The total forested area on Earth is 4.06 billion hectares. 90 million of those hectares, of which 92% are publicly owned, are in a province of Canada called Quebec. It’s a vast area of trees, twice the total area that’s within Sweden’s borders. 1 out of every 45 hectares of the world’s forests are in Quebec, and yet of the ~100 000 species of trees on our planet, only about 50, or 1 in 2000 are native to Quebec. Why is there so little diversity of trees in this province?
According to a recent analysis, climate is the most important factor in determining tree diversity, and the highest number of tree species can be found in the hot, humid tropics. Why? Possibilities include a 365-day growing season which allows ample time to reproduce and recombine genes; higher mutation rates from UV and more isolated niches are my guesses. At latitudes between 45 N and and 63N, there is nothing remotely tropical about Quebec. Its lower latitudes accommodate temperate forests, but north of that is a large area featuring even longer and colder winters. These northern latitudes have the bulk of Quebec’s woodlands: the boreal forest. It is a flat area where genes don’t get isolated easily; the growing seasons are short and speciation of trees suffers. Dominating a vast forest are only five main species. Which one gets the edge partly depends on whether or not the soil retains water: white spruce is found mainly on well-drained upland; black spruce is in the damp lowlands. There is also balsam fir, jack pine and the American larch.
But why do its temperate forests only feature about 40 native deciduous species? The area that is currently temperate was completely covered by ice sheets during ice ages. During periods of glaciation, trees can survive but only in valleys. These are isolated from one another, reducing genetic drift between trees of different valleys, facilitating the formation of different species. But in Quebec, the few mountains existing in the south are too eroded and too low in elevation to block off advancing ice and to shelter the valleys.
Given that we tend to be attached mostly to the trees we grew up with, and since in Quebec’s case, the lack of tree-biodiversity is perfectly natural, I am comforted by the fact that all of its native species are familiar to me.
The genera that have the most Quebec-native species are Acer(maple) with 6; Populus (poplar) with 5; Betula (birch) with 4 and Quercus(oak) with 4. But among the eight genera that have only one lonely representative in Quebec, Rhus typhina, the staghorn sumac is one of my favorites. Elsewhere in the world, there are 200 different species of Rhus ! The staghorn reproduces both sexually and asexually by spreading seeds and rhizomes , respectively. The latter create clones, with older shoots in the middle and younger ones around the mother plant. It’s why sumacs proliferate so easily among the cleared area under hydro towers where they often coexist with wild grapes. It’s only in recent years that I realized that both wild grapes and sumac fruits are edible, although it’s best to use them to make a sweetened drink (red sumac berries) and jam (wild grapes). Sumac belongs to the Anacardiaceae family, which includes interesting warm-climate trees such as the mango (a south Asian native), cashew (of Brazilian origin) and pistachios, originally from Iran.