PERSISTENCE OF RESOURCE ISLANDS UNDER ARTEMISIA TRIDENTATA IN A BURNED SHRUB-STEPPE SITE

Authors: HALVORSON, J - BATTELLE PACIFIC NORTHWES; BOLTON, H - BATTELLE PACIFIC NORTHWES; Smith, Jeffrey

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Artemisia tridentata (big sagebrush) is a prominent shrub of cool desert environments encompassing a large part of the intermountain western United States. There are higher concentrations of soil variables such as total organic C, total N and inorganic N and higher rates of N cycling in soil beneath A. tridentata than in the soil between plants. These zones where nutrients are concentrated under plants are called resource islands. However, because most studies of resource islands in soil have focused on live plants, little is known about the their persistence following the death or removal of the overlying vegetation. The removal of the overlying plant can affect the pattern and functioning of a resource island in soil. How it will do so will be influenced by the plant-soil system, the method of plant removal, and the initial pattern of the resource island. However, at least three possible scenarios are possible once the plant is removed. First, the concentrations of soil resources associated with the former location of the plant may diminish. This will occur as heterotrophic soil microorganisms consume easily utilizable C substrates in the soil leaving less available components of plant litter and soil organic matter and as nutrients such as N are lost from the zones of high concentration via physical and biochemical processes such as leaching and denitrification. Second, concentrations of soil resources may persist in association with the location of the plant, in an unchanged state for a relatively long period of time. There may be a large pool of resources stored in the soil or the soil microbial populations may be stable or their activities low. Finally, a resource island may exhibit positive feedback and become self perpetuating if the relatively high concentrations of elements in the soil

Technical Abstract: Artemisia tridentata is a prominent shrub of cool deserts that supplements the soil in which it grows. However, little is known about the persistence of these so called resource islands following the death or removal of the live plant. We sampled adjacent burned and unburned sites to see if resource islands in soil persist in locations where shrubs were removed by fire 9 years earlier. Generally, the concentrations of soil properties burned A. tridentata were smaller than under live A. tridentata and did not vary as much with distance away from the plant axis. However, total organic C and soil pH were identical in burned and unburned soil. Nearly a decade after the fire, the patterns of some soil variables in the burned site were still significant. Significantly higher total organic C, total N, water soluble C, soil microbial biomass C, and electrical conductivity were observed at the location of a burned A. tridentata stem than at distances further away. The differences between burned and unburned soil were greatest near the plant. In contrast, burned soil was not distinguishable from unburned soil at locations greater than about 50 cm away from a live A. tridentata axis or a burned stump indicating that the resource island effect was most affected by removal of the plant and not by the fire. These ghost islands may represent a significant source of variability of soil properties that is difficult to account for because it is not easily detected or associated with the obvious location of plants.