TD032
A chronosequence of woody root decomposition in the Pacific Northwest, 1995 to 1997

CREATOR(S): Mark E. Harmon

PRINCIPAL INVESTIGATOR(S): Mark E. Harmon

ORIGINATOR(S): Mark E. Harmon

OTHER RESEARCHER(S): Hua Chen, Jack E. Janisch

DATA SET CONTACT PERSON: Mark E. Harmon

ABSTRACTOR: Becky Fasth

METADATA CREATION DATE:

22 Jun 2005

MOST RECENT METADATA REVIEW DATE:

15 Nov 2016

KEYWORDS:

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

PURPOSE:

To study root decomposition of five tree species in forests of the Pacific Northwest.

METHODS:

Experimental Design - TD032:

Description: One chronosequence of commercially thinned and clear-cut stands was located at each site. Current stand vigor and locations, as well as thinning or cutting ages, were considered during stand selection. Vigorous forest stands indicated, to some degree, that the previous stands were healthy and the chance of root rot was small. All sampled stands at each site were close to each other and similar in elevation, topography, and soil type. At CAH, the chronosequence included seven stands. Of these stands, woody roots of Sitka spruce were taken from trees that were cut or thinned 7, 20, 33, 37, and 46 years prior to sampling. Root samples of western hemlock were obtained from trees cut 2, 7, 10, 16, 20, 33, and 37 years prior to sampling. The second chronosequence, located in the western hemlock zone (300–1550 m elevation) at HJA, included eight different stands. Of these stands, woody roots of Douglas-fir were taken from trees that were cut or thinned 8, 10, 14, 21, 31, 36, 40, and 45 years prior to sampling. Root samples of western hemlock were obtained from trees cut 8, 10, 14, 25, 31, and 36 years prior to sampling. The third chronosequence was located at PRF, where ponderosa pine roots were sampled at six stands. Woody roots of ponderosa pine were sampled from trees that were cut or thinned 4, 7, 10, 19, 22, and 25 years prior to sampling. Lodgepole pine roots were obtained from trees cut 7, 10, 16, 19, 22, and 28 years prior to sampling. Samples of undecayed woody roots from fresh uprooted trees of these species were sampled to serve as controls.

Field Methods - TD032:

Description:

Three to five stumps were selected for each species at each stand. We avoided "living" stumps to reduce the time lag between when the tree was cut and when the roots died. Woody roots (diameter greater than 1 cm) were collected by excavating the root systems of chosen stumps at each stand. These roots were sorted into two size classes: small roots (diameter 1-5 cm) and large roots (diameter 5-10 cm, occasionally up to 15 cm). After excavating the soil surrounding roots, 10-20 cm long samples were removed using a handsaw, reciprocating saw, or in the case of very large roots a chainsaw. After removal, the dimension of each root sample was recorded in the field, including the average outermost diameter, the average longitudinal length, average bark thickness, and bark cover in percent. Each average was based on the mean of three measurements. Then the average root wood diameter and longitudinal length were recorded after removing the bark. If a resin core was present, its length and diameter were measured after separating it from the wood. Bark cover was estimated visually, or if this was not possible, we measured the entire bark surface area by forming bark pieces into a regular shape such as a rectangle. For very old decomposing roots, bark could not be recovered completely during root excavation. However, this occurred rarely and the results of bark decomposition should not be influenced significantly.

The whole volume of each root was calculated from the formula for a cylinder.

V = *( D2 * L)/(4)

where V is the volume, D is the average outermost diameter and L is the average longitudinal length. The root wood volume was calculated by the same formula using average root wood diameter instead of average outermost diameter if resin cores were not present. The bark volume of roots was based on the difference between the volumes of whole roots and root wood. If resin cores were present the volume of root wood was the difference of the entire root wood (including resin cores) volume and the resin core's volume.

Laboratory Methods - TD032:

Description: Root samples were returned to the laboratory and were dried to a constant mass at 55°C and weighed. Densities of bark, wood, and resin cores of each individual root sample were calculated as the oven dry weight divided by its green volume. The density of whole roots was obtained based on the density of each component and their proportion of total volume. Dried root samples were 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:

None

ELEVATION_MINIMUM (meters):

ELEVATION_MAXIMUM (meters):

PROGRESS DESCRIPTION:

Complete

UPDATE FREQUENCY DESCRIPTION:

notPlanned

CURRENTNESS REFERENCE:

Ground condition