Principle

Weight loss by bagged leaf litter has been a useful method for measuring leaf litter breakdown for nearly 50 years (Bocock and Gilbert, 1957). Known masses of litter enclosed in mesh bags or envelopes may be exposed in field sites and then retrieved at later times for remeasure-ment of mass. Disappearance or breakdown of bagged litter is a valuable means of comparing substrates such as leaf litter, twigs, or roots. Different habitats or geographic regions may also be compared. Litterbags have been successfully used in hardwood and conifer forests, deserts, agroecosystems, and arctic soil situations. In prairies, ingrowth of grass may present a problem. Litterbags have been used to sample a subset of soil microarthropods, in order to discover which species are active in a given stage of decomposition or to follow the development of microarthropod communities. Litterbags retrieved from field experiments are extracted with Berlese funnels before estimation of mass loss. Fractions of litterbag material may be removed also for nematode extraction. In this experimental context, different mesh sizes may be used to exclude macroarthropods, microarthropods, or microfauna. Breakdown rates are more rapid in bags with larger mesh and slowest in fine-mesh bags that admit only microfauna. Litterbags may be treated with insecticides or fungicides to manipulate specific groups of soil biota for studies of their effects on decomposition.

Litterbags consistently underestimate decomposition rates; thus they are properly used in a comparative context. Such underestimation is most extreme for rapidly decomposing substrates—leaves of Cornus florida or (in agricultural systems) leguminous foliage. For more recalcitrant litter types—Rhododendron or some Quercus species—mass loss from bagged litter more closely approximates that of unconfined leaves.

As an alternative method, a group of leaves secured by a nylon string attached to their petioles may be used in conjunction with litterbags. Loss of leaf area as well as mass loss may be measured (Hargrove and Crossley, 1988). Because entire fragments may be broken off and lost, this string method overestimates decomposition rates and is viewed as a comparative method. Decomposition of rapidly decaying substrates is characteristically overestimated. Some leaf litter species, such as sweetgum, tend to become detached from their petioles early in litter breakdown.

Another method of measuring leaf area loss was employed by Edwards and Heath (1963), who buried leaf disks of known area in lit-terbags. When they were retrieved the leaf area loss was estimated using a grid, and soil animals were enumerated. See Chapter 5 for a discussion of litter decomposition.

0 0

Post a comment