, soft boundaries had little to no effect on the probability of detecting wildebeest or zebra. The results suggest that boundary type affects migratory species occurrence.

show abstract

Cross-boundary human impacts compromise the Serengeti-Mara ecosystem

Cited by 178 publications

References 69 publications

Spatial transitions in tree cover are associated with soil hydrology, but not with grass biomass, fire frequency, or herbivore biomass in Serengeti savannahs

Spatial transitions in tree cover are associated with soil hydrology, but not with grass biomass, fire frequency, or herbivore biomass in Serengeti savannahs

Savannah trees buffer herbaceous plant biomass against wild and domestic herbivores

Non‐local effects of human activity on the spatial distribution of migratory wildlife in Serengeti National Park, Tanzania

Contact Info

Product

Resources

About