The future of Colorado’s forests, farms and open spaces will be determined in part by the usual culprits associated with climate change – the pine-beetle plague and wildfire. But the future is also being influenced by strange bedfellows like bindweed and prairie dogs, according to a presentation given by Tim Seastedt, a professor of ecology and evolutionary biology with the University of Colorado.
Researchers are documenting how climate change – in the form of warmer average temperatures across the West – is contributing to different ecological patterns in the natural world. In addition, the warming trend’s impact on Colorado agriculture could alter historic growing seasons, Seastedt explained to a packed auditorium at Fort Lewis College in Durango on March 26.
“Southwest Colorado’s temperature has [on average] risen two degrees Fahrenheit over the last 30 years. The irrefutable pattern of warming is evident and believable,” Seastedt said. “The real question is, how much control do we have during this change process?”
Precipitation levels are expected to stay the same for Southwest Colorado, but the hotter weather will likely result in a more arid climate overall due to increased evaporation.
Scientists at CU are documenting changes in climate, wildlife populations, and natural and invasive vegetation patterns throughout Colorado.
More fires, worse fires
Warmer weather reduces snowpacks earlier, which contributes to disturbances such as wildfire. And the effect seems to occur even during heavy-snow years.
“Two years ago we had some extreme snows, but in spite of the heavy precipitation at high elevations, the bottoms of the mountains were on fire very early in the year. Already we’re seeing fires this year, so it is worrisome,” Seastedt said.
Last year on June 24, there were eight fires burning at once in the state. Firefighters are bracing for another extreme fire season.
“Historically, the major fire seasons of 2010 and 2012 are not off the record, but they are outliers,” he said. “A new phenomenon is Colorado joining California in being unable to defend subdivisions from fires starting in adjacent forest, as was the case in Colorado Springs last year.”
Climate models using the continuation of the two-degree warming trend predict a startling fire-return interval that is six times greater than it is now.
For wildlife, changes are also happening. The rapidly melting snows and drier conditions have prompted marmots to come out of hibernation on average 38 days earlier than in the past. Bears in the San Juans mountains are reportedly emerging from their dens earlier as well.
The huge forest die-back in Colorado caused by the ravenous pine beetle is a result of prolonged drought. Pine trees defend against the beetle by pushing out sap, but a water-stressed tree runs out of defenses and is overwhelmed by the bugs.
Disturbingly, the longer warm season has created a new life cycle for the beetle, Seastedt explained. Beetles now emerge earlier than before and have time to complete spawn two generations rather than the usual one. One female produces 50 eggs and 50 offspring in one generation. Add a second generation, “and the math gets scary,” he said, with 2,500 larvae being produced.
The result is a more-destructive forest dieback from beetle kill over a shorter period of time.
“This kind of violates the rules of what we have seen as to how these outbreaks work in the past,” Seastedt said. “Historically, they would be watershed-specific. Now it is a severely stressed landscape over an amazing spatial scale and the regional change is in turn amplifying other changes.”
The result: more meadows, fewer forests. This is not necessarily a bad thing from a biologic-diversity standpoint.
What is happening is a lesson in ecology and dendrology, the study of trees. For millions of years forests have bounced back after beetle kills and fires, but because they are getting hit two or three times in a short time frame, that is not happening. The reason is lack of seeds, plus the fact that the hotter, drier soils prevent the establishment of seedlings that do exist.
“Immature forests are getting hit before they produce their propagules (seed banks), then the system essentially lacks a seed source and becomes a herbaceous system,” Seastedt said. “This is becoming the common model.”
The new norm within a forest matrix is expected to go from forests with occasional meadows, to meadows with occasional forests. This favors many “generalist” (nonspecialized) animal species, Seastedt said, but is a disadvantage for others.
“Lodgepole forests have less biological diversity. It is a monoculture with no understory and they have the lowest species richness in Colorado. To be honest [damage by fires and beetle kill] has opened up these areas and we have seen a more interesting landscape.”
But there could be a downside. How this new system will impact snowpack, snowmelt, regional climate, and water-partitioning is poorly known and needs more study, he said.
And now the prairie dog is playing a surprising role in climate change because its unique relationship with bindweed is creating an unexpected destructive force.
Bindweed is the bane of many weekend yard warriors. The invasive weed with its pretty flowers thrives in the drier, hotter temperatures. It is not expected to outcompete native plants overall; however, in and around prairie-dog colonies the weed is proving problematic.
Bindweed contains an alkaloid that is poisonous and most animals, including prairie dogs, ignore it. In a colony, the weed becomes dominant as the prairie dogs select other plants to forage on.
But over winter, bindweed loses its poisonous potency, and it becomes a convenient stored food source for the prairie dogs in spring. The result is a lunar landscape, devoid of vegetation, made worse by hotter, drier weather that hampers the growth of native grasses in spring.
The outcome – once spring winds arrive – is huge dust storms, stripping the topsoil and changing the landscape.
“Dust storms caused by prairie dogs are a fairly new phenomenon, and it is changing the rules of what vegetation is going to exist there,” Seastedt said.
The spread of shrubs is a probable result, he said, with more sagebrush, but the exact effects are unclear and little-studied.
Simply exterminating prairie dogs isn’t the answer, he said. Having fewer prairie dogs (in the Four Corners the species is the Gunnison prairie dog) means less biologic diversity. This charismatic rodent is considered a keystone species, meaning its presence and colonies attract dependent species such as the burrowing owl, mountain plover, and predators like hawks.
More growing time, but not more water
The hotter conditions have researchers forecasting a longer growing period of three weeks for domestic crops and other vegetation. But the precipitation is expected to stay constant, meaning the same amount of moisture is getting spread out over a longer period, Seastedt said, increasing evaporation. This affects dryland farmers more than irrigators with a predictable water supply, although more evaporation is expected to impact the whole region.
Farmers could grow earlier, but drier conditions spell out less production overall. Plus there is the risk of frost if crops are planted too early.
Non-native plants are more adaptable to the drier conditions, which is changing the competitive matrix of vegetation, Seastedt said. For example the non-native cheatgrass is greening up earlier, stealing nutrients and water from those native species that evolved to green up later to avoid frosts.
Cheatgrass is especially insidious because it not only fuels wildfires, it benefits from them afterward, returning to the burnt landscape with more vigor.
Seatsedt said protecting the public against wildfires and preserving water sources are the main social needs of a warmer climate.
“A longer growing season is in play, and the more-arid conditions are setting us up for more-radical changes,” he warned.
The Mountain Studies Institute, headquartered in Silverton, Colo., is a leading research group studying the impacts of climate change on the Southwest. They conduct research on alpine and desert environments in the Four Corners area. Here are some highlights from a comprehensive study called “Climate Change Assessment for the San Juan Mountain Region, Southwestern Colorado”:
• A consistent warming trend in Colorado since 1970 is projected to have significant effects on snowpack, even without a decrease in precipitation. From 1978 to 2004, snowmelt shifted two weeks earlier on average on Colorado’s Western Slope.
• Between 2040 and 2069, decreases in snowpack below 8,200 feet are expected to be between 20 percent and 60 percent. Above 8,200 feet the reduction is expected to be 10 to 20 percent.
• Predicted warming and drying will expand the range of many exotic species including cheatgrass, spotted knapweed, yellow star-thistle, red brome, and leafy spurge.
• Canada lynx may lose habitat following large-scale wildfires, which are predicted to increase as a result of climate-induced warming and drying.
• Warming trends could impact alpine areas as lower vegetation moves to higher elevations. The American pika, a high-elevation species, has limited upward movement from its habitat and may be vulnerable.
• Stream flows for the Upper Colorado River Basin are expected to diminish 10 to 25 percent, compared to flows from 1900 to 1970.
For more, see www.mountainstudies.org.