Response of Soil CO2 Efflux to Simulated Precipitation Pulses in a Canary Island Pine Forest at Treeline

Pulse-like rapidly increasing CO2 effluxes occur in soils under seasonally dry climates in response to summer rain events, and these CO2 outbursts can have a marked influence on the ecosystem carbon balance. Two irrigation experiments were conducted at the end of the dry season in a Mediterranean Pinus canariensis forest at its upper distribution limit in Tenerife, Canary Islands. Soil CO2 efflux was discontinuously monitored along with soil temperature and soil water content during and after irrigation. Correlation analysis suggested that soil moisture is the leading environmental factor regulating soil CO2 efflux during summer rain events. Cumulative CO2 efflux following a precipitation pulse was estimated to be 50% higher than the value calculated for the dry soil, which is approximately 3% of the year round soil CO2 efflux. It is concluded that such CO2 effluxes may have implications for the prediction of forest response to increasing dryness combined with an increase in the irregularity of summer rain events in Mediterranean regions.