Microhabitat is critical for sugar pine emergence and survival in a xeric Jeffrey pine dominated forest

Mature shrubs can provide microhabitats that are beneficial to seedling growth. Sugar pine trees (Pinus lambertiana) grow in a narrow zone on the eastern slope of the Carson Range, an area extensively disturbed by logging and fire. This study identified the most favorable microhabitat conditions for sugar pine seedlings. Jeffrey pine (Pinus jeffreyi), a dominant tree species, was studied for comparison. In the fall of 2002 (cohort 1) and 2003 (cohort 2), 13,000+ seeds of both species were planted in enclosures, at three replicate sites, under various microhabitat conditions, beneath shrubs and in the open. The emerged seedlings were monitored for two growth seasons. Sugar pine seedlings emerged at a higher rate (75%) than did Jeffrey pine seedlings (69.5%) but after growth season 1, Jeffrey pine seedlings survived better (27.2%) than sugar pine seedlings (19.5%). Jeffrey pine seedlings survived better over the first winter (32.3%) than did sugar pine seedlings (18.5%) and grew taller (19.6 mm) than sugar pine seedlings (14.9 mm) after growth season 2. Seedlings in the shade survived through growth season 1 better (37.4%) than seedlings in the open (3.3%). Growth season 2 showed no significant effects. Jeffrey pine seedlings are the more drought resistant species and better suited for the xeric climate found in the Carson Range. But for either species, microhabitat determines recruitment success or failure. After seedlings have established, microhabitat becomes less critical for survival.