BY JOHN BRUSH
We often appreciate plants for very specific, and often obvious, reasons. We value them for the food they provide us; a personal favorite being avocados. Others we value for the clothes they provide (cotton), or the homes they help build (timber trees), or for their aesthetic beauty — the roses and lilies of the world.
Here in the Valley, we especially might value tall, woody plants (trees) for their shade. According to the U.S. Environmental Protection Agency, neighborhoods with mature trees can be 4 to 6 degrees cooler than new suburbs without trees — if that’s the difference between 100 degrees and 94 degrees, I’d quickly choose to live in the first neighborhood.
While these ecosystem services are vitally important to us, there are an array of other benefits that plants give us, and not all of them as obvious or direct. One such benefit is that of biodiversity. Now, yes, this does seem fairly obvious and straight forward on some level — if we have more vegetation in our yards and neighborhoods, the more species of birds and other wildlife we will see. But the value of that biodiversity lies in a few less easily characterized realms; supporting services and cultural services.
While the relationship between biodiversity and ecosystem services is complicated, we do know it affects services through ecosystem functioning. Study into biodiversity and ecosystem functioning has revealed a couple major trends: biodiversity loss reduces functions of ecosystems (such as that of producing biomass and nutrient cycling) and increased biodiversity positively influences the resilience of those ecosystem functions.
Yet despite biodiversity providing and supporting basic needs of life (food, nutrient cycling, etc.), it also has important implications for human happiness and health. A study in the United Kingdom found that if people perceived there to be more biodiversity, the more psychological well-being they felt. A similar study in Chicago found that the valuations of benefits provided by birds positively related to the perception of the number of bird species.
Here we arrive to the heart of the matter: how do different plants affect biodiversity? In a two-year University of Texas Rio Grande Valley study, there was a significant positive relationship between bird diversity and the number of native trees planted in yards, but not one for the total number of trees planted. This implies that native trees are making a difference for overall bird diversity in our neighborhoods!
One reason for this could be that native plants support greater diversity and abundance of insects than non-native plants. In one study, Doug Tallamy, an entomologist from the University of Delaware, found that three generalist caterpillar species either starved or barely grew on non-native plant foliage. In another, he and colleagues found that yards landscaped with native plants supported more caterpillars than those with non-native plants, and that birds of conservation concern were eight times more abundant in native landscaped yards.
All this leads to the general conclusion that biodiversity matters, native plants support more biodiversity, and we can make a difference with the space in our yards and neighborhoods. We can enhance our lives, and the lives of wildlife around us, in a simple way — plant more natives. In celebration of these important and beautiful native plants, Quinta Mazatlan is hosting Tallamy as he gives the keynote presentation for the third annual Planta Nativa event on October 19th. It will feature food, drinks, an art walk and live music. Tickets are available at Quinta Mazatlan. For information, call (956) 681-3370.
John Brush is an urban ecologist for Quinta Mazatlan.