Microbial Processes > Long-Term Soil Productivity (LTSP) Study > Study Details: 7 - Methods - Measurements

Evaluating Management Impacts on Long-Term Soil Productivity: A Research and National Forest System Cooperative Study

Measurements

A core set of measurements must be taken at each installation, both pre- and post-harvest, in order to ensure comparability among sites. These are the responsibility of the P.I., and are not meant to preclude other measurements.

Measurements of Pre-Harvest Stand

• Soil profiles examined based on a 20 m grid interval including bulk density measurements at three depths, soil strength and soil nutrients including N, P, Ca, Mg, and K, pH , and organic matter.
• Nine one acre plots installed (plus 2-one acre plots for extra treatments)
• 5 downed woody debris transects will be installed in each 1 acre plot.
• Plots will be divided into approximate thirds, and ten soil samples (0–10 cm) taken and composited for analyses.
• Ten vegetation samples (.223 m sq) randomly collected per plot. Samples collections include grass, forage, herbaceous and woody material, and conifer litter. An estimate of vegetative understory will be determined for each plot based on percent coverage.
• Diameters (dbh) for all conifers on each plot will be measured.
• Based on diameter averages, three trees per plot will be selected as sample trees. Total height will be measured and sample disks taken at 2 m intervals. Approximately 20 branch samples (3 cm in length) will be taken along with sample needles, from various areas of the crown. This information will be used to construct biomass equations of the site and determine tree nutrition.

Measurements of Harvested Stand

The objectives of making measurements on the stand that is harvested from the LTSP plots are:

1. To obtain a measure of the amount of organic residue removed or left on the various treatments. Also, an estimate of absolute differences between locations, both within a region and among the different timber types across the nation is important. To accomplish this, measurements to be made on the stand existing at the time of harvest include the heights and diameters of the conifers from which biomass measurements are calculated.
2. To obtain an estimate of the rate of tree growth of the past stand. This will allow a rough estimate of the effects of changes in climate, management and unknown factors on tree growth. Also, since the treatment OM₁ C₁ approximates the past management, stern analysis of the harvested stand will enable us to predict how management practices will interact with climatic changes. The stem analysis will be done on three trees from each plot.
3. To obtain a species description and biomass measurement of the understory including the biomass of the litter layer if possible. The composition of the understory will be important in evaluating the effects of management of non-target species. The amount of biomass in the understory and litter layer is also needed to estimate the amount of organic residue removed by the different treatments.
4. To obtain an estimate of the amount of nutrients removed or left by the different OM treatments. This will allow us to explain differences in growth (if any) that seem to be caused by changes in nutrient supply to the trees. The nutrients in the trees will be derived from the biomass calculations and from measurements of tree parts collected and used in the biomass collections made of those components. The nutrients in the soil will be analyzed from the bulk density samples taken before harvest. Nutrients measured will include, but are not limited to; N, P, K, Ca, and Mg.

At a location, the plot identity of the measurements will be kept. Although, because the plots are selected for uniformity, the final summary may be made as if the measurements were collected from one population.

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