This is the third and final data set in a series of basin-scale summer forest soil surveys. We conducted soil survey in 1998 designed to provide an accurate assessment of soil properties over the entire H.J. Andrews Experimental Forest. This dataset represents the results of that effort. Since the 1994 survey, we changed the way we measured soil field respiration rates. Initially we used the 24 hr soda-lime CO2 adsorption method in chambers with only one measurement per site. In 1998 we converted to using the Li-Cor portable respirometer with 5 measurements made per site. Since 1994, it was also discovered that there were significant edge effects to 30 meters from an edge. For this reason, all sample locations were moved at least 40 meters from the road. While conducting autocorrelation analyses, we found that for the variables studied, samples collected at 5 m intervals were not autocorrelated and could thus be considered independent for statistical analysis. Our subsequent work also allowed us to chose those variables that would most likely be influenced by topography.
The previous two surveys were conducted in the late summer when the forests are dry and microbial activity at a minimum. The current study was conduced from mid June to the first of July while the soils were still moist and when microbial activity was more typical of wet months. In the other two studies, only one measurement was made per site. In the current survey, replicate samples were collected and pooled or multiple measurements were made in the field. As a result of experimental design modifications, it is thought that this represents the best and most definitive dataset of basin-scale soil properties on the HJA.
In the first survey, forest floor respiration rates were measured at 130 sites covering a large portion of the HJA. The sample sites were located at 0.5 km intervals along most of the main roads. In addition to field respiration rates measured by the soda-lime method, soil and air temperatures were recorded along with maximum and minimum soil temperatures for the 24 hr CO2 collection period. Only one measurement was made per site. These data and associated metadata can be found in database SP005 under the title of “H.J. Andrews 1993 REU synoptic soil respiration of permanent forest sites”.
The following summer, a much more comprehensive study was conducted. The number of sites studied was expended to 183 sites located at 0.5 km intervals along all passable roads on the HJA. With the exception of the max-min soil temperature data, all variables measured in 1993 were repeated in 1994. In addition, the following variables were measured: pH, soil moisture, bulk density, soil organic matter, laboratory respiration (both long and short-term; with and without amendments), denitrification potential, extractable ammonium, and mineralizable nitrogen. In addition, we scored for the presence of moss on the surface and mycorrhizal mats found in 4.7 x 10 cm cores. These data and associated metadata are located in database SP006 entitled “H.J. Andrews 1994 REU study of soil chemical and microbiological properties”. The main objective of this study was to provide a broad overview of soil chemical and biological properties to guide us in future large-scale HJA soil surveys.
Robert P. Griffiths
In the 1990s, there have been two major objectives Bob Griffiths' soils work at the H.J. Andrews Forest: (1) to determine how climate change and (2) to determine how forest disturbance influences soil nitrogen and carbon cycling. This study is designed to do both. Because of the broad geographical representation of these sites, all climate zones as influenced by slope, aspect and elevation, are represented as well as differing vegetation types, and disturbance histories. As of 1998, we represent different climate zones primarily by elevation. As the climate models are perfected, soils data can be evaluated in terms of annual mean temperatures and precipitation.
Because of the wide range of disturbances represented on the Andrews, these data will be analyzed in terms of disturbance influences on soil N and C cycling. Because of the scope of this study, these data could be used to parameterize nutrient and carbon cycling models in which potential influence of climate change and forest disturbance could be predicted over the Central Oregon Cascade Mountains.