Dark Matters

I learned a new ecological term this week. Johnny Randall, the Director of Conservation Programs at the NC Botanical Garden, mentioned it while we were discussing material for an article we are collaborating on for the spring issue of their magazine, Conservation Gardener. Although the term was new to me, the meaning behind it was not unfamiliar.

Dark Diversity

Three researchers from the University of Tartu in Estonia developed the concept of dark diversity in a paper they published in 2011. Their term was chosen to parallel the notion of dark matter in astrophysics. As with dark matter, dark diversity can be inferred from data, but it cannot be seen or directly measured.

Conservation ecologists, especially those attempting to restore or sustain ecosystems, are using the idea of dark diversity to help them assess the health of the system they are studying. Imagine a healthy ecosystem, one with all its components, where every plant, fungus, insect, bird, etc. that should live there actually does live there. This is almost never true anymore. Humans have fragmented and/or destroyed so much now that nearly every bit of forest, field, stream, coral reef, etc. is missing species that were, until fairly recently, components of those ecosystems.

Soft gold of changing leaves of green ash trees on the floodplain

Thus, these days when conservation ecologists attempt to preserve/restore special examples of ecosystems, often those containing rare plants, they not only must identify the species present on the site; they must also attempt to figure out what species are missing. Species still present can be seen and counted, their viability assessed; this is visible diversity. The absent species, the ones that should be there but aren’t define dark diversity.

I’m oversimplifying the concept a bit, but, basically, ecologists estimate dark diversity by looking at species diversity in the region in which their study site is located. If, for example, a section of forest being restored was missing wood thrushes (one of my favorite summer visitors of our forests), but those birds were known to live in patches of forest in the region, wood thrushes would be identified as part of the dark diversity of the study site – a species that should be there, based on its presence in the region, but is absent.

As I can best understand the concept, by measuring the amount of dark diversity, ecologists can better guess how difficult it would be to restore a given site to full diversity – to bring back all the missing species that should be living on a site but aren’t.

Dark Diversity on Our Five Acres

When Johnny Randall mentioned the concept of dark diversity, it immediately resonated with me, because Wonder Spouse and I have been playing with the dark, as it were, on our five acres for over three decades now. When I first saw this land on a cold January day almost 33 years ago, it was an ecosystem with substantial dark diversity. The previous owner had eliminated almost all the native grasses, wildflowers, shrubs, and understory trees, leaving only towering canopy-level trees and a lawn full of non-native grasses. I could hear birds, but I rarely saw them in our yard. There was nothing for them to eat near ground level, and no good nesting sites.

Snowy floodplain five years after we moved in.

However, the floodplain forest on the other side of the creek teemed with ferns, wildflowers, and a healthy shrub layer. Bird song echoed across our empty yard from that area. I knew that all of those species should also be living on our side of the creek. Those species not present on our land but living nearby were dark diversity – the missing pieces. I wanted to bring them back.

Through trial and error, luck, and hard work, we have rebuilt much of the species diversity that lived on our property before it was damaged by the previous owner. Fruit-bearing shrubs provide food for an array of species. Dense plantings of shrubs, grasses, ferns, and wildflowers provide food and shelter for insects, reptiles, amphibians, birds, and an array of mammals.

A barred owl with a mouthful of mouse caught by a wildlife camera on our side of the creek.

I am certain that our amateur habitat restoration efforts would not pass muster with the professionals, but I think our results speak for themselves. What once was unseen – dark – is now visible. The species that were nearby but absent on our land have returned. I do not have adequate words to describe how deeply gratifying it has been to bring the dark into light, to bring the missing species home.

Contemplating the dark seems an entirely appropriate occupation as we rapidly approach the darkest night – winter solstice. A wise person recently told me that, when navigating dark times, it is important to trust the invisible. It seems wise folks from astrophysicists to ecologists follow this guidance. Darkness – what we cannot see with our eyes – teems with life, with knowledge. It may well be true that we can learn more from the unseen than from our visible world.

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  1. #1 by rosegraham1889 on December 11, 2021 - 11:02 pm

    Thanks for restoring natural diversity on your 5 acres. Most people don’t have nearly that much land, and need to work together in communities to make their yards safe for wildlife.. Local Governments need to implement native planting requirements by all developers and educate homeowners to do it on their own. They also need to ban pesticide use without a permit, Garden shops need to be deterred from selling plants that don’t sustain birds and wildlife if non-native invasive plants aren’t outlawed. In the meantime, schools need to improve educating students about natural habitats in conjunction with other classes, such as math and science. They need to be taught the importance and needs of all living creatures and to appreciate them.

    • #2 by piedmontgardener on December 12, 2021 - 7:43 am

      Welcome, Rose! I think all of your ideas for change are worth considering. However, I think Mother Earth might fare better if we could build consensus from the bottom up. I agree with you that education is essential. We must open humanity’s eyes to the green world all around them, help them learn to love it the way you and I do. Personally, I am focused on the small scale I have some control over. I am blessed to have enough land to increment valuable changes on it, so I do. I am blessed to have writing skills, so I use them to recount stories about my work with my land, and my love for the natural world. I know that, one-on-one, I have reached minds and opened hearts to the natural world. As long as people like us — and I meet more every day — are trying to protect/improve native ecosystems, I believe we have cause to be hopeful. Happy holidays to you and yours.

  2. #3 by James on December 11, 2021 - 11:20 pm

    So glad both see you posting and the results you guys have achieved over time there on your corner of the world.It’s humorous that you made this posting since just this week I was wishing for you guys as neighbors. It’s bad enough to be downsized into this tiny lot but now I am the only dude with trees in the front yard since the guy down the road chopped his 2 maples down last week. My next door neighbor had a mature Black Oak the builder actually spared, only for the neighbor to remove. No wonder I so relate to ” the Lorax”. Merry Christmas to you guys, James

    • #4 by piedmontgardener on December 12, 2021 - 7:34 am

      Hello, James! It is indeed helpful when our neighbors understand the value of the natural world the way we do. Old ways of thinking about our home landscapes can be changed. Several large subdivisions in my areas now have HOA subcommittees about environmental issues. They’ve passed a rule that new landscape plants in common areas must always be native. They send out monthly newsletters describing invasive non-native species to watch out for, or describing a native plant especially favored by bees and/or birds. The process is frustratingly slow and incremental, but minds and hearts are being moved. I believe this can be done anywhere by people of kind yet resolute hearts. Keep walking the talk, James. You may be influencing more than you realize. Happy holidays!

  3. #5 by fiercebeagle on December 13, 2021 - 8:49 am

    We only have a third of an acre but we’re fortunate that the builders complied with our backyard neighbors wish to leave all the trees up when they built 25 years ago. We’ve let the large hill portion of our backyard (at the top of which is a stand of poplar, beech, wahoo elm, and pine) go to seed more than once, and now we have a 25 foot black cherry, another elm, and a maple growing of their own accord in our backyard. All our bird friends helped get us through lockdown.

    • #6 by piedmontgardener on December 13, 2021 - 9:17 am

      That’s wonderful, Erin! This is a perfect example of how a barren suburban yard can recapture its dark diversity — the local species that are supposed to be there — simply by allowing them to move in unmolested. I agree that the birds have been welcome companions during these challenging times.

      Thanks for sharing your story!

  4. #7 by Sharyn Caudell on December 13, 2021 - 2:01 pm

    I wasn’t familiar with dark diversity as a concept. I have 0.4 acres in Durham and have about 175 native species(plus some non-natives). I’ve watched the variety and numbers of birds increase each year. People visiting the garden always comment on how good it smells even when there aren’t fragrant plants blooming! I’ve been especially pleased to have native plants reappear in the garden without my help. You feel that Mother Nature is smiling on you when that happens. Thank you doing the work that you do and sharing what you have learned. Sharyn

    • #8 by piedmontgardener on December 13, 2021 - 3:28 pm

      Hi, Sharyn! Congratulations on the impressive species diversity on your relatively small lot. Your home is proof that you don’t need a lot of land to encourage natives — and to help them multiply. I agree that it feels like a blessing from Mother Nature when volunteer natives pop up unexpectedly. Thank you for your kind words, and thank you for tending your own garden of native delights. Happy holidays.

  5. #9 by Greg on April 4, 2022 - 11:03 am

    Fascinating subject – what is noticed as absent can potentially be made present.

    • #10 by piedmontgardener on April 4, 2022 - 12:40 pm

      Precisely so, Greg. Thanks for stopping by. Your blog, by the way, is magnificent. 🙂

      Cheers!

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