Boreal

Precipitation

Growing degree-day

Ecosystem

Geology

Climate change

Growing season

Arid

Meteorology

Ecology

Geography

Northern Hemisphere

Environmental science

Mediterranean climate

Climatology

Phenology

Temperate climate

Biology

Taiga

Atmospheric sciences

Dry season

Nature Ecology & Evolution

Climatic warming alters the onset, duration and cessation of the vegetative season. While previous studies have shown a tight link between thermal conditions and leaf phenology, less is known about the impacts of phenological changes on tree growth. Here, we assessed the relationships between the start of the thermal growing season and tree growth across the extratropical Northern Hemisphere using 3,451 tree-ring chronologies and daily climatic data for 1948–2014. An earlier start of the thermal growing season promoted growth in regions with high ratios of precipitation to temperature but limited growth in cold–dry regions. Path analyses indicated that an earlier start of the thermal growing season enhanced growth primarily by alleviating thermal limitations on wood formation in boreal forests and by lengthening the period of growth in temperate and Mediterranean forests. Semi-arid and dry subalpine forests, however, did not benefit from an earlier onset of growth and a longer growing season, presumably due to associated water loss and/or more frequent early spring frosts. These emergent patterns of how climatic impacts on wood phenology affect tree growth at regional to hemispheric scales hint at how future phenological changes may affect the carbon sequestration capacity of extratropical forest ecosystems. The authors use tree-ring width data across the extratropical Northern Hemisphere to show that earlier growing season onsets lead to enhanced tree radial growth in cold humid but not in dry areas.

An earlier start of the thermal growing season enhances tree growth in cold humid areas but not in dry areas