Hepper 2003. Hepper, F.N. (2003). "Phenological records of English garden plants in Leeds (Yorkshire) and Richmond (Surrey) from 1946 to 2002. An analysis relating to global warming". Biodiversity and Conservation. 12 (12): 2503–2520. doi:10.1023/A:1025847029377. S2CID37244695.
Hepper 2003. Hepper, F.N. (2003). "Phenological records of English garden plants in Leeds (Yorkshire) and Richmond (Surrey) from 1946 to 2002. An analysis relating to global warming". Biodiversity and Conservation. 12 (12): 2503–2520. doi:10.1023/A:1025847029377. S2CID37244695.