Effects of seasonal drought on gap and understorey seedlings in a Bolivianmoist forest

In tropical moist forests, length of the dry period may have a profound inf luence on leaf dynamics, plant growth and survival. To evaluate the role of light and water availability oil seedling performance, a 1-y experiment wa s carried out in a tropical moist forest in the Bolivian Amazon in which se edlings of three tree species (Brosimum lactescens, Cedrela odorata and Sch izolobium amazonicum) were planted in gaps and the understorey. Variation i n length of the dry period was simulated by subjecting part of the seedling s to a water treatment at the end of the dry period. Gaps and understorey h ad a similar soil moisture content which varied between 39% in the wet seas on and 16% in the dry season. Height and leaf growth rates were higher in g ap compared to understorey plants, and in the wet compared to the dry seaso n. A high growth during the wet season provided gap plants with a decisive size advantage over understorey plants during the dry season. Their larger root system allowed gap plants to explore a larger surface area and deeper soil layers for water. Consequently, gap plants of Cedrela experienced a sh orter deciduous period (22 d) compared to understorey plants (61 d). Wateri ng at the end of the dry season cued the flushing of new leaves by Cedrela, although it did not lead to a higher plant growth.