Photo by Wendy Baxter


Will bedrock save our coastal ecosystems from climate change?

November 23, 2020

We know that global average temperatures are rising due to climate change. This shift in climate has brought not only an increase in wind storms, erosion, heat waves and droughts, but a sense of uncertainty as to how ecosystems will cope in the coming decades.

Jesse Hahm, a physical geographer in SFU’s Faculty of Environment, hopes to change this. “One of the biggest knowledge gaps is understanding how trees will respond to increased drought and warmer temperatures,” says Hahm. In an article published in Water Resources Research, Hahm shares the findings from a study he led that unearthed the mystery behind the Garry oak’s ability to survive long dry spells in the quickly eroding, rocky terrain of Northern California.

Not only is the Garry oak the only native oak located throughout the Canadian West Coast, it is integral to some of its most biodiverse ecosystems. Hahm chose to focus on the water transpiration of these oaks in part due to the significant role plants play in the transfer of water in the hydrologic cycle, the system that depicts how water moves through on Earth.

“More water is actually returned to the atmosphere by plants than runs off to the oceans in rivers and streams. For that reason, transpiration is an extremely important part of how the earth system functions,” says Hahm. 

Hahm aimed to locate where exactly in the subsurface trees get their water to help predict how the Garry oak and others in the area will react to a likely shift in water availability.

The Garry oak was previously thought to use ground water to help survive the long dry spells that accompany the summer season; however, Hahm’s research demonstrated otherwise. Hahm and his team discovered that this species extracts moisture from fractured and weathered bedrock in areas where the bedrock is covered by a thin layer of soil. Knowing that bedrock holds the potential to provide hydration for these trees throughout dry summer months gives us hope for forests here on the West Coast and a new appreciation for the earth beneath our feet.

Photo by Wendy Baxter

What does this mean for the longevity of our West Coast forest ecosystems? Simply put, this research “helps us understand how these trees, and others like them, will fare in a warmer, drier future climate,” says Hahm. If we can better understand this and identify more resilient species, we may be able to help inform and improve conservation and management practices.