Working Parties

SCRUB CLEARING at the LOCAL WILDLIFE SITE at CHALKHILLS

In the winter of 2008-9 WoTHabs volunteered to help the landowner at Chalkhills farm with clearing up and burning the brash left by scrub clearance contractors in August 2008.  The area was about 25 square metres.  

The 3m tall impenetrable scrub had completely shaded the ground, preventing the growth of the chalk grassland flowers.  Chalk downland is a threatened habitat, though the Chilterns is a good area for it.

Less than two dozen species grew on the site before it was cleared (click for Table).  The roots of the trees and bushes were treated with herbicide to prevent regrowth.   In between was much bramble.  So collecting up the brash for burning was a very prickly - and slippery - job as the site is very steep. 

The adjoining Hawthorn hedge was laid by WoTHabs at the same time.

The site was left with nearly bare soil. The species that appeared in March 2009 were recorded, and on the Violet Day walk held that month, children sowed locally collected seed (from Chalkhills) in marked plots along the hedge side.  This seed sowing exercise turned out to have been unnecessary as the area outside the sown plots filled up with grasses and herbs in a very short time, more so than the sown plots.  By August 2009 a total of 88 more species had appeared in addition to those already recorded in March.

The cleared area is adjacent to a field used for growing barley up to 1984.   Some of the arable weeds must have grown from an old seed bank that had survived for 25 years in the soil near the fenceline.  The three scarce weeds that appeared (Small Toadflax, and both Round and Sharp-leaved Fluellen) are in a long list of arable weeds now rare due to the use of herbicides in modern agriculture.

By August 2009 the dominant plant in the upper area of the regrowth was Wild Mignonette, which is a ready coloniser of bare ground and has seed with a very long viability.  The lower side of the area was dominated by Marjoram.  A surprise was the amount of Deadly Nightshade which appeared.

Unfortunately no detailed survey was made of the herb cover in the summer of 2010 but the species list seemed to be about the same.  Wild Mignonette was still frequent, but the upper part of the slope was dominated by Perforate St John’s Wort.  And the Deadly Nightshade plants (perennials) had got even bigger.  Some weeding of undesirable species (eg thistles, nettles, and scrub re-growth) will be necessary to ensure the chalk grassland species develop into a dense sward.

The flowers now replacing the scrub support a different set of insects, feed many butterflies, and birds and small mammals also find food there, by eating the visiting insects, or the plant seeds.