Effect of vegetation cover on millennial-scale landscape denudation rates in East Africa

Abstract

The mechanisms by which climate and vegetation affect erosion rates over various time scales lie at the heart of understanding landscape response to climate change. Plot-scale field experiments show that increased vegetation cover slows erosion, implying that faster erosion should occur under low to moderate vegetation cover. However, demonstrating this concept over long time scales and across landscapes has proven to be difficult, especially in settings complicated by tectonic forcing and variable slopes. We investigate this problem by measuring cosmogenic 10 Be-derived catchment-mean denudation rates across a range of climate zones and hillslope gradients in the Kenya Rift, and by comparing our results with those published from the Rwenzori Mountains of Uganda. We find that denudation rates from sparsely vegetated parts of the Kenya Rift are up to 0.13 mm/yr, while those from humid and more densely vegetated parts of the Kenya Rift flanks and the Rwenzori Mountains reach a maximum of 0.08 mm/yr, despite higher median hillslope gradients. While differences in lithology and recent land-use changes likely affect the denudation rates and vegetation cover values in some of our studied catchments, hillslope gradient and vegetation cover appear to explain most of the variation in denudation rates across the study area. Our results support the idea that changing vegetation cover can contribute to complex erosional responses to climate or land-use change and that vegetation cover can play an important role in determining the steady-state slopes of mountain belts through its stabilizing effects on the land surface.

Resistant rock layers amplify cosmogenically‐determined erosion rates

“…Gravitational collapse of cliff bands and deepseated debris-flows stochastically change cosmogenic isotope concentration significantly and unevenly by inducing locally deep erosion that samples sediment with low 10 Be concentrations, resulting in high calculated erosion rates (see Niemi et al, 2005). Acosta et al, 2015) might affect the depth of sediment sourcing, possibly influencing the concentration of 10 Be in sediment downstream. Slope stability impacted by vegetative cover (e.g.…”

Assessment of soil particle erodibility and sediment trapping using check dams in small semi-arid catchments

“…Slope steepness of each catchment was obtained by the proportion of the height difference of the maximum and the minimum elevation along the gully (ΔH) and the root of the catchment area (A 0.5 ). In order to determine vegetation cover, three locations including: the most upstream point of the gully, and right and left side of the gully were considered in each drainage area and the GSA image analyzer (Acosta et al, 2015) was used to analyses vertical photos of the surface vegetation cover (grasses and wheat) in small vegetation plots 1 m × 1 m with three replicates (Molina et al, 2008) (Fig. 4).…”

Evaluating process domains in small arid granitic watersheds: Case study of Pima Wash, South Mountains, Sonoran Desert, USA

“…In contrast, increases in vegetation cover lower CWDR erosion rates in the Kenya Rift with similar climate and the same granitic lithology from 130 mm/ka on sparsely vegetated slopes to 80 mm/ka on more densely vegetated slopes (Acosta et al, 2015). The key factor at Pima Wash, not factored in Amundson et al (2015) or Acosta et al (2015), is the importance of more closely spaced joints that facilitate an increase in grain porosity, that in turn facilitate surface instability and grus production (Fig.…”

“…The key factor at Pima Wash, not factored in Amundson et al (2015) or Acosta et al (2015), is the importance of more closely spaced joints that facilitate an increase in grain porosity, that in turn facilitate surface instability and grus production (Fig. 11).…”