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.

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.