Light availability analysis of 24 southwest Michigan wetlands

Abstract

Thobaben (2004) presents a unique examination of the relative importance of numerous abiotic factors across a diverse set of wetlands located in southwest Michigan. In his study, Thobaben (2004) measured 24 wetlands' species abundance, pH, soil nutrients, water level, elevation, light, and many other abiotic factors. His findings showed that pH and light were the abiotic factors most highly correlated with the variation in plant communities across the 24 wetlands. Instead of measuring actual light levels in the wetlands, however, Thobaben (2004) used a variable called Canopy. Canopy was calculated as the sum of the percent cover values (abundances) for trees and shrub species that could reach 3 meters in height. While this measurement was adequate for a general comparison of light levels between the sites, it would be desirable to have a more precise and independent measurement. In this study, digital fisheye photography and computer image analysis were used to determine the canopy cover and light transmission of the wetlands in Thobaben's (2004) study. These measurements should provide a more accurate and independent determination of light levels than Thobaben's Canopy variable, and have a higher correlation with the variance in plant community structure across the 24 wetland study sites.