Woodland, scrub and hedgerows

Apart from mountain tops and open standing water, most of England would eventually develop into some sort of woodland environment. In fact it is often referred to as the climax community, meaning it is the final stage of succession. Woodland comes in many guises, ranging from willow and alder woods on waterlogged ground to oak woods on clays and acid soils and ash wood on lime rich soils. In all its forms, it is one of our richest habitats. The vast arrays of plants, fungi, birds, insects and mammals that all rely on woodland for at least part of their life cycle are attracted by the range of niches available and of course the cover and three dimensional element to the structure. The height of the trees substantially increases the amount of space for things to live! The original woodland that colonised Britain after the last ice age is referred to as the wildwood; there is none of this left in the United Kingdom as it has all been affected by man’s activities to some degree.

• Primary woodland is that which has existed continuously since the time of the wildwood, albeit subject to management or otherwise influenced by man. 
• Secondary woodland exists where at some point the land has been ploughed or put to some other use before being replanted with trees or allowed to revert naturally. This can be either recent (post 1600) or ancient (pre 1600)
• Semi-natural woodland is that which has developed with no (or very limited) input from man.
• Ancient woodland is that which has existed continuously since at least 1600. Obviously this cannot be recreated if lost! 
• All primary woodland is ancient by definition

Scrub can exist for several reasons; where there are factors that prevent the development of normal woodland, such as very poor soils or extremes of climate or as an intermediate stage between grassland and woodland. It is worth defining the varying types of scrub:

• Seral scrub – ephemeral vegetation existing as a successional stage between grassland and woodland
• Sub-seral scrub – factors such as grazing, burning or cutting prevent the development of trees but allow scrub to persist. This exists as a deflected successional stage or plagioclimax.
• Climax scrub – factors such as salt spray, strong winds, skeletal soils or substrate instability may not allow succession beyond the scrub stage. Examples may be found on cliff-tops, small islands and in the sub-alpine regions of Scotland.

The addition of a vertical element when compared to herbaceous vegetation offers greater opportunities to invertebrate colonisers. Many non-phytophagous insects take advantage of the increased shelter, basking, prey capture and breeding opportunities afforded by the structural complexity of scrub. The phytophagous species tend to be associated with particular plant families, with willow and hawthorn being especially valuable in this respect. The build-up of leaf litter and increase in humidity provide opportunities for primitive groups such as springtails and other epigeal invertebrates.

Scrub has a great potential for birds; both insectivores and frugivores are well catered for and species most strongly associated with this habitat are warblers, thrushes, pigeons, starlings, robins, tits and finches. It is also worth noting the differences in structure requirements among birds. Some, such as the yellowhammer and whitethroat require low and open scrub, whereas the garden warbler and blackcap are associated with denser, more closed scrub.

Hedgerows are an important part of the landscape, both in character and biological terms. Many miles were planted as a direct result of the Enclosure Acts (1760-1830) as field boundary markers, although some exist as linear remnants of primary woodland. These are usually typified by a diversity of woody species (usually more than five) and certain plants known as indicator species. These include wood sorrel, bluebell, dog’s mercury and yellow pimpernel. Managed sympathetically, hedges allow connectivity between other habitats, acting as wildlife corridors. Birds, mammals and insects may all use these for food, shelter, breeding and hunting. Hedgerows and the headlands next to them often support herb species that have been lost to intensification from the rest of the field.