With the expansion of the Panama Canal and climate change projections indicating temperature rises and reduced precipitation, water is becoming an increasingly vital resource for ecological and economic prosperity. Recent work has shown that forested portions of the watershed may yield more water in the dry season with less flash flow in the wet season than pastures due to large pores, generated from roots and other living soil borers. The primary purpose of this project is to quantify the hydraulic conductance of plants within the Panama Canal Watershed between stands with differing tree ages and hill position during wet and dry seasons. Leaf water potentials (ΨL) from selected trees were taken over two days using a pressure chamber from secondary growth stands with 8, 25, and 80 years of regrowth in October, 2015. The 25 year old stand (YOS) was also sampled along a north facing and south facing slope, and additional measurements will be taken in March, 2016. The secondary objective consists of using electrical resistivity tomography (ERT) to quantify vegetative use of soil water in the 25 (YOS). Electrodes will be placed 0.5 m apart along three lines and measured 3-5 times a day with leaf water potentials, and once at 2.5 m apart down the entirety of the hillslope.
Results/Conclusions
A case study from the wet season measurements indicate that there were differences between the three forests. Average ΨL p for the old growth forest was -1.41 ± 0.13 MPa, -0.86 ± 0.08 MPa for the 8 YOS, and -0.66 ± 0.09 MPa for the 25 YOS. However, there is still considerable variation among trees within stands, and the biodiversity present in the stands resulted in few species replicates across and within stands, so producing generalizations from the data is difficult from this single sampling in the wet season. Another sampling in the dry season will test if variability increases with drying of the system. It is also possible that as succession progresses, forests transition from similar isohydric water use strategies resulting in midday ΨL of -0.3 to -1 MPa as seen in the 25 and 8 YOS, to a more variable functional type in the 80 YOS which shows ΨL of -0.50 to -2.8 MPa. This preliminary result will be tested for differences in the wet season. Enhancing understanding of the hydrologic processes involved between stand age, aspect, and seasons can improve global applications and management patterns.