THE EFFECT OF SEASONALITY OF BURN ON SEED GERMINATION IN CHAPARRAL: THE ROLE OF SOIL MOISTURE

Abstract

Fire represents an important recruitment phase for many chaparral species. Prescribed burns are often scheduled during winter or spring when soil moisture is high in order to minimize risks of uncontrolled fire. However, chaparral wildfires typically occur in the summer or fall when soil moisture is low. Changing the seasonality of burn affects pre-burn soil moisture, burn temperature and timing of germination. High soil moisture during winter or spring burns is hypothesized to lower germination rates of chaparral plants compared to fall burns. The purpose of this study was to evaluate the effects of prescribed spring burns on the germination of chaparral species in the Mendocino National Forest, California. We conducted two experiments to test for effects of moisture on seed germination. In the soil heating experiment, soil collected under chaparral was heated at several temperatures and soil moistures, and germinating seeds were counted. In the seed heat treatment experiment, seeds of 13 species were heated moist and dry to determine the moisture effect on heated seeds. Results indicate a differential response of seeds to heat and soil moisture. Lotus humistratus, Daucus pusillus and Penstemon heterophyllus were negatively affected by temperature in both moist and dry treatments. Ceanothus cuneatus and Genista monspesullana germination increased with temperature in both dry and moist treatments. Germination of six species (Adenostoma fasciculatum, Camissonia contorta, Emmenanthe pendiflora, Epilobium ciliatum, Galium aparine and Malacothrix clevelandii) decreased under moist heat treatments. These results suggest that spring burns may lead to decreased diversity of chaparral due to reduced seed survival and germination of certain species.