Past island landscapes revealed by pollen

The vegetation history of a small island off the south west coast of Wales has long puzzled visitors and archaeologists. In late spring, Skomer Island is carpeted with bluebells, a species normally associated with woodlands, especially ancient natural and semi-natural woodland – but Skomer does not have any trees growing on it presently.

Skomer's vegetation in spring is dominated by a carpet of bluebells

Skomer’s vegetation in spring is dominated by a carpet of bluebells

 

A couple of seasons ago, a small team from Biosciences travelled to the Island to undertake some investigations into the past vegetation of the island – Julia Webb and Matt Wood (Senior Lecturers) with two summer bursary students Mel Evans and Will Carpenter. Using fossilised pollen preserved in Skomer’s soil the team were hoping to discover evidence of rich woodland that would explain the presence of the bluebells.

Julia and Will putting their backs into it! Soil coring sometimes takes a bit of effort...

Julia and Will putting their backs into it! Soil coring sometimes takes a bit of effort…

Initial findings are surprising: the pollen from the soil shows no evidence of significant forested areas on Skomer Island, adding further to the mystery of the occurrence of the bluebells, which must benefit from the shading of competitors by bracken later in the summer. The past vegetation does not seem to have changed very much from the present day. Ferns, sorrel and grasses are dominant with wild flowers such as sea campion and red campion in significant numbers within patches across the island.

Electron micrographs of some of the pollen types found in the study

Electron micrographs of some of the pollen types found in the study. Some have very distinctive morphology to aid identification.

The island has a rich archaeological record of human occupation, evidence of former field boundaries and farm buildings can be seen across the small island, and it’s thought that the peaty soil and any forest trees may have been cut for fuel. Although records show that some fields were ploughed, the pollen record does not show any evidence of cereals growing on the island.

The deeper the soil, the older it is (usually!), so the pollen in the soil at each depth can be analysed as a time capsule of past vegetation

The deeper the soil, the older it is (usually!), so the pollen in the soil at each depth can be analysed as a time capsule of past vegetation

Radiocarbon dating of the soil core allows changes in the vegetation to be studied, and Skomer’s vegetation appears to changed repeatedly from heather to grassland – archaeologists are interested in how these vegetation changes may be linked to human settlement activity. The dating also hints at a hiatus in the peaty soil record, a lost soil layer a few thousand years ago that may contain the evidence for the presence of forest trees and arable farming, but arable farming took place until the early part of the 20th century so some cereal pollen should have been around. The oldest soil layer was dated using luminescence techniques by Phil Toms (UoG Senior Lecturer in Geography) to 13,400 years ago, giving us a glimpse into the last time the island was bare rock – Skomer lies just a few tens of kilometres from the southernmost extent of the ice during the last Devensian Ice Age.

This study is a great example of how students work with staff on research projects, in this case a collaboration between several areas of expertise within one of the University’s Research Priority Areas – Environmental Dynamics and Governance.

The findings are being prepared for publication, and are informing a current review of future conservation management strategies for Skomer Island by Natural Resources Wales.

 

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