The tenth episode of Planet Earth brings us to the biological communities I think of as “home” — seasonal forests. I grew up in rural Pennsylvania, with second-growth deciduous woodland literally in my back yard, went to college within sight of the Appalachian Mountains, and spent my first “real” job in field ecology surveying understory plant diversity northeast of Pittsburgh. Today, I’m working on the other side of the continent, but now studying some of the most widespread tree species in forests from the Pacific Northwest to the Yukon taiga. I could almost illustrate this entire recap with images from my personal Flickr stream.
I’ll try to resist the temptation.
We start at what is, arguably, the most seasonal of forests, taiga, where the growing season may last just a month. These snow-covered woods seems marginal, but boreal forests account for one third of the trees on the planet, Sir David Attenborough tells us. The newest comprehensive assessment of tree density worldwide, published last year, found that a median hectare of boreal forest has as many, or slightly more, trees than an average hectare of tropical forest — but it also puts the boreal share of the global tree count at closer to one quarter of all trees, and finds that “tropical moist forest” accounts for a slightly larger share.