What's happening to Yosemite's big trees?

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    Giant sequoias at Yosemite National Park in California.
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The giant trees on the West Coast are awe-inspiring, but surprisingly, they haven't really been studied much over the long term, notes Peter Bowes of BBC News. The reason?

Unlike studies with smaller plants and almost all animals, no individual scientist is able to track a forest giant for its entire lifespan - from germination to death. They live for hundreds of years and play a vital role in the ecosystem long after they have died.

To remedy that situation, James Lutz of the University of Washington and his team – with the help of volunteers – have set up  an open-ended project to monitor a 62-acre plot in California's Yosemite National Park that hasn't burned in the past 70 years. First they're going to measure and map the estimated 30,000 trees in the area. Then they plan to return each year to see if any trees have died and try to determine why.

This is in response to a study by Dr. Lutz [PDF] and others that determined that "between the mid-1930s and the 1990s, the density of large-diameter trees in Yosemite National Park declined 24 percent."

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This is important, he notes, because "large-diameter trees are important constituents of forest ecosystems.  The decreases in Yosemite National Park, a large protected area, suggest that cumulative human effects on the ecosystem (through fire exclusion and climate change) have been high."

The cause is difficult to pin down, but "we certainly think that climate is an important driver," says Lutz at Green Change.

Lutz also mentions:

A comparison of summer drought in past, present and future climate scenarios suggests that the climate-driven portions of large-diameter tree decline may accelerate.  Furthermore, climate-induced decreases in snowpack and the concomitant increase in fire severity suggest that existing assumptions about fire may be understated – future fires may be more severe, and post-fire recovery may take longer.

But Richard Cable in Climate Change – the Blog of Bloom looks at it differently. "Scientifically-speaking there's nothing in the research that would lead you to stress climate over other possible causes," he says.

And that's one reason that the planned long-term monitoring will be so important, to determine what is really going on.

More tree news:  Pakistan breaks tree-planting record. Volunteers planted 541,176 mangrove trees by hand in one day. The previous record: 447,874 trees planted in India.

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