Bradley Michael Brown knelt over a hole that is home to a newly planted tree in Balboa Park.
"And it looks like we're about there," Brown said as he threw another handful of dirt around the trunk. He turned to a volunteer and encouraged him to help with the finishing touches.
"One more scoop and you’re good. Now go ahead and step on it a little bit and tamp it down," Brown said.
Brown and a handful of volunteers planted a Bauhinea tree on the western edge of the park near Quince Street.
"It’s a Hong Kong Orchid ... and so if it grows right in the next five or 10 years, it's going to be a big flowering tree," Brown said.
Dozens of trees found new homes in the park during a recent Arbor Day celebration. The event marked the completion of an effort funded by CALFIRE that put 500 new trees in the ground in San Diego's largest urban park.
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Brown said trees are one of the things that make the park unique.
"It's such a different feeling than being out in the middle of a concrete or asphalt parking lot and then being under a grove of ficus trees," Brown said. "Everyone can imagine that, right? Who wants to be out in a hot parking lot? I mean, that's what the trees help."
But in spite of the newly planted trees, the park's forest still faces challenges that were uncovered by the nonprofit Balboa Park Conservancy, which has been taking stock of the park's trees. Their efforts include understanding the health of the trees from a two-decade-old survey that was recorded with pencil and paper.
"We digitized the old data from 20 years ago," said Jacqueline Higgins, the Conservancy's director of planning, design and programs.
The information now exists online in an app called OpenTreeMap, which has recorded every single tree in the park. Stand next to a tree and the app can tell you what kind of a tree it is and what its ecosystem benefits are.
Online Tree Finder
OpenTreeMap is a smartphone app that includes a listing for every tree in Balboa Park. Each green dot represents a tree — click on it and the app explains what kind of tree it is, and estimates the plant's ecological value. All of the park's 15,000 trees are in the database.
"We overlaid our new data from the inventory that was done last year, and we're able to compare and contrast the data sets," Higgins said.
The findings were not particularly reassuring: The latest survey found the health of the Balboa Park forest had declined in the two decades between surveys. Today, 4% of the park's trees are dead. Another 4% suffer from poor health.
"When you look at that, it's not a huge number because we're talking over 15,000 trees," Higgins said. "But when you put numbers to that, the structural value of that 8% decrease is $5 million. That's a city asset that has just decreased in value by $5 million."
Conservationists are working to reverse the decline, and they say it is not a mystery why the trees are struggling.
"Over the course of the last two decades there's been a real impact from climate change," said Tomás Herrera-Mishler, president and CEO of the Balboa Park Conservancy. "With increased temperatures, insects that were never here before have been migrating north, and so there’s quite an impact on the health of the trees.”
The Conservancy is making a concerted effort to care for the health of the city's signature urban forest. They replace dead trees and care for sick ones.
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The long term plan is to boost diversity.
"Twenty years ago we had 328 different species of different trees in the park," Herrera-Mishler said. "We're now up to 448 different species in the park. The reason why that's important is that the more diversity, the more resilient this forest is. We need a resilient forest because of all the impacts of disease, old age, insects and drought."
Diversity also means there are fewer eucalyptus trees.
Those tall fast-growing and drought-tolerant trees with shallow root systems are prone to falling when storms hit. The Australian imports used to account for about 40% of the park's trees. That's now down to just over 20%.
And Balboa Park's forest is what the rest of the city could look like.
San Diego's Climate Action Plan calls for a much denser tree canopy outside of the park.
"We’re around 5% in the city," Herrera-Mishler said.
Trees clean the air, filter stormwater, reduce heat and sequester carbon — and that is why they are so valuable to the city.
"Now if you want to see about what 30% (tree canopy) looks like, come to Balboa Park because that's what we have here in the park," Herrera-Mishler said. "It's super important for many reasons (including) improved air quality, and lord knows we need that in San Diego."
The 103-year-old Moreton Bay Fig in front of the Natural History Museum is an example of things going right. The tree has thrived since it was fenced off years ago to protect its roots. The canopy is larger, the trunk is bigger and it remains an attraction.
The Conservancy hopes that success story is repeated with the rest of the park's trees.
