January 2011 Greenbelt
Forest Restoration #175 January 15, search 2011
January’s restoration was a poorly attended affair, but not, I think, because of the snow and cold. Again, several of our regulars were away, and I may have led one astray about just where we were working. Judy Thurmond provided transportation from the ferry, and Dom Durso appeared with our gloves and pruners, despite first having to deal with bags of landscaping material that had been dumped in the street in front of his drive. We walked the nature trail to the entrance of the bike path at Rockland and Forest Hill Road so that Dom could appraise what the trail conditions might be like for next week’s 10 mile Greenbelt hike, and there spent our time removing bittersweet and honeysuckle from shrubs and saplings. Many young trees already had spirally creased bark from the constriction of the vines, but few looked like they would not recover after the vines were removed. The vines will grow back, of course, but in the interval the rescued plants will leaf out with less competition, will grow thicker stems, and will have time to repair their damaged conductive tissues. The day was alternately sunny and overcast, but the temperature was above freezing and, without wind, remarkably comfortable. The only downside was having to wade through the occasional deep snowdrift, and, after a while, suffer wet gloves. We were dressed for it and had a change of gloves, however, so all was well.
Afterwards, we took a short walk along the nature trail, just sightseeing and looking at animal tracks – mostly those of deermice – in the snow. There had been little wind to blow new snow into the tracks, so the numerous traces probably gave us a false impression of the number of deermice about. We remarked at the paucity of squirrel and deer tracks, and puzzled about what appeared to be a deer track that went UNDER a branch buried in the snow and disappeared at a hollow at the base of a small tree. It wasn’t the track of a deer of course; we could make out that the stride was about 8 inches, but couldn’t see a clear impression of the feet in the snow. It was probably a squirrel, but we gave up on that one. The weather continued mild and windless, and the increasingly wet snow began to pack squeakily under our feet – good snowman material I thought. Shortly we were rewarded by the flyover of a Cooper’s Hawk, and then, closer to Forest Hill Road, we began to find clear deer tracks going to and from the hollow. Skies became overcast again, and the temperature began to drop with the waning light, so home we went.
Since we assemble once a month to do these forest restoration sessions, it is worthwhile to examine why we do Forest Restorations and whether in general it is a task worth our time. Although its often assumed that “alien invasive” species are generally a bad thing, there is no consensus of opinion about this. Rather there is a spectrum of attitudes that run the gamut from those who believe that all species are products of nature and that nature should be left to take its course to those who believe that man has disrupted the natural environment and must actively intervene to put nature right – indeed, that man has a duty to intervene and put things right. Some who find themselves at the “hands off” end of the spectrum believe that inevitably a new balance will be struck between native and alien species, and that this balance will be struck faster if we don’t meddle. Many at the intervention end of the spectrum believe that alien species now disrupt the local web of life in “un-natural” ways; that prior to disruptive human activity alien species would be introduced to a new area slowly and sporadically, allowing ecosystems time to adjust to their presence. Obviously in today’s world of high-speed, long-distance transportation local flora and fauna no longer have the luxury of a lengthy period of acclimation to newcomers, or for that matter acclimation to any of the ways that accelerated human activity alters their environment, and the loss or diminution of many species is the result. The introduction of foreign insects and fungi are often implicated as key ingredients in species loss; fungi have been implicated as the cause of Dutch Elm Disease, American Chestnut Blight, the radical loss of amphibian species worldwide, and the decimation of bat colonies by White Nose Disease here in the northeast. Alien plants have been known to displace native species, resulting in a greater total number of species in our area, but with a smaller and smaller proportion of native plants in the mix.
Robert DeCandido, a New York naturalist, has written a number of papers about species loss and gain in New York City, and needless to say those papers reveal that the gainers are mostly aliens and the losers mostly natives. [A later, similar study concentrating on the area’s woody plants was done by Gerry Moore and the late Steven Clemants (author of a very thorough photographic guide to wildflowers of our region) of the Brooklyn Botanic Garden leads to the same conclusions. You can find that study and many others at http://www.urbanhabitats.org] As of this millennium, New York City retained only 57% of its historical native species – in other words almost half of the different plants that used to grow here can no longer be found! Staten Island had by far a greater variety of recorded native plants than any other borough, and likewise suffered a proportionally greater loss. Although the island still has the edge on the number of extant species, continued development of unbuilt areas – I’m tempted to say overbuilding – continues to result in the loss of both native and alien species. DeCandido lists a total of 921 extant plant species on Staten Island, and 126 species now extirpated. In the last 70 years (as of 1999), Staten Island lost 35% of its native plants! – and compared to the other boroughs, SI was doing the best! Staten Island was the only borough in which the number of native species found exceeded the number that had been extirpated, but I suspect this might no longer be true today… Such figures are depressing, but now and then there is a gleam of hope in this gloomy situation; very occasionally a rare species is found again in some corner of our fast disappearing unbuilt areas. A case in point is the Ragged-Fringed Orchis, recorded as rare on Staten Island in 1981, and not noted again until Dick Beugler found a colony again on a Protectors’ walk at Mt. Loretto in 2005.
We recognize many common plants as alien species, but used by itself, the label begs the question of just what makes an alien species “alien.” Obviously all species now present here are not “natives,” i.e. “born here,” but arrived from elsewhere at some time past. Just how long must they be resident before they are considered native plants? Most choose to set the cut-off date with the arrival of the European colonists in the 17th century, while others note that some alien plants must have come along when, it is theorized, Eurasian peoples crossed into North America across a land bridge that is now the Bering Strait when the sea level was much lower during the ice ages over 16,000 years ago. One could go to the extreme and say that native plants would be only those whose ancestors were on the North American land mass when it separated from the Pangean supercontinent some 150 million years ago, but that would be ridiculous! Generally, we date native plants as those pre-existing before European colonization, a perhaps artificial but certainly practical dividing point in time.
No matter where we set the cut-off date, however, it is generally recognized that most aliens manage to fit into their new environments without disruption; they become just another patch of color or texture squeezed in the landscape, and eventually the flora and fauna around them adjust to the new strands in the web of life. A young English gentleman, John Josselyn, voyaged twice to the New World in the 1600’s, and after his return in 1671 published an account of the flora and fauna of New England. His New-England Rarities, published in 1672, included an accounting of the species of “such Plants as have sprung up since the English Planted and kept Cattle there.” [Have you an interest, you can view a later reprint of his book (1865) as one of the thousands of out-of-copyright books that Google has scanned and made available on line. Just Google “Josselyn’s Rarities.”] The plants he lists are very familiar to us: Shepherd’s Purse, Curly Dock, Annual Sowthistle, Chickweed, Dandelion, Stinging Nettle, to name a few. Even in Josselyn’s time, some alien plants had already become so common that they were mistakenly believed to be native to both the old world and the new. Having been with us for so long, I doubt that many but professional botanists are aware that those plants did not always reside here, and it seems to us that they have not much damaged their environment. Then again, we have no valid yardstick to measure by, no way of knowing what surrounding fields and forests would have looked like without the presence of those aliens.
Most alien species struggle to find a niche in which they might survive. Native plants are usually best adapted to fit niches in the local environment, and they keep the number of alien outsiders down. If aliens persist, they usually manage to do so as small, patchy populations that don’t greatly disturb the local ecosystem, and sometimes appear as pioneer species only, disappearing when the natives move in as newly disturbed areas mature. Some aliens, however, find themselves without enemies in their new habitat, become wildly successful colonizers, and become invasive, displacing original native species. These invasives, such as Multi-flora Rose, Japanese Honeysuckle and Barberry, and Oriental Wisteria, don’t find their place without stress and disruption of the local habitat. Often they become a mono-culture where they grow, shading out or in other ways suppressing the growth of competing plants. When we decide what to do during our Forest Restorations we must weight the value of resisting the spread of such disruptive aliens against the potential damage that we might cause to the local ecosystem. Generally we resort to clipping and manual pulling of invasive species, methods that are relatively benign. This is as much a reasoned choice as well as recognition that we lack the authorization and expertise to employ herbicides and powered equipment.
Others do often resort to the use machines and herbicides. The NYCDPR and the Natural Resources Group occasionally resort to wide scale defoliation with chainsaw, earthmover and herbicide, especially when they have decided that a degraded area cannot be restored any other way, but the decision to use these methods may be based on a lack of manpower to do otherwise. We generally agree that hand-pulling is the best alternative and causes less collateral damage to the ecology of disturbed areas, but more often than not this would require the long term employment of an army of hand pullers! Absent such an army, the NYCDPR has resorted to chemical and mechanical defoliation of a few severely degraded areas of Clove Lakes Park, followed by a large scale replanting with native species, and similar work has been done at Conference House Park. Some of the plots treated at Clove Lakes are test plots used to determine what methods will be best employed to clear out invasive species in the future, but no matter what method was used to clear the land, the newly planted shrubs and trees will need attentive care to prevent the regrowth of alien species from overwhelming them before they become large enough to take care of themselves, and it remains to be seen whether in the long term there will be enough volunteer manpower to keep those replanted areas free of opportunistic alien plants while the new plants become established. Invasive species and forest restoration are difficult subjects requiring much experience and forethought; no one method will prove best for all places, and the methods employed probably always will be somewhat controversial.
As an example, local naturalists are uneasy regarding the National Parks Service plan to chemically defoliate Crooke’s Point at Great Kills and, in co-operation with the city’s Million Tree Initiative, replant that area with native species. On the one hand the area is certainly over-run with alien vines and shrubs, especially Japanese Honeysuckle and Multi-flora Rose. On the other, there are native plants mixed in there, struggling to survive on that thin, infertile soil, and a whole host of invertebrates and small mammals and birds that depend on that flora. What will happen to that wildlife when the area is defoliated? If it’s done in stages, will there be opportunity for the small creatures to migrate elsewhere? And what long-term effect will the herbicides have on the local environment, or the water about the Point? And crucial for the success of the project, who will take care of the replanted native trees and shrubs over the long period it will take for them to become re-established in that inhospitable place? There always seem to be volunteers found to help plant, but there are many fewer when it comes to inspecting and weeding, and on that often dry point, watering. Yanking out is not nearly as charismatic as putting plants in the ground.
The city’s plaNYC, I believe, will face much the same problem. Those critical of the city’s Million Tree Initiative believe that the money spend on planting a million new trees over a ten year period would be better employed by planting fewer new trees and paying more attention to funding the repair and maintenance of the existing infrastructure of our parks and natural areas. The new trees, they argue, are not given enough support, and that without proper water and care many if not most have little chance of surviving the long term; I have heard it said that the Department of Parks expects only about 30% of the new trees will survive in areas that are most degraded. I myself find the Million Tree Initiative very laudable but, like the skeptics, have to question where care for these trees will come from in the coming years. Where will the city find money for additional arborists and inspectors when staffing and budgets are being decimated? The “adopt-a-tree” program that solicits citizen help is one solution, but I’ll wager that the number of citizen arborists produced will fall far short of the number that a million new trees would require.
But back to protectors… There seem to be two approaches, not necessarily mutually exclusive, that we might make: we might try to encourage the growth of native species by replanting where they have been extirpated and tending to their growth, or we might fight the intrusion of alien species by various search and destroy missions. Sometimes we try combinations of both. Our usual focus on a Restoration Workshop is to go after the alien, woody, twining vines that we find growing on saplings along many of the Greenbelt trails. The main culprits are Japanese Honeysuckle and Oriental Bittersweet, both of which are capable of strangling small trees with a woody noose and clambering up into their branches to compete with the tree’s leaves for sun. If possible, we uproot the vines, which does disturb the soil but is effective at slowing the vines’ return. Most of the time, however, we prune the vines as close to the ground as possible, unwrap them, and cut them from the shrubs at such a height that new vines cannot immediately use the dead, hanging strands to scramble back into the sun. We try to unwrap the vines to the point where the remaining vines are fragile enough to easily rot away or be broken by the growing plant they twine upon.
In areas of partial shade Honeysuckle especially twists about itself and can form mounds over surrounding vegetation until virtually nothing remains but a shady tents of honeysuckle over herb deprived ground. Honeysuckle and other invaders are not entirely valueless; their blossoms and, in the case of the bittersweet, their fruit has an aesthetic appeal – they add color and contrast to a winter landscape, and who hasn’t, at one time or another, stopped to sample a drop of sweetness from the nectary at the base of a honeysuckle blossom? Ecologically, their fruits provide forage and their tangles of vines provide shelter for birds and small mammals; but this is at the expense of a greater variety of herbs and native vines they displace. The labor to remove them is so demanding, however, that we rarely go after these low lying masses of alien vines unless we can see that they are burying small saplings. We did, however, attempt to remove an expanse of English Ivy that carpeted the ground in the area between the White Trail entrance at London Road and the Meisner Bluebelt Pond (will somebody please tell me if this DEP created pond has an official name!). We spent several sessions there pulling ivy from the ground, cutting it from the trees, and mounding it in discrete piles off the trail. (English Ivy, however, is not a twining vine and posed no great danger to saplings; it did, however, climb into the canopy, burdening the trees, and by carpeting the ground with evergreen foliage, suppressed the growth of herbs and spring wildflowers.) Our intervention was for the most part successful; the herb layer has restored itself and relatively few invasive species have sprung up in place of the removed ivy.
Garlic-mustard is another alien invasive that we sometimes target, although only occasionally. Some believe that efforts to remove Garlic-mustard do more harm than good; that yanking the plants out disturbs the soil, damages the fragile mats of fungal mycelium that lie just under the surface and exposes the underlying soil to potentially desiccating arid air. Tiny invertebrates and micro-organisms in the leaf layer and top layer of soil are rooted up with the extracted plants and left to dry and die, and root systems of nearby plants are disrupted. The disturbed soil then becomes fertile ground for the growth of another generation of opportunistic and, more often than not, alien plants. The application of herbicides to control these mustards does not disturb the soil, and is often considered the only effective means to suppress them, but this is difficult to accomplish without damage to neighboring plants, and there have been to my knowledge few studies of the long term effects on native species of such chemical control. If Garlic-mustard, a prolific seeder, has been growing in a location for several years, there can be no doubt that the soil bank contains several year’s worth of Garlic-mustard seeds waiting patiently to be exposed and spring up to replace those plants rooted out, necessitating yet another round of control. Many Staten Island naturalists endorse the viewpoint of John Andrew Eastman, a Michigan wildlife biologist who has written three fascinating accounts of habitat ecology in the northeast, who believes that efforts to control invasives often do as much harm as good, and that a decision to intervene should be made only after much deliberation.
I think that the jury’s still out on this subject. We know that Garlic-mustard is what is called allelopathic, that it inhibits the growth of competing plants by contaminating the surrounding soil, and that there is evidence that it disturbs the growth of mycorrhizal fungi which grow in the soil around various trees in the forest and give the trees more access to nutrients than they could achieve on their own. Studies have shown that tree seedlings in forests in which the shrub layer has been invaded by large amounts of Garlic-mustard are less successful than those growing in areas that have not been invaded, and that in those invaded areas the forests seem to mature without normal regeneration. The trees grow larger and older, and the forest more shady, but there are few saplings beneath waiting to exploit clearings created by the fall of elderly inhabitants and become the next generation of woody giants.
Protector’s doesn’t have an official stance about the removal of Garlic-mustard, or any other invasive for that matter. We have joined several of the Department of Park’s sessions pulling Garlic-mustard in High Rock Park, and in our Restoration workshops we occasionally go after the tall, flowering second-generations of the plant (the first generation rosettes are too many and too small, I think, to countenance hand pulling), especially in limited areas where it is beginning to make inroads along the trails. We did this twice along part of the White Trail in the Egbertville Ravine, where Garlic Mustard is starting to be prevalent along trail edges and is spreading down toward the stream paralleling Rockland Avenue, and in subsequent years we have seen a notable reduction of the number of these flowering mustards. Where the Garlic Mustard grew we see Sarsasparilla, Avens, Virginia Waterleaf and other natives again. In a case like this, where we can schedule a follow-up in later years to remove new Garlic Mustard and any Japanese Honeysuckle and Multi-flora Rose that may begin to grow on those former mustard sites, I believe we can achieve a limited success. (We might even try eating them away; see the postscript at the end of the report!) A look uphill from the trail toward Meisner Road, however, reveals still more Garlic Mustard whose seeds will work their way down toward the trail.
Some invasive species, such as varieties of Japanese Knotweed and Phragmites, are just too much for us to handle. Japanese Knotweed is difficult to root out, and sprouts again readily from any root fragments left behind. Having few native enemies, it spreads rapidly in any but the deepest shaded areas. It is a powerful sprouter; the shoots, edible when young and tender and reminiscent of rhubarb when nibbled or used in a salad, are never-the-less capable of piercing asphalt roads. Successful eradication at present requires a chemical attack or power equipment, indiscriminately destructive methods that we cannot and do not employ. However, unless some biological agent can be found to control it – and employment of biological agents always carries with it the danger that the cure might become worse than the disease – the use of chemicals and graders may be a lesser evil than allowing Japanese Knotweed to continue to spread and make inroads along the edges of our forests. It’s worthwhile, I think, to uproot isolated stands or cut them to the ground when we encounter them on restoration sessions, in the hope that we can slow its cloning into bigger and bigger patches where it didn’t exist before. A big, established patch, however, is beyond our means to remove.
PS: Judy Thurmond pointed me to a Maryland organization that uses a Garlic Mustard “harvest” in the form of a yearly food festival as part of their invasive removal scheme. I doubt that an appetite for garlic can make a dent in the vast number of Garlic-Mustards that seem to spring up almost everywhere, but the idea is entertaining and served the Maryland organization as a focus for volunteers removing the plants. The festival centers around a Garlic-Mustard cooking competition, and the web site includes a few recipes of past winners. Some of these look pretty good, but, alas, it only includes winners from 2001 and 2002! I looked at their site and see that the Garlic-Mustard Challenge continues to be a part of their calendar, so I wondered if they might be saving later recipes for a fund-raiser recipe book… If you want to try this flavorful invasive this spring, you might also want to look at the recipes or the cooking tips sidebar on their site.
Another site – which in part draws recipes from this challenge – is