Do plants ever compete for space?

Abstract

The term “competition for space” occurs often in ecological literature, but there has never been a direct demonstration of this competition. In fact it has been shown that plant canopies are mainly empty of plant organs. F.E. Clements recognized this. He suggested that one of the few situations in which competition for space would occur was in an unthinned row of radishes. Even this has never been demonstrated. We sowed radishes (Raphanus sativa) in a dense row and let them grow to maximum size in favourable conditions. For comparison, the same number of radish seeds were sown in a double, offset row. Squeezing the radish plants into one row was largely compensated by sideways movement of their hypocotyl/taproots, but total plant mass was reduced by 7.5%. Even this cannot be definitely attributed to competition for space. We conclude that competition for space, if it exists at all, is only a small effect even in conditions very favourable for it. It can, as Clements said, be ignored for natural communities.