July 2014, LaTourette Bike Path
Eastern LaTourette Bike Path
By Don Recklies, hospital Naturalist
Forest Restoration #215 July 19, 2014
The July restoration was a casual walk along the eastern leg of the bike path at LaTourette, pausing to cut woody twining vines beside the trail. We didn’t anticipate that the recent series of rains we would have caused any difficulty, but they did…
This month 3 new volunteers joined us, two of them students needing volunteer hours. We pointed out the vines we were after, and they set to cutting them from trees close by the trail. Poison ivy was abundant, and we tried to avoid it where possible, but it just doesn’t cooperate by growing distant from the vines we have to cut. Soon one of the ladies remarked that she had encountered some, and her exposed skin was burning. “That’s not right,” I said, “because unless you are very allergic to poison ivy it usually takes several hours for a reaction to occur.”
I looked at the tree where they were cutting away a net of strangling vines and discovered that not only was poison ivy present, but also stinging nettles. She was suffering from irritation caused by having brushed against the nettles. To ward off herbivores the nettles store a cocktail of chemicals in tiny, fragile needles on stem and leaves. When one brushes bare skin against them, they break off and sharp fragments inject the irritants. One of the main components in the nettle cocktail is said to be formic acid, the same chemical employed by many stinging ants, hence the burning sensation. Luckily the acute burning sensation lasts only a few minutes, although the skin remains sensitive for several hours. I doubt, however, that the volunteer considered that kind of “luck” to be of any consolation.
What discomforts the summer can bring! Not only must we put up with mosquitoes and ticks, but also poison ivy and nettles! Long sleeves and pants help, but not with the heat. You choose your poison (no pun intended), and I prefer to wear short clothes and deal with the irritants and not the heat. It doesn’t take long to develop a good mental image of poison ivy and stinging nettles, and I’d become pretty good at avoiding them, but hadn’t thought that we’d encounter stinging nettles along the bike path. We expect them on the hillside above around the Hessian Spring, where they grow in profusion, but didn’t expect them – and probably should have expected them – below where the spring flows under and across the path.
After the workshop we made a walk west on the “bike path” and then returned by way of the Blue Trail on top of the hill. On the way we passed stands of Japanese Knotweed and on the downhill of side the path an extent of struggling trees and shrubs mounded over by layers of Porcelain-berry far too thick for us to attempt removal. We also passed colonies of Impatens, Touch-me-nots, that had been stripped of their tops by feeding deer, and that brings me to…
A small rant about the number of White-tailed Deer on Staten Island… I have observed that our growing deer population has become more and more unsupportable. Every year we see more deer than the year before, and can hardly walk any wet trail in the woods without encountering hoofprints that betray their presence. About 15 years ago I encountered very few deer when I first started to nose about Clay Pit Ponds and Sharrott Shorelands, areas which are suspected to be where deer swam across the Kill to begin re-colonization of Staten Island. In 2008 the NYSDEC estimated the population of deer on the island to be about 25, although I am convinced it was then much greater! Now it is not uncommon to read about collisions with automobiles (34 carcasses reportedly removed by the DOS in 2013 alone), and almost impossible to walk through a “Forever Wild” area without seeing a least one deer or occasionally even small herds. Recently the NYCDPR announced an attempt to more accurately measure the deer population by an aerial survey, and I await that new tally, although I must note that areas with some of the largest deer populations, such as many west shore areas, were not included in the initial announcement about the extent of the survey and may still underestimate them. Certainly deer on the island must number in the hundreds.
Even a lowball estimate of 50 deer is, I think, more than Staten Island can support without further impoverishing the natural ecosystem of which we are so rightly proud. For a long time study after study had shown that the natural areas of Staten Island retained more species diversity than any other borough of the New York City, but now an ever increasing deer population is combining with continued development to put more and more pressure on local plant populations. Studies of the effect of deer browsing agree that one may have a diverse plant understory and healthy forest or can have a large deer population, but not both.
Pennsylvania, for instance, has managed deer herds in vast forest lands under state control since the 1930s. Organized hunters in that state insured that the aim of regulation was to produce the largest herds that forests could support, with little regard to maintaining the best, most diverse ecosystems. Since for the most part large deer predators had long been killed off, the only control on the number of deer – aside from the yearly bag taken by hunters – was disease and the amount of vegetation they could browse. Increasing urbanization and fragmentation of the landscape favored the deer, which are creatures of forest edges, and restricted hunting seasons and buck-only hunting allowed their numbers to explode. The resulting browsing pressure on the diversity of forest herbs and shrubs was drastic; one study which compared selected forests in 1929 and again in 1995 saw the number of families of plants in the forest decline from 27 to only 10. These forests had become “deer savannas” in which the deer had consumed the understory of plants that ought to have been there. (In a few areas the species diversity actually increased due to an influx of alien species, often invasive, but the total number of native species declined.)
The ill effects of this growing population of a top herbivore was repeated throughout the Midwest, and now where there once were 2 to 5 deer/sq. km. there were sometimes up to 20 – in the urbanized parks around Washington, Dc the density exploded even higher. ln all these places the diversity of plants that ought to be in the forest declined severely. And on Staten Island? Here the deer have found a paradise: lots of green protected edges in which to feast and no hunters or predators to fear – only automobiles – no wonder their numbers are exploding…
In just the past 5 years I have noticed that in many places where once I saw lush colonies of Canada Mayflower (Maianthemum canadense) and Touch-me-nots (Impatiens capensis), I now see many fewer blossoms, or almost none. The Touch-me-nots that survived in those spots display stems stripped by browsing deer and fewer blossoms that manage to produce seeds. Often they appear as if someone had walked through the patch with a weed-wacker, chopping off the tops of the plants and leaving a strangely level surface. I rarely see hummingbirds in those places anymore, and in spots the Touch-me-nots that provided shade have been so stripped back that the soil beneath them has become dry. The whole ecosystem is being changed.
In many places where once I saw carpets of mayflowers blooming in the Spring, I now see fewer plants and only widely scattered blossoms. The sweet nectar-bearing blossoms of Canada Mayflower are said to be a preferred deer browse. There are still lots of Canada Mayflower leaves – the plants are perennials and will sprout again year after year if the leaves are not too heavily browsed – but there is a reduction in the number of flowers that set seed. One wonders what the prognosis is for both the flowers and the insect pollinators that depend on them.
Spring becomes an especially rough time for flowering ephemerals. Spring wildflowers usually have to make the most of a very brief growing season. They have to produce leaves, blossom, set seed and photosynthesize enough food to see them through the coming year before the trees above leaf out and shade slows their further growth. It’s a kind of balancing act and many plants survive on the edge of getting just enough light to prosper. Come Spring the deer are very hungry for soft greens, and when deer browse the new spring shoots they can leave the plant without enough leaves to enable them to put resources into producing seed or rhizomes or even to store food for the next season. As more and more barely surviving plants die off eventually scattered populations become too small to survive and yet another colony of plants disappears from the woods.
As the natives disappear their place is often taken by alien plants that the deer do not prefer. Asian Bittersweet (Celastrus orbiculatus) and Japanese Honeysuckle (Lonicera japonica), for example, have tougher, more indigestible leaves than the native vines they replace, and Garlic-mustard (Alaria petiolata) makes itself unpalatable to deer by producing distasteful chemicals. Long stretches of moist trails in the Greenbelt have become corridors of Japanese Stiltgrass (Microstegium vimineum), a lush looking grass that the deer shun. The deer browse shrubs in the understory, sometimes trimming away branches and leaves as high as they can reach. What is most in reach, of course, are new, tender shoots. The deer eat these, and the shoots of trees that they prefer often can’t grow fast enough to put their leaves out of reach before they die. The forest starts to loose these trees, and where the understory has been browsed away begins to dry, making survival of new sprouts even harder.
The dryer forest starts to favor Hay-scented fern (Dennstaedtia punctilobula), and colonies of that fern begin to grow greater in extent. Soon the fern, which is accustomed to grow in partial shade, becomes a ground-cover, and prevents other plant seeds from growing. In moister areas Japanese Stiltgrass does the same, and builds up messy mounds of dead grass stems. Unless a catastrophe occurs to upset this new equilibrium, the forest becomes a kind of impoverished dead end with a small variety of taller and fewer trees lording it over expanses of fern dotted with a few shrubs unpalatable to deer.
Paradoxically some trees that are a preferred food manage to survive deer browsing, and American Beech (Fagus grandifolia) is one such. Forest ecologists have suggested that our local hickory-oak woodlands are slowly becoming dominated by Beech and Oak, in part because Beech is so successful in sprouting saplings from the roots of existing trees. It has been suggested that their ability to sprout this way probably evolved as a survival mechanism that enabled thin-barked trees of southern origin to survive forest fires; the above ground part of the tree might burn, but after the flames new shoots spring up from unharmed roots. Often these saplings begin to grow under the canopy of a still living parent tree, and survive in the shade because they are nourished by the parent tree’s roots. This “super power” of theirs also enables them to survive even when heavily browsed. The deer might strip their leaves, but they continue to grow nourished by their parent’s roots until they are tall enough for their buds and foliage to be out of reach. Oaks don’t grow from suckers so readily, so that future beach-oak forest ecologists imagined may, if Beech-bark disease doesn’t intervene, become Beech dominated woodlands.
I believe the situation on Staten Island is becoming critical and that the changes now occurring may be irreversible, at least in our lifetimes. Once the forest balance has shifted toward dry fernland, it can take hundreds of years to re-introduce species that will produce a more humid and varied woodland – if it can happen at all. Once a moist herb layer has dried out because the deer have eaten the understory that shaded it, how are the Touch-me-nots and other plants going to return? We have long known that populations of animal and plants on islands, especially small islands, are particularly susceptible to extinction. Once a local population has been killed off, often there are no others within reach from which to recruit new inhabitants. Well, Staten Island is a small island, but we are very close to New Jersey, and it would not be difficult to imagine plant seeds and animals somehow crossing the Kill – after all, that’s probably how deer reintroduced themselves after they themselves were extirpated by the early 1800’s. However, Staten Island is a patchwork of small natural oases in the midst of a sterile urban and suburban environment fragmented by development, and the Jersey side of the Kill is almost completely industrialized. There are no reservoirs of uncommon native plants anywhere nearby from which to recruit those which are lost. Anything that disappears from our palate of plants (and some animals) will have to be reintroduced by us – nature by itself just isn’t going to be able to accomplish all of it.
But are we going to value our woodlands and grasslands to the extent that we will devote vast amounts of money and energy to restore them as they once were, even if it were possible to effect such restoration? At best we might clear some areas at great expense and replant some of that which has been lost, as in the ongoing major restoration effort of the NYCDPR in Buck’s Hollow – a very, very labor intensive and expensive proposition. This assumes, of course, that we could find viable populations of native plants growing in similar environments to replace those lost species. For the most unusual plants that’s very unlikely; as an extreme case, some 30 varieties of orchids were found historically in New York City, and if I recall correctly 26 of these occurred on Staten Island – now there may be but 8 growing in small and vulnerable populations. Orchids have extremely demanding requirements, and it is unlikely that they can ever be brought back. Lost habitat, not deer, extirpated the orchids – as well as other plants such as Trailing Arbutus (Epigaea repens) – and now deer are putting additional pressure on those that survived.
As you can sense, I’m not a fan of deer, especially on Staten Island; there’s just too many of them for our diminished open space to support. They do have devotees. Who doesn’t admire suddenly coming across these large, charismatic animals in the woods and watching their flashing white tails as they bound away? To be honest, I would too – IF THERE JUST WEREN’T SO MANY OF THEM! What’s the problem one might ask, they were here before the European settlement and now they are back. The island supported their numbers then, and it should be able to do it again. But it can’t. There are no longer large predators and indigenous hunters; there is nothing to control their numbers other than disease, encounters with automobiles and the ability of the remaining open space to feed them. They threaten much of the native flora remaining, and I’m afraid that in part because of them and untrammeled development Staten Island is no longer the great plant refuge in New York city that it once was. Unless the number of deer can be controlled Staten Island is likely to become just another ecologically impoverished NY borough. Unfortunately we have not yet found a solution. Our woods have not been enriched by the advent of White-tailed Deer.