Microclimate influences on red fir seedlings in the Sierra Nevada
Projected climate warming in the mountainous Western US is creating considerable challenges for forest managers. Given observed increases in the mortality of conifer species, recruitment is especially critical to future forest health. Microclimate (approximately 1 m3) is thought to play an important role in successful recruitment, but little is known about which specific environmental factors are most influential. During 2009-2013 in the red fir forest of Sequoia National Park, we measured air and soil temperatures, soil moisture, potential evaporation, canopy cover, topography, and soil characteristics at 225 sites in a 1-ha study plot (elevation 2,500m). We predicted each environmental factor at every location on a 1m x 1m grid using spatial statistics. We also tracked 4,000 seedlings annually. We correlated three different measures of the seedlings’ annual growth with the environmental factors. To determine the relative importance of the factors, we used model selection.
For each environmental factor, we present landscape patterns, highlighting the differences in heterogeneity between factors at the 1-m spatial scale. Then, we discuss the relative importance of the environmental factors on each growth metric for 1) a group of multi-aged seedlings that survived the entire study period and 2) a single cohort that we tracked over four years. Preliminary results suggest that soil degree days, potential evaporation, and snowmelt date may be more important to seedling growth than minimum and maximum temperatures. Knowing which of these environmental factors are most critical to seedling recruitment will enable forest mangers to implement more effective adaptive management strategies for red fir and other similar conifer species.