An Oikos of Relationship
Of course I was delighted to unwrap the heavy Christmas gift, obviously a book of some density. And I was especially glad to open it up at random pages there amidst the wrapping paper and see the wonderful glossy images of nature for which National Geographic is famous. What I didn't expect was to become so enthralled in the text--of a 300 page book about Africa, a companion to the PBS series we missed not having television. Ann had seen me at the computer, zooming down to the points of interest on Google Earth that show and tell tantalizing details from the recent extended aerial and ground exploration of the Dark Continent. Santa brought me a version of Africa I can view from the chair in front of the woodstove. There is nothing like the feel of a good book in your hands on a cold winter night.
I've only just begun to savor its pages. To do so makes me ache for the immersion in biology topics that I've recently left behind. The older I get (and I find that happening rather consistently) the more I feel the urgency to follow my heart and speak my mind. I can follow, and I will. But I can't always speak on this page without feeling the constraints of benign censorship when the topic becomes colored with threat or conflict on global issues. Nature-at-risk is not a popular blog topic, even--or especially--if the threats are real and relevant to our children's future on this beleaguered planet. Even in the blogging world, the politics of 'environment' raise the red flags related to the 'who owns the land' issue. But Nature-at-work seems neutral enough. So let me leave this digression and tell you what I wanted to tell you before my typing hands took control of this blog post.
Listen to this: the trees are talking.
One early anecdote from the book describes what has probably become a cliche, an image in our minds from the African savanna that is this: giraffes in exaggerated slow-motion strides feed among the widely-spaced, flat-topped Acacia trees. But there is more to this image than meets the eye. Or the human nose, for that matter.
The giraffe only nibbles a few leaves from the top of each tree, and then moves on--a pattern of feeding that seems energy-inefficient. But this here-and-there snacking is not the giraffe's idea but the tree's. Upon being nipped by the animal's first bite, the tree responds almost instantly by changing its inner chemistry of defense. Within less than a minute, its leaves produce tannins (a bitter substance common in oak bark and acorns as well) that can reach lethal levels. Of course this gives the leaves an off-flavor after a few bites, so the giraffe moves on. But even then, he may remain hungry for some time until he moves away not only from this nibbled tree but from this grove of trees.
The tree that has been attacked raises a danger signal to other acacia trees by emitting ethylene gas--the same gas that causes fruits to ripen more quickly in a paper sack on your kitchen counter. The gas blows down-wind, and within a short while, unnibbled trees 150 feet away have also stepped up their tannin production. A giraffe succeeds in feeding only on about one tree in ten. And so the giraffes are fed, and the trees give up only as much as they can afford so that they live to grow new leaves to sustain just enough but not too many nibbling herbivores.
If there are more vignettes like this one in the three hundred pages I haven't yetturned, there will likely be more 'book reports' in the weeks ahead. But I know I can expect that, in the ecology of human relationships on this massive continent, the story is not one of such beautiful balance.