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West Harlem Marshlands
Abstract
|
The restoration of
degraded habitat, especially in urban areas,
is as an important component in the stewardship of urban ecosystems. Harlem River Yard is a 96 acre site in the
Table of Contents
|
Title
Page……………….............………………………..…………….
Abstract
……………….........................……………………….………
Table
of Contents ……………..........………………………….………
Introduction…………………………..........…………………………….
Site
Description and History…………….….......................….………
Rationale
for Restoration……………….............................….………
Restoration
Plan ……….........................….......................….………
Restoration
Areas - Species Selection and Site
Layout.....…...…....
Evolutionary
Ecology and Population Genetics
………....……..…....
Metapopulation
Dynamics…………………..………...…………..…....
Community
Ecology………………..…............…….......………..…....
Abiotic
Filters
.........………………..…............…....……………..…....
Measuring
Success……………..…..…...............………………..…....
Time
Line
................………………..….............…………………..…....
Funding
and Budget.…….......……………....…………………..…….
Summary....….………………………………..........................…..…….
References…...……………..……………........……..........……………
Introduction
|
The
Harlem River Yard (HRY) is a 96
acre site located in the Mott Haven area of the
Site Description and
History
HRY is
sited on the north bank of
the
During the construction
of the rail/road intermodal
facility, areas of the site were covered with fill and paved to contain
contaminants 
discovered
during hazardous waste
assessments (Fiteni 2001). Contaminants
discovered included abandoned underground storage tanks (UST), lead and
other
metals, and polyaromatic hydrocarbons (PAHs), apparently from coal and
ash
(Fiteni 2001). Non-native grasses
maintained by mowing have been utilized in unpaved areas.
There is also a 
stand of trees
including tree-of-heaven (Ailanthus altissima) and eastern
cottonwood (Populus
deltoids) present (SWMP FEIS, 2005).
Rationale for Restoration
The
Harlem River
Yard Waste Transfer Station forms an integral part of the New York City
Waste
Management Plan and the company managing the site has been given a
ninety-nine
year lease. It is therefore unlikely
that a large component of the site will ever be used for anything but
industrial purposes. However, the New
York State Governor’s Hudson River Estuary Action Agenda states that
river and
shoreline habitats should be enhanced, biodiversity & habitat
diversity be
conserved, and
Restoring
even the
foreshore portion of HRY would result in numerous aesthetic, habitat
health and
environmental services improvements. The
aesthetic improvement would consist of the visual screening the HRY
Waste
Management Facility from the nearby Randall’s
The
river edge
would be restored, in so far as is possible, by removing non-native
grasses and
planting native semi-aquatic herbaceous plants with the aim of creating
natural
stabilization and enhancing habitat for aquatic fauna.
Another important area for
action is treatment of the site for
compaction. The US Army Corps of
Engineers (USACE) Critical Restoration Implementation Plan for the
bordering
lower
In addition to aesthetic enhancement
and improved environmental services, the restored habitat at HRY would
form
part of the urban forest described by Dahlin in the Crotana Park Urban
Forest
Management Plan (Dahlin,
iii). HRY would form an
important link between nearby greenspace areas including the previously
mentioned Randall’s
Restoration Plan
|
Setting
and meeting
goals is one of the key factors in the development of a successful
restoration
project. As already stated, one of the
main goals for this project is the replacement of non-native species
with native
species. However, there are several
possible scenarios for the final appearance of HRY, each presenting
different
advantages and problems with regard to final appearance, utility and
cost. Table 1 summarizes possible
scenarios along
with advantages and disadvantages of each.
|
Scenario |
Plant types |
Examples of Plants Used |
Advantages |
Disadvantages |
|
1 |
Non native herbaceous
plants |
Pennycress (Thlaspi
caerulescens) |
Low cost, potential for phytoremediation
including heavy metals |
Potential to be invasive
in surrounding areas. Does not meet stated
goal of screening site structures and using native species |
|
2 |
Native herbaceous plants |
Salt
marsh Cord
grass (Spartina alterniflora) |
Relatively low cost, in
keeping with stated goal of using native plants |
Does not meet stated
goal of screening site structures |
|
3 |
Non-native trees |
London Plane (P. × hispanica) |
Extant in surrounding
areas, lower potential to introduce diseases etc. to metapopulation |
Does not meet stated
goal of screening site structures and using native species |
|
4 |
Native trees |
|
Meets goal of using
native species. Cottonwoods have
phytoremediation potential for TCE |
Trees not appropriate
for all areas of site, e.g. river edge |
|
5 |
Combination of 1&2 |
As above |
Low cost, closer to
extant communities in surrounding area |
Does not meet stated
goal of using native plants |
|
6 |
Succession of 1 to 2
& 4 |
As above |
High potential for phytoremediation, will eventually meet stated goal of using native plants |
Succession may be
difficult to implement |
|
7 |
Combination of 2&4 |
As above |
Meets goal of using
native plants |
Lower potential for phytoremediation |
Table 1:
Summary of restoration scenarios for HRY
The
most
appropriate restoration scenario described in Table 1 is scenario 6. However, due to the ongoing presence of
contaminants at HRY, the large scale planting of large trees would
conflict
with the remediation strategy currently in place. Therefore,
the best option will be the
maintenance and enhancement of the existing cottonwood stand and the
replacement of non-native grasses with native grasses in the landscaped
areas
of the site. The next section describes
details of species selection and propagules for the envisaged plan and
is
followed by a summary of several theoretical issues in context of this
plan.
Restoration Areas - Species
Selection and Site Layout
The
HRY restoration
area is divided in to three main areas as shown in Figure 4. The areas were conceived based on the main
habitat type; however the climax point for each area will depend to a
certain
degree upon how each area is colonized during the restoration process.
Figure 4: Restorations areas. Site
1, eastern cottonwood stand; Site 2,
native grassland; Site 3, salt marsh
Area
1: Consists
of the existing cottonwood (Populus
deltoids) stand, which will be maintained and expanded in the
future if
possible. Due to the size of this stand,
development will depend on a number of issues such as interaction with
surrounding populations. These issues
are discussed in greater detail in the following sections summarizing
ecological
theory.
Area
2: Envisioned
as a native grassland area. Grasses in
this area would initially be
selected from those appropriate for phytoremediation such as switch
grass (Panicum
virgatum), followed by the introduction of native grasses such as
Area
3: The
former barge docking area, which is
currently silted to a shallow depth, would be further filled to create
a salt
marsh habitat. The suite of grasses and wet land plants most
appropriate for
this area include salt marsh cord grass (Spartina
alterniflora), saltwater cord grass (Spartina
cynosuroides) and two species of bulrush, water hemp (Acnida
cannabinus)
and salt marsh bulrush (Scirpus robustus),
marsh elder (Iva frutescens), swamp rose-mallow (Hibiscus
palustris), and groundsel bush (Baccharis halimifolia). This
list of species is extant in the salt marsh areas of Shorakapok
Preserve area
of
Evolutionary Ecology and
Population Genetics
Current
research
suggests evolutionary pressures on a population should be considered in
the
formulation of a restoration project due to the importance of such
pressures in
the long term viability of the population (Stockwell et al., 113). From the classic Darwinian evolutionary
perspective, the existence of heritable traits and the action of
selective
pressures on those traits will cause the loss of individuals less well
adapted
for the subject habitat and a resulting selection for the best adapted
population. Traditionally, this process
has been
understood to take place over long time periods, often in the geologic
time
scale. In terms of restoration projects,
however, there is a need to consider what has been termed “contemporary
evolution” (Stockwell et al., 113). Contemporary
evolution is the action of evolutionary
forces on a much
shorter time scale, and for the restoration ecologist, this means that
what has
been determined as the existing set of pressures facing the species of
interest
may alter as the environment changes during the restoration process.
In the HRY project, restoration would alter many evolutionary agents currently found at the site, thereby changing the fitness of the existing eastern cottonwood population. Examples of evolutionary agents that might be changed include soil pH, soil composition and water content, type and populations symbiotic soil bacteria and changes in the shade regime due to the introduction of other plant types. For example, using non-native herbaceous plants for bioremediation may alter the abiotic nature of the site. Even if members of populations originally found at the site are maintained, such changes may present selective pressures for them. For example, the eastern cottonwood has a pH tolerance in the 5.5-7.5 range and prefers moist soil. Introduction of competing species may alter the soil acidity or moisture content, placing an evolutionary pressure on this population. Decisions as to the importance of the survival of the extant population would need to be made. If maintaining the specific population is deemed important, it may be necessary to undertake common garden experiments to ascertain the tolerance of the existing plants and plan restoration efforts accordingly.
Another of key factor in
the survival
of a population is the existing genetic diversity (Falk et al., 15). Interaction with the environment places
selective pressures on populations and in order for the population to
succeed
it must contain sufficient heritable traits to allow adaptation to
environmental changes (Falk et al., 14). Such
selective pressures should also mean an existing
population will
have a high frequency of alleles (genotype) associated with the
physical traits
(phenotype) adapted for the existing environment (Falk et al., 15). However, if sufficient genetic diversity does
not exist in a population it will be not be able to adapt to
disturbance events
such as extreme weather, disease infestation, or the introduction of
predators
(Falk et al., 15). This problem is of
special
concern in small areas such as HRY, where limited area restricts
population
size.
When small populations
inbreed,
there is an increase in the probability of homozygousity.
While heterozygous individuals carry
different copies of a specific gene, homozygous individuals have two
identical
copies. Genetic diversity is therefore
reduced in populations with a higher level of homozygousity, and the
availability of potentially adaptive traits is reduced (Falk et al.,
16). The negative effects of homozygousity
may be
solved by introducing genetic material from outside populations; a
process
termed genetic rescue (Falk et al., 16). Due
to the probabilistic nature of genetic variation, only
a small
number of outside genes are required to propagate genetic rescue in a
population. For this reason, it is
important for any restored species at HRY to have a connection with
other
sources of genetic material, i.e. nearby populations.
The existing species in surrounding areas
such as
In addition to increased
homozygousity as a result of inbreeding, restoration projects that
introduce
outside genetic material must consider the possibility of introducing
alleles
that produce phenotypes poorly adapted to the restoration site. By reducing the number of potentially
positive existing alleles, such genes will reduce the adaptive ability
in the
same manner as inbreeding (Falk et al., 16).
Since the eastern
cottonwood
population at HRY is very small, it may be feasible to carry out
genetic
testing of this and members of nearby populations to determine
relatedness. Male clones of the species
are often planted for soil stabilization purposes, so the breeding
status of
the existing population should also be determined.
The area available and
the higher
relative population density for both terrestrial and aquatic native
grasses as
well as the proximity of nearby populations may allow these species to
be more
self-sustaining with regard to gene flow.
Metapopulation Dynamics
The
spatial arrangement of urban
environments means that where populations of plants and animals occur,
they are
generally small and isolated to a lesser or greater degree from other
populations of the same species. Together
these smaller populations form metapopulations. Metapopulation
theory offers a tool to help understand the
interaction
of several populations of the same species and the survival of the
species at
the local and regional level (Maschinski, 64). A
population’s chance of survival in a specific area
increases as the
size of the area, or patch, increases, or when the number of patches
increases
(Maschinski, 66). While direct analysis
of metapopulations is difficult due to the need for long term data and
the
complex biology of most species (Maschinski, 62), metapopulation
analysis, with
the aid of modeling, makes it is possible to define the minimum number
of
interacting populations necessary for the metapopulation to persist.
In the context of the HRY
restoration project and the eastern cottonwood, metapopulation analysis
would
be a useful tool for determining whether site is of sufficient size to
support
an isolated population, or if interaction with other populations will
be
necessary. The estimated minimum viable
population (MVP) ranges 50-1000 individuals (Maschinski, 60), so a
large
increase in the extant population would be necessary.
From a metapopulation standpoint, 15 to 20
well connected local populations are necessary to maintain a viable
metapopulation. Census of other
populations of eastern
cottonwood in nearby areas such a Randall’s
Community Ecology
By
definition, a large fraction of
the available land in an urban area is utilized for buildings, roads
and other
structures, severely reducing the amount of space available for flora
and
fauna. Therefore, one of the greatest
challenges for an urban restoration project is managing the community
ecology of
the restored area. Community ecology
refers
to the species richness of an area and is generally presumed to be a
function
of the competition and prey/predator relationships (Menninger and
Palmer,
90). Alternatively, Wilson and
Simberloff, argue that species richness is a function of patch size
combined
with a species’ ability to disperse, while the most recent theories of
community ecology are based on disturbance theory and stochasticity
(Menninger
and Palmer, 90). Disturbance theory
states that diversity is impacted by natural processes such as forest
fires or
hurricanes that some species require to reproduce or disperse. Stochasticity is the effect of community
demographics, where, for example, a population size is reduced due to
natural
occurrences, and if it falls below a certain size it goes extinct.
For the
eastern cottonwood population and other species that would form the
eventual
community as part of this restoration project it is presumed stochastic
and
disturbance events would be minimized by management.
However, community ecology theory would be
useful for modeling the number of species that could be successfully
introduced
to the site.
Abiotic Filters
The
survival of a species at specific site is affected by factors such as
the amount
of light and shade and soil chemistry and texture (Menninger and
Palmer,
95). Due to the relatively high degree
of development at HRY, with large paved areas and buildings,
consideration and
monitoring of abiotic factors will be important. As
mentioned previously, changing soil
composition due to soil remediation efforts may affect the extant
eastern
cottonwood population. The flow of water
during periods of high rainfall will be of particular importance to the
health
of salt marsh areas created by softening the riverbanks and the main
salt marsh
area. Water flowing from access roads
may potentially cause rapid changes in water salinity which would be
detrimental to semi-aquatic plants such as spartina. While one of the main advantages of marsh
grasses
is their ability to stabilize river banks and decrease point source
pollution,
high water flow from paved areas may also cause excessive erosion and
changes
in water chemistry outside of the plants’ level of tolerance. It will therefore be necessary to control
erosion by engineering methods such as the provision of erosion control
matting
at least in the short term.
Selection
of plant species may also impact decisions relating to the management
abiotic
factors, such the control of soil pH. For
example, the eastern cottonwood and the native grass, sideoats
grama,
both have ph ranges around 5.5-7.5 (USDA, 2006), simplifying the
management of
the contiguous area these species will share.
Measuring Success
A
comprehensive assessment of biodiversity and population estimates will
be
required at the outset and at intervals to be determined in order
quantify the
success of the project and allow for modification of restoration plans
and/or
goals if necessary. Such experiments
should be carried out using a control with before and after
measurements as
described by designs such as Before-After Control-Impact (BACI) design. BACI studies consider both the area of
interest and a control site both before and after a perturbation (i.e.
the
restoration activity) takes place (Osenberg et al., 2006).
For HRY
specific measurement regimes would be required for the different
restoration
areas. For example the eastern
cottonwood may be sampled for population density, while the native
grass areas
would additionally be sampled for soil contaminant concentrations.
Time Line
The time
line for this project will initially be reliant to a great extent on
the
phytoremediation aspects of the project. For
example, a significant reduction of residual PAHs
using grasses
requires treatment times greater than one year (Parrish, Banks et al.,
2004). If it is possible to retain
extant cottonwood populations, the time necessary to reach a
sustainable
community will be greatly reduced for Area 1. Experience
from other restoration projects has shown that
grasses and
wetland planting generally takes in the region of six months. Projected times for the completion of various
aspects of the project are detailed in Table 2.
|
Phase |
Time for Completion |
Projects |
|
1 |
6 months |
Commence BACI testing for
all areas. Removal of non-native turf
grass & trees, Areas 1 & 2. Softening
of banks by filling along river edge. Filling
of Area 3 |
|
2 |
6 months |
Planting of
phytoremediation grasses, Area 2. Planting of aquatic and semi-aquatic
plants, Area 3. Monitoring of Area 1 |
|
3 |
1-4 years |
Removal of
phytoremediation grasses and planting of native grasses, Area 2. Monitoring of Areas 1 & 3 |
|
4 |
TBD |
Monitoring of all areas
for ecosystem functioning, with additional monitoring for contaminant
levels |
Table
2: Project
phases and expected completion times
Funding and Budget
Restoration
cost can vary greatly depending of the complexity and scale of the
restoration
project. Berger and associates (1995)
found the restoration cost of 11 salt marsh restoration projects range
from
1000 to 1 million dollars adjusted to 2005 dollars (RIHR, 2001). Projects at the lower end of the range
involved
simple removal of phragmites using volunteer labor, while the most
expensive
project involved the removal of ten feet of fill over and ten acre site
with
the subsequent planting and monitoring of native grasses (RIHR, 2001). A project involving the construction of dykes
cost $20,000 ($22,000 in 2005) per acre (RIHR, 2001).
The
proposed restoration at HRY involves engineering of the riverbank to
restore
wetland areas, suggesting the cost of restoration would be in the range
of
$22,000 per acre. The total area of the
waste management and transfer facilities at HRY is approximately 42
acres. Therefore, the total area
undergoing
restoration is approximately 54 acres with a restoration cost, assuming
$20,000
per acre, of approximately 1 million dollars. Unfortunately,
because the HRY site is an operating
industrial facility
under lease, it is unlikely that volunteer labor would be appropriate.
A
potential source of funding will be Federal Brownfields funds allocated
for the
remediation of the site. If the site is
to be treated to as parkland, and will be actively managed there will
be a
shift in focus from a single restoration budget to an ongoing
maintenance
budget. Additionally, economies of scale
could be achieved by sharing resources, for example suppliers of
propagules
with similar restoration projects that occur in nearby areas such as
Summary
The
restoration of HRY, including
the conservation of native species such as the eastern cottonwood, in
accordance with initiatives to improve the general environmental health
of
References:
Condit, C. W. (1980). The
Dahlin, Kyla.
Dietz, A. C. and J. L.
Schnoor (2001). "Advances in
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Flagg, Thomas R.
Falk, Donald A., Richards, Christopher M.,
Montalvo, Arlee M. and Knapp, Eric E.
“Population and Ecological Genetics in Restoration
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Ecology. Ed.
Donald A. Falk, Margaret A. Palmer, and Joy B. Zedler.
Lehman
College Library (CUNY)
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/lc&CISOPTR=75&REC=16
Loeb, Robert E. “Plant Communities of Inwood
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Maschinski, Joyce. “Implications of Population Dynamic and
Metapopulation
Theory for Restoration.”
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Palmer, and
Joy B. Zedler.
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Palmer, and
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Banks, et al. (2004).
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polycyclic
aromatic hydrocarbons (PAHs) in composted soil." International Journal
of Phytoremediation
6(2): 119-137.
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Restoration. (2001). "Restoring
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http://www.edc.uri.edu/restoration/html/tech_sci/biblio.htm
Stockwell, Craig A., Kinnison, Michael T., and
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USDA (2006) http://plants.usda.gov/java/profile?symbol=BOCU