Methods

Each 400m x 400m forest stand (n=32) was prescribe-burned in spring 2000. Stands were located in heavier (open to tracked vehicles) or lighter (closed to tracked vehicles) military use compartments and on sandy or clayey soil.

Yearly Monitoring
Initial and year-to-year edaphic conditions were surveyed in a 100m x 100m plot in each stand using the following procedures:
Soil texture was determined from 9 points per stand using a micro-pipette method. Soil bulk density was measured from eight cores in each stand. Samples were oven dried at 105oC and weighed, and the bulk density was calculated from the core volume. Soil horizon depths were measured in 12 locations in each site in June 2001. Pooled Oi, Oe, and Oa horizons were harvested from 8 – 0.2 m2 plots in each site in May and June 2001, 2002 and 2003; dried; ground in a Wiley mill; and a subsample was ground in a Spex ball mill. The O layer sample was then analyzed on a Carlo Erba Elemental Analyzer (NA1500). Soil nitrogen availability was determined from 4 soil samples per site collected with a hammer corer to a depth of 15.2 cm in May 2001, 2002, and 2003 (2003 samples currently being analyzed). In the lab, the samples were sieved (6.3mm), an initial subsample was removed for a 2 M KCL extraction, and the remaining soil was placed in a closed jar and kept aerobic and incubated in the dark at room temperature (21oC). Soils were then extracted at 6 and 12 weeks to determine the production of ammonium and nitrate-N.

Short-term Response
Half of the 32 stands were burned in early (1/11 – 4/17) 2002. Access to the sites varied due to military training and burning schedules. Here, we present data from 6-9 stands that were accessible for immediate pre and post burn sampling. Soil temperature was recorded at three random locations in each stand using ibutton® integrated temp data loggers. Sensors at 1 cm depth logged temperature at 1 min intervals. Soil parameters were sampled at 8 locations within each site. The pooled organic layer was harvested (8 x 494 cm2), dried at 70oC, and weighed. Mineral soil samples were collected in each site (8 x 10 cm). Samples were extracted with 2M KCL. They were analyzed for NH4 and NO3 with an autoanalyzer, and for Al and Ca using ICP spectroscopy. Analysis of variance (ANOVA) was used to compare edaphic conditions and burn responses between military use (H=heavier, L=lighter) and soil texture (C=clayey, S=sandy) categories and, if applicable, pre- and post-fire.