Environmental Engineering Reference
In-Depth Information
impact of species facilitation increasing the stress tolerance of beneficiaries is highest at high
stress levels. These impacts would increase the species richness in intermediate and high
stress zones. Xiao et al. (2009) employed simulation techniques to assess the impact of
species facilitation on species richness patterns across stress gradients. They found that
species facilitation indeed increased species richness in medium and high stress zones but not
in very high stress zones, thus supporting the Michalet et al. (2006) model. On the other hand,
from low to medium stress zones, species facilitation decreased species richness.
Figure 2. Framework of interspecies facilitation and productivity of coastal wetland plant communities.
However, to reveal the relationship of species facilitation and species richness, more
research on how species facilitation influences the humped-back shape of the stress gradient-
species richness curve is needed, especially through experiments on natural plant
communities along strong stress gradients and for longer periods of time. Coastal wetlands
provide a perfect ecosystem to test these models because species composition is relatively
simple and the stress gradient is strong.
S
PECIES
F
ACILITATION AND
I
NVASION IN
C
OASTAL
W
ETLANDS
Invasion of exotic species into native plant communities presents a challenge to preserve
local and regional species diversity. Invasions due to anthropogenic impacts are also an
ecological problem for coastal wetland ecosystem (Gedan et al. 2009). For example, the
invasive species
S. alterniflora
occupies large areas of southeast coast of China (Yuan et al.
2011) and
Phragmites australis
has invaded the east coast of North America. Both invasive
