Satellite Remote Sensing for Monitoring Cork Oak Woodlands—A Comprehensive Literature Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General Comments:
The authors present a bibliographic review on the use of remote sensing for the analysis and monitoring of cork oak forests. The manuscript is generally well-written, logically structured, and clearly outlines the study’s objectives. The methodology is appropriate and effectively applied, and the results are clearly communicated. The authors demonstrate a solid understanding of remote sensing techniques; however, their knowledge of cork oak forest systems appears less robust. There are some factual inaccuracies and conceptual oversights that should be addressed prior to publication.
Overall, I recommend the article for publication after minor revisions.

Specific Comments:

Introduction:

• Lines 48–49: Cork oak forests are not limited to dehesas and montados. Two main structural types can be distinguished, primarily based on stand density, but also considering ecological, productive, and silvicultural characteristics: open cork oak systems (such as dehesas and montados) and denser cork oak woodlands. I suggest the authors rephrase this section for clarity and accuracy.
• Line 68: The minimum legal cork harvesting cycle in all cork-producing countries is 9 years—not 8 as stated. Please correct this factual error.

Discussion:

• I find the explanation provided for the uneven distribution of studies among cork-producing countries insufficient. While it is accurate that Portugal and Spain have a significantly higher volume of publications, attributing this solely to the progressive abandonment of cork oak stands in other countries is overly reductive. A more plausible explanation lies in the relative ecological and economic importance of cork oak woodlands in Portugal and Spain compared to countries like Italy and France, which share broadly similar socioeconomic conditions. Furthermore, the lower number of studies from North African countries is unlikely to reflect a progressive abandonment of cork oak systems. Rather, it likely results from limited scientific resources and investment, which constrains research capacity and dissemination. I suggest that this section be reviewed and refined.

Table 1:

• Please clarify the meaning of the column title "AOI." I assume it refers to the country in which each analyzed study is focused.
• If so, I recommend using standardized ISO country codes (e.g., ES or ESP for Spain) for clarity and consistency.

Author Response

General Comments:
The authors present a bibliographic review on the use of remote sensing for the analysis and monitoring of cork oak forests. The manuscript is generally well-written, logically structured, and clearly outlines the study’s objectives. The methodology is appropriate and effectively applied, and the results are clearly communicated. The authors demonstrate a solid understanding of remote sensing techniques; however, their knowledge of cork oak forest systems appears less robust. There are some factual inaccuracies and conceptual oversights that should be addressed prior to publication.
Overall, I recommend the article for publication after minor revisions.

We sincerely thank the reviewer for the helpful suggestions and for the effort in reviewing our manuscript. We have carefully addressed all the points raised, and we believe that the comments have helped us improve the manuscript.

Specific Comments:

Introduction:

• Lines 48–49:Cork oak forests are not limited to dehesas and montados. Two main structural types can be distinguished, primarily based on stand density, but also considering ecological, productive, and silvicultural characteristics: open cork oak systems (such as dehesas and montados) and denser cork oak woodlands. I suggest the authors rephrase this section for clarity and accuracy.

Thanks for the comment. In order to better clarify the introduction to the Cork Oak ecosystems, we expanded and improved the description of cork oak forests in the Mediterranean according to your suggestion.

Introduction section, revised lines 48-57: ‘Cork oak (Quercus suber L.) woodlands have a key ecological and economic value in the Mediterranean region and cover approximately 2.2 million hectares mainly distributed across seven countries: Portugal, Spain, Morocco, Algeria, Tunisia, Italy, and France [1] (Figure 1). Cork oak ecosystems refers broadly to two main structural types, primarily based on stand density, but also taking into account their ecological functions, productive uses, and silvicultural management: (1) open cork oak systems characterized by low tree density and integrated grazing or cropping; and (2) dense cork oak woodlands, with higher canopy cover, reduced understory management, and more continuous forest structure [2]. Open cork oak stands are mainly known as agroforestry and silvopastoral systems, structurally similar to savannas, and locally identified by various regional names—montado in Portugal, dehesa in Spain, azaghar in North Africa, and meriagos in Sardinia.‘

• Line 68:The minimum legal cork harvesting cycle in all cork-producing countries is 9 years—not 8 as stated. Please correct this factual error.

Thanks for highlighting this transcription error. We corrected the text accordingly.

 Introduction section, revised line 84: ‘every 9 to 14 years’.

 

Discussion:

• I find the explanation provided for the uneven distribution of studies among cork-producing countries insufficient. While it is accurate that Portugal and Spain have a significantly higher volume of publications, attributing this solely to the progressive abandonment of cork oak stands in other countries is overly reductive. A more plausible explanation lies in the relative ecological and economic importance of cork oak woodlands in Portugal and Spain compared to countries like Italy and France, which share broadly similar socioeconomic conditions. Furthermore, the lower number of studies from North African countries is unlikely to reflect a progressive abandonment of cork oak systems. Rather, it likely results from limited scientific resources and investment, which constrains research capacity and dissemination. I suggest that this section be reviewed and refined.

Thank you for your comment. We have revised the manuscript to provide a more nuanced explanation for the uneven geographic distribution of studies. Discussion section 4.1.1, revised lines 72-94: “Most of the reviewed studies were conducted in Portugal and Spain, accounting for 12 and 9 studies, respectively. This geographic concentration reflects the significant ecological and economic weight of cork oak systems in these two countries, which together represent approximately 80% of global cork production. In addition to being the primary non-wood forest product in Southern Europe [65] cork harvesting remains deeply embedded in the socio-cultural fabric of Iberian rural areas and constitutes a key pillar of the local bioeconomy [9]. Morocco has shown a recent rise in publications of satellite-based monitoring of cork oak ecosystems, especially after 2022, reflecting increased attention to sustainable forest management, certification initiatives, and conservation of Mediterranean silvopastoral systems. Morocco’s efforts aim to support both biodiversity and the livelihoods of smallholders and local communities [14]. In contrast, research output remains limited in Italy (3) and North African countries like Algeria (1), while France and Tunisia showed no satellite-based studies specifically focused on cork oak, despite being part of the natural distribution of Quercus suber (Figure 1). This spatial imbalance may stem from a decreasing economic interest in cork oak woodlands, as their lower economic returns—compared to western Mediterranean countries with shorter harvest cycles and higher yields [14]—reduce their appeal and the incentive for active management. Additionally, the relatively low number of studies originating from North African countries can be largely explained to structural constraints, including limited access to scientific infrastructure, insufficient research funding, and a lack of sustained international collaboration. These dynamics highlight the urgent need for integrated, transboundary strategies to effectively monitor, conserve, and manage cork oak ecosystems under increasing socio-ecological pressures across the Mediterranean basin [66]. ‘

 

Table 1:

• Please clarify the meaning of the column title "AOI." I assume it refers to the country in which each analyzed study is focused.
• If so, I recommend using standardized ISO country codes (e.g., ES or ESP for Spain) for clarity and consistency.

Thanks for the comment. We have revised the table by replacing the country names with standardized ISO country codes (as suggested) for clarity and consistency. Additionally, we confirm that “AOI” stands for Area of Interest, referring to the country or region in which each analyzed study is focused.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript provides a literature review of Satellite Remote Sensing for Monitoring Cork Oak Wood-2 lands. The topic is interesting, and the manuscript is well written. After reviewing the manuscript, I would like to present some aspects that I believe need to be revised and improved by the Authors.

 

• I'm wondering if Diversity is the most appropriate journal for this manuscript. Although traditional cork oak forests, agroforestry and silvopastoral ecosystems are "among the most distinctive fe tures of the ancient Mediterranean landscape, protected under the Pan-European Natura 2000 network and classified as “biodiversity-based product systems” by the Convention on Biological Diversity", and the Authors included some paragraphs about it (lines 51-55), I'm not convinced that the overall context of the review is aligned with the journal scope.
• Lines 132-137: The remote sensing related keywords included in the search are mainly focused in optical multispectral satellites. Why were not included hyperspectral satellite sensors? Also, why were not included keywords like LiDAR?

I understand that Authors only focused satellite, in accordance to the manuscript title. But why not make it broaden to include UAV, as it is a EO-based technology currently with large use in Earth Observation?

• Lines 174-183: No topic specifically related with biodiversity (which is the focus of Diversity journal) was included. I believe this would be a key topic considering that the Authors are submitting the manuscript to a Diversity journal.
• Table 1: In the description of abbreviations, below the table, the topics are

indicated as groups. Please use the same designation for better understanding and consistency

• Sections 4.1: Overall, this section doesn't seem to provide an actual and deep discussion of the review made. I mean, what are the main gaps to be further explored? What are the satellite RS technologies that are being applied in the monitoring of other ecosystems that are not being used in cork oak ecosystems, and why? Why there are no studies using hyperspectral data as there are new sensors providing such data (free and open access)? Is biodiversity being assessed in studies focusing cork oak, which do not use satellite data? I believe that this discussion section should go much deeper.
• Lines 154 – 155: It is not clear what Authors mean by “highly heterogeneous reflecting lack of standardization”. The studies where the various machine learning techniques were considered focused the same kind of topic or purpose? Or focused different kind of topics/purposes? If the analysis being made focus different kind of purposes and the input data has different kind of characteristics, it's not expectable that the same ML techniques are adequate. So what exactly is meant by lack of standardization?
• Section 4.2: Although this section provides interesting information and content, it doesn't seem to appropriately address the results of the review made. No topic specifically related with NbS was considered in the keywords selected for the revision, so it seems that this section is out of context. Why are NbS being discussed here? Why not discussing other management practices or the performance of these agroforestry ecosystems in new geographical distributions? It is not clear the liaison specifically to NbS.
• Lines 222-225: I believe that a discussion of this topic should be provided instead of simply referring it as a future research direction. The Authors made a review of studies addressing different topics. Is it expectable a common standardized framework for different topics?

Author Response

The manuscript provides a literature review of Satellite Remote Sensing for Monitoring Cork Oak Wood-2 lands. The topic is interesting, and the manuscript is well written. After reviewing the manuscript, I would like to present some aspects that I believe need to be revised and improved by the Authors.

We sincerely thank the reviewer for taking the time to review our manuscript and for providing constructive feedback. We appreciate the reviewer’s recognition of the manuscript's strengths and have carefully revised the text in response to the suggestions provided. We believe these revisions have helped to further improve the manuscript’s clarity and overall quality.

 

• I'm wondering if Diversity is the most appropriate journal for this manuscript. Although traditional cork oak forests, agroforestry and silvopastoral ecosystems are "among the most distinctive features of the ancient Mediterranean landscape, protected under the Pan-European Natura 2000 network and classified as “biodiversity-based product systems” by the Convention on Biological Diversity", and the Authors included some paragraphs about it (lines 51-55), I'm not convinced that the overall context of the review is aligned with the journal scope.

Thank you for your thoughtful comment. We appreciate your concern regarding the fit between our manuscript and the journal’s scope.

While the primary focus of our review is on the application of spaceborne remote sensing to cork oak (Quercus suber) ecosystems, we believe this approach is strongly aligned with Diversity’s aims. Cork oak landscapes—particularly in their traditional forms as agroforestry and silvopastoral systems—are not only cultural and economic assets but also biodiversity hotspots, as acknowledged by their protection under the Natura 2000 network and classification as “biodiversity-based product systems” by the Convention on Biological Diversity. To address this issue we have enriched the Introduction section, revised lines 58-67: ‘The ecological significance of cork oak systems extends beyond species richness to include their role in supporting globally and regionally threatened taxa [3]. These landscapes are recognized as biodiversity hotspots, sustaining high alpha-diversity across multiple taxa—including birds, mammals, amphibians, and reptiles—many of which are endemic or threatened. They also serve as critical habitats for migratory and overwintering bird species [4]. Variation in plant species composition among cork oak communities is shaped by geographic location, structural complexity, management regimes, and local ecological conditions [2]. As such, their sustainable management is of strategic importance for preserving biodiversity across the Mediterranean basin.’

And in the Conclusions section, lines 298-302: ‘Cork oak woodlands represent one of the most emblematic agro-silvo-pastoral systems of the Mediterranean basin, renowned for their sustainable production of cork—one of the most valuable non-wood forest products worldwide—and for supporting a wide range of flora and fauna, including endemic and threatened species, while playing a vital role in sustaining ecosystem services and rural livelihoods.’

Furthermore, remote sensing represents an increasingly essential tool for biodiversity monitoring and ecosystem conservation. We revised the document and emphasized this concept in the Conclusions, lines 306-309: ‘In particular, RS represents an increasingly essential tool for monitoring forest dynamics, enabling the tracking of ecological health, species habitat quality, and forest degradation on cork oak systems—topics directly relevant to biodiversity and conservation.’

We hope this clarification supports the relevance of our manuscript to Diversity’s interdisciplinary mission.

 

• Lines 132-137: The remote sensing related keywords included in the search are mainly focused in optical multispectral satellites. Why were not included hyperspectral satellite sensors? Also, why were not included keywords like LiDAR?

I understand that Authors only focused satellite, in accordance to the manuscript title. But why not make it broaden to include UAV, as it is an EO-based technology currently with large use in Earth Observation?

Thank you for your comment. Our review focuses on spaceborne remote sensing data, including optical, hyperspectral, and radar (e.g., Sentinel-1) satellite sensors. This choice reflects the advantages of satellite data, such as broad spatial coverage, regular temporal revisits, and widespread accessibility through free missions like Landsat and Sentinel-2. Nevertheless, we recognize the growing role of airborne platforms such as LiDAR and UAV in Earth observation, thus these were included in the review where they were explicitly integrated with satellite data—to maintain a consistent focus on satellite-based monitoring, as outlined in the manuscript title and objectives.

In order to clarify these points, we have now revised the Introduction, see lines 121-128: ‘However, airborne surveys are extremely resource-demanding in terms of both costs and time, and less feasible for large-scale assessments. Given these considerations, this review focuses on spaceborne RS data, as only satellite-based observations provide consistent, comparable, and frequently updated information across broad areas at no cost—an essential requirement for monitoring cork oak systems, which are widely distributed across multiple Mediterranean countries and experiencing an overall decline.’

and the Materials and Methods section, see lines 156-160: “The search terms were intentionally designed to focus on spaceborne remote sensing applied to cork oak woodlands, ensuring a focused scope for the review. Consequently, terms related to airborne remote sensing technologies (e.g., “LiDAR”, “UAV”, “drone”) were not included, except in cases where such technologies were explicitly combined with satellite data.”

Furthermore, hyperspectral satellite sensors were included implicitly in the search through the terms “remote sensing”, “satellite”, “earth observation”, but no articles were found applying hyperspectral satellite sensors for monitoring cork oak woodlands. This has now been further explored in the Discussion section 4.1.3, revised lines 170-176: ” Interestingly, while hyperspectral data from airborne platforms or portable spectrometers have been frequently used to study cork oak ecosystems [72–75], no studies were found that applied hyperspectral data from spaceborne sensors to these environments. Considering the recent availability of free and open-access hyperspectral satellite missions (e.g., PRISMA, EnMAP) and their ability to cover much larger study areas compared to the methods mentioned above, this gap presents a promising opportunity to expand cork oak monitoring with detailed spectral information at a broader spatial scale”.

• Lines 174-183: No topic specifically related with biodiversity (which is the focus of Diversity journal) was included. I believe this would be a key topic considering that the Authors are submitting the manuscript to a Diversity journal.

Thank you for your comment. We have revised the manuscript to explicitly emphasize the relevance of biodiversity to the thematic areas covered. Materials and Methods section, revised lines 205-208: “Collectively, these thematic areas also provide key insights into the biodiversity dynamics of cork oak systems, highlighting how disturbances, forest structure, species distribution, and environmental conditions interact to shape ecosystem integrity and resilience.”

• Table 1: In the description of abbreviations, below the table, the topics are indicated as groups. Please use the same designation for better understanding and consistency

Thank you for the comment. We have revised the description of abbreviations to ensure consistent terminology throughout the document. Specifically, we have harmonized the terms used in Table 1 in the abbreviations below the table.

• Sections 4.1: Overall, this section doesn't seem to provide an actual and deep discussion of the review made. I mean, what are the main gaps to be further explored? What are the satellite RS technologies that are being applied in the monitoring of other ecosystems that are not being used in cork oak ecosystems, and why? Why there are no studies using hyperspectral data as there are new sensors providing such data (free and open access)? Is biodiversity being assessed in studies focusing cork oak, which do not use satellite data? I believe that this discussion section should go much deeper.

Thank you for your insightful comment. We appreciate your suggestions to deepen the discussion section. We agree that the current version could be expanded to better highlight the main knowledge gaps and future research directions. In response, we have revised Section 4.1 to:

• Gaps to be further explored. Section 4.1.2, revised lines 113-132: “For example, the assessment of cork oak forest post-wildfire resilience [38] provides valuable insight into resilience but is restricted to specific contexts. Studies on groundwater dependency [61] and soil organic matter [60] explore environmental variables relevant to cork oak ecosystems, yet they are disconnected from broader ecological assessments. Similarly, research on landscape connectivity [55] focuses on aspects related to biodiversity but remains standalone analysis. Collectively, these cases underline the fragmented nature of current research and highlight the need for more integrated approaches.

An important step forward for a more comprehensive understanding of resilience would be to leverage satellite-derived recovery metrics. [69] demonstrated how long-term Landsat time series can effectively quantify disturbance and recovery dynamics at large scale using metrics such as Year to Recovery (Y2R). Adapting similar methodologies to cork oak ecosystems, which are increasingly exposed to multiple pressures and disturbances, could provide scalable and repeatable insights into resilience patterns, supporting informed management decisions.

In terms of biodiversity, [70] showed that spectral diversity derived from high-resolution IKONOS satellite imagery can successfully predict habitat heterogeneity and plant species richness in temperate mixed forests.  Applying such methods to cork oak woodlands could enhance biodiversity monitoring across large spatial scales, offering an opportunity to connect remote sensing indicators with ecological processes and overcoming the limitations of isolated field-based studies.”

• Why no studies with hyperspectral data? Section 4.3, revised lines 279-284: “Furthermore, the lack of hyperspectral satellite data in cork oak studies highlights an area for future exploration. With the availability of free hyperspectral missions like PRISMA and EnMAP, there is an opportunity to enhance monitoring efforts. For example, [80] demonstrated PRISMA’s potential for detailed forest fuel types mapping in Mediterranean holm oak forests, a methodology that could be adapted to cork oak ecosystems.”

 

• Is biodiversity being assessed without satellite data focusing on cork oak?
  Section 4.1.2, lines 127-132: “In terms of biodiversity, [70] showed that spectral diversity derived from high-resolution IKONOS satellite imagery can successfully predict habitat heterogeneity and plant species richness in temperate mixed forests. Applying such methods to cork oak woodlands could enhance biodiversity monitoring across large spatial scales, offering an opportunity to connect remote sensing indicators with ecological processes and overcoming the limitations of isolated field-based studies.”

 

• Lines 154 – 155: It is not clear what Authors mean by “highly heterogeneous reflecting lack of standardization”. The studies where the various machine learning techniques were considered focused the same kind of topic or purpose? Or focused different kind of topics/purposes? If the analysis being made focus different kind of purposes and the input data has different kind of characteristics, it's not expectable that the same ML techniques are adequate. So what exactly is meant by lack of standardization?

Thank you for your comment. You are right that the phrase “highly heterogeneous reflecting lack of standardization” was not sufficiently clear. We revised the text to make it clear that there were few studies that didn’t use specific metric accuracy or that used metric accuracy not reported in other studies, and thus it was impossible for us to make comparisons. In this context, the adoption of a more standardized methodology (especially to those studies on similar topics) could facilitate more robust comparisons and integrated analyses in future research.

We revised the text in Section 4.1.4, lines 182-195: “However, their use was highly heterogeneous, not only in terms of the variety of algorithms but also in the diversity of topics addressed (e.g., forest disturbances, productivity, land cover classification) and the characteristics of input data (e.g., sensor type, temporal extent, spatial resolution), which complicates direct comparisons of results and integration of findings across studies. Moreover, many studies could not be included in a direct comparison of accuracy because they used unusual accuracy metrics that were not adopted by any other studies. This lack of standardization was particularly evident in studies focusing on carbon stock, biomass, and productivity [16,53,54], where different accuracy metrics were used, making it difficult to compare with studies on the same topic like [51], which used R², or [52], which used RMSE. Similarly, research on environmental variables such as [38,60,62] lacked standard accuracy evaluation methods. On the other hand, land cover classification studies were generally more consistent, with most adopting OA as accuracy metric, enabling more direct cross-comparison.”

• Section 4.2: Although this section provides interesting information and content, it doesn't seem to appropriately address the results of the review made. No topic specifically related with NbS was considered in the keywords selected for the revision, so it seems that this section is out of context. Why are NbS being discussed here? Why not discussing other management practices or the performance of these agroforestry ecosystems in new geographical distributions? It is not clear the liaison specifically to NbS.

Thank you for your feedback. We have thoroughly revised section 4.2 to address your comment. In the new version, we have removed the detailed focus on Nature-based Solutions (NbS), which indeed appeared out of context considering the scope and methodology of our review. Instead of introducing the concept of NbS, we now emphasize how remote sensing (RS) can effectively support the monitoring and management of cork oak ecosystems, as well as provide critical insights to inform policy-making and ensure the long-term sustainability of these landscapes.

Revised lines 231-248: “A proactive, forward-looking approach is needed for managing these agroforestry ecosystems. Remote sensing (RS) constitutes an essential tool for informing and supporting ecosystem management, providing scalable, cost-efficient, and continuous monitoring of ecological conditions. By harnessing satellite-derived data, it is possible to detect areas of decline, evaluate stressors such as drought and canopy degradation, and prioritize targeted interventions, including thinning, pest management, and water regulation. These data-driven insights facilitate the implementation of a wide array of adaptive management strategies—from wildfire prevention and rotational grazing to the enhancement of landscape connectivity—that collectively bolster ecosystem resilience and promote the long-term sustainability of cork oak woodlands. Among these, certain nature-based approaches, such as restoring degraded areas or promoting multifunctional land use, can complement technical and silvicultural measures to enhance overall system functionality [14,78]. The adoption of integrated management approaches also requires strong political will and policy support for sustainable forest management and ecosystem restoration, ensuring the long-term sustainability of cork oak forests and addressing global ecological challenges [77,79]. Combining cutting-edge monitoring technologies with adaptive management and supportive policy frameworks is essential to address current challenges and maintain the ecological integrity and productivity of these ecosystems.”

Section 4.3, lines 290-296: “Finally, remote sensing research should move beyond technical accuracy and align more closely with practical management needs and policy frameworks. A stronger integration with adaptive forest management strategies, such as the EU Biodiversity Strategy, is essential to ensure that scientific innovations effectively support operational and policy-relevant actions. This involves designing RS tools not only for academic purposes, but also as practical instruments for restoration planning, early-warning systems, and performance monitoring of conservation efforts.”

Section 5, lines 328-332: “Third, to fully support more effective agroforestry management, future research should expand toward more functional and ecosystem-based indicators, incorporating variables such as biodiversity and ecosystem resilience. Strengthening the connection between RS outputs and practical management strategies and policies can provide critical support for adaptive decision-making and the implementation of sustainable practices.”

 

 

 

• Lines 222-225: I believe that a discussion of this topic should be provided instead of simply referring to it as a future research direction. The Authors made a review of studies addressing different topics. Is it expectable a common standardized framework for different topics?

Thank you, you are fully right that simply suggesting standardization as a future research direction is not sufficient. In the revised version, we clarified that, while the reviewed studies indeed address different topics (e.g., forest disturbances, productivity, land cover classification, environmental variables), certain components of the methodological workflow, such as the use of specific validation metrics (e.g., OA, RMSE, R²) and data pre-processing protocols, can and should be standardized to improve comparability and integration across studies (especially across studies relating to the same topics). At the same time, we acknowledge that the specific objectives and data characteristics of each study require flexibility in other aspects of the workflow. We have now clarified this in Section 4.3, revised lines 255-263: “The reviewed studies addressed a variety of topics, from forest disturbances to productivity, to land cover classification and environmental variables, which naturally leaves to differences in objectives in data characteristics. However, certain components of methodological workflow could benefit from greater standardization. For example, the consistent use of validation metrics (e.g., OA, RMSE, R²) would improve comparability across studies on similar topics and enable clearer benchmarking of model performance. Rather than aiming for a universal framework that covers all possible research questions, a more feasible approach would be to establish standardized components within flexible workflows, allowing for both comparability and thematic specificity.”

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The Authors addressed all the comments made in the previous revision round and the manuscript improved.