||New York City as a Time
Listed By Borough
Listed By Ecosystem
Bayside Acacia Cemetery
Central Park's North End
East River Oyster Beds
Fresh Creek Marshland
Harlem River Yards
Inwood Marsh & Nature Center
Manhattan Marsh Re-creation
Manhattan Maritime Holly Forest
Northern Manhattan Forests
Operation Renovo Gardens
Time Capsule NYC
West Harlem Marshlands
The NYC Time Capsule:
An Urban Genetic Diversity Preserve
It’s alarming. Over the past century, tens of thousands of alien invaders have crept past our borders and settled here. They often move into undesirable areas, reproduce, and spread out, using a disproportionate share of resources. But this isn’t politics – it’s ecology. Introduced, exotic, and invasive species are competing for resources and “jobs” in ecological communities – and they’re winning. An invasive species can be defined as a species that achieves reproductive success and some measure of dominance in an ecosystem to which it has been introduced – usually through human intervention. (So, ecologically speaking, humans are the ultimate invasive – worse than kudzu, zebra mussels, or cane toads - no matter where they’ve immigrated from.)
Commonly, a species is considered exotic or introduced until it wreaks some ecological havoc and damages its adopted ecosystem, at which point it is an invasive. Carla D’Antonio and Jeanne Chambers include a further distinction in their chapter of Foundations of Restoration Ecology – terming species that have caused significant ecological or economic damage “invasive and damaging,” which seems like a useful but fine distinction, resting on the question of significance. Invasive species can damage an ecosystem several ways – direct or indirect competition with native species for resources; predation or parasitism on native species; interfering in the natural successional regime; and altering the ecosystem beyond the native species’ tolerance levels.
and predation on
native species can be one of the easiest ways for exotics to claim the
“invasive and damaging” title – just as smallpox devastated the
Americans while the European settlers who introduced the disease to the
World were blissfully immune, native species have no defensive
adaptations to many foreign parasites and predators that may have been
check in their own native habitats. For
example, several of the native tree species that once were dominant or
prevalent species in the forests of the
The American Elm, once a dominant species in four major forest types as well as the most popular street tree in “Main Street” America, is now reduced to isolated stands, solitary survivors, and immature understory in the forests over which it used to loftily preside. The culprit behind this arboreal genocide is an Asian fungus, commonly known as Dutch Elm Disease.
Asian elm species are adapted to resist this
parasite, but when it was introduced in shipments of lumber in the
Elms still grow in
the understory of many forests throughout the
Now, there is hope that Dutch Elm Disease is waning; the fungus having nearly exhausted its host species. Although currently, nearly all American Elms are still vulnerable, there may come a time when elms can once again flourish – in 20 years, 50 years, or 100 years. When that time comes, however, too much of the genetic diversity of the species may have been lost to restore American Elms to their natural extensive range.
The American Chestnut, once “the hallmark of the Eastern Woodlands” (American Chestnut Cooperators’ Foundation) and an important economic resource for both its wood and nuts, has been devastated by another Asian fungus, the chestnut blight. Where Chinese and Japanese Chestnut species have adapted to the presence of this fungus, and are thus resistant, American chestnuts had/have no such evolutionary defenses. Although many chestnut trees still sprout in forests where mature trees used to stand, growing from the root systems of trees that were destroyed in the blight, these saplings are struck down before they reach reproductive age.
Hemlock can live
to 800 years old, and commonly surpasses 400, making it one of the best
indicators of the ecological history of an area. Hemlocks
can be studied to determine climate
variation, historic land use, acid rain levels, and disturbance regimes. Due to an extremely high shade tolerance, the
trees can survive as understory trees for decades or even centuries
opens up in the forest canopy. The
Hemlock Woolly Adelgid, a species of aphid native to
Dutch Elm Disease, the chestnut blight, and the Hemlock Wooly Adelgid are invasive and devastating species, causing severe ecological and in some cases economic damage to the communities and ecosystems they strike. Losing these significant and historic tree species entirely is unthinkable, but all-too-possible. It is essential that the genetic diversity of these species be preserved against the time when the alien invaders can be defeated – by breeding, engineering, or encouraging adaptations for resistance, developing chemical and biological controls, or simply extirpating the invasives from the natural range of the trees.
Of course, the very urban setting that provides these benefits presents a number of challenges – the ecosystem must tolerate perpetual disturbance, increased exposure to pollution, and provide “ecosystem services” to the human population of the city. Also, the frightening persistence of the invading species mandates that the success of a Genetic Diversity Preserve will require continued and rigorous observation and maintenance.
these pitfalls, the
Preserve will benefit the economy, ecology, and community of
Elms, Chestnuts, and Hemlocks will be introduced to the city’s urban ecosystems in three ways. First, through planting as street trees, individuals will be provided an isolated and conspicuous growing environment, where fungus transmission and insect dispersal are unlikely, and invasions will be readily obvious. Second, stands of trees will be introduced to barren areas – new parkland, remediated areas, and land where cleanup efforts and invasive removal have left no remaining functional ecosystems. Third, the desired tree species will be introduced to existing forested areas in city parks. This last method of introduction requires the most consideration in drafting plans, so as not to disturb what are already functioning ecosystems in their own right.
has a motley
history compared to the towering vision and scope of city parks such as
far away, in
[Parks Commissioner] Mr. Benepe, who expressed both skepticism and surprise at the park's condition when told about it, said the city's plan was: "Let nature take its course." "Trees are growing, insects are buzzing, oxygen is being produced, and there's nothing wrong with that," he said.” (Williams 2005).
Each restoration/introduction plan for a city park will be just that – a two-pronged approach that combines the cleanup and restoration of the parkland with the introduction of time capsule species. The plan will include a comprehensive site survey, cleanup, removal of invasive (and in many cases exotic) species, and re-introduction of natives and time capsule species in particular.
The site survey will provide the basis for the rest of the plan. Using a BEF perspective, ecologists will gather data about the primary productivity, nutrient cycling, carbon budget, and decomposition cycles of the existing ecosystem (Naeem 2006). Imperatives will include evaluating the soil structure, determining the extant plant and animal species, estimating population sizes, and classifying species as native, exotic, invasive, or invasive and damaging. Research and observation will provide a basis for determining the role each species plays in the ecosystem. Particular care will be paid to determining whether exotics or invasives now play a functional role in ecosystem processes – for example, whether a native species may have adapted to the presence of the exotic as a food source or habitat. If this is the case, the restoration efforts may leave an exotic or an invasive species in place, or search for a niche replacement for an invasive and damaging species.
Cleanup and removal of invasive species will need to be intensive. The New York Restoration Project, working on the Highbridge Shoreline, recovered over 8,000 old tires (New York Restoration Project 2003). Sites designated as ‘remediated’ will only be cleaned up, while the other three types of sites (excluding the control sites as well) will also undergo invasives removal.
Norway maple and other invasives like garlic mustard have been observed in the park and are notoriously difficult to remove. In the case of Norway Maple, physical removal seems to be the best strategy (Webb 2001). Canopy trees will be girdled or sawn down, while seedlings will be clipped. Webb, Pendergast, and Dwyer (2001) showed that Norway Maple responds favorably to soil disturbance, so neither mature trees or saplings will be uprooted. Both top-down and bottom-up controls (D’Antonio and Chambers 2006) will be necessary to ensure invasives are fully removed and cannot re-colonize the ecosystem. Sites designated as ‘invasives removed’ will only be restored to this point, in order to determine the successional structure of the sites. The other two types of site will have native species re-introduced.
After the removal and cleanup processes, there will be available niches and ecosystem roles that were previously occupied by the invasive species. To keep the ecosystem functioning as fully as possible, these niches will be filled with native species that were outcompeted by the invasives, but share the same ecosystem role. For example, Norway maple will be replaced with sugar maple, its close relative that has been largely vanishing from forests where Norway maple has taken hold. The similar biology of the two trees should insure that any species (of Lepidoptera, primarily) that feed on or inhabit the Norway maple will be able to utilize the sugar maple instead. Using data collected through the BACI time series experiment, comparing the Lepidoptera species in the control sites and in the sites where Norway maple has been removed and replaced with sugar maple, we can determine if the sugar maple is an appropriate replacement.
species previously mentioned share a similar, very broad range and
levels, and so can be introduced throughout a wide range of the acreage
available at the park. Small
differences, such as the Hemlock’s preference for higher altitudes and
sides, the Chestnut’s for well-drained soils, and the Elm’s for
floodplains, will determine where to preferentially place higher
of the trees. The extensive topographical heterogeneity
capsule species, in
addition to being a living genetic diversity preserve, will restore
ecological functions to the park. The
Eastern Hemlock provides highly specialized habitat to certain types of
including warblers and wood thrushes (Save Our Hemlocks).
The American Chestnut
provides food for numerous species of wildlife, and can be expected to
stimulate the food-web interactions at the park by providing another
source for birds, squirrels, and other small mammals.
This in turn will stimulate the higher
trophic levels such as the pair of peregrine falcons and the population
red-tailed hawks that nest in the park. All
these time capsule species can be expected to benefit
Other time capsule species that will be introduced where appropriate to fill the ecosystem roles left by the removal of garlic mustard and Japanese knotweed, among others, are two of New York’s six threatened or endangered plant species. Northern wild monk's-hood, a herbaceous perennial, shares many habitat requirements with the Hemlock, preferring cool stream banks or cliff sides. Hart's-tongue fern, which thrives in moist, sheltered locations, will be planted alongside the elm trees (New York State Department of Environmental Conservation).
Introduced individuals will be sourced as seeds from as wide a source population as possible, with NYC as the epicenter. In order to restore a large meta-population of each time capsule species that would represent a sufficient gene pool to help reestablish the species in the future and preserve its evolutionary potential, seeds will be harvested from as many surviving trees as possible. Stands in the city parks and throughout the tri-state area will be preferential source populations, with the hope that they may have favorably adapted to the area, but seed collection will extend as far as possible within the species’ range to collect a suitable sample size. Trees will likely be sprouted in nurseries or greenhouses, to protect from early predation and trampling, and transplanted.
It has been
through a number of common garden experiments in which thousands of elm
saplings were inoculated with the fungus that an extremely small number
American Elm individuals (approximately 1
are naturally resistant to or tolerant of Dutch Elm Disease. These individuals have been reproduced many
times to create DED-resistant cultivars. It
is unlikely that this desirable genetic variation will
breed true, so
these cultivars are cloned using purely vegetal reproduction. There are about six of these cultivars that
are not patented (and therefore do not incur a royalty if cloned)
Ongoing maintenance and bottom-up control regimes will be developed, similar to the plan detailed below for the American Elm. Fungicide, pesticide, and hypoviral injections, along with biological controls (Pt beetles for the Hemlock) and physical maintenance of the trees will be used to control any outbreaks of dutch elm, chestnut blight, or wooly adelgids.
Dutch Elm Disease is caused by the micro-fungus Ophiostoma ulmi, or more frequently by a more virulent species of the same fungus, Ophiostoma novo-ulmi. The fungus infects the vascular system of the elm, causing the tree to grow tissues that clog its phloem and prevent it from transporting water.
DED can be spread in two ways. The first, direct transmission through root grafts, causes a domino effect among trees that have bonded their root systems at one or more points, extremely common among elms grown less than 50 feet apart. The disease is transmitted from one infected tree directly into the vascular system of its neighbors. This, then, is the root cause of the rapid demise of the elms on the tree-lined streets – the monoculture’s fatal flaw. This method of transmission spreads the disease throughout the tree, causing a full crown wilt when the water columns are blocked, and inevitably causing the death of the tree. This is a key feature in the plan to preserve elms in NYC’s urban forest – no susceptible elms will be planted within root-grafting distance of each other or in monocultures. Hopefully, this will ensure that this deadly and swift method of transmission is eliminated.
The second way DED is spread between American Elms is through the movements of elm bark beetles. There are two species of beetles that specialize on elm bark and act as vectors for the micro-fungus: the smaller European elm bark beetle (the larger of the two) and the native elm bark beetle. These beetles spend their entire life cycles in elm trees – the European beetle feeds on twig crotches and the native beetle feeds on the inner bark of lower stems. Both lay eggs by tunneling into dead or stressed elm wood, where the larvae can feed on the sapwood and inner bark. Adult beetles carry the spores of the micro-fungus from diseased trees to healthy trees, where they enter the vascular tubes the beetles chew through in their feeding. Although the beetle populations can rapidly reach large numbers, and can introduce the fungus to several different sites on a previously healthy tree (behavior more common to the European beetle) infected branches can usually be identified as they begin to wilt, and the tree can often be saved.
Frequent monitoring of the translocated trees is vital. Disease incursion sites must be identified and remediated as quickly and efficiently as possible, before the disease has a chance to spread. Obviously, the city maintenance staff from the Department of Parks and Recreation does not have the extra person-hours to inspect 1,000 trees on a daily or weekly basis, so a public awareness campaign will need to be introduced. It will feature a small reward for each person who correctly identifies DED on one of the city elms, and include information on recognizing elms, identifying Dutch Elm Disease, and on the historical and ecological significance of the American Elm. Similar plans will be introduced for the Chestnut and the Hemlock.
Reproductive success of the time capsule populations will depend heavily on the success of these control regimes in maintaining a healthy, parasite-and-predation free, invasive-free population. Manual propagation may be necessary to ensure reproductive success for the more isolated trees, and also to foster resistant adaptations as they are discovered in the populations.
invasives, and introduction of species phases of the restoration plan
1998. "How to Identify and Manage Dutch Elm
2006. "American Elm." The Wikimedia
2006. "American Chestnut." The Wikimedia
Cooperators’ Foundation. (Date Unknown). Website. Virginia Tech: Department of Plant
Pathology. http://www.ppws.vt.edu/griffin/accf.html Accessed
Chambers, J.C. 2006. Chapter 12: Using
Ecological Theory to Manage or Restore Ecosystems Affected by Invasive
Species. in Foundations of Restoration
Palmer, and Zedler,
2006. Chapter 10:
Biodiversity and Ecosystem Functioning in Restored Ecosystems:
Principles for a Synthetic Perspective. in
of Restoration Ecology. Falk, Palmer, and Zedler,
2005. Parks Even the Parks Dept. Won't Claim.
New York State
Department of Environmental Conservation.
Hemlocks. (Date Unknown). Saving Our Hemlocks from
the Hemlock Wooly Adelgid. http://www.saveourhemlocks.org/pdf_docs/hwafactsheet.pdf Accessed
Webb, S. L., Pendergast, T. H. IV, Dwyer, M. E. Response of native and exotic maple seedling banks to removal of the exotic, invasive Norway maple (Acer platanoides). Journal of the Torrey Botanical Society, Apr-Jun 2001.