Influence of Tree Community Characteristics on Carbon Sinks in Urban Parks: A Case Study of Xinyang, China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

General Comments

The paper titled Influence of Tree Community Characteristics on Carbon Sink in Urban Parks: A Case Study of Xinyang, China investigates the carbon storage (CS) and carbon sequestration (CSG) in urban parks, focusing on the role of tree community characteristics. The study provides valuable insights into how park attributes, community structure, biodiversity, and spatial distribution influence urban carbon sinks. The research is well-structured and addresses an important topic in urban ecology and environmental management.

 

Specific comments

1. The study focuses primarily on small, recently established parks in Xinyang. This limits the generalizability of the findings to larger or more mature parks.Future research should include a broader range of park sizes and ages to provide a more comprehensive understanding of carbon sink dynamics in urban parks. Therefore, I suggest authors can add section to imply that how does this specific study send more information for general scopes.

 

2. The study excludes the carbon sink contributions of grasslands and herbaceous plants, potentially underestimating the overall carbon sequestration rate.This omission could lead to an incomplete assessment of the total carbon storage and sequestration potential in urban parks. However, the area of grassland in the urban parks in China may contribute lot, therefore, I suggested authors send more discussion to explain the impact of exclusion of grassland when calculating the carbon sink.

Overall, the paper is well-researched and provides significant insights into urban carbon sink management. It is recommended for publication with minor revisions to address the limitations and suggestions outlined above.

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

1 - There are numerous missing citations or mismatches with the reference list.  Please check on this and make it perfect.

2 - The English is very clear, but it needs one more edit for minor errors, such as line 161 where there is an issue with capitalization, and 23 where there is an odd apostrophe in "reveal." Check singulars and plurals one more time. 

3 - The illustration in the lead is very nice but it says "Abstract art" in the banner - it needs a meaningful title and caption., Figure 2 needs a proper caption and the print is small.  Perhaps it should be broken into more than one illustration.

4 - The methods seem fine except for the practice of computing CS values by family.  Some of these families have a very wide range of growth rates and ultimate size at maturity. The Fabacea, for example, with both temperate and tropical species, and everything from small thorn bushes to large stature canopy trees in the mix, seem like an odd family to merge. I wonder if some of the values aren't artifacts of the diversity of the family in terms of ecological strategy. The very ancient Magnoliaceae, for example, are primarily larger trees and not shrubs, and should give higher values. Would it be better to select ecological analogs for the species where data are available?  

5 - The trees in these parks are on average very small and some species like Populus deltoides appear to be largely falling short of their potential mature height and dbh (which is a good deal more than 15 cm where I've conducted research.)  This is very disturbed forest vegetation. The state of the stands suggests that soil condition and soil organic matter may be important factors relative to stand age in terms of carbon sequestration.  It's beyond the scope of this paper to consider it directly, but it is likely important to the question of whether carbon fixation is optimized by middle-aged forest stands or by older growth. I suggest considering this briefly in the discussion. 

6 - The conclusions suggest that park management should forward species that are relatively fast growing and reach larger size to optimize carbon storage.  Populus deltoides certainly fits the models. Among the commonest species, though, are tough invasives like Ligustrum lucidum, which is notorious for suppressing competitors via its evergreen cover. It also produces phenolics that modify soil chemistry.  Between its shade and its alleopathy, it can suppress seedlings and saplings of many other tree species, and influences nutrient cycling and decay rates of leaf litter. Ligustrum spp. can easily eliminate young Populus spp. Another aspect of the urban dynamic is some tree species are more resistant to pollution, impervious concrete surfaces, and shallow soils. Some start better in open sun, while others are more competitive in shade.  Some species make more of a mess with shedding leaves and branches. In addition, some faster growing species - like Populus - have lower density wood.  It depends on local conditions, but they may be more vulnerable to having their canopies blown out in storms. In my home region, Populus deltoides does not cope well with more xeric soils, while some of the Cypress and Acacia species do.  The popularity of Ginkgo as a street planting is partially due to its pollution resistance and ability to cope with sidewalks.  The conclusion is simplistic in this regard.  Some of the best choices could have intermediate properties - moderate levels of carbon pick-up, but are stronger competitors against invasives or better able to resist elevated ozone levels. The conclusion should be less single focus, and consider how to select for balance. And for success in terms of reaching reasonable goals. 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript presents an empirical study on how various factors—park attributes, woody plant spatial characteristics, biodiversity indices, etc.—influence carbon storage (CS) and carbon sequestration (CSG) in urban parks in Xinyang City, China. Using field surveys, high-resolution remote-sensing data, and i-Tree Eco models, the authors quantify CS/CSG of woody plants and examine the drivers responsible for variations across 81 urban parks. The results highlight how park size, proportion of woody vegetation, and community biodiversity indices (e.g., Shannon-Wiener Index, Margalef Richness Index) strongly correlate with improved carbon sequestration potential. Overall, the manuscript addresses an increasingly relevant topic: the role of urban parks in climate-change mitigation strategies. It provides a valuable framework that can help city planners and ecologists maximize carbon benefits in cities through targeted design and tree selection.

The manuscript deals with a timely topic, aligning well with global interests in nature-based solutions for greenhouse gas mitigation. It combines remote sensing with on-the-ground surveys to accurately quantify both carbon stocks and annual sequestration rates—a solid approach that strengthens confidence in the results. The focus on different drivers of carbon storage (biodiversity indices, spatial morphology, park attributes) broadens our understanding beyond simple biomass estimates.

Areas to Improve:

While the manuscript clearly covers park attributes and community-level factors, it would benefit from a slightly deeper treatment of socioeconomic drivers or climate variables if data are available. For example, differences in management intensity or urban development history might be relevant for explaining variation in carbon sequestration. Some comparisons with other similar urban contexts (e.g., cities of similar size or climate) could clarify how your results might generalize or differ from broader trends.

Major comments:

The manuscript uses the i-Tree Eco model for tree biomass, plus an allometric model for shrubs. Although justified, further detail on the specific uncertainties or errors introduced by the allometric equations for local shrub species would strengthen the methods section.

You note that the high-resolution satellite data come from two distinct satellites (PNEO and Inner Mongolia-1) on different dates. Briefly clarifying how data from these sources were harmonized would improve reproducibility.

Interpretation of Spatial Structure Indices

The results show strong relationships between fragmentation (PD, SPLIT) and carbon storage. Since certain indices (e.g., CONTIG_MN, LSI) can be somewhat technical to non-specialists, consider adding a bit more ecological rationale or examples (analogies) to explain why a higher patch density or a more complex shape fosters or hinders carbon storage.

The notion of a “threshold effect” in the connectivity index for carbon sequestration is intriguing; however, it could be expanded. Do you suspect an optimal connectivity for maximizing tree vigor or biodiversity? Elaborating would increase the practical takeaways for urban planners.

Future Directions

Although the Discussion acknowledges limitations, the text might benefit from a more detailed future outlook, especially regarding climate-change scenarios or potential expansions to include other carbon pools (e.g., soils, understory vegetation). I suggest to the authors to explore synergy or tradeoffs between carbon sequestration, social benefits (public well-being), and biodiversity conservation. It might appeal to a broader readership in Land.

 

Minor Comments and Suggestions

The title effectively conveys the study’s main topic. Consider adding an indication that the study employs a multi-method approach (field census, remote sensing) to quantify carbon benefits.

In the abstract, briefly mention the number of parks (81) studied and highlight the significance of biodiversity more explicitly, as that emerges as a critical driver in your results.

 

Introduction

You cite multiple studies and highlight the importance of urban green space for carbon sequestration. A succinct statement on the state-of-the-art methods (e.g., i-Tree Eco, LiDAR, remote-sensing approaches) and how your approach is distinct would help underscore your methodological novelty.

Methods

While the method and the equations are clearly stated, you could cross-reference them (e.g., “see Eq. (3) in Section 2.2.2.”) to help readers follow the text more easily.

Clarify briefly how the branching point height (g) was measured or estimated in the field. That ensures replicability.

 Results

Tables or graphical representation: The figures are quite comprehensive. If feasible, provide an additional map figure illustrating average CS and CSG in each park for a more direct visual representation—though Figure 3 does partially address this.

The paper frequently references boxplots and distributions (Figures 3–4). These are informative, but consider merging or comparing certain distributions in a single figure (if it does not become too cluttered) to emphasize patterns.

 Discussion

You give a solid overview of how local socio-environmental contexts (urbanization, species composition, etc.) shape carbon storage. Emphasizing any specific management recommendations or generalizable strategies would strengthen the “Implications” subsection.

Mention possible “win–win” strategies for biodiversity and carbon objectives, as part of the urban planning perspective.

 Conclusion

The conclusion is concise, but do ensure you restate the main numeric findings (e.g., average CSD = 4.01 kg/m², average CSGD = 0.39 kg·C·m²·yr⁻¹) and highlight how Xinyang’s results compare to other cities for broader policy or management insights.

 

Language and Readability

The overall English quality is clear, but there are a few grammatical or phrasing issues (e.g., “park green space … associated with…” in the abstract). A careful copyedit will ensure the final text flows smoothly.

Terminology around fragmentation metrics (NP, PD, SPLIT, AI) is used consistently; just be sure to define each acronym fully in the text where it first appears.

Based on the overall scientific merit, the robust methodology, and relevance to Land’s readership, I recommend “Minor Revisions” before acceptance. The paper is nearly publication-ready, with some clarifications and additional context beneficial for readers outside the immediate field. Incorporating the suggested improvements in future revisions will enhance the paper’s clarity and impact.

Thank you for the opportunity to review this interesting manuscript. I hope these suggestions aid the authors in refining and improving their final version for publication.

Comments on the Quality of English Language

Overall, the manuscript is written in clear and understandable English, but there are a few places where minor improvements can be made to enhance fluency and precision:

Use consistent terms for the same concepts (e.g., “carbon storage” vs. “carbon stock” or “carbon sink”).

Some sentences can be slightly rephrased for greater clarity. For instance, “a research in Muscat Province showed…” could be refined to “Research in Muscat Province showed…,” and so on.

Occasional minor grammar or phrasing issues appear (e.g., verb tense shifts), but these do not impede comprehension.

In a few places, sentences are long and could benefit from splitting or reorganization to ensure a more natural flow.

Some vocabulary (e.g., “promoting biodiversity and carbon fixation”) might be better phrased for simplicity—e.g., “enhancing biodiversity and carbon sequestration.”

None of these issues are severe enough to obscure meaning. A standard proofreading pass by a native or highly proficient English speaker (or a professional editing service) would readily address these points. Once polished, the overall quality of English will be well within publication standards.

Author Response

Please see the attachment

Author Response File: Author Response.docx