At a field in Dornburg, Germany, winter oilseed rape grew beside poplar trees that had been standing for eight years—yet its harvest matched crops grown in open fields without trees. That finding points to a practical way farmers can combine food and wood production without giving up crop yields.
Alley cropping places rows of trees among fields of crops such as wheat, barley and rye. The trees can support wildlife, improve soil and capture carbon, while also shielding crops from wind. But they compete with crops for sunlight, water and nutrients. Researchers have long seen both losses near trees and, farther away, possible gains from wind protection. A six-year study led by the University of Göttingen helps explain how farmers can manage that trade-off.
The team measured winter and spring crop yields at four sites in Germany, at different distances from poplar rows. The trees were grown as short-rotation coppice: they were cut close to the ground every three to nine years and allowed to regrow. Researchers compared the crops across tree ages from one to nine years.
Spring crops were more affected as the poplars grew. When trees were five years old or older, spring crop yields in the tree-lined system were 10% to 35% lower than yields in open farmland. The biggest drop was within four meters of the rows, where shade limited the light reaching crops.
Winter crops told a different story. Their yields remained similar to those in treeless fields throughout the trees’ one-to-nine-year growth period. This gives farmers a way to match crops to the stage of the tree cycle: grow spring crops during the first three years after the trees are cut, then rely on winter crops as the poplars grow taller and cast more shade.
The study also found that poplar wood production was three times higher after the second tree harvest than after the first two harvests. Together, the crop and tree results suggest that choosing the right crop for each part of the rotation can help make an alley-cropping field productive in more than one way. The researchers say the combined system can outperform open farmland in productivity when crop choices account for tree age.
The work was led by Professor Edzo Veldkamp at the university’s Faculty of Forest Sciences and Forest Ecology. Dr. Sarah Choe, who carried out the research for her Ph.D., said winter crops were less affected by tree shade and could be grown throughout the rotation. The results were published in Agronomy for Sustainable Development.
The findings offer a clear next step for farmers considering trees in their fields: plan crop seasons around the poplars’ growth and harvest cycle. Rather than treating shade as a problem that rules out crops, the study shows that different crops can fit different stages—and that trees can keep producing wood as the field continues to deliver harvests.