Response to the letters by Kun et al. and Booth et al.,Global Change Biology Bioenergy

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Response to the letters by Kun et al. and Booth et al.
Global Change Biology Bioenergy ( IF 5.9 ) Pub Date : 2020-06-29 , DOI: 10.1111/gcbb.12724
Ernst‐Detlef Schulze ₁ , Carlos Sierra ₁ , Vincent Egenolf ₂ , Rene Woerdehoff ₃ , Roland Irsinger ₄ , Conrad Baldamus ₅ , Inge Stupak ₆ , Hermann Spellmann ₃

Affiliation

We would like to respond to the letters by Kun et al. (2020) and Booth, Mackey and Young (2020) making general comments first, and then adding a few specific remarks to some of their concerns. It seems to us that most comments in these two letters are the result of a misunderstanding of applied spatial and timescales, and maybe also a human dimension, that has to do with emotions. Some of their comments are correct and valid at particular scales and for particular carbon management problems, but not necessarily for the specific problem associated with accounting for greenhouse gas emissions from bioenergy originating from sustainably managed forests.

Land Use and Land‐Use Change: In the introduction of our opinion letter, we clearly state that our analysis is valid only under the condition of sustainable forest management, NOT for land‐use change, and NOT for exploitation forestry involving forest degradation. Thus, we object to the summarizing sentence of Booth et al. (2020), who state that we pave the way for destruction of the remnants of untouched forest in Europe or for land‐use change in the tropics. We agree that some land‐use changes release large amounts of CO₂, but this was not the topic of our opinion letter. We focus on the spatial scale of a landscape with sustainably managed forests, and not on landscapes that are subject to land‐use change, including deforestation.
Pristine Forest: We fully agree with the statement of Kun et al. (2020) that what is presently seen as unmanaged forests in Europe have nearly all been harvested at some time in the past. Indeed, the degree of “unmanaged” is a question of timescales. If you let any cleared managed land regenerate, it will look like “pristine” after some time. For example, large parts of the Carpathian forests in Romania may look pristine to some (e.g., Schickhofer & Schwarz, 2019), but in fact these forests were destroyed during World War I, and again during World War II (Figure 1). With enough time to regenerate and recover, such forests give the impression today of “pristine” forests, but only because the timescale of observation does not consider previous management. There are no pristine forests in Romania. As we stated above, it is a question of timescales: Amazonia was under management by pre‐Columbian groups (Levis et al., 2017). The bogs of Siberia were most likely drained by human beaver hunters in earlier times (Schulze, Lapshina, Filipov, Kuhlmann, & Mollicone, 2015). The biotas of Australia were shaped by the earliest human inhabitants and their use of fire (Bowman, 1998). Every continent has its anthropogenic history, and most forests have been intensively used and managed in the past. In Germany, numerous reports exist about the overexploitation of forests in the early 19th century (Hess, 1898) at a time, when we had most likely a biodiversity maximum in Europe (Schulze et al., 2019).
Fluxes versus stocks: Stocks are the integral of the net fluxes of carbon in and out of the forest, and one has to know the dynamics of the fluxes to understand the dynamics of the stocks. It is the CO₂ concentration in the air (the stocks of the atmosphere) that affects our climate, but we can only control this concentration by knowing the fluxes to and from the atmosphere. There is the major flux of fossil fuels (and not biogenic fluxes) that perturb the atmosphere but only slightly decreases the vast amounts of fossil fuel stocks. Another major fossil fuel use, and thus CO₂‐flux to the atmosphere, comes from cement production. It is not the fossil C‐stocks stored in limestone that affect the atmosphere. Also, it is the EU‐target of highest priority to reduce the annual CO_2‐equiv emissions by 40% until 2030 compared to 2005 levels (http://ec.europa.eu/clima/policies/strategies/2030_de). The energy that is needed for domestic and industrial purposes should increasingly be generated from renewable energy sources, as stipulated in the Renewable Energy Directive (EU 2018) and bioenergy is one of those renewable technologies. It is the flux of greenhouse gases from energy production that is important in our case, and not the installed capacity of energy plants.

Incentives to store carbon in ecosystems in order to compensate the ever increasing fossil fuel emissions give people a false sense of having solved the problem, but it does not give an incentive to solve the biggest problem of all, which is reducing the large fossil fuel flux from the fossil stores to the atmosphere. Thus, we clearly support the above‐cited EU regulation that CO₂ emissions, originating mainly from fossil fuel fluxes, should be reduced and not compensated by biomass storage.

In addition, we would like to confirm that the carbon stocks of managed and unmanaged forests per area unit in Germany are not statistically different. At the time, when we wrote our opinion letter, we had access only to a limited dataset, reported in our original Table 1. However, meanwhile we had access to a reanalysis of data from the German national forest inventory (NFI), sorted by management and unmanaged forests based on original data records.

**FIGURE 1**
Open in figure viewerPowerPoint

The original map of the movement of Austrian and German troops across the Southern Carpathian alps in World War I. Green areas: “Pristine” forest according to Schickhofer and Schwarz (2019), with the troop movements of World War I shown in black arrows, and battle fields shown as cross bars according to von Falkenhayn (1921). This is one of 13 “unmanaged” reference site of the Primofaro project (Schickhofer & Schwarz, 2019). Photos of the sites can be visited in the war archive of Vienna. Map prepared by Mihai Nita, University of Brasov, Romania

TABLE 1. Average and maximum C stocks in living and dead volumes for forest registered as managed and unmanaged in Germany, based on plot data from the national forest inventory, independently of conservation status. Data obtained from the von Thuenen Institute, Eberswalde, Germany

	Broadleved (Fagus)		Significance	Coniferous (Picea)		Significance
	Un‐managed	Managed	Significance	Un‐managed	Managed	Significance
Average stocks (m³/ha life and dead wood)	435 ± 34, n = 332	366 ± 6, n = 9,104	****** P < .01	421 ± 37, n = 308	425 ± 6, n = 15,073	n.s.
Maximum stocks (m³/ha live and dead wood, >94.Percentile)	981 ± 148, n = 46 of 732	919 ± 195, n = 776 of 15,519	n.s.	1,118 ± 202, n = 43 of 859	1,098 ± 201, n = 1,456 of 29,113	n.s.
Area weighted age (years)	115	101		94	69
Increment (m³ ha⁻¹ year⁻¹)	8.99 ± 0.9, n = 327	10.28 ± 0.16, n = 8,746	****** P < .01	9.01 ± 1.04, n = 271	13.95 ± 0.16, n = 14,219	***

*** P < .01

The data differ from those published in our original Table 1, because the scale has changed from plot level observations to a regional grid‐based landscape scales. The average stocks of stem volumes are higher for Fagus under unmanaged conditions (worth 7 years of “average” growth) as stipulated by management to enhance growth of selected trees, but they do not differ significantly for Picea. More important is that the maximum stocks at the time of harvest are not significantly different, neither for Fagus nor for Picea. However, it takes a shorter time to reach maximum stocks for forest under management. Thus, non‐intervention does not lead generally to higher stocks in the living and dead biomass at landscape scale, but biomass is accumulated faster under management. The difference in growth rate (increment) between managed and unmanaged is smaller than shown in our earlier report, probably because some of the included unmanaged plots were put aside from management at recent times. In an earlier studies, Schulze (2017, 2018) showed that the highest and oldest Fagus trees were found in managed and not in protected forests. The volumes of Fagus reach an upper limit at an age of about 150 years, also based on observations in the old reserve of Nera (Romania) and Uholka (Ukraine). Beyond this age, trees or stands collapse, mainly because roots of Fagus are affected by Armillaria mellea, and then they become unstable and are over thrown by wind. Thus, trees do not get old in Central Europe. Coring hundreds of trees on a grid‐based inventory, the oldest Fagus‐tree we found was 286 years old.

High stocks contain a high risk of loss caused by climatic and biotic extreme events (drought, wind) and pests (bark beetles; Schulze, 2018). The collapse of the beech forest “Heilige Hallen” or “Solling” in Germany may be examples of that situation (personal observations). Thus, stocks of old‐growth forest are not resistant to these extreme events and are equally vulnerable to rapid carbon losses, as it happens in managed forests by harvesting. The bark beetle outbreaks in Bayerische Wald and Harz National Parks are additional examples (e.g., Wegener, 2018). In the unmanaged forest, the dying trees are transferred to the deadwood pool that start to decay at different rates, faster for needles and small twigs and slower for the trunk. Accordingly, harvested wood is transferred to the pool of harvested wood products (HWP) where different wood products get out of use with various “decay rates” (lifetime). At the end, carbon fixed by photosynthesis and stored in the wood will eventually be released back to the atmosphere independent whether it is used as a raw material for human use or not. The time scales of decay are very similar. As shown in Table 1 of our publication, the average half‐lives of natural decay and product use are not different.

Plot studies versus regional surveys: We already discussed the difference between observations at stand level and grid‐based inventories at landscape scale for Table 1. The same difference exists with soil surveys. The study of Mayer et al. (2020) about effects of management on soils is based on site‐specific plot studies. Grid‐based studies do not show such a difference (Schulze et al., in preparation).
Carbon sink capacity of old growth forests: The original study by Luyssaert et al. (2008) was a review based on plot studies of flux measurements. It was the main objective of that study to show that fluxes were larger than zero at high stand age. Clearly, in‐ and outfluxes of carbon will always be larger than zero in living systems, even though Net Ecosystem Productivity (NEP) declines with age. In the study by Luyssaert et al. (2008), NEP reached a maximum at stand age of 20 years after regeneration and a minimum at age 200 years. The later slight increase was due to new regeneration. Meanwhile Nord‐Larsen, Vesterdal, Bentsen, and Larsen (2019) and Gundersen (2020) questioned these results of a carbon sink in old stands. In a reply, Luyssaert, Schulze, and Knohl (2020) state that, given the huge variation, more data are needed to resolve this issue. Thus, after all, and in a long‐term perspective, Odum (1973) may be confirmed: under steady‐state conditions, ecosystems reach a balance between carbon sequestration and respiration. It is again a question of scale: the C‐balance trajectory over time of regions is different from that of a single tree, or a stand.
IPCC guidelines and accounting: Indeed, the IPCC guidelines are complicated, and the separation between a forestry (including HWP) and an energy sector makes accounting for a closed supply chain of wood cumbersome even at national scale, especially when wood is imported and exported beyond borders. The IPCC rules were made to address a global scale problem and the accounting of carbon emissions and removals at the national level. They do not allow comparison of activities within a country. This is why we showed a table with national level fluxes in our original publication to make the main point clear that carbon sequestered by photosynthesis returns to the atmosphere by decomposition or by combustion of biomass for energy, regardless of the scales used for accounting. It is the same amount of carbon that is sequestered and released, irrespective of the fact that wood contains less energy by volume or mass than fossil fuels. The societal objective is to reduce greenhouse gas emissions from fossil fuels, because such carbon is not returned back to fossil stores. It is misleading to say that consumption of wood for energy leads to more CO₂ entering the atmosphere than by the natural process of decomposition. This is again a problem of spatial and temporal scale, whether we are referring to a single tree or stand, or a region or the whole globe, or whether we refer to a decade or a century. The scale of analysis complicates the type of statements that can be made with respect to the benefits of forest management activities on climate. We reiterate here that our focus is on sustainable forest management at subnational and landscape scale, where the IPCC accounting rules, designed for global scale accounting, show limitations to make sound judgments.
Climate targets. It is the objective of the international agreements on climate change to limit the increase in global average temperature to 1.5–2.0 K. It is up to the nations to translate this general goal into national targets for greenhouse gas emissions reductions. Reaching the goal will require a substantial reduction in fossil fuel emissions for all nations. There are few nations, where a reduction of land‐use change may also significantly contribute to improve the national greenhouse gas balance. However, in our paper, we were not dealing with land‐use changes.

Some specific comments to Kun et al. (2020).

Clearly, trees and soils do not increase their carbon stocks unlimited. The famous rule of Körner (2003) of “slow in and rapid out” brings the problem to the point. NEP estimates potential changes in carbon stocks. This is not suitable as a measure of climate mitigation, because lateral fluxes (i.e., fluxes across landscapes and time) are not reported. This is why additional terms have been defined for accounting of lateral fluxes (Schulze et al., 2009), or for dealing with the degree of permanence of the sequestered carbon (Brandao et al., 2013). Fossil stores are by far the most important stocks that should be left in the ground as the fluxes from these stocks have the largest effect on climate.
We did include the fossil fuel demand for harvesting and processing. Our data are net emissions. Other studies further show that such emissions are often relatively small for wood fuels. Only about 3%–20% of the photosynthetic carbon is contained within the wood fuels, depending if it is from local sources or from international supply chains (Taeroe, Mustapha, Stupak, & Raulund‐Rasmussen, 2017).
The age class distributions of forests in Germany are public data.
Fagus and Picea contribute about two‐thirds of the forest area in Germany. We suggest that our data would also be representative also for Pinus because it is managed in systems similar to Picea. Quercus is different, as it can only survive in managed conditions because it is overgrown by Fagus under natural conditions.

Some specific comments concerning Booth et al. (2020).

Fires: Indeed, forest fires act in a similar way as bioenergy with respect to carbon emissions to the atmosphere. In most countries, wildfires are of anthropogenic origin (Mollicone, Eva, & Achard, 2006), and should thus be accounted for as an emission. The difference between combustion and wildfires is that the energy released is being used or not. As said above, the full carbon balance needs to be considered and it will only get complete, if all processes, including ecosystem respiration from managed and protected areas and other losses, for example, by natural disturbances, are included.
Recent photosynthesis: We used this term to separate present‐day carbon sequestration by trees, from the sequestration that generated fossil fuels in very long‐term geological processes. The fossil fuels we use today were also produced by photosynthesis, but millions of years ago.
Wood balance: We believe we compiled the most comprehensive wood balance possible for Germany, even if it still contains a number of gaps, which appear to exist for the wood balances of most OECD countries. Gaps are likely due to the fact that wood is removed from forests, which is not officially recorded, such as firewood, bark, and oversize. In some countries, this may also be illegal cuttings.

The factor 10 between the climate change mitigation potential of managed and unmanaged forest as stated in our original article is based on a limited dataset that was available to us. Based on a reanalysis of the grid‐based German national forest inventory (Table 1), this difference becomes smaller (see Table 1), but remains significant (about factor 2 for spruce).

The statement of Booth et al. (2020) that our paper may be cited in support of increased harvesting craving for Europe's last remnants of untouched natural forest points at an additional dimension: The human dimension. As most citizens in Germany live in cities, there is an increasing demand for recreation, outdoor sport activities, stress release, and other services provided by forests. Paragraph one of the German conservation law lists not only biodiversity but also recreation as an objective. We suggest that this human dimension, together with biodiversity, is the main reason for the desire of society to set aside forests as unmanaged or unmanaged‐looking forest, that is, for conservation and recreation. If these objectives are the focus, the harvesting and transport of trees by large machines become an obstacle, while forwarding of wood by horses is welcome, because it contributes to the recreational experience. Especially for recreation, old‐growth stands act as a surrogate for pristine conditions that are perceived as desirable for a number of more or less well‐argued reasons. There are many good societal reasons to preserve forests as unmanaged, but climate change mitigation is not one of them. Also, biodiversity turns out to be supported by management and not by conservation (Schall et al., 2020). There is an urgent need to disentangle arguments based on carbon and diversity management versus other dimensions of forest management.

中文翻译：

对Kun等人信件的回应。和布斯等。

我们想回应Kun等人的来信。（2020）和Booth，Mackey and Young（2020）首先发表一般性评论，然后再对他们的一些关注发表一些具体评论。在我们看来，这两个字母中的大多数评论都是由于对所应用的空间和时间尺度以及可能与情感有关的人类维度的误解造成的。他们的某些评论在特定规模和特定碳管理问题上是正确和有效的，但对于与核算源自可持续管理森林的生物能源产生的温室气体排放有关的特定问题，则不一定是正确的。

土地利用和土地利用变化：在我们的意见书的开头，我们明确指出，我们的分析仅在可持续森林管理的条件下才有效，不适用于土地利用变化，也不适用于涉及森林退化的采伐林业。因此，我们反对Booth等人的概括句。（2020年），他指出，我们为销毁欧洲原始森林的残留物或为热带地区的土地利用变化铺平了道路。我们同意某些土地用途的变化会释放大量的CO ₂，但这不是我们意见书的主题。我们关注的是具有可持续管理的森林的景观的空间尺度，而不关注受土地利用变化（包括森林砍伐）影响的景观。
原始森林：我们完全同意Kun等人的说法。（2020年），在欧洲，目前被视为未经管理的森林，几乎在过去的某个时候都被采伐了。实际上，“不受管理”的程度是时间尺度的问题。如果您让任何清理过的管理土地再生，一段时间后，它将看起来像“原始”。例如，罗马尼亚大部分喀尔巴阡山脉的森林可能看起来有些原始（例如Schickhofer和Schwarz，2019年），但实际上这些森林在第一次世界大战期间以及第二次世界大战期间遭到了破坏（图1）。这些森林有足够的时间进行再生和恢复，今天给人的印象是“原始”森林，但这仅仅是因为观察的时间尺度并未考虑先前的管理。罗马尼亚没有原始森林。如上所述，这是一个时间尺度的问题：亚马孙时期由前哥伦布时期的组织管理（Levis等人， 2017年）。西伯利亚的沼泽很可能在早期被人类的海狸猎人消耗掉了（Schulze，Lapshina，Filipov，Kuhlmann和Mollicone， 2015）。澳大利亚的生物群系是由最早的人类居民及其对火的使用造成的（Bowman， 1998年））。每个大陆都有其人类活动的历史，过去大多数森林都得到了密集的利用和管理。在德国，有许多关于19世纪初森林过度开发的报道（Hess， 1898），当时我们最有可能在欧洲创造最大的生物多样性（Schulze et al。， 2019）。
通量与存量的关系：存量是森林中进出森林的净碳通量的组成部分，必须了解通量的动态才能了解存量的动态。空气（大气储量）中的CO ₂浓度会影响我们的气候，但是我们只能通过知道进出大气的通量来控制该浓度。化石燃料的主要通量（而非生物通量）会扰动大气层，但只会略微减少大量化石燃料的存量。水泥生产是另一种主要的化石燃料用途，因此向大气中的CO ₂排放。储存在石灰石中的化石碳储量不会影响大气。此外，降低年度二氧化碳排放量也是欧盟的最高优先目标到2030年，与2005年的水平相比，二氧化碳_当量的排放量将减少40％（http://ec.europa.eu/clima/policies/strategies/2030_de）。根据《可再生能源指令》（EU 2018）的规定，用于家庭和工业目的的能源应越来越多地从可再生能源中产生，而生物能源是其中的可再生技术之一。在我们的案例中，重要的是能源生产产生的温室气体通量，而不是能源工厂的装机容量。

为补偿不断增加的化石燃料排放而在生态系统中存储碳的激励措施使人们对解决问题有错误的认识，但并没有激励人们解决最大的问题，即减少了大的化石燃料通量从化石商店到大气。因此，我们明确支持上述欧盟法规，即应减少主要来自化石燃料通量的CO ₂排放，而不能通过生物质存储来补偿。

此外，我们想确认，德国每单位面积的管理和非管理森林的碳储量在统计上没有差异。当时，当我们写意见书时，我们只能访问原始表1中报告的有限数据集。但是，与此同时，我们可以访问来自德国国家森林清单（NFI）的数据的重新分析，排序方式为基于原始数据记录的管理和非托管林。

图1
在图形查看器中打开微软幻灯片软件

第一次世界大战中奥地利和德国军队穿越喀尔巴阡山脉南部阿尔卑斯山的原始地图。绿地：根据Schickhofer和Schwarz（2019年）的“原始”森林，第一次世界大战的部队运动用黑色箭头表示，和战场根据冯·法肯汉（von Falkenhayn，1921年）显示为横杆。这是Primofaro项目的13个“非托管”参考站点之一（Schickhofer＆Schwarz，2019年）。可以在维也纳的战争档案中访问这些站点的照片。地图由罗马尼亚布拉索夫大学的Mihai Nita准备

表1.根据国家森林清单中的地块数据，与保护状态无关，在德国注册为管理和非管理的森林中，活着的和死体积的碳储量的平均值和最大值数据来自德国埃伯斯瓦尔德的冯·图嫩研究所

	广域网（Fagus）		意义	针叶树（Picea）		意义
	未管理	管理	意义	未管理	管理	意义
平均存量（m ³ / ha生命和枯木）	435±34，n = 332	366±6，n = 9,104	****** P <0.01	421±37，n = 308	425±6，n = 15,073	ns
最大库存量（m ³ / ha活木和枯木，> 94。百分位数）	981±148，n = 732（46）	919±195，n = 776（共15,519）	ns	1,118±202，n = 859中的43	1,098±201，n = 1,456，共29,113	ns
区域加权年龄（年）	115	101		94	69
增量（m ³ 公顷- ¹ 年^-1）	8.99±0.9，n = 327	10.28±0.16，n = 8,746	****** P <0.01	9.01±1.04，n = 271	13.95±0.16，n = 14,219	***

*** P <0.01

数据与原始表1中发布的数据有所不同，因为该比例已从地块级别的观测更改为基于区域网格的景观尺度。的平均股票茎体积是高水青冈规定通过管理提升选择树木生长的非托管条件（价值700多年的“平均”增长）之下，但他们不为显著不同的云杉。更重要的是，无论是对Fagus还是Picea，收获时的最大种群数量都没有显着差异。但是，要花更多的时间才能达到所管理森林的最大数量。因此，不干预一般不会导致景观尺度上生活和死生物量的增加，但在管理下生物量的积累速度更快。托管与非托管之间的增长率（增量）差异小于我们先前报告中显示的差异，这可能是因为最近所包括的一些非托管地块已被管理之外。在早先的研究中，舒尔茨（2017年，2018）显示，最高和最古老的水青冈发现树木管理，而不是在受保护的森林。的体积水青冈根据对尼拉（罗马尼亚）和乌霍尔卡（乌克兰）的旧保护区的观测，在约150岁时达到上限。在这个时代以后，树木或林分倒塌，主要是因为Fagus的根受到蜜环菌的影响，然后变得不稳定并被风吹倒。因此，树木在中欧不会变老。在基于网格的清单上为数百棵树取芯，我们发现的最古老的Fagus-树已有286年的历史。

高存量具有因气候和生物极端事件（干旱，风）和害虫（树皮甲虫； Schulze，2018年）而造成损失的高风险。在德国，山毛榉森林“ Heilige Hallen”或“ Solling”的倒塌可能就是这种情况的例子（个人观察）。因此，老龄林的存量不能抵抗这些极端事件，并且同样容易遭受迅速的碳损失，因为在人工采伐的森林中会发生这种情况。Bayerische Wald和Harz国家公园的树皮甲虫暴发是另外的例子（例如Wegener， 2018）。在未管理的森林中，垂死的树木被转移到沉木池中，并开始以不同的速度腐烂，针叶和小树枝的腐烂速度更快，树干的腐烂速度更快。因此，将采伐的木材转移到采伐的木材产品（HWP）池中，在这里不同的木材产品以各种“衰减率”（使用寿命）停用。最后，通过光合作用固定并存储在木材中的碳最终将独立于其释放到大气中，无论它是否用作人类使用的原材料。衰减的时间尺度非常相似。如我们出版物的表1所示，自然衰变和产品使用的平均半衰期没有差异。

地块研究与区域调查：我们已经讨论了表1的林分一级观测值与景观尺度上基于网格的清单之间的差异。土壤调查也存在相同的差异。Mayer等人的研究。（2020）关于管理对土壤的影响基于特定地点的样地研究。基于网格的研究没有显示出这种差异（Schulze等人，正在准备中）。
老生长林的碳汇能力：Luyssaert等人的原始研究。（2008）是基于通量测量的情节研究的审查。该研究的主要目的是表明，在高林分年龄时通量大于零。显然，即使净生态系统生产率（NEP）随着年龄的增长而下降，生物系统中的碳流入和流出也总是大于零。在Luyssaert等人的研究中。（2008年），NEP在再生后20年的林分年龄达到最大值，在200年的林分达到最小值。后来的轻微增加是由于新的再生。同时Nord-Larsen，Vesterdal，Bentsen和Larsen（2019）和Gundersen（2020）质疑旧看台上碳汇的结果。Luyssaert，Schulze和Knohl（2020）在答复中指出，鉴于巨大的差异，解决此问题需要更多的数据。因此，从长远来看，毕竟，Odum（1973）可以被证实：在稳态条件下，生态系统在固碳与呼吸之间达到平衡。这又是一个规模问题：区域的C平衡轨迹随时间的变化与单棵树或林分的不同。
IPCC指南和会计：确实，IPCC指南很复杂，林业（包括HWP）和能源部门之间的分离使得即使在全国范围内，也难以解释木材的封闭供应链，特别是当木材进出口超出边界。制定了IPCC规则是为了解决全球规模的问题以及国家一级的碳排放量和清除量的核算。它们不允许比较一个国家内的活动。这就是为什么我们在原始出版物中显示了一张具有国家水平通量的表格的原因，以明确要点：光合作用所固存的碳是通过分解或通过燃烧生物质获取能源而返回大气的，而与核算的规模无关。固存和释放的碳量相同，不论木材在体积或质量上所包含的能量都比化石燃料少。社会目标是减少化石燃料产生的温室气体排放，因为这种碳不会返回到化石存储中。误以为木材消耗能源会导致更多的二氧化碳₂进入大气比会通过自然过程分解。这又是一个时空尺度的问题，无论我们是指一棵树或林分，还是一个地区或整个地球，还是我们指的是十年还是一个世纪。分析的规模使关于森林管理活动对气候的好处的陈述类型变得复杂。我们在此重申，我们的重点是在国家以下和景观规模的可持续森林管理中，为全球规模的会计而设计的IPCC会计规则显示出做出合理判断的局限性。
气候目标。国际气候变化协议的目标是将全球平均温度的升高限制在1.5-2.0K。各国应将这一总体目标转化为减少温室气体排放的国家目标。要实现这一目标，就需要大幅减少所有国家的化石燃料排放量。在少数几个国家，减少土地用途的变化也可能大大有助于改善国家温室气体的平衡。但是，在本文中，我们并未处理土地用途的变化。

对Kun等人的一些具体评论。（2020年）。

显然，树木和土壤不会无限增加其碳储量。Körner（2003）的著名规则“慢进快出”使问题变得很明显。NEP估计碳储量的潜在变化。这不适合作为缓解气候变化的指标，因为未报告横向通量（即，跨景观和时间的通量）。这就是为什么要定义附加术语来解释侧向通量（Schulze等，2009）或处理固存碳的永久程度（Brandao等， 2013）的原因。化石商店是迄今为止应留在地下的最重要的种群，因为这些种群的通量对气候的影响最大。
我们确实包括了对采伐和加工的化石燃料需求。我们的数据是净排放量。其他研究进一步表明，木质燃料的此类排放量通常相对较小。木质燃料中仅包含约3％–20％的光合碳，具体取决于其是本地来源还是来自国际供应链（Taeroe，Mustapha，Stupak和Raulund‐Rasmussen， 2017年）。
德国森林的年龄等级分布是公共数据。
Fagus和Picea贡献了德国森林面积的三分之二。我们建议我们的数据也可以代表Pinus，因为它在类似于Picea的系统中进行管理。栎属不同，因为它只能在自然条件下被Fagus过度生长，因此只能在管理条件下生存。

有关Booth等的一些具体评论。（2020年）。

火灾：的确，森林火灾与大气中碳排放的行为类似生物能源。在大多数国家，野火是人为起源的（Mollicone，Eva和Achard， 2006年），因此应将其视为排放物。燃烧和野火之间的区别在于释放的能量是否正在使用。如上所述，需要考虑全部碳平衡，只有包括所有过程，包括来自受管理和保护区的生态系统呼吸作用以及其他损失（例如自然干扰），碳平衡才完整。
最近的光合作用：我们用这个术语将当今树木的碳固存与在很长的地质过程中产生化石燃料的固存分开。我们今天使用的化石燃料也是通过光合作用生产的，但距今已有数百万年的历史了。
木材天平：我们相信，尽管德国仍然存在许多缺口，但我们还是为德国编制了最全面的木材天平，而大多数OECD国家的木材天平似乎都存在缺口。缺口可能是由于从森林中砍伐了木材而未正式记录，例如木柴，树皮和特大型木材。在某些国家/地区，这也可能是非法砍伐。

如我们的原始文章所述，介于人工林和非人工林的气候变化缓解潜力之间的系数10是基于我们可用的有限数据集。根据对基于网格的德国国家森林资源清查表（表1）的重新分析，这种差异变小（请参见表1），但仍然很明显（云杉的系数约为2）。

布斯等人的声明。（2020年），我们的论文可能被引用来支持对欧洲未触及的天然林点的最后残余物的更大的采伐渴望，这是一个附加的维度：人类的维度。由于德国大多数公民居住在城市中，因此对娱乐，户外运动，缓解压力以及森林提供的其他服务的需求不断增长。德国保护法的第一段不仅列出了生物多样性，而且还把娱乐列为目标。我们建议，这种人类层面以及生物多样性是社会渴望将森林划为未经管理或外观未经管理的森林（即用于保护和娱乐）的主要原因。如果以这些目标为重点，那么使用大型机器进行树木的采伐和运输将成为障碍，同时欢迎使用马匹运送木材，因为它有助于娱乐体验。尤其是对于娱乐活动，旧的看台可作为原始条件的替代，这些原始条件由于许多或多或少有争议的原因而被认为是理想的。有很多良好的社会理由将森林保持为未管理状态，但是减轻气候变化并不是其中之一。而且，生物多样性最终得到了管理的支持，而不是保护的支持（Schall等， 2020年）。迫切需要消除基于碳和多样性管理与森林管理其他方面的争论。

更新日期：2020-06-29

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