Conservation Gardening

In the previous Acorn, I discussed our work conserving rare plant species through careful reintroduction in collaboration with ecologists from the Fairfax County Park Authority. The stakes are high with this kind of detailed restoration work, and there are very real risks to getting it wrong. That is why, in general, we don’t advocate for moving rare and uncommon species onto private property where they lack the protections that allow for enduring conservation.

That isn’t to say that protecting and restoring native plants to private lands isn’t important. In fact, it is a necessary component of our work and, locally and globally, we must do more to create better quality habitat through native plants on private lands if we wish to address the extinction and biodiversity crisis we undoubtedly currently face.

This sort of conservation landscaping comes in many forms: it may be a pollinator garden in the front yard, it may be preserving native canopy already present, maybe it’s advocating for native street trees in your HOA, or creating a rain garden. It could be as simple as replacing non-native invasive vegetation with native alternatives, or as involved as going entirely “no-lawn” across your entire property.

Whatever form it may take, it’s arguably the most direct contribution we as individuals can make to address collapsing biodiversity. I often try and focus on the optimistic side of restoration, but to adequately understand why conservation landscaping is so important, I should quickly lay out the scenario we find ourselves in:

Study (1) after study(2) after study(3) suggest that we may already have lost an outright majority in the number of flying insects worldwide. Birds, the vast majority of whom depend on insects as a food source for at least part of their lifecycle, have declined in the US by 30% in the last 50 years(4). Our plant communities, facing increasing rates of local extirpations driven by invasive flora and fauna(5), are increasingly homogeneous and less diverse(6). Without intervention, 40% of insect species are threatened with extinctions(7), which will certainly have reverberations for other flora and fauna. Amidst all this, over the decade from 2010 to 2020, governments have failed to meet even one of the 20 targets for biodiversity conservation set by the UN.

(1) Hallmann, C., Sorg, M., Jongejans, E., Siepel, H., Hofland, N., & Schwan, H. et al. (2017). More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLOS ONE, 12(10), e0185809. https://doi.org/10.1371/journal.pone.0185809

(2) Lister, B., & Garcia, A. (2018). Climate-driven declines in arthropod abundance restructure a rainforest food web. Proceedings Of The National Academy Of Sciences, 115(44). https://doi.org/10.1073/pnas.1722477115

(3) Hallmann, C., Zeegers, T., Klink, R., Vermeulen, R., Wielink, P., & Spijkers, H. et al. (2019). Declining abundance of beetles, moths and caddisflies in the Netherlands. Insect Conservation And Diversity, 13(2), 127-139. https://doi.org/10.1111/icad.12377

(4) Rosenberg, K., Dokter, A., Blancher, P., Sauer, J., Smith, A., & Smith, P. et al. (2019). Decline of the North American avifauna. Science, 366(6461), 120-124. https://doi.org/10.1126/science.aaw1313

(5) Mathiasson, M., & Rehan, S. (2020). Wild bee declines linked to plant‐pollinator network changes and plant species introductions. Insect Conservation And Diversity, 13(6), 595-605. https://doi.org/10.1111/icad.12429

(6) Daru, B., Davies, T., Willis, C., Meineke, E., Ronk, A., & Zobel, M. et al. (2021). Widespread homogenization of plant communities in the Anthropocene. Nature Communications, 12(1). https://doi.org/10.1038/s41467-021-27186-8

(7) Sánchez-Bayo, F., & Wyckhuys, K. (2019). Worldwide decline of the entomofauna: A review of its drivers. Biological Conservation, 232, 8-27. https://doi.org/10.1016/j.biocon.2019.01.020

We know the recipe for a turnaround: extensive conservation of the natural lands and waters we have left, and restoration of the huge swaths of the planet we have badly degraded, with a goal of protecting up to half the planet. Phrased that way, success may seem impossible, but if we focus on managing what we can, we can create an interconnected web of backyard habitats where the total value is far greater than the sum of its parts. Indeed this line of thinking is behind Dr. Doug Tallamy’s Homegrown National Park efforts, and in-line with existing programs locally like Audubon at Home certification.

To specifically address biodiversity and habitat in one’s own property, the prescription is surprisingly simple: Remove negative stressors from the landscape and cover as much of the area as you can with native plants, most of them common.

To the first point, effective interventions are ceasing the use of insecticides (even those advocated as “bee friendly” kill moths, sawflies, and other ecologically significant native insects), reducing light pollution, reducing the area and frequency of mowing, keeping leaf litter on site, and removing invasive species. Without these simple, no-or-low-cost changes in management, native plants and the fauna that depend on them cannot thrive.

When it comes to replanting, we should think of horses not zebras. In sunny areas, common forbs like goldenrods (Solidago spp., Euthamia graminifolia), sunflowers (Helianthus spp.), various other asters (Symphyotrichum spp., Rudbeckia spp,), mountain mints (Pycnanthemum spp.) and bonesets (Eupatorium spp.) along with various native warm-season grasses (e.g., Schizachyrium scoparium, Andropogon virginicus, Sorghastrum nutans, Tridens flavus) form the basis for many of our dry to mesic meadows in our region. Though the plants are common, they support many specialist insects. Research by Jarrod Fowler and Sam Droege found that along the eastern US, goldenrods alone supported 39 pollen-specialist bees, with native sunflowers, asters, and Rudbeckia following closely behind.

Where we have specific conservation targets in mind, we can be sure to include specific host plants. Perhaps including Zizia aurea to support black swallowtails, or Chelone glabra for the endangered Baltimore checkerspot butterfly and of course Asclepias spp. for the monarch.

While the constituents shift as we move into forested habitats, the general maxim of common plants first stays the same. Oaks (Quercus spp.) and hickories (Carya spp.) are some of the best choices across a wide range of wet to dry forests. These too are ecologically significant with Dr. Tallamy noting that oaks host more butterflies and moth caterpillars than any other genus of tree. Along forest edges black cherry (Prunus serotina) is another great option both for supporting insects and birds. Species like pawpaws (Asimina triloba), persimmon (Diospyros americana), and even chokeberry (Aronia spp.) could fit into food forest or other forage-friendly landscapes for people and animals. More ambitious foragers may even find a use for all those extra mast-year acorns!

Filling in gaps in the structure of your landscape can have huge benefits by unlocking habitat for new species. Understory trees and shrubs (e.g., Carpinus caroliniana, Corylus americana, Cornus florida, Euonymus americanus, Viburnum spp.) provide nesting spots for songbirds, branches from which phoebes and peewees can hunt for insects, and more options for insect pollinators. Some early-flowering trees and shrubs (e.g., Lindera benzoin, Acer rubrum) can help support early-emerging pollinators in forested or forest-edge conditions at a time in the year when most meadows haven’t begun to leaf out.

By laying the foundation by using some of the common species mentioned above, it is possible to support more specialist or more delicate species later. That meadow with plenty of goldenrod, may become a haven for showy Liatris spp. or the forest fragment that has its understory layer repaired may now better function as a refuge for various spring ephemerals.

Not only have the ecological value of the individual garden improved, but if a few neighbors become similarly inspired, or the garden is near enough to parks or other fragments of habitat that already exist, the positive effects are magnified by reconnecting these fragments. These reconnections have been shown experimentally to reduce the risk of extirpations, provide better more expansive habitat for wildlife, and genetically connect plants to one another protecting against long-term risks like inbreeding depression. Not a bad benefit for an individual garden!

The future of plant conservation looks to be difficult, but we’re lucky enough to know what the solutions look like. While we undoubtedly need big top-down intervention, we can make a difference with individual action here, and indeed we absolutely must if we’re to come anywhere close to the sorts of ambitious conservation targets set out ahead of us. We have to act and quickly – to protect and replant – to reclaim our planet’s biodiversity. It’s not an easy task, but as long as there are plants worth protecting here (and abroad!) we’ll be here to do it – and hopefully you all will be along with us too.

- Matt Bright

Conservation Manager