Dissimilar effects of human and elephant disturbance on woodland structure and functional bird diversity in the mopane woodlands of Zambia

Abstract

Context Humans and elephants are major disturbance agents in the African savanna woodlands. While both species remove trees, humans selectively harvest larger stems, which are less vulnerable to elephants. Increasing human pressures raise the question of how the altered disturbance regime will modify woodland structure, and in turn biodiversity and ecosystem function.Objectives Here we investigate this process in the mopane woodlands of Zambia by examining relationships between woodland structure, species and functional bird diversity, and human and elephant disturbance intensity. Methods We conducted a single-season comparison of 178 plots from 45 sites using Bayesian mixed models.Results The effect of elephants on tree density (-7.7 ± 1.6%; deviation from intercept) and bird species richness (-15 ± 6%) was greater than that of humans (density: -3.5 ± 1.5%; bird richness: -11.6 ± 4.7%). Despite this, elephants did not significantly affect woody biomass or functional bird Electronic supplementary material The online version of this article (https://doi.Landscape Ecol (2019) 34:357-371 https://doi.org/10.1007/s10980-019-00774-2( 0123456789().,-volV) ( 01234567 89().,-volV) diversity, whereas humans had a negative effect on both (woody biomass: -9.3 ± 2.3%; functional bird diversity: -5 ± 2%). Elephants were associated with reductions in species and functional turnover (5.3 ± 2.5% and 6 ± 3%, respectively). Conclusions Replacement of elephants by humans is likely to reduce woody biomass and functional bird diversity affecting the woodland structure, sustainability, and functioning. Concentrated elephant disturbance could lead to spatial homogeneity in bird species and functional compositions, potentially reducing the spatial resilience of bird communities. This is the first study to highlight how the difference between elephant and human disturbances leads to dissimilar effects on biodiversity.

Protected areas reduce deforestation and degradation and enhance woody growth across African woodlands

“…It is equally as important to note that for many PAs, though perhaps more so for wildlife reserves, the finding of positive carbon outcomes is unlikely a core target of protection, nor in some PAs, is such an outcome necessarily desirable if it conflicts with efforts to protect faunal diversity. For example, elephants, and other browsing herbivores are known to be a limiting factor to AGC 14,51 , meaning our findings of positive carbon outcomes may indicate negative trends in animal densities. However, we consider it more likely that this will impact on the prevalence of minor losses, and on the suppression vegetation growth, with observed reductions in deforestation and degradation more likely to indicate reductions in human activity 36 , which may be a positive outcome 26 .…”

“…Indeed, whilst much work has focused on the ability of PAs to reduce deforestation, it has been harder to quantify if they can mitigate habitat degradation. These subtle changes in vegetation structure, which are typically caused by processes including overharvesting, inappropriate fire regimes, and other changes in land management, and can be important in driving carbon emissions [10][11][12][13] , and lead to major changes in biodiversity 14,15 . There is similar lack of knowledge over the extent to which aboveground woody carbon (AGC) storage may be increasing via vegetation growth 16 and whether PAs have a role in mediating these patterns, e.g.…”

Detecting and predicting forest degradation: A comparison of ground surveys and remote sensing in Tanzanian forests

“…The latter is challenging to establish—particularly in systems where little is known about regeneration and growth rates. However, while systems adapted to frequent natural disturbance may be resilient to some resource extraction, the selective extraction of larger trees in old‐growth forest can negatively impact ecosystem function and biodiversity (Jew et al., 2015; Tripathi et al., 2019; Yguel et al., 2019). In addition, while there is controversy over the role of wood products in carbon storage, the damage to the surrounding vegetation in denser forests, as well as the associated transportation and processing of the timber, tend to lead to substantial emissions (Ingerson, 2009; Pearson et al., 2014).…”

Precipitation gradients drive high tree species turnover in the woodlands of eastern and southern Africa

“…However, this could result from the coarse nature of available fire and herbivory data, which may not accurately capture the disturbance experienced by these systems as these drivers may operate on smaller spatial scales. Species richness declined with increasing human footprint index, potentially due to widespread utilisation of savannas by local people (Ryan et al 2016) which can reduce tree diversity (Tripathi et al 2019(Tripathi et al , 2021.…”