Abstract: In Australia, since the late 1990s the issue of vegetation ‘thickening’ has become controversial. The semi-arid mulga lands of eastern Australia typify the debate. One view held by landholders, and some researchers, is that woody vegetation thickening is, at least partially, anthropogenic and leads to productivity loss and biodiversity decline. An alternative argument is that a narrative of vegetation thickening is unsubstantiated and is used by some landholders to justify management practices of clearing, thinning or burning. Absent in the literature has been research into the local knowledge of those who obtain their livelihoods from the region. This study presents an analysis of landholder responses to a survey about vegetation change in the mulga lands of south-west Queensland. Local knowledge is dominated by a view that woody vegetation thickening has occurred and is ongoing, and that it is driven by three interacting factors: (1) climate, especially decadal and multi-decadal extreme variations of both very wet and very dry conditions; (2) fire, particularly the absence of fire; and (3) total grazing pressure, including domestic stock and harder to control feral and native herbivores. Decline in pasture quality and quantity is also noted as an outcome of those same three factors but that it is ultimately linked to greater competition between the increased densities of woody species and the herbaceous layer. Most of the respondents to this survey had three or more generations of accumulated knowledge in the region. The value of local knowledge in land management and policy, although considered of value in many contexts, has received relatively little formal attention in vegetation management. In summary, the landholders view the dense woody component of the vegetation as an unnatural and undesirable ‘artificial wilderness’, which those from outside the region may consider natural and therefore worthy of preservation in its current state.