Increasing fire severity and frequency may stress ecosystems also impacted by climate change. We studied the physical limitations to regeneration after fire in an ecosystem that already experiences high summer temperatures and drought and is therefore a possible analog of the future. We compared soil respiration as an indicator of microbial activity in burned and unburned forest soils in central Texas, where two recent wildfires have occurred (2011 and 2015). We also measured soil temperature, water content, soil water δ 18 O and δD values, total C, N, pH, and δ 13 C values of total organic matter. Burned soils had lower total C and N than unburned soils; however, lab-based respiration measurements, which controlled for temperature and water content, suggest that microbial activity in burned and unburned soils are similar. Conversely, field measurements show that during hot and dry months respiration rates in burned soils were much lower than they were in unburned soils due to differences in soil temperature and water content. Soil temperature at 5 cm reached 60°C in burned soils due to the removal of canopy cover, the removal of organic matter insulation, and the deposition of black ash on the soil surface. Higher temperatures increased evaporation as indicated by significantly lower deuterium excess of water in soils burned in 2015 than unburned soils. If the disturbance of vegetation by fire is substantial enough, the resulting perturbations to soils persist for years, most importantly increased heat absorption which results in lower water contents and ultimately reduced microbial activity.

Mangrove ecosystems with high sediment deposition and active carbon cycling are a source of methane (CH 4 ) to the coastal atmosphere. We investigated diurnal and seasonal variations in CH 4 emissions from a subtropical mangrove estuary in southern Texas, northwest Gulf of Mexico. Tidal processes, amplitude (spring vs. neap tides) and topographic characteristics are crucial factors controlling CH 4 cycling in mangrove creeks. Higher CH 4 concentrations were observed during the ebb in spring tides due to the combination of processive export of CH 4 along the creeks during ebb tides and the addition of porewater CH 4 in upper intertidal sediment under water inundation in spring tides. The annual CH 4 emissions offset approximately 0.15% of the carbon stock in normal years, indicating that these mangrove creeks are a weak CH 4 source. However, significantly elevated CH 4 emissions were observed from mangrove dieback after the extreme cold-freezing event in February 2021. The average CH 4 flux from the mangrove creeks (126.1 AE 128.3 μmol [m 2 Ád] À1 ) increased 45% in 3 months after mangrove die-off in comparison with the overall average in normal years (87.0 AE 64.4 μmol [m 2 Ád] À1 ). It is obvious that the previous small CH 4 offset of the healthy mangrove forest was enlarged by the dieback event.Because the mangrove forests in this study live close to the limit of their survival range, our study highlights the important management considerations for blue carbon projects in vulnerable areas.

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