accumulate carbon in the trunk at even faster rates as they mature, suggesting that not
only the amount of carbon, but also carbon sequestration is highest in those trees
(Stephenson et al. 2014; Fichtner et al. 2015). Moreover, stand age and tree species
richness enhance the stability of carbon sequestration in forest ecosystems (Musavi
et al. 2017), and old forests continue to sequester carbon for many centuries
(Luyssaert et al. 2008). This is particularly relevant for the current debate on natural
carbon dioxide removal measures (Griscom et al. 2017), as these findings suggest
that restoring natural forests by allowing for senescence and promoting biomespecific tree diversity would offer a high potential for meeting global climate and
biodiversity agreements (Körner 2017; Lewis et al. 2019). In addition, maintaining
old and large-diameter trees is functionally important for belowground networking.
Trees can transfer carbon, water, nutrients and biochemical signals belowground via
mycorrhizal networks (Simard et al. 1997; Gorzelak et al. 2015) and can become
more connected as they grow larger in size (Beiler et al. 2010). Such common
mycorrhizal mycelium links the roots of trees by which mature trees transfer
substantial amounts of carbon (280 kg carbon per hectare and year, equivalent to
4% of the forest’s net primary productivity) from one tree to another– even between
species (Klein et al. 2016). Belowground transfers have therefore important implications for local tree-tree interactions, facilitation of conspecific regeneration,
maintaining biodiversity and may become increasingly important in a changing
climate (Beiler et al. 2010; Simard et al. 2012). The development of mycorrhizal
networks might also one reason why trees growing in unmanaged forests were found
to be less sensitive to drought-induced growth decline than trees growing in
managed forests (Mausolf et al. 2018a). This implies that intensive logging and
logging-associated soil compaction might disrupt mycorrhizal networks and induces
long-lasting impacts on the soil microbiome (Hartmann et al. 2014), which in turn
would lead to a decline in ecosystem functioning and eventually to a loss of
ecosystem stability. Moreover, ecological continuity is closely linked to legacies
of former land use, and such land-use legacies have been suggested to mediate the
response of forest ecosystems to global environmental change (Perring et al. 2016).
For example, soil legacies have been shown to alter carbon and nutrient cycling
(Compton and Boone 2000; von Oheimb et al. 2008; Leuschner et al. 2014) due to
changes in the soil microbiome (Fraterrigo et al. 2006; De la Peña et al. 2016)—even
after more than one century (Fichtner et al. 2014). These altered edaphic conditions
in turn can impose long-lasting impacts on a trees’ fine root system, which is crucial
for its nutrient and water uptake. In this context, it has been demonstrated that forest
continuity increases the resistance of adult beech trees (Fagus sylvatica) to drought
by modulating fine root morphology and increasing standing fine root biomass
(Mausolf et al. 2018b).
These examples highlight that forests associated with a long ecological continuity
not only host a high diversity of biome-specific forest species, but may be even more
resilient to multiple environmental changes. Sustaining and promoting ecological
continuity would therefore benefit both biodiversity conservation and the mitigation
of adverse climate change impacts, which in turn would resolve conflicting assumptions about biodiversity and climate goals.
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A. Fichtner and W. Härdtle
only the amount of carbon, but also carbon sequestration is highest in those trees
(Stephenson et al. 2014; Fichtner et al. 2015). Moreover, stand age and tree species
richness enhance the stability of carbon sequestration in forest ecosystems (Musavi
et al. 2017), and old forests continue to sequester carbon for many centuries
(Luyssaert et al. 2008). This is particularly relevant for the current debate on natural
carbon dioxide removal measures (Griscom et al. 2017), as these findings suggest
that restoring natural forests by allowing for senescence and promoting biomespecific tree diversity would offer a high potential for meeting global climate and
biodiversity agreements (Körner 2017; Lewis et al. 2019). In addition, maintaining
old and large-diameter trees is functionally important for belowground networking.
Trees can transfer carbon, water, nutrients and biochemical signals belowground via
mycorrhizal networks (Simard et al. 1997; Gorzelak et al. 2015) and can become
more connected as they grow larger in size (Beiler et al. 2010). Such common
mycorrhizal mycelium links the roots of trees by which mature trees transfer
substantial amounts of carbon (280 kg carbon per hectare and year, equivalent to
4% of the forest’s net primary productivity) from one tree to another– even between
species (Klein et al. 2016). Belowground transfers have therefore important implications for local tree-tree interactions, facilitation of conspecific regeneration,
maintaining biodiversity and may become increasingly important in a changing
climate (Beiler et al. 2010; Simard et al. 2012). The development of mycorrhizal
networks might also one reason why trees growing in unmanaged forests were found
to be less sensitive to drought-induced growth decline than trees growing in
managed forests (Mausolf et al. 2018a). This implies that intensive logging and
logging-associated soil compaction might disrupt mycorrhizal networks and induces
long-lasting impacts on the soil microbiome (Hartmann et al. 2014), which in turn
would lead to a decline in ecosystem functioning and eventually to a loss of
ecosystem stability. Moreover, ecological continuity is closely linked to legacies
of former land use, and such land-use legacies have been suggested to mediate the
response of forest ecosystems to global environmental change (Perring et al. 2016).
For example, soil legacies have been shown to alter carbon and nutrient cycling
(Compton and Boone 2000; von Oheimb et al. 2008; Leuschner et al. 2014) due to
changes in the soil microbiome (Fraterrigo et al. 2006; De la Peña et al. 2016)—even
after more than one century (Fichtner et al. 2014). These altered edaphic conditions
in turn can impose long-lasting impacts on a trees’ fine root system, which is crucial
for its nutrient and water uptake. In this context, it has been demonstrated that forest
continuity increases the resistance of adult beech trees (Fagus sylvatica) to drought
by modulating fine root morphology and increasing standing fine root biomass
(Mausolf et al. 2018b).
These examples highlight that forests associated with a long ecological continuity
not only host a high diversity of biome-specific forest species, but may be even more
resilient to multiple environmental changes. Sustaining and promoting ecological
continuity would therefore benefit both biodiversity conservation and the mitigation
of adverse climate change impacts, which in turn would resolve conflicting assumptions about biodiversity and climate goals.
396
A. Fichtner and W. Härdtle