PARTNERSHIP: IMPACTS OF FERTILIZATION TREATMENTS ON THE MORTALITY AND POST-FIRE PRODUCTIVITY OF NORTHWESTERN AND SOUTHEASTERN PINUS SPECIES

The overarching goal of this project is to assess how the post-fire productivity of key southeastern and northwestern Pinus species are affected by varying levels of heat from fire and whether fertilization can mitigate (or worsen) post-fire negative growth impacts.This goal is approached through assessing two central hypotheses with four objectives as outlined below.Ourfirst central hypothesis is that the primary fire-induced mortality mechanism in Pinus species is due to phloem and cambium death. This is presented by the symptoms of carbon decline in the roots due to phloem failure and the inability to grow new phloem because the cambium is dead. The result is that fine root production slows due to reduced carbon availability and because carbon is still being consumed for maintenance respiration. Ultimately, hydraulic failure occurs because there are not enough fine roots to supply the plant with the necessary amounts of water. Our alternate hypotheses are that mortality arises due to (i) soil nitrogen deficiencies, (ii) emboli induced xylem hydraulic failure, or (iii) pre-fire structural overshoot. Identifying the causes of why trees die from fires is critical to improve the efficacy of predictive fire effects and forest growth and yield models.Our second central hypothesis is that Pinus saplings that survive fire, will grow at reduced growth rates, where the duration and magnitude of the reduced growth increases with the fire intensity dose, but is moderated by the amount of available non-structural carbohydrates (NSC) and soil nitrogen. In essence, saplings with more NSC and soil nitrogen supply will recover and return to pre-fire conditions faster.We will test these hypotheses through controlled laboratory-experiments following four specific objectives:1) Assess mechanisms of fire-induced mortality in saplings of selected Pinus species.2) Determine the 'fire intensity dose to mortality and productivity responses'.3) Determine how these relationships change when the saplings have been treated with fertilizer (a proxy for soil nutrient richness) several months before and immediately after the fires.4) Share data and results with forest productivity and fire effects modeling teams.