Environmental Engineering Reference
In-Depth Information
humanity, such as food, storm protection, shoreline protection and fishing nurseries (Gedan et
al. 2009). However, human activity (
e.g
., agriculture and urban development) and climate
change (
e.g.
, rising sea level) diminish these areas and strongly disrupt coastal ecosystem
functions (e.g. Comeaux et al. 2012). Restoration of disrupted coastal wetlands has been an
urgent issue (Spencer & Harvey 2012). Understanding when and how interactions among
plants influence ecosystem functions (e.g. productivity, ecosystem stability) of coastal
wetlands will provide basic knowledge for us to protect and recover these important
ecosystems (Halpern et al. 2007). On the other hand, it is wildly known that coastal wetlands
provide an ideal ecosystem to investigate the basic hypotheses of community ecology because
of their simple plant community composition and long-length distinct and strong abiotic
stress gradients from sea to inland. The influences of plant-plant interactions and their
interactions with environmental stress on coastal wetland community organization have been
well studied. Here, we review recent developments in the field of direct plant-plant
interactions including: (1) the prevalence of direct plant-plant interactions in coastal wetland
plant communities (e.g. salt marshes, cobble beaches, mangroves, and coastal forests); (2)
mechanisms of direct plant-plant interactions in coastal wetlands and how to determine if
plant-pant interactions are positive or negative; (3) how the strength of interspecies
interactions vary across stress gradients and how these interactions influence species zonation
and species diversity patterns along stress gradients; (4) the relationships between species
interactions and species invasions. Then we propose a hypothesis of how species facilitation
affects ecosystem function of coastal wetland.
D
IRECT
P
LANT
-P
LANT
F
ACILITATION IN
C
OASTAL
W
ETLANDS
Direct plant-plant interactions include positive and negative interactions (i.e., species
facilitation and competition). Plant-plant facilitation occurs when the presence of neighboring
plants enhances survival, recruitment or growth of the target plant through modifying
environmental conditions or providing associational defenses against herbivores. Almost a
century ago, ecologists discovered that both species competition and facilitation were
ubiquitous in natural plant communities. Subsequently, the influence of species competition
on community organization has been thoroughly investigated; however, the importance of
species facilitation has been largely neglected.
Recently, accumulating evidence suggests that species facilitation is essential in
structuring plant communities, particularly in high stress environments (Bertness & Yeh
1994; Bruno et al. 2003; Brooker et al. 2008). Both competition and facilitation among plants
have been observed in coastal wetlands. For example, species showed a hierarchical structure
in terms of competitive ability in a New England salt marsh. Species investigated, in order of
competitiveness, were
Iva frutescens
,
Jucus gerardi
,
Spatina patens
and
Spartina alterniflora
(Pennings & Bertness 2001). Competition among these species and species tolerance of
environmental stress formed distinct plant zonation in the salt marsh. However, in the
Spartina-Juncus zone of high salinity the salt tolerant but less competitive species,
S. Patens
ameliorated the abiotic stress of high salinity and facilitated colonization by the salt intolerant
J. Gerardi
(Bertness & Shumway 1993).
