Prevailing notions of responsible landscaping and gardening in California have long focused on a single metric: water use. By ignoring the importance of native plants, this formula disastrously undermines biodiversity.
Most of California lies within one of Earth's five temperate biodiversity hotspots and the only one in North America. We have an undeniable responsibility to the valuable variety of species with which we share our state. But for more than a century, we have filled our communities with non-native plants that are not part of the natural ecosystem.
We must stop thinking of urban landscapes as purely ornamental and recognize the need for them to serve as lifeboats for California's natural biodiversity, helping to preserve the species we have endangered. California has seen striking declines in its populations of bees, butterflies, moths, songbirds and other native pollinators in recent decades due to habitat loss.
With the additional pressures of climate change, we could lose 50% of all species by the end of the century. In one generation, our fire seasons have gone from a few months to a year-round threat, endangering the lives that are essential to the health of our ecosystems.
No one should be so confused as to believe that exotic plants from remote corners of the world can be “as good” as native plants. In fact, there is no scientifically compelling argument for planting non-native species for ornamental landscaping. Bring a tree from another part of the world and you are planting an island of sterility that will not help our natural and interconnected flora and fauna adapt to climate change.
Only native species can sustain existing ecosystems. Almost all herbivorous insects depend exclusively on native plant species for their life cycle. Although some pollinators use the flowers of non-native plants as a food source, native pollinators generally rely on native plants to support their caterpillars and other forms of offspring.
Additionally, exotic plants often promote the proliferation of invasive insects such as the European bee, which drives out native bees and other threatened species. Having already lost more than 90% of our native pollinators, we must take advantage of our limited urban green spaces by planting the best plants for the ecosystem: native ones.
One justification for exotic species promoted within the landscaping industry arises from a fundamental misunderstanding of biodiversity. Many growers and landscapers have been incorrectly taught that what is essential is the number of species planted.
In fact, while having a diverse palette of plants helps prevent the spread of disease, increasing diversity with non-native species is counterproductive. Because exotic plants do not support local soil chemistry or native microbes, insects, birds and mammals, or any other life forms that co-evolved with our native plants for millions of years, every non-native plant added to a landscape effectively reduces its biodiversity. worth. At a time when we are facing critical species loss, we cannot afford to make those decisions.
The good news is that it is not necessary. With almost 7,000 native plants in the biodiversity zone known as California Floristic Provincemany of which have been introduced into horticulture, landscapers have a wealth of options for every purpose.
Unfortunately, much of this is lost in the commercial landscaping industry. At a recent trade show covered by the Times, many growers promoted “California-friendly” non-native plants as abundant and attractive options for designers. The Los Angeles Department of Water and Power's grass removal rebate program has also adopted this marketing term.
However, there are no established scientific metrics to determine that a foreign plant is “California-friendly.” Even if an exotic plant has similar water needs to our native plants, that does not make it friendly to our state or part of its web of life.
The public sector is arguably even worse in this regard than private industry. Less than 3% of Los Angeles' street trees are native and the city continues to plant non-native trees almost exclusively. Despite expert and community feedback to the contrary, most city staff and their professional organizations resist change.
Municipal forestry groups like California ReLeaf and the California Urban Forest Council wrongly downplay native plants for politicians, city employees, nursery owners, landscapers, and those who advocate for native species. They fought legislation that would have set very modest goals for native plantings. The California Native Plant Society, a group of environmental organizations, and every scientist with any credibility in biodiversity supported the measure. Assembly Bill 1573but it was defeated by those who propagate, sell and habitually plant non-native species.
They prefer the familiar (the same handful of non-native species that have been grown and planted in California for decades) and claim, for example, that there are almost no native tree species. And yet, the Los Angeles Community Forest Advisory Committee recently put together a list of 87 native species suitable for use as street trees in the city.
The idea that humans know more than millions of years of evolution is the height of arrogance. Next spring, when you see the beautiful purple flowers on non-native jacaranda trees planted all over Los Angeles, stop and notice that not a single butterfly is pollinating them. It is time for city leaders, the landscaping industry, and home gardeners to recognize that we live in a vital native ecosystem that we must support.
Charles Miller is the president of the Los Angeles chapter of the Climate Reality Project and its Biodiversity Committee.
