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The Utilisation of Molinia caerulea (Purple Moor-grass) Tussocks
by Overwintering Beetles at Epping Forest
ANDY SWAN*
* Contact: 466 West Green Road, London, N15 3PT
Ecology Dept. University of North London, Holloway Road, N7
Abstract
Beetles were sampled by coring Purple Moor-grass {Molinia caerulea) tussocks from a wet heath
and wooded site at Epping Forest in February. Flooded and non flooded tussocks were sampled.
Individuals were extracted from core samples by Tullgren funnel. 235 individuals of 14 species and
4 families were found. The species' relative abundances are briefly compared with those reported
in other works. The absence of carabids from the flooded tussocks is discussed. The possible
relationships between tussock and inter-tussock diversity are also examined. Finally, the implications
for restorative heath management are briefly considered.
Introduction
Initially, this study set out to explore how Molinia caerulea (Purple Moor grass) tussocks are utilised
as overwintering sites for a range of invertebrates. In broad terms, overwintering is simply the way
in which an organism passes the winter (Leather et al. 1995). More specifically, Mansingh (1971)
defines insect hibernation as a physiological condition of growth retardation or arrest primarily
designed to overcome lower than optimum temperatures in winter.
Two preliminary samples of whole Molinia tussocks were taken from an open Birch woodland and
an area of wet grass-heath known as Deer-shelter Plain. Initial results revealed a high invertebrate
diversity; 5 Orders of Insect (Hymenoptera, Coleoptera, Hemiptera, Diptera, Collembola) 2 of
Diplopoda (Polydesmida, Chordeumatida) 2 of Chilopoda (Geophiloamorpha, Lithobiomorpha) as
well as crustaceans (Isopoda) arachnids and oligocheates, a total of > 13 invertebrate families.
Concluding that the total diversity was too great a subject for this study it was decided to focus on
one Order The Coleoptera were chosen partly due to their relative abundance and diversity.
Studies specific to the Beetles of grass tussocks are few. Luff (1965) recorded highest density of
beetles in tussocks during winter and describes how microclimate features are important in forming
a favourable overwintering habitat. In utilising tussocks for overwintering, beetles benefit from the
relatively stable micro climate within and this is thought to be an important factor in dictating winter
habitat selection (Leather et al. 1995).
Site Description
Site 1. Grid. Ref. TQ 541299. Mean tussock density 0.13/m2.
This site is an area of deciduous woodland (mostly birch with beech, oak and ash present) with gaps
in the canopy allowing growth of Molinia and bramble. The water table was approximately 10cm
below ground although higher in places resulting in localised boggy areas; a deep layer of leaf litter
was present.
Site 2 & 3. Grid Ref. TQ 542298. Mean tussock density 1.14/m2.
Both sites 2 and 3 were within the larger area of Deer-shelter Plain. The non-flooded tussocks of site
Essex Naturalist (New Series) 17 (2000)