the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 10 Apr 2025
Forestlines in Italian mountains are shifting upward: detection and monitoring using satellite time-series
Abstract. The growing interest on the ecological effects of global warming and land use changes on vegetation, along with development of remote sensing techniques, fostered applied research on the successional dynamics at the upper limits of forests. The aims of this study were: i) to develop an automated methodology for mapping the current position of the uppermost italian forestlines; ii) to identify hotspots of change by the analysis of long-term greenness and wetness spectral dynamics. We carried on a Landsat-based trend analysis in buffer zones along the forestlines, testing differences between sparse and dense canopy cover classes and at different elevations and distances to the forestline. We used regional scale datasets and avoided to fix a minimum elevation threshold, in order to make the method replicable at different mountain ranges. For the spectral dynamics analyses, we used Landsat time-series of common vegetation indices for the period 1984–2023 and tested the significance of their long-term spectral trends with the Contextual Mann-Kendall test for monotonicity. We assessed that the highest forestlines are at the western sector in the Alps, and at the central one in the Apennines. We observed a common increase of the forest cover mainly close to the forestline and at lower elevations. Comparing greenness and wetness indices trends with the current canopy cover, the highest values were respectively in the sparse tree cover class, and in the dense one, particularly in the Alps.
Competing interests: Matteo Garbarino is guest editor of the special issue “Treeline ecotones under global change: linking spatial patterns to ecological processes” in Biogeosciences.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.-
Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(1944 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1944 KB) - Metadata XML
- BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-1552', Anonymous Referee #1, 08 May 2025
This manuscript presents an ambitious and methodologically rich study on the upward dynamics of forestlines in Italian mountain ranges, using a 40-year Landsat time series and robust trend detection techniques. The authors propose a semi-automated workflow for delineating the uppermost forestlines and interpreting spectral greenness and wetness trends across canopy classes and topographic gradients.
The paper offers valuable insights into large-scale forest recolonisation processes and is grounded in a solid conceptual framework. However, a key aim listed in the abstract is the mapping of the current position of the uppermost Italian forestlines. This core claim is not supported by any form of spatial validation or uncertainty assessment. While statistical comparisons (e.g. Wilcoxon tests, GAMs) are used effectively to interpret spectral trend variability, they do not establish the accuracy or ecological credibility of the detected forestlines themselves. Given the reliance on an automated method to infer a critical ecological boundary, this omission undermines confidence in one of the study’s central contributions.
The manuscript is generally well written, although there are scattered typographic and formatting issues. Figures would benefit from improved labelling and clarity, particularly in terms of geographical referencing and scalebar readability.
I recommend major revisions to address the validation gap and improve clarity for an international audience.
Specific Comments
- Forestline validation missing: A core objective stated in the abstract is to “map the current position of the uppermost Italian forestlines.” However, there is no spatial accuracy assessment of these delineated lines. The method’s reliability is only indirectly supported through descriptive summaries (e.g. mean elevation), but not through comparison with independent references. I strongly recommend including a validation step - this could involve:
- Visual comparison with high-resolution imagery or historical orthophotos,
- Use of GEDI canopy height profiles,
- Manual digitisation for a subset of sites,
- Field plot data where available.
Including even a partial validation would significantly strengthen the credibility of the forestline mapping method.
- Use of Landsat over Sentinel-2 (ll. 151–155): The authors should clearly justify the exclusive use of Landsat imagery, given that Sentinel-2 offers higher spatial resolution and comparable temporal coverage (since 2018). If the decision is based on the 40-year archive or data processing/infrastructure concerns, this should be explicitly stated.
- Line 60: Remove placeholder Italian text: "Fare clic o toccare qui per immettere il testo...".
- Lines 113–114: The transition into peak selection is abrupt. Clarify why peaks were chosen before introducing the selection process, to improve narrative flow.
- Line 115: Non-European readers may not be familiar with the Tinitaly DEM. Add a brief description including spatial resolution and accuracy compared to existing sources
- Line 118: Typo — "affetced" → "affected".
- Line 119: Typo — "alpine bel" → "alpine belt".
- Figure 1b: Scalebar tick labels are not legible. Improve contrast and font size.
- Figure 2: No need to highlight the exact location, but indicate whether the example is located in the Alps or Apennines. Add scalebar.
- Figure 3: Typo in caption header — “statistical analysis” should be corrected.
Technical Corrections
- Typographic and formatting issues: Address minor typos such as “affetced” (l. 118), “alpine bel” (l. 119) and inconsistent spelling of the indices (e.g. “grenness”)
- Figures: All figures should include legible scalebars and clearer geographical context where relevant.
Citation: https://doi.org/10.5194/egusphere-2025-1552-RC1 - AC1: 'Reply on RC1', Lorena Baglioni, 11 Jun 2025
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RC2: 'Comment on egusphere-2025-1552', Joanna L. Corimanya, 14 May 2025
The manuscript presents a valuable and timely contribution to the study of forestline dynamics in mountain ecosystems under the influence of climate and land use change. The authors propose an automated, reproducible method to detect the uppermost forestlines in the Alps and Apennines, and evaluate long-term trends in greenness and wetness using Landsat time-series and the Contextual Mann-Kendall (CMK) test. The combination of robust spatial datasets, a long temporal window (1984–2023), and a detailed comparison of canopy cover classes adds substantial weight to the conclusions. The literature review is quite thorough, and the flexibility and scalability of the proposed method enhances its utility across global mountain ranges. In addition, the integration of multiple spectral indices (NDVI, EVI, NDMI, TCW, etc.) offers a nuanced perspective on ecological processes such as tree encroachment and canopy densification.
Major revisions:
The manuscript would benefit from a careful linguistic edit. There are numerous typographical and grammatical errors (e.g., "threfore", "rispectively", "forestline uo ti 200 m") that impede readability. Sentence structure could be simplified in some sections for clarity and flow.
While the methodological design is sound, a more explicit discussion of the sources of uncertainty (e.g., compositing effects, spatial mismatch between TCD and Landsat, potential overestimation of greening trends due to observation frequency) would improve the robustness of the conclusions.
The authors correctly report that GAMs relating TAU values to elevation and forestline distance were not statistically significant. However, this result could be better contextualized—what does this imply about the spatial consistency or heterogeneity of trends?
Minor revisions:
Line 15: Should say “carried out,” instead of, “carried on.”
Line 16: I am not sure what is meant by “..and avoided to fix..” Please clarify.
Line 22: There is an extra space between ‘respectively’ and ‘in’.
Line 29: Remove paragraph break.
Line 40: Begin a new paragraph at “The ongoing development of remote..”
Line 43: Remove ‘an’.
Line 44: Should be ‘treeline monitoring’ instead of ‘treelines monitoring’.
Line 44: The authors should mention the strengths of aerial photography as well, similarly to how they describe the strengths and weaknesses of other methods. For example, aerial photography allows for broader temporal scales compared to satellite-based remote sensing.
Line 57: The clarity of this sentence could be improved with a rewrite. I would suggest changing the sentence to, “..and to study alpine treelines by applying greening proxies like vegetation indices.”
Line 60: A comment appears to be left in by mistake? Remove sentence of a different font color which states, “Fare clic o toccare qui per immettere il testo.”
Line 68: Spelling error. ‘Overcaming’ should be ‘overcoming’.
Line 75: Change ‘photosintetic’ to ‘photosynthetic’.
Line 78: ‘This’ should be ‘these’.
Line 87: ‘Forestlines’ should be ‘forestline’.
Line 97: Remove paragraph break.
Line 98: This sentence should be rewritten for clarity. I suggest, “..while wetness indices are better for detecting gap-filling processes by intercepting the the spectral signal of lower leaf strata.”
Line 104: Remove one of the periods after ‘SE’.
Line 105: Should be ‘ranges’ not ‘range’.
Line 107: Change ‘and/or’ to ‘and’
Line 108: Should be ‘ranges’ not ‘range’.
Line 109: Should be ‘elevations’ not ‘elevation’.
Line 113: Remove ‘A’ from, “Alps and Athe Apennines.”
Line 118: Fix typo in ‘affected’.
Line 121: ‘Others’ should be ‘other’.
Line 122: Remove ‘of’.
Lines 133 - 134: Rewrite the sentence for clarity and grammar.
Line 138: Are the points every 10m? If so, authors should increase clarity by stating the points are at 10m intervals instead of 10m distance.
Figure 1 (c): Yellow is difficult to read in legend. I suggest changing to a different color to indicate the buffer.
Line 178: Explicitly state the predictor variable(s) that were compared with greenness and wetness to evaluate significance.
Line 195-196: The authors would benefit from increased clarity and specificity in this sentence. Why did they choose two sets of only 40 points? Or is it two sets of 40,000 points, and there is a typographic error? How were the points randomly sampled? Are these different points than the points discussed earlier in the paragraph? Splitting this up into two sentences and providing more detail will greatly improve the readability of the manuscript.
Line 196: ‘a’ should be ‘an’.
Figure 3: This diagram is excellent! It is very thorough and communicates the analysis well.
Line 297: There is an extra space before ‘Italian’.
Line 297: ‘emisphere’ should be ‘hemisphere’.
Line 305: ‘forestlines’ should be ‘forestline’.
Lines 311 - 312: Clarity would improve by rewriting the beginning of this sentence. I suggest, “Overall, rising greenness and wetness trends were recorded at both mountain ranges in line with the ongoing natural reforestation processes.” The authors should also note that, in my suggested rewrite, I corrected a typo in ‘reforestation’.
Line 321: Add a comma after ‘general’.
Line 326: Change ‘plant’ to ‘plants’.
Line 327: Change ‘associated to’ to ‘associated with’.
Line 331: Remove the comma after ‘Apennines’.
Line 352: Add a comma after ‘Furthermore’.
Line 363: Change ‘climate’ to ‘climatic’.
Line 381: Remove the extra period at the end of the last sentence.
Citation: https://doi.org/10.5194/egusphere-2025-1552-RC2 - AC2: 'Reply on RC2', Lorena Baglioni, 11 Jun 2025
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2025-1552', Anonymous Referee #1, 08 May 2025
This manuscript presents an ambitious and methodologically rich study on the upward dynamics of forestlines in Italian mountain ranges, using a 40-year Landsat time series and robust trend detection techniques. The authors propose a semi-automated workflow for delineating the uppermost forestlines and interpreting spectral greenness and wetness trends across canopy classes and topographic gradients.
The paper offers valuable insights into large-scale forest recolonisation processes and is grounded in a solid conceptual framework. However, a key aim listed in the abstract is the mapping of the current position of the uppermost Italian forestlines. This core claim is not supported by any form of spatial validation or uncertainty assessment. While statistical comparisons (e.g. Wilcoxon tests, GAMs) are used effectively to interpret spectral trend variability, they do not establish the accuracy or ecological credibility of the detected forestlines themselves. Given the reliance on an automated method to infer a critical ecological boundary, this omission undermines confidence in one of the study’s central contributions.
The manuscript is generally well written, although there are scattered typographic and formatting issues. Figures would benefit from improved labelling and clarity, particularly in terms of geographical referencing and scalebar readability.
I recommend major revisions to address the validation gap and improve clarity for an international audience.
Specific Comments
- Forestline validation missing: A core objective stated in the abstract is to “map the current position of the uppermost Italian forestlines.” However, there is no spatial accuracy assessment of these delineated lines. The method’s reliability is only indirectly supported through descriptive summaries (e.g. mean elevation), but not through comparison with independent references. I strongly recommend including a validation step - this could involve:
- Visual comparison with high-resolution imagery or historical orthophotos,
- Use of GEDI canopy height profiles,
- Manual digitisation for a subset of sites,
- Field plot data where available.
Including even a partial validation would significantly strengthen the credibility of the forestline mapping method.
- Use of Landsat over Sentinel-2 (ll. 151–155): The authors should clearly justify the exclusive use of Landsat imagery, given that Sentinel-2 offers higher spatial resolution and comparable temporal coverage (since 2018). If the decision is based on the 40-year archive or data processing/infrastructure concerns, this should be explicitly stated.
- Line 60: Remove placeholder Italian text: "Fare clic o toccare qui per immettere il testo...".
- Lines 113–114: The transition into peak selection is abrupt. Clarify why peaks were chosen before introducing the selection process, to improve narrative flow.
- Line 115: Non-European readers may not be familiar with the Tinitaly DEM. Add a brief description including spatial resolution and accuracy compared to existing sources
- Line 118: Typo — "affetced" → "affected".
- Line 119: Typo — "alpine bel" → "alpine belt".
- Figure 1b: Scalebar tick labels are not legible. Improve contrast and font size.
- Figure 2: No need to highlight the exact location, but indicate whether the example is located in the Alps or Apennines. Add scalebar.
- Figure 3: Typo in caption header — “statistical analysis” should be corrected.
Technical Corrections
- Typographic and formatting issues: Address minor typos such as “affetced” (l. 118), “alpine bel” (l. 119) and inconsistent spelling of the indices (e.g. “grenness”)
- Figures: All figures should include legible scalebars and clearer geographical context where relevant.
Citation: https://doi.org/10.5194/egusphere-2025-1552-RC1 - AC1: 'Reply on RC1', Lorena Baglioni, 11 Jun 2025
-
RC2: 'Comment on egusphere-2025-1552', Joanna L. Corimanya, 14 May 2025
The manuscript presents a valuable and timely contribution to the study of forestline dynamics in mountain ecosystems under the influence of climate and land use change. The authors propose an automated, reproducible method to detect the uppermost forestlines in the Alps and Apennines, and evaluate long-term trends in greenness and wetness using Landsat time-series and the Contextual Mann-Kendall (CMK) test. The combination of robust spatial datasets, a long temporal window (1984–2023), and a detailed comparison of canopy cover classes adds substantial weight to the conclusions. The literature review is quite thorough, and the flexibility and scalability of the proposed method enhances its utility across global mountain ranges. In addition, the integration of multiple spectral indices (NDVI, EVI, NDMI, TCW, etc.) offers a nuanced perspective on ecological processes such as tree encroachment and canopy densification.
Major revisions:
The manuscript would benefit from a careful linguistic edit. There are numerous typographical and grammatical errors (e.g., "threfore", "rispectively", "forestline uo ti 200 m") that impede readability. Sentence structure could be simplified in some sections for clarity and flow.
While the methodological design is sound, a more explicit discussion of the sources of uncertainty (e.g., compositing effects, spatial mismatch between TCD and Landsat, potential overestimation of greening trends due to observation frequency) would improve the robustness of the conclusions.
The authors correctly report that GAMs relating TAU values to elevation and forestline distance were not statistically significant. However, this result could be better contextualized—what does this imply about the spatial consistency or heterogeneity of trends?
Minor revisions:
Line 15: Should say “carried out,” instead of, “carried on.”
Line 16: I am not sure what is meant by “..and avoided to fix..” Please clarify.
Line 22: There is an extra space between ‘respectively’ and ‘in’.
Line 29: Remove paragraph break.
Line 40: Begin a new paragraph at “The ongoing development of remote..”
Line 43: Remove ‘an’.
Line 44: Should be ‘treeline monitoring’ instead of ‘treelines monitoring’.
Line 44: The authors should mention the strengths of aerial photography as well, similarly to how they describe the strengths and weaknesses of other methods. For example, aerial photography allows for broader temporal scales compared to satellite-based remote sensing.
Line 57: The clarity of this sentence could be improved with a rewrite. I would suggest changing the sentence to, “..and to study alpine treelines by applying greening proxies like vegetation indices.”
Line 60: A comment appears to be left in by mistake? Remove sentence of a different font color which states, “Fare clic o toccare qui per immettere il testo.”
Line 68: Spelling error. ‘Overcaming’ should be ‘overcoming’.
Line 75: Change ‘photosintetic’ to ‘photosynthetic’.
Line 78: ‘This’ should be ‘these’.
Line 87: ‘Forestlines’ should be ‘forestline’.
Line 97: Remove paragraph break.
Line 98: This sentence should be rewritten for clarity. I suggest, “..while wetness indices are better for detecting gap-filling processes by intercepting the the spectral signal of lower leaf strata.”
Line 104: Remove one of the periods after ‘SE’.
Line 105: Should be ‘ranges’ not ‘range’.
Line 107: Change ‘and/or’ to ‘and’
Line 108: Should be ‘ranges’ not ‘range’.
Line 109: Should be ‘elevations’ not ‘elevation’.
Line 113: Remove ‘A’ from, “Alps and Athe Apennines.”
Line 118: Fix typo in ‘affected’.
Line 121: ‘Others’ should be ‘other’.
Line 122: Remove ‘of’.
Lines 133 - 134: Rewrite the sentence for clarity and grammar.
Line 138: Are the points every 10m? If so, authors should increase clarity by stating the points are at 10m intervals instead of 10m distance.
Figure 1 (c): Yellow is difficult to read in legend. I suggest changing to a different color to indicate the buffer.
Line 178: Explicitly state the predictor variable(s) that were compared with greenness and wetness to evaluate significance.
Line 195-196: The authors would benefit from increased clarity and specificity in this sentence. Why did they choose two sets of only 40 points? Or is it two sets of 40,000 points, and there is a typographic error? How were the points randomly sampled? Are these different points than the points discussed earlier in the paragraph? Splitting this up into two sentences and providing more detail will greatly improve the readability of the manuscript.
Line 196: ‘a’ should be ‘an’.
Figure 3: This diagram is excellent! It is very thorough and communicates the analysis well.
Line 297: There is an extra space before ‘Italian’.
Line 297: ‘emisphere’ should be ‘hemisphere’.
Line 305: ‘forestlines’ should be ‘forestline’.
Lines 311 - 312: Clarity would improve by rewriting the beginning of this sentence. I suggest, “Overall, rising greenness and wetness trends were recorded at both mountain ranges in line with the ongoing natural reforestation processes.” The authors should also note that, in my suggested rewrite, I corrected a typo in ‘reforestation’.
Line 321: Add a comma after ‘general’.
Line 326: Change ‘plant’ to ‘plants’.
Line 327: Change ‘associated to’ to ‘associated with’.
Line 331: Remove the comma after ‘Apennines’.
Line 352: Add a comma after ‘Furthermore’.
Line 363: Change ‘climate’ to ‘climatic’.
Line 381: Remove the extra period at the end of the last sentence.
Citation: https://doi.org/10.5194/egusphere-2025-1552-RC2 - AC2: 'Reply on RC2', Lorena Baglioni, 11 Jun 2025
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Lorena Baglioni
Donato Morresi
Matteo Garbarino
Carlo Urbinati
Emanuele Lingua
Raffaella Marzano
Alessandro Vitali
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1944 KB) - Metadata XML