Capstone project

Population Dynamics of the Island Torrey Pine (Pinus torreyana ssp. insularis) on Santa Rosa Island, CA

Torrey pine (Pinus torreyana and Pinus torreyana ssp. insularis) is the rarest pine species in North America, with populations limited to Del Mar, CA and Santa Rosa Island (SRI), CA (IUCN 2013). Over the past 150 years, grazing by non-native ungulates and ground disturbance by feral pigs resulted in landscape level disturbance, erosion, and negative impacts to island flora (Moody 2000). We completed a census on the SRI Torrey pine population to determine (a) its population size and whether it is stable, growing, or declining; (b) the spatial variation in population structure; (c) the spatial patterning of trees in different life stages; (d) the environmental factors that are related to germination and seedling recruitment; and (e) the conservation gains associated with non-native ungulate removal. In total, 24,194 individuals make up the SRI Torrey pine population, 3,062 of which are sexually mature. The proportion of juveniles to adults for SRI is 7:1, compared to Del Mar’s 1:2. SRI’s population is dominated by younger trees: 79% are < 160 cm tall. Cores were taken from 19 trees of different sizes to determine the relationship between diameter at breast height and age. We tested distance bands (m) of trees that had the most seedlings & saplings with high and low densities using a local Moran’s I test within ArcMap. Results were then used in a hot spot analysis to find significant recruitment areas within 3 groves (p<0.01). We evaluated the recent recruitment by sampling reproductive trees (n=31) for seeds. Soil and leaf litter were also collected from reproductive areas (n=24) across the population. On December 31, 2014 we conducted a common garden experiment to evaluate the effect of leaf litter and precipitation on germination (time and success) and seedling survival. We are continuing to monitor the survival and growth rate of the plants in 45, 10 x 10 m permanent plots. Results from this study will provide resource managers with the current areas of reproduction and environmental variables associated with the reproductive success of the SRI Torrey pine.

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