In seasonal tropical forests, which comprise the majority of tropical forests globally, canopy trees may compete directly with lianas and neighboring tree saplings for resources. Competition for water, especially during the seasonal dry period, may limit canopy tree photosynthesis, and ultimately growth and reproductive output. We investigated whether the water use of canopy trees is affected by competition with either 1) lianas or 2) tree saplings in a secondary moist tropical forest in the Barro Colorado Nature Monument, Panama. At each of four sites, we selected four target canopy trees (16 trees total), such that half the trees were surrounded by many lianas, and the other half were surrounded with a roughly equal biomass of tree saplings. The basal area of woody stems rooted within 4 m of each target canopy tree was quantified. We began continuously monitoring sap velocity in all 16 canopy trees near the end of the dry season when soil moisture was at its yearly minimum. After completing initial sap velocity measurements, we cut a similar biomass of either lianas or tree saplings from a 4 m radius around two of the four target trees at each site, with the other two serving as paired controls.
Results/Conclusions
We did not observe a substantial change in the daily maximum or mean of sap velocity for canopy trees within 10 days of cutting neighboring lianas or tree saplings. Surprisingly, only two of 15 trees (two of 11 species) had substantially increased sap velocity in response to the onset of the rainy season and the concomitant increase in soil water potential. These initial results suggest that, in this forest, even at the end of the dry season, water use of these canopy trees was not limited by low soil water availability or competition with lianas or tree saplings.
