Quantifying anthropogenic fire influence in forest-grassland mosaics: A sensitivity modelling approach

Understanding the occurrence and strength of anthropogenic fire in shaping vegetation dynamics through deep time is critical for reconstructing cultural pyroscapes, yet feasible methods to achieve this are extremely limited. Palaeoenvironmental proxies reveal changes in fire regimes and broad-scale vegetation responses but typically cannot uncover the dynamics of change and specific precipitating factors. Process-based models can potentially address this limitation by isolating the role of climate and determining which dimensions of human fire use—spatial patterns, seasonal timing, frequency—most strongly drove observed vegetation transitions. Such insights into historical fire stewardship would provide essential context for developing sustainable wildfire management and landscape resilience strategies today. Therefore, this work aims to develop a model capturing the interplay between climate-driven fire and human fire manipulation that quantifies the relative effects of anthropogenic and non-anthropogenic fire on vegetation.

The complexity of representing both fire types and their effects on diverse vegetation at resolutions aligned with human activity across deep time makes this exceptionally difficult. Existing models are typically unsuitable for this intersection of spatial and temporal scales and lack necessary representations of anthropogenic fire use. To make this tractable, we restrict attention to forest-grassland systems—enigmatic ecosystems likely shaped by long histories of human occupation that support reduction to an effective two-state system. We dramatically simplify representation by focusing on a theoretical ecotonal boundary between vegetation types, where stability determines whether mosaics persist or collapse. Within these bounds, we adapted and extended an existing spatially-explicit model of fire-vegetation dynamics designed for millennial timescales (Bowman and Perry, 2017).

Our model operates at individual-tree resolution with annual timesteps over multiple millennia. It incorporates vegetation state transitions, sub-annual climate cycles, and realistic fire spread dynamics as a function of flammability supported by empirical data. We integrate fundamental representations of anthropogenic fire use spanning spatial and temporal dimensions: where fires are preferentially ignited, when fires burn, and how frequently ignitions occur. Through systematic sensitivity analysis across these dimensions and climate contexts, preliminary results reveal that anthropogenic fire's contribution to boundary dynamics is highly context-dependent, particularly regarding moisture regimes. These results provide process-based understanding of mechanisms through which human fire use drives vegetation state transitions under different climatic conditions, revealing how humans—particularly Indigenous people—could have shaped and sustained landscape mosaics through strategic fire management across deep time. By successfully isolating these mechanisms, we achieve our aim of quantifying relative effects of anthropogenic versus climate-driven fire. This modeling framework offers a crucial tool for reconstructing cultural pyroscapes and understanding the deep-time relationship between humans and fire-shaped landscapes.