The Development of Holocene Floristic Diversity

A rich diversity of organisms and ecological communities are commonly perceived as essential to planetary processes, on which humans ultimately rely. Despite this, our knowledge of where, how, and why biodiversity has changed over the last ~100 years is far from clear. Even less clear is how biodiversity has changed over the much longer-term past. This thesis contributes to filling this knowledge gap by quantifying and modelling how global rates of pollen-inferred floristic community change (turnover) and diversity (richness, evenness) have changed over the Holocene; the last 11,700 years. These analyses identify generally accelerating rates of floristic turnover from 9,000 cal yr BP onwards, which have generated varying responses in the richness and evenness of communities among continents, biomes and sites. Modelling these floristic diversity data in relation to two measures of human ecological impact (a simulation of anthropogenic land cover change and a pollen-based measure of human impact) finds that human action typically generated increased diversity in once forested landscapes, but more mixed diversity changes in more open ones. These later-Holocene diversity increases are not associated with floristic communities in different locations becoming more similar to one another; i.e. ecological homogenisation. The analyses suggest that accelerating human-driven disturbance regimes led to increases in spatial heterogeneity among communities over the later portion of the Holocene. Taken together, these works underscore an often-missed, or intentionally sidelined, nuance central to human–biodiversity relationships. Calls from sections of the conservation world to rid humans from landscapes to save biodiversity could, in some circumstances, be counterproductive. In many cases, biodiversity is present because of, not in spite of, the multi-millennial interactions between humans and the Earth’s biota.