9 Questions about the forest

Forests are among the most biodiverse and productive habitats on earth and have many functions. They produce oxygen, sequester carbon and regulate the climate. They provide habitat for people, animals and plants. They protect the soil and filter the water. Humans claim their natural resources – using trees for wood products and energy and the forest as a recreational space.

What is the status of these functions in the forest in Germany?? How would the forest vision change the forest? Using the forest model FABio these questions can be answered. Based on nine questions, the oko-Institut presents the most important results.

One third of Germany is forested. Globally, forests also cover about 30 percent of land area. But not all forests are the same. Depending on the nature of the forest, the forest can fulfill its functions better or worse. Sustainable use is characterized by maintaining all forest functions over the long term.

The demands on the forest are increasing – also in Germany. The use of energy wood in particular is increasing. There are still many areas worth protecting, but they are intensively managed. Forest features important for conservation, such as old and dead trees, are too rare.

In the Forest Vision the oko-Institut ventures a look into the future and analyzes the potential of more ecological management in various scenarios. What happens when we take less wood from forests and leave trees in the forest longer? See also pillar more ecological forest management. What are the implications if we manage the forest less actively and leave more work to nature? If we want to let more forest areas develop naturally, what should they be?? See also pillar protected areas. More natural forest means deciduous trees play a greater role. What this means for forest composition, forest carbon storage and wood production? – See also pillar forest conversion.

The Forest Vision Is not a fixed goal. Rather, it represents a process in which many adjusting screws must be set for a near-natural, species-rich and climate-protecting forest. To shape this process, we need clues as to what future development might look like. Among other things, we learn from past observations, for example from forest inventories of the Federal Republic of Germany – see also Information on the model – Data basis.

We also learn through simulations with computer models that calculate how the forest is likely to develop under certain conditions. Any model is a gross simplification of reality. There are uncertainties in the input data and unknown or even known influencing variables that are not considered at all. This also applies to the model FABio, which scientists at the oko-Institut have developed to look specifically at forest development issues in Germany – see also Information on the model – Modeling.

Scenarios presented by models do not represent an accurate forecast of reality. Rather, they describe an if-then development and we can learn through them how the forest behaves under certain conditions. The Forest vision is a scenario developed by the oko-Institut as part of the project Forest Vision Germany developed with Greenpeace Germany. It can be compared with two alternatives: a baseline scenario and a wood scenario. Further information on modeling – see also Information on the model – Scenarios.

Figure 1: How the Fabio model works for scenario development

The theory of many experts is that if forests are used less intensively, they will grow less well. The oko-Institut’s model results indicate, however, that tree growth could be slightly improved by less intensive forest use. This is partly because forests can apparently become denser than we assume. On the other hand, the growth of deciduous trees in particular is improved, because they often develop their strongest growth only when they are older.

Higher increment means that the wood stock in the forest, i.e. the wood created in the logs, increases faster. In the Forest vision the additional growth of around eight to ten percent would initially be used to build up the timber stock, i.e. left in the forest (see figure). In the future, the amount of sustainably usable wood would also increase again.

Figure 2: Mean annual increment of wood supply by tree species group

The scenario Forest Vision aims to reduce the intensity of use of the forest. This means that trees should be removed less frequently. These are then thicker and have formed more wood over time. Overall, in terms of the forest in Germany, the stronger growth of the wood stock in the Forest Vision, that less wood can be removed from the forest over the next decades than in the base scenario. However, depending on the tree species, the removal varies greatly. Spruce wood can still be harvested in the same way as in the other scenarios with more intensive use. This would result in only minor bottlenecks for the timber industry for this type of wood, such as construction wood. However, hardwoods in particular will be harvested less initially (see figure).

The implementation of the Forest Vision presupposes that less hardwood will be needed as a result of more efficient utilization. This is an important change from today. Half of the hardwood harvested today is burned to produce heat, often in low efficiency fireplaces and wood stoves. Not only for nature conservation reasons, but also for climate protection reasons, this wood would be better off in the forest. Overall, the valuable raw material wood must be used several times in the future in so-called cascades and used more often as a building material and less as an energy source.

Figure 3: Annual potential timber harvest by tree species group

Today, there is significantly more wood in the forest than there was a few decades ago. Nevertheless, wood stocks in a natural forest could continue to grow. The results of Forest Vision show that trees in Germany could become significantly thicker. This is especially true for deciduous forests but also for coniferous forests. Since in the forest vision hardwoods are used less than softwoods, the share of hardwoods in the total wood supply therefore increases particularly.

In the scenario Forest Vision is harvested less frequently, but thicker trees are harvested, yielding more wood per operation. This can reduce the impact on the ecosystem. More wood in the forest means at the same time a higher storage of carbon.

Figure 4: Annual wood supply by tree species groups

Through photosynthesis, trees absorb carbon dioxide (CO2) and store carbon in wood. As a result, growing forests act as so-called natural carbon sinks. When trees die, carbon escapes again as CO2 through natural decay. When wood is removed, it matters what the life span of the manufactured wood products is. If the wood is burned, emissions of CO2 are produced. A shift in use to more long-lived wood products would be able to hold carbon longer after harvesting. In 2015, the forest in Germany thus absorbed a total of about 53 million tons of CO2 in biomass, litter and soil. In addition, the wood product store increases by 2 million tons of CO2. This sink would decrease with more intensive use, especially if the proportion of energy wood is high.

The scenario of the Forest Vision provides for longer life spans of trees in the forest and gentler interventions. Since trees continue to grow when they are not harvested, the sink effect continues as well. This increases the carbon stock in the forest and allows the sink to be maintained at similar levels as today. Although less carbon is converted into wood products when less wood is harvested, these losses are compensated by the higher forest storage.

An important condition for the implementation of the Forest vision, but which has not been modeled, is that wood use becomes more efficient. If wood is recycled more often, demand for fresh wood would be reduced. The reduced logging would otherwise possibly lead to more timber imports, which could mean intensification outside Germany.

An important climate protection effect of forest management, which was also not considered, arises from the use of wood instead of aluminum, steel or concrete. This so-called substitution effect assumes that these materials cause more emissions than using wood in their place. This is still the case for many materials today. However, the effect will diminish in the future as more renewable energy becomes prevalent.

Figure 5: Forest as a climate protector: storing carbon in biomass, soil and wood products

It is not only important for the ecology of the forest how many trees are in it. Much more important is the tree species composition and the distribution of diameters and heights – i.e., how differently thick and tall the trees are. The presence of elements important for conservation, such as old and dead trees, also plays a role. Old deciduous trees in particular provide numerous habitats for endangered species. If the forest is more structured, there are more habitats for living organisms than in a uniform stand. The structure of the forest can be controlled through management. If rather single trees are used, small and large trees can be located in a narrow area and thus increase habitat diversity. In contrast, extensive use of trees, for example by clear-cutting, tends to produce a poorly structured forest.

In the Forest Vision trees are used individually or in small groups. This leads to a mixing of young and old trees but also to a continuous forest climate other ecological benefits. For example, the soil also remains protected. The lower level of intervention and additional areas without logging also mean that there are more old trees that provide potential habitat for creatures adapted to them. In the medium term Forest Vision including more dead trees – another important structural element in the naturally developing forest.

Figure 6: Wood stocks in trees with diameters greater than 50 cm

By nature, i.e., without human intervention, beech would dominate the forests of Central Europe in most locations, sometimes mixed with other broadleaf and conifer species. Intensive management of forest land over the past 150 years has resulted in monotonous conifer forests at many deciduous forest sites. Germany, for example, beech grows on only about 16 percent of the forest area, oaks on 11 percent, behind spruce (28 percent) and pine (23 percent). Spruce and pine trees not only grow quickly, they’re also easy to harvest and process because of the way they grow.

In the Forest Vision the tree species composition is largely left to nature. Where deciduous trees would naturally grow in meadows, they are specifically promoted. This also applies to conifers in locations where they are naturally native. Where they are not, deciduous forests are encouraged. Conifers are increasingly taken out and natural regeneration of deciduous trees is left in the stand. No planting takes place. As early as 2052, and in combination with more extensive use, hardwood stocks will already account for half of the total stock in the forest in Germany.

Figure 7: Development of the wood supply in the forest vision according to tree species

Forests grow slowly and trees live long. Even in intensively managed forests in this country, trees are usually not harvested until they are over 70 years old. Interventions occur at intervals of several years, sometimes decades. Today’s forest in Germany is the reflection of more than 100 years of changing management practices. This also means that it takes many decades for a change in management to have any effect at all over the entire area. If z.B. young forest areas are placed under protection and excluded from timber harvesting, differences from managed forests only become visible after several decades.

The Forest vision Is not a fixed goal that can be considered achieved at a certain point in time. Rather, it should be understood as a process in which we must also learn from the development of the forest. Some measures should be prioritized and implemented quickly: Old forests, old individual trees and rare forest communities must be protected while they still exist. One third of the German forest is in public hands. Here, measures can be implemented more quickly than in private forests for which more economic incentives and persuasion are needed.

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