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Archive for February, 2007

Crow’s Nest: Student Research–“How to Conserve Native Plants More Effectively”

The Senior Seminar in Ecology last semester at Bryn Mawr College made use of Crow’s Nest Preserve for fieldwork and as a case study. The focus of the class was the value of ecosystem services—those functions that support human life and well-being but are not usually commodities bought and sold: clean air and water, erosion control, climate regulation, and pollination.

The work brought up the importance of collecting raw data from the preserve: it would be difficult to know too much about a place!

Daniela Miteva wrote a study entitled How to Conserve Native Plants More Effectively that included an effort to estimate the monetary value of the native plants at the preserve as well as predictions—using flower and bee abundance data—of the impact of habitat disturbance and fragmentation on the native plant communities in Crow’s Nest’s meadows.

The benefit of the native plant habitat includes intrinsic values of its ability to support wildlife, manifest biodiversity, and contribute to the relative stability of an ecosystem. The report also estimated the value to Natural Lands Trust of the native habitat as a place to host environmental education and research projects, and to promote hiking and walking, bird and wildlife watching and nature photography. The study also estimated the value visitors place on the preserve (how much are they willing to pay to travel to get here) and the increase in market value of homes located near protected open space.

The study also accounts for management costs to maintain natural areas: that minimum intervention to keep a meadow open and free of invasive plants. It doesn’t, however, make an attempt to quantify future benefits (with inflation) of open space protected today.

The part of the study that most affects our land management is the flower and bee abundance surveys. One of the conclusions is that the factor that most affected native bee abundance is the presence of forested sites within 2,300 meters; these provide the bees’ nesting sites.

Fortunately Crow’s Nest’s meadows are embedded in a matrix of forested areas; the study also suggests that loss of surrounding continuous forest habitat could increase management costs here long-term.

The study also concluded that bee species diversity is most affected by frequency of mowing. Most of our meadows are mowed once per year to control invasives and keep them open. But sites that had the greatest number of different bee species were sites that had not been mowed for 2 – 3 years, so it may make sense for us to have more "reserves" of less-frequently-mowed areas, something I have begun to experiment with this winter.

Crow’s Nest: Three Colors

WinterIt has been a beautiful winter, a landscape in only three colors: the white of the ground and of the sky, the gray of the trees, and the tan of grasses and dead oak and beech leaves clinging to the trees.

We had a taste of mud season last week, and when it returns it is going to be fierce. People were getting stuck in their own driveways.

Crow’s Nest: Student Research–“An Evaluation of the Ecosystem Services Provided by Beavers”

Beavers have long had a commodity value; this research seeks to identify this and other values associated with them. Rebecca Donatelli conducted her research last semester on the value of beavers for their role in flood reduction, erosion control, water quality, and habitat diversity. We have had a population of beavers on French Creek for a number of years, at the preserve and beyond.

BeaverchewingI have long heard that the geomorphology—the very shape of the landscape we live in: rolling hills surrounded by wide, fertile valleys—is a direct result of beavers, including the now-extinct species of giant beaver. The valleys are here as a result of eons of beaver dams trapping sediment followed by a period of abandonment when a forest re-colonizes the site.

Sediment falls out in the relatively still waters behind a dam; since excess sediment is the number one pollutant in Pennsylvania streams this is a major benefit to humans because it offsets flood control and water treatment measures that would otherwise be necessary. The report also suggests that there is more microbial activity decomposing organic matter in beaver flowages. There is a decrease in available nitrates, phosphorus, silica, and aluminum ions and sulfate.

BeaverdioramaBeavers are called a keystone species because their habitat manipulation influences what other species inhabit a site. The slow-moving open water behind a dam is also warmer and encourages some wildlife: geese, mallard ducks, frogs and toads, and pileated woodpeckers all make use of beaver flowages. Wood ducks are mainly found where there is beaver activity; they make use of cavities in the trees directly over water for nesting.

The report also suggests that beavers need a 150-foot wide corridor around the stream in which to carry out this activity. The photo at top is of recent chewing on a tree along the banks of the creek at Crow’s Nest; note that they also chewed through the poison ivy and Virginia creeper vines! The lower photo above is of a diorama of beaver habitat the kids at the daytime WebWalkers program are making this winter.

Crow’s Nest: Student Research–“The Economic Value of Deer Hunting as an Ecosystem Service”

Bryn Mawr student Louisa Smythe wrote her senior project on deer hunting, evaluating the impact of hunter spending, use of deer for food, potential reduction in rates of the human Lyme disease (of which deer are an alternate host) and deer-vehicle collisions, and reduced damage to crops, timber, and residential and nursery plants.

Densities of deer populations increased dramatically in the twentieth century causing a high level of damage to heavily browsed vegetation. The report cites figures from the Pennsylvania Department of Agriculture on the economic cost of deer damage to timber, agriculture, and the nursery industries. High deer densities also can diminish the value of the habitat for other wildlife. And Lyme disease, caused by the spirochete Borrelia burgdorferi and transmitted by infected ticks of the species Ixodes ricinus, has high rates in Pennsylvania and Chester County in particular. (According to the Chester County Health Department there were 660 reported cases in 2005.)

Ms. Smythe surveyed hunters to determine how they spent money on hunting, how they used the deer for food, and gathered data on time spent hunting and success rates. She noted the benefits of outdoor recreation and hunters’ financial contributions to conservation but made no attempt to quantify them.

The report then uses rates of human infection, deer and human population size, and calculations of the cost of treatment at four stages of the disease to estimate the economic savings of lower deer densities for Lyme disease. A similar analysis was also done for deer-vehicle collisions.

Like all of these reports on the values of ecosystem services there are factors that are difficult to quantify and assumptions that limit the applicability of the results. But the studies also highlight how interrelated are the species around us, and the environment in which we live.

Crow’s Nest: Student Research–“Carbon Sink Potential in the Forests of Crow’s Nest Preserve”

James Pena, a Haverford College Student enrolled in the Senior Seminar in ecology at Bryn Mawr, wrote a paper last semester that estimates the volume and value of carbon sequestered in the trees growing at Crow’s Nest Preserve. A little global background from his paper is necessary here:

The carbon cycle describes the change in carbon from four places: geological (fossil fuels), oceanic, terrestrial (plants & trees), and atmospheric. These are listed in order of decreasing size.

Any place that releases carbon—a net decrease in stock—is a "source" and any place that has a net increase in stock is a "sink."

Trees are sinks because they uptake carbon through photosynthesis from the carbon dioxide in the air. Some of that is returned to the air through cellular respiration but half is converted to sugars, starches, and cellulose and stored in the above- and belowground biomass. Significant carbon storage also occurs in forest soils, particularly in the older growth woods that aren’t sequestering relatively as much carbon in rapidly growing young trees.

Estimating the rates of carbon sequestration is much more difficult to do in a diverse, natural forest than it would be in a plantation. In a plantation all the trees are the same species and age and the carbon sequestered is the largely same in each. Research at other forests has used a process called the eddy-covariance technique to measure net ecosystem exchange (NEE) of carbon each hour. Since this is measuring the reduction of carbon dioxide in the air around the trees it is not based on an estimate of the size or growth rate of the trees.

Mr. Pena drew upon these published rates of carbon sequestration in similar forests—particularly the Harvard Forest in Massachusetts—and applied it to the conditions found here at Crow’s Nest Preserve. Based on our 158 hectares of forest area (1 hectare = 2.471 acres), and the estimate of +/- two tons of carbon sequestered per hectare per year, our total carbon uptake at Crow’s Nest is about 315 tons per year. That’s about enough to offset the yearly emissions of 70 average U.S. cars.

To put a monetary value on that uptake, this service can be thought of in terms of carbon credits. Carbon emissions reductions are now traded on a market and have a range of $5 to $12 per ton of carbon dioxide emissions. Based on these figures the value of the forests at Crow’s Nest as a carbon sink range from $1,575.62 to $3,781.49 (U.S.) per year. However there are some regulations that would have to change before forest conservation projects qualify for the trading of carbon emission reductions. For more information about these figures go to the Ecosystem Marketplace.

If you have questions about this or any of the research being conducted at Crow’s Nest please contact me.

Crow’s Nest: More from the tractor seat

Farmers all know this, but perhaps other people don’t: John Deere (the person) never built a tractor. He lived from 1804 to 1886, before the motorized farming age. Nevertheless he arguably was a key figure in farming mechanization, since his company first manufactured self-scouring cast-steel plows, originally horse-drawn, that till and turn the soil. This was an early part of a transition from pastoral farming techniques to modern mechanized farming, with all of its simultaneous benefits and problems.

Even though our tractor (which we use for mowing, not plowing) can take a much sharper turn than a car, our four-wheel drive tractor doesn’t turn quite as easily as the old narrow-wheel row-crop tractors. Ours does has the right- and left-hand brakes that help the tractor pivot, but this is more effective on plowed soil than on the wildflower meadows we mow—the pivot can “turf” the vegetation down to bare soil.

So the pattern I choose when I mow meadows minimizes the turns the tractor has to make. Sometimes this pattern is a series of ever-narrowing concentric circles around the field, spiraling down until just the middle is left. This is the way we mow the lawn here, but that is with a zero-turn walk-behind mower. With the tractor those last few stripes require a series of three-point turns, or backing up over some distance.

With some of the fields I instead apply a lesson I learned from watching a Zamboni ™ dress ice at a rink. The first pass goes up the center then loops around one side, and then the oval loops—each is the same size—keep moving across the rink until all the ground is covered. At either end the ground is mowed multiple times, but the tractor never needs to stop, reverse, or do a three-point turn.

Instead of Science FICTION…

This Friday evening will be our second movie night at Mariton.  We are featuring two videos from Dr. Ron Goor and the folks at NatureFlix Productions.  These are educational videos, but are also entertaining to watch.  (You probably won’t be screaming, "Don’t go down in the basement!")

"How Birds Eat" will be shown first.  It looks at physical adaptations (bills, feet, etc.) as well as behavioral adaptations that help birds find food.  It features some wonderful wildlife photography.

Following a break, we will watch "Insect Defense".  A great companion to the first film, "Insect Defense" demonstrates different ways that insects have evolved to avoid becoming food.  This film stars some intriguing looking insects that were made for the camera.

Each film is about 30 minutes long.  We will start at 8:00 p.m. on Friday.  If you plan to attend, please call Mariton at 610-258-6574.  We will have popcorn and lemonade and want to plan accordingly. 

From the tractor seat

Our tractors have come a long way in the fifteen years I’ve worked for Natural Lands Trust. In the “old days” we were using old two-wheel drive tractors that lacked rollover protection—often what came with a farm when we protected the property. The tractors lacked power brakes so it was essential to choose the correct low-enough gear when mowing down a hill. Too high a gear and the tractor would run away with you. We still use gears to determine working speed, but it’s nice to know modern brakes could stop you if you need to.

Four-wheel drive also offers a major safety advantage: most tractors are safer when they are pointing face-front down a hill; they are far less likely to flip over forward than backward (or sideways). But a two-wheel drive tractor cannot back up a steep hill easily, for example when you meet an obstacle ahead, or you’re mowing a slope above a pond, or you need to get to the top of the hill again to mow the next strip of field. The vehicle weight transfers to the front wheels backing up a slope and two-wheel drive tractors, even with ballast, may just spin their rear wheels. Four-wheel drive allows you to use the vehicle in the safer face-downhill orientation.

TractorOur tractor is twelve years old, and yet has just 1,200 hours on it. That’s not a lot compared to a farmer’s, but we get a lot of utility out of it. In addition to mowing meadows and trails with it, we move loads of wood chips for the trails, haul logs from hazard trees and load them on the sawmill, rip out old fences, and use it to lift other things too heavy to lift by hand.

Yesterday I spent a few hours on the tractor: one job was one where I would rather drive over the hard snowpack than sensitive turf: I moved six loads of horse manure from our neighbors’ barnyard to our compost pile.

Plastic_lumberThen a delivery of recycled plastic landscape timbers arrived and I used forks on the tractor’s loader to help get them off the tractor-trailer. We’re going to use these timbers to build raised beds for the teaching garden. Raised beds offer many advantages to garden plants and the recycled plastic lumber should last a very long time and won’t leach toxic chemicals into the soil.

Each landscape timber contains 350 recycled milk jugs. So that stack contains 13,500.

I finished the morning by mowing a little more meadow. It felt like very productive time spent.

Heavy Snow

Have you shoveled any of your Valentine’s Day snow?  Did you think to yourself, "Boy, I must be getting old, this feels like a ton."  Well, that’s what I thought with the first couple of shovels that I moved.  Then I remembered that there was several hours of sleet and freezing rain sandwiched between those layers of snow.  So, that 4" of snow had a lot more moisture in it than you would think.

When all the snow and ice in my rain gauge melted, I had 1.36" of water.  By itself, that would be a large rain event.  Under the right conditions, that could have yielded over a foot of snow.  (Of course, that would be light fluffy snow.)

Okay, I am getting old, but this makes me feel better.  That much precipitation on a 12" X 18" shovel weighs just under 11 pounds.  Scoop 100 shovels and you have moved 1/2 ton.  It makes me feel old just thinking about it.  So, don’t try to shovel all the way down to the sidewalk.  Take the snow off in small slices, either horizontally or vertically.


The snow from the Valentine’s Day storm is easy to cut into blocks.  We received snow and then sleet and freezing rain, followed by more snow.  The sleet and rain holds everything together, as you will discover when you try to shovel it. 

Anyway, it is perfect snow for making igloos.  As a kid, we would make wonderful snow forts with this kind of snow.  (It was worthless for snowmen or snowball fights.)  We would make a snow knife out of 1/4" plywood, or a scrap of aluminum siding.  Then we would lay a snow block wall, just like a masonry wall.  After we had a wall to block the wind, we would start the other walls and tie them all together.  Shoulder height was a good place to stop.

We didn’t have the skill or patience to arch our walls inward, like you would with an igloo.  In hindsight, that was probably a good thing.  (At least, we are all still alive.)  Instead, we would scrounge for wood scraps, or even cut pine boughs to make our roof.  We would end up with a cozy little clubhouse.  It was a good place to rest after tromping around the woods and fields.  Of course that was in the "good old days" when parents had to drag kids indoors kicking and screaming.  So, we had little shelters and leantos scattered around the countryside.  That way, we could stay outside when it was dangerously cold.

Building an igloo or snow fort with your kids is a great family project.  You can do it in your backyard.  You can do it in the evening, after work and dinner.  A plastic tarp will make a quick roof.  Then throw a tarp, or old rug on the ground.  Once you have your shelter built, the whole family can squeeze inside and listen to the wind howl outside.  Bring a candle or flashlight for light.  Now that’s entertainment.


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