the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Aug 2025
Soil erosion in Mediterranean olive groves: a review
Abstract. Olive groves are a defining feature of the Mediterranean landscape, economy, and culture. However, this keystone agroecosystem is under severe threat from soil erosion, a problem exacerbated by the region's unique topographic, climatic conditions and agricultural practices. Although soil erosion in olive groves has been extensively studied, significant uncertainties remain due to the high variability of scales and measurement methods. Knowledge gaps persist regarding the average soil loss rates and runoff coefficients as well as the effects of different management approaches and the influence of triggering factors on soil erosion rates. So far, an effort to quantify this effect on Mediterranean olive cultivation has not been made comprehensively. Therefore, the aim of this literature review is to discern clearer patterns and trends that are often obscured by the overall heterogeneity of the available data. By systematically analysing the data according to measurement methodology, this review provides clear answers to these knowledge gaps and reveals a consistent narrative about the primary drivers of soil loss. While natural factors like topography, rainfall intensity and soil properties establish a baseline risk, this review shows that agricultural management, particularly the presence of groundcovers, is the pivotal factor controlling soil degradation. The long-standing debate on erosion severity is largely reconciled by the finding that reported rates are highly dependent on the measurement methodology, and hence on the spatial and temporal scale. Conservation practices consistently reduce soil loss by more than half, an effect far more pronounced for sediment control than for runoff reduction. Ultimately, the path to sustainability requires a shift away from conventional tillage and bare-soil management towards the widespread adoption of vegetation/groundcover, driven by effective policies and a commitment to multi-scale and multi-proxy research to improve predictive models.
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RC1: 'Comment on egusphere-2025-3542', Anonymous Referee #1, 22 Oct 2025
- AC1: 'Reply on RC1', Andres Peñuela, 05 Dec 2025
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RC2: 'Comment on egusphere-2025-3542', Anonymous Referee #2, 23 Nov 2025
This paper deals with the assessment of soil erosion rates and the drivers of soil loss in Mediterranean olive groves. The paper is a review paper, gathering heterogenous data on studies of soil erosion/runoff rates in Mediterranean olive groves, considering separately different measurement methodologies, and distinguishing management practices. It is easy to read and straightforward.
It is a very useful approach, as there was so far no review giving consistent values of soil erosion rates in such environments. A very interesting focus is made on results differences between erosion/runoff rates regarding the various measurement methodologies and corresponding contrasting spatial and temporal scales. The major role of soil managmeent practices on erosion mitigation is evidenced. I have no major issue with this paper and recommend its publication providing a few minor to moderate edits are made.
Line 35 : provide a figure of the total area of olive coltivated in the Mediterranean basin.
Lines 52 to 62 : I would shorten this paragraph : too much emphasis is put on soil trunctation results, while many more methods are discussed after in the paper. I would rather highlight the large differences in erosion rates by mentioning two constrasting results. The detailed data about ST methodology is anyway presented in Table 2.
Lines 63-65 : Please mention that most if not all the methods mentioned are as well widely used for soil erosion studies for many other agricultural systems.
Lines 75-76 : I would invert the terms 'large-scale' and 'small-scale' in the text : 'large-scale' for a local study, vs. 'small scale' for a lesser detailed study.
Lines 88-100 : Please provide some references supporting your assumptions.
Lines 134-138 : the two sentences are repeting the issue with the normality of the residues distribution, this could be simplified and clarified.
Lines 153-157 : I would put this paragraph in the methods section.
Line 160, Table 2 : For runoff plots, the erosion rate unit should be either t/ha/year or t/ha.
Line 160, Table 2 : I would for the runoff plots method separate/sort the studies at the event/yearly scale for clarity purpose.
Line 215, Table 3 : I do not understand how you calculated the average erosion rate for each method, I cannot find the same values through calculation with Table 2. Could you add a sentence or two in the methods section describing briefly how you calculated the average erosion rate for each method?
Lines 177-185 : when we look at the values of soil erosion for ST studies, there is a large difference between FRN and tree-mound measurements. How could this be explained?
Lines 186-193 : I was wondering if the FG studies mentioned are only measuring suspended (0.45-63µm) sediments, as it is the case for many studies, or if the bedload is accounted for as well. While this should not change the explanations about sediment redeposition within the catchment, I wonder if this could not represent a non negligible part of the sediments that are transferred through the streams in Mediterranean landscapes.
Lines 245-251 : how was the reduction in soil loss/runoff calculated ? This % could be added as a new column in Table 2.
Lines 254-257 : some repetition in the two sentences, please simplify to clarify.
Lines 259-263 : it could rather be in the methods section.
Line 269, Table 4 : was the vegetation cover information provided in each study or how did the authors quantify this information ?
Line 269, Table 4 : the authors do present some combinations of factors for Multiple OLS regression. Are the other combinations (e.g. clay + veg cover) not statistically significant?
Lines 272-280, 284-285, 347-349 : since the methods section deals with the issue of log-normal transformation, I wonder if the detailed procedure is necessary to present here. Should we not directly consider the results using only log transformation?
Lines 283-296, 328-338, 360-361 : it is not straightforward to present here the results of Multiple OLS regression as the title of the section is 'slope' or 'vegetation' or 'rainfall intensity'. Perhaps a specific section dealing with Multiple OLS regression would clarify the text.
Line 323, Figure 3 : I do not understand the units for soil loss, as the variable was log-transformed?
Lines 418-422: I do not understand why these sentences are written here in the text. I think they could be removed or relocated elsewhere more appropriate in the text.
Lines 426-434 : I do not agree with the equation that is presented, due to timescale issues. Indeed, the soil truncation method integrates multi-decadal erosion, providing a fairly robust average of combined water and tillage erosion rate. Runoff plots are to the best implemented over a few years. This latter method does not alllow to have a robust average of multi-decadal soil water erosion rate (considering the elusive occurrence of higly erosive events).
Lines 490-525 : there are ten key-takeaways, all relevant. But this is quite a lot to remember. Would there be a possibility to merge some takeaways (for example 2-3-4) to help the reader to have a clearer view of these messages?
Minor edits :
Line 83, Figure 2 : why is '137Cs studies ?' mentioned ?
Line 85 : 'spatial and temporal scaleS', 'land measurement methods', 'olivE grove'
Line 115 : remove '(microplot, plot, catchment)' to avoid repetition with lines 118-119.
Line 219 : separate as a new paragraph.
Line 219 : 'For RP studies, RP corresponds to an artificial setup where bounded plots have restricted flow interactions that can lead to...'
Line 288 : 'combined effectS'
Line 309 : 'larger areas than for RS studies'
Line 379 : 'significantly lowerS'
Citation: https://doi.org/10.5194/egusphere-2025-3542-RC2 - AC2: 'Reply on RC2', Andres Peñuela, 05 Dec 2025
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EC1: 'Comment on egusphere-2025-3542', Olivier Evrard, 24 Nov 2025
This review manuscript provides a synthesis on data published regarding soil erosion in Mediterranean olive groves. Overall, the text is rather concise, well written and of interest to the international research community.
In my opinion, the database compiled by the authors should be made accessible in open access (I apologize if it is; then it means that I missed the link).
The manuscript would also gain from further contextualization (i.e., about what is considered as ‘Mediterranean’ whether the climate or the region is investigated; about the surface covered by olive groves in the area under investigation; about the implementation of conservation techniques under olive groves – e.g. are there agricultural statistics available?)
It would also gain from a general bibliometric analysis: what was searched for in the literature? Using which tools and relying on which queries? General information about the study locations (a map would be useful), the journals in which data was published, etc. would also be useful.
Detailed comments
LL.53-60: could these erosion rates be converted into equivalent soil depth loss by erosion to further evaluate whether they are meaningful?
LL.92-100 this text is interesting but does it rely on any reference?
L.145 a map of all study sites would be helpful (maybe all regions of Spain are not equally covered?) – a general bibliometric evaluation would be useful as well.
Table 2; is it all data available from the literature or did you make a selection? If so, based on which criteria?
L.176 about ‘tolerable soil loss’: maybe this should be further discussed in your manuscript (in the final thoughts?) given you are making strong suggestions to go further towards sustainability.
L.195… is there always a validation in the modelling studies compiled? If not, what proportion of studies do include a validation? Are there studies simulating scenarios before having conducted such a validation beforehand?
Table 3: I would add the number of studies related to each method in the table; I guess some general information about the spatial scale/temporal scale under investigation should also be calculated and added?
L.230 ‘heighten uncertainty’: please rephrase
L.245… the associated data would be super helpful
Section 3.3.2 and beyond about the ‘vegetation cover’: what is considered by the authors (the main trees, their canopy, understory vegetation, both the trees and understory vegetation?)
L.308 is ‘compelling’ the right term to use here?
L.349 I guess that this sentence is unclear and should be rephrased.
L.354 is ‘dislodges’ the right term here?
LL.360-361 this sentence is somewhat disconnected from the main text.
L.372 low in organic matter >> depleted in organic matter?
L.388 I would avoid the use of terms such as “seemingly”
L.401 I guess that these studies do not miss these events, they integrate and cumulate all of them, which is different.
L.408 ‘before it can exit the catchment’ >> before it is exported from the catchment?
L.416 “models, when properly calibrated…” >> do you have this important information from your database?
L.416 another technique that may connect all the scales would be the use of sediment fingerprinting; is it something that you think may be useful/encouraged?
LL.426-433 I don’t really understand this suggestion of study ‘in areas close to the catchment limit’
L.440 is data available on olive yields to support this statement?
LL.460-485 instead of incentives only, we may also think about another political approach, which is the one of ‘cross-compliance’: if farmers do not implement good practices, they are not eligible to public support. This section could also benefit from relying more on data from your compilation.
Conclusions
L.487 ‘diverse body of research’: maybe this could be further contextualized in the text
L.504 I do not think that this statement on connectivity is supported by data provided/compiled in this research, is it?
L.513 see my comment above on which is considered as ‘vegetation cover’
LL.526-530 this is interesting but it reads as an advocacy, do you think that it is appropriate?
Citation: https://doi.org/10.5194/egusphere-2025-3542-EC1 - AC3: 'Reply on EC1', Andres Peñuela, 05 Dec 2025
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The manuscript “Soil erosion in Mediterranean olive groves: a review” by Andres Peñuela et al. present the results of a review study including several studies conducted across last decades about the estimation of the entity of soil erosion processes that occur in olive groves in some Mediterranean countries. Many studies report estimation made by direct measurements, some using erosion models. The topic addressed by the manuscript is relevant in the context of soil science applied to agriculture, since soil erosion is known as one of the main soil degradation processes affecting olive groves (and other permanent crops) in the Mediterranean area. Many studies have been conducted in last decades, but the absence of a common framework for soil erosion assessment has led to heterogeneous results, as this work highlights. In this framework, the review collects results obtained from tens of studies with different evaluation approaches, with the aim to identify the extent of soil erosion in this agroecosystem and the factors influencing it, taking into account of different scales (temporal and spatial) of the problem. Data collection was performed in order to obtain a homogeneous dataset to be analysed accordingly to methods usually adopted for similar studies. Considering the broad issue, the results of the data collection and analysis are presented in a concise form, in general complete but that can be improved, and discussion help the reader to understand a clear picture on the topic. In my opinion the work is well structured and written, even if a revision of English can be beneficial. The abstract provides a concise and complete summary. Some specific comments on other sections follow:
- introduction: this section provides an overview on the research about soil erosion in Mediterranean olive groves, specifically on its quantification with different methods and over different temporal and spatial scales; whereas for direct measurement methods, they were briefly introduced with some references, example of models used for soil erosion estimation are not cited in this section, thus I suggest to add some references to most used models, beyond RUSLE. In fact, as a review, some readers could not be aware of models for this purpose. See some other details in the attached pdf.
- Methods: data collection: vegetation cover is not mentioned among collected variables, but it is used in the analysis. Please add it. Statistical analysis: I suggest to add here details about test performed to check assumptions (now they are named in results)
- Results: Table 2: I suggest to add the variable vegetation cover and indicate the plot’s dimension. Section 3.2: since they are mentioned, I suggest add in the Table 3 results for CP and No-CP. Section 3.3: I suggest not to indicate results for model that are not definitive, thus only discuss log-transformed model’s results id assumptions are not satisfied. Section 3.3.2: no information is given about variable vegetation cover in the presented dataset: is it vegetation cover only between tree’s rows or also under trees? What method is used to measure it? Section 3.4: since this section does not present results, I suggest to consider it as discussion.
Please see minor comments in the attached pdf, also in conclusion sections.
In my opinion the requested changes are of minor significance with respect to the relevance of the manuscript, even if I suggest the authors to consider my suggestions. Finally, I suggest to accept the paper with request of minor revisions.