Regeneration of Oak Woodlands is problematic in northern California. Our research focuses on the below ground aspects of regeneration; more specifically our work investigates how mycorrhizal fungi may facilitate the survival of tree species in the dry and nutrient poor oak woodlands. We are examining the hyphal biomass associated with four tree species growing at the Sierra Foothills Research and Extension Center located 70 miles NE of Sacramento, California, USA. Root restrictive 25 μm nylon bags were constructed and filled with medium coarse sand and 100 μg/g apatite additions. In April 2004, the bags were placed in the ground beneath mature blue oaks, interior live oaks, foothill pine, and Ponderosa pine. One year later, the bags were removed and contents freeze dried. Hyphal biomass was determined by removing and weighing the hyphae. Hyphal length analysis was conducted using microscope pictures and Tennant’s equation for root length (1975) to measure hyphal length. Additionally, ergosterol analysis is being performed by HPLC and related to hyphal length and weight. Fungal material is being analyzed using molecular techniques such as polymerase chain reaction (PCR), restriction length polymorphisms (RFLP) and sequencing to determine fungal species frequency and any tree specific fungal species affinities. Data obtained from this experiment will be compared to a concurrent experiment being conducted at a site located near San Luis Obispo, California, USA where oak woodland regeneration efforts have been more successful. The same root restrictive bags were placed under blue oaks at the San Luis Obispo site for 1 year and are currently being analyzed.