productivity (Hector et al. 1999; Gamfeldt et al. 2013; Grace et al. 2016; van der Plas
2019). Across a wide range of biomes, tree species richness has been demonstrated
to enhance forest productivity (Paquette and Messier 2011; Zhang et al. 2012; Liang
et al. 2016; Huang et al. 2018) by resource partitioning (Jucker et al. 2015; Schmid
and Niklaus 2017; Williams et al. 2017), facilitation (Fichtner et al. 2017), natural
enemy (e.g. pathogens or herbivores) partitioning (Jactel and Brockerhoff 2007;
Grossman et al. 2019) or selection effects (the increased likelihood of including
dominant and well-performing species in diverse communities; Tobner et al. 2016).
Detailed information on processes underlying relationships between biodiversity and
ecosystem functioning is provided by Forrester and Bauhus (2016), Wright et al.
(2017) or Barry et al. (2019).
The positive effects of biodiversity on forest ecosystem functioning often arise
due to local species interactions. Mixed-species plant communities are a network of
locally interacting individuals. Consequently, the response of tree communities to
species mixing should be—at least to a certain extend—the result of aggregated
small-scale variations in neighbourhood interactions (Stoll and Weiner 2000).
Results from a large-scale biodiversity-ecosystem functioning experiment in the
subtropics support this theory by demonstrating that neighbourhood interactions
explain over half of the variation in forest community productivity along a tree
diversity gradient (Fichtner et al. 2018). This implies that diversity-mediated interactions among local neighbours are highly relevant for enhancing productivity in
mixed-species forests—particularly in highly diverse forest communities of the
subtropics and tropics. Maintaining high tree diversity not only supports ecosystem
functioning, but also socio-economic issues. For example, both experimental
(Huang et al. 2018) and observational (Liang et al. 2016) studies predicted that a
10% decline of tree species richness might result in a reduction by 2–3% of forest
productivity on average at the global scale. Although biodiversity has an intrinsic
value, Liang et al. (2016) estimated a monetary value of tree species richness in
maintaining commercial forest productivity of $166 billion to $490 billion per year.
Forest biodiversity may also play a critical role in mitigating adverse climate
change impacts on forest ecosystem functioning (Hisano et al. 2018; Ammer 2019;
Anderegg et al. 2018). Globally, forests sequester and store immense amounts of
carbon (Pan et al. 2011). This role, however, can be altered by biodiversity loss, as
higher tree productivity of species-rich forests translates in higher amounts of carbon
stored above- and belowground in the ecosystem (Chen et al. 2018; Liu et al. 2018).
Moreover, tree species richness increases the stability of forest productivity (Jucker
et al. 2014; Morin et al. 2014; Schnabel et al. 2019), which in turn favours future
carbon sequestration. For example, aboveground biomass production was shown to
be higher and aboveground biomass loss due to tree mortality was lower in speciesrich than in species-poor boreal forest over the last five decades (Hisano et al. 2019).
In the context of ongoing global insect decline (Hallmann et al. 2017) recent
results from two of the world’s largest biodiversity-ecosystem functioning experiments in different ecosystems (grasslands and forests) provided evidence that
maintaining high levels of plant diversity and the associated structural diversity
increases the abundance and richness of insects (Schuldt et al. 2019). This
392
A. Fichtner and W. Härdtle
2019). Across a wide range of biomes, tree species richness has been demonstrated
to enhance forest productivity (Paquette and Messier 2011; Zhang et al. 2012; Liang
et al. 2016; Huang et al. 2018) by resource partitioning (Jucker et al. 2015; Schmid
and Niklaus 2017; Williams et al. 2017), facilitation (Fichtner et al. 2017), natural
enemy (e.g. pathogens or herbivores) partitioning (Jactel and Brockerhoff 2007;
Grossman et al. 2019) or selection effects (the increased likelihood of including
dominant and well-performing species in diverse communities; Tobner et al. 2016).
Detailed information on processes underlying relationships between biodiversity and
ecosystem functioning is provided by Forrester and Bauhus (2016), Wright et al.
(2017) or Barry et al. (2019).
The positive effects of biodiversity on forest ecosystem functioning often arise
due to local species interactions. Mixed-species plant communities are a network of
locally interacting individuals. Consequently, the response of tree communities to
species mixing should be—at least to a certain extend—the result of aggregated
small-scale variations in neighbourhood interactions (Stoll and Weiner 2000).
Results from a large-scale biodiversity-ecosystem functioning experiment in the
subtropics support this theory by demonstrating that neighbourhood interactions
explain over half of the variation in forest community productivity along a tree
diversity gradient (Fichtner et al. 2018). This implies that diversity-mediated interactions among local neighbours are highly relevant for enhancing productivity in
mixed-species forests—particularly in highly diverse forest communities of the
subtropics and tropics. Maintaining high tree diversity not only supports ecosystem
functioning, but also socio-economic issues. For example, both experimental
(Huang et al. 2018) and observational (Liang et al. 2016) studies predicted that a
10% decline of tree species richness might result in a reduction by 2–3% of forest
productivity on average at the global scale. Although biodiversity has an intrinsic
value, Liang et al. (2016) estimated a monetary value of tree species richness in
maintaining commercial forest productivity of $166 billion to $490 billion per year.
Forest biodiversity may also play a critical role in mitigating adverse climate
change impacts on forest ecosystem functioning (Hisano et al. 2018; Ammer 2019;
Anderegg et al. 2018). Globally, forests sequester and store immense amounts of
carbon (Pan et al. 2011). This role, however, can be altered by biodiversity loss, as
higher tree productivity of species-rich forests translates in higher amounts of carbon
stored above- and belowground in the ecosystem (Chen et al. 2018; Liu et al. 2018).
Moreover, tree species richness increases the stability of forest productivity (Jucker
et al. 2014; Morin et al. 2014; Schnabel et al. 2019), which in turn favours future
carbon sequestration. For example, aboveground biomass production was shown to
be higher and aboveground biomass loss due to tree mortality was lower in speciesrich than in species-poor boreal forest over the last five decades (Hisano et al. 2019).
In the context of ongoing global insect decline (Hallmann et al. 2017) recent
results from two of the world’s largest biodiversity-ecosystem functioning experiments in different ecosystems (grasslands and forests) provided evidence that
maintaining high levels of plant diversity and the associated structural diversity
increases the abundance and richness of insects (Schuldt et al. 2019). This
392
A. Fichtner and W. Härdtle