Coarse Woody Debris as a Function of Age, Stand Structure, and Disturbance in Boreal Newfoundland

Abstract

We examined the structural attributes of coarse woody debris (CWD) in balsam fir and mixed balsam fir‐black spruce forests in western and central Newfoundland. The purpose of the study was to document CWD abundance and structure within various stages of stand development, and to generate simple models to predict CWD availability as habitat for forest wildlife. Our objectives were threefold: (1) determine the temporal patterns of CWD following clear‐cut disturbance, and compare these second‐growth stands to old sites (>80 yr) of natural origin; (2) relate the temporal patterns of CWD to stand development; and (3) demonstrate how factors such as site conditions and disturbance may influence these temporal patterns. Our chronosequence included 19 second‐growth stands with a mean tree age ranging from 33 to 80 yr, and 7 old‐growth stands ranging from 87 to 110 yr. The volume of coarse woody debris (CWD), here defined as downed wood, was relatively low to intermediate early in the chronosequence (e.g., 32.3 m3/ha in a 36‐yr‐old stand), lowest in a 58‐yr‐old stand (15.2 m3/ha), and highest in an 80‐yr‐old stand (78.1 m3/ha). Results indicated that CWD volume followed the general “U‐shaped” temporal trend observed in other forest systems. The presence of CWD early in the sequence was strongly influenced by residual hardwoods (i.e., birch) left by the original logging operation. The highest observed volume of CWD corresponded with stand senescence and appeared to be maintained within old‐growth stands. Snag (standing dead wood) density was low within the youngest stands (<200 snags/ha), and peaked within mature second growth. Defoliation disturbance increased both the volume and the structural diversity of CWD within silviculturally mature second‐growth stands. Results from our study indicate that CWD in stands >50–60 yr of age is not residual but generated primarily from regenerating tree structure. Factors affecting the rate of stem growth, e.g., site quality and initial stocking levels, should influence the accumulation and overall abundance of CWD within later stages of forest development. We therefore applied yield‐density relationships as a method of examining stand‐level dynamics of CWD.

Plant Debris and Its Contribution to Ecosystem Carbon Storage in Successional Larix gmelinii Forests in Northeastern China

“…We demonstrated that tree biomass C storage exhibited an S-shape growth trend (Figure 3b), which is consistent with other studies on the relationship between live biomass and stand age [24,34,35]. Mature forest stand had relatively higher production of plant debris than younger plantations [15,36]. In addition, because the C storage of woody debris was persistent and slow to break down [8,9,37], its decomposition rate should be lower than that of litter.…”

“…However, this proportion is substantially lower than that of temperate forests in other regions of the world (8-47%) [44][45][46][47]. Numerous factors, e.g., forest structure, stand age, site productivity, decomposition rate and disturbance regime, may influence the accumulation of plant debris [5,15,48]. The large discrepancy of plant debris C storage and the relative contribution to ecosystems from these forests in northeastern China and those of similar forest types in other regions of the world may be derived not only from the variability in ecosystem development but also from the difference in stand history and disturbance regime.…”

“…Thus, insight into the dynamics of plant debris will help forest managers understand the impact of current management regimes on material cycles and energy flow of forest ecosystems. At an ecosystem scale, several studies of coarse woody debris (CWD) described a general "U-shaped curve" in the age sequence of different forest stands, where young and old stands have the highest CWD amount [13][14][15]. The establishment of the curve requires the assumption that the beginning of succession is due to a catastrophic disturbance, e.g., residual fallen logs and standing snags after a catastrophic fire [4,14,16].…”

“…Here, we examined the C storage of plant debris and its contribution to total ecosystem C storage in an age sequence of six larch (Larix gmelinii) forest stands (15,36,45, 54, 65, and 138 years old) in northeastern China. The plant debris C storage increased from 6.0 ± 0.5 Mg·C·ha −1 in the 15-year-old stand to a maximum of 9.3 ± 1.8 Mg·C·ha −1 in the 138-year-old stand.…”

Dynamics of Coarse Woody Debris Characteristics in the Qinling Mountain Forests in China

“…Thus, we considered that the "U" shape pattern was also to be found in the tree mortality. The same "U" shape pattern was also observed by other studies described in References [27,58,59].…”