The Challenge of Drought

Pinyon pine (above left). Illustration of an engraver beetle (right).

 

As the spring heat returns to Canyonlands and the pools and streams filled with winter snowmelt diminish, a race begins. Trees, flowers, animals – all living things – will compete for water. But this race is nothing new: drought is common in the desert. Defined as an extended period of lower than average precipitation, drought has gripped the Canyonlands area since 1999.

Lack of water tests the fitness of plants and animals. Organisms that survive drought, whether by finding new water sources or tolerating some degree of dehydration, pass on their abilities and genes to the next generation. If droughts were abnormal, they would be accompanied by a massive die-off of plants and animals. Though there has been no catastrophic species loss during the current drought, scientists working in Canyonlands have noticed many changes.

Although only a few animals are monitored closely in the park, there are indications that many populations are shrinking. Researchers doing small mammal inventories from 2000 to 2003 were unable to trap sufficient numbers. Mexican spotted owls, which are monitored closely in Canyonlands, have had lower than average reproductive rates. Mountain lions and bears may be roaming farther in order to locate sufficient food. In the past two years, there have been more and more bear sightings along the rivers as well as in the Maze and Needles Districts.

Generally, animals are dependent on plant production and seed output, which has also been low. The current drought has had a negative effect on the growth of most perennials, especially trees and shrubs. Of these, the pinyon pine has been hit particularly hard.

Pinyon pines (pinus edulis) occupy a significant niche in canyon country, making up nearly 60% of the forest cover in Utah. In the southeast corner of the state, they normally grow from 5,000 to 7,000 feet above sea level. Pinyon pines contribute much to the desert ecosystem, including habitat for birds and insects, shade for overheated hikers, erosion control and, of course, delicious nuts. However, a combination of circumstances now threatens the population of this important tree.

The pinyon pine has one effective defense against infestations: sap. When an insect like an engraver beetle tries to burrow into the bark of a tree, the flow of sap can prevent the beetle from advancing. In a normal forest, a small percentage of trees will be infested with engraver beetles. These are usually unhealthy trees whose demise may very well improve the overall health of the forest.

However, during a drought even the healthiest trees can suffer infestations. Lack of water decreases a tree’s ability to produce sap and causes a buildup of sugars in its cells. This makes the tree both better tasting (to a beetle, anyway) and defenseless. Over the last five years, this unfortunate combination has caused the death of millions of pinyon pines in the Four Corners region. Unless an army of woodpeckers swoops in to eradicate the beetles, this trend shows no sign of abating.

Interestingly, this large scale die-off comes on the heels of twenty years of above average precipitation and forest growth. From 1976 to 1995, the southwest United States experienced some of its wettest weather in the past 1,000 years. This allowed the forests to grow denser and perhaps set them up for an inevitable pruning. After all, nature loves a cycle, and the recent beetle infestation may simply be a display of the ebb and flow that is part of the natural world.