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Protectors of Pine Oak Woods · Current
Issues · High Rock |
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Forest Restoration at High Rock Forest Restoration #177, March
19, 2011 On Saturday we returned to do further invasive removal to the Red Dot Trail below High Rock Parks administration buildings. Our regulars were again a little “thin”; Dom had recently undergone rotator cuff surgery and although he had declared that he would be present and “still had one good hand,” he was probably wise to stay away, and Chuck could not come to both Saturday’s restoration and Sunday’s semi-annual meeting. On the other hand, Jacky, one of our new numbers showed up with Gabriel Willow from New York City Audubon in tow. Together with Elaine C. and John H, we made a small crew of five. We had planned to remove two small, dense stands of Aralia elata (the Japanese Angelica Tree, better known to us as the alien version of the Devil’s walking Stick), but as I have previously related we have been instructed not to remove any more until the Department of Parks can give us clarification of recent NYC law regarding tree removal. Instead we trolled the trail looking for shrubs or saplings encumbered with Japanese Honeysuckle and Oriental Bittersweet. I didn’t know whether to be disappointed that we didn’t find a lot of saplings in obvious need of rescue or to be happy that our efforts and that of other volunteers in the past had left the trail pretty clear. We proceeded to pull or cut away honeysuckle, and used weed hooks to yank whatever Multi-flora Rose and Japanese Barberry we could out of the ground. The dense stands of rose that were there in the past are almost gone or at least much thinned out. There was so little that we might bump the frequency of our Red Dot Trail visits to once every two years or so. We did encounter a large Japanese Holly (Ilex crenata) and several clumps of Burning Bush (Euonymus alata) that we would normally remove from the park, but given the current uncertainty about removal of woody plants, we left them alone. The alien Devil’s Walking Stick has been a bit of a bugbear for me. There are spots in the Greenbelt where its numbers recently have increased astronomically, such as along the unmarked trail that leads from Moses Mountain up toward Seaview Hospital. My fear is that if we continue to ignore it, it will become so extensive that only heroic efforts will be able to bring its numbers down. By then manual control such as Protectors does may be ineffective and the choice may become whether to ignore it or to resort to herbicides. In truth, because of the vast area infested by Aralia elata, there is really little hope that we can accomplish its total removal. The best that we might do is to keep its numbers down in sensitive forest areas by removing as many sprouts as possible before they become mature enough to seed. There is always a chance that some other reasonable way to suppress it will be discovered, and to that end many people look to biological control rather than mechanical eradication which would require the application of considerable manpower or herbicides that can be destructive to the environment. We often hear the remark that a search should be made for some kind of biological agent, some insect or fungus or other plant pathogen that can be introduced at little cost and will do the job without supervision. An insect herbivore or pathogen that feasts only on elata would be ideal and one might think that the perfect antidote probably resides somewhere in its native land. Control of an invasive pest by introducing something antagonistic into the environment has been known to work and has the virtue of probably being both low cost and low tech, but this technique has been known to go horribly wrong too. Before introducing something that might attack Aralia elata, one would first have to find that such a enemy exists, and then - a incredibly more difficult task - make as close to 100% sure as possible that the new found enemy would cause no harm except to elata, or at the very least that the harm it caused was acceptably less than that of just leaving the elata alone. A successful example of biological control - as far as we know - was the introduction a century ago of a species of ladybug to the citrus groves of California where they speedily controlled a scale insect that was causing a great amount of fruit damage. In a similar way an Asian ladybug was introduced about forty years ago to pecan orchards in the southeast to control aphid infestations. These ladybugs and a similarly introduced European relative did a fine job on the aphids, but also on numerous other non-targeted insects. They quickly spread up the coast and inland across the Mississippi, and are implicated in crowding out the New York native Nine-spotted Ladybug, now extirpated in the state. Although much research has been devoted to biological control agents for agricultural pests, only recently has there been much research done to examine the collateral effects that introduced pathogens have on native plants and the community of animals that depend on them, but that research has highlighted that there can be many unforeseen consequences. European weevils introduced to control Canada Thistle (Cirsium arvense) in pastures in the US quickly became at home in open, non-cultivated fields and just as happy to feed on the buds of native thistle as the Canada Thistle that was their target (despite the common name, that thistle didn’t move south from Canada, it is a Eurasian import). In another instance, a South American moth that was successfully introduced in Australia to control Prickly Pear Catus which had become invasive in pastures (it must have worked wonders, the Australians subsequently erected a monument to the moth), was used for the same purpose in the Caribbean and from there made its way to the US southeast where it is beginning to destroy our native Prickly Pear. Regarding moths, on winter hikes we very infrequently find large, webby cocoons of caterpillars of the “giant” silkworm moths in the family of large moths called Saturnids. In former years naturalists frequently found their cocoons, and since the caterpillars have been found able to feed upon a large number of different trees one would expect to encounter them often in the forest. Should the leaves of one type of tree be in short supply, the insects can always lay eggs and their caterpillars feed upon some other. As for the adult moths themselves, I myself have only seen two alive in the past eight years; one a Luna Moth - like that in the Lunestra commercials - in grass on the blue Trail, and a Polyphemus Moth with prominent eye-spots on its rear wings on a Brooklyn sidewalk beside a Lowes parking lot. I had supposed that this was because the moths were naturally uncommon, and because I am rarely in the woods on Staten Island in the evening in seasons when they might be flying. Then I read in Bernd Heinrich’s Summer World that some years ago in the Northeast he was accustomed to find hundreds of cocoons of the giant Promethea Moth (Callosamia promethea) each winter on Ash and Cherry trees but that in recent years, even with the help of ecology students scouting the woodlands, he often found none at all. He traced their decline to the Gypsy Moth (Lymantria dispar) outbreaks in eastern forests in the 1900's, when thousands of acres of forest were sprayed with insecticide to control the spread of the moth, and later when, in what seemed to be a more ecologically friendly solution, there had been a shotgun release of a variety of biological control agents. Two of these agents were a parasitic fly and wasp that laid their eggs on developing caterpillars or the pupas they formed when they were transforming into moths. When the eggs hatched, the wasp and fly larvae literally ate the caterpillars or their pupas alive from the inside. Unfortunately the giant silkmoth caterpillars appear at the same time as the Gypsy Moth, and the parasites don’t discriminate. I am not crusading against biological control of unwanted pests; I’m just recognizing that such introductions often have unforeseen effects and must be must be tested with great care. The interactive network of living organisms is so complex that I suspect we can never be certain of all the results of our interventions. Indeed, most of the time we can only see what happens at the gross level - to the big, dramatic animals and plants that are visible with the naked eye. Nobody much studies what happens to tiny organisms such as the tiny invertebrates that live in streams or in soil litter when new, larger organisms are introduced into their environment. The list of unforeseen consequences is constantly growing; a new field guide I’m reading recounts how tiny freshwater shrimps from the far north were purposefully introduced to hundreds of northern lakes because it was thought they would become a good food source for fish and thus better support sport fishing. Unfortunately these shrimp avoided the higher layers of the water column where larger fish occurred and instead stayed further down where they competed with young fry for food and even ate newly hatched fish! Intervention is indeed complicated... - - - Following the work session we took a leisurely stroll around Loosestrife Swamp to see what was going on. Spring Peepers were calling there loudly all through the day, and small water striders that had hibernated overwinter darted over the water’s surface where they make their living by capturing and sucking the juices from small insects that happen to fall in. The water striders are so light that their feet, covered with minute hairs, allow them to rest on the surface of the water without breaking through the force of attraction that molecules of water at the surface have on each other. The weight of these tiny bugs dimples the water’s surface tension, but isn’t enough to allow them to break through. Next time you see them on a sunny stream, notice how the dimples focus light on the bottom so that one can count their legs and even tell which legs are supporting the most weight by the size of the dimples. The middle pair of legs is used as oars to scull across the water, and makes the biggest dimples; the two small front legs are used to seize prey and detect vibrations in the water from insects that have fallen in and have been caught by the water’s surface tension. Vibrations in the water also let them sense the presence and activity of other water striders. (They seem to be perfectly happy to be cannibalistic, so being sensitive to one’s neighbors probably has significant survival value!) Since it was early spring there was little algae or mold growing in the water; there was no wind to make ripples and no recent rain run-off to roil the bottom so the shallows were crystal clear, and if we positioned ourselves in shadows so that we weren’t looking at reflections we could clearly see details below the surface. At the small bridge at the outlet of the swamp Gabriel Willow began to turn over submerged leaves until he uncovered and fished out a hellgrammite, the aquatic larva of a Dobson Fly or, perhaps an Alder Fly. These are peculiar looking creatures, having 3 pairs of legs like all insects, and a series of leg-like protrusions along their abdomen that in the Alder Fly serve as an organ in place of gills with which to absorb oxygen from the water (the larvae of Dobsonflies - which as adults are fierce-looking flies several inches long - have the same protrusions with the addition of small tufty gills). These predacious larvae live in the water beneath the layer of leaf litter, and capture their prey with a pair of stout curved jaws, in the case of a Dobson Fly capable of giving an incautious finger a strong bite. They may take a few years to mature, but eventually these larvae will crawl onto land to pupate and change into their adult form - a dark, awkward, net-winged fly that in mid-summer can be found flying by the water’s edge where they will lay a large quantity of eggs on grass or other vegetation overhanging the water. Fishermen prize these larvae as bait; impaled on a hook they are said to be almost irresistible. The thought of fish reminded me that about six years ago I was surprised to find 10 or so dead fish in the stream just below this bridge. It didn’t occur to me at the time, but now I wonder if someone hadn’t tried unsuccessfully to introduce them to the stream there, or if Parks had treated the swamp with rotenone or some other piscicide that killed the fish. Loosestrife swamp is a prime breeding area for Spring Peepers, but once fish move into a pond, the small amphibians often disappear. Fish find the frog eggs and tiny tadpoles to be very tasty, and the frogs either gradually die off or find some other place to breed. (that’s why so many amphibians breed in ephemeral pools; although they have to complete their development to adults before summer dries the pools, they are not subject to predation by fish). Despite the fact that Spring Peepers were VERY vocal Saturday, trying to follow their calls I, as usual, couldn’t spot a single one of these tiny spring singers. In fact, every time I have spotted one it was because someone else with sharper eyes pointed them out. These are small tree frogs, and like all tree frogs have little suction-cup toes that enable them to cling to the surface of leaves, although now they probably would be found low on vegetation beside the swamp. Mostly a grey-green in color, they are easily identified - if you can spot them - by a pair of darker crossed lines in the form of an “X” on their backs. This is reflected in their biological name Hyla crucifer, which translates as “cross-bearing frog.” If you want to hear what these serenaders sound like without looking for an appropriate pool in the breeding season, you can try this web site which has recordings of the various frogs found in New York State: http://nyfalls.com/wildlife/Wildlife-reptiles-frogs.html. At the far end of the swamp where trees had fallen in the spring storms Gabriel turned over several rocks to expose two tiny Red-backed Salamanders (Plethodon cinereus), one each of the reddish striped form and the slate grey form. Red-backed salamanders belong to a group of salamanders that have no lungs or gills, and have to breathe through their skin. For this reason they have to keep their skin moist and can be found only in wet places beneath stones or leaf litter, from which they will come out to hunt at night when they are less likely to dry out. After a look-see, Gabriel replaced each rock and then released the salamanders in the adjacent leaf litter (that was reminiscent of walks with Clay Wolney who takes great care not to harm the animals he finds; he constantly reminds the kids to put the stones or rocks back as they found them, and to be careful not to crush the creatures they have exposed). Unlike some other salamanders, Red-backed Salamanders are terrestrial and don’t have to find suitable pools in which to breed; they deposit their eggs in damp spaces beneath rocks and rotting logs. For this reason they have become one of the most widespread and common salamanders in the Northeast, and possibly the only kind of salamander left on Staten Island. The salamanders’ thin and moist skin, necessary to allow passage of oxygen into their bodies and waste gasses out, also makes them very sensitive to chemical pollutants. Like frogs, they are another kind of “canary in the coal mine,” their presence telling us the waters are pure, and their absence warning us of environmental problems. Pollutants may be why so many different salamanders have disappeared from Staten Island, but it is equally likely that some have disappeared because their habitats have become too fragmented for them to survive. Those that require ponds and streams to breed have seen much of the wetlands filled in and built upon, and stream channels covered over and run into culverts. When ponds become too few and far between, it is difficult for these creatures to replace any small, local population of these creatures that die out from one cause or another. Other salamanders that could repopulate may be just too far away. Fragmentation of habitat may be a similar problem for plants as well as these small animals. Those plants that depend on seed dispersal by birds or mammals can often repopulate areas from which they have disappeared, given that the habitat hasn’t changed so much that it has become inhospitable. Consider again the Japanese Angelica (Aralia elata, the alien cousin of our Devil’s Walking Stick); we may pull it out, but as long as there are other trees within the range a bird can fly before it defecates, tree seedlings will show up again. Wind dispersed seeds also easily re-establish a plant where it might have died out; those who resent Dandelions in the yard don’t need a reminder of that! Some plants have evolved a strategy of being dispersed by small insects such as ants, however, and these are much more vulnerable to fragmentation of their habitat. Soon Bloodroot will be blooming in Bloodroot Valley, and it’s a good example of seeds are dispersed by ants. As the seeds in the Bloodroot seedpod mature, they develop a gooey crescent along one edge that is nutritious and attractive. They general name for this kind of seed structure is an elaiosome. There’s a great close-up photo on Flickr if you want an example: http://www.flickr.com/photos/pcoin/523765454. The ants haul the Bloodroot seeds into the granaries of their mounds, and consume the nutritious elaiosomes. The intact remainder of the seed finds itself buried in a good position to grow when the nest is abandoned and safe from being eaten by other insects. The ant method of seed dispersal is not uncommon; botanists have estimated that such seed dispersal occurs in 17% of the families of seed-bearing plants in the world, and Wikipedia claims that over 11,000 species of plant produce seeds with elaiosomes. But these seeds usually don’t travel far. Marielle Anzelone, a local botanist who is an ardent proponent of wild-flower preservation, says that on average the seeds are moved only 2 meters (about 6-1/2 feet) from the parent plant. If, as in the case of our wildflowers, plants succumb to being crowded out by invasive species or are extirpated by being overly collected in a particular spot, they may not be able to return. Our woods and fields are increasing gridded by ever widening roadways, and although ants may easily migrate across, they are not so likely to forage and carry seeds across from the other side. An awareness of problems like this and the repeated sight of squished animal bodies where our roads pass through woodlands or fields are a reminder of the value of protecting out woodlands and other natural areas from un-necessary fragmentation. That’s all for this month. In April we’ll meet again at High Rock Park to go to the unmarked trail between Moses Mountain and Seaview where we will remove vines from shrubs and saplings. ...hope to see you there. DfR 3-26-11 |
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