How deep-time climate change has influenced the diversity of plants

Biodiversity loss and climate change are interlinked crises with global ecological and societal impacts. Common explanations for how climate shapes biodiversity focus either on spatial scale (whereby more extensive and/or isolated climates promote species richness) or on temporal scale (whereby older, or more stable, climates foster biodiversity). However, these hypotheses overlook the intrinsic link between the spatial and temporal dimensions of climate.

We investigated how spatio-temporal climate changes over deep time may have influenced global patterns of plant diversity through the lens of climate analogues. By compiling global occurrence records for 350,864 vascular plant species, we produced the most comprehensive and precise global map of plant diversity to date. We identified analogues of recent (1851–1989) climate conditions across several geohistorical time periods: the Early Eocene (ca. 50 Ma), the Mid-Pliocene (3.3–3.0 Ma), the Last Glacial Maximum (LGM, 22–18 ka) and the Mid-Holocene (ca. 6 ka). We quantified spatial climate change within temporal periods, temporal change across spatial gradients, and the integrated spatio-temporal dynamics of climate. We evaluated the relative contributions of these metrics in explaining global plant diversity variation and examined the correlations between the spatial and temporal dimensions of climate change.

Our findings extend previous hypotheses by showing that species richness is higher in climatic conditions that were historically more extensive and/or isolated and have remained so through time. We also reveal a previously unrecognized mechanism by which climatic conditions that have undergone geographic expansion and slower movement over deep time tend to harbour higher plant diversity. Moreover, the combination of temperature stability and precipitation variability has facilitated species accumulation in low-latitude regions.

Spatial and temporal dimensions of climate change are thus interconnected, with long-term trends and short-term variability influencing the geography and movement of climate analogues, which in turn shape species richness. By incorporating the spatio-temporal climate changes into models, we can almost completely (> 90%) explain the global patterns of plant diversity today.