The stony ground and prominent rock formations of Pound Ridge in Westchester County, New York elicit curiosity in many people, some of whom attended our recent guided hike focused on geology. I will summarize our tour of the geologic history that can be seen at the Bye Preserve, owned by the Pound Ridge Land Conservancy (link to map and directions). Trails at the Preserve are open everyday from dawn until dusk.
Imagine that your arm represents geologic time, with your armpit being the Big Bang and the tip of your middle finger representing today. The dawn of life occurs just above your wrist. Between your wrist and the middle of your palm, all of the bedrock that shapes this land was formed by a process known as the tectonic cycle: erosion of mountains, deposition of materials in layers, subduction (movement of the earth’s crust), and volcanism. There was something on the earth’s crust prior to the formation of our bedrock, of course, but we cannot see evidence of that now. Geologists have discerned that an ancient Acadian Mountain Range once rose east of us, to the height of the Himalayas, and then eroded into particles that were later metamorphosed into our bedrock. Add folding from the movement of tectonic plates, deformation by glaciers, and erosion, and you have a punctuated record of history etched on the landscape.
In its western half, the Bye Preserve is underlain by Fordham gneiss, which formed in the Precambrian era, 1.1 billion years ago. This layer measures up to 500 feet thick and is extremely resistant to weathering. There are many kinds of gneiss, and it is variable in color from brown to buff and can be pink or green. Fordham gneiss contains quartz, biotite mica, silicates, garnet, and other minerals. Bedrock along the eastern side of Bye belongs to the Hartland Formation, which is half as old and is a mixture of gneisses, schists, and amphibolites. It formed when shales and sandstones from a deep ocean metamorphosed and retains its layers of alternating color. Many of these rocks were inverted when the Hartland Boundary Fault displaced older layers and brought in new rocks.
Subsequent to the last great tectonic shifts in the Paleozoic era, the bedrock at Bye has endured at least four episodes of folding and associated metamorphism, which is visible in many rocks where layers are curved rather than straight. The first stage of folding produced large ENE-WSW trending ridges and valleys, while the second stage trended NNE. Later stages produced tight folds that reoriented earlier folds. Where rock is resistant to bending, brittle faulting may occur, which produced the Mill River Gorge just northeast of Bye Preserve and the Mianus River Gorge as well. In the midst of these changes, magma intruded the bedrock at Bye and produced a very pretty white-to-pink granite that is rich in quartz and mica.
More recently in geologic time, between your furthest knuckle and fingertip on our imaginary time scale, the glaciers of the Ice Age left their mark. An ice sheet more than one mile thick ground back and forth across this landscape for nearly 100,000 years in freeze/thaw cycles. Each advance brought in new rock from afar. Each period of retreat caused mass deposition, flooding, and a rise in sea levels. Bye Preserve is now only ten miles from the Long Island Sound and was at times submerged by ocean, although fresh water has played a greater role in carving this landscape. We can see evidence that great torrents once ran in the boulder fields that line two now-intermittent streams, scouring away soil such that even today, only ferns and moss grow there.
The last glacial ice disappeared from Pound Ridge about 12,0000 years ago, leaving behind piles of sand, rock, and even huge boulders on the surface of our scoured bedrock. These are the clues from which we can piece together millions of years of history on the land. To end our story, I invite you to sit with a favorite rock and to ponder what it has endured to bring you both to this moment in time.
Sixteen people attended our end-of-year Saturday morning work session at Halle Ravine and helped to remove old bridges from deep in the Preserve. Students and seniors, mothers, and dads all carried out boards and even one entire bridge, as shown in this video. Together we are stronger! We leave the forest, stream, and trails in better shape after much work in Halle Ravine in 2016. Projects are ongoing to control invasive species around the pond, with planting planned for this Spring. We also plan to replace the decking on one or more bridges next year. Be in touch to lend a hand!
Forests in Pound Ridge and surrounding areas are under siege by one of the gentlest of animals, the white-tailed deer. Deer are keystone herbivores and eat from five to seven pounds of vegetation per day. In summer, deer dine richly on the buffet of tender plants provided by home landscaping. In winter, our subsidized deer herds turn to the forest to browse buds, tender saplings, and even tree bark. At ideal densities of 10-15 per square mile, deer browse checks the growth of plant life without hindering forest regeneration. At higher densities, they can strip the understory bare. With deer density in Pound Ridge as high as 65 per square mile, we face the loss of wildflower species first, and then the pollinators that depended upon them, and then the birds that can’t find shelter or food, and finally, the forests themselves as trees are not replaced.
Is the situation really so dire? Scientists and natural historians have documented all of these effects, including our friends at Mianus River Gorge who found that tree sapling diversity in a local protected forest decreased from 15 species to 4 over the last thirty years, due to overbrowse by deer. Local land managers seek solutions, but first we must know our problem. I will describe here a simple method for assessing the level of deer browse in virtually any patch of forest in Pound Ridge. Rather than counting deer or deer density, we are going to measure the effect of deer browse on each plot and use that as a baseline that guides future management. This methodology was developed by Thomas Rawinski of the United States Forest Service, who shared his knowledge and skill with us in a training session this summer.
We begin by choosing a site for our study plot(s). The circular plot covers 100 square meters and must include at least ten measurable saplings of one of the indicator species. Measurable means that the sapling is still below the average browse line and therefore vulnerable. Indicator species include any browsed species with beech and sassafras preferred followed by the shrubs; maple-leaf viburnum, sweet pepperbush, alternate-leaf dogwood, red elderberry, choke-cherry, and even the invasive burning bush. I do not mean to imply that deer prefer these plants – rather, they avoid them – so that browse levels reliably indicate the severity of deer pressure on forest growth.
Once the indicator plant has been selected and the plot margins delineated, we set out to find the ten tallest measurable saplings of our chosen species. Then we average those ten measurements to find the definitive “tallest” for that plot. In itself, this doesn’t tell us much. Over time though, we can discern trends and hope to associate those with management actions. We can also make comparisons among plots to measure relative levels of browse across landscapes. For example, Sugar maples at Armstrong were browsed down to 8.9 inches, while those at Halle measured 8.1 inches. Deer pressure may be more severe at Halle than it is at Armstrong.
We can avoid the costly and time-consuming task of measuring deer density by using this simple approach to assess deer impact on our preserves. We will measure again next year and compare our findings both within PRLC holdings and with a larger community of land managers and report back to you then.
For more information, please see http://www.na.fs.fed.us/pubs/2014/NA-IN-02-14_WhitetailedDeerNEForestsWEB.pdf
Twenty-three people attended our guided geology tour of Bye Preserve on Nov. 12 and saw firsthand how history has shaped this land for the last 1.1 billion years. Stay tuned for a summary and photos of what you can find on your next visit.
A dozen community members assisted in native plant restoration at Halle Ravine at our most recent Volunteer Work Session on October 1. A lively group of students, neighbors, town officials, and PRLC board members spent the morning working on and off trails in the north end of the Preserve and along the steep bank of the eastern side of the ravine. They cleared invasive weeds, planted a variety of native plants that will better support wildlife, and fenced valuable trees and shrubs from deer browse. Our aim is to encourage more shade cover in the Preserve to protect soils from erosion and drought and to provide for the needs of animals. Come out for a tour with us next summer and see the results!
We also completed the installation of a new staircase along the steepest section of trail in the Preserve. Help is still needed to carry out construction materials and begin bridge repairs, so please join us on Saturday November 5, 10am-noon to lend a hand.
These projects were supported by funding from the Land Trust Alliance Conservation Partnership Program and by private donors.
We had a great turnout for the mushroom hike at Armstrong Preserve on October 23, 2016 and turned up some interesting finds. The most distinctive was a single specimen of the Dog stinkhorn, Mutinus ravenii, so-named for its shape and strong odor. We also found a few edibles, noted in the captions below. Please use caution when foraging for wild mushrooms and refrain from eating any that are not verified by an expert. Please also note that collection of mushrooms, along with plants and animals, is not permitted on Pound Ridge Land Conservancy preserves except during our guided hikes. If you would like to join our email list to be notified of future mushroom forays, email PRLC’s land steward or call our office at 914-205-3533.
Thank you to our event participants for the photographs, and happy hunting!
Mycophile or mycophobe? Most people fall into one of these two categories, being either mushroom-loving or mushroom-fearing. European and Asian cultures are generally mycophilic, passing on knowledge of favorite edibles and medicinals, along with hunting grounds for finding them, from generation to generation. Americans tend to mushroom-phobic, being more concerned with the potential for toxicity, or perhaps simply lacking in knowledge due to the shorter history of our culture.
In this installment of the Living Lighter on the Land blog, I will provide a brief overview of fungal life forms in hopes of inspiring you to take another look, for this is the time of year to find them. I also encourage you to join our Guided Walk and Talk in search of mushrooms, scheduled for September 21st. Please email me to register for this free and family-friendly event.
Mushrooms, or fungi, are an exceedingly diverse group of organisms whose taxonomy and biology are bound by certain genetic contraints, which is why they can be described as comprising a kingdom of life. They are known as the decomposers and are vital to ecological processes such as nutrient cycling. By transforming matter on the molecular level, making it available for trees and plants for example, mushrooms support all life on this planet.
Fungi come in forms both familiar and not, from the molds on our food to the classic polka-dotted parasol to vast networks of underground hyphae or mycelium. They generally reside in the substrate upon which they eventually “flower,” or more accurately, fruit. What we see are highly modified extensions of the hyphae which are formed in order to disperse spores, or reproductive cells, into the environment. In this way, harvesting mushrooms is akin to picking berries from a bush.
Mushrooms can be divided into categories based upon their growth forms, and knowing these groupings is a first step for any budding mycologist:
Slime molds Sac Fungi Puffballs Jelly fungi Corals Bracket Fungi Boletes Gilled
Like plants and animals, fungal species have specific habitats and substrates that they are best adapted to and which provide clues to the kinds of fungi we can expect to find. Most mushroom identification guides include keys to identifying species, and these will include details on growth form and environment, in addition to physical characteristics of the mushroom itself.
When I find a mushroom that I would like to identify, I take immediate note of the following: the substrate upon which it grows, surrounding trees, fruiting habit (single, scattered, or clumped), and color, odor, and moisture level of the mushroom itself. At home, the first thing I do is make a spore print: break the cap off (if there is one) and lay it gill- or pore-side down on a sheet of paper. It works best to use a half black/half white sheet of paper, laying the mushroom down in the center, so that white or black spores show up against the contrasting color of the paper. It might take a day or more for the spores to drop out.
While I wait, I make note of the following characteristics of the mushroom’s form (a good field guide can help to familiarize you with descriptive terms used for each factor):
cap diameter, shape, edge, surface texture and color
gill attachment, spacing, color, thickness, depth, and margin
stalk size, shape, texture, color, hollowness, ring structure, cup structure
There is quite a lot of information that goes in to identifying a mushroom to species, and sometimes the differences between them are so subtle that genetic analysis is necessary. Don’t be discouraged! The joy of mushrooming is in experiencing the wonder of their ephemeral form and their place in nature. With practice and the help of other mushroomers, you might one day enter the world of foraging fungi for food and medecine. I recommend joining on-line groups such as Facebook’s Mushroom Identification Forum, as well as groups that meet in-person for forays, such as the Connecticut Westchester Mycological Assocation (COMA).
All photographs courtesy of the author.
The Pound Ridge Land Conservancy is committed to allowing dogs on our preserves, but we need you to keep your dog on a leash.
We have had some incidents that could have been prevented if the dogs had been leashed. In addition, dogs going off trails because they are not leashed can cause significant unintentional damage to the plant growth we are trying to protect. During hunting season (October 1 – December 31), roaming dogs can interfere with deer control efforts as well.
Your cooperation will enable us to keep our preserves dog-friendly.
Volunteers continued to make trail improvements at Halle Ravine this summer and are about halfway done with the staircase project on the eastern side of the ravine. At our next work session on October 1, hands are needed to carry materials to/from the worksite, including plants that will be used to remediate the steep and easily eroded banks. We have made great progress in the conservation of Halle’s ecosystem through control of invasive species, particularly Wineberry, Asiatic bittersweet vines, and Japanese barberry, and now we turn our attention once again to Burning bush, aka Winged euonymus. These troublesome woody plants outcompete our native flora, taking up valuable space, light, and nutrients, but don’t provide the same level of ecosystem services as our native plants do. Controlling invasive plants requires diligence and we are grateful to our volunteers for their assistance. Please join one of our upcoming work sessions, October 1 and November 5, to learn more about what you can do on your own property, including what plants you can foster to support native biodiversity and protect water quality.
PRLC concluded another successful intern season this year with an evening presentation on August 17th at the Armstrong Preserve and Education Center on Route 121 in Pound Ridge. Snowden and Olivia each presented a slideshow of photographs, maps, and charts documenting their work in our preserves this Summer, garnering much praise from event attendees. Our audience included parents, community members, PRLC board members, and staff and leaders from local partners, the Pound Ridge Conservation Board, Westchester Land Trust, and the Rusticus Garden Club. You might have seen this article in the Record Review! Check back to see their work on our updated web page this fall, or better yet, take an easy hike on the trails at Armstrong, Bye, Carolin’s Grove, Clark, Halle Ravine, Richards, or Russell Preserve. What you won’t see are the invasive species that they cleared this summer!