Editing IPCC:AR6/WGII/Chapter-5 (section)

=== 5.6.1 Observed Impacts ===

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The IPCC AR5 stated that there is high confidence that numerous plants and animal species have already migrated, changed their abundance, and shifted their seasonal activities as a result of climate change ( [[#Settele--2014|Settele et al., 2014]] ). The report highlighted the widespread deaths of trees in many forested areas of the world. Forest die back could significantly affect wood production among other impacts.

The SRCCL ( [[#Barbosa--2019|Barbosa et al., 2019]] ) concluded that climate change will have positive and negative effects on forests, with varying regional and temporal patterns. For example, the SRCCL noted the increasing productivity in high-latitude forests such as those in Siberia. In contrast, negative impacts are already being observed in other regions such as increasing tree mortality due to wildfires.

In the past years, tree mortality continued to increase in many parts of the world. Large pulses of tree mortality were consistently linked to warmer and drier than average conditions for forests throughout the temperate and boreal biomes ( ''high confidence'' ) ( [[#Sommerfeld--2018|Sommerfeld et al., 2018]] ; [[#Seidl--2020|Seidl et al., 2020]] ). Long-term monitoring of tropical forests indicates that climate change has begun to increase tree mortality and alter regeneration ( [[#Hubau--2020|Hubau et al., 2020]] ; [[#Sullivan--2020|Sullivan et al., 2020]] ). Climate-related die back has also been observed due to novel interactions between the life cycles of trees and pest species ( [[#Kurz--2008|Kurz et al., 2008]] ; [[#Lesk--2017|Lesk et al., 2017]] ; [[#Sambaraju--2019|Sambaraju et al., 2019]] ). A recent example of the impacts of climatic extremes is the European drought of 2018 ( [[#Buras--2020|Buras et al., 2020]] ), which led to a significant browning of the vegetation and resulted in widespread tree mortality ( ''high confidence'' ) ( [[#Brun--2020|Brun et al., 2020]] ; [[#Schuldt--2020|Schuldt et al., 2020]] ). This brought markets for conifer timber close to collapse in parts of Europe, posing considerable challenges for timber-based forestry and leading to cascading impacts on society ( [[#Hlásny--2021|Hlásny et al., 2021]] ). Overall, there is ''robust evidence'' and ''medium agreement'' that provisioning services of boreal and temperate forests are affected negatively by forest disturbances, while for cultural services only ''limited evidence'' with ''medium agreement'' exists ( [[#Thom--2016|Thom and Seidl, 2016]] ).

Increasingly, climate impacts on the recovery of forests after disturbance are observed: using data from the past 20 years and 33 wildfires, it has been shown that post-fire regeneration of ''Pinus ponderosa'' and ''Pseudotsuga menziesii'' in the western USA has declined because of climate change and increased severity of fires ( [[#Davis--2019|Davis et al., 2019]] ). However, the observed patterns of post-disturbance recovery vary with region, with reduced tree regeneration reported for the western USA ( [[#Stevens-Rumann--2019|Stevens-Rumann and Morgan, 2019]] ; [[#Turner--2019|Turner et al., 2019]] ) but robust recovery observed in Canada ( [[#White--2017|White et al., 2017]] ) and Central Europe ( ''medium confidence'' ) ( [[#Senf--2019|Senf et al., 2019]] ).

Also, the distribution and traits of trees are increasingly influenced by climate change, with impacts for local ecosystem service supply. In the USA, a study of 86 tree species/groups over the past three decades showed that more tree species have shifted westward (73%) than poleward (62%) in their abundance ( [[#Fei--2017|Fei et al., 2017]] ). This was due more to changes in moisture availability than to changes in temperature. As climate has warmed, trees are growing faster with longer growing seasons. However, a study of forests in Central Europe revealed that wood density has decreased since the 1870s ( [[#Pretzsch--2018|Pretzsch et al., 2018]] ). This means that increasing tree growth might not directly translate to increased total biomass and carbon sequestration.

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