Measuring Carbon in Shrubs

Abstract

Although shrubs are a small component of the overall carbon budget, shrub lands and shrub cover within forested lands warrant monitoring with consistent procedures to account for carbon in shrubs and to track carbon accumulation as communities change from shrubs to trees and vice versa. Many different procedures have been used to sample and measure shrubs (Bonham 1989) but only three types are selected here, to represent a range from simple and subjective to more time-consuming but objective measurements. Although the goal is to measure shrub carbon, the methods outlined here estimate biomass-which is about 50% carbon. For sample design, we advocate compatibility with the USDA, Forest Service, Forest Inventory and Analysis (FIA) program by using transects, microplots, or quadrats arranged within or near FIA subplots. Three basic methods are suggested for measuring shrub biomass: (1) cover estimations along transects, including point-intercept and line-intercept; (2) visual cover estimates in fixed area units; and (3) diameter measurement within fixed-area sampling frames. The 3rd method for measurement of individual shrub stem-diameters provides the most robust data for estimating biomass (and by extension, carbon) but requires the most field time. The other two methods allow more rapid measurements of shrub cover along transects or within plots. Our summary provides a framework for collecting shrub measurements three different ways; however, more work will likely be needed to develop appropriate equations that equate cover or stem measurements with biomass for various species.