Because Treswell Wood is under active coppice management, the habitat is in a constant state of change. There is sudden, major loss of mature trees and shrubs when coppicing is carried out followed by regeneration over the next few years. These changes impact on bird life; for example a newly coppiced area will have very restricted nesting sites for tits but be excellent open hunting ground for Kestrels.
Analyses of bird populations changes will require some knowledge of the habitat. We have, therefore, recorded the age of coppice from the beginning of the Trust’s ownership of the wood and this record is at the resolution of the 63metre ‘McMeeking grid’. In addition to differences in coppice age the wood has differences in composition of tree species. In the north, the mature trees are almost all Ash gradually changing to reach about 40% of Oak in the south-east.
Above: Coppice areas and ages 2015
The effects of coppice age on bird populations have been studied in various places only during the breeding season using territory mapping techniques. Our ringing extends throughout the year which has enabled us to examine the effects of coppice age using capture rates of birds in different seasons and to see whether adults and juveniles are similarly affected. There are some intriguing results. Do juvenile Wrens really have different preferences from adults in autumn or do adults dominate prime habitats forcing juveniles into less favourable parts?
Fixed point photography is useful for documenting habitat change. A limited attempt to do this was made in the 1980s but processing time and cost of films together with the removal during coppicing of the fixed point tree ended the attempt. More recently we have restarted using the standard net sites for fixed points. Digital photography, with its instancy, low cost and ease of storage has allowed seasonal rather than annual records of habitat. The images below illustrate the dramatic changes within one year; the rapid recovery after coppicing and also the barely perceptible changes in uncoppiced areas.
We anticipate further major changes in habitat as Ash dieback takes hold. We are working on a system of recording its progress which will give a representative picture but is not too time consuming.
We have also begun to record leaf cover at the frass traps in order to relate frass production to it. As with fixed point photography, the advent of digital methods has considerably enhanced the possibilities for this. The vertical sighting tube requires several time-consuming readings to assess percentage cover in one place. The digital image is instant and gives a permanent record and percentage cover estimated by the overlaid grid.