Winter desiccation and rapid changes in the live fuel moisture content of Calluna vulgaris

Abstract

Background: Dramatic reductions in early-spring Calluna vulgaris moisture content have been linked to extreme fire hazard and plant die-back.

Aims: To investigate spatial and temporal variation in the fuel moisture content of Calluna vulgaris.

Methods: Calluna vulgaris plants were sampled in different sites and seasons to examine vertical profiles in moisture content. Live moisture content was monitored throughout autumn 2003 and spring 2004. Changes were compared to trends in temperature, soil resistance and rainfall. The effect of exposure was examined by comparing shoot moisture content in sheltered and exposed locations.

Results: Significant spatial and temporal variation in moisture content was observed. In spring rapid fluctuations in moisture coincided with periods of dry weather, low temperatures and frozen ground. Shoots from exposed locations had significantly lower moisture content when the ground was frozen.

Conclusions: Significant declines in the live fuel moisture content of Calluna vulgaris are associated with physiological drought caused by cold, clear conditions and frozen ground. Over-winter damage to leaf cuticles reduces the ability of the plant to regulate water loss. Changes in moisture content can be rapid, and managers should be aware of the potential for extreme fire behaviour.

Keywords:

• cuticle
• dead fuel moisture
• fire danger
• frozen ground
• moorland
• moss
• Scotland
• winter browning

Acknowledgements

Thanks are due to the owners and gamekeepers of Ralia Enterprises, Whitburgh Estates and Phones Estate and to the Scottish Agricultural College and the Ministry of Defence for access to field sites. Oyunn Anshus and Elaine Boyd contributed to data collection. Maurizio Mencuccini (The University of Edinburgh) and Adam Butler (Biomathematics and Statistics Scotland) provided useful advice on the mixed effects modelling – their help was much appreciated. The study was funded by the Natural Environment Research Council (NERC), the Game and Wildlife Conservation Trust, The Scottish Government and Scottish Natural Heritage. This paper forms part of the FireBeaters project: http://firebeaters.org.uk.