Warm and Fertile Sub-Humid Conditions Enhance Litterfall to Sustain High Soil Respiration Fluxes in a Mediterranean Cork Oak Forest

Saharan Hot and Dry Sirocco Winds Drive Extreme Fire Events in Mediterranean Tunisia (North Africa)

With hot and dry summers, the Mediterranean basin is affected by recurrent fires. While drought is the major driver of the seasonal and inter-annual fire distribution in its northern and mildest climate conditions, some extreme fire events are also linked to extreme winds or heat waves. The southern part of the Mediterranean basin is located at the driest range of the Mediterranean bioclimate and is influenced by Saharan atmospheric circulations, leading to extreme hot and dry episodes, called Sirocco, and potentially acting as a major contributor to fire hazard. The recently created fire database for Tunisia was used to investigate the ±10-day pre- and post-fire timeframe of daily weather conditions associated with fire events over the 1985–2006 period. Positive anomalies in minimum and maximum temperatures, negative anomalies in air relative humidity, and a preferential south-eastern wind during fire events were identified, which were characteristic of Sirocco winds. +7 °C anomalies in air temperature and −30% in relative air humidity were the critical thresholds for the most extreme fire conditions. In addition, meteorological anomalies started two days before fire events and lasted for three days after for large fires >400 ha, which suggests that the duration of the Sirocco event is linked with fire duration and final fire size. Lastly, the yearly number of intense Sirocco events better explained the inter-annual variability of burned area over the 1950–2006 period than summer drought based on Standardized Precipitation Evaporation Index (SPEI) indices.

Soil respiration and its environmental response varies by day/night and by growing/dormant season in a subalpine forest

Comparisons of soil respiration (R_S) and its components of heterotrophic (R_H) and rhizospheric (R_R) respiration during daytime and nighttime, growing (GS) and dormant season (DS), have not being well studied and documented. In this study, we compared R_S, R_H, R_R, and their responses to soil temperature (T₅) and moisture (θ₅) in daytime vs. nighttime and GS vs. DS in a subalpine forest in 2011. In GS, nighttime R_S and R_H rates were 30.5 ± 4.4% (mean ± SE) and 30.2 ± 6.5% lower than in daytime, while in DS, they were 35.5 ± 5.5% and 37.3 ± 8.5% lower, respectively. DS R_S and R_H accounted for 27.3 ± 2.5% and 27.6 ± 2.6% of GS R_S and R_H, respectively. The temperature sensitivities (Q₁₀) of R_S and R_H were higher in nighttime than daytime, and in DS than GS, while they all decreased with increase of T₅. Soil C fluxes were more responsive to θ₅ in nighttime than daytime, and in DS than GS. Our results suggest that the DS and nighttime R_S play an important role in regulating carbon cycle and its response to climate change in alpine forests, and therefore, they should be taken into consideration in order to make accurate predictions of R_S and ecosystem carbon cycle under climate change scenarios.