the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Primary succession and its driving variables – a holistic approach applied in three proglacial areas in the upper Martell Valley (Eastern Italian Alps)
Katharina Ramskogler
Bettina Knoflach
Bernhard Elsner
Brigitta Erschbamer
Florian Haas
Tobias Heckmann
Florentin Hofmeister
Livia Piermattei
Camillo Ressl
Svenja Trautmann
Michael H. Wimmer
Clemens Geitner
Johann Stötter
Erich Tasser
Abstract. Climate change and the associated glacier retreat lead to considerable enlargement and alterations of the proglacial systems. The colonisation of plants in this ecosystem was found to be highly depending on terrain age, initial site conditions and geomorphic disturbances. Although the explanatory variables are generally well understood, there is little knowledge on their collinearities and resulting influence on proglacial primary succession. To develop a holistic understanding of vegetation development, a more interdisciplinary approach was adopted. In the proglacial area of Fürkele-, Zufall-, and Langenferner (Martell Valley/Eastern Italian Alps), totally 65 plots of 5 × 2 m were installed to perform the vegetation analysis on vegetation cover, species number, and species composition. For each of those, 30 potential explanatory variables were collected, selected through an extensive literature review. To analyse and further avoid multicollinearities, 26 of the explanatory variables were clustered via Principal Component Analysis (PCA) to five components. Subsequently, generalised additive models (GAM) were used to analyse the potential explanatory factors of primary succession. The results showed that primary succession patterns were highly related to the first component (‘elevation and time’), the second component (‘solar radiation’), and the third component (‘south-eastness’) as well as snow free freeze-thaw days, and landforms. In summary, the analysis of all explanatory variables together provides an overview of the most important influencing variables and their interactions, and thus a basis for the debate on future vegetation development in a changing climate.
- Preprint
(1619 KB) -
Supplement
(466 KB) - BibTeX
- EndNote
Katharina Ramskogler et al.
Status: final response (author comments only)
-
CC1: 'Comment on bg-2022-248', Danilo Godone, 25 Jan 2023
Dear authors,
concerning the investigation of primary succession and related environmental variables, I suggest, if I may, checking the work by Garbarino et al. (2010) entitled "Patterns of larch establishment following deglaciation of Ventina glacier, central Italian Alps", published in Forest Ecology and Management. The paper focuses only on larch invasion in deglaciated areas in the forefield of Ventina glacier (Val Malenco, central Italian Alps) and tries to summarize several influencing factors of the phenomenon and can be considered, to a certain extent, a precursor of your research which copes with the issue in a broader context.
Thanks for your kind attention.
Citation: https://doi.org/10.5194/bg-2022-248-CC1 -
AC1: 'Reply on CC1', Katharina Ramskogler, 31 Jan 2023
Dear Danilo Godone,
of course we will look at the work by Garbarino et al. (2010) and also take notes on the drivers they mentioned. Some drivers could be similar or the same, but as we are analysing primary succession in the whole proglacial the drivers could also be different. Furthermore, we are also taking climate variables into account.
Kind regards,
Katharina
Citation: https://doi.org/10.5194/bg-2022-248-AC1
-
AC1: 'Reply on CC1', Katharina Ramskogler, 31 Jan 2023
-
RC1: 'Comment on bg-2022-248', Anonymous Referee #1, 03 Mar 2023
The paper aims to provide a “holistic approach” to investigate the ecological factors driving the primary succession on glacier forelands. On a case study in the Italian Alps, the authors tested the effects of a set of variables deriving from the previous literature in order to analyze their effects on plant cover and plant species composition.
The paper is interesting for the holistic approach, which takes into accounts the different “spheres”, and for the nice literature review. Data are well collected and the analytic methods are sound. The paper addresses scientific questions that are within the scopes of BG
.
However, some points need to be taken into account before publication. Sometimes the paper seems to be somewhat in the middle between a review and a research paper. The choice of the variables is somewhat constrained by their use in previous paper, while, in my opinion, the authors should have made their own choice. As a consequence, the hypotheses tested are a little bit trivial, and thus the paper does not tell anything really new.
The main problem, in my opinion, is that a true holistic approach cannot exclude completely the biotic factors as drivers of the succession. Although the role of facilitation, competition etc have been part of the theory of primary succession since its beginning, no biotic variable is considered as potential explanatory variables. Many papers, included some considered in the literature review (e.g. Losapio et al. 2021) showed that interspecific interactions are a strong driver, as facilitation in the early phases and as competitive exclusion in the latter ones. It would have been nice to take into account such topic, at least in the discussion. Also propagule availability (under the form of distance from potential sources) could have been taken into account, as well as the microclimatic effect of ice on the earliest phases. I acknowledge that it is impossible to take into account everything, but given the “holistic” emphasis, a broader consideration is expected. Also a comparison with other forelands described in literature could be useful, as the importance of some of the considered variables (e.g. temperature of the growing season) can be appreciated comparing areas in different bioclimatic contexts.
Sometimes the discussion of the drivers is not very convincing: from one side, it does not provide ecological hypothesis for the role of a variable (for example “south-eastness”- see below in the specific points); from the other, it provides explications that sound a little bit too stretched. For example, to explain the role of slope (component 5) it is said that its influence could be linked to the consequent soil properties, which lead to a lower C:N ratio (line 425): but soil N content is one of the variables included in the independent component 4, so I would expect a connection between the two.
The first paragraph of the conclusions should be placed at the end of the discussion, as a separated paragraph dealing with the potential effects of climate change. The conclusions should not treat a topic that has not been treated elsewhere.
I suggest to strengthen the paper with a more robust description of the observed succession and its comparison with the numerous case studies occurring in literature: does the succession imply addition and persistence or replacement? Can we hypothesize from such features a role for biotic vs abiotic drivers? Which variables must be taken into account and/or discussed?
Specific points
- 73-75 sentence unclear
- 79 Why giving only data for July? Yearly mean rainfall is important, as well as temperature at least for th whole growing (or snow-free) season
Line 124. I would not use the term “climax” for stages that are max 200 years old. Succession requires a much longer time span to reach such stage (if it does)
- 179 and following Data for the pedosphere are derived from Landolt’s indices, which means that they derive from plant species occurrence. Even if they are correlated with soil analyses performed on a small subsample, they are not very appropriate as explanatory variables for plant species composition, as they are not independent. I don’t understand why the interesting soil analyses weren’t performed in all the plots and used as independent explanatory variables.
- 200 and following. I agree that the human impact is of great importance for vegetation development. I wonder if data collected only for the present time are appropriate for explaining the development of the succession. Are there historical data about the past load of livestock somehow available, to check how representative is the present situation?
- 295. How can bee that PCA variables 3, 4 and 5 show an increasing explained variance?
- 302. If RC2 is linked to solar radiation, what could be the ecological meaning of “south-eastness” of RC3? In the discussion a possible explanation for this variable should be provided, particularly because in the conclusion, its influence on vegetation cover is reported to be the main difference between vegetation cover and species richness.
Line 411. I would not say that this hypothesis is not supported, as variable 1 is by far the most important. The fact that variable 1 includes other factors than those cited in the hypothesis is not meaningful: by definition, factors included in the same PCA axis cannot be disentangled, so the really significant ones could be just one or another of them, or all of them. So the hypothesis is very likely supported: the factors that were supposed to be the most significant are among those mainly contributing to the main variance. It’s up to the authors’ knowledge discuss which of them could or could not be important. For example, altitude and terrain age are correlated, as usual on glacier foreland: is the altitudinal interval big enough to represent an important factor? A comparison with similar intervals outside the LIA moraines could provide some insights.
Maybe it’s just me, but I don’t find the figure 4 very clear
Line 431. I would not say that grazing “slowed down” the development of vegetation cover we see an effect on plant cover and diversity but it is unclear its role from the point of view of the succession.
Line 442. Replace “individuum” with “individual”
Citation: https://doi.org/10.5194/bg-2022-248-RC1 -
AC2: 'Reply on RC1', Katharina Ramskogler, 08 Mar 2023
Referee comment Reply Common points 1 The paper aims to provide a “holistic approach” to investigate the ecological factors driving the primary succession on glacier forelands. On a case study in the Italian Alps, the authors tested the effects of a set of variables deriving from the previous literature in order to analyze their effects on plant cover and plant species composition. Thank you for the positive evaluation of the study. We are confident that the revision of the manuscript helps to resolve the points of criticism. 2 The paper is interesting for the holistic approach, which takes into accounts the different “spheres”, and for the nice literature review. Data are well collected and the analytic methods are sound. The paper addresses scientific questions that are within the scopes of BG Thank you for confirming that the scientific questions of the manuscript are within the scopes of BG. 3 However, some points need to be taken into account before publication. Sometimes the paper seems to be somewhat in the middle between a review and a research paper. The choice of the variables is somewhat constrained by their use in previous paper, while, in my opinion, the authors should have made their own choice. As a consequence, the hypotheses tested are a little bit trivial, and thus the paper does not tell anything really new. Our intention behind this paper was indeed to consider all potential explanatory variables known from the literature for the important drivers (spheres) in the study. In doing so, we want to live up to our claim of presenting a study that is as holistic as possible. However, as the reviewer will have noticed, we have also included some additional indicators for certain drivers in the study (e.g. snow free freeze-thaw days, curvature). Above all, however, we wanted to combine all known explanatory variables and consider them in a joint analysis in order to work out the decisive variables. Thus, for example, combinations such as snow-frost-frost days, curvature, and temperature were used together as explanatory variables for the first time. However, we will take the hint very seriously in the revision and make the hypotheses more specific. 4 The main problem, in my opinion, is that a true holistic approach cannot exclude completely the biotic factors as drivers of the succession. Although the role of facilitation, competition etc have been part of the theory of primary succession since its beginning, no biotic variable is considered as potential explanatory variables. Many papers, included some considered in the literature review (e.g. Losapio et al. 2021) showed that interspecific interactions are a strong driver, as facilitation in the early phases and as competitive exclusion in the latter ones. It would have been nice to take into account such topic, at least in the discussion. Also propagule availability (under the form of distance from potential sources) could have been taken into account, as well as the microclimatic effect of ice on the earliest phases. I acknowledge that it is impossible to take into account everything, but given the “holistic” emphasis, a broader consideration is expected. Also a comparison with other forelands described in literature could be useful, as the importance of some of the considered variables (e.g. temperature of the growing season) can be appreciated comparing areas in different bioclimatic contexts. Thank you for the very interesting suggestion. We will include as a variable the proportion of competing (ccc, ccs, ccr) and non-competing species (all other strategy types) in the analysis. In addition, we will also consider the proportion of life forms (grasses, forbs, dwarf shrubs, lichens and mosses) as potential explanatory variables . Finally, we will also include the availability of propagation material and the microclimatic effects of soil surface structure in the discussion. 5 Sometimes the discussion of the drivers is not very convincing: from one side, it does not provide ecological hypothesis for the role of a variable (for example “south-eastness”- see below in the specific points); from the other, it provides explications that sound a little bit too stretched. For example, to explain the role of slope (component 5) it is said that its influence could be linked to the consequent soil properties, which lead to a lower C:N ratio (line 425): but soil N content is one of the variables included in the independent component 4, so I would expect a connection between the two. The discussion will be adapted; some parts will be deepened and others reduced. 6 The first paragraph of the conclusions should be placed at the end of the discussion, as a separated paragraph dealing with the potential effects of climate change. The conclusions should not treat a topic that has not been treated elsewhere. We will place the first paragraph of the conclusion at the end of the discussion. 7 I suggest to strengthen the paper with a more robust description of the observed succession and its comparison with the numerous case studies occurring in literature: does the succession imply addition and persistence or replacement? Can we hypothesize from such features a role for biotic vs abiotic drivers? Which variables must be taken into account and/or discussed? We will show the observed successional sequence and its driving variables more decisively in the results by indicating when which species appear and disappear and which species persist over a long period of time. Regarding the importance of biotic vs. abiotic factors, we will deepen the discussion. Specific points 1 73-75 sentence unclear This sentence will be rewritten. 2 79 Why giving only data for July? Yearly mean rainfall is important, as well as temperature at least for th whole growing (or snow-free) season We will give the yearly mean rainfall, as well as the mean temperature for the whole growing season and the mean annual temperature. 3 Line 124. I would not use the term “climax” for stages that are max 200 years old. Succession requires a much longer time span to reach such stage (if it does) Thank you for this hint. Climax will be replaced to dwarf shrub stage. 4 179 and following Data for the pedosphere are derived from Landolt’s indices, which means that they derive from plant species occurrence. Even if they are correlated with soil analyses performed on a small subsample, they are not very appropriate as explanatory variables for plant species composition, as they are not independent. I don’t understand why the interesting soil analyses weren’t performed in all the plots and used as independent explanatory variables. Due to financial constraints, we were unfortunately only able to sample a few sites in a first phase. In the course of analysing the first results, however, we also realised that we needed concrete measurement data for all sites. Therefore, we have now subsequently sampled all sites. We sampled all the vegetation plots in summer 2022 and since end of december we have the results of the soil analyses from the lab. We will integrate the measured soil data into the new analysis. 5 200 and following. I agree that the human impact is of great importance for vegetation development. I wonder if data collected only for the present time are appropriate for explaining the development of the succession. Are there historical data about the past load of livestock somehow available, to check how representative is the present situation? We have historical data of livestock density in this area. Instead of grazing (yes/no) we will use a max-standardised value for grazing density. 6 295. How can bee that PCA variables 3, 4 and 5 show an increasing explained variance? Sorry for confusing you with our presentation of the components' results. Of course you are right when you point out that usually the explanatory share of the individual components decreases successively. This is of course also the case with us. However, we wanted to rank the components in terms of the known effects. In the revised version, however, we will now re-order the sequence according to the statistical output (so that the declining explanatory share is again apparent). 7 302. If RC2 is linked to solar radiation, what could be the ecological meaning of “south-eastness” of RC3? In the discussion a possible explanation for this variable should be provided, particularly because in the conclusion, its influence on vegetation cover is reported to be the main difference between vegetation cover and species richness. The solar radiation and the exposure to the east/south do not correlate with each other so strongly that they are condensed into a single component. We therefore interpret that the exposure stands as a placeholder for additional processes/characteristics. Specifically, we are thinking above all of associated differences in precipitation patterns and the resulting soil water contents. Unfortunately, there is no high-resolution measurement data on this, so we cannot prove it. However, we will take up this topic in the discussion. 8 Line 411. I would not say that this hypothesis is not supported, as variable 1 is by far the most important. The fact that variable 1 includes other factors than those cited in the hypothesis is not meaningful: by definition, factors included in the same PCA axis cannot be disentangled, so the really significant ones could be just one or another of them, or all of them. So the hypothesis is very likely supported: the factors that were supposed to be the most significant are among those mainly contributing to the main variance. It’s up to the authors’ knowledge discuss which of them could or could not be important. For example, altitude and terrain age are correlated, as usual on glacier foreland: is the altitudinal interval big enough to represent an important factor? A comparison with similar intervals outside the LIA moraines could provide some insights. Our explanations are too imprecise. The reviewer is absolutely right with the critism and we will adjust the text accordingly. As far as the comment to the ranks considered for the individual variables is concerned, our statements apply to comparable natural situations. However, in order to enable more general statements, we are currently in the process of investigating and analysing other glacier areas. In the current study, we have an elevation gradient of 500 m within the proglacial area - we think that the elevation interval is large enough to underline the importance of this variable. However, in order to enable more general statements, we are currently in the process of investigating and analysing other glacier areas with different elevation distributions. 9 Maybe it’s just me, but I don’t find the figure 4 very clear Figure 4b (trampling/grazing) will change due to the changes described. In addition, we will reflect again on the current form. 10 Line 431. I would not say that grazing “slowed down” the development of vegetation cover we see an effect on plant cover and diversity but it is unclear its role from the point of view of the succession. We will take up this hint in order to deepen the discussion in this regard. 11 Line 442. Replace “individuum” with “individual” We will replace "individuum" with "individual Citation: https://doi.org/10.5194/bg-2022-248-AC2
-
RC2: 'Comment on bg-2022-248', Anonymous Referee #2, 07 Mar 2023
General comments
The paper, after a necessary and important literature review, applies a multidisciplinary approach for studying primary succession along a glacier foreland on European Alps. The aims of the paper fit well with the scopes of the journal.
The review effort is a very important part of this paper, and has a very international interest and application.
The other part of the work (the application of the multidisciplinary approach to a case study) is, in my opinion, less “holistic” than expected for different reasons:
- it is a single case study, while it was already pointed out in literature that now, for having a new, innovative view of proglacial habitat (“holistic”?), is necessary to have a synthesis of a wider spectrum of case studies. And it is evident that some variables, at small scale, could not have a great importance, but, at bigger scale, are decisive (like lithology). De facto, you compared two glacier foreland (not three; see comment below) of the same glacial site. Some things, that you could not consider at small scale on a single site, should be considered in the discussion.
- among explanatory variables (mainly) only physical variables have been considered, excluding biological variables like, for example, arthropods successions (see comments below) or plant interactions (see comment from the other reviewer)
This considerations do not give less importance to the work, that is very interesting, but suggest to valorise the fact that a very detailed work on a single case study has be done focusing, with a great detail, on physical explanatory variables. In my opinion, it could not be considered “holistic”, it would be an error.
Specific considerations and technical corrections:
Line 19: “proglacial areas …. undergo considerable enlargement and structural changes”: this sentence should be explained. The enlargement is clear, Is less clear what do you mean with “structural Changes”
Line 23: “which has been supported by a large number of studies”. I think you should add some example of studies
Line 29: after “as a result” insert a comma
Line 30: after “processes” insert a comma
Line 61: I would correct “Our objectives were: (1) We conducted…(2) We investigated..” in “Our objectives were: (1) to conduct…(2) to investigate.. etc”
Line 67: if your objective is also to test hypothesis
Line 63: “three proglacial areas”: from the map I see only two proglacial succession. I checked Knoflach et al. (2021) and I have seen that for the third proglacial area only lateral moraine has been sampled: in my opinion you could not consider this sampling on the third glacier foreland as a sampling of a proglacial succession. In addition, you compared proglacial areas of the same site, thus, they should be considered as replicates
Line 63: I think it should be useful to add the successional steps reported by Knoflach et al. (2021) in the Fig. 2
Lines 64-69: “to test the following hypotheses: i) Many of the known potential explanatory variables are correlated….. ii) The most important explanatory variables for vegetation cover development include …. iii) Disturbances such as geomorphic disturbance and grazing/trampling reduce ….. iv) We expected that there are no single potential explanatory variables, and we will provide a better understanding of primary succession for prediction of future development.”: the hypothesis iv) should be written in the same format of the others “no single potential expl. Variables are expected….”
Line 67: better to explicit what do you mean with “climatic variables”
Line 74: it is not clear in this sentence if vegetation survey itself was performed by Knoflach et al. (2021) or only plot identification. It should be clearer
Line 93: repetition of “for primary succession”
Lines 101-102 “we excluded variables only mentioned once or twice (e.g., wind exposure, snow depth, or soil type), except they could be relevant due to climate change”: It is not clear this criterion, since I would have said that snow depth could be strongly related to climate change
Line 102: Premise: since it is not explained, I interpreted “soil type” as “lithology”. Considering a single site with quite uniform rock composition, you didn’t considered the importance of soil type on succession; this is reasonable. However, limestone and crystalline succession are very different and this should not be ignored. You said that soil type was mentioned only once or twice: this could be done to the fact that there are very few works, unfortunately, that compare successions on different soil types. You should specify that it is not important in a homogenous site, but important at larger scale
Line 104: I would add a reference to the 31 explanatory variable list : (Tab1)?. It could be confusing to report in the text also the 39 variables found in literature, especially if you put in the text at first the table with only the 31 selected explanatory variables. Since, in another point, you report the 26 explanatory variables selected for PCA, the risk is that it become very confusing. Maybe, fig. 3 should be removed and the same information should be added in Tab1?
Line 118: I would change the title of the paragraph “3.2 Dependent variables: Vegetation indicators (Biosphere)” in “3.2 Dependent variables: Vegetation sampling (Biosphere)”
Lines 119-120: “The vegetation surveys in the three glacier forelands of Fürkele-, Zufall-, and Langenferner were carried out in July/August of 2019 and 2020 (n = 65)” if vegetation was sampled by Knoflach et al. (2021) I would add reference
Lines 122-124: “According to the change in species composition along the chronosequence, Knoflach et al.
(2021) discriminated four successional stages: (i) a pioneer stage, (ii) an early successional stage, (iii) a late successional stage with snowbed and grassland communities, and (iv) a climax stage with dwarf shrub—” I would make clear in the Fig. 2.c the four successional stages
Line 124: it is not a “climax” if the terrain deglaciated only 200 years ago
Line 126: you did not consider any variables linked to arthropod succession. I think that in a “holistic approach” this component should not be ignored along a glacier foreland: it is known, especially in pioneer stages, the importance of arthropods as colonizer, even before plants appears. Then, their importance as disperser and pollinators could not be ignored. In general, biosphere influences biosphere during succession and this point is not considered in the paper, that is mainly focused in considering the impact of (mainly) physical factors on vegetation. Thus, I would not have used the term “holistic”.
Line 150: “of these ice-dammed lakes.(Fig. 1b)Further” delete dot before brackets, move it after bracketsLines 149-151: are you sure that the succession restarted from zero? Organic matter should be present in soil after glacier lake outburst floods. I think you should better contextualized this point: have you checked the organic matter deposited and the grain size distribution?
Lines 152-153: “The parameter ‘distance to the glacier front’ was determined as the shortest distance from every single study plot to the glacier tongue using the ‘near’ function in ArcGIS 10.6”. I would specify the year you are considering, even if it is guessable
Line 157: insert dot after the reference
Line 158: “The distinction between no snow and snow cover was defined by a threshold of 5 mm snow water equivalent.” Specify on which basis do you fix this threshold. Is it trustable?
Line 161: “TWI”: since it is the first time TWI appears in the text I would explicit it: "Topographic wetness index (TWI)"
Lines 183-185: why didn't you do soil analyzes of all the points to get direct values of some soil variables?
Line 185 “for a subsample of the 65 study plots (n = 15).” How did you select this subsample? Which samples are they?
Lines 196-97: “Finally, the estimated cover of coarse-grained material (scree cover) in the field was
used as an additional independent variable (scree cover).” I would specify “for each plot”
line 200: the current signs of livestock grazing does not consider the effective influence in the past. If it is not possible to have information about past usage, it is better to clarify this point…
Line 253: I would add “The most frequently analysed vegetation-related, dependent variables (biosphere)”
Line 258: add “:” after “variables”
Table 3: why sometimes you use the name “RC1 etc” extrapolated from PCA and sometimes you use the full name of the variables?
Line 409-413: “In our study, we have now demonstrated that – contrary to our initial expectation – a series of
other variables correlates with our hypothesised three variables, jointly described by the components RC1 (‘elevation and time’), RC2 (‘solar radiation’), RC3 (‘south-eastness’), and RC5 ‘(low inclination’). Thus, hypothesis (ii) that the most important explanatory variables for vegetation cover development include years since deglaciation, elevation, and climatic variables, cannot be confirmed.”: demonstrating that many variables are correlated also with years since deglaciation, elevation, and climatic variables does not means that they are less important. You should comment these result, even in relation to NMDS results, were there is clearly a pattern related to years since deglaciation
Line 424: delete “a”
Line 440: “grazing and/or trampling showed no significant correlation” could be related to the fact that you did not considered grazing during all the period you considered (from LIA to now)
Citation: https://doi.org/10.5194/bg-2022-248-RC2 -
AC3: 'Reply on RC2', Katharina Ramskogler, 17 Mar 2023
RC2 Referee comment Answer Common points 1 The paper, after a necessary and important literature review, applies a multidisciplinary approach for studying primary succession along a glacier foreland on European Alps. The aims of the paper fit well with the scopes of the journal. Thank you for the positive evaluation of the study. We are confident that the revision of the manuscript helps to resolve the points of criticism. Also, thank you for confirming that the scientific questions of the manuscript are within the scopes of BG. 2 The review effort is a very important part of this paper, and has a very international interest and application. 3 The other part of the work (the application of the multidisciplinary approach to a case study) is, in my opinion, less “holistic” than expected for different reasons: The reviewer is of course correct in considering the implementation of the approach in our study. Due to missing data (e.g., consumers) or missing variability (e.g., geology), the implementation does not correspond to a holistic approach. However, we have predominantly applied the term to the approach of extracting all potential drivers based on a literature review. However, to avoid creating the wrong impression in the title, we will replace the term 'holistic' with a more appropriate term (probably 'sphere-spanning' or 'cross-spheres'). a it is a single case study, while it was already pointed out in literature that now, for having a new, innovative view of proglacial habitat (“holistic”?), is necessary to have a synthesis of a wider spectrum of case studies. And it is evident that some variables, at small scale, could not have a great importance, but, at bigger scale, are decisive (like lithology). De facto, you compared two glacier foreland (not three; see comment below) of the same glacial site. Some things, that you could not consider at small scale on a single site, should be considered in the discussion. Thank you for this suggestion. We will consider the differences between different elevations and on different geology as well as further topics which are important on a broader scale in the discussion. b among explanatory variables (mainly) only physical variables have been considered, excluding biological variables like, for example, arthropods successions (see comments below) or plant interactions (see comment from the other reviewer) Thank you for the very interesting suggestion. We will include as further variables the proportion of competing (ccc, ccs, ccr) and non-competing species (all other strategy types) in the analysis. In addition, we will also consider the proportion of life forms (grasses, forbs, dwarf shrubs, lichens and mosses) as potential explanatory variables . Finally, we will also elaborate the availability of propagation material, the microclimatic effects of soil surface structure and the role of arthropods in the discussion. 4 This considerations do not give less importance to the work, that is very interesting, but suggest to valorise the fact that a very detailed work on a single case study has be done focusing, with a great detail, on physical explanatory variables. In my opinion, it could not be considered “holistic”, it would be an error. We will change the title according to what was said before. Specific considerations and technical corrections: 1 Line 19: “proglacial areas …. undergo considerable enlargement and structural changes”: this sentence should be explained. The enlargement is clear, Is less clear what do you mean with “structural Changes” We will concretise this: We mean under structural changes - changes due to geomorphic processes and also as a consequence of vegetation development 2 Line 23: “which has been supported by a large number of studies”. I think you should add some example of studies We will add some example studies here. 3 Line 29: after “as a result” insert a comma We will insert the comma. 5 Line 61: I would correct “Our objectives were: (1) We conducted…(2) We investigated..” in “Our objectives were: (1) to conduct…(2) to investigate.. etc” Thank you, we will change it. 6 Line 67: if your objective is also to test hypothesis We will rewrite the sentence: Therefore, we used the from literature known potenial explanatory variables and tested the following hypotheses: 7 Line 63: “three proglacial areas”: from the map I see only two proglacial succession. I checked Knoflach et al. (2021) and I have seen that for the third proglacial area only lateral moraine has been sampled: in my opinion you could not consider this sampling on the third glacier foreland as a sampling of a proglacial succession. In addition, you compared proglacial areas of the same site, thus, they should be considered as replicates We will clarify the reference to "three proglacial areas" accordingly by changing this in the title to 'Primary succession and its driving variables - a cross-shere approach applied in the proglacial areas of the upper Martell Valley (Eastern Italian Alps)'. Moreover, in the study area description we will precisely state that we are dealing with two proglacial areas and one sampling of lateral moraine. As for the issue of replicates, we don't see it that way. The individual measurement points became glacier-free at different times and also underwent different developments. Therefore, they are real replicates. We will describe this in the text also in such a way. 8 Line 63: I think it should be useful to add the successional steps reported by Knoflach et al. (2021) in the Fig. 2 Thank you for the valuable suggestion. We will modify the figure and make the succession stages evident. 9 Lines 64-69: “to test the following hypotheses: i) Many of the known potential explanatory variables are correlated….. ii) The most important explanatory variables for vegetation cover development include …. iii) Disturbances such as geomorphic disturbance and grazing/trampling reduce ….. iv) We expected that there are no single potential explanatory variables, and we will provide a better understanding of primary succession for prediction of future development.”: the hypothesis iv) should be written in the same format of the others “no single potential expl. Variables are expected….” We will reformulate it: (iv) no single potential explanatory variables are expected. With the four tested hypotheses we aim to provide a better understanding of primary succession for prediction of future development 10 Line 67: better to explicit what do you mean with “climatic variables” Thank you for your suggestion: we will concretise it - temperature and precipitation. 11 Line 74: it is not clear in this sentence if vegetation survey itself was performed by Knoflach et al. (2021) or only plot identification. It should be clearer We will clarified it: The vegetation surveys were performed by Ramskogler and used for the analysis in Knoflach et al. (2021). We did not only do a plot identification. 12 Line 93: repetition of “for primary succession” We will delete the repetition. 13 Lines 101-102 “we excluded variables only mentioned once or twice (e.g., wind exposure, snow depth, or soil type), except they could be relevant due to climate change”: It is not clear this criterion, since I would have said that snow depth could be strongly related to climate change Of course, a variable that has hardly appeared as a driving variable in the literature so far can also make a significant explanatory contribution. However, our approach was a compromise one: we focused on the previous literature and included those variables that were mentioned more than 1-2 times. However, we did not subject all other variables to in-depth analysis (which was not methodologically possible). However, we assume, for example, that snow depth is very closely correlated with the number of snow free days and therefore the essential information is also covered by this variable. 14 Line 104: I would add a reference to the 31 explanatory variable list : (Tab1)?. It could be confusing to report in the text also the 39 variables found in literature, especially if you put in the text at first the table with only the 31 selected explanatory variables. Since, in another point, you report the 26 explanatory variables selected for PCA, the risk is that it become very confusing. Maybe, fig. 3 should be removed and the same information should be added in Tab1? Thank you for the valuable advice. We will take them up and rewrite the manuscript accordingly. We hope that this will help us eliminate the confusion. 15 Line 118: I would change the title of the paragraph “3.2 Dependent variables: Vegetation indicators (Biosphere)” in “3.2 Dependent variables: Vegetation sampling (Biosphere)” We will change it. 16 Lines 122-124: “According to the change in species composition along the chronosequence, Knoflach et al. 2021 discriminated four successional stages: (i) a pioneer stage, (ii) an early successional stage, (iii) a late successional stage with snowbed and grassland communities, and (iv) a climax stage with dwarf shrub - "I would make clear in Fig. 2c the four successional stages. Thank you, we will implement the succession stages. 17 Line 124: it is not a “climax” if the terrain deglaciated only 200 years ago Climax will be replaced to dwarf shrub stage. 18 Line 126: you did not consider any variables linked to arthropod succession. I think that in a “holistic approach” this component should not be ignored along a glacier foreland: it is known, especially in pioneer stages, the importance of arthropods as colonizer, even before plants appears. Then, their importance as disperser and pollinators could not be ignored. In general, biosphere influences biosphere during succession and this point is not considered in the paper, that is mainly focused in considering the impact of (mainly) physical factors on vegetation. Thus, I would not have used the term “holistic”. Thank you for the very interesting suggestion. Unfortunately we have no data about arthropods at all. But we will include as a variable the ratio of competing (ccc, ccs, ccr) and non-competing species (all other strategy types) in the analysis. In addition, we will also consider the proportion of life forms (grasses, forbs, dwarf shrubs, lichens and mosses) as potential explanatory variables . Finally, we will also include the availability of propagation material, the microclimatic effects of soil surface structure and the role of arthropodes in the discussion. 19 Line 150: “of these ice-dammed lakes.(Fig. 1b)Further” delete dot before brackets, move it after brackets We will move the dot after the brackets. 20 Lines 149-151: are you sure that the succession restarted from zero? Organic matter should be present in soil after glacier lake outburst floods. I think you should better contextualized this point: have you checked the organic matter deposited and the grain size distribution? We are sure as there is no significant difference in the soil parameters of these plots and similar plot not affected by the glacier lake outburst (affected plots: for humus [%] 3.62 (±0.44) in comparison to similar not affected plots humus [%] 2.61 (±0.25) did not differ significantly). This will be mentioned in the methodoical section. 21 Lines 152-153: “The parameter ‘distance to the glacier front’ was determined as the shortest distance from every single study plot to the glacier tongue using the ‘near’ function in ArcGIS 10.6”. I would specify the year you are considering, even if it is guessable We will specify it: The glacier tongue extents are from the years when we did the surveys. 22 Line 157: insert dot after the reference We will do this. 23 Line 158: “The distinction between no snow and snow cover was defined by a threshold of 5 mm snow water equivalent.” Specify on which basis do you fix this threshold. Is it trustable? The threshold of 5 mm SWE for the differentiation between snow and no snow coverage is commonly used in previous studies (e.g., Warscher et al. 2013, Brutel-Vuilmet et al. 2012, Najafi et al. 2016, Thorton et al. 2021, Conway et al. 2021, Hofmeister et al. 2022). However, the sensitivity of the threshold value is not often addressed. In the work of Hofmeister et al. (2022), two different SWE threshold values (i.e., 0 mm and 5 mm SWE) were evaluated against observed snow cover duration at one snow station. The 5 mm SWE threshold slightly outperformed the 0 mm threshold as it attained a slightly higher prediction accuracy. Conway et al. (2021) observed a smaller mean bias between modeled and observed snow cover duration when using a 5 mm threshold compared to 30 mm, which lead to a negative bias because the simulated snow cover duration is underestimated. We revised the sentence accordingly:“The distinction between no snow and snow cover was defined by a threshold of 5 mm snow water equivalent, which has been used in multiple studies (e.g., Warscher et al. 2013, Brutel-Vuilmet et al. 2012, Najafi et al. 2016, Thorton et al. 2021, Conway et al. 2021, Hofmeister et al. 2022).” Warscher et al. 2013 (DOI: 10.1002/wrcr.20219), Thorton et al. 2021 (
https://doi.org/10.1016/j.jhydrol.2021.126241), Brutel-Vuilmet et al. 2012 (doi:10.5194/tc-7-67-2013), Najafi et al. 2016 (https://doi.org/10.1007/s10584-016-1632-2), Conway et al. 2021 (DOI: 10.2307/27127990)24 Line 161: “TWI”: since it is the first time TWI appears in the text I would explicit it: "Topographic wetness index (TWI)" We will do this. 25 Lines 183-185: why didn't you do soil analyzes of all the points to get direct values of some soil variables? Due to financial constraints, we were unfortunately only able to sample a few sites in a first phase. In the course of analysing the first results, however, we also realised that we needed concrete measurement data for all sites. Therefore, we sampled all the vegetation plots in summer 2022 and since december we have the results of the soil analyses from the lab. We will integrate the measured soil data into the new analysis. 26 Line 185 “for a subsample of the 65 study plots (n = 15).” How did you select this subsample? Which samples are they? We will specify it: The subsamples were only taken on less disturbed plots. We will remove this as we will use the new data of the soil analysis and do not use the community weighted mean of the Landolt indicator values any more. 27 Lines 196-97: “Finally, the estimated cover of coarse-grained material (scree cover) in the field was used as an additional independent variable (scree cover. "I would specify "for each plot". We will specify this. 28 line 200: the current signs of livestock grazing does not consider the effective influence in the past. If it is not possible to have information about past usage, it is better to clarify this point… We have historical data of livestock density in this area. Instead of grazing (yes/no) we will use a max-standardised value for grazing density. 29 Line 253: I would add “The most frequently analysed vegetation-related, dependent variables (biosphere)” We can add ",dependent variables ". 30 Line 258: add “:” after “variables” We will change it. 31 Table 3: why sometimes you use the name “RC1 etc” extrapolated from PCA and sometimes you use the full name of the variables? Thank you for this comment. We will be consistent with the names. 32 Line 409-413: “In our study, we have now demonstrated that – contrary to our initial expectation – a series of other variables correlates with our hypothesised three variables, jointly described by the components RC1 (‘elevation and time’), RC2 (‘solar radiation’), RC3 (‘south-eastness’), and RC5 ‘(low inclination’). Thus, hypothesis (ii) that the most important explanatory variables for vegetation cover development include years since deglaciation, elevation, and climatic variables, cannot be confirmed.”: demonstrating that many variables are correlated also with years since deglaciation, elevation, and climatic variables does not means that they are less important. You should comment these result, even in relation to NMDS results, were there is clearly a pattern related to years since deglaciation The reviewer is right, of course. We will be happy to take this suggestion/note into account when rewriting the text. 33 Line 424: delete “a” We will change it. 34 Line 440: “grazing and/or trampling showed no significant correlation” could be related to the fact that you did not considered grazing during all the period you considered (from LIA to now) We have historical data of livestock density in this area. Instead of grazing (yes/no) we will use a max-standardised value for grazing density. Citation: https://doi.org/10.5194/bg-2022-248-AC3
Katharina Ramskogler et al.
Katharina Ramskogler et al.
Viewed
| HTML | XML | Total | Supplement | BibTeX | EndNote | |
|---|---|---|---|---|---|---|
| 318 | 103 | 23 | 444 | 38 | 7 | 8 |
- HTML: 318
- PDF: 103
- XML: 23
- Total: 444
- Supplement: 38
- BibTeX: 7
- EndNote: 8
Viewed (geographical distribution)
| Country | # | Views | % |
|---|
| Total: | 0 |
| HTML: | 0 |
| PDF: | 0 |
| XML: | 0 |
- 1