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Introduction

Key facts

Introduction

The site is well-known locally for its large anthills that are such an attractive and unusual feature of the site. The ants (Yellow Hill Ants, Lasius flavus) that construct the anthills are extremely common, but it is unusual to find such large anthills, and Marshalls Heath has one of the finest colonies among the Hertfordshire nature reserves. 

Heathland - a fast disappearing habitat

The site includes one of the last remaining fragments of acid grass heathland in Hertfordshire.  It is very rich in butterflies, moths and other insects which depend upon the unusual vegetation for their survival.  Wild heaths, which develop on poor, usually acid, sandy or gravelly soils, have been gradually lost to arable farming and urban development over the last century, and particularly since the last war. 

The loss of heathland in Hertfordshire has been quite devastating: in 1940, 83% of Hertfordshire commons supported a good heath habitat, but by 1984, this had fallen to only 2%. In 1990, it was estimated that only about 75 acres (30 hectares) remained in the entire county.  The planting of trees, liming of the soil and the development of golf courses, recreation areas, cricket pitches and gravel extraction have been responsible for much of this loss.  In some cases, the simple act of applying fertiliser or sowing with grass to "improve" the grassland has resulted in the crowding out and elimination of the natural heathland plants, and the insects, animals and birds which depend on them. However, even the heath which remains is fast disappearing due to another less obvious cause which is no less threatening: the encroachment of brambles, scrub and woodland. 

Heathlands are maintained in the natural state by the grazing of wild animals.  As man gradually hunted these animals to extinction in Britain, he replaced them with sheep, cattle, and rabbits, which over the centuries have kept the vegetation short and maintained the heathland in its natural state. Most remaining heaths in Britain today are the result of past exploitation and management practices on soils of low fertility.  However, modern intensive farming practices have gradually removed grazing animals from heathland, and myxomatosis has severely curtailed the rabbit population.  The result is that heaths have become overgrown by scrub and woodland, which in many places have destroyed for ever these havens of wild nature. 

The situation at Marshalls Heath reflects this wider trend.  The site was composed of nearly 100% heathland in 1948, but this had decreased to 8% by 1992. 

Woodland and scrub

Despite the threat to the heathland by scrub and woodland encroachment, these are habitats for other species, and are important as structural (windbreaks etc.) components, and contribute much of the attractive nature of the site.  There are some Ancient Woodland indicator species present, suggesting that the wildwood which covered most of Hertfordshire after the Romans left has always been present in the hedges and tall trees that have surrounded the site within living memory.  It is therefore important to keep a balanced mosaic of all three habitat types: acid grass heath, woodland and scrub, to maintain the present high biodiversity of the site. 

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