After a Ph.D. at University College, London and a short appointment in Aberystwyth University, Dr Peterken was for two years co-ordinator of part of the International Biological Programme and then scientific officer in the Biological Records Centre. He was then appointed to the Nature Conservancy's woodland management section at Monks Wood in 1969, and remained a woodland ecologist with NC and successor bodies until 1992, spending much of his time as the senior woodland ecologist in the Chief Scientist's Team, where his work ranged from policy negotiations through research commissioning, personal research and lecturing to on-site management advice, in fact anything and everything that might advance woodland ecology and nature conservation. He took a sabbatical for 18 months in 1989-90 to study so-called virgin forests in mainland Europe and to hold a Bullard Fellowship at Harvard University. In 1993, he went independent. For a decade he was part-time nature conservation advisor to th