Climate change puts southern Arizona’s ‘sky islands’ in its crosshairs

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Jacob Owens

TucsonSentinel.com

Southern Arizona may appear at first glance to be nothing more than a dry paradise for saguaro cacti and mesquite trees, but it includes an area internationally known for its biodiversity – the Madrean Sky Islands. These high mountains that dot the landscape are threatened by climate change and risk losing some of the characteristics that support such a wide variety of plants and animals.

Drought and fires are expected to permanently alter ecosystems on the sky islands, with pine forests in the upper reaches threatened with extinction and water sources such as natural springs and stressed winter snows.

The “islands” high above the desert valleys are getting hotter and drier, said Emily Burns, program director at the Sky Island Alliance, a group focused on conservation in the region. This endangers forests on mountain tops, she said.

“The ecosystems that depend most on water and the coldest night or winter temperatures, we risk losing them,” Burns said.

The Sky Islands are a series of 55 mountain peaks that stretch from Arizona and New Mexico to Mexico. The mountains are each an “island of habitat – like a forest surrounded by desert”, according to the Sky Island Alliance.

The peaks range from desert scrub and grassland at their lowest elevations to ecosystems with pines and firs near the summit. The Rincon, Catalinas and Santa Ritas mountains are part of this group.

The mountains are an “incredible crossroads” for northern US animals such as black bears and tropical species such as jaguars and ocelots, said Burns, who attributes the islands’ biodiversity to their structure.

“It’s kind of like an apartment building, with so many different types of people (who) can live in an apartment building because there’s a lot of space vertically,” she said. . There are about 1,300 species of bees in the region, more than anywhere else in the world, Burns told the Tucson Sentinel.

Climate change has brought extreme fires to the region, Burns said, such as the Bighorn Fire on the Catalina Mountains in 2020, which scorched nearly 120,000 acres. Drier vegetation combined with less water makes parts of the Sky Islands a “powder keg”, she said.

Traditionally, the Catalina Mountains have seen frequent fires every 10 to 20 years among lower trees and other vegetation, but the fires are becoming more severe due to climate change and past fire suppression, said Laura Marshall, postdoctoral researcher on seedling fire survival in the state of Colorado. University.

The Catalinas fell victim to the fire suppression surge in the 20th century, Marshall told the Sentinel, meaning natural burning was limited, leading to dense forests today.

“And that causes problems when climate change becomes an issue because all of those trees are going to suffer from drought, much more than they would in a more open stand,” she said.

Instead of burning smaller plants and letting fire-dependent species such as pines grow, larger fires now reach the tops of taller trees and can burn everything in certain areas.

Severe fires can also hamper future generations of pine forests, which are typically found in the upper layers of sky islands. Seedlings need more moisture and cooler conditions, Marshall said.

“So even if we can prevent severe fires from directly burning all the mature trees, the forest may not reproduce seedlings if it gets too hot and too dry too often, which is expected for the future. future,” she said.

Forests growing in places like the Catalinas could become oak-dominant if fires wipe out ponderosa pine, Marshall said. The remaining pines would likely be around springs and cooler areas, she told the Sentinel.

Rincon’s pine forests are also in danger. Some scientists think ponderosa pine forests in the range east of Tucson could be lost within decades due to drought affecting the species’ regeneration, Marshall said.

The loss of pine trees would in turn affect the biodiversity of the ecosystem, such as birds that nest in old trees, she said, in addition to animals like deer that could be preyed upon more. Years like 2020 will likely be “very typical” as climate change continues with more drought and fires, Marshall said.

Several species, including migratory birds, still haven’t fully recovered from the 2020 lack of rainfall, Burns said. The year was the driest on record for Tucson with just 4.17 inches of precipitation and a record 108 days of temperatures exceeding 100 degrees, according to the National Weather Service.

“So if we’re going to have more of these droughts, how many droughts can we have before we completely lose species?” Burns asked. “And I don’t think any of us know the answer to that question.”

Springs of the Sky Islands

The few natural springs in the area are home to species that live nowhere else, said Larry Stevens, director of the Springs Stewardship Institute. One such species is the Chiricahua leopard frog, which lives in wet grasslands and spring-fed areas, he said.

The green and black-spotted frog is listed as “threatened” by the US Fish and Wildlife Service. The animal is about two to five inches long and can live for up to 18 years, according to the Center for Biological Diversity.

Places like Mount Lemmon see less snow accumulation, which reduces water uptake into the ground and less to replenish high-altitude springs, Stevens told the Sentinel. Water sources lower in the mountains are also affected, he said.

“It’s a bit of a complicated story because climate change means there’s less water available overall, less surface water,” Stevens said. “That means more people are taking groundwater from wells.”

Over the past five years, the Mount Lemmon Ski Valley has averaged about 75 inches of snowfall, said Nicholas Aldinger, Ski Valley’s director of operations. The 2000s were “random” with snowfall, he told the Sentinel. The last major snowstorm was in 1997-98 when 14 feet fell, he said.

The snowpack is very important for getting water into the ground, Stevens said. “One thing that’s quite shocking to people is to learn that most precipitation, over 90 percent of precipitation that comes into Arizona, especially at lower elevations, just evaporates,” he said.

The Sky Island Alliance has a three-year “erosion control campaign” to help restore springs in the Bighorn fire area and eight “spring rescue projects,” Burns said. One of the ways the group protects valuable springs is by piling rocks on top of them, causing soil to build up, while preventing landslides from interfering with the resource.

The effects of climate change can be mitigated through individual efforts like rainwater harvesting, Burns told the Sentinel. Keeping hope alive is vital, she said.

“Otherwise, if we all feel like there’s nothing we can do and we give up, the game is really over, but it doesn’t have to be like that,” Burns said.

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