It is a consensus among climate scientists that the planet's atmosphere has been warming. Of interest to us mountain dwellers is how that will affect the plants and animals that surround us.

The most common understanding of the warming effect regarding mountains has been that higher temperatures push plants and animals to higher elevations. Around here that would mean that our tree line would move up, and chaparral would take its place. There would be more pines at higher elevations, fewer at lower elevations where they now grow. Chaparral species like manzanita, redshank, and chemise would move higher.

Given this view, a study that made it into some large newspapers in January caught my interest. It was a surprising finding that showed plants moving down in elevation rather than up (Crimmins, et. al, Science, January 21, 2011).

This study used old data collected by the US Forest Service in the 1930s to compare with recent data on the elevations of 64 plant species. What the researchers found was that most species actually moved down in elevation about 80 meters (240 feet). Their explanation was that though temperatures went up, so did available moisture. In their view, it was this increase in moisture that allowed these plants to expand down slope.

I found this to be an encouraging finding, since I hate to think that many species would be driven out of their current environments (and I like the pines in Idyllwild). There is a catch for us, however. Their study focused on California mountains above 35° latitude, which are roughly the mountains north of Tehachapi to the Oregon border. Whether this would apply to our mountains I can't say.

On the other hand, a study recently published (A. Park Williams, et.al., Proceedings of the National Academy of Sciences, 2010, 107) focused on the high altitude forests of the southwest and concluded that increases in temperature and aridity have led to increased tree mortality over the last several decades and would likely lead to more in the future. Essentially, the present drought, which is expected to continue in the southwest (mainly Arizona and New Mexico, with southern portions of Utah and Colorado), has led to tree deaths by the bark- beetle and forest fire. According to their climate predictions for the SW this should continue to cause a slower growth of high altitude trees, as well as more significant tree mortality. They expect that some areas will likely convert from forest to grass and scrublands as trees die and can't re-establish.

So where do we stand in all this? The lesson I would take is that it all depends on the moisture we get. If in the years ahead we get rain like we did this past December throughout our winter months, we could see trees moving down the mountain from present areas. If we revert to our past dry years, we could expect chaparral to push further up the hill, more tree mortality, a resurgence of the bark-beetle, and more danger of wildfire. But I don't think anyone is sure about how much precipitation will fall.

One thing is clear: climate change, as researchers emphasize, will have various and complicated local and regional effects. With my beginner's viewpoint, I hope to write more about expert opinion in this space over the next year.