(Fujii 2014; Terborgh 1992). Thus, a high rate of primary productivity can be
explained by both the external supply of resources and the internal cycling of
resources. However, highest rates seem to be related to herbaceous vegetation of
tropical swamps with C 4 grasses. Neither woody nor annual vegetation types have
been shown to have such high productivity values.
The conclusions about the relationship between species diversity and productivity
drawn from time series observations in natural communities, from plantations,
species additions or reductions are numerous and inconsistent. Functions have
been described as linear, non-linear (e.g. hump-backed), positive, negative, or
independent. However, an increasing number of plant individuals and plant species
generally lead to a more efficient use of the resources and to an increase of the
productivity. This is particularly the case if other influences were excluded
(cf. e.g. Morin et al. 2014, Cardinale et al. 2013, Simová et al. 2013, Keeling and
Phillips 2007, Grace et al. 2007, van Ruijven and Berendse 2005, Braakhekke and
Hooftman 1999).
Another effect seems to be contradictory, fertilization (e.g., in grassland or forest
communities) often leads to a strong decrease in species numbers: Rosenzweig’s
paradox of enrichment (cf. Rosenzweig 1971). However, in the first example the
(high) species diversity is the cause and the productivity is the effect, in the second
example the addition of nutrients is the cause and the (decreasing) species diversity
is the effect (Hobohm 2016). Still we see that the relationship is not linear, and
increase in productivity can be obtained with a decrease in species diversity, yet it
could be argued that the addition of nutrients creates a temporal inbalance in the
system.
World records of the diversity of vascular plant species have been described from
forest (100 m
2 or larger) and grassland communities (plots <100 m
2 ). For example,
mountain grassland in Argentina and semi-dry basiphilous grassland in Romania can
harbour up to 89 or 98 vascular plant species in a plot of a single square meter or ten
square meters, respectively; and 233 species were counted in 100 m
2 of a tropical
lowland forest in Costa Rica (Wilson et al. 2012). The forests are old growth in the
wet tropics which are relatively unaffected by humans, whereas most of the rich
grasslands in the temperate zone are regularly mowed (Chytrý et al. 2015; Wilson
et al. 2012). This example shows that humance influence doesn’t always cause a
decline in species diversity. On the contrary, human influence via transportation can
result in worldwide increases in species diversity. The patterns of extreme species
diversity in both ecosystems are not yet well understood. However, a few basic
points can be determined:
Both maxima represent late succession stages, thus, a long time of development.
Both have relatively stable turnover and structure. Both are part of rich species pools
indicating speciation of taxa in the same or in neighbouring regions.
Eutrophic conditions seem to exclude the development of communities with high
species richness. This is probably related to the evolution of most vascular plant
species under oligotrophic or mesotrophic conditions, resulting in a very different
resource use optimization. Waters or soils with high nutrient levels were formerly
88
C. Hobohm and S. E. Vanderplank
explained by both the external supply of resources and the internal cycling of
resources. However, highest rates seem to be related to herbaceous vegetation of
tropical swamps with C 4 grasses. Neither woody nor annual vegetation types have
been shown to have such high productivity values.
The conclusions about the relationship between species diversity and productivity
drawn from time series observations in natural communities, from plantations,
species additions or reductions are numerous and inconsistent. Functions have
been described as linear, non-linear (e.g. hump-backed), positive, negative, or
independent. However, an increasing number of plant individuals and plant species
generally lead to a more efficient use of the resources and to an increase of the
productivity. This is particularly the case if other influences were excluded
(cf. e.g. Morin et al. 2014, Cardinale et al. 2013, Simová et al. 2013, Keeling and
Phillips 2007, Grace et al. 2007, van Ruijven and Berendse 2005, Braakhekke and
Hooftman 1999).
Another effect seems to be contradictory, fertilization (e.g., in grassland or forest
communities) often leads to a strong decrease in species numbers: Rosenzweig’s
paradox of enrichment (cf. Rosenzweig 1971). However, in the first example the
(high) species diversity is the cause and the productivity is the effect, in the second
example the addition of nutrients is the cause and the (decreasing) species diversity
is the effect (Hobohm 2016). Still we see that the relationship is not linear, and
increase in productivity can be obtained with a decrease in species diversity, yet it
could be argued that the addition of nutrients creates a temporal inbalance in the
system.
World records of the diversity of vascular plant species have been described from
forest (100 m
2 or larger) and grassland communities (plots <100 m
2 ). For example,
mountain grassland in Argentina and semi-dry basiphilous grassland in Romania can
harbour up to 89 or 98 vascular plant species in a plot of a single square meter or ten
square meters, respectively; and 233 species were counted in 100 m
2 of a tropical
lowland forest in Costa Rica (Wilson et al. 2012). The forests are old growth in the
wet tropics which are relatively unaffected by humans, whereas most of the rich
grasslands in the temperate zone are regularly mowed (Chytrý et al. 2015; Wilson
et al. 2012). This example shows that humance influence doesn’t always cause a
decline in species diversity. On the contrary, human influence via transportation can
result in worldwide increases in species diversity. The patterns of extreme species
diversity in both ecosystems are not yet well understood. However, a few basic
points can be determined:
Both maxima represent late succession stages, thus, a long time of development.
Both have relatively stable turnover and structure. Both are part of rich species pools
indicating speciation of taxa in the same or in neighbouring regions.
Eutrophic conditions seem to exclude the development of communities with high
species richness. This is probably related to the evolution of most vascular plant
species under oligotrophic or mesotrophic conditions, resulting in a very different
resource use optimization. Waters or soils with high nutrient levels were formerly
88
C. Hobohm and S. E. Vanderplank