Intercanopy community structure across a heterogeneous landscape in a western juniper-encroached ecosystem

Questions How does landscape position influence biotic and abiotic attributes of western juniper (Juniperus occidentalis) encroached ecosystems? How does intercanopy plant community structure respond to changes in soil moisture and temperature based on juniper cover and topographic position? Location Steens Mountain, southeast Oregon, USA. Objectives Competition with western juniper modifies plant community composition, alters soil hydrology, and reduces plant productivity. Research is needed to understand these influences across heterogeneous landscapes. This study characterizes the relationship between juniper encroachment and soil water, soil temperature, topographic position, and intercanopy plant community structure. Methods Using a completely randomized block design, plant density and cover, percent bare ground, percent soil moisture, soil temperature, heat accumulation, and elevation were sampled in 10 m2 plots representing low (< 1%), moderate (similar to 14%), and high (similar to 27%) juniper cover at four aspects. The relationship and difference between vegetation patterns and environmental variables were analyzed using AOV, NMS, and MRPP (alpha=0.1). Indicator species analysis tested for shifts in dominant species along ecological gradients. Results Soil moisture remained higher in low juniper cover sites than moderate and high juniper cover sites. North-facing sites had highest soil moisture at 5 cm depth with low and moderate juniper cover levels. With increasing soil temperature from May to June, soil moisture declined by 19.7% at 5 cm depth. Achnatherum lemmonii and Pseudoreogneria spicata occurred in closed juniper stands while Achnatherum occidentale and Leymus cinereus were common when encroachment was limited. Application This approach can be used to predict ecosystem response to western juniper encroachment across heterogeneous landscapes.