By Jeremy Hance
18 September 2013
(mongabay.com) – One of the richest ecosystems on the planet may not survive a hotter climate without human help, according to a sobering new paper in the open source journal PLoS ONE. Although little-studied compared to lowland rainforests, the cloud forests of the Andes are known to harbor explosions of life, including thousands of species found nowhere else. Many of these species—from airy ferns to beautiful orchids to tiny frogs—thrive in small ranges that are temperature-dependent. But what happens when the climate heats up?
"Shifts in temperature will require upslope migration for most species to remain in equilibrium with climate and therefore potentially avoid extinction," the scientists write in the paper.
However looking at aerial photos and satellite imagery of Manu National Park from 1963 to 2005, the researchers found that Andean cloud forests may run into an insurmountable border as they attempt to migrate up mountain sides: puna grasslands. Although the temperature has warmed significantly since the 1960s, the researchers found that the treeline bordering the Andean cloud forests and high-altitude grasslands had hardly moved. In fact, according to the research, 80 percent of this border remained stable in the study area since 1963. This transition area between one ecosystem (cloud forest) and another (puna grasslands) is known to scientists as an ecotone.
"Previous work we've done shows that the trees in the forest are migrating upwards [in response to climate change], but this work shows the ecotone isn't," notes co-author Miles Silman with Wake Forest University. "The ecotone presents a wall to species migration."
While Andean trees are already moving rapidly upslope in response to climate change, they have not been able yet to penetrate the ecotone barrier, according to the study. The scientists aren't certain why the puna grasslands aren't making way for cloud forests more rapidly as temperatures rise, but it appears that this colonization needs considerably more time than cloud forests species have under current climate predictions.
"From a biological perspective, cloud forest tree seedlings have major difficulty establishing themselves in puna grassland," lead author David Lutz explained to mongabay.com. "The exact reasons why are still a subject of debate among plant physiologists, but generally field work has found the survival of tree seedlings to be low when exposed to the open sky in puna. Instead, tree seedlings fare far better under the forest canopy, indicating that a slow prolonged march, generation by generation, has been the typical mode of movement, often out from isolated patches who weathered the change in climate in a sheltered spot."
In the past, cloud forests were able to make this march, as climate changed relatively slowly. But the pace of climate change today could simply outstrip the forests ability to migrate into the grasslands, notes Lutz.
Historically, with slow rates of change, forests and puna have been able to shift up and down accordingly with likely minimal issue. Current rapid climate change projections, however, indicate that these cloud forests will need to move upslope at a very fast pace. Unfortunately, these tree species are not evolutionarily prepared to move this quickly."
Human practices are likely exacerbating the situation, according to the researchers. Cattle grazing and manmade fires are commonly employed in puna grasslands. These practices "entrench puna grass species and eliminate tree seedlings, adding another wrench in the spokes for upslope migration of cloud forest trees," says Lutz.
In fact, the researchers found that cloud forests migrated into grasslands slightly faster in protected areas—however still not nearly quick enough to keep pace with anticipated climate change.
"Even when a majority of the disturbance from grazing and fire were removed in Manu National Park, forests migrated upslope extremely slowly, at a rate of just around a quarter of a meter upslope per year," Lutz explains. "To put that in perspective, this pace is around 2% of what it needs to be to stay in equilibrium with climate change by 2100." [more]