Thinning involves (in theory) removing some trees in order that others will develop more quickly ("promotion by selection"). It is a very ancient principle of woodland management and some of the best woodlands in the UK, especially England, have benefited from this policy – provided it is carried out with skill and as part of a thought out plan. The suggestion that in cutting down trees you were loosing cover would have surprised medieval wood cutters. To them it was part of a 'long cycle' approach to managing woodlands that left us, hundreds of years later, superb stands of trees. Ironically, a modern reluctance to intervene has produced a loss of variety and vigour in some woods.
A noticeable effect of thinning is an increase of ground cover plants. These daffodils and bluebells were originally planted; other plants blow in or are produced when seeds pass through birds guts. Increased daylight penetrating the leaf canopy in summer will encourage ground cover plants to spread. Beneficiaries will include invertebrates and birds feeding on either insects or seed set by plants.
Emerging Bluebells Hyacinthoides non-scripta and Daffodils Narcissus pseudonarcissus. February 2008.
Red Dead Nettle Lamium purpureum flowers all year round. February 2008.
However, timing is crucial. My one anxiety about this procedure is timing; it is imperative to consider the effect the disturbance and removal of shrubs in particular can have on breeding birds.
Global warming and associated climate change have made some birds breed earlier. Many common species are exhibiting signs of breeding activity now and some have been doing so for several weeks past. It would be most unfortunate if, as part of a enlightened policy of tree management, an unintended consequence prejudicial to birds resulted.
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