the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Sep 2023
A synthesized field survey database of vegetation and active layer properties for the Alaskan tundra (1972–2020)
Abstract. Studies in recent decades show strong evidence of physical and biological changes in the Arctic tundra largely in response to exceptionally rapid rates of warming. Given the important implications of these changes on ecosystem services, hydrology, surface energy balance, carbon budgets, and climate feedbacks, research on the trends and patterns of these changes is becoming increasingly important and can help better constrain estimates of local, regional, and global impacts as well as inform mitigation and adaptation strategies. Despite this high need, scientific understanding of tundra ecology and change remains limited largely due to the inaccessibility of this region and less intensive study compared to other terrestrial biomes. A synthesis of existing datasets from past field studies can make field data more accessible and open up possibilities for collaborative research as well as for investigating and informing future studies. Here, we synthesize field datasets of vegetation, and active layer properties from the Alaskan tundra, one of the most well-studied tundra regions. Given the potential increasingly intensive fire regimes in the tundra, fire history and severity attributes have been added to data points where available. The resulting database is a resource that future investigators can employ to analyze spatial and temporal patterns in soil, vegetation, and fire disturbance-related environmental variables across the Alaskan tundra. This database, titled Synthesized Alaskan Tundra Field Database (SATFiD), can be accessed at the Oak Ridge National Laboratory Distributed Active Archive Center (ORNL DAAC) for Biogeochemical Dynamics (Chen et al., 2023: https://doi.org/10.3334/ORNLDAAC/2177).
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RC1: 'Comment on essd-2023-222', Anonymous Referee #1, 13 Dec 2023
Overall quality/General comments
This paper presents and describes a new data synthesis product for field collections of vegetation, active layer, and fire severity measurements from the Alaskan tundra. This dataset is particularly useful to the scientific community because 1) these areas are rapidly changing in response to climate change and permafrost thaw, 2) access to tundra regions is difficult and thus empirical datasets are sparse compared to other biomes (and housed in different data repositories), and 3) Alaska in particular is a tundra “hotspot” given observations of fire activity in this region of the past ~70 years. Data was collected for this synthesis from direct contact with PIs, existing repositories, and literature searches.
The authors have done an excellent job of filtering, harmonizing, and organizing the disparate datasets into a cohesive structure. What makes the dataset the most useful is that it can be used in different ways depending on research question. For example, one can identify a location of interest, see the data available at that site, and then go back to the original publication or dataset. That in and of itself makes the data compilation extremely useful to Arctic researchers. Furthermore, the synthesis itself is organized by most commonly measured variables, which allows users to quickly collect data for larger comparative questions (e.g., a metric in one region compared to another, or one time period to another), comparisons to other datasets (e.g., measurements compared to remote sensing data), and comparisons between variables (e.g., relationships between fire occurrence and vegetation turnover). This type of flexibility is wonderful for scientists working in this region to start to design new research projects and generate new hypotheses.
Overall, I see no issues with this manuscript as written. There is a clear explanation of the what the dataset has in it, how the data were organized, how it might be used by researchers, what is missing in the data, and potential issues with sampling design differences. The only thing I would like to see added is a description of whether or not this database will be open to new submissions in the future and if so, how it will be maintained.
Specific/Technical Comments:
In terms of technical issues, the paper is well-written, and the figures are informative and designed well, and the paper is structured in a logical way. I see nothing that needs to be edited for clarity, as the paper is very easy to read. I appreciated reading such a well-conceived paper!
Citation: https://doi.org/10.5194/essd-2023-222-RC1 -
RC2: 'Comment on essd-2023-222', Michel Allard, 27 Mar 2024
Review of “A synthesized field survey database of vegetation and active layer properties for the Alaskan tundra (1972-2020)” by SHU et al.
The authors went to considerable efforts to compile this data base from 37 datasets originating from field measurements by different authors working in the tundra zones of Alaska over 50 years. Almost 200 000 data points were compiled and located with their geographic coordinates and the observed/measured data on vegetation cover (mostly structural), basic soil properties, active layer thickness were uniformized and compiled. In addition, the authors overlay the remote sensing mapping data of wildfires from the Alaska Large Fire Database (ALFD), thus allowing for future research to be carried on the impact of fires on the ecosystems. Some sites were surveyed by their authors after one or more fires (post-fires), other between fires and some before fires (pre-fire). An index of fire severity is also one data in the file (the dNBR attribute). The paper (supporting text) for this new, integrated, SATFiD data file, presents the compilation methodology, the “averaging” approach that was sometimes used to uniformize the data collected by different field researchers applying different survey methods with unequal precision. All considered, this is important work.
The authors state three objectives for their work: “(1) Gather datasets and synthesize them in a way that will facilitate further analysis by investigators and promote synthesis research efforts, (2) deepen our understanding of ecosystem processes within the Alaskan tundra, particularly fire-vegetation-permafrost interactions, and (3) identify areas of interest for future research where knowledge is lacking or there is great potential for follow-up research to study change and long-term trends.” I suggest to add a fourth one: to provide basic data on properties of the components of the ecosystem such as soil physical properties, active layer thickness, organic layers, water content, vegetation composition and dynamics, as measured parameters for modelers to validate their simulations as well as for providing a better understanding of processes for their modelling. The authors are conscious that the data compiled in the different regions of the Alaskan tundra provide “snapshots” of the state of the vegetation and basic soil conditions at the time the various surveys were carried on the field. Maybe, this should be explained in a stronger statement in the text. We understand that fires are a major factor that may have induced ecological changes and that revisiting the field sites shall allow to assess its impacts of ecosystems. However, fire is only one factor of change. For instances climate change is also associated with shrub dynamics and snow cover variations, a factor not part of the dataset. Active layer thickness, surface erosion and deposition, organic layer growth (particularly through moss cover thickening) have also varied over the past 50 years. Therefore, although providing fundamental basic information, the SATFiD data will need to be used with some circumspection.
Here are a few editing and technical comments:
- Line 36: “exceptionally rapid rates of warming”, exceptional relative to what? Maybe just say very rapid.
- Line 54: I suggest replacing “biological changes” by ecological changes.
- Line 73: I suggest replacing “strong warming” by fast or rapid warming
- Line 80: replace “expeditions” by field work or field surveys
- Line 81: “The Alaskan tundra is an important component of the Arctic tundra biome…” Maybe say differently like.. represents an important fraction of the Arctic tundra with an area over 8.5 million km2 and shares similarities with other Arctic regions.
- Line 86: I suggest replace “included” by inventoried.
- Line 97: delete “we argue that”, not necessary.
- Table 2: last procedure: daily calculation. Unclear to me. Do you mean repeat measurements over a long time period, i.e. months, years?? As it is written now I understand that the mean of a small number of measurements taken within one day is considered a daily mean..?!. Maybe I misunderstand… For instances, are temperature data taken over time with dataloggers averaged daily?
- Figures 5 and 6. I suggest you reorganize the figures and captions so as not to repeat a and c in both figures.
Citation: https://doi.org/10.5194/essd-2023-222-RC2 -
AC1: 'Comment on essd-2023-222', Xiaoran Zhu, 12 Apr 2024
Dear Referees,
Thank you for your reviews and encouraging, insightful comments for our manuscript. We greatly appreciate that you see the value in this data synthesis effort and are grateful for your helpful feedback. We have incorporated your suggestions into our revised manuscript. Please also find our responses (in italics) to each suggestion below.
RC1: The only thing I would like to see added is a description of whether or not this database will be open to new submissions in the future and if so, how it will be maintained.
- We agree that we should include a description of whether and how we plan to maintain this database. We intend to update SATFiD biennially to include newly acquired field data in the Alaskan tundra, allowing the further expansion of SATFiD’s utility in studies of long-term changes in the tundra. We will actively seek funding to support these future updates. This information has been added to section 5.1 Scientific Implications within the Discussion section.
RC2: I suggest to add a fourth one [objective]: to provide basic data on properties of the components of the ecosystem such as soil physical properties, active layer thickness, organic layers, water content, vegetation composition and dynamics, as measured parameters for modelers to validate their simulations as well as for providing a better understanding of processes for their modeling.
- Thank you for this suggestion. It is true that this database can function as a resource for modelers, and we have added this in as a fourth objective in the Introduction.
RC2: The authors are conscious that the data compiled in the different regions of the Alaskan tundra provide “snapshots” of the state of the vegetation and basic soil conditions at the time the various surveys were carried on the field. Maybe, this should be explained in a stronger statement in the text. [...] Therefore, although providing fundamental basic information, the SATFiD data will need to be used with some circumspection.
- As you indicate, we are well aware of the limitations of the field data and hope to convey the importance of considering them when using the data. To clarify this, we have added a statement at the end of section 5.2 Uncertainties to convey that users should take into account this non-static nature of the Arctic tundra when adopting SATFiD for long-term analyses, given the various warming-induced ecological changes in the Arctic that are not necessarily captured by the “snapshot” data within this database.
RC2: Editing/technical comments
Line 36: “exceptionally rapid rates of warming”, exceptional relative to what? Maybe just say very rapid.- We have rephrased it as “rapid rates of warming”.
Line 54: I suggest replacing “biological changes” by ecological changes.
- We have rephrased this as “ecological changes”.
Line 73: I suggest replacing “strong warming” by fast or rapid warming
- We have rephrased it as “rapid warming”.
Line 80: replace “expeditions” by field work or field surveys
- We have rephrased it as “field surveys”.
Line 81: “The Alaskan tundra is an important component of the Arctic tundra biome…” Maybe say differently like.. represents an important fraction of the Arctic tundra with an area over 8.5 million km2 and shares similarities with other Arctic regions.
- We have rephrased this to “The Alaskan tundra represents an important fraction of the Arctic tundra biome that spans over 8.5 million km2 and shares similar characteristics with other Arctic regions”.
Line 86: I suggest replace “included” by inventoried.
- We have rephrased it as “inventoried”.
Line 97: delete “we argue that”, not necessary.
- Removed.
Table 2: last procedure: daily calculation. Unclear to me. Do you mean repeat measurements over a long time period, i.e. months, years?? As it is written now I understand that the mean of a small number of measurements taken within one day is considered a daily mean..?!. Maybe I misunderstand… For instances, are temperature data taken over time with dataloggers averaged daily?
- Your understanding of the data measured at the same site being averaged daily is correct. This is done in cases when multiple samples were taken for certain variables. Average values are reported in this synthesis. We rephrased this in the chart as “Repeat measurements from the same day and plot, as defined by the latitude and longitude, were averaged for all quantitative variables.”
Figures 5 and 6. I suggest you reorganize the figures and captions so as not to repeat a and c in both figures.
- Thank you for pointing this out. In Figure 5, a and c should be the distribution of all burned data points within our dataset by fire history, whereas in Figure 6, a and c exclude the Schaefer_2021 dataset as it dominates the data. We have updated Figure 5 to show the correct plots a and c. On the other hand, we will remove Figure 6 as it is repetative, serving only to show the data distribution when taking Schaefer_2021 data out. We already discuss the dominance of this data at various points in the text as well as in Figures 2 & 3 and Table 4. As Figure 6 was not referenced in the text and does not contribute sufficient new, meaningful information, we will exclude it from the revised manuscript.
Citation: https://doi.org/10.5194/essd-2023-222-AC1
Data sets
Field Data on Soils, Vegetation, and Fire History for Alaska Tundra Sites, 1972-2020 D. Chen, X. Zhu, M. Kogure, E. E. Hoy, X. Xu, N. H. F. French, L. T. Berner, A. L. Breen, S. Bret-Harte, S. J. Davidson, J. J. Ebersole, G. V. Frost, S. J. Goetz, R. E. Hewitt, J. K. Y. Hung, C. M. Iversen, G. Iwahana, R. Jandt, L. K. Jenkins, A. N. Kade, I. Klupar, T. V. Loboda, S. Ludwig, M. J. Macander, M. C. Mack, C. R. Meyers, R. J. Michaelides, E. A. Miller, S. Natali, T. W. Nawrocki, P. R. Nelson, A. D. Parsekian, E. Rastetter, M. K. Raynolds, A. V. Rocha, K. Schaefer, U. Schickhoff, E. A. G. Schuur, S. Tsuyuzaki, C. E. Tweedie, S. V. Zesati, D. A. Walker, P. J. Webber, M. Williams, and D. Zona https://doi.org/10.3334/ORNLDAAC/2177
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