CO2 boosts tree growth less reliably when crops share the space
Mahmud M, Gosme M, Lecomte I, Barbault N, Dupraz C
Climate Adaptation
Black walnut trees planted alongside your vegetable rows or pasture will respond to rising CO2 differently than those grown in a woodlot, and knowing that gap helps you plan whether a food-forest layout will actually deliver the shade, nuts, and resilience you're counting on decades from now.
Scientists built a virtual simulation of trees growing next to crops and tested what happens as the air fills with more CO2 and temperatures climb. More CO2 did help trees grow taller and push roots deeper, but when those trees had to share space and water with crops, the benefit was patchier and less reliable than in a stand-alone forest. A hotter, drier climate still slowed growth overall, though the extra CO2 softened the blow somewhat.
Key Findings
Elevated CO2 (550 ppm) increased black walnut height, diameter, and root development in both agroforestry and forestry, but effects were stronger and more sustained in forestry than in crop-mixed systems.
In agroforestry, CO2-driven growth gains were more variable over time and suppressed by tree-crop competition, while below-ground root plasticity was notably greater than in forestry.
A combined climate-change scenario (+3°C, -10% precipitation) reduced tree growth in both systems, but elevated CO2 partially offset these losses, with the offset more pronounced in forestry.
chevron_right Technical Summary
Researchers updated a computer model to simulate how trees in mixed tree-crop farming systems (agroforestry) respond to rising CO2 and a warmer, drier climate. Higher CO2 boosted tree growth, but competition from crops made that response less consistent than in pure forests, and warmer/drier conditions still reduced overall growth even with the CO2 boost.
Abstract Preview
Original paper
Simulating tree responses to elevated CO2 and climate change in agroforestry system.
This study extends the Hi-sAFe agroforestry model by incorporating the effects of elevated atmospheric CO2 on tree growth. Hi-sAFe is a process-based biophysical model that represents tree-crop int...
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Juglans nigra, the eastern American black walnut, is a species of deciduous tree in the walnut family, Juglandaceae, native to central and eastern North America, growing mostly in riparian zones.