By Mary O’KEEFE

There is a perfect balance for the Earth. From atmosphere to dirt, the cycle that makes the Earth work is a perfect dance where one false step may not be seen immediately but, if followed by more, the dance is done. One focal point of this graceful balance agreed upon by both philosophers and scientists is the importance of trees.

Often when trees fall after a heavy rain, like the Crescenta Valley has experienced recently, the thought is the wet ground caused the tree to topple. But often it is the years of dry soil that affects trees more; it is the drought that caused the tree to fall, which is a concern because many times there is no warning that it is about to fall. The tree may have been weakened from the inside out.

There is, to some, a question as to whether California is out of its drought. According to the USGS, the state’s drought lasted five years, from 2012 to 2016; however, there is a discussion in scientific circles as to whether it actually lasted longer than five years and, in fact, is still a part of the state’s future.

Whatever direction the debate takes, the drought that Californians have been facing has taken a toll on everything, including trees, especially in Southern California.

A recent research project looked at how the drought and consequences of the drought has affected local trees. The research findings were released in December 2017. The Resource Conservation District of the Santa Monica Mountains (RCDSMM) gathered a group of “citizen science” volunteers to study the drought impacts in 2015. They tagged over 350 trees in 41 randomly selected 25-meter square plots in critical park areas near the urban wildland interface throughout the western Santa Monica Mountains. Then, in 2017, another aspect of the study was added with the deployment of 46 beetle traps. The beetles’ impact and movement were monitored. NASA DEVELOP Project joined the research and used remote sensing tools to assess the landscape level impacts over the same period of the study, according to the research.

According to their findings, as of 2017 the drought was a more significant problem than mortality from invasive beetles. Despite the rains throughout the Santa Monica Mountains, drought conditions persisted. Of the 110,183 live acres in 2013 in the Santa Monica Mountains, only 77, 840 live acres remained in 2016. Trees and shrubs died in over 32,343 acres in that time frame. Over 9,000 coast live oak and 114,000 riparian trees died in this period.

DEVELOP is a program that works with state and federal agencies on environmental issues. Natasha Stavros, Ph.D., is an applied science system engineer at Jet Propulsion Laboratory and worked with Rosi Dagit, a senior conservation biologist with RCDSMM.

The DEVELOP project was contacted by the U.S. Forest Service as it celebrated 100 years. The DEVELOP scientists worked on a series of projects throughout the country to celebrate the century mark of the National Parks Service, Stavros said.

Stavros added Dagit worked with the NPS looking at how the California drought affected the oak trees.

“[The death of an oak] can be extremely rapid. A tree may look like it is okay and six months later is dead,” Stavros said.

DEVELOP was able to use sensors in aircraft for the project.

“For many observations, AVIRIS [Airborne Visible/Infrared Imaging Spectrometer] was used,” she said. “It allows us to see the chemical fingerprints of what is on the ground.”

The equipment can give scientists data on the amounts of nitrogen, carbon and lectins (proteins).

“There is a special fingerprint when plants stop photosynthesis,” Stavros said. “We were able to map [the trees’/plants’] mortality.”

She added that drought has direct impacts on trees in a couple of ways.

“It creates stress on the tree,” she said. “Just like in [humans], when resources like water are [scarce] trees are more susceptible to disease.”

Adding that, like humans, when trees become sick their immune systems become weak leaving them more vulnerable to disease. The oaks become an easy target for beetles that bore into them.

“That makes the trees more susceptible to fungi,” she said.

She equated the damage by the beetle to an open wound that allows infection, or fungi, to enter.

“It may look like a solid tree but is [dying] from the inside out,” she added.

And don’t think that these sudden bursts of rain will solve the years of drought damage. Trees have memory, drought memory.

“Trees that have drought memory are not going to respond because you put water on them,” she said. “Replenishing needs to come from the bottom up.”

Also, just like humans, trees sweat. When they have a good water source they drink and sweat to cool themselves down.

“When they are not sweating, they are not releasing moisture into the atmosphere,” she said.

If a tree doesn’t sweat, the moisture isn’t released into the atmosphere, which affects the humidity, which affects the weather. The balance is off.

Dagit said LA County has various departments working on how to mount a drought response, an early warning system, so-to-speak, for drought.

“[Crescenta Valley] already has a bad beetle [problem],” Dagit said. “In Santa Monica the effect is patchy.”

One cause of concern specifically in the Santa Monica Mountains is the variety of tree species that populate the area and how each is affected by the drought.

“The thing that surprised me the most [about the study] was the damage to the trees along creeks,” Dagit said.

She often hikes the area and noticed that trees were being affected but didn’t realize to what extent. The data from this extensive multi-year drought, with the number of higher temperature days, was the most sobering, she said.

“If the ground water table is low, it can no longer support deep rooted trees,” she said. “Tree roots go where they can find water. Where you get that tipping point, where a tree begins to fall, is when the tree is no longer able to support the above ground biomass … when the water table drops faster than the roots can follow. That is the disconnect,” she said.

The drought watch continues, despite Gov. Jerry Brown stating the drought is over.

“We have gone from abnormally dry to exceptionally dry since June 2012,” Dagit said.

The data collected by the study, which was titled, “How can we save our native trees? Drought and Invasive Beetle impacts on Wildland trees and Shrublands in the Santa Monica Mountains,” will be shared with several agencies throughout LA County and U.S. Forest/National Parks Service, as well as related agencies. The information will be used in a variety of ways including wildfire risk assessment.

“So that is the bigger picture and mostly what we wanted to do with the report is to get a sense of how bad things are and to identify locations where things are problematic. The next step in the process is [to determine] where we would want to do strategic replanting,” Dagit said. “Where do we think we can plant those trees that [will survive] for the next 100 years given the climate change we are facing?”

  Mary Okeefe