To survive climate change forest trees will have to shift seed production poleward. However, warming will not stimulate tree fecundity in the north if it is limited by other habitat variables. Anticipating changes like this suggests the need for full uncertainty in process, parameters, and data using hierarchical state-space models. However, when there are tens of thousands of time series with dependence within and between trees, and the response is erratic, traditional forecasting with autoregressive terms (for example) cannot offer useful predictions. We evaluated the responses of tree fecundity to climate change for 292 tree species in North America and Europe, using response velocity, defined as climate sensitivity X climate change rate. The sensitivities to climate were estimated for each species and combined with rates of climate change to quantify how temperature, moisture deficits, and late freeze are influencing biogeographic shifts in tree reproduction. Results show that moisture deficit and late freeze, not annual temperature, drive changing seed production. Unlike annual temperature, which is increasing generally, change in these climate variables is not driving poleward shifts in seed production. Results do not challenge the expectation that forests might eventually shift poleward. Rather, they show why current efforts offer divergent interpretations. The changes happening now are not consistent with annual temperature trends. As warming continues, fecundity changes can best be anticipated from temperature interactions with precipitation and extremes that impact flowering and fruiting in winter and spring. Response velocity can exploit spatio-temporal information to anticipate how climate is driving ecological change where traditional methods fail.

References:

Clark, J. S., et al. 2026. Despite rapid warming, seed production is not leading poleward migration in North American and European forests. New Phytologist, in press.

Clark, J.S., et al. 2021. Continent-wide tree fecundity driven by indirect climate effects. Nature Communications DOI: 10.1038/s41467-020-20836-3. pdf: s41467-020-20836-3

Qiu, T., Bell, A. J., Swenson, J. J., & Clark, J. S. 2023. Habitat–trait interactions that control response to climate change: North American ground beetles (Carabidae). Global Ecology and Biogeography, 32, 9871001. https://doi.org/10.1111/geb. 13670