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Arnold Arboretum

Dangerous trees

May 16, 2011 by Cam Webb

The general health of our team members has been good, but two have been suffering from serious dermatitis caused by exposure to the sap of trees in the Anacardiaceae—the poison ivy family. Trees in this family are common in the forest, and exposure is hard to avoid. It does seem like these cases were caused by handling collections and by sniffing the slashed bark, a standard practice to help identify the tree (more on the smell of trees in a later post). Anacards (as we call them) usually ooze a sinister black sap from cut parts that warns one not to get too close. The tree that team member Pak Manto sniffed, however, was a Buchanania that has a watery brown sap, easily mistaken for less troublesome species. Severity of reaction to the tree’s toxins (urushiols) varies greatly from person to person. I’m fortunate in seldom getting a reaction, but it appears that repeated exposure increases the likelihood of a reaction and one day I may also be unable to touch these wonderful trees. Pak Manto’s face swelled up and he was unable to sleep for a couple nights. In the end, he went down to the village clinic, believing he could be cured by an injection they offer there. They probably administered a steroid injection to quell the intense itching, but the rash that follows exposure to urushiol is the result of an immune reaction and cannot be treated—it must run its course over a couple of weeks. He’s back from the village now, but clearly still bothered by the itching.

A moment of irreverent levity following the relief of still being alive as the wind storm begins to pass

Probably the most serious danger in the forest is being hit by a falling branch or trunk. The canopy is full of dead limbs precariously held aloft by vines. Most of the time, being in an equatorial position out of the zone of tradewinds, the forest is windless; but occasionally there are strong winds associated with convection storms. When a wind comes, it is accompanied by snaps and thumps as leaves, twigs, and branches snagged in the canopy come crashing down to the ground. This is a time to pay full attention to one’s surroundings and to find a place to stand that is not below a vine tangle or dying tree. Once or twice a year there will be a very strong wind, when even healthy trees might be blown down. Right at the beginning of our project, when we were surveying the B plot on the crown of a hill, we experienced just such a wind. It kept increasing in strength until the canopy above was a swirling mass of flailing limbs. Leafy branches were transformed into silvery skeletons as the leaves were flattened along the twigs. Forty-meter trees swayed back and forth through as much as twenty degrees, looking more like giant blades of grass than solid woody organisms. Our excitement turned to fear and from fear to panic as we searched for a place to hide, but in a forest there is nowhere to hide from falling trees. Ultimately, we found a large rock on the side of the  hill to protect us from being crushed. The windstorm lasted for about twenty minutes before dying away, only to be followed by a drenching rain. While truly concerned about being flattened, I was also entranced by this awesome demonstration of the power of the natural world. It was one of those moments when you are forced to recalibrate your perception of your physical permanence in this large, wonderful world.


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