Dogwoods in the Anthropocene Forest

Until recently, we had a number of dogwoods (Cornus florida) on our wooded North Carolina property. Every April, we’d enjoy their beautiful, saucer-like white blossoms peeking through the other foliage, virtually the only reminder of their existence through the thick undergrowth. In September, their berries were enjoyed by a riot of birds. Mockingbirds, bluebirds, thrushes, cardinals, catbirds, warblers, robins, and half a dozen species of woodpecker all had a go at the tasty fruit. (See a wonderful blog post about the flower parts of the dogwood, our State Flower, by my colleague Melissa Dowland.)

Then, last year, the dogwoods in the back, shadier part of the section failed to appear. Investigating further, we found that they had all died or were hanging on by a thread. They had been attacked by a fungus – Discula destructiva. As the name implies, this is a serious problem for dogwoods and, if left untreated, will kill them.

Accounts of the spread of D. destructiva are reminiscent of those of pathogens of other trees: hemlock, beech, American chestnut. In the 1970s, New York gardeners began noticing that the lower branches of their dogwoods were dying and, in a few months to a few years, the whole plant was dead. At the same time, wild trees as far away as Seattle were showing the same symptoms. Over the next decades, the blight spread through gardens and forests and, in 1991 the fungus, new to Science, was named. Its origins are still unknown but its rapid appearance points to a foreign import.

Early symptoms (left) and powdery mildew on dogwood (right). Photos: Bob Mulrooney, University of Delaware (2021), courtesy of University of Maryland Extension.

Decades on, it has been worse in the East, killing many thousands – up to 90% – of dogwoods across 17 million forested acres. Trees growing above 3,000 feet, in heavier shade and drier soil have been most affected. Most of the vulnerable trees are now dead, so the disease is today much less prevalent (except – apparently – in our garden.)

However, the aftermath of this pathogen has had greater implications than simply the extirpation of a single species. Loss of this iconic seasonal blossom has reduced the draw of the forest for many ecotourists, keeping critical dollars out of the hands of remote communities who rely on natural resources for their livelihood. Reduction of this important seasonal food source also has an impact on bird populations, for which a background of changing climate and depleting biodiversity make survival increasingly challenging. (As of 2019, the net population of breeding birds in North American birds was down by 2.9 billion individuals. Forests alone have lost 1 billion.)

This is a glimpse of an Anthropocene forest – the Sixth Extinction happening before our eyes. The last century has been a deadly one for our trees, in the face of introduced fungi, nematodes, insects and other threats augmenting an already devastating history of deforestation. In the last 30 years, fully a quarter of the death toll of trees in Shenandoah National Park VA, say Smithsonian scientists, has been because of pests introduced by us.

Western Bluebird eating dogwood berries in Siskiyou, California. Photo: Deb Parker (2017)

While many native landscapes are now unable to harbor dogwoods, gardeners (at least those of us with a sunny exposure and a bottle of fungicide) can keep the native dogwood going. Is this the forest of a New Age, where each species must be carefully tended to keep it going in the face of mounting pathogens? Increasing urbanization and a blurring of the idea of wilderness, underscores the importance of urban green infrastructure to plant communities and the wildlife that depends on them.

Garden design, however, too often fails to live up to its potential as wildlife habitat. Our obsession with lawns, pesticides, and concrete seriously undermines many gardens for the very landscape values (birdsong, butterflies) we appreciate. These are habitat characteristics that native forests are increasingly unable to provide. Those of us lucky to steward some proportion of the Earth’s surface – however small – have an important gift.

Two years ago, I was fortunate to co-host an in-depth interview with the late Professor E. O. Wilson on our podcast, Love Nature. In it he talks about the need to set aside half of Planet Earth for nature to save it – and us – from a global collapse of ecosystem function. Of course, we can’t carve it in half like an apple. Wildlife, over much of the Earth’s land surface, has to live wherever humans allow, which means that our ability to facilitate an integration makes a big difference. If you’re in North Carolina, you can get started at home with this great page from the North Carolina Wildlife Federation’s information about gardening for wildlife. Through them, you can even certify your garden as wildlife habitat, a fantastic initiative. For anywhere else in the country, try this link.

Even for those of us in cities, every action – digging a frog pond, keeping a fruiting tree alive, planting a community garden, or simply putting out a flower pot for a passing hummingbird – helps to green our urban landscape and pave the way for a healthier future. The benefit of the sum total of these actions is immeasurable.

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