Estimating leaf area index and coverage of dominant vegetation on an extensive green roof in Syracuse, NY

Abstract

Roofs with full or partial coverage of vegetation, also known as green roofs, are perceived to restore ecosystem services in urban areas. Research investigations have been carried out to evaluate green roof performance on reducing stormwater runoff, improving runoff water quality, decreasing urban heat island effects, and several other benefits. The leaf area index (LAI) or an estimate of vegetation coverage on a roof may aid in evaluating these benefits. This study evaluates the leaf area index and plant area index as well as spatial coverage of two dominant species of vegetation on a 5550 m2 extensive green roof in downtown Syracuse, NY. Stems with attached leaves within individual patches of Phedimus takesimensis and Sedum floriferum were picked to estimate leaf area index using geometric models, and a ceptometer was used to provide an approximate range of values for the plant area index (PAI). Patches were picked in the summer of 2020 when plants were flowering, but the surface area of the flowers was not included in measurements. Sizes were measured for 8522 leaves from four patches of Phedimus takesimensis and 7751 leaves from five patches of Sedum floriferum. The estimated LAI for a patch of Phedimus takesimensis is 4.97 +/- 0.52 cm2 leaf area cm−2 ground area, while the LAI for a patch of Sedum floriferum is 2.70 +/- 0.37 cm2 leaf area cm−2 ground area. Furthermore, 154 photos were taken in the fall of 2020 and late spring and summer of 2021, representing 7.1% of the roof area in several categories. Results show the following fractions of area: 0.226 (Phedimus takesimensis), 0.381 (Sedum floriferum), 0.074 (moss), 0.029 (other vegetation), and 0.290 (bare soil). Using a weighted average, the LAI of the entire area of this green roof is 4.03 cm2 leaf area cm−2 ground area if the other vegetation has an LAI of 0.92 cm2 leaf area cm−2 ground area and the moss has an LAI of 25 cm2 leaf area cm−2 ground area. Excluding moss from the weighted average, the LAI of the roof is 2.18 cm2 leaf area cm−2 ground area.