The Isle of Scilly is filled with a great many species and geographical features that affirm exactly why this quaint archipelago is such a unique place to visit, work and live. Something that I, being a born and bred Scillonian, have often overlooked on our island home is our abundant population of elms.  

Elms belong to the genus Ulmus and family Ulmucadae. Identifying the species of elm found on Scilly, and elsewhere, is very difficult due to the family's tendency to hybridize. It is believed that the species found on Scilly are Dutch elm (Ulmus Hollandica), field elm (Ulmus Minor ssp. Sarniensis) and Cornish elm (Ulmus Minor ssp. Angustifolia), with Dutch elm being the most prominent on the islands. 

On the mainland UK you would be hard pressed to find mature elms thriving in their historically abundant habitats. This is due almost entirely to a fungal disease known as Dutch Elm Disease, carried by species of bark beetles. 

The large elm bark beetle bores into the bark of elms, embedding themselves into the tree to lay their eggs. Once the eggs have hatched to larva, they feed upon the trees' phloem till they pupate and metamorphosize into their adult beetle stage. Once the new adults emerge from the elm they act as a vector for the Dutch Elm Disease fungus, carrying spores to other elms both when they go onto feed and when laying eggs. 

This gives the spores from Dutch Elm Disease access to the xylem, a thin layer under the bark of a tree responsible for carrying water and nutrients up vascular plants, which is one half of what's known as the vascular bundle, the other being the phloem which carries sugars produced by the trees foliage, through photosynthesis, back down to rest of the plant. 

So, why has is it that Dutch Elms Disease hasn't made it to Scilly's shores? The answer is actually rather simple. Due to the large stretch of sea between the Isle of Scilly and mainland Cornwall, it is highly unlikely that a bark beetle would try to make the flight across the sea in search of Elm. The only other way for a spore infected bark beetle to reach the islands would be as a stowaway in wood and timber brought to the islands. As of writing this blog, thanks to biosecurity efforts made at Penzance Quay no high-risk materials have made it to Scilly.

By Apprentice Ranger Ari