PARENT SESSION
Poster Session #18: Fire Ecology I.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Prescribed fire effects on understory light environment and seedling performance of oak and red maple in eastern Kentucky.

Chiang, Jyh-Min^*,1, Arthur, Mary¹, ¹ University of Kentucky, Lexington, KY

ABSTRACT- In many oak-dominated forests in the northeastern U.S. oak regeneration is poor and prescribed fire is assumed to benefit oak seedlings compared to fire sensitive species. However, the mechanisms and effectiveness remain poorly documented. We examined the effects of single and multiple fires on canopy structure and openness and seedling response. Hemispherical photography showed an increase of 3.8 % in canopy openness after burning, followed by a gradual reduction of 0.7 % per year after burning. We predict the canopy openness of burned sites will be similar to the control sites in 6 years. Canopy openness (R² = 0.53, p = 0.01) was highly correlated with midstory stem density (stems 2-15 cm dbh), which increased gradually after burning. We measured specific leaf mass (SLM, g/cm²), leaf nitrogen content (LNA, g/cm²), photosynthetic response curve and maximum photosynthesis rate (Amax, mol CO₂/m² /sec), stomatal conductance (mol H₂O/m²/sec), height growth, total leaf area (TLA), and root collar diameter of oak and red maple seedling across light gradients in burned and control sites. Burning significantly increased SLM, LNA, Amax, potential photosynthetic nitrogen use efficiency (ppnue, mol CO₂/mol N), and height growth (p<0.0001). Canopy openness was significantly and positively correlated with SLM, LNA, TLA, stomatal conductance, height growth, and root collar diameter, suggesting that factors in addition to increased light may influence seedling performance. Oaks had greater SLM, LNA, Amax, and stomatal conductance than red maple, which may indicate greater light, N, and water demand by oaks than red maple. Higher aboveground biomass allocation and photosynthetic water use efficiency (pwue, mol CO₂/mol H₂O) of red maple (p <0.02) compared to oaks may explain the successful colonization of red maple without burning. Multiple burnings may promote oak performance by increasing nitrogen, water, and light availability.

KEY WORDS: oak regeneration, prescribed fire, photosynthesis, water use efficiency