This Wild Side column comes to you from Kent, England, where I’ve been sampling the local wildlife for the past week or so. From our base in the seaside town of Whitstable, we’ve been exploring the downs and marshes of this interesting region, and as always, I’m finding the process of learning new plants and animals to be exhilarating.
It has been the downs — chalk hills often characterized by thin soil supporting grassland — that have especially interested me. I’ve always been fascinated by the biological diversity that emerges in the places featuring the harshest conditions, and downland, like the sandplain of Martha’s Vineyard, fits that description.
The underlying chalk is essentially a thick layer of fossil plankton. As one can see at the most famous site featuring chalk downs, the White Cliffs of Dover, this layer can be hundreds of feet thick. Tectonic uplift and erosion over millions of years have carved this layer into an often spectacular topography of hills and valleys.
The chalk is porous, rapidly draining away rainwater, so like the Vineyard sandplain, chalk grassland is a drought-prone ecosystem. Especially on hilltops, the soils tend to be thin and nutrient-poor. As humans began developing pastoral and agricultural lifestyles in this region, as the last Ice Age waned some 10,000 years ago, these areas were rapidly found to be unsuitable for most crops. But grazing was another story, and across the millennia, industrious cows and sheep have disturbed the vegetation over and over again. (One might think of the shorter but even more intense histories of grazing and fire on Martha’s Vineyard as a similar ecological force.)
As on the Vineyard, chalk grassland evolved under this pressure into an ecosystem dominated by species highly specialized for these specific conditions. However, modern economic patterns have reduced the utility of grazing livestock on inaccessible, marginal land, and the resulting loss of grazing has altered the character of the vast majority of chalk downland. Also as on the Vineyard, ecologists have noticed the loss of diversity, and begun campaigns to reintroduce grazing onto these unique lands.
One of the most characteristic downland species I encountered was the chalkhill blue, a smallish butterfly essentially limited to this habitat, often (notes my field guide) “on short turf interspersed with flowers.” Specialized it may be. But this species flourishes where it occurs. During a good seven miles of hiking on the clifftops near Dover, I was rarely out of sight of this butterfly, and in the most flower-rich meadows, it was about as abundant as butterflies get.
Related to the spring and summer azure butterflies of Martha’s Vineyard, the chalkhill blue is, like most of its British relatives, sexually dimorphic — that is, males and females differ dramatically in appearance. Males are pale blue on top and pale beneath, marked with an intricate pattern of white-ringed black dots. Females show the same underwing pattern, but a darker overall below and muddy brown above, with no trace at all of the male’s ethereal blue. Mating pairs are always jarring to my eyes, registering as paired members of two different species.
While of course I kept an eye out for chalk grassland rarities, it is the nature of rarities to be rare, and without the benefit of experience of detailed local knowledge, I had to depend mostly on dumb luck for an encounter. Perhaps my most interesting find was a modest population of stripe-winged grasshoppers, an elegant green grasshopper with a patchy distribution on downland across southern England.
I was exploring the Lydden-Temple Ewell Nature Reserve, not far from Dover. The reserve had not been easy to find, and once there, I was a bit underwhelmed. While there were traces of good grassland, most of the area had been “improved” into hay fields with deeper, richer soils than what I was looking for, supporting mainly just the common generalists I had seen in many other places.
I finally found a good-size patch of the real thing, though: recently grazed grasses and wildflowers spread meagerly on soil so thin that large areas of smooth chalk showed at the surface. This was the moment when I finally understood what the fuss is all about! Insect abundance and diversity on this small area was astonishing, especially relative to what I had observed in nearby hay fields, and I spent nearly two hours working a rough circle barely 100 feet in diameter.
Even at that, stripe-winged grasshoppers were a bit of a challenge to pick out among the hordes of other, more common grasshopper species. But with persistence, I found about five, and managed to photograph two.
The experience was a rewarding one, and faintly jarring. Superficially, very little about this open ridgetop suggested Martha’s Vineyard. Yet the incredible diversity, and that diversity’s clear connection to the harshest conditions to be found, seemed intimately familiar. Wherever you go, challenging conditions represent opportunities for the species that can find strategies to survive. That’s where I like to be.