Are Secondary Forests Ready for Climate Change? It Depends on Magnitude of Climate Change, Landscape Diversity and Ecosystem Legacies
Round 1
Reviewer 1 Report
This paper provides a framework for considering secondary forest management in the context of climate change, showing 5 possible frames. The overall organization and writing are clear, but I don't feel like it feel like it provides enough of a synthesis of the current state of research or a framework that is sufficiently different from what has been presented in previous papers (e.g., Millar et al. 2007).
It also seems to ignore a lot of the research being done on identifying resilient landscapes (work by Mark Anderson and others at the Nature Conservancy), and forestry adaptation research, such as the Conifer Strongholds and adaptation forestry projects being undertaken by Mark White and Meredith Cornett or the Adaptive Silvilcuture for Climate Change network, for example research by Brian Palik and others. Finally, there has been significant modeling undertaken by Matthew Duveneck, Frank Thompson, and others using the LANDIS model that looks at forest dynamics that was largely ignored.
Finally, a lot of assertions were made about what "will" happen without this being backed up by any research.
I recommend the authors rework this manuscript in light of more of the current research and spend some time refining their framework.
Specific comments:
Page 2:
Line 49:extra comma
Line 56: these may benefit from short definitions here. Facilitation is also referred to as "transition" and "response" in some papers.
Line 56: extra of? Or of what?
Line 76: Spell out FAO and what the definition is.
94: define “intactness”
Page 4:
154: define what is meant be "tightness"
171: 1 to 10s: this is a sort of arbitrary scale. I think of landscape diversity to at much smaller and broader scales than that.
179: also differences in albedo, latent heat flux, wind patterns.
184-185: This is being studied in the "conifer strongholds" project TNC is doing in northern MN
Page 5:
211: define what you mean by ecoregion. is this smaller than biome?
Page 6:
Figure 2: I find this figure hard to interpret. Does "50 years past" mean 50 years into the future? Why does the low magnitude climate change lead to a bunch of dead-looking conifers but more change least to a more diverse deciduous ecosystem?
243: “perhaps by clear-felling” is this needed? Also clearcutting is more commonly used.
Given you later talk about uneven aged stands it sounds like you are including other types of harvests.
Page 7:
263: should this be legacy?
268:where do ecological restorations fit in? Does this fit here? In some cases there have been intentions to increase the diversity of trees through planting?
276: wouldn't it be easier to say "low resilience"?
287: these would be useful to be named something to better track them. Instead of numbers can they be "persistence", "moderate change", "forest type shift","biome change", and "novel ecosystem"?
Figure 3: this makes it look like the novel ecosystem lacks any diversity, but it could be diverse
Page 9:
Page 359: As well as the biology of different species and the management goals of organizations.
364 (any many statements thereafter that say "are" or "will") “ecological resilience levels are highest” Maybe you hypothesize this? There isn't a lot of evidence to say for sure. All of these statements shoudl be more hypothetical or questions for future research.
Table 1: This is confusing. Consider an alternative way of illustrating concepts through a figure/diagram.
Conclusions: be sure to
Author Response
This paper provides a framework for considering secondary forest management in the context of climate change, showing 5 possible frames. The overall organization and writing are clear, but I don't feel like it feel like it provides enough of a synthesis of the current state of research or a framework that is sufficiently different from what has been presented in previous papers (e.g., Millar et al. 2007).
Reply: We thank the reviewer for a number of constructive comments that improved the paper in revision. We have detailed replies and rebuttals below.
Previous schemes for climate change adaptation in forests, such as the most well-known one by Millar et al (2007), suggests a very different type of framework than we do here. Millar et al present three different management strategies, while this paper suggests a framework for assessing the magnitude of change in a given forest depending on the landscape and regional setting, which would in turn lead to choosing a management strategy. A lot of papers have been published about management techniques and strategies to respond to climate change, which mention that small, medium and large projected changes in forests as the climate warms would require resistance, resilience or facilitation management strategies, respectively (or something similar), but they say very little about how to place a given forest into those categories of likely magnitudes of change. This paper fills that gap.
It also seems to ignore a lot of the research being done on identifying resilient landscapes (work by Mark Anderson and others at the Nature Conservancy), and forestry adaptation research, such as the Conifer Strongholds and adaptation forestry projects being undertaken by Mark White and Meredith Cornett or the Adaptive Silvilcuture for Climate Change network, for example research by Brian Palik and others. Finally, there has been significant modeling undertaken by Matthew Duveneck, Frank Thompson, and others using the LANDIS model that looks at forest dynamics that was largely ignored.
Reply: Good point that Landis and related types of simulations of future conditions for varied climate change scenarios could help one decide which of the frames proposed here their particular forest may experience in the future. We point this out and mention the Landis simulations in the revised manuscript (lines 497-503 of the revised ms). Although the silvicultural experiments underway by TNC and Brian Palik and colleagues are very nice work, they still are only experiencing frame 1, or possibly beginning of frame 2 conditions, at this time, and these experiments are unlikely to illuminate the higher frame levels that we propose here, which this region is very likely to experience by mid-to-late 21st century. Nevertheless, we do cite this work in the revised ms (lines 544-547). Two of the Anderson papers are also cited (Anderson et al 2014, Lawler et al 2015).
Finally, a lot of assertions were made about what "will" happen without this being backed up by any research. I recommend the authors rework this manuscript in light of more of the current research and spend some time refining their framework.
Reply: After thoroughly checking the occurrence of the word ‘will’ throughout the manuscript, it is evident that we are using it properly, and not in the sense of making specific predictions (e.g. ecosystem legacies will interact with climate as it changes; what thresholds will trigger each of the frames?). These are not the types of usages that need back up by references.
Specific comments:
Page 2:
Line 49:extra comma
Reply: Comma removed.
Line 56: these may benefit from short definitions here. Facilitation is also referred to as "transition" and "response" in some papers.
Reply: These are very commonly used concepts and do not require definitions.
Line 56: extra of? Or of what?
Reply: Of ‘Millar et al. 2007’, we added the author name as requested: Millar et al. [6]
Line 76: Spell out FAO and what the definition is.
Reply: We decided to delete this sentence, so no longer applicable.
94: define “intactness”
Reply: The following phrase defines it, but it was not clearly worded. Now it reads: ‘intactness—continuous canopy of cover over time.’
Page 4:
154: define what is meant be "tightness"
Reply: The concept of tight versus leaky nutrient cycling systems are so basic and commonly used that no definition is required given the readership of the journal.
171: 1 to 10s: this is a sort of arbitrary scale. I think of landscape diversity to at much smaller and broader scales than that.
Reply: This is true on the smaller end of the scale. We reworded to say ‘scales from a 10s of m to 10s of km.’
179: also differences in albedo, latent heat flux, wind patterns.
Reply: True enough, although latent heat flux is implied, but we did mention the other two factors in the revised manuscript: ‘...albedo, wind patterns, evaporation and soil texture...’
184-185: This is being studied in the "conifer strongholds" project TNC is doing in northern MN
Reply: True, but this is a much broader review and synthesis than TNC work in northern MN, and the Stralberg et al reference [26] covers the topic very broadly, which is what was needed here. We do cite the work of the conifer stronghold project later on (see response to your second point above).
Page 5:
211: define what you mean by ecoregion. is this smaller than biome?
Reply: Yes, it is smaller, but as it turns out, the term is not needed here, it is best to just use the broader term ‘region’ in the revised ms.
Page 6:
Figure 2: I find this figure hard to interpret. Does "50 years past" mean 50 years into the future? Why does the low magnitude climate change lead to a bunch of dead-looking conifers but more change least to a more diverse deciduous ecosystem?
Reply: Thank you for pointing out that the wording was not clear. Yes it means 50 years into the future. However, we decided to make a completely new version of this figure—the old version was trying to do too many things at once. The new figure shows the difference in moving 50 years ahead in diverse and not diverse landscapes.
243: “perhaps by clear-felling” is this needed? Also clearcutting is more commonly used.
Reply: Yes, it is needed to explain to the reader that even clearcutting does not necessarily disrupt the forest floor and soils. We changed the terminology to clearcutting.
Given you later talk about uneven aged stands it sounds like you are including other types of harvests.
Reply: Yes, that is true, but stands could convert to uneven-aged status through partial cutting or natural stand development. No changes made.
Page 7:
263: should this be legacy?
Reply: Yes it should, thank you for pointing that out.
268: where do ecological restorations fit in? Does this fit here? In some cases there have been intentions to increase the diversity of trees through planting?
Reply: This paper is not primarily about restoration, but it does fit in, and increasing tree diversity is mentioned on line 369-371 and 586-592 of the revised ms.
276: wouldn't it be easier to say "low resilience"?
Reply: Not really, having high resilience debt is sometimes, but not always, the same as low resilience. We decided to leave it as is.
287: these would be useful to be named something to better track them. Instead of numbers can they be "persistence", "moderate change", "forest type shift","biome change", and "novel ecosystem"?
Reply: Yes, this would make the terminology easier for the reader to follow, so we adopted the suggested name changes in the descriptions and the figure, although for brevity we revert to the numbers in some places.
Figure 3: this makes it look like the novel ecosystem lacks any diversity, but it could be diverse
Reply: Yes, novel ecosystems could be diverse, and that is mentioned in the text, which also makes the point that mixed species plantations are rare. Therefore, we are showing a representative plantation with one species.
Page 9:
Page 359: As well as the biology of different species and the management goals of organizations.
Reply: True enough, but that point is made elsewhere, and this paragraph is covering the climate change scenario aspects of the problem.
364 (any many statements thereafter that say "are" or "will") “ecological resilience levels are highest” Maybe you hypothesize this? There isn't a lot of evidence to say for sure. All of these statements shoudl be more hypothetical or questions for future research.
Reply: Is it really possible for a forest facing a frame 1 scenario to not be more resilient than one facing a new climate in frame 4 which will not support forests at all? This is not a hypothesis, especially since everything here is from the viewpoint of maintaining a given forest type (frames 1 versus 2), or maintaining any type of forest at all (frames 3 versus 4). From the viewpoint of maintaining any vegetation type, resilience is higher, for example if a prairie is thought to be just as good an outcome as forest, then forest loss does not represent a resilience loss, however, from a forest-based perspective of what may happen to the currently existing forest type, it does represent resilience loss. Furthermore, the new paleoecology references and figure 4 showing changes that are already occurring or occurred in response to pre-historic changes in climate (response to reviewer 2) establish these facts.
Table 1: This is confusing. Consider an alternative way of illustrating concepts through a figure/diagram.
Reply: Yes, it does take some time to understand this table. However, we do not think it is confusing to show that if a currently forested area experiences a small change in climate, that resilience should be very high all across the legacy types (except for planted forests that may have had species out of synch with the current climate), and that forests in areas where the future climate will not support forest at all, forest resilience is low across the legacy types (and that remaining cases fall somewhere between). Figures 2 and 3 show specific examples, while the table attempts to be a more comprehensive but concise way to summarize the information.
That said, we deleted the frame 5 row in the table, which simplifies it by having fewer ‘NA’ and variable entries in cells. Hopefully that helps, because this summary of information presented in the text is inherently tabular rather than graphical (calling something high or low in a figure is no different from doing it in a table).
Conclusions: be sure to
Reply: Sorry, but we are not sure what this refers to (perhaps some of the reviewers words got cut off at some point), and made no changes.
Reviewer 2 Report
Review of the manuscript forests-887275
The manuscript is logically structured and easy to read. It provides a valuable review of vegetation change scenarios under different magnitudes of climate change, taking into considerations the influence of factors in the limelight of the research in forest science disciplines, such as resilience, ecological memory, ecosystem legacy, among others.
The discussion is well-supported by relevant references to a broad and up-to-date literature on applied vegetation science and forest management. From the theoretical standpoint the paper is accurately designed and highly informative, but it does not provide concrete examples to figure out the hypothesized scenarios of change. It lacks description of emblematic cases where the expected environmental changes have already occurred. This should be accompanied by necessary pictures showing vegetational landscapes before and after the discussed disturbances, in order both to significantly improve the understanding of the Discussion and increase the quality of the graphical materials, which is poor in the present version.
Although the information of palaeobotanical data is not considered, it would be very interesting whether the authors could write some lines in the paper describing advantages and disadvantages of the use of palaeobotanical data in assessing the ecological memory of vegetated ecosystems, which often is the legacy of thousands years of vegetation history. Despite this seems beyond the scope of the present paper, it would be interesting to know the point of view of the applied forest researchers on potentials and limitations of the integration of the palaeobotanical evidence in forest management plans.
The paper, on the whole, can meet the interest of a wide international audience of scholars dealing with the evolution of plant landscapes, and not exclusively forest engineers.
Author Response
The manuscript is logically structured and easy to read. It provides a valuable review of vegetation change scenarios under different magnitudes of climate change, taking into considerations the influence of factors in the limelight of the research in forest science disciplines, such as resilience, ecological memory, ecosystem legacy, among others.
The discussion is well-supported by relevant references to a broad and up-to-date literature on applied vegetation science and forest management. From the theoretical standpoint the paper is accurately designed and highly informative, but it does not provide concrete examples to figure out the hypothesized scenarios of change. It lacks description of emblematic cases where the expected environmental changes have already occurred. This should be accompanied by necessary pictures showing vegetational landscapes before and after the discussed disturbances, in order both to significantly improve the understanding of the Discussion and increase the quality of the graphical materials, which is poor in the present version.
Reply: Thank you for your positive comments! We did add some examples of current and pre-historic vegetation response to changing climate in a new figure 4, which has pictures, and illustrates emblematic examples of boreal forest currently in frame 2 and the start of frame 3 situations in northern Minnesota and Wisconsin. These include spruce and pine boreal forest recently converted to birch forest by high disturbance frequency, spruce-fir boreal forest with sugar maple invading the understory in the last 4 decades, which is a frame 2 situation, which could easily progress to frame 3 if the maple continues to invade. We also show frame 3 completed—conversion of boreal forest to almost pure sugar maple in western Upper Michigan during the mid Holocene due to increasing temperatures, and frame 4—prairie/oak woodland in Minnesota that converted from boreal forest during the mid Holocene due to increasing aridity. We also added some lines of text about the paleo evidence in the conclusions.
Although the information of palaeobotanical data is not considered, it would be very interesting whether the authors could write some lines in the paper describing advantages and disadvantages of the use of palaeobotanical data in assessing the ecological memory of vegetated ecosystems, which often is the legacy of thousands years of vegetation history. Despite this seems beyond the scope of the present paper, it would be interesting to know the point of view of the applied forest researchers on potentials and limitations of the integration of the palaeobotanical evidence in forest management plans.
Reply: The main advantage of the paleo data is that it proves that climate changes similar in magnitude to those projected by the end of the 21st century caused Frame 3 and Frame 4 changes in forests during the mid Holocene. What has happened can happen. The disadvantage is that the mid Holocene changes occurred more slowly and there were a lot fewer human-caused stressors than there are now, and those two factors cannot be resolved using the paleo data. However, as you stated, this is really beyond the scope of the paper, so we did not discuss these advantages/disadvantages.
The paper, on the whole, can meet the interest of a wide international audience of scholars dealing with the evolution of plant landscapes, and not exclusively forest engineers.
Reviewer 3 Report
The topic of the manuscript is relevant and it may be of interest for an International audience. Yet there are some points that should be carefully revised and clarified, to ensure the soundness and accuracy of the recommendations made.
1- My first concern regards the type of forests/biome the authors are referring to, as there is no clear statement or definition through the text. From Figure 1 and some aside comments it seems that they are mostly thinking on boreal or temperate forests from northern latitudes, but this should be presented and clarified at the very beginning of the ms. Indeed, the interaction among climate change, landscape configuration and ecosystem legacies can be expected be to be different for different types of forests (e.g. tropical, Mediterranean, boreal forests). Thus, it is hard to imagine that a single type of recommendations may be useful for all these forests. Without knowing which are the forest types and management practices that the authors have in mind it is difficult to assess whether their recommendations make sense or not. The need of more details (i.e. tree species name, type of management, etc.) would be especially necessary in section “4 Secondary and Planted Forest Legacies” and, to a lesser extent, in section “5 Management Options: Resilience frames”. Otherwise, everything is somewhat general and vague.
2 – I have a concern regarding the definition of secondary forests as the authors provide a working definition of secondary forests that excludes planted forests (Lines 91-91). This is unusual and confusing as either arising from afforestation of former agricultural lands (non-forest to forest) or forest recovery after disturbance (forest to forest), planted forests must be considered secondary forests. Including them into this category would very much simplify the reading of the paper and make further and artificial distinctions unnecessary (e.g. Secondary and Planted Forest Legacies).
3- Another concern refers to the differences in ecosystem legacies among secondary forests established into former agricultural lands and those arising from forest regeneration after disturbances. Up to now, there is extensive literature that has emphasized these differences, e.g. among many other :Fraterrigo et al. 2005. forests. Ecol. Monogr. 75, 215–230., Freschet et al. 2014. Ecology 95, 963–977., Leuschner et al. 2014. Ecosystems 17, 497–511. Yet, these differences are hardly considered in the current paper, although the authors claim that it is a “review” (Line 15). Moreover differences in ecosystem legacies among these two types of secondary forests may result in differences to their resilience to climate change mediated disturbances. Again, this has been reported in previous studies that authors miss and are highly recommended to check and include in their review, e.g.: von Oheimb et al. 2014. PLosONe, Mausolf et al. 2018 Oecologia, Alfaro-Sánchez et al. 2019 Agriculture and Forest Metereology, Espelta et al. 2020. Journal of Applied Ecology.
4- The second part of section 3.3 Landscape diversity and forest resilience (from Line 200 forward) and section 4. Secondary and Planted Forest Legacies are somewhat vague and lack of references to support the statements presented. When dealing with landscape configuration and forest resilience I would suggest the authors to check the Discussion paper by Messier et al. 2019 in Forest Ecosystems and references therein to go a step further and support the recommendations made in the current paper.
5- Overall, I think the paper needs a more in deep review of the current literature to make clearer and more precise recommendations to forest managers.
Author Response
The topic of the manuscript is relevant and it may be of interest for an International audience. Yet there are some points that should be carefully revised and clarified, to ensure the soundness and accuracy of the recommendations made.
Reply: Thank you for your overall positive response to the paper, as well as constructive comments below.
1- My first concern regards the type of forests/biome the authors are referring to, as there is no clear statement or definition through the text. From Figure 1 and some aside comments it seems that they are mostly thinking on boreal or temperate forests from northern latitudes, but this should be presented and clarified at the very beginning of the ms. Indeed, the interaction among climate change, landscape configuration and ecosystem legacies can be expected be to be different for different types of forests (e.g. tropical, Mediterranean, boreal forests). Thus, it is hard to imagine that a single type of recommendations may be useful for all these forests. Without knowing which are the forest types and management practices that the authors have in mind it is difficult to assess whether their recommendations make sense or not. The need of more details (i.e. tree species name, type of management, etc.) would be especially necessary in section “4 Secondary and Planted Forest Legacies” and, to a lesser extent, in section “5 Management Options: Resilience frames”. Otherwise, everything is somewhat general and vague.
Reply: This is a good point. We did chose to illustrate the new conceptual framework here using the transition from boreal to temperate to savanna/grassland biomes, but did not make that clear in the original ms. We revised language in the introduction to make it clear in the revised ms. The reviewer is correct that there would be a lot of variability in species and types of trajectories in different forest biomes around the world, such as Mediterranean and tropical ecosystems. We are not attempting to cover all possible forest transitions in the world, although hopefully others could adapt our system of frames to other parts of the world.
2 – I have a concern regarding the definition of secondary forests as the authors provide a working definition of secondary forests that excludes planted forests (Lines 91-91). This is unusual and confusing as either arising from afforestation of former agricultural lands (non-forest to forest) or forest recovery after disturbance (forest to forest), planted forests must be considered secondary forests. Including them into this category would very much simplify the reading of the paper and make further and artificial distinctions unnecessary (e.g. Secondary and Planted Forest Legacies).
Reply: Yes, thank you for pointing out the confusion. We decided to adopt our own simpler definition rather than use the one that had been cited. Here is the revised definition: any forest which was clearcut, or removed and converted to other land uses (most commonly agriculture), and reforested or afforested with natural or planted regeneration.
3- Another concern refers to the differences in ecosystem legacies among secondary forests established into former agricultural lands and those arising from forest regeneration after disturbances. Up to now, there is extensive literature that has emphasized these differences, e.g. among many other :Fraterrigo et al. 2005. forests. Ecol. Monogr. 75, 215–230., Freschet et al. 2014. Ecology 95, 963–977., Leuschner et al. 2014. Ecosystems 17, 497–511. Yet, these differences are hardly considered in the current paper, although the authors claim that it is a “review” (Line 15). Moreover differences in ecosystem legacies among these two types of secondary forests may result in differences to their resilience to climate change mediated disturbances. Again, this has been reported in previous studies that authors miss and are highly recommended to check and include in their review, e.g.: von Oheimb et al. 2014. PLosONe, Mausolf et al. 2018 Oecologia, Alfaro-Sánchez et al. 2019 Agriculture and Forest Metereology, Espelta et al. 2020. Journal of Applied Ecology.
Reply: We do not agree with the reviewer on this point for the following reasons. This manuscript needs to concisely review several complex topics (ecosystem legacies, memory, resilience, landscape diversity), to set the stage for the main thrust of the paper on the frames through which to view potential change. We only need to review those parts of these topics relevant to the frames that are introduced later in the paper. The papers the reviewer mentions give details on specific cases of differences in legacies of various second growth forests, with different management histories. The issues highlighted in these papers are mainly differences in fertility, in species composition of the understory, in tree-ring response to climate variability, in tree growth and in response to insect herbivory and drought, showing that differences persist for variable periods of time after a given land use legacy ends. Although this is important information, it is at a level of detail way too small in scale and too site-specific to review here. The coauthors that are on this paper have published detailed reviews of legacies, resilience, and related concepts (with varied groups of additional coauthors), such as Stanturf et al. 2014, Johnstone et al. 2016, Jogiste et al. 2017, Jogiste et al. 2018, Webster et al. 2018, and Stralberg et al. 2020, which readers can see (in addition to the paper the reviewer suggests) for details.
4- The second part of section 3.3 Landscape diversity and forest resilience (from Line 200 forward) and section 4. Secondary and Planted Forest Legacies are somewhat vague and lack of references to support the statements presented. When dealing with landscape configuration and forest resilience I would suggest the authors to check the Discussion paper by Messier et al. 2019 in Forest Ecosystems and references therein to go a step further and support the recommendations made in the current paper.
Reply: We agree that sections 3.3 and parts of the following section 4 were not clear. Therefore, we made a new figure 2 and moved figure 1 into the previous section to improve the flow of ideas, and added some references (three new ones and a few that had already been used elsewhere in the paper but that are relevant here) that hopefully make these sections more clear. We are not making specific recommendations about landscape configuration in this paper, so the Messier et al. 2019 reference is not needed.
5- Overall, I think the paper needs a more in deep review of the current literature to make clearer and more precise recommendations to forest managers.
Reply: The purpose here is to present a general framework for viewing possible future changes, not to provide precise recommendations to forest managers. It is a review that develops a new way to visualize future changes that happens to have a lot of concepts that contribute to it, so that we need only cite the more general references on each of those concepts (although we did add eight new references). Note that reviewer #2 states that the paper is well-supported by relevant references to a broad and up-to-date literature on applied vegetation science and forest management
Instead of reviewing management techniques and details—which would make a good future paper, but are tangential to this paper—we decided to follow the advice of reviewer #2 and make a relatively large change showing how forests have responded to past and current climate changes in the boreal-temperate forest-grassland sequence of changes with warming climate, which is directly related to this paper.
Round 2
Reviewer 3 Report
I am fine with the revison of the ms.
