Environmental Engineering Reference
In-Depth Information
communities than species diversity and diversity of functional groups. This is likely because
species and functional group diversity do not necessarily bring about functional trait diversity.
However, if functional traits are not evolutionary niche conservative, benefactors may
facilitate closely related species with different functional traits and enhance species diversity
but not phylogenetic diversity in that community. In such cases, niche complementarity is still
an important process of species diversity functions. On the other hand, sampling effects and
species facilitation can also be central processes of species diversity functions through
increasing productivity. Loreau & Hector (2001) and Mulder et al. (2001) have suggested
methods to separate the effects of these processes leading to a positive relationship between
species diversity and productivity.
When considering the interrelationships among environmental stress, productivity and
diversity, we predict that environmental stress is the most important factor regulating
productivity in coastal wetland plant communities and that productivity decreases as
environmental stress increases along the environmental stress gradient of the coastal wetland.
On the other hand, environmental stress and species diversity have a humped shape with
positive or negative relationships depending on the level of environmental stress (Figure 3).
At low stress levels, species diversity has a negative relationship with productivity due to
intense species competition. At intermediate stress levels, species diversity has a positive
relationship with productivity due to niche complementarity, sampling effect and/or species
facilitation. At this level of stress, phylogenetic diversity may be a better factor than species
diversity to explain changes in productivity. At high stress levels, species diversity has a
positive relationship with productivity due to processes of species facilitation. These
predictions about the relationships between diversity and productivity are suggested to test in
future studies.
C
ONCLUSION
Plant-plant competition and facilitation have been observed and reported in coastal
wetland ecosystems and the balance between species competition and facilitation depends on
environmental stress. Plant-plant facilitation is important for the establishments of species and
thus affects community structure including species zonation, species diversity, phylogenetic
diversity and ecosystem functions (Figure 3). The influence of species competition on plant
communities is well-known, whereas, the influence of species facilitation on species diversity
patterns and ecosystem functions in coastal wetland plant communities are poorly understood.
Furthermore, plant-plant facilitation may increase spread of invasive species in coastal
wetlands but also promote restoration of disturbed wetlands. Hence, the significance of
facilitation for conservation and restoration is context dependent.
A
CKNOWLEDGMENTS
This research is funded jointly by National Natural Science Foundation of China
(31100313; 41171216), Important National Basic Research Program of China
2013CB430403, One Hundred-Talent Plan of Chinese Academy of Sciences (CAS), the
