Botanizing at Devil’s Dyke

botanize (or botanise): v., to study plants in their natural habitat (akin to birdwatching)

When I heard that Ed Tanner, retired plant ecology professor from my department who still sits in on ecology group meetings, was taking a few other students out on Saturdays to nature reserves around Cambridge to botanize, I didn’t waste time in inviting myself along. I was delighted by the chance to explore new places and absorb some of the decades of plant and place knowledge that Ed has to offer (not to mention being one of the most Cambridge-y ways I could possibly spend an afternoon). The next trip planned was to Devil’s Dyke. All I really knew about Devil’s Dyke was that it was a very old landmark somewhere out in the countryside—near Newmarket, of horse racing fame—and, Ed told us via email, is habitat to rare orchids.

Devil’s Dyke is obvious as we approach it through the fields: a long, straight, pyramidal green mound intersected by the road, with walkers rambling along the top for scale. Ed pauses in the parking lot to give us some context, and in true naturalist fashion, he starts at the beginning. He unfurls two colorful geological maps of southern England on the hood (ahem, bonnet) of the car and describes how the underlying strata of England laid down by ancient seas have been tilted and eroded to stripe England with progressively older strata from east to west (stands to reason the first scientist to figure out stratigraphy was British, he quips). He points out the chalk band running through Cambridgeshire, and then points to the second map, which shows the Quaternary sediments laid over the top, mentioning in passing the extent of glaciation during the Ice Age (down to London), the places that would have been forest when the ice retreated and people moved in to cut it down, and the clay and alluvium and peat flanking the chalk on either side of Cambridge. This is where we come to Devil’s Dyke: the chalk was much easier to navigate and build on than the clay or the marshy peat, and the forests here had been cleared, so the narrow chalk band became the main thoroughfare across this part of East Anglia (people can still walk the ancient Icknield Way). The Anglo-Saxons presumably wanted to control it, so they built four huge dykes across Cambridgeshire to hedge up the way. Devil’s Dyke—or Ditch, for the ditch running alongside the dyke—is the biggest at up to 30 feet high and 7 miles long; I had also heard of Fleam Dyke, but not the more eroded Brent Ditch or Bran Ditch.

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That’s the geological and anthropological history, but the main reason Ed is interested in Devil’s Dyke is for its current ecology: it hosts one of the most extensive chalk grasslands in the area, which is in turn one of the most biodiverse plant habitats in England. This is thanks to chalk soil’s poor nutrient content, providing a haven for many scrappy plants that are outcompeted by nutrient-loving plants on richer soils but come into their own on chalk. It’s funny, Ed says, because chalk grassland is a human-made landscape—originally there were woodlands on chalk, but people cleared them millenia ago and their livestock kept them clipped and free of woody shade. When chemical fertilization hastened agricultural revolution in early 20^th century, monoculture fields became more feasible and profitable on these lands, and grazing stopped—except for a kink in the story where rabbits were introduced by the Normans after 1066, and they took over the grazing of chalk grasslands centuries later. They eventually became too well-adapted for their own good, however, drawing the ire of farmers (e.g. McGregor) and ending in a rabbit apocalypse when myxomatosis, a rabbit virus, broke out and was allowed to run its course and wipe them out in the mid-20^th century. Thus—coming back to Devil’s Dyke—the chalk grasslands were overrun by shrubs and common weeds. But ecologists and conservationists wanted the biodiversity and rarity of the chalk community back, so they began clearing the shrubs themselves, with mixed success, and sometimes running sheep, which is expensive. The section of Devil’s Dyke that we are about to walk are a mosaic of these strategies, leaving some patches of chalk grassland to flourish and others choked.

With that story told, we can go up onto the dyke and walk along the worn chalk track. The dyke commands a view of vivid green pastoral idyll with an industrial streak: fields sentried by towering pylons strung with electrical wires, skylarks trilling somewhere in the air between wheat and wire. Farther out in various directions we can see old windmills and new wind turbines, the white pavilion of the Newmarket racecourse grandstand, and just barely, Ely cathedral. Just below us is the steeply pitched Devil’s Ditch, full of shrubs the Devil’s Dyke conservators haven’t bothered to clear because too many soil nutrients accumulate down there for chalk grassland to thrive.

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We pause every few steps for Ed, tall and lanky in a straw hat and suspenders, to point out a plant in the tangle of the bank. Some are introduced species from Europe or Asia but still of ecological interest; some are native but not chalk grassland elites; others are weeds and ignored entirely (including a common but bonny member of my study genus, Veronica chamaedrys, with flowers like blue eyes). The stars of the show are the chalkland species, some of them thrillingly rare. Most of them are in flower, little splashes of color in the grass, but not flamboyant. They’re flowers to be bent over, some to be looked at with a magnifying loupe, which Ed does frequently. I write down the names phonetically, unfamiliar with many and having to decode Ed’s understated British accent, and try to quiz myself on the flowers as we pass.

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There’s sainfoin, a tall and unfurling magenta legume; bird’s-foot trefoil, another legume with bright yellow winged flowers and frilly pinnate leaves; salad burnet—the name makes me chuckle—with bunchy green bracts dangling the tiny red flowers; rock rose, Helianthemum, sunny yellow saucers that I keep confusing with buttercups; wild thyme, ground cover with quaint purple flowers; milkwort, Polygala, ubiquitous dark pink and purple flowers with splaying winged petals; dropwort, Filipendula, long stems crowned with elegant white flowers, one of my favorites of the day; quaking grass, Briza, with dainty quivering clusters of small seed heads; marjoram, with its strong sweet-tangy herb scent; horseshoe vetch, Hippocrepis comosa, more yellow pea-flowers arranged in a companionable circle; Leontodon, sunny and dandelion-like; purple milk vetch, Astragalus danicus—a very rare chalk grassland plant with delicate upright violet flowers. Gromwell, knapweed, mignonette, Plantago, Medicago, bugloss, bryony, forget-me-not—the list goes on.

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The shrubs are diverse in their own right: elder—a bush with pretty, dense white clusters, the ones used to make the ubiquitous British elderflower cordial; rose—Ed’s not sure which of the half-dozen native varieties, but it has large, attractive blushed white petals in the natural set of five (only artificially bred roses have the dense layers of petals we’re used to); native privet (related to the privet hedges lining the streets of Cambridge); hawthorn with wavy leaves similar to oak and prim white flowers; Cornus, dogwood relative whose leaves have elegant veins that stay threaded together by the uncoiling inner fibers when torn in half; buckthorn, Rhamnus, a handsome leafy shrub with clusters of green flowers.

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The orchids are our main quest. You may be imagining the flamboyant, tropical blooms on your windowsill, but orchids are one of the most diverse plant families in the world, and can take on as many shapes as there are species (fascinating article on British orchids here). In the chalklands, orchids are dainty spikelets of flowers with recognizable orchid shape—wide lower lip, curved upper tepal, inner tepals brought into the center, wings on either side—only when you look closely. Ed was tipped off as to where particular orchids have been sighted before, so he tells us when to start looking for the pinkish spikes. When we spot one on the steep dyke bank, we take turns kneeling over it to catch its scent (I don’t succeed) and look for its unusually long spurs, eventually identifying it as a fragrant orchid—not the rarest species, but a nice find.

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I also pull out my binoculars to track the skylarks and a whitethroat singing its heart out in a hawthorn bush. No one else in our group shows the same zeal for creatures as for plants today, but Ed does remark on the skylarks and the yellow brimstone butterflies floating around. I can’t name the white or blue ones. We pass several tent caterpillar nests seething with furry caterpillars. Once we pass a gate where the management of the grassland changes hands, we start to see snatches of wool on the branches and fences. Along the east side of the dyke is a succession of small fenced fields meant for both grazing sheep and maintaining biodiversity, an unusual sight—but Ed doesn’t know how long that farmer’s method will last now that Brexit has cut off EU livestock subsidies.

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The dyke goes on for several more miles, but botanizing is too slow-paced to go far. We run into some of Ed’s botanist friends also searching for orchids, so we turn back to show them the ones we found. They reciprocate with a pyramidal orchid, purple flowers, bunched at the top of a thick stem and not yet fully opened into their pyramid. The friends had been looking for a lizard orchid from past visits but are afraid it was chomped by sheep (we helped them sweep the ditch for it with no luck).

On our way back I catch a comment from Ed bemoaning the dominance of computers in the research we’re doing as students in the ecology group. He says his heart sank the last time we announced a programming training session in group meeting with the tagline that working with big data (genomes, satellite images, climate data) is 80% of what we do. “You’re ecologists,” Ed says. “This isn’t how it’s supposed to be.” It’s an irony that also tugs at my heartstrings. I took up computational approaches to ecology research early in my education because it’s seen widely as the future of ecology, working on larger and larger scales to predict and combat climate change, biodiversity loss, you name it. Computational skills are in demand and I enjoy the challenges of learning them. But I was painfully aware, from the beginning and to this day, of how difficult it is to keep a hold on local, immediate ecology—the names of plants, the dynamics of nearby streams, the communities in small patches of grassland—when you elect to center your research in your computer.

This is a big reason why, I think, Ed is so keen to invite us students on these trips, and why I was so keen to accept. Regardless of what I’m doing with 0s and 1s for my PhD, or indeed what I’m doing with my career at all, I’ve resolved to get to know the nature where I live. Noticing and naming the sainfoin, the dropwort, the rock rose, the purple milk vetch, the fragrant orchid—this is the beginning of befriending a whole community, and the ancient chalk that brings their roots together. I still have so much to learn.

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