Forest Ecosystems Impacted By Climate Change
November 29, 2012

Climate Change Could Affect Entire Forest Ecosystems

April Flowers for - Your Universe Online

Off the southern coast of California, the fog rolls in over Santa Cruz Island coating the needles of the Bishop pines with moisture. Water drops form on the needles and roll down to fall to the forest floor, happening over and over on every needle of every tree. The forest ecosystem depends on this fog drip to stay alive.

Bishop pines are thought to have proliferated all along the West Coast of the US and Mexico thousands of years ago when the environment was cooler and wetter. Today, the pines are found only on Santa Cruz Island, Santa Rosa Island, an island off Baja California, and in northern California where low-altitude clouds known locally as "June gloom," along with the cooler and wetter climate of the north help keep the trees growing.

A research team from the University of California — Santa Barbara, led by Mariah S. Carbone, studied the influence of clouds on the largest Bishop pine forest of Santa Cruz Island.

"When people think about climate change, they're often thinking about temperature and precipitation," said Carbone. "When you think about precipitation, it's rain and snow, depending on where you are. What this study showed is that you can have really important water inputs coming from clouds that influence the carbon cycle."

Clouds are one of the largest uncertainties in global climate, according to Carbone, and the rather large impact they have on forest ecosystems has rarely been studied before, particularly in Southern California.

The types of forest ecosystems that grow in coastal California will be altered by changes in cloudiness or cloud height that occur with global warming. While predictions about how California rainfall will change over the next half century are uncertain, scientists believe fog and low-stratus clouds might decline as sea-surface temperatures warm. Forests such as the relic Bishop pines on Santa Cruz Island and the Sequoias of coastal Northern California remove and store carbon from the atmosphere, making them important in understanding concentrations of greenhouse gases in the future. Additionally, these forests are prized for their aesthetic and recreational qualities.

From May through August, fog is often present in coastal California occurring when the land warms in the spring and summer as moist ocean air is pulled over the cold, upwelling coastal waters. This creates clouds or fog banks as the moist air condenses under a stable atmospheric inversion layer.

"The finding that summer fog strongly impacts carbon cycling highlights the need for improved understanding of whether we should expect coastal summer cloud behavior to change in a warmer world," said A. Park Williams, a former graduate student in UCSB's Geography Department, now at Los Alamos National Laboratory. "A change in summer fogginess could produce temperature, moisture, and carbon feedbacks in coastal ecosystems that easily swamp out the effects expected from increased greenhouse gases alone."

Billions of tons of carbon move between the oceans, lands and atmosphere every year in the carbon cycle, causing increasing amounts of carbon dioxide to be released into the atmosphere. This potent greenhouse gas contributes heavily to climate change.

The UCSB team received help collecting information from both NASA and NOAA.

"We used satellite data to map the spatial distribution of cloud cover across the western portion of Santa Cruz Island," said Christopher J. Still, formerly an associate professor at UC Santa Barbara, now at Oregon State University. "We had some evidence of a cloud cover gradient from the coast to inland, based on our own observations and our weather station data, but the satellite data —— from NOAA and NASA satellites —— really allowed us to quantify this gradient across the western half of the island and in particular at our two study sites." This study, linking clouds to soil microbial activity, is unique.

"While most previous research on fog and ecosystems has focused on its role in plant-water relations —— such as the well-known linkages between fog and coast Redwoods —— we show that soil microbial activity and metabolism in these coastal ecosystems may be very dependent on the light but frequent fog drip that occurs during the rainless summer months," said Still.

Another unique aspect of the study is the linking of fog and low clouds to the carbon cycle of a coastal ecosystem and how this link impacts tree growth and soil respiration.

"What we found was that there are two major effects of the clouds," said Carbone. "One is shading, which keeps the temperatures cooler and the soil moisture higher. The other is fog drip, which is a water input into the soil."

Where the trees were under more cloud cover, the soil moisture content depletes at a slower rate, allowing the trees to grow longer into the dry season. While water pulses from fog drip immediately stimulates microbes in the litter and soil beneath, it does not directly enhance pine tree activity. The microbial activity does, however, release carbon dioxide into the atmosphere.

"This study provides us with a greater understanding of how fog and the low coastal clouds which Californians commonly call 'the marine layer' affect plant growth and the activities of microorganisms in the soil," said John Randall, scientist with The Nature Conservancy. "Their findings of the importance of fog and low clouds in influencing plant growth and survival and microbial metabolism in the soil will help us understand how changes in coastal fogs and low clouds that may accompany climate change will affect the forests and soils on Santa Cruz Island, other islands off the coast of California and Mexico, and all along the coast of the adjacent mainland."

The Nature Conservancy owns and operates Santa Cruz Island in cooperation with the National Park Service and the University of California. From varied landforms supporting more than 600 plant species, to a wide diversity of animal life, to remnants of Native American and European settlements, Santa Cruz Island is an environment rich in biodiversity and cultural resources.

The findings of this study have been published in the journal Global Change Biology.