the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 31 Mar 2026
Erosion and dispersal processes drive vegetation trajectories in a highly erosive badland catchment
Abstract. Badlands are among the most erosive places on earth, providing large sediments fluxes to rivers and oceans. In these environments, erosion is strongly controlled by vegetation, whose cover and composition both vary in space and time. Quantifying vegetation dynamics and their drivers is therefore essential to understand and predict badland erosion. Here, we use time series of high-resolution aerial and Landsat satellite imageries to reconstruct 40 years of vegetation change in a highly erosive badland catchment of French south-western Alps. Vegetation cover increased from 38.7 % to 46.2 % of the studied area), primarily through the colonization of bare surfaces by young pines. Spatial patterns of colonization and extinction are driven both by geomorphic factors, such as slope stability and local erosion rate, and by ecological factors, such as grain dispersal. Remotely sensed greening trends are correlated with climate, initial vegetation type and colonization intensity, suggesting that both climate changes and ecological succession are contributing to the greening of badlands. Quantifying these spatial and temporal trends reveals that vegetation dynamics are tightly coupled with erosion, as they both control and respond to erosion patterns.
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Status: open (until 01 Jun 2026)
- RC1: 'Comment on egusphere-2026-834', Anonymous Referee #1, 13 May 2026 reply
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- 1
This paper attempts to quantify the topographic and erosion-rate controls on vegetation changes in a badland drainage basin. Based on the data, feedback mechanisms involving vegetation changes and geomorphic processes are proposed.
Concerns:
1) Suitability for the journal: the analysis is heavily focused on vegetation dynamics. Four of the five figures showing results (i.e., Figs. 2-5 out of Figs. 2-6) are focused on different remote-sensing methods for quantifying vegetation change. As such, the paper would be more suitable for Biogeosciences or a similar journal that focuses on vegetation. A lidar difference map is discussed but isn’t presented and so cannot be assessed or reviewed.
2) The paper discusses how differencing of lidar surveys conducted between 2015 and 2021 were adjusted for the “best alignment” and then combined with measured sediment losses to obtain erosion rates. The paper states that erosion rates obtained in this way assume uniform erosion across the study area (line 174). That contradicts Figure 6, which shows that slope and erosion rates are positively correlated. The authors should explain more convincingly how their "best alignment" procedure and and the assumptions inherent in that procedure may or may not be consistent with other results they present. Also, the paper presents contradictory statements about who filtered vegetation from the lidar. On lines 164-165 it states that the producer did this filtering while line 170 states that the authors did this.
3) Mismatch in time scale between vegetation changes and measured erosion rates: Vegetation changes occurred almost entirely as a transition of grassland to forest between 1994 and 2012 (Fig. 2c). The erosion rates were measured later (2015-2021). So, there is no overlap in time between the vegetation changes and the erosion rates.
4) Comments regarding Figure 6: C1: The results presented in the figure lead the authors to conclude that slope (line 311) and drainage area (line 314) are the main controls on spatial trends in vegetation change. Figure 6d (there are no letters labeling the panels of this figure, so I am just guessing that this is supposed to be panel d) shows that the transition probability to extinction approaches 1 and colonization approaches 0 as drainage area approaches 10^5-10^6 m^2. Figure 5 does not seem to show this. Areas of extinction tend to occur throughout the study area – they are not clustered in valley bottoms with drainage areas 10^5-10^6 m^2 as far as I can tell. If they are, please visualize this clearly. C2: Please help me understand how the transition probability for colonization of areas with 25% slope could be 0.5 (meaning non-colonized areas with 25% slope have a 50% probability of becoming colonized, and, as Fig. 6a shows, with all areas of slopes between 10% and 60% having transition probabilities of at least 0.3) when colonization is, in fact, extremely rare (i.e., the dark green pixels in Fig. 5 seem to make up less than 1% of the study area). This is another example in which the results presented in Figure 6 just do not seem to align with the trends (or lack thereof) in Figure 5
5) Variability in the data about mean trends: please present box plots (min, max, median, and quartiles) for each bin, rather than just the average) in Fig. 6 so that we can see how much variability is present.
6) Lines 289-290 suggest that increased veg cover and/or greening is happening worldwide. In North America, the primary temporal trend is increasing tree mortality due to an increase in wildfire size/frequency/intensity and pest infestations, both driven in part by greenhouse warming (https://doi.org/10.1016/j.foreco.2009.09.001).
7) Why focus on greening? I can understand how changes in vegetation type (Fig. 5) may be influenced by, and in turn influence, erosion rates. But I don’t see how greening (which comprises a large portion of this study) is related to erosion rates (which are primarily related to vegetation through vegetation type or percent bare ground) because greening can occur without any change in root cohesion or other aspect of vegetation that tends to be more directly related to erosion. This concern dovetails with point 1 on how this is primarily a vegetation study with limited connection to geomorphology or landscape evolution.