Maize and soybeans were intercropped with hybrid poplar ('Populus deltoides' x 'nigra' DN-177) and silver maple (' Acer sacharrimum') at a within row spacing of 5 m and between row spacing of 12.5 or 15 m. In 1997, overall yield of maize was reduced to 71% and 81% of a control in the poplar and maple intercrops respectively. In 1998, yields were 61% and 85%, respectively. Soybean yields were 71% and 75% (1997) and 70% and 101% (1998) of a control in the poplar and maple intercrops, respectively. Daily rates of carbon assimilation were generally lower near the trees where competition for light was the greatest and coincided with the lowest yield. Maize appears to compete effectively with the trees for soil moisture and benefits from microclimate changes. Soybean receiving morning shade and afternoon sun did not fully respond to improved light conditions. The soybean crop was susceptible to moisture competition, likely a result of a relatively small root system and inherently low water use efficiency.