Nature's Best Hope

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Created: Monday, 24 April 2023 13:31

NATURE’S BEST HOPE:

A New Approach to Conservation That Starts in Your Yard
Douglas W. Tallamy
214 pages, richly referenced, dozens of beautiful color photographs
$29.95, 2019, Timber Press, Portland, Oregon
Also available in a young readers edition, adapted by Sarah H. Thompson, $19.00 (not reviewed)
Available in the Kendal Library and the Oberlin Public Library (with the author’s autograph) There are numerous lectures by Tallamy that are available on YouTube.

In this New York Times bestseller, Douglas W. Tallamy, Professor of Entomology and Wildlife Ecology at the University of Delaware makes the case for planting native species in our home gardens to create what he refers to as miniature Homegrown National Parks. Through his own research and that of others, he meticulously builds his case in easily-understood prose. He begins his argument with the work of Rand Aldo Leopold (1887 - 1947) labeled by Tallamy as “perhaps the most influential conservationist of the twentieth century.” Edward O. Wilson (1929 - 2021), the father of sociobiology, known for his book The Ants is another hero, one of the first to recognize the conflict between the need to preserve biodiversity and Earth’s growing population.

Chapter Seven, Are Alien Plants Bad, and chapter 8, Restoring Insects, the Little Things That Run the World, form the core of the book. Based on the study of Forister et al, Tallamy notes that around 90% of insect herbivores are very fussy eaters, feeding on one or only a few plant species.(1) Eliminate the plant and you eliminate the insect. Tallamy also writes that “... as we homogenize plant diversity around the world by replacing diverse native plant communities with a small palate of ornamental favorites ... the insects that depend on local native species decline.”

In his field research, he and his students identified sites that were inhabited primarily by native species and others invaded by introduced plants. They counted and weighed caterpillars at each site in June and again in July. Although the mass of the plants in the invaded sites was higher than in the native sites, there were 68 fewer caterpillar species, 91% fewer caterpillars and a 96% reduction in the caterpillar biomass in the invaded sites! This translates into a 96% reduction in food availability for insectivorous birds. Tallamy and one of his students studied Carolina chickadees by measuring their reproductive success in areas with variable amounts of native and non-native species.(2) The biomass of caterpillars in tracts dominated by non-native species was reduced by 75% when compared to native species tracts and were 60% less likely to have any breeding chickadees. This resulted in chickadee nests that contained 1.5 fewer eggs. Hatchlings in those nests were 29% less likely to survive. If a study areas contained more than 30% non-native species, chickadees were not able to replace themselves and the population declined.

Tallamy takes us on a deep dive into the infrastructure that supports birds. He writes that plants that provide bountiful support for this effort are those that host a largest number of species of caterpillars from the order Lepidptera, the moths and butterflies. He notes the work of field observers who watched a nest of Wilson’s warblers for a continuous five day interval. They counted the number of times adults fed their young. In that period, the warblers fed their hatchlings 4060 times. Downy woodpeckers fed theirs 4095 times in 10 days. We humans should never complain about the nocturnal feedings that our children demanded! Tallamy crowns the oaks (Quercus species) as the caterpillar support champions, particularly the white oak (Quercus alba). As shown in the figure, oaks are hosts to the largest number of species of caterpillars, over 500. Somewhat predictably, non-native trees (e.g. zelkovas and ginkos) host virtually no caterpillars and thus provide no food for birds.

In the John Bartram Arboretum, ArborScope identifies 3 white oaks (but does not list at least 4 others) and 3 zelkovas. Ginko bilobas are identified as Maidenhair trees on AroborScope. There are 10 of them listed. The tulip tree (Liriodendron tulipifera), named as the signature tree for the Arboretum because of its links to John Bartram, supports only 21 species of caterpillars. The adjacent figure shows the probability of finding a caterpillar on various native and non-native trees during a 5 minute search (from Narango (2)). The number of caterpillars on native trees is significantly greater than the number on non-native trees, P<0.001. This very low P value means that odds that the two curves are identical is less than one chance in one thousand. For caterpillar abundance, the native trees are clear winners.

Tallamy provides a link to the National Wildlife Federation’s native plant and butterfly listing. Click here and enter your zip code for a detailed guide to native plantings.

In addition to providing terrific support for caterpillars, white oaks are also winners from the standpoint of carbon sequestration in urban forests. Click here for the blog entry on carbon dioxide removal by urban forests and the location of white oaks in the plantings adjacent to parking area 7.

Tallamy concludes with advice on what each of us can do to in what he refers to as a call to action to foster biodiversity by creating a Homegrown National Park: 1) shrink the lawn and replace turf grass with species of plants that support a native ecosystem; 2) remove invasive species; 3) plant keystone genera (for a guide see the National Wildlife Foundation link above) ; 4) plant for specialist genera; 5) network with neighbors to create linked areas that support native species; 6) build a conservation hardscape, including setting mowers no lower than three inches; 7) create caterpillar pupation sites under your trees by leaving leaves in place and planting appropriate ground cover; 8) do not spray or fertilize; and 9) educate others.

Tallamy’s advice is directly applicable to the John Bartram Arboretum and our mission to become a “model of responsible urban arboriculture.”

Figure 1. A model of the probability of Lepidoptera (moths and butterflies) being found during a 5-minute search period for native and non-native plant species. P<0.001 for difference between curves. From Narango (2).

Figure 2 The white oak (Quercus alba) located on the west side of Heiser Boulevard, one of the oldest trees in the Arboretum. ArborScope number 1487. Photo credit: Alan Lockwood

References cited

1. Forister ML, Novotny V, Panorska AK et al. The global distribution of diet breadth in insect herbivores. Proc Natl Acad Sci USA 2015;112(2):442-447.
2. Narango DL, Tallamy DW, Marra PP. Native plants improve breeding and foraging habitat for an insectivorous bird. Biological Conservation 2017;213:42-50.

ADDENDUM

Tallamy and his colleagues make a convincing case for choosing the native keystone genera needed to support the Lepidoptera species that are a critical element in healthy ecosystems. Although the trees themselves are critical, so too are other elements in the life-cycle of Lepidoptera. To complete their life-cycle a large number of these caterpillars drop to the ground in order to pupate in their cycle of egg to caterpillar to pupa to mature moth or butterfly. Turf grass and hard compacted soils are incompatible with this process (shown in the photograph of the base of white oak 629). Although the white oak is an ideal keystone tree, the hard scrabble landing at the base does not allow caterpillars to burrow easily into the ground and pupate. “Soft landings” a term used by Heather Holm are needed. She defines soft landings as “diverse native plantings under keystone trees ... [that] provide critical shelter and habitat for one or more life cycle stages of moths, butterflies, and beneficial insects.” Click here for a link to the soft landings web site that provides a list of appropriate plants. For more information on keystone trees that support Lepidoptera species click here and see the figure below.

Photo credits: Left, Alan Lockwood, Right, Diane Stauner

Figure legend: Keystone genera that support Lepidoptera genus. Final score 1.0 is best, 0.0 is worst. Box plot, line is median, top and bottom are first and third quartiles, whiskers are interquartile range. Dots are outliers. From Narango et al.

Narango DL, Tallamy DW, Shropshire KJ. Few keystone plant genera support the majority of Lepidoptera species. Nature communications 2020;11(1):1-8. Open source.