Changes in resilience to fire disturbance in lowland pine forest ecosystems

The effect of major disturbances on the structure of pine forests in the interfluve of the Chernaya and Pugai rivers has been retrospectively analyzed back to the late 19th century. The results show that intensive timber harvesting and fires produced a synergistic effect so that the natural fire regime in these forests has changed; in particular, the severity of fires and the frequency of stand-replacement fires have increased. The ecosystem of lowland pine forests, adapted to periodic fires, largely loses its resilience to fire disturbance if the age structure of pine populations becomes relatively homogeneous and communities at early succession stages gain significant prevalence in the vegetation. The main cause of the largest fire that occurred in pine forests of the Nizhni Novgorod Transvolga region (Nizhegorodskoe Zavolzhie) in 1972 was human activity rather than natural and climatic features of this territory.