Editing IPCC:AR6/WGII/Chapter-2 (section)

=== FAQ 2.6 | Can tree planting tackle climate change? ===

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''Restoring and preventing further loss of native forests is essential for combatting climate change. Planting trees in historically unforested areas (grasslands, shrublands, savannas and some peatlands) can reduce biodiversity and increase the risks of damage from climate change. It is therefore essential to target tree planting to the appropriate locations and use appropriate species. Restoring and protecting forests reduces human vulnerability to climate change, reduces air pollution, stores carbon and builds the resilience of natural systems.''

Like all living plants, trees remove carbon dioxide from the atmosphere through the process of photosynthesis. In trees, this carbon uptake is relatively long-term, since much of it is stored in the trees’ woody stems and roots. Therefore, tree planting can be a valuable contribution to reducing climate change. Besides capturing carbon, planting trees can reduce some negative impacts of climate change by providing shade and cooling. It can also help prevent erosion and reduce flood risk by slowing water flow and improving ground water storage. Restoring forest in degraded areas supports biodiversity and can provide benefits to people, ranging from timber to food and recreation.

There are some areas where replacing lost trees is useful. These include forest that has been recently cut down and where reforestation is usually practical. However, it is very important to correctly identify areas of forest that are degraded or have definitely been deforested. Reforesting places, especially where existing native forest patches occur, brings benefits both in sucking up carbon from the atmosphere and helping us to adapt to climate change. Plantations of a non-native species, although offering some economic benefits, do not usually provide the same range of positive impacts, generally have lower biodiversity, reduced carbon uptake and storage, and are less resilient to climate change.

Reforestation options include the natural regeneration of the forest, assisted restoration, enrichment planting, native-tree plantations, commercial plantations and directed tree planting in agro-forestry systems and urban areas. Reforestation with native species usually contributes to a wide range of sustainability goals, including biodiversity recovery, improved water filtration and groundwater recharge. It can reduce the risks of soil erosion and floods. In cities, planting trees can support climate change adaptation by reducing the heat of the area, and promote a wide range of social benefits such as providing shade and benefitting outdoor recreation. Urban trees can also lower energy costs by reducing the demand for conventional sources of cooling like air-conditioning, especially during peak-demand periods. It is therefore important to recognise that there are a wide range of different planting and forest management strategies. The choice will depend on the objectives and the location.

'''Not everywhere''' is suitable for tree planting. It is particularly problematic in native non-forested ecosystems. These natural ecosystems are not deforested and degraded but are instead naturally occurring non-forested ecosystems. These areas vary from open grasslands to densely wooded savannas and shrublands. Here, restoring the natural ecosystems instead of afforesting them will better contribute to increasing carbon storage and increasing the area’s resilience to climate change and other environmental changes. It is important to remember that, just because a tree can grow somewhere, it does not mean that it should. These systems are very important in their own right, storing carbon in soils, supporting rich biodiversity and providing people with important ecosystem services such as grasslands for animal grazing. Planting trees in these areas destroys the ecosystem and threatens the biodiversity which is adapted to these environments. They can also impact on ecosystem services such as forage for livestock, on which many people rely.

Many of these open areas also occur in low-rainfall areas. Planting trees there uses a lot of water and can cause reductions in stream flow and groundwater. Many of these locations also burn regularly, and planting trees threatens the establishing trees but can also increase the intensity of the fires from that of a grass-fuelled fire to that of a wood-fuelled fire. Swapping grassy ecosystems for forests may contribute to warming, as forests absorb more incoming radiation (warmth) than grasslands. Aside from the negative impacts to adaptation, it is also questionable just how much carbon can be sequestered in these landscapes as planting trees in grassy ecosystems can reduce carbon gains. Furthermore, a high below-ground carbon store prevents carbon loss to fire in these fire-prone environments.

Another example is peatlands. Peat stores an incredible amount of carbon; maintaining and restoring peatlands is therefore important to reduce atmospheric carbon. However, the restoration actions depend on what type of peatland it is and where it is located. Many temperate and boreal peatlands are naturally treeless. Here, planting trees is often only possible following drainage, but draining and planting (especially of non-native species) destroys native biodiversity and releases GHGs. Many peatlands, especially in the Tropics, are naturally forested, and restoring them requires re-wetting and restoring the natural tree cover (see Figure FAQ2.2.1) which will increase carbon storage.

There are actions we can perform instead of planting trees in non-forested ecosystems, and these include:

* Address the causes of deforestation, forest degradation and widespread ecosystem loss
* Reduce carbon emissions from fossil fuels
* Focus on ecosystem restoration over tree planting. For example, in restoring tropical grassy ecosystems, we can look at actions that cut down trees, enhance grass regrowth and restore natural fire regimes. We then have a much better chance of both enhancing carbon capture and reducing some of the harmful effects of climate change.

In between the two extremes of where planting trees is highly suitable and areas where it is not, it is important to remember that the context matters and that decisions to (re)forest should look beyond simply the act of planting trees. We can consider '''what the ecological, social and economic goals are of tree planting''' . It is then important to verify the local context and decide '''what restoration action will be most effective''' . It is also more efficient and effective to conserve existing forests before worrying about reforesting.

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'''Figure FAQ2.6.1 |''' '''Some places are more appropriate for tree planting than others and caution needs to be applied when planting in different biomes, with some biomes being more suitable than others.''' This figure highlights some basic biome-specific guidelines when planting in natural and semi-natural vegetation.

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