Temperature variations in the Santa Monica Mountains are drastic at times, which may be affecting the local plants. To determine the repercussions of these variations in temperature, we measured the xylem diameters of freezing and non-freezing Malosma laurina and Umbellularia californica. U. californica was chosen because it has a large xylem diameter, yet is known to survive freezing conditions. We thought that this plant could provide the most significant results to prove or disprove our hypothesis. M. laurina was chosen because it is abundant in the Santa Monica Mountains and has different physical dimensions than U. californica. Smaller xylem diameters may affect water transport , possibly resulting in physically smaller plant sizes. Natural selection may be acting on these species in the Santa Monica Mountains, eliminating plants with larger xylem diameters in freezing areas. We hypothesize that M. laurina and U. californica in freezing zones will have smaller xylem diameters compared to those in non-freezing zones. We collected samples of M. laurina and U. californica from freezing and non-freezing sites located in Tapia Park and Solstice park in the Santa Monica Mountains and on Pepperdine University’s Malibu Campus. We then prepared slides of the plants’ stems and measured the diameters of the xylems. Using Kaleidagraph, we statistically analyzed our data and found the average values for each plant; freezing M. laurina had an average xylem diameter of 33.3 μm, non-freezing M. laurina had an average xylem diameter of 48.7 μm, freezing U. californica had an average xylem diameter of 33.4 μm, and non-freezing U. californica had an average xylem diameter of 53.8 μm. These results indicate significance as revealed by a p value <0.05.
Nakamatsu, Nicole A.P.M.K.O.M.; Ordog, Theadora V.; and Sauer, Kaitlyn E., "The Effect of Freezing Conditions on Xylem Diameter of Malosma laurina and Umbellularia californica in the Santa Monica Mountains" (2013). Pepperdine University, All Undergraduate Student Research. Paper 130.