For the last ten years, researchers have amassed considerable evidence that the insect population worldwide is experiencing a sharp decline, with many species becoming extinct. To date, most of us have focused on the collapse of a few species like the honeybee and the Monarch butterfly.
|Dung beetles have a charm of their own
It’s comparatively hard to get people to worry about, for example, the devastating drop in dung beetles in the Mediterranean countries. (Wait a second…a quick internet search shows I may not be right about dung beetles. They have a lot of fans out there.)
But there are many reasons to worry about cute as well as noncute insects. Without an abundant and diverse population of insects neither we nor the charismatic vertebrates will survive either. The loss of a gnat deprives a bird of food, which is then not available to pollinate the plants needed to feed the antelope that is in turn a source of food for the gorgeous cheetah. It’s the circle of life, people!
|”I’ll eat anything”
|“Nothing but milkweed for me”
Abundance vs. Diversity
Data emerging from studies world-wide suggests that warnings of an insect apocalypse are no exaggeration. For instance, a comprehensive research review published in 2019 by Sánchez-Bayo and Wyckhuys estimated that more than 40% of insect species are threatened with extinction. And the overall number of insects is also dropping, at a rate of 2.5% per year.
Why focus on both diversity and abundance? Well, if a region is abuzz with bees that’s great, but if they are all from the same species then we lose the benefits that members of those lost species provide.
Factors Associated with Insect Declines (Source: Sánchez-Bayo & Wyckhuys)
Most highly successful species are generalists in the sense that they will eat anything. I am looking at you, cockroaches and opossums! Meanwhile, those with more specific dietary preferences are much more vulnerable if their sole food source is not available.
The most powerful driver of insect decline is habitat destruction caused by intensive agriculture, urbanization, and deforestation as well as pollutants such as pesticides and fertilizers.
These same factors are also contributing to a global decline in biodiversity, of which the insect apocalypse is one important part.
Learning to Share in Urban Spaces: A Conversation with Dr. Paul da Silva
In order to zero in on the situation in Marin, I spoke with Dr. Paul da Silva, a local expert in environmental science and resource management. Paul earned a PhD in Entomology from UC Berkeley in 1994. He was a professor at the College of Marin from 1997 until 2020, teaching classes in biology, botany, environmental landscaping, and entomology. He is also a newly elected member of the College of Marin Board of Trustees.
|Paul da Silva
Paul began our conversation by introducing me to the concept of “spare or share,” a debate among environmentalists as to whether it is more important to spare large tracts of land for nature’s exclusive use, or to share with nature by finding ways to integrate biodiversity conservation into human landscapes.
Entomologists like E. O. Wilson have long advised that we spare 50 percent of the earth’s land surface for pristine nature, finding ways to manage agricultural activities and urban development in the remaining half.
However, strong arguments for sharing have been made by others, including Kremen and Merenlender at UC Berkeley, who favor “working lands” conservation. They argue for the establishment of buffer zones surrounding open space to protect habitat and resources for some species while facilitating dispersal and climate change adaptation for others.
Expanding our Horizons
How can we create effective ways of sharing space in the urban and suburban landscapes in Marin and throughout the Bay Area? Paul da Silva is particularly adamant that we include as many native plants in our gardens and public spaces as possible in order to support insect diversity.
Why has this goal been harder to achieve than you might have thought? Paul identifies one stumbling block, noting that we humans are generalists and that makes it hard for us to realize that many of our local insects need specific native plants in order to survive.
Also, in Marin we can grow a huge variety of gorgeous plants from all over the world. I admit that I am very partial to Japanese gardens and have definitely strayed from a steady diet of Manzanita! But the more I have learned about the native options, the more able I am to create an interesting garden from ecologically supportive plants.
Looking at the Lawn
Any move in the direction of biodiversity requires close scrutiny of our county’s abundant lawns. Lawns are prized for their appearance and they are great for running around on. But they do little to enhance insect diversity.
|To mow or not to mow…
Paul suggests that we reflect on the following goals before putting in a lawn: How desirable is the aesthetic look of a homogenous green lawn? Do we want the space to hold up to a lot of foot traffic? How prepared are we to put in the time and costs associated with mowing, fertilizing, watering, and weeding? And how important are the environmental goals of avoiding pesticides, enhancing biological diversity, maximizing carbon sequestration, and increasing soil permeability?
Then, having identified our goals, how do we figure out what to actually do? To help us take this next step, Paul has developed a taxonomy of ten types of lawn or lawn substitute. Each contains a particular grouping of plants that meets a particular constellation of goals. Here are four types that are most consistent with the goals pertaining to enhanced diversity and that require relatively little maintenance.
If you highly value the environmental goals, do not want to devote time and money to mowing, watering, etc., and do not want to use the space for tossing around a frisbee, you can consider a meadow garden. A meadow garden approximates a native California meadow, with bunchgrasses like California or blue fescue, needlegrass, or deergrass mixed in with flowering herbs like California poppies and lupines.
- If you share those environmental goals but would really like to be able to walk or run around in the space, you can create a meadow lawn. A meadow lawn does not include bunchgrasses, so it can be mowed occasionally and can withstand some foot traffic. Thingrass is useful for this type of lawn, along with some forms of red fescue. Paul suggests the use of perennial native plants like the suncup, ground iris, mariposa lily, soap lily, and blue dick.
- Moving farther away from a grass-like lawn, you can plant the space with a woody groundcover. It’s best to avoid the invasive non-natives (e.g., ivy), and think in terms of California natives like dwarf coyote brush or ceanothus as well as low-growing manzanitas. These native plants are particularly good for sequestering carbon, compared to the herbaceous plants in the meadow garden and lawn. They do require some weeding, but little or no water.
- If you really want to be able to walk and run around on the lawn and are willing to sacrifice some of the environmental objectives, consider a bee lawn. Bee lawns typically include the kinds of grass used in conventional lawns along with compatible plants that provide nectar or pollen for bees. Some common examples are clovers and creeping thyme. You can mow these just as you would a conventional lawn and will need to water and fertilize them as well.
Paul’s lawn matrix really helped me think through my options as I continue to transition toward using native plants in my yard. Click here if you want the details.
Last Thoughts on Biodiversity
I also learned some good news about biodiversity in Marin from a webinar recently sponsored by One Tam.
The webinar, Birds and Bees of Mt. Tam, featured two great talks, one by Renee Cormier, avian ecologist at Point Blue and the other by Gretchen LeBuhn, professor in the Department of Biology at San Francisco State. Both scientists described their own recent research to document the abundance and diversity of species in various regions and ecosystems within Marin.
Some highlights from their talks:
- LeBuhn’s team found that Marin supports a high diversity of bee species. Particularly exciting was the diversity found in the coastal chaparral sites, which are less often studied and about which little is known.
- Cormier and her team found evidence that most landbird species in the Marin Municipal Water District are stable or increasing relative to numbers represented in data collected as early as 1996. She also noted that the nationally threatened Northern Spotted Owl is doing well in Marin, possibly because few Barred Owls have entered the county.
Contact One Tam to access the video from this webinar, which was held on February 11. You may have to become a member first, but that’s not a bad idea either!
That’s it for this installment of the EFM Notebook! Thanks very much to Dr. Paul Da Silva for sharing his ideas for enhancing biodiversity here in Marin.
Banner photo credit: Thanks to Rob Badger and Nita Winter for sharing Rob’s beautiful image.
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