Quantifying ecological drivers of ecosystem productivity of the early-successional boreal Larix gmelinii forest

Wildfire area and severity are projected to increase in Eurasian larch (Larix spp.) forest, potentially altering ecosystem dynamics and carbon balance under warming climate. However, the ecological drivers that influence post-fire ecosystem productivity in larch forest are poorly understood. Here we assess the influence of several factors controlling plant aboveground net primary productivity (ANPP) on the early successional stage of Dahurian larch (Larix gmelinii) forests following fire. We quantified the relative importance of fire severity, competition, topography, and soil inorganic N [NH4+ and NO3-] availability on ecosystem productivity 11 years post-fire in a Dahurian larch forest of Northeast China using a boosted regression trees technique. Results showed that fire severity had the strongest negative influence on ANPP of saplings, followed by a positive influence of soil inorganic N availability and negative influence of elevation. Sapling density had the strongest negative influence on ANPP of understory (shrub and grass), followed by positive influence of aspect and inorganic N availability. N may limit ANPP of sapling, but not of understory vegetation. Fire severity had a dominant influence on the proportion of total ANPP contributed by the understory. Fire severity was positively correlated to understory productivity and proportion of total ANPP contributed by understory, but negatively correlated to sapling productivity. Our analysis suggests that increasing fire severity may increase understory productivity, while decreasing the sapling productivity, which may contribute to the potential changes of vegetation type and carbon cycling in Dahurian larch forests of Northeast China under warming climate.