Field Studies of Ceanothus leucodermis Chaparral Burned Sites in California

Populations of the chaparral shrub were sampled in southern California and further north in Monterey and Santa Clara counties and it was discovered that postfire regeneration modes were different. The southern California populations had substantial resprouting with some seedling recruitment. The Monterey populations had no resprouting ability and recovery was entirely by seedlings. However, there is an age effect in that when young these northern California populations fail to recruit seedlings due to lack of a seed bank buildup in the short interval since the last fire. These populations likely will be extirpated. I hypothesize that this obligate seeding mode has been selected for because seed reproduction is more reliable when intervals between fires are very long, longer that resprouting shrubs would survive. Support for this is provided by demonstrating substantially higher lightning fire frequencies in southern California than in the Monterey and Santa Clara area.

研究对加利福尼亚南部，以及更北侧的蒙特雷县与圣克拉拉县的查帕拉尔灌丛灌木（chaparral shrub）种群开展了采样调查，结果发现不同种群的火烧后更新模式存在显著差异。加利福尼亚南部种群具备较强的萌枝能力，同时伴随一定比例的实生苗补充；而蒙特雷种群则完全不具备萌枝能力，种群恢复仅依赖实生苗定植。但该类群存在年龄效应：由于末次火灾后的间隔时长较短，尚未形成充足的种子库，年轻的北加州种群无法完成实生苗补充，这类种群大概率将走向灭绝。本研究提出假说：该专性播种（obligate seeding）策略是自然选择的结果——当火灾间隔时间极长，且长于萌枝灌木的存活年限时，种子繁殖的可靠性显著更高。该假说得到了数据支撑：研究证实加利福尼亚南部的雷击火发生频率远高于蒙特雷与圣克拉拉地区。