Friday, 24 August 2012

Dicing with Dangerous Natural History

Recent postings on Facebook from a naturalist who decided to acquire personal experience of the effects of giant hogweed on her arm reminded me of someone I knew in the New Forest who wanted to find out about the effects of the bite of the large tabanid fly Tabanus sudeticus. There cannot be many who have not been plagued by that silent but deadly pest, the horse-fly but how many have actually been bitten by other tabanid flies in Britain. Of course in Africa, it is a tabanid fly, the tsetse fly that carries the deadly sleeping sickness.

Giant Horsefly, Tabanus sudeticus, New Forest
The Giant Horsefly Tabanus sudeticus is comparatively common in the New Forest where it preys on horses. New Forest ponies can often be seen rushing around to avoid being bitten by the noisy Tabanus sudeticus which is certainly not as insidious and silent as the horse-fly we all know and hate. However once on a horse’s back, and in a part of its anatomy where the tail cannot brush, Tabanus sudeticus can cling on and will not be disturbed as it feeds. The chances of any human being bitten by Tabanus sudeticus, as it is such a clumsy, noisy beast are remote. A naturalist friend of mine decided he wanted to experience personally the effects of this fly. He caught one in a jam jar, and then applied it to his hand. The fly took some time to take the hint, but eventually began by scything with its mouth parts to make a wound. Blood began to escape from the wound, and the fly enjoyed its meal. My friend’s first reaction was “Well that’s pretty innocuous.” However, a few hours later his hand swelled up like a balloon, and he became really very ill.

Poison Ivy, Dallas, Texas
I remember the first time I visited Texas being tempted to see if I were effected by poison ivy. In retrospect, I think to have conducted an experiment on myself would have been both foolish and unpleasant. I remember my wife telling me about an Indian colleague of hers at work who complained that in Britain, brushing against vegetation was strangely unpleasant and hurtful. The fact was she had never experienced stinging nettles before. A few years ago, I was undertaking an ecological survey in East Sussex when I found a nettle with narrow leaves. I had recently heard about the Fen Stinging Nettle Urtica galeopsifolia that has narrow leaves, and is supposed not to sting. Having looked at the leaves carefully and being fairly reassured that there were few, if any stinging hairs, I touched it gingerly. I was not stung. Was this a good enough indication that I had found the species? In fact, I still believe that the actual status of Urtica galeopsifolia is in doubt, and that it may simply be a form of the normal, unpleasantly painful stinging nettle we all know and avoid.

As a naturalist, reactions to danger can be less healthy than those of other humans. I well remember being in the Pamir Mountains in Uzbekistan when a member of the party I was leading shouted up to me that he had spotted an Asian Cobra. My immediate reaction was to rush down the hillside, and I was rewarded by seeing the snake as it slid off into the undergrowth. On another occasion, my party was stranded in Tashkent. Our transport onwards to Kirghizia was delayed as senior soviet officials had purloined all the seats on the flight we were to have taken. We had a day that was fallow, and the local organisers of our trip wondered how to keep us amused. We were taken to a zoological institute, and shown cabinets full of bird skins. This did not keep us occupied for long. Then someone had a brainwave. Would we like to see the snakes? We were taken to the relevant part of the building and ushered into a rather small office. In the corner was a cage. Between us and its contents there was nothing but a layer of chicken wire. I was at the front of our group, and to say I was uncomfortable when the cage was opened would be an under-statement. The inhabitants of the cage reared up, fanning their heads as our host pushed his hand towards them. They were Asian Cobras. “They’re quite harmless,” our host explained, “Rearing up like that is all show. You really have to positively persuade a cobra to bite you.”

For the next stage of the visit, we were ushered into laboratory where a taciturn scientist was handling a Soviet species of pit viper. The most poisonous snake in the Soviet Union, he told us. He held it behind its head, and pushed its fangs into a beaker. Two jets of a colourless liquid squirted into the beaker, and these would be used to produce anti venom.

“Do you ever make any mistakes?” a member of the party asked. For answer, the scientist held up his hand. One of his fingers was missing, and he explained that he had to decide whether to use an axe lying close to him, or die.

Silk-moth caterpillar, with poison spines, from Ecuador
I am lucky in that I am not affected by the hairs on the tails of brown-tail moths. I have never actually done an experiment to prove this, but have come into contact with sufficient of them, and of other British caterpillars to know that I am probably immune. In Ecuador once, I came across the caterpillar of a species of silk-moth armed with vicious looking spines. Our local guide told us that those spines contained a venom quite powerful enough to put you in hospital.

There is a certain thrill that many humans, and probably many naturalists have in close encounters with dangerous plants and animals after they have got away with the encounter. On one occasion, a local guide told me of an eyelash viper behind a vine on a massive rain forest tree in western Costa Rica. I went down to investigate and failed to spot it.

“Your eyelash viper has gone,” I told the local guide when I saw him later.

“When was that?” He asked

“Oooh, about an hour and a half ago,”  I replied.

“Well it was there twenty minutes ago.” He assured me. After he told me exactly where it was, I went back and sure enough, looking obvious it was very much still there. I shuddered when I remembered that I had looked for lichens with a handlens on that tree when I thought it was safe to do so.

Eyelash Viper, Costa Rica
On another occasion in Costa Rica, the rest of my party went off horse riding for the day. I decided to have a day to myself. I walked off down several lanes, and found a dry hillside which looked promising. I became aware of a bird call which consisted of two whistle like notes. After a while, I found I could do the top notes, and the bird would reply with the lower note. Very gingerly, I began to approach the sound and I was rewarded with good views of a delightful Lesser Ground Cuckoo. When I got back to the centre, I told the local guide where I had been. After satisfying himself with my location he said. “That was not very sensible. That particular hillside is home to a large number of tropical rattle snakes.”

Thursday, 16 August 2012

Woodland Continuity

Common Lungwort - Lobaria pulmonaria
It was Francis Rose who, way back in 1974, first recognised the value of lichens in assessing ecological continuity in woodland. A list of seventy species was compiled by the British Lichen Society which were found to be most closely associated with ecological continuity and lack of disturbance. This list was used to arrive at the New Index of Ecological Continuity (NIEC). Added to this, a list of rarer, bonus species could be used to calculate a second index. These indices work well for much of Britain, however further indices were formulated for areas where other lichens were found to indicate continuity. Where the large and showy common lungwort Lobaria pulmonaria works well as an indicator throughout much of England, it is a common species in Western Scotland, and its presence there cannot be used as an indicator of continuity. For upland England and Wales, as well as in Western Scotland, the Eu-Oceanic Calcifuge Woodland Index is used. Further indices are used in Scotland and Western Ireland.

Heterodermia japonica growing amongst a form of
Hypnum cupressiforme
It was noticed while undertaking a survey in Eastern Cornwall in a nature reserve known to consist of ancient woodland, that the nationally scarce lichen Heterodermia japonica occurring on a beech branch was fertile, and supported a number of small, disc like fruits or apothecia. A day or two later, there was a depression in the lichen where the fruits had been. It seemed most probable that a slug had browsed them off. Some six months later, the site was revisited, and small daughter colonies of the lichen were found up to six feet away from the parent lichen. If, as seems probably the main vector for spreading the spores of ancient woodland indicator lichens is the digestive system of slugs, then distribution is going to be very slow indeed. No slug will ever take the trouble to cross a major road simply to spread a particular species of lichen.  Slugs are also ideal as vectors as the spores are conveniently attached to the substrate in their slime trail. It would be interesting to experiment by collecting slugs from known ancient woodland sites and introduce them to more recent sites to see if indicators of continuity became established.

Francis Rose, and Richard Hornby of the then Nature Conservancy Council, made a list of higher plants reckoned to be associated with ancient woodland. While the clear felling of a wood totally removes the corticolous lichen flora, higher plants are more robust, and are therefore useful in assessing ancient woodland sites. It is most important to remember that the higher plant list consists of common species, and that it is the total of species present that is significant. The absence of rarer species lacks significance just as does the presence of one or two of the common indicators. Higher plant indicators are all photosynthetic, and therefore need adequate light levels. In many ancient woodlands, due to the current lack of grazing, the ancient woodland flora is confined to rides, or to the roadside banks of the edge of woods.

The British Bryological Society have also made a list of mosses and liverworts most closely associated with woodland continuity that works well and I understand that in the insect world, similar lists of beetles and hoverflies have been made. It would be most interesting to know if there are correlations between all ancient woodland indicator lists.

Barnacle Lichen - Thelotrema lepadinum
One of the difficulties of using lichens, and to a lesser extent bryophytes as indicators of ecological continuity is their sensitivity to air pollution. Throughout most of Central and South-eastern England until some thirty years ago, acid rain and industrial pollution all but destroyed the lichen flora totally, and with it the information it could give. It is lucky that the Barnacle Lichen, Thelotrema lepadinum, which is a most useful indicator, is relatively tolerant of sulphur dioxide in the atmosphere, and it has been found, as would be expected due to the ecological continuity of the sites, in both Epping Forest and Hatfield Park. Even low lichen indices of continuity in these areas can be treated as significant.

Most of the early work that related lichen richness with ecological continuity took place in the deciduous woodlands of England, Wales and North-western Scotland. In Central and Eastern Scotland there are pine forests of great ecological importance and continuity. The lichen flora associated with these trees is very different, as are the habitats they provide. Dr Brian Coppins, the foremost Scottish lichenologist, is known to say that the only good pine tree [for lichens] is a dead pine tree. He points out that a pine provides habitat for lichens for a longer period as a standing dead tree than it does when alive. While coppice woodlands with hazel or hornbeam in England can be important for lichens, and the coppice poles can support a rich flora, this is nothing compared with the incredible richness found in a few very important and ancient hazel woodlands in western Scotland and in the Hebrides.

A further index using lichens is also used, but these days only occasionally. This is the Revised Index of Ecological Continuity (RIEC). In this case thirty species are used, and by multiplying the number of species by 5, a figure for the index is found as a percentage. A score of 100% is reckoned to equate to a wood with perfect ecological continuity. However scores higher than a hundred are possible such as Glen Shira in Scotland with a score of 130%. Using the New Index of Ecological Continuity, a total of thirty or more species that includes bonus species is thought to indicate a wood of high conservation value. Parham Park which is arguably the best example of ancient woodland in Sussex has a total of 27 NIEC species added to which should be 3 bonus species bringing a total score of 30. In other parts of Britain, much higher totals are found.

Francis Rose was never keen to indicate the meaning that should be given to higher plant indicator totals. However, he told me he was of the opinion that a score below twenty species indicated a wood of low conservation interest. Similarly a score of twenty bryophytes indicate conservation value, though this is reduced to fifteen throughout South-eastern England.

Hoverfly - Calliprobola speciosa
Beetle - Helops caeruleus
Some groups of insects also contain species that are good as indicators of ecological continuity. Two groups certainly spring to mind which are  hoverflies and beetles. Two illustrated here are the rare New Forest hoverfly Calliprobola speciosa which could be used, as could the beetle Helops caeruleus. There are many more hoverflies and beetles that could be used as indicators of ecological continuity.

This account has been to do with ancient woodland with continuous canopy cover. This type of woodland is not rich in butterflies. For butterfly richness, it is the woodland rides and their floristic richness that are important.  Woods such as Bernwood in Oxfordshire are soft wood plantations, but the richness of the rides make them outstanding for insects such as butterflies. Beautiful bluebell woods are not examples of woodland with long continuity, but are none the less very important. Similarly, it is coppiced woodland that generally provides habitat for greatest flowering plant biodiversity. It is a balance that is required as well as the importance that is given to woodland with a long history.