Limitations of Current Indicators of Ca Depletion
Evidence from laboratory experiments and a growing number of field assessments indicate that anthropogenic Ca depletion may pose a unique threat to forest health and productivity. In particular, connections between contemporary species declines and Ca depletion highlight the need to monitor forests for indicators of change, including Ca loss. Direct measures of soil and plant Ca concentrations provide one traditional means of assessing the Ca status of forests. Although often valuable, there are several reasons why these measures alone may not support a comprehensive and practical assessment of the biological threat posed by Ca depletion across the landscape. Chief among these are difficulties associated with the high spatial variability of Ca storage and availability within forest soils, substantial differences in Ca uptake and nutritional requirements among tree species, and a lack in historical data to serve as a reference to gauge the timing and extent of Ca depletion.
- Soils : As noted in section 1.2, direct evidence of cation depletion is limited to a few retrospective studies that were able to use archived soil samples and contemporary measurements of the exact field locations to determine changes in soil chemical properties (Bailey and others 2005, Lawrence and others 2005).
- Vegetation : Ca deficiency thresholds for trees in native forests exist for some species with established nutritional vulnerabilities.
- Lack of Historical Data : One-time measures of soil or plant Ca concentrations can provide useful information of the current status of a site, particularly if Ca concentrations are clearly aberrant relative to limited established standards.
Encyclopedia ID: p3192
