restricted to local situations such as estuaries, colonies of breeding birds or special
localities in pastures that are richly manured by herds of grazers.
The succession from white to gray dune communities in Europe is normally
related to a decreasing sedimentation rate, productivity and biomass, in combination
with an increase in species diversity (Petersen et al. 2014; Pott 1996). How could this
type of succession be interpreted along with optimization of the resource use? A
relatively high sedimentation rate of sand in the white dune is the reason for the
relatively high nutrient supply, productivity and biomass of the dominant species,
often the grass Ammophila arenaria. If the sedimentation rate is decreasing also the
input of nutrients, productivity and biomass is decreasing. In this case, only a higher
number of species with a more closed layer of roots under the soil surface can
minimize the loss of nutrients by leaching. However, a succession with declining
biomass is a special case.
The succession from pioneer vegetation to forest is often characterized by
increasing productivity and biomass caused by the required space of growing shrubs
and trees at least during the first succession stages. In this case, the reduced space and
light at the ground results in a declining number of vascular plant species at local
scales. The resulting number of species presumably reflects the evolution of vascular
plants at larger scales, the wide range of species with a higher demand on light, and
the lower number of shade-tolerant species (Silva Pedro et al. 2017; Ellenberg and
Leuschner 2010).
The different relationships and feedbacks obviously do not allow maximization of
the biomass, productivity and diversity within the same assembly.
High biomass is usually found in forest ecosystems with timber production.
High productivity is usually related to perennial non-woody vegetation units.
High diversity reflects evolutionary and ecological continuity in regions with
relatively low or intermediate amount of biomass and productivity.
5 Natural Catastrophes, Invasive Species, Human
Influences
Whatever the influences are, there are no such things as untouched natural ecosystems which are in an ecological equilibrium, and artificial or heavily impacted
ecosystems which are not in an ecological equilibrium. The ecological equilibrium
(balance of nature) was an idea during the second half of the last century to explain
species compositions and ecosystem functioning (cf. DeAngelis and Waterhouse
1987; Zimmermann 2007; Kricher 2009). However, we do not see any empirical
evidence to promote this hypothesis.
Sometimes vegetation structures collapse even if there is no apparent reason for
this. According to Müller-Dombois et al. (1983) some forest diebacks are cohort
senescence phenomenons due to a combination of aging and increasing environmental stress caused by depletion of certain soil nutrients.
Resources for Humans, Plants and Animals: Who Is the Ruler of the Driver? And:. . .
89
localities in pastures that are richly manured by herds of grazers.
The succession from white to gray dune communities in Europe is normally
related to a decreasing sedimentation rate, productivity and biomass, in combination
with an increase in species diversity (Petersen et al. 2014; Pott 1996). How could this
type of succession be interpreted along with optimization of the resource use? A
relatively high sedimentation rate of sand in the white dune is the reason for the
relatively high nutrient supply, productivity and biomass of the dominant species,
often the grass Ammophila arenaria. If the sedimentation rate is decreasing also the
input of nutrients, productivity and biomass is decreasing. In this case, only a higher
number of species with a more closed layer of roots under the soil surface can
minimize the loss of nutrients by leaching. However, a succession with declining
biomass is a special case.
The succession from pioneer vegetation to forest is often characterized by
increasing productivity and biomass caused by the required space of growing shrubs
and trees at least during the first succession stages. In this case, the reduced space and
light at the ground results in a declining number of vascular plant species at local
scales. The resulting number of species presumably reflects the evolution of vascular
plants at larger scales, the wide range of species with a higher demand on light, and
the lower number of shade-tolerant species (Silva Pedro et al. 2017; Ellenberg and
Leuschner 2010).
The different relationships and feedbacks obviously do not allow maximization of
the biomass, productivity and diversity within the same assembly.
High biomass is usually found in forest ecosystems with timber production.
High productivity is usually related to perennial non-woody vegetation units.
High diversity reflects evolutionary and ecological continuity in regions with
relatively low or intermediate amount of biomass and productivity.
5 Natural Catastrophes, Invasive Species, Human
Influences
Whatever the influences are, there are no such things as untouched natural ecosystems which are in an ecological equilibrium, and artificial or heavily impacted
ecosystems which are not in an ecological equilibrium. The ecological equilibrium
(balance of nature) was an idea during the second half of the last century to explain
species compositions and ecosystem functioning (cf. DeAngelis and Waterhouse
1987; Zimmermann 2007; Kricher 2009). However, we do not see any empirical
evidence to promote this hypothesis.
Sometimes vegetation structures collapse even if there is no apparent reason for
this. According to Müller-Dombois et al. (1983) some forest diebacks are cohort
senescence phenomenons due to a combination of aging and increasing environmental stress caused by depletion of certain soil nutrients.
Resources for Humans, Plants and Animals: Who Is the Ruler of the Driver? And:. . .
89