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Will our trees regrow?

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By Roger Snodgrass

Biologist Craig Allen has a special vantage for studying the effects of climate change in the Southwest.For one thing, he’s been perched in the Jemez Mountains for 20 years, doing what has evolved into long-term, place-based ecological research.“By being based in this place, by hook or crook, we’ve been able to conduct research on long-term phenomena,” he said this morning in an interview.He has watched certain trees grow for 18 years, has vegetation transits he monitors and erosion transects that have divulged decades-long data sets that are otherwise hard to find.Associated for most of that time with the U.S. Geological Service at the Jemez Mountain Field Station at Bandelier National Monument, Allen said his overall work has been involved with changes in the landscape of the Jemez mountains, looking at patterns and trying to understand why we see the vegetation that is there now and how it got there.“By temperament, I suppose, I use multiple lines of evidence to tell the most complete, multi-perspective stories about the ecological patterns and conditions we see out there,” he said.A few years back, he and David Brashears of LANL, along with other researchers, connected the sudden “dieback” of pion and juniper and other species across 14 million acres of arid western lands to something more than the obvious drought between 2002 and 2003. They also found evidence that this rapid change was most likely aggravated by the warming effects of climate change.“We can get abrupt ecological responses from gradual climate change,” Allen said in a talk at Los Alamos National Laboratory on Tuesday, underpinning his rationale for an ecological perspective.Allen’s research, while intensely local, has broadened into an international viewpoint that has revealed similar phenomenon on all the wooded continents of the world and has led to a wider investigation of how climate drives other environmental disturbances.In his talk, he said that dieback – the mortality of vegetation over a large ecological area – was only one type of disturbance that may now, on closer inspection and wider comparison, be related to climate variability.He has now added prevalent wildfires and erosion to his watchlist of phenomena that can interact and reinforce climate effects in surprising ways.Some of these disturbances cross thresholds that are hard to predict, he said.Speaking of the Cerro Grande Fire of 2001, Allen said the Ponderosa pine trees that once graced the mountain behind the Los Alamos town site might not return for hundreds of years.He emphasizes the conditional – “may” not – because these kind of fires that wipe out a whole stand of trees and create a fifteen square mile hole in the eco-system are highly unusual, at least over the last thousands of years of the record.“The Ponderosa pine has a big heavy seed that only moves a 100 meters from the tree with little help from the birds,” he said. “How do the seeds get back in there?”Meanwhile the site is steep and rocky, the soil is running off rapidly and shrubs have gained a strong foothold, particularly the Gambel oak, which sprouts.“A clonal-sprouting shrub is a good life form to be in face of these types of disturbances,” Allen said, in a difficult environment, that is hot, unshaded and in degraded soil, because the top can burn and the shrub will still sprout.Ecological models depend on climate models, but as Allen noted, “Our crystal balls aren’t so perfect.”With a better understanding of the ecological complexities at work and perhaps a deeper awareness of where the tipping points may occur, Allen said, land managers may be able to develop strategies for making natural systems more resilient to big disturbances.“Ecologists are conservative,” he said, “Gradual change enables systems to adapt.”Craig’s talk was part of a series hosted by the Atmospheric, Climate and Environmental Dynamics group at the laboratory.