Becky Fasth

Decomposition of coarse woody debris originating by clearcutting of an old-growth conifer forest

ABSTRACT Decomposition constants (k) for above-ground logs and stumps and sub-surface coarse roots originating from harvested old-growth forest (estimated age 400–600 y) were assessed by volume–density change methods along a 70-y chronosequence of clearcuts on the Wind River Ranger District, Washington, USA. Principal species sampled were Tsuga heterophylla and Pseudotsuga menziesii. Wood and bark tissue densities were weighted by sample fraction, adjusted for fragmentation, then regressed to determine k by tissue type for each species. After accounting for stand age, no significant differences were found between log and stump density within species, but P. menziesii decomposed more slowly (k = 0.015·y−1) than T. heterophylla (k = 0.036·y−1), a species pattern repeated both above- and below-ground. Small-diameter (1–3 cm) P. menziesii roots decomposed faster (k = 0.014·y−1) than large-diameter (3–8 cm) roots (k = 0.008·y−1), a pattern echoed by T. heterophylla roots (1–3 cm, k = 0.023·y−1; 3–8 cm, k = 0.017·y−1), suggesting a relationship between diameter and k. Given our mean k and mean mass of coarse woody debris stores in each stand (determined earlier), we estimate decomposing logs, stumps, and snags are releasing back to the atmosphere between 0.3 and 0.9 Mg C·ha−1·y−1 (assuming all coarse woody debris is P. menziesii) or 0.8–2.3 Mg C·ha−1·y−1 (assuming all coarse woody debris is T. heterophylla). Including coarse roots increases these loss calculations (averages of all decomposition classes for the study year) to 0.5–1.9 Mg C·ha−1·y−1 or 1.0–3.5 Mg C·ha−1·y−1, respectively. Our results support substitution of log k in C flux models when stump k is unknown. Substitution of log k for coarse root k could, however, substantially overestimate C flux back to the atmosphere from these forests.

Differences between standing and downed dead tree wood density reduction factors: A comparison across decay classes and tree species

Woody detritus or dead wood is an important part of forest ecosystems and has become a routine facet of forest monitoring and inventory. Biomass and carbon estimates of dead wood depend on knowledge of species- and decay class-specifi c density or density reduction factors. While some progress has been made in determining these parameters for dead and downed trees (DD), there are very few estimates of these key parameters for standing dead trees (SD). We evaluated indicators of decay to relate subjective SD and DD decay classifi cations then compared SD and DD density and density reduction factors by decay class for a total of 19 tree species at nine sites in the United States and Russia. Results indicate that SD density declined with decay class for all examined species. By applying these results, a new set of SD density reduction factors was developed for 260 species inventoried by the U.S. Forest Services Forest Inventory and Analysis program in forests of the United States.

Decomposition of fine woody debris in a deciduous forest in North Carolina1

Abstract We examined the effect of position with respect to the soil surface, species, and piece size on the decomposition rate of fine woody debris (< 15 cm diameter) in a North Carolina forest disturbed by hurricane. To examine year-to-year trends, pieces of two species (Carya tomentosa ((Lam.) Nutt.) and Quercus alba (Lam.)) in four size classes were placed on the forest floor and collected annually for ten years. In addition, to examine position effects samples of the same species and sizes were suspended in the air and buried underground at a depth of 20 cm and collected at years 2, 4, and 8. Nine other species were placed on the forest floor and collected at years 2, 4, and 8 to determine the range of variability among species. Decomposition was slower the first year than subsequent years, therefore the lag exponential equation was used to determine time trends and an integrated decomposition rate-constant (kI) reflecting the overall decomposition rate-constant was calculated. The kI for C. tomentosa and Q. alba ranged from 0.17–0.25 year−1 with a significant interaction between species and size. The buried and suspended samples generally decomposed more slowly than the samples on the surface and kI ranged from 0.11–0.24 year−1 and from 0.10–0.18 year−1, respectively. There was a significant interaction between position and size; while drying limited decomposition of suspended pieces regardless of size, high moisture may have limited decomposition in the largest buried pieces. The kI for all eleven species and sizes averaged over all size classes ranged from 0.06–0.33 year−1. There was a highly significant interaction between species and size with the smaller sizes tending to decompose faster than the larger sizes and in general species with the most decay-resistant heartwood having the largest response to increases in size. Our experiments and comparison to other studies suggests that the interactions between species, size, and position relative to soil surface are highly complex and dependent on site climate.

Uncertainty analysis: an evaluation metric for synthesis science

The methods for conducting reductionist ecological science are well known and widely used. In contrast, those used in the synthesis of ecological science (i.e., synthesis science) are still being developed, vary widely, and often lack the rigor of reductionist approaches. This is unfortunate because the synthesis of ecological parts into a greater whole is critical to understanding many of the environmental challenges faced by society. To help address this imbalance in approaches, we examine how the rigor of ecological synthesis science might be increased by using uncertainty as an evaluation metric—as a parallel to methods used in reductionist science. To estimate and understand uncertainty we propose that it be divided into four general classes: (1) measurement uncertainty (i.e., experimental error) as defined by precision and accuracy, (2) sampling uncertainty that reflects natural variation in space and time as quantified by classical statistical moments (e.g., mean and variance), (3) model prediction...

Evaluation of techniques for determining the density of fine woody debris

Evaluated various techniques for determining the density (i.e., bulk density) of fine woody debris during forest inventory activities. It was found that only experts in dead wood inventory may be able to identify fine woody debris stages of decay. Suggests various future research directions such as development of a 2-class fine woody debris decay class system.