Читать книгу Mutual Aid - Pablo Servigne - Страница 15

Imagine a beautiful sunny valley where snow-capped peaks stand out against the blue sky, overlooking a mix of multicoloured meadows and dark forests. In these forests in North America, it is common to see two species: the whitebark pine (Pinus albicaulis) and Rocky Mountain fir (Abies lasiocarpa). But – ecologists ask – how do these two species get along? Do they tread on each other’s toes or, on the contrary, do they need each other?

Across the valley floor, the distribution of pines and firs is random. Researchers have also noticed that when a pine tree dies, the neighbouring fir trees grow more healthily. In other words, the trees seem to hamper each other. You could say they’re in competition. Nothing unusual about that: we all imagine the forest as a place where the trees overshadow each other and where the small shoots have to make their way up to the light, or die.

Science is fully aware of this: for more than a century, ecologists have observed these interactions. These ecologists are steeped in the classical theory which, in the ecology of communities (of plant populations), gives pride of place to competition. However, on rare occasions during the twentieth century, a researcher would occasionally observe something odd: for example, that in some places the grass grew better under poplars. But nobody really paid any attention, because it didn’t fit into the theory.

Let’s return to the cohabitation between pines and firs. It was in the 1990s that the team run by Ragan Callaway, an ecologist at the University of Montana, started to take an interest in these ‘exceptions’. The researchers compared the situation of trees at the bottom of the valley, an environment where life is good, with the situation on the mountainsides, at a certain altitude, where living conditions are much more difficult.¹ What a surprise! At altitude, things were utterly different: not only did the firs grow only around pines, but, when a pine died, the surrounding firs fared less well… These trees compete when living conditions are good, but help each other when they become tougher (in cold or windy weather, poor soil, etc.). Until then, people had seen only half the picture.

Callaway and his colleagues were the first to take these observations seriously in plants and measure them accurately on a large scale. For more than twenty years, they travelled the world and accumulated experimental data, published in major international scientific journals,² which show the extent of mutually beneficial relationships between plants (which they call ‘facilitation’).³ Quite enough to radically change our vision of the world!