Competition and disturbance affect elevational distribution of two congeneric conifers

Area of Science:

• Ecology
• Forest Science
• Climate Change Biology

Background:

• Elevational vegetation distribution is influenced by thermal conditions, but biotic and abiotic factors determining species distributions are not fully understood.
• Long-term plot censuses are crucial for clarifying the mechanisms of elevational tree species distribution.
• Two congeneric conifers, Abies veitchii (less shade-tolerant) and Abies mariesii (shade-tolerant), dominate low and high elevations, respectively, in Japan's subalpine zone.

Purpose of the Study:

• To investigate the population dynamics of Abies veitchii and Abies mariesii over 13 years across three elevations (low, middle, high).
• To examine the roles of competition and disturbance in determining the elevational dominance of these two species.
• To understand how changing environmental conditions impact tree species distribution.

Main Methods:

• Conducted a 13-year plot census study along an elevational gradient in the Japanese subalpine zone.
• Monitored population dynamics, including growth, survival, and recruitment rates, for Abies veitchii and Abies mariesii at low, middle, and high elevations.
• Analyzed data in relation to observed disturbance events and interspecific competition.

Main Results:

• Growth and survival rates were not highest at the species' most dominant elevations.
• At high elevations with frequent small disturbances, Abies mariesii showed the highest recruitment, while Abies veitchii recruitment decreased due to competition.
• At low elevations after large disturbances, Abies veitchii dominated due to its higher growth rate compared to Abies mariesii.

Conclusions:

• Elevational distributions of Abies veitchii and Abies mariesii are determined by shifts in population dynamics influenced by competition and disturbance.
• Abies mariesii is superior at high elevations due to recruitment dynamics and competitive exclusion of Abies veitchii.
• Abies veitchii is superior at low elevations post-disturbance due to its faster growth rate.
• Long-term forest dynamics studies across elevations are essential for predicting vegetation responses to climate change.