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Ellen McCallie's Diary

Day 10: Earthquakes

This was a great day. If every day were like this, I would do television forever.
Challenges were given and I ended up needing to determine when the last major earthquake in this area occurred. This seemed impossible until we got a look into the equipment box — tree corers. That's a major clue.

Photo: Site of landslideFor at least the last 15 years, New Zealand scientists have been worried about their forests. In any given forest here, most all of the canopy trees — the trees that "reach the sky" — are old and about the same age. This is unusual. Most of the time you find trees of all different ages making up the canopy. Thus, a mature forest in the US can have canopy trees from 50 to several hundred years old. That doesn't seem to happen here. First, the common tree species are long-lived (500 to 1000 years old) conifers. Second, they don't survive well as saplings in the understory waiting for a mature tree to die, so they sprout, grow for a while and then die waiting to get enough light to become canopy trees. But why are the canopy trees in an area all about the same age?

Scientists worried for a while that New Zealand forests must be dying — that all the forests were made of old trees that weren't regenerating. Then someone started aging the trees. Most of the trees in a stand were about the same age, given or take 50 years. And the dates at which these tree stands began corresponded to several years after major earthquakes in New Zealand. Viola! It isn't that the forests are dying out, but that earthquakes are major factors in shaping forests here.

Basically, New Zealand earthquakes are big, and they cause massive landslides that can wipe out entire areas, especially when combined with raging rivers. So, the rock and gravel carried down by rivers after massive earthquakes decimate previous forest, covering it with gravel and rock. It is in this new substrate, "soil", that new trees start to grow, all at approximately the same time — soon after the earthquake.

If we can figure out the age of these trees, we'll know the approximate date of the last big earthquake. We are looking for the absolute oldest tree in order to be the most accurate.

Photo: Ellen and Kate tree coringIn picture-perfect weather, Kate and I went helicopter hiking, as they call it around here, to find a piece of land out of a big river's normal flood plain, but within range of a mighty river carrying earthquake landslide wash. We found such a place, and was it exquisite. I'd never been in such a wet, mossy, old conifer forest before. Kate joined us for half of the day. She and I took tree cores.

I came bouncing back to our base, pleased as pie and ready to count rings. This will be really tough as slow growing trees have narrow growth rings, which makes them really difficult to count. At least I am working with plant material — beautiful, interesting plant material. The question remains, did I get all the way to the center of the trees?

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Photo: Ellen McCallie
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