The net uptake and storage of nutrients such as N and P in live and dead vegetation can be calculated from the concentration of these elements and the amount of organic matter in these pools. In most of the small watersheds there are estimates of live and dead plant biomass, and for some net changes in these pools. Unfortunately there is no comparable set of data on nutrient concentrations to make estimates of nutrient pool sizes or net changes in these pools. The only dataset available for small watersheds is for WS10 when it was in an old-growth condition. There are no concentration data for other old-growth watersheds or for other age-classes.
We sampled 7 of the small watersheds at Andrews Forest (WS01, WS02, WS06, WS07, WS08, WS09, and WS10) to determine the concentration of major elements within dead and live vegetation. We conducted this sampling so that it can be repeated in time to determine if concentrations are changing. The data is stored online and can become a general resource for investigators at the site. Specifically, concentration data was determined for: 1) the forest floor, 2) fine woody detritus, 3) trees, 4) shrubs, and 5) herbs. Concentrations in coarse woody detritus and soil were not determined, although rough values for the former have been published. Samples were taken systematically throughout each watershed so that a watershed average can be determined. The intent is therefore not to collect data that shows seasonal trends, only to provide reasonable bulk concentration data for general estimates of long-term stores and fluxes of these elements. Nitrogen and carbon were determined on a C/N analyzer. Cations and P were determined using ICAP.
1) Forest floor nutrient concentrations were determined from cores collected from each vegetation plot within each watershed. In each plot 4 cores (taken at 4, 5, 6, and 7 meters from plot center) of forest floor above mineral soil were collected and pooled. Very decayed wood (red mush) was separated from other types of forest floor materials before placing into sample bag.
2) Fine woody debris nutrient concentrations were determined from pieces of branches and other small woody material that was collected for density determination after transects were done to determine volume.
3) Tree components were sampled adjacent to existing vegetation plots. The range of species and sizes were selected to represent the distribution observed in the permanent plots, with sampling using a stratified random design so that sample trees represented a wide diameter range. At least 10 trees of dominant species and 5 trees of subordinate species were sampled. Samples of foliage, twigs, branches, bark, sapwood, and heartwood were taken from each tree. Foliage and branches were taken at multiple heights using a clippers where possible and a shotgun when necessary. Bark was removed using a cork cutter or chisel. Wood was sampled using an increment corer. Coarse roots were not sampled as there is already a database that provides approximate numbers.
4) Shrubs were sampled in two forms: large shrubs and small shrubs that are usually inventoried with herbs. Both had foliage and woody tissues collected from shrubs near vegetation plots. These samples were taken from a range of species at the site, with the intent of getting a reasonable average. It is unlikely the store in these life forms will be large enough to warrant species level sampling.
5) Herbs were sampled similarly to shrubs, with multiple species and life-forms being mixed together to get a reasonable average value.