The decomposition of windrowed, chipped logging slash and tree seedling response: A plant growth and nuclear magnetic resonance spectroscopy study

Forest management practices historically have reduced the mass of logging slash to facilitate planting and reduce fire risk. However, coarse woody debris (CWD) is considered an important component of unmanaged forests of western and coastal North America. An experiment was established in northern California using chipped logging slash concentrated in windrows to emulate large fallen logs to determine the effects of alternative logging residue treatments on soil fertility and the performance of planted ponderosa pine. Chip piles warmed faster than mineral soil, but upper regions dried quickly during the dry summers. Fourteen years after planting, growth response was positive, as seedling volume declined with distance from the windrows. After 6 and 10 years, chip samples showed little variation in total C, but total N was higher for 10-year samples, with slightly higher values at the base and for N-fertilized sections. Analysis by solid state ¹³C CPMAS NMR, verified by spin-counting and triplicate analysis showed only subtle differences among 10-year samples, with non-carbohydrate C slightly more abundant at the base of the piles and for windrows originally fertilized with N. However, proton spin relaxation editing (PSRE), based on differences in T_1H relaxation rates, was able to distinguish between C in relatively undecomposed lignocellulose (slowly relaxing) and more decomposed material and microbial residues (rapidly relaxing). The small differences between top and base, and between fertilized and control samples were concentrated in the rapidly relaxing component. Bulk composition of 10-year chip windrows was similar to CWD naturally decomposed by white-rot fungi, but PSRE offers a new approach to monitor spatially heterogeneous development of microsites more characteristic of brown rot.