The effects of the various manipulations can be broadly categorized into those involving 

 physical properties (temperature, structure of the vegetative canopy, etc.) and those involving 

 nutrient availability. Effects in the first category should be evident soon after the manipulation 

 is applied; however, effects related to nutrient availability may become evident only after several 

 seasons. :This is particularly true for bound nutrients in the form of litter or mulch. Thus, the 

 lack of noticeable effect in the parameters measured should not be interpreted as proof that the 

 manipulation did not influence the functioning of the system. For this reason, duplicate plots of 

 several of the manipulations were reserved for sampling in future seasons. In addition, the high 

 degree of variability encountered makes it difficult to draw conclusions from a single, peak-of-sea- 

 son, sampling. In cases where data from a single interval wiU suffice sampling should be more 

 intensive than in this study. 



Track Disturbance 



E^ul Gersper* University of California Bob Benoit* Virginia Polytechnic Institute 



Josephine Challinor* Univeristy of CaUfomia Walt Campbell Virginia Polytechnic Institute 



Rod Arkley University of California Bob Breedlove Yale University 



Steve MacLean University of Illinois Larry Tieszen* Augustana College 



Jim Bumbarger University of Montana Doug Johnson Augustana College 



Don Smith University of Montana John Dennis University of Calgary 



The sensitivity of the wet tundra to visible damage is seen most dramatically following a 

 disturbance caused by tracked or wheeled vehicles. The effects of these disturbances are apparent 

 throughout the North Slope not only from current activity but, to a large extent, from events dating 

 as far back as the 1940's. Thus, the consequences of the disturbance have short-term effects as 

 well as long-term effects in that they persist for many years, indicating the slowness at which the 

 tundra recovers from a given stress. 



Increased human activity in recent years, and prospects of even more activity in the future, 

 emphasize the need to examine critically the effects of vehicular disturbance on the tundra 

 ecosystem. The objectives of this study were to measure and to evaluate the effects of past track 

 disturbance on the tundra ecosystem with respect to dynamic interactions among ecosystem compo- 

 nents. 



Disturbances by surface vehicles are basically of two types. One type, less apparent than 

 the other, is the passage over the tundra which causes the compression of the standing vegetation 

 (live, and especially dead) to a layer a few centimeters thick directly above the wet moss and 

 organic interface. Such areas are seen in subsequent years as "green belts" stretching over the 

 tundra. They appear to be increased plant growth but this may be an illusion caused by the re- 

 moval of contrasting brown and tan standing dead material due to increased rate of decomposition. 

 The effects of these disturbances are certainly evident in the plant canopy where air, temperatures, 

 wind, and light penetration are altered. This type of disturbance commonly results from traffic 

 over a tundra with shallow snow cover. Even snowmobiles may produce this effect. As the number 

 of passes increases over the snow-covered trail the effects can grade into those of the second type 

 of track disturbance. 



The second and more destructive type of disturbance results from physical disruption of the 

 vegetative and soil organic layer. This drastically changes the thermal balance with the vegeta- 

 tion and soil, and increased soil thaw occurs. These tracks typically result in depressions over 



♦Principal authors. 



fifi 



