Masters Thesis

Cone serotiny and seed viability of fire-prone California Cupressus species

Fire-prone interior California Cupressus (cypress) species have been experiencing low or zero seedling recruitment possibly due to decades of fire exclusion, subsequent encroachment of shade-tolerant conifers, and unknown stand responses to different fire severities. This study investigated the specific heating conditions required to break cone serotiny and to promote seed dispersal by focusing on five Cupressus species of interior California most prone to fire: Cupressus arizonica ssp. nevadensis (Piute cypress); C. bakeri (Baker cypress); C. forbesii (Tecate cypress); C. macnabiana (McNab cypress); and C. sargentii (Sargent cypress). A muffle furnace was used to conduct eight temperature treatments of 250 - 700o C, ranging in duration from 30 seconds to 5 minutes of exposure to cones of each species. The heat-released seeds were tested for viability using a tetrazolium red stain. Logistic regression analysis of seed viability indicated that the duration of heating alone was highly significant (P 0.005) for all species, regardless of temperature. Models predicting seed viability reflected species differences in geographic range and habitat requirements. Species comparisons revealed that C. arizonica ssp. nevadensis and C. forbesii shared the same model for predicting seed viability, while C. macnabiana and C. sargentii shared a different model, but C. bakeri had a separate model. In addition, factors related to tree age and cone position on the tree were investigated in C. sargentii. Neither factor affected seed viability. This is an important finding with regard to management in that older stands of C. sargentii may not experience fire for many decades but still produce viable seed.

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