Physiological and Regenerative Plant Traits Explain Vegetation Regeneration under Different Severity Levels in Mediterranean Fire-Prone Ecosystems

Round 1

Reviewer 1 Report

This is a very interesting research, although the results can only be related to a fairly narrow and specific area of forests - fire-prone ecosystems in the Mediterranean Basin. The results can be relevant for pre- and post- fire management of forests in the Mediterranean areas only.

I have just two comments:

Line 27 Do not use an abbreviation  in the abstract (SLA – specific leaf area)

Line 122-139, What were the criteria for the selection of research areas? The size of the burnt area as well as its surroundings (e.g. vegetation or lack of it) may influence the results obtained.

Author Response

Manuscript ID: forests-1074696

 “Physiological and regenerative plant traits explain vegetation regeneration under different severity levels in Mediterranean fire-prone ecosystems” by Sara Huerta, Víctor Fernández-García, Elena Marcos, Susana Suárez-Seoane and Leonor Calvo.

Dear Editor-in-Chief of Forests,

We resubmit the revised version of manuscript ID: forests-1074696. Following the Reviewers suggestions, and in order to improve the original text according to their indications, we submitted a point-by-point response, indicating the changes we made to the original text and answering to their comments.

We hope that these changes will be satisfactory.

Yours sincerely,

Leonor Calvo on behalf of all the authors.

RESPONSE TO REVIEWER 1 COMMENTS

General comments

1 COMMENT. This is a very interesting research, although the results can only be related to a fairly narrow and specific area of forests - fire-prone ecosystems in the Mediterranean Basin. The results can be relevant for pre- and post- fire management of forests in the Mediterranean areas only.

ANSWER. Thank you very much for your comment.

Specific comments

2 COMMENT. Line 27: Do not use an abbreviation in the abstract (SLA – specific leaf area).

ANSWER.We made the change proposed.

3 COMMENT. Line 122-139: What were the criteria for the selection of research areas? The size of the burnt area as well as its surroundings (e.g. vegetation or lack of it) may influence the results obtained.

ANSWER. The main criteria to select the Cabrera and Gatova study areas were: (1st) The size of burn areas, that means of more than 500 ha, which are considered as big fires and (2^nd) areas with differences in terms of vegetation and climatic conditions. In this way, we could evaluate vegetation regeneration as a function of plant physiological and regenerative traits based not only on burn severity but also on the type of pre-fire vegetation and on temperature and precipitation patterns in each study area. Therefore, we were able to analyse the most characteristic plant traits of each zone, as well as their behaviour according to burn severity, assuming that both vegetation type and climate may interfere in post-fire regeneration.

Author Response File: Author Response.docx

Reviewer 2 Report

This manuscript describes short-term vegetative response to fires in two contrasting sites on the Iberian Peninsula and categorizes plant regeneration by functional group. This is an empirical study that supports fairly accepted theoretical frameworks for plant responses to disturbance based on plant functional traits. The approach and analysis are reasonable. The results are not particularly novel and I think data from a longer time series would be more interesting, but the study and write are sound. One thing I think that could be improved is maybe including some discussion about the long term successional implications of the results in the face of global change. I've included some specific comments in the attached PDF. 

Comments for author File: Comments.pdf

Author Response

Manuscript ID: forests-1074696

“Physiological and regenerative plant traits explain vegetation regeneration under different severity levels in Mediterranean fire-prone ecosystems” by Sara Huerta, Víctor Fernández-García, Elena Marcos, Susana Suárez-Seoane and Leonor Calvo.

Dear Editor-in-Chief of Forests,

We resubmit the revised version of manuscript ID: forests-1074696. Following the Reviewers suggestions, and in order to improve the original text according to their indications, we submitted a point-by-point response, indicating the changes we made to the original text and answering to their comments.

We hope that these changes will be satisfactory.

Yours sincerely,

Leonor Calvo on behalf of all the authors.

RESPONSE TO REVIEWER 2 COMMENTS

General considerations

In relation to grammar and spelling, all the changes proposed throughout the text have been made.

In comments, lines refer to the revised text, provided in a PDF file by the reviewer 2.

In answers, lines refer to the text modified and revised by the authors.   

General comments

1 COMMENT. This manuscript describes short-term vegetative response to fires in two contrasting sites on the Iberian Peninsula and categorizes plant regeneration by functional group. This is an empirical study that supports fairly accepted theoretical frameworks for plant responses to disturbance based on plant functional traits. The approach and analysis are reasonable. The results are not particularly novel and I think data from a longer time series would be more interesting, but the study and write are sound. One thing I think that could be improved is maybe including some discussion about the long term successional implications of the results in the face of global change. I've included some specific comments in the attached PDF. 

ANSWER. Thank you very much for your comment. In order to follow your suggestion, we made several changes in the final part of the discussion. Specifically, we have modified lines 433-468 to show evidences of the most vulnerable vegetation and most adversely affected environments in relation to global change factors. In this sense, we suggest (i) that climatic conditions characterized by higher average temperatures and lower annual rainfall may have played an important role in vegetation recovery, (ii) we identified plant functional traits that could be advantageous to face future scenarios of fire regimes under a climate change, and (iii) we highlighted the value of this study in providing the scientific basis for the management of Mediterranean forests in the framework of global change.

Specific comments

2 COMMENT. Line 22-23: “The main results showed that burn severity had significant effects on vegetation regeneration, regarding all physiological and regenerative traits, which cover increased under high severity situations during the second year, mainly in Cabrera.” This sentence is confusing.

ANSWER. We have modified this sentence according to the reviewer comment (L22-24).

3 COMMENT. Line 25-26: “Thereby, the cover of obligate seeder species with no heat-stimulated germination resulted negatively affected by burn severity even after two years.” Awkward sentence. Maybe change to “The cover of species without heat-stimulated germination was negatively correlated with burn severity.”

ANSWER. We have done the change (L25-26).

4 COMMENT. Line 27: Maybe, “Cover of plants that had low SLA or did not fix N₂ was reduced at high burn severity” instead of “Among physiological traits, low SLA and no N₂-fixing showed a negative effect of the high severity levels.”

ANSWER. We have done the change (L26-27).

5 COMMENT. Line 39: “By land use abandonment” Be more specific.

ANSWER. In order to clarify what “land use abandonment” makes reference, in line 38-41, we modified the sentence: “In recent decades, climate change and increasing fuel accumulation caused by land use abandonment (mainly driven by a reduction in traditional agriculture, livestock grazing and rural population density) have contributed to the alteration of fire regime in the Mediterranean Basin (Moreno et al., 2014).”

6 COMMENT. Line 40: Can you simplify to just “fire regime”, if not be specific about what parameters or at least provide an example or two.

ANSWER. We have done the change (L43).

7 COMMENT. Line 41: Change “increment” to “increase”.  

ANSWER. We have done the change (L44).

8 COMMENT. Line 45: Change “conditioned” to “affected”. 

ANSWER. Done (L48).

9 COMMENT. Line 45: “The regeneration of plant communities is strongly conditioned by burn severity, because high burn severity affects negatively to the regeneration of the vegetation.” Confusing sentence.

ANSWER. We have simplified the sentence for clarity and conciseness (48-49).

10 COMMENT. Line 46: “In addition, climatic conditions characterized by a decrease in the water availability for plants constrains their response to wildfire.” Maybe more detail or an example here.

ANSWER. We have extended this sentence (L51-52): “In addition, climatic conditions characterized by a decrease in the water availability for plants constrains their response to wildfire, mainly because of its implication in the productivity of the plant community after fire (Pausas and Bradstock, 2007).”

11 COMMENT. Line 122: Change “forestry” to “plant”. 

ANSWER. Done (L126).

12 COMMENT. Line 142-143: “In each burned plot, we evaluated burn severity by the application of the Composite Burn Index procedure (CBI), adapted by Fernández-García et al. (2018).” It would be good to very briefly describe the procedure.

ANSWER. As you suggested, we expanded the description of the procedure and we have indicated the burn severity indicators evaluated (L148-152).    

13 COMMENT. Line 147: “Every burned and unburned plot was divided into four 1 m x 1 m sampling units.” Can you clarify the reason for subdividing into 1m x 1m plots and what data was collected at what scale?

ANSWER. We established 2 m x 2 m field plots to evaluate burn severity by the CBI procedure. Then, we decided to subdivide each plot into four 1 m x 1 m sampling units just with the aim of easily estimate the percentage cover of each woody species. After that, we calculated the average cover value of each species in every 2 m x 2 m plot. In line 157-158, we made some changes with the aim of clarifying the field sampling procedure developed.   

14 COMMENT. Line 150: “One and two years after the wildfires” What time of year.

ANSWER. In line 160-161, we added: “Specifically, field samplings were carried out during the months of June and July 2018 and 2019.”

15 COMMENT. Line 179-180: “Species with different SLA showed an opposite pattern between study areas (Figure 2). Species with high SLA dominated in Cabrera, while the cover percentage of low SLA species was higher in Gátova.” In unburned plots or in all plots?

ANSWER. We referred both situations so, in line 191, we added: “both in unburned and burned plots.”

16 COMMENT. Line 181: “A negative effect of fire” Negative effect of fire on what?

ANSWER. We referred to the negative effect of fire on regeneration so, in line 193-195, we changed: “In both areas, we observed a negative effect of fire during the first year, regardless of burn severity levels (Figure 2)” to “In both areas, we observed a negative effect of fire on the regeneration of species with low and high SLA during the first year, regardless of burn severity levels (Figure 2).” 

17 COMMENT. Line 202: For all these figures, some indication of statistical significance would be nice. Either use 95% CI for the error bar instead of standard error or use letters above each bar to indicated groups that are and are not significantly different.

ANSWER. We have specified in figure captions that model outputs and significances are available in Tables 3 and 4 (supplementary materials). We have not included neither confidence intervals nor post-hoc results in these figures because the following reasons:

(i) Figures 2 to 6 show the mean values (±SE) of the variables in relation to burn severity, with years in different panels. However, the statistical analyses were carried out using severity, time and their interaction as predictors (L176-178). Thus, model significances should be interpreted with the outputs shown in Table 3 rather than in figures separated by years.

(ii) The glmmPQL function uses penalized quasi-likelihood method, which is thought to yield accurate estimates but does not allow to calculate stable and accurate confidence intervals in complex models.

Table 1. Results of the one way ANOVA for the variable low SLA in Cabrera study area.

18 COMMENT. Line 211: “Pre-fire values” Unburned values unless you are comparing to values from the same plot prior to the burn.

ANSWER. In line 226, we changed “pre-fire values” to “unburned values”. We also changed this expression in line 393.

19 COMMENT. Line 309-315: “However, vegetation cover according to plant functional traits increased over time in both study areas. In Cabrera, the area with shorter summer drought, burn severity levels did not significantly influence regeneration during the first year. Nevertheless, vegetation cover as a function of plant physiological and regenerative traits increased under high severity two years after fire, compared to low and moderate severities. In Gátova, which is characterized by higher average temperatures and lower annual rainfall, opposite response patterns were observed between plant functional traits, with the dominant vegetation being negatively affected by burn severity.” This is a little confusing to me. It isn't clear what you mean by vegetation cover as a function of plant physiological and regenerative traits, since there are multiple of each. Similarly, the last sentence seems to conflate dominant vegetation and unspecified functional traits.

ANSWER. We have modified the sentence to state clearly that (i) vegetation cover increased over time in both study sites (L331); (ii) that in Cabrera vegetation cover increased more with time in high severity situations than in low and moderate severity situations (L337); and (iii) in Gátova the regeneration of vegetation with predominant traits (species with low SLA, without N2-fixing capacity, obligate seeder species and with no heat-stimulated germination) resulted negatively affected by burn severity. (L331-349).

20 COMMENT. Line 317: “Dominance of species” I suggest saying, “cover” rather than “dominance” since you measured cover and not dominance.

ANSWER. Thank you very much for your suggestion. As you proposed, in line 341, we changed “dominance” to “cover”.

We also clarified this idea in other parts of the text: Line 222, 249, 276, 352, 373, 408.    

21 COMMENT. Line 320: “Which regeneration increased under the effect of high burn severity compared to low and moderate severities two years after fire.” Maybe important to note that it never returned to unburned levels.

ANSWER. As you proposed, in line 354, we added: “Despite of this, the cover of high SLA species did not reach unburned levels.”

22 COMMENT. Line 342-350: This is a good discussion point about P:N. Plants with N-fixing associations are also often pioneer species and colonize after almost any disturbance.

ANSWER. Thank you very much for your comment. We really appreciate that you liked the approach of this part of the discussion. In line 456-457, we included an idea related to your contribution about N₂-fixing species.

References

Moreno, M.V.; Conedera, M.; Chuvieco, E.; Pezzatti, G.B. Fire regime changes and major driving forces in Spain from 1968 to 2010. Environ. Sci. Policy 2014, 37, 11-22, doi: 10.1016/j.envsci.2013.08.005.

Pausas, J.G.; Bradstock, R.A. Fire persistence traits of plants along a productivity and disturbance gradient inmediterranean shrublands of south-east Australia. Glob. Ecol. Biogeogr. 2007, 16, 330–340, doi: 10.1111/j.1466-8238.2006.00283.x.

Author Response File: Author Response.docx