You can spend all the time you want having academic discussions in offices, but when it comes to field work, you've really got to go have a meeting in the field.
For those of you who don't know, I'm in New Zealand studying an invasive tree, Pseudotsuga menziesii, better known to most of you as Douglas-fir. Doug-fir's also known as "Oregon" around here in New Zealand because it's found all across that state back home. It's actually one of my favorite trees -- I adore the Pacific Northwest, and though Doug-fir wasn't part of my Juneau experience, I've subsequently seen it in British Columbia, been surrounded by it on the Olympic Peninsula, and spotted it all over Oregon and California.
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| Douglas-fir growing happily in the rainforests of Olympic National Park. |
Unfortunately, as they say, one man's meat is another man's poison. In New Zealand, Douglas-fir has been widely planted since the mid-1800s for forestry purposes. It grows fast (particularly in this country) and produces excellent wood. One of the best documents I have on the natural history of Douglas-fir in New Zealand comes from the Forestry Research Institute -- and it's all about how to locate seed for your plantations, what types of slopes have been sown, when to harvest, etc. etc.
Douglas-fir isn't the only non-native tree that's been introduced to New Zealand. In particular, pine trees (you name it, we've got it: Corsican Pine, Lodgepole Pine, Bishop Pine, the list goes on) were used both in forestry plantations, and especially for erosion control. Native forests in this area (primarily Mountain Beech, Nothofagus solandri var. cliffortioides) are extremely slow to come back after fire, so managers planted pine seedlings on all the steep slopes that were bared by land-clearing fires.
As those of us from fire-prone areas with native pines (like New Jersey's Pine Barrens) know, pines quickly take hold after fires, when the canopy has been burnt away and there's lots of sunlight. Pines will often also invade the grasslands nearby (also plenty of sunlight), which is what they do here in New Zealand. There's a whole management question about this grassland invasion: The grasslands are man-made, the product of tremendous land-clearing efforts. They're filled with species introduced from all over the world. Yet they're familiar. Should we work to maintain them, and prevent the spread of an invasive species? Or should we accept the pines as the first step in the return of New Zealand's forests?
You see, pines are quite particular. They'll rush into open landscapes with lots of light, but they can't regenerate under their own canopy because it's too shady. They also won't invade native forests -- also too dark.
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| Douglas-fir seedlings establishing in a grassland. |
But Douglas-fir is a different story. Its seedlings are shade-tolerant, able to establish in the shadow of adult trees and either grow slowly with glimmers of light, or wait for a tree to fall, opening a gap in the canopy through which the sapling can shoot up. So unlike the other introduced trees, Douglas-fir poses a real threat to the existing native forests.
And we're starting to see the threat become reality. Yesterday, Ian, Duane, Jess, and I had our "field meeting" in a beautiful mountain beech forest near Craigieburn, about an hour and a half away from Lincoln. Nearby, an old Douglas-fir plantation was thriving -- and raining seeds into the native beech forest. The beech canopy was speckled with Douglas-fir seedlings, and we passed many a gap in the canopy crowded with up-and-coming "Oregon" trees.
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| Duane and Ian lead us into a beautiful Mountain Beech forest. |
Yet the seedlings are not ubiquitous. While this site was a prime example of ongoing invasion, Douglas-fir hasn't been so successful elsewhere. And much of its success has come in the last few years, even though these plantations have existed for decades.
Why?
We think it has something to do with belowground biology. Most trees -- indeed, the vast majority of plants -- rely on fungal partners called mycorrhizae, which gather nutrients from the soil and deliver them to the tree in exchange for energy stores the tree produces via photosynthesis. These tree-fungal mutualisms can be highly specific: for example, we know that at least one species of pine requires co-invading fungi from its native range in order to spread.
Perhaps Douglas-fir (known to associate with a particularly wide array of fungal partners back home) can associate with native New Zealand fungi, allowing it to establish under native canopy. Or perhaps the critical native fungus has finally arrived.
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| Amanita muscaria, a particularly charismatic, but unfortunately non-native, mycorrhizal fungus. |
If we want to preserve New Zealand's native forests, this is the sort of question that we need to answer. Sooner rather than later.
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