Historical records for the Bcga district wcix' examined to chart the environmental changes wixiught by Europeans thivugh habitat alteration and the introduction of exotic species, and to intcrpi-ct the anpact of these on native manimals. Early recorded increases in native mammal populations, particularly koalas, niay have been attrihutahle to a decline in Aboriginal hunting pressure. .After settlement in IS30. the valley forest was cleared pivgi'cssively, ecosystems were altered by grazing and impi-oved pastures, and many introduced plants became weeds in the disturbed enviivnment. The timber industry exploited the foi'ests of the valley and then the slopes of the sunvunding mountains. Three exotic manunal species had a major impact on the district -hai'cs. I'abbits and foxes. Ofthe native fauna, the large and medium sized mammal species were those recoided most frequently. Dramatic fluctuations in numbers occurred in most of these species, and many reached plague proportions between 1880 and 1910, after which their numbers fell sharply. The peaks of exotic mammals and the decline of native mammals coincided with the clearing of the i-emaimngforests in the Bega \ 'alley. Many native mammal species are now rare, four aiv in danger of extinction, and at least six species have become locally extinct since settlement. As most ofthe native mammal populations in the district now occur in the State Forests suri-ounding the Bega I'alley, the importance of presei'ving or managing these foi'ests for wildlife must be weighed against proposals to manage the forests for pulpwood (woodchip) production.