The Steppe Altai is a natural transition zone between the Central Asian steppes and deserts and the Siberian taiga. Various lakes located in the Kulunda lowland, the biggest part of the Steppe Altai, provide a unique archive of the environmental history of the Altai Mountain piedmont and adjacent plains. Palaeorecords from two lakes, Maloye Yarovoye and Kuchuk, provide the longest high-resolution records of the Steppe Altai and south-western Siberia, allowing us to describe the environmental history of the region with high accuracy since the last deglaciation. The main objective of this study was to establish the interrelationship between plant biodiversity, climate, and fire dynamics in the Steppe Altai from postglacial time to present day. We used several techniques for this task, including pollen and geochemical analyses, quantitative reconstruction of climate and biodiversity using multivariate statistics, and estimation of macrocharcoal accumulation rates and sources of fuel. Based on analyses of the two palaeorecords, we conclude that plant diversity and evenness show a strong positive correlation with annual precipitation. Pinus sylvestris spread throughout Kulunda lowland after 10.8 ka BP, and maximal spread of mixed coniferous-deciduous forests in south-western Siberia occurred between 7.2 and 2.7 ka BP. We propose that the maximum development of the ribbon-like forests dominated by Scotch pine characterized the Steppe Altai at that time. Forest fires occurred sparsely during the Holocene but were not inherent in pre-Holocene time. Before 650 CE, the main fuel for the fire was grass; however, forest fires rapidly increased in the Steppe Altai after 650 CE and prevailed over steppe fires after 1420 CE. Increased fire activity over the last millennium was likely human-induced.