TD031
Decomposition of Fine Woody Roots: a Time Series Approach, 1995 to 2006

CREATOR(S): Mark E. Harmon

PRINCIPAL INVESTIGATOR(S): Mark E. Harmon

ORIGINATOR(S): Mark E. Harmon

OTHER RESEARCHER(S): Hua Chen

DATA SET CONTACT PERSON: Mark E. Harmon

ABSTRACTOR: Becky Fasth

METADATA CREATION DATE:

28 Jun 2005

MOST RECENT METADATA REVIEW DATE:

4 Mar 2013

KEYWORDS:

Inorganic nutrients, Organic matter, decomposition, inorganic nutrients, nitrogen, organic matter, roots, fine roots

PURPOSE:

We examined the effects of species, initial substrate quality, and site differences on woody root decomposition and its nitrogen dynamics in Sitka spruce (Picea sitchensis), Douglas-fir (Pseudotsuga menziesii), and ponderosa pine (Pinus ponderosa) dominated forests in Oregon, U.S.A. using a time series approach. Roots of fourteen species and five size classes were placed in the field to incubate and then collected at pre-planned intervals to determine mass loss and nitrogen content.

METHODS:

Experimental Design - TD031 :

Description: The overall experimental design for the root decomposition study was a split-plot with 3 sites, 4 replicates, 5 size classes, and 4 backbone species. The three incubation sites were Cascade Head Exp. For. , H.J. Andrews Exp. For., and Pringle Falls Exp. For. The 5 size classes included fine roots (< 2 mm diameter), small roots (2-10 mm), medium roots (10-50 mm), large roots (50-100 mm), and jumbo roots (greater than 100 mm). The backbone species were Alnus rubra (red alder), Pseudotsuga menziesii (Douglas-fir), Tsuga heterophylla (western hemlock), and Pinus pondersoa (ponderosa pine). For fine roots another 11 species were included. They are Acer macrophyllum (bigleaf maple), Acer rubrum (red maple), Abies magnifica (California red-fir), A. concolor (white fir), A. procera (noble fir), Calocedrus decurrens (incense-cedar), Fraxinus latifolia (Oregon ash), Picea engelmanni (Engelmann spruce), Pinus contorta (lodgepole pine), P. monticola (western white pine), and Thuja plicata (western redcedar). An additional 3 species were included in the small and medium root classes besides the backbone species. In the large root category, we studied lodgepole pine, ponderosa pine, and Douglas-fir. Jumbo roots included ponderosa pine and lodgepole pine.

Field Methods - TD031:

Description:

Fine root collection

A total of 15 species of fine roots, which are dominant or common at Pacific Northwest, were obtained from local tree nurseries including Bend Pine, H. J. Stone, and Wind River Nursery in Oregon and Washington in early spring of 1994. Of these species, 4 deciduous and 11 coniferous species were obtained. After fine roots (< 2 mm) were trimmed from seedlings at nurseries they were transported to Corvallis, Oregon. Fine roots of each species were cleaned by tap water and then they were spread in trays and air-dried at 15 to 20ºC room temperature to a constant mass (10 days). Approximately 10 g of air-dry fine roots were weighed and put into 20 x 20 cm polyester cloth litter bags and sealed with six monel staples. Sub-samples were retained for initial moisture, ash and nutrient content.

Selection of small and other size roots

All of the other size classes used in this study were collected from recently uprooted trees. Either wind throw or road building uprooted the chosen trees. The roots obtained from the field were sorted into small (2 - 10 mm), medium (10 - 50 mm), large (50 - 100 mm), and jumbo roots (greater than 100 mm). The roots were then cut into 20 cm long segments (samples). The root segments were air-dried at 15 to 20ºC room temperature to a constant mass (20-50 days). Approximately 10 g of air-dried small roots were weighed and put into 20 x 20 cm polyester cloth litter bags that were sealed with six monel staples. We used the same type of cloth bag as with the fine roots. Sub-samples of small roots were retained for initial moisture and nutrient content.

Considering the wide variation of moisture content of the different segments of roots that were large as compared to the small roots, we determined the total air-dried weight of each root segment individually after measuring its moisture content by sub-sample. Before field placement, each segment was sealed at the ends using epoxy to prevent end rot effect before putting it into a mesh bag (mesh size= 0.4 mm). Therefore, the initial dry weight of each sample varied for all the medium, large, and jumbo roots as compared to the fine and small roots which were all roughly the same weight. Each sample was tagged with a numbered aluminum tag on a cable tie.

Root incubation and decomposition

Root samples that were to be harvested at the same time were tethered together by a nylon line through a cable tie attached to the aluminum tag and the mesh sample bag. Tethered root samples were buried in the top 20 cm of soil. Each site had four replicates with the same set up of root species and sizes. Additionally, one wooden dowel (species: GOBA) was placed at the end of each tethered line in such a way that half of the dowel was above ground and half was belowground. Dowels were 1 cm in diameter, 61 cm long, and composed of Gonystylus bancanus, a non-decay-resistant tropical tree species. The bottom half of the dowel was encased in a 1 mm mesh sleeve for improved sample removal. Samples were placed for incubation in the field in June of 1995.

Root samples were harvested in different time intervals within the planned 10 year incubation period of the study. We retrieved fine root litterbags of the backbone species 14 times and the other species 4-6 times within the 10 year period. The fine roots of the four backbone species were harvested in 0.25, 0.5, 0.75, 1, 1.5, and 2 years, respectively. Small and medium roots of the backbone species and large roots of Douglas-fir and ponderosa pine were harvested annually.

Laboratory Methods - TD031 :

Description: Decomposition of the roots was estimated from the change in ash free dry weight (mass) of the root samples. Root and dowel samples were returned to laboratory, carefully brushed free of soil and other debris, plus and in-growing roots were removed. Samples were dried to a constant mass at 65 C and then weighed. If the roots were large they were chopped into small pieces before drying. Weight loss from the roots and dowels were calculated after correcting for ash content. Dried root samples were then ground in a Wiley mill and passed through a fine screen (1 mm). Samples were stored in 20 ml vials to prevent moisture changes prior to analyses for ash and nitrogen.

TAXONOMIC SYSTEM:

Garrison et al., 1976

GEOGRAPHIC EXTENT:

Andrews Experimental Forest, Cascade Head Experimental Forest, Pringle Falls Experimental Forest

ELEVATION_MINIMUM (meters):

ELEVATION_MAXIMUM (meters):

PROGRESS DESCRIPTION:

Complete

UPDATE FREQUENCY DESCRIPTION:

notPlanned

CURRENTNESS REFERENCE:

Ground condition