Can TCI protect its National Tree from an introduced pest?

By B. Naqqi Manco, Senior Conservation Officer, TCI National Trust and Martin Hamilton, UK Overseas Territories Programme, Royal Botanic Gardens at Kew

Biologists often ponder what thoughts were going through the minds of the people who witnessed the death of the last member of an entire species. What did the Cincinnati Zoo’s keeper of Martha, the last living passenger pigeon, feel in 1914 as he froze the bird’s body for the Smithsonian Institution? As a late 1600s sailing ship’s crewmember scornfully ate the last bite of the last of that despised Indian Ocean sailors’ food source, the dodo bird, was he aware it would be the last time he would have to taste it? When a Rapanui man on Easter Island felled the last toromiro tree, did he know that it signified the collapse of his advanced, literate Pacific culture?

Extinction is a natural process — the dinosaurs are a good example of a natural extinction. But since humankind has been dominating the Earth, extinctions caused by our activities have increased dramatically. Through habitat loss by our greed for land, introduction of non-native invasive species, over-harvest of natural resources and pollution, many of the world’s plants and animals have been put in a position where their long-term survival is in question.

One would like to think that in the “Beautiful by Nature” Turks & Caicos Islands, we would never have to face the prospect of witnessing the extinction of a native species. At this time, the Turks & Caicos National Trust is working in partnership with the Royal Botanic Gardens at Kew (London) and the Turks & Caicos Islands Government to make sure that one very special species will not become extinct in the Turks & Caicos Islands. In doing so, we hope to set a precedent that no native plant or animal extinctions will occur in our backyard.

The backyards that are in danger are the pine yards of Middle and North Caicos and Pine Cay. The Bahama Pine (Pinus caribaea variety bahamensis) forms vast stands of savannah-like scrub in the northern Bahamas, entirely skips the islands of the central and southern Bahamas, and appears again only on Middle and North Caicos and Pine Cay. These trees are true cone-bearing pines, not related to the “cedar” or Australian pine, a noxious invasive tree that invades the Turks & Caicos coastlines.

Few people outside of the islands of its native range ever see a “Caicos pine,” as their habitat is difficult to access and not a particularly comfortable one in which to be. Caicos pines grow on low-lying limestone bedrock with flooded solution holes on Middle and North Caicos, and on hard-packed sand on Pine Cay. Both of these habitats are extremely hot, with uneven ground and thorny shrubs. Despite this, walking past a healthy pine yard on a warm, breezy day will fill one’s nose with the unmistakable, strong, pleasing scent of long-leaf pine.

The pine yards are an ecosystem rich in plants and animals, some of which can occur nowhere else. The critically endangered Kirtland’s warbler, a small North American songbird, winters in the pine yards of the Bahamas and Turks & Caicos Islands. Several species of iridescent beetles only develop in the trunks of dead pines that have been burned in lightning-ignited fires. Even the fire is “native” to the pine yards — periodical fires started by lightning strikes burn out thick underbrush and allow pine seedlings to grow up, remaining the dominant and defining species of their realm. The adult trees shade out the underbrush from growing too quickly, so young trees are dependent on the presence of older trees to reach maturity. The tall, lush, deep forest green pines have been so useful to the history of the Islands (for making pitch and boat staves before both were available commercially), and such an icon of natural beauty, that they have been selected as the Turks & Caicos Islands’ National Tree.

Around 2001, residents of Pine Cay began noticing that something was wrong with their population of the national tree. Later, National Trust-affiliated botanical researchers noted the same problem on some trees in Middle Caicos — a sticky, dusty black coating on the needles accompanied by a sticky white flocking. Whatever it was, these coatings were killing the pine trees — fast. The trees threw off infected needles more quickly than they could replace them with new, healthy ones. The leaf quality was not good enough to allow the trees to produce seeds in their cones; later, they did not even have enough energy to set new leaves.

Royal Botanic Gardens at Kew researchers Martin Hamilton and Michele Sanchez began working on an identification of the problem in 2004. Martin Hamilton, head of the UK Overseas Territories Programme at Kew, found the source of the problem by drawing from his extensive horticultural training. The white flocking on the needles was a scale insect — later submission of samples to an insect pest specialist in the United Kingdom revealed the insect to be the pine tortoise scale, an important pest on pine trees in North America. Scale insects only move as larvae; when they find a suitable place on a pine needle, they clamp down onto it and become fused to its surface with a waxy coating. There, they suck sap from the needles. Living on a diet of pure tree sap makes the little insects hyperglycaemic — they consume so much plant sugar, they must pass most of it out their back ends as waste. This “honeydew” drops on the pines’ needles and other plants, and becomes infested with a fungus called sooty mould — which is the black coating noticed on the pines and other plants. This is the same fungus that makes sapodilly and citrus trees turn black in the Caicos Islands, and it blocks out light available to trees, resulting in reduction in food productivity. This, coupled with the parasitism of the scale insect, is killing our national tree.

Martin Hamilton returned in April 2007 along with new UK Overseas Territories Programme colleague Marcella Corcoran to further assess the infestation and damage. Research this year has shown that well over half of the individuals in our pine yards have died. Arduous hikes brought our team deep into the pine yards, where we assessed a number of points on each island where pine is present. Using measurement methods developed specifically for this project, the researchers documented percentage of trees killed, infestation level, tree health and recruitment (reproduction). Seedlings are present in many dying stands, but most are infected with scale and without newly dropped pine needles to feed forest fires, they are threatened by the understory scrub growing up and blocking out their light. While in some habitats there are natural predators to eat scale insects, our native ladybug beetles and wasps do not seem to find the pine tortoise scale appetising. If nothing is done to counteract this problem (which was very likely of human origin), the Kew team estimated that within ten years, our complete pine population would become functionally extinct.

How did the pine tortoise scale, an insect that cannot move in its adult female form, and whose adult male form is a weak, short-distance flyer, come to be on our native pines when the insect hails from the American northwest? While we have not yet been able to verify the material source, the most likely method of introduction was on live, cut pine trees imported at Christmas time. The Turks & Caicos Islands have few restrictions on plant importation, though laws requiring imported plants to be pest treated before importation are in the works. Pest treatment (usually by high-intensity ultra-violet light, a process called “phyto-sanitisation”) prior to export is expensive for plant sellers and buyers, and they will typically forego the phyto-sanitary process if it is not required by law. Unfortunately, this means that insect pests, fungi and even mammals, reptiles, and birds can be transported on plant material and introduced to our islands. Some of these introductions may be of little consequence. Others, like the introduction of the pine tortoise scale, can lead to the swift collapse of an entire ecosystem.

Will the pine tortoise scale cause the extinction of our national tree? Not if the National Trust and Royal Botanic Gardens can stop it. Our research has identified several stands of trees that are apparently resistant to the scale — most notably on Pine Cay and Middle Caicos, where a few remote patches of seedlings are eagerly growing up, lush and clean, in direct proximity to heavily-infested trees. A similar phenomenon occurred on Bermuda with their native cedar, which was nearly extirpated by an introduced scale insect but which was brought back from the brink of extinction by earnest propagation of seeds from a few resistant trees.

The National Trust has been collecting seeds of apparently resistant trees when possible, and has also begun a trial rescue nursery to grow seedlings in a carefully maintained area, free of scale insects. Marcella Corcoran concentrated her April 2007 fieldwork on acquiring pine needle samples from both infested and apparently resistant trees for a DNA analysis to find possible solutions to the problem. The Trust and Kew Gardens will also look into options such as vegetative propagation and cloning. A long-term species recovery project has been written and is currently being considered for funding by the Turks & Caicos Government.

One complication for habitat rehabilitation is that the pine trees maintain their own ecosystem, and it is likely that important considerations will have to be made about replanting, controlled burning and scale presence monitoring. Spraying stands of trees with insecticidal oils, injecting systemic pesticides and direct application of treatments would be extremely expensive and difficult, as well as detrimental to all of the other insects in the pine yards (many of which are probably yet unknown to science), but are still being considered for limited areas. There is hope for the future in using seeds and clones of naturally resistant trees to increase the population, and certainly the Trust is working with the most renowned plant research institution in the world to solve the problem.

National Trust staff members share a common sentiment — that if we do not love what we’re working to protect, then we won’t be good at it. Our research team, made up of National Trust staff members as well as international colleagues, keeps this as our unofficial team slogan as we carry out the work to save our national tree from extinction. We do not want to have to lament the loss of another species by human hand, and do not wish to be the observers documenting the loss of a magnificent tree. We hope that our work will prevent the need for any child in the future to ever ask the questions, “What was a Caicos pine? What did they look like? Where did they go?”

The Turks & Caicos National Trust is a non-governmental organisation established by TCI Government mandate in 1992 to safeguard the natural, historical and cultural heritage of the Turks & Caicos Islands for present and future generations and the enjoyment of all.

For more information on our Pine Project and how you can help, please contact the National Trust at (649) 941-3536 or by email at tc.nattrust@tciway.tc.