Coastal Forest Dieback in the Northeast USA: Potential Mechanisms and Management Responses

Round 1

Reviewer 1 Report

 

There is not enough new information since several fairly recent reviews, e.g. Tully et al. 2019 and Fagherazzi et al. 2019 to warrant this review. Furthermore, I did not find this review to contain novel insight or synthesis. For example, conceptual Fig. 1 does not provide insight and is quite similar to a figure in Fagherazzi et al. 2019. The authors claim a distinction between their review and those prior in saying that this review places heavier emphasis on rising freshwater groundwater tables, but there is not substantial evidence presented in the paper to warrant this revision, which should be evidence-based.

 

The regional assessment presented in this manuscript is primarily a summary of NOAA SLR Viewer data, a bathtub model, overlain on NLCD. While this summary may be useful for public communication and planning purposes, it is not elucidating of ecosystem-level effects, since it incorporates no biological or geological processes. The summary in Fig. 3 is rudimentary and repetitive from Table 1. No error, uncertainty, or breakdown by habitat, is presented.

 

The SLR Viewer data is compared with data from a thesis (Sacatelli 2020) which has not been peer-reviewed. There is not enough detail about the methodology of the historical analysis in Sacatelli 2020 to inform the comparison. It would be more appropriate to publish the thesis and add the comparison to the NOAA SLR Viewer data in a data paper.

 

Minor comments

L24 & 25 - and throughout - use metric units

L323-324 - poorly worded, sounds like the greatest risk comes at the lowest rate of slr

Table 1. Maryland row should be moved above Virginia to order from largest to smallest SUM

 

Key references missing:

Carr et al. 2020 GRL

Chen and Kirwan 2022 Nature Geoscience

Molino et al. 2022 L&O

Taillie et al. 2019 Ecosystems

White and Kaplan 2021 Remote Sensing of the Environment

White et al. 2022 Ecosystems

Author Response

Authors’ Response

Based on this and other reviewers’ comments we have shifted to focus more on the management recommendations that were an outcome of the workshop and expert interviews, as well as the identified knowledge gaps.

We have updated our literature review as well as included additional suggested citations. We have included a Methods sections providing further specifics on the literature review, expert interviews and the workshop (Lines 110-138). Though our focus was on the MidAtlantic/southern New England region, studies from these other regions (i.e., Gulf of Mexico, Southeast US) are often pertinent as the topography, landforms and plant communities share many similarities. 

We have included text to clarify the distinctions between the prior work of Tully/Fagherazzi/Carr et al. and the conceptual model as developed here.  We don’t disagree with these studies but are trying to emphasize how rising groundwater levels might contribute to coastal forest dieback and the need for additional research to clarify their significance in comparison to the well documented role of ”pulse” disturbances. We have revised the text to include the following

Lines 398-408  One subtle distinction is that our conceptual model places a greater emphasis on the role of rising fresh groundwater levels in increasingly stressing the forest vegetation and decreasing regeneration potential. The emphasis we place on rising groundwater levels is based on the critical role that fresh groundwater flow plays in the hydrology of the coastal zone [30] as well as the recent three-dimensional groundwater-flow modeling conducted by the US Geological Survey that predicts that the depth to the water table and the thickness of the unsaturated zone will decrease with rising sea levels [44-46]. In inland areas of coastal forests, freshwater recharge and inflow of fresh groundwater from upland areas result in a freshwater-only environment (Figure 3a). The upland edge of the transition zone, where there is a mixing of fresh and saline water, is proximal to the marsh-forest ecotone (Figure 3a). In our conceptual model, the “press” disturbance of sea level rise is working through the proximate mechanisms of rising groundwater levels increasing saturated soils, as well as the movement of the transition zone landward (Figure 3b & 3c). Given the well documented effect of saturated soils on impeding tree growth and reproduction [42, 49-50, 52, 54] rising groundwater levels appear to contribute to coastal forest dieback but additional research is needed to clarify their significance in comparison to the well documented role of ”pulse” disturbances [78, Carr].

Authors’ Response

We have removed the section on the regional analysis to focus on the management recommendations that were an outcome of the workshop and expert interviews as well as the identified knowledge gaps.

Reviewer 2 Report

General comments: This manuscript intends to review the scientific literature on coastal forest dieback in the Northeast - Mid Atlantic USA, the goal of which (although somewhat unclear) to understand the main drivers of change and plan for future change. Though, a very interesting topic with potential contributions to the body of knowledge on the topic, this manuscript reads more like a textbook chapter rather than a true review. I was unable to discern whether any sort of systematic review methods were applied. As such, they seem to be missing a large body of work on the topic (i.e., Henman, Poulter, Smart, Aguilos on carbon or ecosystem services dynamics; Martinez on state changes in coastal forests; Anderson, Taillie on vegetation composition changes; Krauss on biogeochemistry in freshwater forested wetlands affected by sea level rise; White Jr on regional scale mapping of coastal forest change; foundational studies from Young, Williams, Moorhead and Brinson on the topic, etc.). And because there are no methods documenting their approach to the literature review, it's difficult to tell if these fell outside their search criteria or they were just msised, etc.

Also, they discuss the inclusion of interviews but provide no specifics on how those interviews were conducted (in person, virtual, focus group vs individual, how many people total) or what types of interviews they were (semi-structured, etc). It's also unclear how the interviews were used in the research to inform their outputs. Assuming they used them in some way to develop the conceptual model, but how?

Because of these major concerns listed above and the inability to discern whether or not they applied a rigorous approach to their research, I cannot recommend this for publication in its current form. I recommend rejecting the manuscript, revising to highlight the specific work done to come to the conclusions in their paper, and resubmitting as a new manuscript. 

Specific comments: 

There is literature also indicating that drought is another driver of coastal forest dieback but do not see that included in your conceptual model. 

I really like Figure 2 graphics. A nice visual of the process. 

Are there any maps that could accompany the region-wide assessment? 

I did not have access to the Appendix A they reference in their manuscript which supposedly details the methods for their regional assessment of vulnerability. 

 

Author Response

Authors’ Response

Based on this and other reviewers’ comments we have shifted to focus more on the management recommendations that were an outcome of the workshop and expert interviews, as well as the identified knowledge gaps.

Accordingly, we have included a Methods sections providing further specifics on the literature review, expert interviews and the workshop (Lines 110-138).  As part of the Literature Review, the geographic region (i.e., Gulf of Mexico, Southeast, MidAtlantic/New England of the US) and year of publication were recorded. That information is now included. Though our focus was on the MidAtlantic/southern New England region, studies from these other regions are often pertinent as the topography, landforms and plant communities share many similarities. 

The Literature review was updated and a new section was included that explicitly discusses the results of the Literature review and a breakdown by year and geographic region (lines 140-154).

We have expanded the text to include additional references but do not consider all aspects of coastal forest dieback. For example, we do not delve into some of the implications of dieback on carbon dynamics. While we have included literature for the Gulf And Southeast US coasts we focus on the MidAtlantic/southern New England states, drought does not appear as relevant (or at least has not been explicitly studied). We have included a new sentence

Lines 267-270. Similarly, extended drought can also have negative effects on tree health and regeneration. Some work on the Gulf coast forest [Desantis et al., 2008] has documented drought as potentially contributing to dieback, the role of drought has not been a focus in MidAtlantic research studies to date (Figure 2).

Figure 2 (now labelled Figure 3) was modified to increase the font size and improve the readability.

Reviewer 3 Report

The manuscript "Coastal Forest Dieback in the Northeast US" provides a review of effects of sea level rise on coastal forests along the northern Atlantic coast of the United States of America, with some previsions of forest area loss over a range of future sea levels and concluding management suggestions. The manuscript is, by its topic, US-centred but with a little effort the authors make it quite interesting also for an international readership (see detailed remarks below). As there are already many reviews regarding sea level rise and the effects of stress factors affecting vegetation coupled with sea level rise, the main focus of this review should be on demonstrating the effects of sea level rise on the study region, which is without doubt relevant due to its size, research history and special exposure to sea level rise. Perhaps the authors could highlight the significance of the area more clearly in the Introduction. I also would suggest to talk only briefly about the mechanisms affecting plant growth when the research on which corresponding assumptions are based is not derived from field studies in the study region. The information necessary to understand these concepts could be given in the context of the "conceptual model" presented in Figure 1, citing the relevant existing reviews. Then, the effects and modelling efforts for the study region could be presented more succinctly, giving a stronger focus on the geographical area mentioned in the title, without necessity to cite references from other regions. Overall the article is well written and structured (there might just be some duplicity with existing reviews without the regional focus).

When considering the suggestions I made, please bear in mind that I am not a native speaker of English.

Introduction: The Introduction may be a little bit too US-centred. It would be beneficial to emphasise more clearly why this region is important also for an international readership, without presuming that the readers have geographical and ecological knowledge of the study region.

 44    "Nor'easters": seems to be a local denomination -- necessary?; "our": maybe find a less personal way of referring to the coastline of the study area?
 49    "communities". "types"?
 50    "[9]" (in fact, l. 527 ff.): the author list of this reference is incomplete. https://mdpi-res.com/data/mdpi_references_guide_v5.pdf suggests to add "et al." when the author list exceeds 10 authors (or to cite all authors) -- check also for other, similar references. When citing a large document like this, it would be helpful to cite the corresponding chapter(s) explicitly.
 54    "[9-11]": [10] is from the Gulf of Mexico -- possibly better not to cite these references in one batch and be clear about the geographical distance, if it is really necessary to cite [10] in this context
 55    "[12-14]": regarding coastal forests, e. g. [13] refers almost exclusively to mangroves -- when you give these examples perhaps state briefly that you think the cited results will also apply to Northeast US coastal forests
 69f    "VA ...": I'm not sure whether the abbreviations of US states are known to readers from other regions of the world. If necessary, cite full names. However, citing the latitudinal range would be more informative, anyway.
71    "experts": shouldn't the experts ("leading experts" in the abstract + in the conclusions) be mentioned and the type of interview described at some point in the manuscript?

Conceptual model: State briefly where this model came from. Also, see suggestion above about changing this section to provide here the general information on which the model is based.


Physical Environment and Vegetation Zonation: There is, in fact, not much information about vegetation zonation here. Possibly, tables with plant species known to occupy certain ranges along the flooding/salinity gradients could improve the review.

132     "complex": without explanations of the complexity in comparison to other coastal systems, this statement is somewhat void; "flows" -> "flow" (the aquifers?)
144     "[30]": I guess this reference is supposed to account for all of the above text? I would suggest to cite the reference (with chapter/page specification) repeatedly with every subtopic presented, possibly also providing the original literature cited within [30] (or more recent specific studies, if available)


Potential proximate mechanisms controlling forest dieback: Here and in the previous section, ecophysiological responses of plants to flooding are presented. However, much of this is not based on research in the study region. It might be a better strategy to put a very brief summary of factors associated with sea level rise and stress in plants (mainly citing the exiting literature reviews) with the "conceptual model" (see above) and then focus on the studies from the study region, to avoid jumping back and forth. I assume that the text could become shorter and more focused this way.

180ff      this paragraph does not really bring any new ideas; most important seems to be that the following text will report details of the current changes affecting the system.
217      "Figure 1": better cite (at least in addition) the studies from the study region that document these changes?
218      "slow but steady": will depend on the area affected -- if a certain limit is reached, there might be a sudden dieback of unexpectedly large areas, depending on local topography
257      "breakage": not in your conceptual model
260      "can come in contact with ... cambium": just contract all this to "may cause physical damage to the trees' cambium"? "nutrient transport": that sounds a little bit strange, as the cambium does not transport anything itself; it is possibly not even necessary to get too much into the details here
262      "78]": does South Carolina belong to the study area?
271      "subtle distinction": make clear on which studies/interviews you base your greater emphasis on rising groundwater levels


Region-wide assessment: "feet", "acres" etc. -- use the metric system!!


Management responses to coastal forest dieback

378       "Phragmites": scientific names in italics; for non-locals it might not be clear why Phragmites is important in the region, so please include a brief characterisation of its role in the described ecosystem


Conclusion: First two paragraphs are somewhat redundant as they mainly sum up previous findings. Perhaps try to shorten.

398    "leading experts": see remark in "Introduction"
413    "2'": metric system!
415    "did not consider": I already wondered about that -- it would be worthwhile to indicate somewhere why these factors have been excluded from the analysis (lack of study? possibly of minor importance in the study region?)
419    "companion ...": better mention this before in the section "Region-wide assessment" when citing the same study?
420    "1'" metric system, please!! (also,  482, 486, ...)


Figure 1: there is no direct effect of storms and storm surges on tree health? Is this linked to the considered time scale (-> include in the caption)

Figure 3: convert o metric units


Table 1: convert metric units

Author Response

Authors’ Response:

We thank the reviewer for his/her close read of the text. We have paid close attention to these comments and included their editorial suggestions. As we have removed the Regional Analysis, some of the comments related to metric units are no longer relevant.  We have rewritten large sections and changed the titling of some of the sections in attempt to improve the flow and readability.

Based on this and other reviewers’ comments we have shifted to focus more on the management recommendations that were an outcome of the workshop and expert interviews, as well as the identified knowledge gaps.  We have tried to clarify that the conceptual model as outlined in Figure 2 (was Fig 1)) is based on a combination of the Literature Review, expert interviews and the workshop.

As part of the Literature Review, we included papers from several geographic regions (i.e., Gulf of Mexico, Southeast, MidAtlantic/New England of the US). Though our focus was on the MidAtlantic/southern New England region, studies from these other regions are often pertinent as the topography, landforms and plant communities share many similarities.  We excluded studies that dealt with mangroves as not sufficiently relevant.  However, the papers we have included on ecophysiological studies, though from different regions, we deemed as pertinent as these were usually on the same, or similar tree species.

We agree that  storms (both the surge as well as wind) can directly impact tree health. The proximate effects are discussed in the text (Lines 256-264) but not included in Figure 1. We have modified Figure 2 to include Storm Winds and to draw a direct link with and Tree Health.

Reviewer 4 Report

This is a timely and engaging review of the suite of drivers of ghost forests formation in the northeastern United States. The review summarizes the relevant literature and produces a synthesis that makes the argument that both saltwater inundation and rising groundwater tables associated with SLR are driving ghost forests. The paper highlights the need for understanding of mechanistic drivers as coastal managers pursue strategies to prepare for marsh migration. This is a well written and timely review, and I only have minimal suggestions for revision.

First, when the Conceptual Model figure (Figure 1) is introduced, the figure is poorly explained. In particular, the authors need to lay out how the connections in the figure were developed (i.e. is this figure a result of the literature review and expert elicitation or is it something that was used as an a priori model to drive the synthesis and conversations with experts?) Centering the Figure within a narrative trajectory of the review more appropriately is needed.

Secondly, the paper as currently written lacks a clear narrative organizational structure. The paper starts with Figure 1 and then refers back to it consistently while it reviews different aspects of the literature. More work is needed on the organizational structure to make it clear that the review will first focus on evidence around groundwater table, then on inundation, then on a region-wide assessment of impacts, then on management. There is no clear logic laid out in the introduction and framing of the article for the current organization.

Third, Figure 2 is of low quality. It is important to the review but the image quality needs to be greatly improved (this could be a function of the review process but it is unreadable in the document provided).

Fourth, the Management section is under developed in terms of its literature review. There is extensive coastal management literature focused on preparing for the impacts of sea level rise, including non-inundation impacts on communities through long-term landscape-scale changes. Communities and non profits are already preparing for marsh migration and a better synthesis of this literature would help bolster the impact of this paper.

 

A few minor points
Line 131: northeastern as an adjective should not be capitalized.

The paper alternates between one space after a period and two spaces after a period, without consistency.

Table 1 and Figure 3 show the same data.

Author Response

Authors’ response

Based on this and other reviewers’ comments we have shifted to focus more on the management recommendations that were an outcome of the workshop and expert interviews, as well as the identified knowledge gaps.  We have tried to clarify that the conceptual model as outlined in Figure 2 (was Fig 1)) is based on a combination of the Literature Review, expert interviews and the workshop. 

We have rewritten large sections and changed the titling of some of the sections in attempt to improve the flow and readability.  The conceptual model (Figure 2) provides the nexus of the text that delves into different components of the model system, thus our repeated references.

We have greatly expanded the Management suggestion with a special attention to the knowledge gaps.

We have expanded the size of the font within Figure 2 (now Figure 3). The new figure itself is a high resolution graphic but once inserted into my version of the document the appearance is compromised. Hopefully the publishers can included a full resolution copy of the figure for download.

Reviewer 5 Report

1. The work is very well done, but the problem is very local, and the exact effects of sea level rise are present in the coastal zone worldwide, but we need the data that the U.S. government generates.
2. It is exciting how the subject is approached, and they have the facility of a federal agency concerned about the effects of climate change on the country: Sea Level Rise Marsh Migration data product developed by the NOAA Office for Coastal Management (as designed for the U.S. Digital Coast Sea Level Rise Viewer https://coast.noaa.gov/digitalcoast/tools/slr.html).
3. Proposals to manage a forested area without land use change pressures may be feasible. Still, in other regions with few forested areas and high land use change pressures, sea level rise will affect human settlements more than other areas.
4. The concept of the rising groundwater table is very interesting. This component in other regions is probably already overexploited and contaminated with seawater (for example, in the Yucatan Peninsula). It could exacerbate this effect with the rise of the mean sea level.

Suggestions

It is necessary to increase the font size in figure 2.

The units used in work should be of the International System.

 

I have no comments on the document.

Author Response

Authors’ response

We have expanded the size of the font within Figure 2 (now Figure 3). The new figure itself is a high resolution graphic but once inserted into my version of the document the appearance is compromised. Hopefully the publishers can included a full resolution copy of the figure for download.

As we have removed the Regional Analysis, some of the comments related to metric units are no longer relevant. 

Reviewer 6 Report

Dear authors,

the manuscript (ms) "Coastal Forest Dieback in the Northeast US" is an interesting work.  The ms displays a scientific synthesis in order to develop a conceptual model of coastal forest dieback, identifying the main driving processes, mechanisms and responses of the ecosystem. The subject is interesting for the purpose of the periodic, so it is a good contribution. The ms is well presented and the English writing is good. In this way, I consider that the manuscript could be accepted for publication and would be an interesting theme for the Sustainability readership.

Author Response

Authors’ response

Thank you for the comments.