Chihuahuan Desert Vegetation Development during the Past 10,000 Years According to Pollen and Sediment Data at Upper Arroyo, Saltillo, Mexico
Round 1
Reviewer 1 Report
The manuscript entitled 'Chihuahuan Desert vegetation development during the past 10000 years according to pollen and sediment data at Upper Arroyo, Saltillo, Mexico' provides an interesting study about vegetation response in relation to climate change in a desertic area in Mexico. The discussion and conclusions are aligned with well described results. Nevertheless, the graphical part of the manuscript must be improved. The quality of pollen diagrams (figues 9, 10, 11) needs to be checked by the author. The small font used makes the diagram unreadable and the bars used are too narrow. And in general these 3 figures are blurred.
In table 4 I suggest that the time periods should be written in chronological order. For example, change 8875-10000 to 10000-8875
A part from this minor remarks, the content of the manuscript is appropriate for its publication in Quaternary
Author Response
Dear Reviewer 1,
The manuscript entitled 'Chihuahuan Desert vegetation development during the past 10000 years according to pollen and sediment data at Upper Arroyo, Saltillo, Mexico' provides an interesting study about vegetation response in relation to climate change in a desertic area in Mexico. The discussion and conclusions are aligned with well described results. Nevertheless, the graphical part of the manuscript must be improved. The quality of pollen diagrams (figues 9, 10, 11) needs to be checked by the author. The small font used makes the diagram unreadable and the bars used are too narrow. And in general these 3 figures are blurred.
Figures converted to TIFF format for higher resolution with increase also in FONT size. Hopefully this will improve quality. If still inadequate, a more radical change in the diagram formatting might be done through drawing office.
In table 4 I suggest that the time periods should be written in chronological order. For example, change 8875-10000 to 10000-8875
Done
Author Response File: 
Author Response.docx
Reviewer 2 Report
The paper ‘Chihuahuan Desert vegetation development during the past 10000 years according to pollen and sediment data at Upper Arroyo, Saltillo, Mexico’, by Bruce A. Albert, uses pollen and sedimentology from several alluvial exposures to reconstruct Holocene vegetation and environmental history in an arid region from central Mexico.
I found this paper interesting, and a valuable addition to the palaeodata repository of the area, since there are not a lot of studies focused on the relationships between vegetation and environmental dynamics in the Upper Arroyo. However, I think that some adjustments are required before recommending this paper for publication. First of all, the elements of novelty brought by this study are not highlighted enough. For instance, I found it difficult to see what the knowledge gaps are that this study aims to fill. Second, the pollen diagrams have such a poor resolution, that it was nearly impossible for me to distinguish all the taxa names and thus made it way harder to follow the description of the results. I would also recommend going thoroughly through the manuscript to simplify the wording and correct the very many spelling mistakes and missing words, which make reading and understanding of the text much harder.
Minor comments:
Introduction and Study Area
It is not entirely clear to me if Upper Arroyo is a river, or a former river currently dried out, or an area. Please, clarify.
Figure 1 caption: There is no information in the text about the Laguna Project, nor about the sites included in the project. It is therefore hard to grasp the relationship between this study and the aims of the Laguna Project. Also, please clarify in the caption what the black rectangle represents.
L. 80 What does ‘context sediments’ mean?
Figure 2: Perhaps a hypsometric map background would have been more suitable here, to help the reader get a picture of the local landscape morphology.
L. 193-199 – Please cite additional or more recent studies to support this inference. One reference which is over 30 yr old for an assumption that stands at the basis of the pollen record interpretation in this study is, in my opinion, not enough.
L. 225-226 To my knowledge, LOI is a method used to derive organic matter content (which is the proxy) expressed as a percentage of dry weight. See for example Heiri et al., 2001, Journal of Paleolimnology. So please, do not use the method instead of the proxy.
Also, please provide the proper reference for the particle size data, because the reference provided does not refer to such data. How was sorting determined?
L. 277 What does ‘brachiation’ in this context stand for? Please clarify.
Figure 5. Please replace LOI with the proxy, i.e., organic content. Also, χ definitely does not refer to sorting, and in the cited paper it denominates magnetic susceptibility, which can hardly be used to determine sorting, and is different from particle size. Please correct these inconsistencies.
L 291-295 Please explain in detail the reason(s) for rejecting the 14C dates from the models.
Tables 1-3. It is not clear if these radiocarbon dates are new or were extracted from a published study. If they are already published, please provide the original reference. Also, there is no information regarding the method used for radiocarbon analysis, and the calibration curve used. This is important information and should be highlighted.
L. 348 What does ‘trace values’ mean in this context?
Figures 9, 10 and 11. Figures are nearly impossible to read, due to the very poor resolution. Also, why was the pollen sampling so uneven in the profiles? Please discuss the potential implications of the uneven sampling on your results and interpretations. It would also help adding a lithology column next to the pollen stratigraphies.
L. 470-481 Why not compute a DCA on the pollen data presented in the study and then compare it with the results shown by Caballero-Rodriguez et al?
L 480-481 In my opinion, it is extremely difficult to reconstruct elevation changes in tree limit in the absence of plant macroremains data. If you use only pollen for such reconstructions, then these are merely assumptions and should be regarded as such, or the interpretation should be backed up by more references.
L 546 Please explain what ‘Global patterns’ means in this context. Because the comparative assessment which shortly follows is regional, not global.
L 553 ‘with temporal horizons of cycles being significant at secular timescales’. Does this refer to statistical significance? It’s confusing; please reword.
Figure 14. Which is temperature and which is precipitation? Please, explain clearly in the caption. Also, why is the second y axis titled ‘Depth’? Perhaps this figure is better suited to ‘Study area’, than to ‘Conclusions’.
Author Response
Dear Reviewer 2,
Corrections and changes (with minor exceptions noted below) are made to the manuscript.
Minor comments (my comment s italics):
Introduction and Study Area
It is not entirely clear to me if Upper Arroyo is a river, or a former river currently dried out, or an area. Please, clarify.
Seasonally dry-river meant here and clarified but historic water management also noted (see you r magnetic susceptibility.
Figure 1 caption: There is no information in the text about the Laguna Project, nor about the sites included in the project. It is therefore hard to grasp the relationship between this study and the aims of the Laguna Project. Also, please clarify in the caption what the black rectangle represents.
The black rectangle represents sites focal to present study while full map represents all sites contributing to composite wet-dry cycle graphic, this is clarified.
- 80 What does ‘context sediments’ mean?
Refers to mutual indicative values pf the pollen vs. sediment data, for example, Potomogeton pollen, derives from an aquatic plant, being found in layers where calcareous (spring vent) calcareous tufas are found indicating deep perennial waters in tandem (Zone 1 in Early Holocene sequence), made explicit in text in simple statement. Another example that is sequential and inferential in nature, gravels in Unit E (Late Holocene) representing major erosion, being immediately bracketed by samples in Units D upper part, and Unit F, having Ephedra as dominant flora, this thriving in rocky and poorly developed soils.
Figure 2: Perhaps a hypsometric map background would have been more suitable here, to help the reader get a picture of the local landscape morphology.
This is the purpose of Figure 3, the caption of Figure 3 now identifies the orientation explicitly.
- 193-199 – Please cite additional or more recent studies to support this inference. One reference which is over 30 yr old for an assumption that stands at the basis of the pollen record interpretation in this study is, in my opinion, not enough.
This is a question mostly of the trajectory of studies, North Mexico relative to Central Mexico has fewer studies, the Ortega-Rosas et al. study of 2008 remains the most important for a large land area despite its relative age. I think this work was done as a post-doc based in France, she is at Sonora U. presently but publishes rather on ecology topics (a more recent pollen paper by her is cited, but this bears purely on Pleistocene, not Holocene flora from a lowland cienega). The only other pollen studies are already cited, the three articles in Quaternary International in 2015, these are the small Laguna Project sites that I published when at CZU. A selection of geochemical and other non-pollen sediment studies DOES contain more recent work, this includes those articles published by Roy and co-workers in Quaternary studies.
- 225-226 To my knowledge, LOI is a method used to derive organic matter content (which is the proxy) expressed as a percentage of dry weight. See for example Heiri et al., 2001, Journal of Paleolimnology. So please, do not use the method instead of the proxy.
Here the LOI % expresses the loss-on-ignition in the Figure that is cited as slightly modified (colour enhanced) from the parent Laguna Project paper that discusses this raw data in terms of interpretation, here it is marginal to discussion and probably not worth modifying. The current paper is oriented on the 2008 interpretations as opposed to re-analyzing that data.
Also, please provide the proper reference for the particle size data, because the reference provided does not refer to such data. How was sorting determined?
Yes, I noticed that upon re-reading the 2008 Butzer et al. paper [13], also to look up the Chi (magnetic) data. This particle-size work was done by Paul Lehman and I assisted him partially in that work (Paul is also cited in [13]). He (Paul) is no longer active, and Butzer is passed away (see Acknowledgements), but I have added the appropriate reference for the sieve hydrometer cylinder method as requested in the references. As I understand it, the manual, hydrometer method produces more accurate results in relation to laser-based methods in relation to assessing clay content. I am not an expert on this matter.
- 277 What does ‘brachiation’ in this context stand for? Please clarify.
Figure 5. Please replace LOI with the proxy, i.e., organic content. Also, χ definitely does not refer to sorting, and in the cited paper it denominates magnetic susceptibility, which can hardly be used to determine sorting, and is different from particle size. Please correct these inconsistencies.
I will keep LOI for the present, as this is not inappropriate, as noted above, but figure caption (and text) now alludes to the Chi in proper (magnetic susceptibility). There is a note to the effect that the eolian component indicated ALSO relates to the restriction of water-flow, this was previously noted with respect to pollen data and accords with that inferemce.
L 291-295 Please explain in detail the reason(s) for rejecting the 14C dates from the models.
All rejected dates are now enumerated in the main text. The main series of rejected dates from Early Holocene sequence are more thoroughly explained as this comprises the main problem thuuus:
- A presence of spring vents in-situ within a limestone bedrock geology (Fig, 3) giving rise to a hard-water local hydrology. Note presence of calcareous tufas.
- A presence of aquatic and semi-aquatic flora according to pollen data of Zone 1 in the lower part of the main sequence (see 5.2.1.) present an ecology that would permit a hard-water error, as opposed to that of terrestrial plants.
- An apparent non-random error factor of circa +1000 y calculated in this part of the sequence in the rejected date series (4). A systematic error resulting from hard water (as opposed to a random re-working of old, or intrusion of young sediments) would be expected to be at a relatively constant differential. (I add here that this differential is also consistent with a fractional uptake of hard water in the spring vent ponds, some, non-hard, will also derive from precipitation).
- Pollen dating of the Terminal Pleistocene/Earlies Holocene site of La Angostura at a 10 km remove from Upper Arroyo. An early dating of Upper Arroyo (i.e., an acceptance of the series of rejected dates) would place Zone 1 within the timeframe of an Artemisia steppe formation in the basin of Upper Arroyo. This vegetation unit is not apparent in Zone 1 pollen data in the lower aspect of the Upper Arroyo sequence.
Tables 1-3. It is not clear if these radiocarbon dates are new or were extracted from a published study. If they are already published, please provide the original reference. Also, there is no information regarding the method used for radiocarbon analysis, and the calibration curve used. This is important information and should be highlighted.
These are cited from the parent article [13] and section relies on those methods. The citation is added.
- 348 What does ‘trace values’ mean in this context?
Clarified, less than 1% total land pollen, typically 1-3 pollen grains.
Figures 9, 10 and 11. Figures are nearly impossible to read, due to the very poor resolution. Also, why was the pollen sampling so uneven in the profiles? Please discuss the potential implications of the uneven sampling on your results and interpretations. It would also help adding a lithology column next to the pollen stratigraphies.
New diagrams are drawn and changed to TIFF format and inserted.
- 470-481 Why not compute a DCA on the pollen data presented in the study and then compare it with the results shown by Caballero-Rodriguez et al?
Excellent idea for a new article, but I think the present study is enough to introduce the primary material. This statistical analysis might be done with respect to ALL Laguna Project sites including those published in three articles in B. Albert (sole author) 2015 in Quaternary International. The latter include the small pollen sites for the project. This would be best done in cooperation also with Mexico-based palynologists. My employment on the Laguna Project was contingent upon expertise in alluvial materials of Central and East European (Czech, e.g. Vransky potok and Slovak, e.g. Mytna Nova Ves, Včelince, see also more recently Nebelivka in Ukraine) lowland sites and was thus technical in nature as alluvial materials per se are hard to work with compared to peat and lacustrine sites. I am not a Mexico specialist as such.
L 480-481 In my opinion, it is extremely difficult to reconstruct elevation changes in tree limit in the absence of plant macroremains data. If you use only pollen for such reconstructions, then these are merely assumptions and should be regarded as such, or the interpretation should be backed up by more references.
Agreed, thus most statements about elevation changes are relative, one exception is the exclusion of a desert belt on-site in the earliest pollen zone due to practical absence of such flora with exception of isolates of the most anemophilous xerophytes (Amaranthaceae) in tandem with high levels of mesophytic trees and aquatics.
L 546 Please explain what ‘Global patterns’ means in this context. Because the comparative assessment which shortly follows is regional, not global.
Changed in different parts of text to “inter-regional”.
L 553 ‘with temporal horizons of cycles being significant at secular timescales’. Does this refer to statistical significance? It’s confusing; please reword.
Yes, century-level timescales are mean, all statements are made regarding environmental changes at that time scale or broader. This is made explicit now.
Figure 14. Which is temperature and which is precipitation? Please, explain clearly in the caption. Also, why is the second y axis titled ‘Depth’? Perhaps this figure is better suited to ‘Study area’, than to ‘Conclusions’.
Actually, I have decided to remove the figure as redundant and entirely within public domain, it is too peripheral to article which is not a climate-specific work.
Note, a final statement on species diversity in the desert flora is added to conclusion as this ties-into initial references [1-2]. There is a separate botanical literature to consider here. Azonal vegetation changes influence endemism. Thus:
“Because the formation of the Chihuahuan Desert also takes place in a variegated manner incorporating both zonal and azonal aspects, the high level of species diversity of middle-slope scrub flora presently defined in this desert region [1-2] is also explained over Pleistocene timescales by virtue of isolation and endemism of species between mountain ranges of the Sierra Madre.”
Final sentence added to manuscript, referring back also to initial citations, de Leon [2] having previously cited the “Hydrological cycle” paper from Quat. Int. 2015 [21], that also considers this topic in the landscape evolution. There is a continued high rate of new species identification also in adjacent regions, a new, xerophytic Quercus species having been identified this year by Mike Eason of the L. Johnson Wildflower Center (Austin, Texas) this year from the Arizona basin-and-range province this year. This might occur through restriction of species migration by cross-cutting environmental niches that exclude this according to local edaphic conditions.
Author Response File: Author Response.docx
Reviewer 3 Report
See the file attached with some comments.
Comments for author File: 
Comments.pdf
Author Response
Dear Reviewer 3,
No specific corrections noted here but style and spell check will be made throughout manuscript according to following check marks (2 noted here). This will be done in conjunction minor point corrections made for other reviewers.
1.
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Are the results clearly presented? |
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(x) |
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( ) |
Can be improved
(x) English language and style are fine/minor spell check required
Author Response File: Author Response.docx
