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The DIRT Project (Detritus Input, Removal, & Transfer) |
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FIELD TREATMENTS The Harvard Forest DIRT treatments were begun in 1990 and are as follows: CONTROL (normal litter inputs) NO LITTER (aboveground litter excluded from plots) DOUBLE LITTER (twice aboveground litter inputs) † NO ROOTS (roots excluded from plots by lined trenches) † NO INPUTS (no aboveground litter and no roots) O/A-LESS (Installed 1991; organic and A horizons replaced with B horizon soil, normal inputs thereafter) (Treatments not included in the original Wisconsin experiment are preceded by "†") Replicated plots (3m x 3m each, n = 3; for CONTROL n = 6) are located beneath an intact forest canopy located in the Tom Swamp tract of the Harvard Forest. One plot of each treatment and two CONTROL plots are located in each of three adjacent blocks. The blocks represent upslope, midslope, and downslope positions. No tree boles are present on the plots and ground flora is either absent or removed as needed by clipping and periodic herbicide applications. During the time of maximum leaf-fall each year (September to November), aboveground litter inputs are excluded from NO LITTER plots with mesh fabric. Aboveground litter inputs are augmented in DOUBLE LITTER plots by adding litter taken from NO LITTER plots. Root ingrowth was prevented in the NO ROOTS treatment initially by lining backfilled trenches (dug into the C horizon) with fiberglass sheeting or reinforced polyethylene (Griffolynâ ). The lining in all root-exclusion plots was replaced in year 9 (1999) with a combination of Griffolynâ and polyethylene sheeting. The NO INPUTS treatment is a combination of the NO LITTER and NO ROOTS treatments. Soils in the O/A-LESS treatment were experimentally impoverished by replacing the forest floor and 0-15 cm mineral soil with B horizon material. The O/A-LESS treatment does not involve chronic manipulation of either above- or belowground litter inputs and the plots require no maintenance. This treatment is intended to allow estimation of 1) the fraction of total litter inputs (above- plus belowground) that are eventually transferred from litter to SOM and 2) the time course required for impoverished soils to recover to pre-disturbance conditions. Coarse woody debris inputs (CWD) larger than 2.5 cm in diameter is excluded from all treatments and controls. |