What's good for the trees may be bad for people. That's because the trees are soaking up a lot more water that would normally be filling up many of the state's reservoirs, which are at very low levels because of three years of severe drought.
"More trees means more water stays in the forest," said Roger Bales, a hydrologist at the University of California at Merced, who was co-author of the report on increased mountain vegetation from the effects of climate change.
"It's the same idea like planting more plants in your garden," he said. "The more plants you have, the more water you need for them."
"But the alarm bells on the research we've done are really for the future," he said. "It's a wake-up call for scientists to do a lot more study on the issue."
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One of the major problems contributing to the overgrowth of brush and trees in California is the lack of forestry management, said Lindsey Nitta, spokesperson for the California Forestry Association.
"It doesn't happen much anymore," she said.
Nitta said that there's less thinning of forest vegetation, mainly because of a lack of money. Most of the money in state and federal allocation for fire control has been spent on fighting bigger fires.
Since 2002, the U.S. Forest Service has had to transfer $3.2 billion from other accounts to pay for active fire suppression in the U.S. In 2013 alone, they transferred $505 million to fight fires.
This year, California has experienced 4,503 wildfires, burning nearly 700,000 acres.
"The fires are bigger now because there's so much brush," Nitta said. "The climate is getting hotter and drier."
Nitta said that removing the extra vegetation would help rid forests of fuel for fires. And more controlled fires, she said, might help the forests get to healthier conditions with less water absorption.
But not everyone thinks the denser forests are a problem.
Bill Solinsky, a forester with the California Department of Fire and Forestry Protection. He said thinning the state's forests might create more available water for the population but he added that the water used by trees has benefits.
"They do soak up a lot," Solinsky said. "But the water's not completely lost. Trees act as a filter system to clean up water that goes down to creeks and the provide soil stability."
This past year for measuring rainfall and water runoff in California turned out to be the fourth-driest year ever for the state.
It got only around 60 percent of the yearly average precipitation.
While most of the state's reservoirs are at nearly 59 percent capacity, water supplies in the three largest reservoirs are only about 30 percent of capacity. Other water sources are also drying up.
"Groundwater demand is normally around 40 percent a year," said Doug Carlson, information officer at the California Department of Water Resources (DWR). "Now it's at 60 percent demand."
Besides the work done by Bales and Goulden, more research is being done on the state's forest vegetation.