5-23-09 Stress and stressors; introducing two perspectives on stress in ecolgoical systems

First, I want to thank my friend Rebecca Oreskes, Public Service Staff Officer for the White Mountain National Forest, and Thomas Wagner, Forest Supervisor for the WMNF, for giving me permission to conduct research on “soil development and plant succession” at the 1954 Mt. Garfield landslide site on the Gale River Trail this summer. That’s very cool and I'm appreciative of their time and consideration.

The next couple of entries focus on stress or stressors in plant communities. The stressor is significantly different in each entry. The first paper is titled “Timberline” and was written 75 years ago by Bob Monahan who was, some of you may remember, one of the founders of the Mt. Washington Observatory and who we’ve introduced earlier in the blog. He is also the author of “Mt. Washington Reoccupied”, published by Stephen Daye Press (Brattleboro, VT) in 1933; in which he describes in detail the first year of the "new" Obs and accompanies the narrative with outstanding photos.

The second entry is on Beech Bark Disease (BBD) that’s killing American beech (Fagus grandifolia Erlh.) throughout the White Mountain National Forest and in a broad swath extending from Nova Scotia, and Quebec southwards to West Virginia. BBD is a major stressor in the eastern Boreal forests as it is slowly eliminating one of the defining tree species of this extensive forest ecosystem. BBD was introduced to North America from Europe coming ashore in a shipload of European Beech seedlings destined for a city park in Halifax, Nova Scotia in the late 1800s. It’s actually two stressors in one: a tiny insect called Beech Scale, or Cryptococus fagisuga that bores into the bark of the beech trees. Then, along comes a parasitic fungus called Nectria cocina var. faginata that moves into the tiny hole made by the scale. A second closely related and less prevalent fungus, Nectira galligena, also infects Beech in the same range as the Nectria cocina.

Monahan was affectionately known as “Gramps” by those who knew him. I took this photo of him (he's on the right) with George Hamilton at a party celebrating George’s retirement as AMC huts manager way back in August 1966. Bob was the Dartmouth College Forester at that time.

Monahan’s paper was actually his thesis at Yale Forestry School in 1930. A few years later he helped re-established the Mt. Washington Observatory (MWO) on the summit of Mt. Washington. The thesis was shortened so it could be published in “Appalachia”, the journal of the Appalachian Mountain Club. The paper appeared in Volume 19 of “Appalachia” in 1933 (it begins on page 401). I want to particularly thank Becky Fullerton, librarian at the AMC prestigious library at 5 Joy Street in Boston, for helping me retrieve this article.

It’s tempting to scan the entire paper because it’s excellence in a couple of areas. First, it’s well written. It’s clear and concise (in comparison to mine). Second, it’s as a model ecological monograph of the phenomenon we refer to as Timberline, or sometimes “tree line”, it’s pure science and for that reason alone it is a good read from cover to cover. The paper covers the ground well, literally and figuratively, as an excursion along the timberline but also across the area above timberline we refer to as the alpine zone of the Presidential Range. He analyzes the role of each of the stressors that impact plant communities at their highest elevations on mountain slopes.

“Timberline” is a perfect follow up to Andrew Riely’s paper that appears earlier in the blog and talks about the world record wind of 231 miles per hour measured at the Mt. Washington Observatory in April 1934, and also explores the impact (stress) wind has on the White Mountains and mountains in general.

Looking at stressors in biological systems is fascinating because stressors usually define boundaries, the edges of things (like the timberline). Stress tests the equilibrium in all systems. Ecology is, generally speaking, the study of stress in living systems over time. It is, in some ways, similar to medicine as the study of stress in the human body. Humans have a good idea what stress is and how it impacts us. As a psychotherapist most of my work is studying stress in humans and creating strategies for mitigating it. I try to use an ecological perspective in which I separate stressors the way an ecologist does. The illustration above is a clinical tool I use to help my clients recognize and deal with the impact of their stress.

I’m using the term “stressor” as a way of introducing the concept of “tension” within ecological systems. In Bob Monahan’s paper the stressors are an interweaving of variables, all which have the potential to cause stress in diverse plant communities trying to grow at the limt; at high altitudes. The evidence that stress is occurring is the “timberline”. It represents a boundary, or edge, or limit. Stressors run the gamut. They can be ephemeral like an early or late freeze, a temporary drought, an insect infestation, or something large like a continental glacier and possibly permanent like Global Warming. A stressor is pretty much anything that disrupts the dynamic within the status quo or equilibrium (or homeostasis).

In Darwinian terms either you die or adapt to certain stressors. Plants have adaptive strategies for stress. Several years ago a number of experiments conducted by plant physiologists became newsworthy because they provided dramatic evidence that some trees can communicate with each other. The research showed that trees are sensitive to stress and as an adaptation to a stressor have developed a mechanism to communicate information about the stressor to neighboring trees as a kind of warning. One study involved trees responding to an infestation of Gypsy Moth caterpillars and demonstrated that trees could communicate with other, nearby, trees alerting them to the approach of the insects. The communication was in the form of an aerosol that the stressed trees dispersed to neighboring trees. It was described as a stress related response.

Jack Schultz was one of the researchers and he made observations in a large grove of red oaks (Quercus rubra) growing over several acres on the Pennsylvania State University campus. By wrapping some tree limbs with huge plastic bags he was able to isolate the aerosol the oaks were using to “warn” the other trees of a gypsy moth caterpillar infestation. The question, or one of them, is whether the warning is an adaptive response by one tree to the stressor, or is it an altruistic attempt by one tree to warn others of the impending threat.

After conversing with Schultz I did my own research of this mechanism because the idea that plants could “talk” to each other was exciting. I remembered those 8th and 9th grade science fair projects where three tomato plants or geranium are placed in separate rooms for a few months and each is subjected to different sounds. One sound was an awful scrreeching noise. The other plant listened to rock music constantly and in the third room the plant listened to Beethoven’s late string quartets. At the science fair we got to see the results and of course the plant that enjoyed Beethoven was thriving while the others were at near-fatal stages of stress. This experiment was supposed to prove that plants have feelings. We know plants are highly sensitive to a number of stimuli primarily light including the absence of light. Maple sugar producers know that sugar maples trees can be very sensitive to both sunlight and temperature in late winter. For instance, on a good sugaring day with the temperature around freezing the sap stops dripping instantly when the sun is behind a cloud and then commences again when the sun comes back out. This is really a thermal effect but it feels as though the tree is waiting for the sun to come back out from behind the cloud.

In the small experiments I conducted I used mixed species tree stands and I found that there’s definitely a connection between stress in individual plants and a rapid increase in phenolic chemicals in leaves of nearby trees that will deter predators to an extent. More recent research has broadened the discussion regarding communication between individual plants and blurred some of the earlier research with extenuating circumstances including some experiments that showed that it was not the predator stress that trees were responding to so it’s not quite as elegant as first thought. The newsworthy research helped the public become aware, however, that plants are sensitive

I refer to small local stressors “perturbations”. It might include the upheaval sometimes caused by snow avalanches, the destruction caused by a landslide, or damage from an average sized hurricane in which trees have been torn up and toppled. An exception would be a storm the size of Hurricane Katrina that caused major stress in a number of ecological systems. According to a Washington Post article published on November 7, 2007 Hurricane Katrina killed 320 million trees as it swept across Louisiana and Texas. It wasn’t the wind that killed the trees; it was the large scale flooding. The cause of death was drowning.

While plants can’t jump out of the way of an oncoming stressor, animals have that edge: mobility. Some, like humans, even have social groups for mutual aid but in a lot of cases animals do not fare well with stress. Some animals go into a nosedive when stressed beyond certain thresholds just like humans do perhaps because of psychological implications.

Beech Bark Disease represents a stressor larger than Katrina in scope. It, too, has most likely killed millions of beech trees over the past 100 years. The time dimensions of the stress increases it’s impact exponentially because it tests the resiliency of the species under attack. Time, in this case, is double edged. If there more time a number of plants might adapt and this may eventually be the case. As it is, though, the only thing favoring the survival of the beech is that some individual trees seem to have immunity, or at least a resistance, to the beech scale. This may be a prior adaptation, or not.

In the same 100 years, or a little more, in which we have seen Beech in the northeast area of North America die-off we have also witnessed the destruction of a tree closely related to Beech, the American Chestnut (Castanea dentata) from Chestnut-bark Disease as well as the American Elm (Ulmus americanus) that has been compromised by Dutch Elm Disease. Humans introduced all these diseases to North American. At the present time other tree species in North America are threatened by imported, “invasive” predators. The Asian Long Horned Beetle (Anoplophora glabripennis) (ALB) is one of the more recent introductions and was first identified in NewYork City in 1996 and is now know to be in areas of Massachusetts and southern Canada. It is a threat to all hardwood species growing in northeastern North America. The soft wood species, Eastern Hemlock (Tsuga Canadensis) is threatened by the Wooly Adelgid (Adelges tsugae), an Asian import, that was originally found in the Pacific Northwestern area of North America in the 1920s had now moved to the east coast and has infested trees in both New Hampshire and Vermont.

So that’s not very good news. And even though some of the players are new the mobility of infestations and infections within species and between species is not. Human's mobility to every corners of our beloved planet has repeatedly given invasive species a free ride to a new environment where they die, live marginally or find a place to thrive. It is provident that a lot of these “accidents” cause slight harm, but in others, as with the Asian Long Horned Beetle, there is possibility of catastrophe.