Biology Reference
In-Depth Information
achieved when in fact the restored systems are simply making the transition from
one degraded state to another degraded state. Even the existence of appropriate
indicators may not be sufficient to assess the progress of a project as it often is
necessary to recalibrate protocols when applied outside the “home” region
(Pennings et al. 2003).
Rigorous assessment protocols for complex ecological systems require true
replication of treatments and controls. When such replication is not possible, as
was the case with Sandpiper Pond, alternative experimental designs are required
(e.g., BACI). Difficulties and assumptions associated with applying alternative
designs and statistical approaches continue to be identified (Underwood 1994;
Walters and Coen 2006). The use of a BACI approach to design Sandpiper sam-
pling efforts overcame the lack of restored treatment replication but suffered from
a single before sampling and a limited number of control sites. Even if sampling
was more extensive, a BACI design assumes that the impact is identifiable in terms
of time, intensity, and spatial distribution. Unfortunately, the “impact” at Sandpiper
Pond turned out to be variable in all aspects. Impact variation often was unpredict-
able and uncontrollable and included the recent prevalence of extremely high tides
and coastal storms that have accelerated beach erosion leading to occasional over-
wash events at sites other than the excavated inlet. The very method of applying
the impact (i.e., inlet vs. culvert) changed during the course of the study and is
likely to change again if park personnel determine original restoration goals have
not been met.
The initial monitoring of Sandpiper and control marshes at best may provide
background for developing a set of new hypotheses that can be tested with more
precise approaches. Salt tolerance is an important factor limiting the invasion
of
Phragmites australis
(Burdick et al. 2001; Bart and Hartman 2002).
Greenhouse experiments examining plant growth responses to various salt con-
centrations and species combinations would increase understanding about the
responses of marsh vegetation to the reestablishment of tidal influence. Marshes
in transition from brackish conditions to salt water conditions also may provide
excellent opportunities for field experiments aimed at understanding the struc-
ture and composition of salt marsh communities (Pennings et al. 2005).
Previous research suggests that salt marsh recovery from
Phragmites
invasion
can be slow (Warren et al. 2002), and one possible explanation could be the
significantly greater amounts of invader biomass and detritus that persist in
invaded marshes (e.g., Sandpiper Pond). Experiments designed to tease out the
role of detritus accumulation in inhibiting rapid community change and the
connections to fundamental differences in patterns of senescence between
invaders (e.g.,
P. australis
) and native marsh plants (e.g.,
S. alterniflora
) easily
could be conducted. The unexpected establishment of sea-beach amaranth, a
threatened and endangered species, at the site of inlet excavation also solicits
further studies on the interaction between marsh and dune seed banks and soil
disturbance. Finally, the Sandpiper project provides an excellent arena for
addressing the issue of appropriate restoration targets and the value of adaptive
management to achieving stated targets.
