|Abstract or Summary
- Post-settlement juniper expansion in the western states has been reported for decades,
including western juniper (Juniperus occidentalis Hook ssp. occidentalis) woodlands in the northwestern states. A 15 km2 study area in the Sheep Rock Unit of John Day Fossil Beds National Monument in eastern Oregon was selected to study spatial and temporal distribution patterns of western junipers, and build statistical models for the patterns. Environmental characteristic data are from soil, vegetation and contour maps. Western juniper data are from aerial photos. Image processing techniques and geographical information system (GIS) were used to process data. Nonparametric statistical methods, including Kruskal-Wallis one-way analysis of variance by ranks, Spearman rank correlation coefficient, chi-square test and chi-square partitioning, and classification and regression tree (CART) were used for data analysis and building statistical models. The results show a clustering spatial distribution pattern. Western juniper is more abundant above elevations of about 900 to 1,000 meters MSL, on sites with soil type 15f- Gwin-Rock outcrop complex or 43f- Simas-Badlanci association, and on medium slopes, but
probabilities of juniper occurrence on less steep slopes are higher at lower elevations.
Northeastern aspects have significantly lower juniper abundances than other aspects. Junipers prefer sites with higher surface flow accumulation, except extremely high flow
accumulation supporting only low juniper abundances. The CART spatial model shows three density classes classified by four out of five environmental characteristics with a
misclassification rate of 0.27. Temporally, juniper density in the study area has increased from 37 junipers/ km2 to 1,404 junipers/ km2 during the last century. However, relationships of this expanding pattern to environmental characteristics are obscure. There is no conspicuous difference between habitats of young and old jumpers, except perhaps soil types. The likelihood for finding mature or old junipers is higher in sites with soil type 41e- Simas very stony clay loani, 43f- Simas-Badland association or 46f- Snell-Anatone complex. The spatioteniporal distribution pattern of western juniper in the study area could be described as a clustering pattern with chronologically increased abundances. Juniper may continue to increase its abundance and expand from high density areas to low density or non-juniper areas. Unless juniper density is controlled, it seems likely that junipers will dominate most of the monument's landscape in the future.