Monitoring the effect of an invasive pine scale insect on the national tree of the Turks and Caicos Islands

By: Sara Green - 21/11/2011

Caicos pines in trouble

Dead pine trees dominate much of the pineyard landscape

A large part of my MSc Conservation Science course at Imperial College London, involved my being lucky enough to work with the UKOTs team at Kew on the research for my MSc thesis. My project was part of an on-going study of the effects of an invasive pine scale insect on the national tree of the Turks and Caicos Islands – the Caicos pine (Pinus caribaea var. bahamensis). This insect is making a huge impact on the populations of Caicos pine in the pineyards on this UK Overseas Territory (UKOT), and the resulting loss of tree cover is likely to affect other plants and animals found in this habitat.

Examining the effects of pine scale insect on an immature pine tree

What we did

My main research objectives were to:

1. Undertake the first year of monitoring the effectiveness of various management practices on the numbers of invasive scale insects
2. Estimate the size of the pine population and levels of decline
3. Investigate the influence of the Caicos pine on the surrounding plant community

Harry Earle-Mundil (another Imperial College MSc student who carried out his dissertation project on TCI last year) set up a series of monitoring plots and began trials of different treatments to investigate their effects on the levels of scale insect infestation:

• Treatment 1: broadleaf clearance (clearing plants that are competing with the pines and which prevent new pine seedlings establishing themselves)
• Treatment 2: broadleaf clearance accompanied by spraying the pines with insecticidal soap
• These treatments were compared with control plots without any form of treatment.

Using the baseline data Harry collected, combined with data I collected this year, the effects of the treatments on the numbers of scale insects and health of the pines treated remain inconclusive, which is not surprising after only one year of monitoring. Continued monitoring is important for true trends to be determined.

Recording measurements of tagged pine seedlings in one of the monitoring plots

What we are finding

The total population of Caicos pine on the TCI is estimated at less than 735,000 with almost 99% of the live pines being immature (i.e. not yet producing cones and seeds). The three islands where the pine occurs show a variance in pine densities and population structures, and show a variety of different stages of succession towards the mature pineyard vegetation. The overall decline in pine numbers is estimated at almost 60%; however the decline of mature trees stands at almost 98%. Although mature pines can often survive fire, the majority of immature pines are likely to die if a fire spreads throughout the pineyards, after agricultural burning or a lightning strike, for example. With the huge decline of mature trees of reproductive age, a fire is likely to result in catastrophic effects on the population of Caicos pine.

On Middle Caicos, an increase in the number of dead pine trees was found to cause a significant reduction in the surrounding plant species richness, showing that the invasive scale insect also has a wider impact on the whole plant community within the pineyard. High densities of dead pine trees were also found to reduce the diversity of the surrounding plant community. In addition, areas with live mature pines showed different plant species compostion compared to those which had no surviving trees. This invasive scale insect therefore has the potential to affect the whole ecosystem, not just the Caicos pine.

Working together

I am extremely grateful for the opportunity to contribute to the conservation work undertaken by the UKOTs team in the Turks and Caicos Islands and for the wealth of support received from the staff at both Kew and the Department of Environment and Coastal Resources in TCI. Although continued monitoring and further research is clearly needed, I am hopeful that the UKOTs team will be able to use these preliminary findings and that they will provide a solid foundation for the conservation of the Caicos pine.

- Sara -

Find out more

Turks and Caicos Islands Pine Recovery Programme

Insects and invasives: investigating threats to Turks and Caicos Islands plants

Turks and Caicos Islands Online Herbarium

Earle-Mundil, H. (2010) Permanent monitoring plots for the national tree Pinus caribaea var. bahamensis and assessment of the distribution and conservation status of an associated endemic species Stenandrium carolinae in the Turks and Caicos Islands (pdf). (MSc dissertation)

Green, Sara (2011). The Caribbean Pine (Pinus caribaea var. bahamensis): monitoring and ecology, in the Turks and Caicos Island (pdf). (MSc dissertation)

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