Most efforts to expand LA City’s tree canopy – and thus strengthen the urban environment – have focused on planting street trees. Yet the majority of the trees of America’s second largest city grow around its bungalows, cottages, mansions, and ramblers.
It is in residential yards that about 80% of the city’s trees are located: more than 5 million in these private landscapes compared to about 700,000 street trees and 150,000 to 300,000 park trees. That’s one of the key findings from a recent report commissioned by City Plants, a nonprofit that works with city departments to plant public trees.
This is important because a study by USC scientists saw that most of the tree canopy and greenery loss occurred on single family lots in these areas due to increasing home sizes (Lee et al. 2017). As much as 55 percent of the green cover was lost from 2000 to 2009, with almost no single area spared the decline.
The study’s findings confirm that the majority of LA’s trees are squarely in development’s sights. Even the city’s protected tree ordinance does not make them immune to legal or illegal removal, whatever lip service L.A. city policy makers may pay to them. Trees get in the way when soaring prices induce developers to max out their lots, and the city to allow more housing units in the hope that supply will outrun demand and hold prices down.
The USC study suggests the urgency for conservation and management strategies that focus on single family residential areas which are providing valuable ecosystem services for millions of Angelenos.
Some of these areas are essentially places that look and feel like “the woods” as opposed to urban forest areas typified by street trees and park trees. Trees in these more wooded residential areas can be naturally occurring and exist in stands, or groups of stands of native trees such as the coast live oak, black walnut and sycamore, often growing together – and thus being cut down for bigger houses – in patches.
You can plant street trees that promote biodiversity and increase tree canopy by planting a lot of different trees. But it’s not the same as having these wooded spaces. Street trees rarely reach their full potential because of harsh growing conditions, limited planting space and lack of care – they are like street kids, isolated and struggling against the odds without strong roots. One research study showed that a quarter of newly planted public trees will die in the first six years (Lu, Svendsen, Campbell, Greenfeld, Braden, King, and Falxa-Raymond, 2010).
Don’t look to city parks to fill the gap. Los Angeles is short on parks, ranking 74th out of 100 cities. And much of its park trees are in rough shape, beset by inadequate management, drought, air pollution, pests and climate change. Some 14,000 trees were lost by withholding water in LA parks, a decision which undervalued all the benefits trees provide such as stormwater mitigation, improved air quality, carbon sequestration and reduction of the “heat island effect”.
There’s only so much space for trees in LA’s parks anyway. Some park areas have been turned into ball fields. To take a particularly poetic example: Earlier this year a grove of healthy 50 foot tall shade trees were cut down to make room for an astro-turf soccer field at Whitsett Park in North Hollywood.
Given that most of LA City’s trees are in its yards, saving them requires that property owners make trees a priority and save the spaces they grow in, which means preserving the structures they grow around rather then replacing them with lot-busting McMansions and McPartments. Plans and policies should address—through rules, fees, and incentives—how private land owners contribute to the overall health of the urban forest and the benefits it delivers.