Category Archives: global warming
UPDATE (6/22): Listen to Emily Reddy’s interview with John in Plummer’s Hollow for a news story on our local NPR station, WPSU.
We’ve been honored to host John Davis from the Wildlands Network for two nights in Plummer’s Hollow as part of his epic, 6,000-mile journey to raise awareness of wildlands connectivity — “no protection without connection” — in the Eastern U.S. and Canada. He started in Key Largo in February and hopes to make it to the Gaspe Peninsula by October, traveling by boat, hiking, and biking, visiting as many wildlands in the East as possible. You can follow along via the TrekEast blog on the Wildlands Network website, and/or follow @TrekEast on Twitter for more up-to-the-minute photos and brief audio blogposts.
John pitched camp in the woods up beyond the garage, and uploaded three different audio posts last night and this morning, before getting underway around 7:00. Here are those three posts in the order he uploaded them: Energy Assault (3:04); Woodrat (2:48); Nature and Energy (3:21).
John was one of the founders of Wild Earth magazine and the Wildlands Project, as it was then called, which together played a pivotal role in shaping our own thinking as eco-centric forest stewards, helping us see how our property fit into the larger conservation picture, and making us strong advocates for ecosystem recovery and large carnivore restoration, among other things. So we were pleased to be able to meet John and show him around the property, and compare notes about the environmental movement over the past 25 years. Also, as a long-time blogger and multimedia guy, I must say I’m very impressed by the electronic communications system John and his support staff have set up. He’s an excellent extemporaneous speaker, as the audio posts demonstrate, and also a gifted listener, so if you get a chance to go see him as TrekEast continues, don’t miss it. (His next appearance is this very evening in State College — see the Centre Daily Times for details.)
Let their habitation be desolate; and let none dwell in their tents.
Psalm 69:25 (KJV)
Eastern tent caterpillars (Malacosoma americanum) are a common sight this time of year, especially in their last instar, after they abandon their tents. They stray onto the porches and wander over the furniture, looking for protected places in which to pupate. On a visit this past Monday, my three-year-old niece Elanor decided that they were cute — not typically my own reaction — and began petting them, prompting the caterpillars to arch their heads back like housecats. Yesterday afternoon, I watched one crawling up the neck and across the face of a box turtle, which merely shut one eye while the caterpillar took its measure.
The tents began appearing at the end of April in unusual numbers, especially on black cherry trees, which are the favorite food source for tent caterpillars and occur in unnatural abundance across Pennsylvania due to 150 years of clearcut logging practices and the reversion of old fields and pastures. Black cherry is a common first-succession tree species in many forest types, and thanks in part to its relative unpalatability to white-tailed deer, it can form almost pure stands in many areas that would have formerly hosted oak-hickory, beech-hemlock, or mixed deciduous forests. Here in Plummer’s Hollow, many of our southeast-facing slopes are dominated by black cherry stands, and I figured they’d be completely defoliated by this time.
Instead, Sapsucker Ridge is white with blossoms, filling the air with an ambrosial scent. One finds only a few black cherries as badly defoliated as the one in the second photo; the tree above is more typical. Though dotted with tents, only scattered branches have actually been stripped of their leaves.
A closer look reveals that most of these tents are filled with dead caterpillars. The few still alive twitch spasmodically. What happened? I’d guess that the unusually cold, wet weather over the past few weeks is at fault. Nighttime temperature routinely dropped into the low 40s this month, and sometimes even into the high 30s; daytime temperatures rarely exceeded the mid-50s; and rain was almost constant for the first three weeks of the month. Not only would the cold have shut down their temperature-sensitive digestive systems for prolonged periods, but the rain would have kept them confined to their silken tents, and the two together would’ve made them much more susceptible to starvation and disease. According to the Wikipedia article on tent caterpillars,
The tent is constructed at a site that intercepts the early morning sun. The position of the tent is critical because the caterpillars must bask in the sun to elevate their temperatures above the cool ambient temperatures that occur in the early spring. Studies have shown that when the body temperature of a caterpillar is less than about 15 °C [59 °F], digestion cannot occur. The tent consists of discrete layers of silk separated by gaps and the temperature in these compartments varies markedly. Caterpillars can adjust their body temperatures by moving from one compartment to another. On cool mornings they typically rest in a tight aggregate just under a sunlit surface of the tent. … Later on in the spring, temperatures may become excessive at mid day and the caterpillars may retreat to the shaded outside surface of the tent to cool down.
Entymologist Vincent G. Dethier’s wonderful and evocative classic, The World of the Tent-Makers: A Natural History of the Eastern Tent Caterpillar (University of Massachusetts Press, 1980) describes in Chaper 13 (appropriately enough) the battery of predators and diseases that keep this native insect in check. He details the spread of a deadly virus from colony to colony, then adds:
As if that were not enough the unusually wet late spring had been kind to molds, mildews, smuts, blasts, and bacteria. A particularly virulent spore-forming species of bacterium struck many of the colonies. … The enormous population of tent caterpillars had been cropped by weather, starvation, ants, bugs, parasites, fungi, viruses, bacteria, and misadventure in general. It had been a particularly trying year. Summer had hardly begun and the die had already been cast for the year to come. There would be fewer moths, fewer egg masses, and fewer colonies of the next generation.
So a spring that spells bad news for many farmers is good news for the wood products industry, which relies heavily on black cherry in Pennsylvania. Unlike fall webworms, which come too late in the season to have much of an impact on the trees they defoliate, tent caterpillars can greatly stress the trees they defoliate during their periodic outbreaks.
As global climate change plays hob with our weather patterns, it will be interesting to watch the effects on insect outbreaks, and over the long term, on forest succession. For example, if black cherries continue to predominate as many foresters would like, more-frequent icestorms would have a much greater impact than they would if less brittle species such as red oaks and tulip poplars took their place. Warm winters are said to promote the spread of pest insects, but what about warm winters followed by cold springs? I’d heard that the state was due for some pretty large gypsy moth outbreaks this summer as well, but here in Plummer’s Hollow, at least, their caterpillars are few and far between.
Cross-posted to Via Negativa.
The cover story in the current (Spring 2008) issue of OnEarth magazine, called The Giving Trees, includes some important information about the value of intact, mature forests. The author, Sharon Levy, describes something called the eddy flux method of measuring the flows of carbon dioxide and water vapor into and out of forests. Devices mounted on towers in forest stands measure winds and gas exchanges at incredible levels of detail and accuracy.
For anyone who might be a little fuzzy on the chemistry involved here, Levy offers a brief refresher course:
Plants take in CO2 and harness the energy of the sun to drive the chemical reaction that melds carbon with water, producing the substance of stem and leaf and releasing oxygen. When darkness or drought bring this process of photosynthesis to a halt, plants respire, just as humans do. That is, plants breathe in oxygen and exhale CO2. But over the long life span of trees in an undisturbed forest, huge reservoirs of carbon are stored for great stretches of time in the organic matter in soil as well as in living wood.
Most relevant to Plummer’s Hollow, Levy describes measurements of the intake and storage of carbon done at the Harvard Forest, in Petersham, Massachusetts, starting in 1989. The stand that scientists measured, predominantly an oak-maple forest, had been flattened by a hurricane in 1938. In the first year of the study, the 50-year-old forest was absorbing 0.8 tons of carbon per acre per year.
Previous calculations by ecologists had suggested that a forest of that age should be reaching its maximum ability to absorb carbon, but measurements at the Harvard Forest 15 years later showed that the rate of carbon sequestration had doubled. In other words, a 65-year-old forest absorbed 1.6 tons of carbon per acre per year. Other studies suggest that much older forests may continue to store carbon as they age — the older the trees, probably, the more and more carbon they store.
The idea the author is driving at is that there may be some very convincing arguments, in addition to familiar ones about wildlife habitat and water conservation, for preserving a lot of forest lands uncut. Older forests help in the fight against global warming.
The Harvard Forest is of course not Plummer’s Hollow, but we also own a mostly oak-maple forest. Excluding about 80 acres out of our 650 acres of land, where a savage cutting was performed 16 years ago before we could buy it, and excluding another 70 acres of recent blowdowns, open meadows, talus slopes, and places that have been selectively logged in the last 30 years, we still have at least 500 acres of forest ranging from 80 to 120 years old.
A 15- to 20-acre section of Laurel Ridge inside and above the large deer exclosure is closer to 200 years old, but much of the remaining 500 acres was last cut in the late 19th or very early 20th centuries. Thus, if the comparison to the Harvard Forest is roughly valid, I would speculate that the forest land in Plummer’s Hollow may be capturing 800 tons of carbon per year, and perhaps quite a bit more.
But other than showing that the property captures so many tons of carbon per year, how does this stack up against the amount of carbon we as a family contribute to the atmosphere through our annual activities? A variety of websites provide simple calculators so people can input data relating to their daily lives — home heating, transportation, consumption of goods — and get an estimate of how much carbon they contribute to the global atmospheric problem.
Ignoring the carbon footprint of the Guest House and its occupant, but including our one jet flight this year, the Carbon Footprint Calculator adds together a variety of estimates and comes up with a figure of 14.134 tons per year. The calculator provided by the Nature Conservancy returns a figure of 42 tons of carbon per year. A third calculator shows that we contribute 10.2 tons per year. Averaging those three calculations we come up with 22 tons per year.
The conclusion: our (mostly) healthy, moderately old, primarily hardwood forest offsets the carbon footprint of roughly 36.3 households with a reasonably low-consumption lifestyle like ours. Or to express it another way, we could live 25 times more extravagantly, wasting resources wildly, and still be net savers of carbon simply by preserving our private forest from being logged.
Not to sound greedy, but if state and federal governments are serious about combating global warming, perhaps forest landowners should get tax credits for not cutting their woods, comparable to the subsidies long enjoyed by farmers who enroll arable land in the Conservation Reserve Program.
— Bruce Bonta
“Ah! A rare sighting of the Lesser Spotted Woodland Jellyfish!” says Hydragenic in a comment on this photo at my Flickr site. He’s right. But rare sightings like this will only become more common as global climate change accelerates and all species, even imaginary ones, find their ecological niches suddenly shifting or disappearing. Here in Pennsylvania, we can expect a lot less snow and a lot more ice in the years to come, with possibly devastating effects on native forest ecosystems.
Last weekend’s ice storm was marvelous: the kind that drops plenty of pellet ice first, providing a nice, granular surface for easy walking, and then just enough freezing rain to make things all glittery — or grotesque, as the case may be — without bringing down any trees. My mother was in heaven, since her poor sense of balance and bad back keep her house-bound after most ice storms, and nothing is quite so frustrating to a naturalist as being confined to quarters. The cold weather held the ice for a day and a half, and hoar frost coated the ice on the morning of the second day. (I have a series of five photos taken that day set to appear at my photoblog, Visual Soma, Feb. 8-12).
Now everything’s melted again after two days of unseasonable warmth, and another cold front has blown in. Unlike many folks to the north and northeast of us, we have yet to receive any dramatic snowfalls this winter, which is bad news for shrews, voles, and other subnivean creatures whose population ecology depends on a couple months of the year to reproduce realtively unmolested by the usual battery of predators.
That was the view of Laurel Ridge on the day after Thanksgiving, showing that well over half the oaks not only retained their leaves, but retained their colors, as well. Most years, the trees would be bare by now.
Using freely rooted, field-grown Populus in two Free Air CO2 Enrichment Experiments (AspenFACE and PopFACE), we present evidence from two continents and over two years that increasing atmospheric CO2 acts directly to delay autumnal leaf coloration and leaf fall.
In an atmosphere enriched in CO2 (by ~ 45 % of the current atmospheric concentration to 550 ppm) the end of season decline in canopy Normalized Difference Vegetation Index (NDVI) – a commonly used global index for vegetation greenness – was significantly delayed, indicating a greener autumnal canopy, relative to that in ambient CO2. This was supported by a significant delay in the decline of autumnal canopy leaf area index (LAI) in elevated as compared to ambient CO2, and a significantly smaller decline in end of season leaf chlorophyll content. Leaf level photosynthetic activity and carbon uptake in elevated CO2 during the senescence period was also enhanced compared to ambient CO2. The findings reveal a direct effect of rising atmospheric CO2, independent of temperature in delaying autumnal senescence for Populus, an important deciduous forest tree with implications for forest productivity and adaptation to a future high CO2 world.
“Future atmospheric CO2 leads to delayed autumnal senescence,” by Gail Taylor, Matthew J. Tallis, Christian P. Giardina, Kevin E. Percy, Franco Miglietta, Pooja S. Gupta, Beniamino Gioli, Carlo Calfapietra, Birgit Gielen, Mark E. Kubiske, Giuseppe E. Scarascia-Mugnozza, Katre Kets, Stephen P. Long, and David F. Karnosky, Global Change Biology (OnlineAccepted Articles). See also Why Autumn Colors Are So Late, which summarizes the findings. (Hat tip: Meanwhile, back in the holler.)
Nineteen red-winged blackbirds flew in this morning around 7:30, in the middle of a snowstorm, and joined the other birds mobbing the feeders. This marks the first official 2007 entry in our Spring Arrivals and Blooming Dates list (click on list to magnify). Actually, red-winged blackbirds aren’t a particularly reliable species, since they can show up here on the mountain any time between late February and early April, sometimes well after they’ve returned to the area. They don’t migrate far. They almost always show up at the farm on foggy, rainy mornings in early spring; this is only the second time I can remember them making their first appearance in the middle of a snowstorm. Though one of the most common species in North America, they don’t breed on the mountain, so they’re always a bit of a novelty for us. Sometimes we see large flocks of them in the autumn, too, but in general they stick to the valleys.
The snow tapered off by 11:30 a.m. We got six inches of powder in all. Snowy, wintry Marches have become the norm for us in the last ten years or so: winters tend to start in mid- to late-December and continue through March. That’s a shift of at least two weeks from the 1970s, when I was a kid. This is one of the reasons we’ve kept such careful records of spring arrivals over the years — to help document the seasonal shifts associated with global climate change.