|Riegel, Gregg - USDA - FOREST SERVICE|
Submitted to: Journal of Vegetation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 7, 1997
Publication Date: N/A
Interpretive Summary: There is a great deal of interest in riparian (streamside) ecosystems, yet we know relatively little about the growth habits of species that dominate these ecosystems. In this study we compared two distinct locations within a mountain meadow riparian ecosystem. One location was 8 feet from the stream and the second location was 60 feet from the stream. In spite of the fact that the two locations were only about 50 feet apart, there were differences in the depth of the water table and the temperature of the plant canopy. Apparently, the additional growth of vegetation at the streamside has a significant cooling effect. Plants adapt to the dryer, slightly dryer environment of the mid-meadow by producing less leaf area (only one-third of the value for streamside location). Our results indicate mountain meadows can have steep environmental gradients and the dominant species are adapted to a range of conditions. Assessing management impacts based only on species composition alone will prove difficult given the adoptability of the dominant species.
Technical Abstract: We compared gas exchange, water relations, and leaf area index (LAI) of three dominant montane meadow graminoids growing at both streamside and mid-meadow locations (2.5 and 20.0, respectively from the stream edge). The two locations were environmentally very different in spite of their close proximity. When averaged over season and species, photosynthetic rates were only 12.5% higher at the streamside compared to the mid-meadow location, and both conductance and transpiration were similar between locations. The similarity in stomatal response was surprising given that streamside plants had xylem potentials that averaged 0.72 MPa less negative (less water-stressed) than that of mid-meadow plants. There was no clear relationship between xylem potential and conductance for the species studied. Total LAI for the three species was nearly three times higher at the streamside compared to mid-meadow location. Thus, differences in plant growth between the two locations appear more morphological than physiological in nature. Carex nibrascensis had a more conservative gas exchange strategy (lower photosynthesis and transpiration) than Juncus balticus or Deschampsia cespitosa, yet developed more leaf area than either of the species. Based on growth form, we suggest that Juncus balticus is less morphologically plastic than the other species, but maintains higher rates of carbon gain per unit leaf. The other species, and Carex nebrascensis in particular, maintain relatively conservative gas exchange rates, but can adjust morphologically to environmental conditions to maximize canopy carbon gain.