A strategy for concurrently monitoring the plant water potentials of spatially separated forest ecosystems
A technique for estimating plant water potentials in plant communities was used in six forest stands representing a jack pine (Pinusbanksiana Lamb.) and a black spruce (Piceamariana (Mill.) B.S.P.) successional sequence. A set of 31 plants composed of 16 species were measured at 4-day intervals from early May to late August 1982. The six stands had similar patterns of summer plant water potentials with greatest differentiation among species occurring during periods of maximum water stress. Plant water potentials varied more in jack pine stands on sand than in black spruce stands on organic soil. Shallow-rooted ericaceous and (or) evergreen species (e.g., Vacciniummyrtilloides Michx., Vacciniumvitis-idaea L., and Pyrolaasarifolia Michx.) had the widest range of water potentials during summer, whereas deep-rooted Alnuscrispa (Ait.) Pursh had the narrowest range. Maximum morning (0700) water potentials reached−3.1 MPa. All species had fine roots (<2 mm) within the upper 20 cm of the soil, but some species of the Jack Pine Series had roots to 230 cm depth. Soil moisture was usually more available in the upper 20 cm and below 60 cm in mineral soils; the lower amount of soil moisture at middle depths resulted from depletion by plants and lack of downward percolation of precipitation in 1982.