The Carnivorous Habits of Christmas Trees By RON SULLIVAN Special to the Planet

Tuesday November 29, 2005

We don’t have a lot of eastern white pines (Pinus strobus) in Berkeley. There are lots of domestic cultivars—weeping, or tall and narrow, or bluer than the usual—and if I’m remembering correctly, it’s the species Mom and Dad used to get for the Christmas tree when I was a kid in Pennsylvania. That was partly a matter of tradition, I guess, but also because its soft needles weren’t hazardous when we were all hanging ornaments and tinsel. 

But I don’t see it much in landscapes here, probably because it prefers well-drained, slightly acid, humusy soil and cool humidity. It dislikes city air pollution, too, but in its own range, it’s quite tough. Maybe we should leave it there. 

I already get alternating jibblies and schadenfreude when I sit on the front steps opening the mail and listening to flies buzzing in despair as they’re digested alive by one of Joe’s pitcher plants, sundews, or Venus flytrap. I really don’t want to walk the streets thinking I might be attacked by some malicious tree from below as well as from above. 

Turns out that this innocent Christmas tree of the northern forests is a carnivore. And it gets its prey underground. 

Of course it isn’t that straightforward. What’s going on with white pines, as John N. Klironomos and Miranda M. Hart of Ontario’s University of Guelph found out and published in Nature in 2001, is a refinement of the mycorrhizal web, a mostly invisible and still-mysterious part of that big web of all life on Earth. Many, maybe most plants growing in their native habitats benefit from—and are part of, really—a soil network of living things, largely fungi, that connect with each other and with plants via the growing bits of the root systems. 

Fungi aren’t plants, by the way. I’m fascinated to learn that they have cell walls, like plants (we animals have cell membranes) but that those walls are chitin, like shrimp shells—which I’d thought of as an animal thing. It’s like finding your doppelganger in the Antipodes—honestly, how can anyone be anything but thrilled by what Darwin and his successors have been discovering anew with every generation, the literal kinship of all life? 

And with mycorrhizae, the literal connection of huge communities, we discover the functioning of whole forests as a single superorganism. That part’s not quite news: people have been selling and buying and surreptitiously moving mycorrhizae into their gardens and bonsai pots for years. People have also realized that disturbing or destroying this web is one of the things that trigger invasions by weeds, exotic plants like star thistle and pampas grass, plants out of place that push out natives and make sites effectively useless for the local animals and plants that depend on the original plant community. Plants not interwoven with the web can then “outcompete” the plants that were part of the original, now ruptured, living polity. The originals have effectively had part of themselves amputated. 

What white pines are doing in their home forests, it turns out, is being part of a more active feeding process than anyone had thought. Nitrogen from de-caying animals—“animals” here includes bugs and even nearly microscopic stuff like springtails, centimenter-or-so-long arthropods that feed on decaying matter in leaf litter and soil—is a well-known plant nutrient. 

The news is that pines and their “fungal partners” in the mycorrhizal web might not be waiting for something to die before digesting it. (Picture an impatient vulture.) Laccaria bicolor, a fungus that joins with white-pine rootlets in the forest, has been shown to actively infect and kill Folsomia candida springtails in the soil, and even seems to inject a paralyzing agent into them. It then “barters” the nitrogen of the springtails for carbohydrates from the pines’ root hairs, a well-known step in the soil nutrient exchange. 

Many of us have a dream of being laid to rest under a tree when we die, contributing our remains to the life and substance of the tree and so living on in the world. It’s just a little unsettling to think that the peaceful plant community might not passively wait for us.