poorly correlated (Keeling and Phillips 2007), making it difficult to infer forest
biomass levels from NPP values. Boreal forests, for example, constitute important
carbon sinks and thus are considered vital for climate change mitigation, despite
their low productivity. Particularly soils of boreal forests are characterized by the
highest carbon stocks across forest biomes: In boreal forests, 60% of the total carbon
is stored in soils and only 20% in biomass, whereas in tropical forests 56% of the
ecosystem’s carbon is located in biomass, and only 32% in soils (Pan et al. 2011). As
a consequence, carbon densities (i.e. quantity of carbon stored per ha) in boreal
forests are as high as in tropical forests (239.2 Mg ha
À1 vs. 241.6 Mg ha
À1 ). Temperate forests, in contrast, show lower carbon densities (mean: 154.7 Mg ha
À1 ),
although peak values up to 260 Mg ha
À1 are possible (Pan et al. 2011); data for the
year 2009). When total areas of forest biomes are taken into account, tropical forests
constitute the most important carbon sink (471.0 Pg ha
À1 ), followed by boreal and
temperate forests 271.5 and 118.6 Pg ha
À1 , respectively (Pan et al. 2011). In
summary, forest ecosystems contain about 50% of the world’s terrestrial global
carbon stocks, and their biomass constitutes about 80% of the terrestrial biomass.
This underpins the pivotal role of forests in the global carbon cycle, and hence the
potential of sustainable forest management in mitigating global climate change (Erb
et al. 2018).
3 Biodiversity Patterns and Drivers of Biodiversity Losses
3.1 Biodiversity Patterns: A Comparison Across Forest
Biomes
Tropical forest ecosystems represent the world’s most preeminent biodiversity
hotspots (Giam 2017; Myers et al. 2000). It is estimated that tropical rain forests
support about two-thirds of the global biodiversity, despite covering less than 15%
of the world’s land surface (Gardner et al. 2009; Giam 2017). It has been hypothesized that this extraordinary species richness is attributable to several processes and
mechanisms, for example the long persistence of evolutionary processes,
mid-domain effects (i.e. effects related to geometrical/geographical characteristics),
climatic conditions prevailing in the tropics, and the structural (i.e. habitat/niche)
diversity typical of tropical forests (which in turn supports many stenotopic species;
Sherratt and Wilkinson 2009; Nice et al. 2019). The tremendous diversity of tropical
forests has been observed across different taxonomic groups (Myers et al. 2000),
such as vascular plants, arthropods, reptiles, amphibians, fishes or birds. Forests of
the upper Amazonian, for example, are considered the most tree species-rich in the
world: In two study plots established in tropical forests near Iquitos (Peru), Gentry
(1988) recorded about 300 tree species per hectare. Besides the Amazonian basin,
tropical forests in China and Indonesia are also known to constitute hotspots for
(woody) vascular plants (Barthlott et al. 2007). Related to plant diversity, tropical
Forest Ecosystems: A Functional and Biodiversity Perspective
387
biomass levels from NPP values. Boreal forests, for example, constitute important
carbon sinks and thus are considered vital for climate change mitigation, despite
their low productivity. Particularly soils of boreal forests are characterized by the
highest carbon stocks across forest biomes: In boreal forests, 60% of the total carbon
is stored in soils and only 20% in biomass, whereas in tropical forests 56% of the
ecosystem’s carbon is located in biomass, and only 32% in soils (Pan et al. 2011). As
a consequence, carbon densities (i.e. quantity of carbon stored per ha) in boreal
forests are as high as in tropical forests (239.2 Mg ha
À1 vs. 241.6 Mg ha
À1 ). Temperate forests, in contrast, show lower carbon densities (mean: 154.7 Mg ha
À1 ),
although peak values up to 260 Mg ha
À1 are possible (Pan et al. 2011); data for the
year 2009). When total areas of forest biomes are taken into account, tropical forests
constitute the most important carbon sink (471.0 Pg ha
À1 ), followed by boreal and
temperate forests 271.5 and 118.6 Pg ha
À1 , respectively (Pan et al. 2011). In
summary, forest ecosystems contain about 50% of the world’s terrestrial global
carbon stocks, and their biomass constitutes about 80% of the terrestrial biomass.
This underpins the pivotal role of forests in the global carbon cycle, and hence the
potential of sustainable forest management in mitigating global climate change (Erb
et al. 2018).
3 Biodiversity Patterns and Drivers of Biodiversity Losses
3.1 Biodiversity Patterns: A Comparison Across Forest
Biomes
Tropical forest ecosystems represent the world’s most preeminent biodiversity
hotspots (Giam 2017; Myers et al. 2000). It is estimated that tropical rain forests
support about two-thirds of the global biodiversity, despite covering less than 15%
of the world’s land surface (Gardner et al. 2009; Giam 2017). It has been hypothesized that this extraordinary species richness is attributable to several processes and
mechanisms, for example the long persistence of evolutionary processes,
mid-domain effects (i.e. effects related to geometrical/geographical characteristics),
climatic conditions prevailing in the tropics, and the structural (i.e. habitat/niche)
diversity typical of tropical forests (which in turn supports many stenotopic species;
Sherratt and Wilkinson 2009; Nice et al. 2019). The tremendous diversity of tropical
forests has been observed across different taxonomic groups (Myers et al. 2000),
such as vascular plants, arthropods, reptiles, amphibians, fishes or birds. Forests of
the upper Amazonian, for example, are considered the most tree species-rich in the
world: In two study plots established in tropical forests near Iquitos (Peru), Gentry
(1988) recorded about 300 tree species per hectare. Besides the Amazonian basin,
tropical forests in China and Indonesia are also known to constitute hotspots for
(woody) vascular plants (Barthlott et al. 2007). Related to plant diversity, tropical
Forest Ecosystems: A Functional and Biodiversity Perspective
387