Effects of prescribed burning and thinning on oak regeneration in northeast Kansas

Abstract

Mature oak woodlands are being converted to shade-tolerant lower value species in the eastern United States, and several studies indicate that the situation started after fire suppression policies were implemented. This study was conducted on a 90-acre tract of oak-dominated woodland near Manhattan, Kansas. The study aimed to assess the effectiveness of burning and thinning to encourage oak regeneration. The experimental design was 2 (Burn) x 2 (Thin) factorial in a repeated measures design. The resulting treatment combinations were burn and thin (BT), burn and no-thin (BNT), no-burn and thin (NBT), and no-burn and no-thin (NBNT – control). The burning and thinning operations were conducted in the Spring 2015 and Spring 2018. Vegetation inventories were conducted on permanent plots before burning in 2014, Fall 2016, and Fall 2018 to assess the effects of the treatments on vegetation composition and fuel loading. The thinning treatment reduced the total number of trees per acre after the second thinning operation. The burning and thinning combined treatments significantly reduced the basal area of the primary competitor species. While the number of oak saplings per acre is not different from the main competitors in thinned plots, main competitors outnumbered oak saplings in no-thin plots, and burning significantly reduced the total number of saplings per acre. The burn in 2018 also significantly reduced the total number of seedlings per acre. However, burn and thin treatments did not affect the seedlings species composition, and eastern redbud outnumbered oaks in 2018 averaged across all treatments. Fuel loading was measured pre- and post-burning, in 2015 and 2018, using both nondestructive (sampling plane or transect) and destructive (quadrat) methods, to evaluate fuel consumption and recovery. Overall, both methods showed the same trends for the fuels; however, the quadrat method was more conservative. There was a significant recovery of litter fuel load from 2015 to 2018 and a significant decrease from pre- to post-burning in 2018 of the litter and duff layer. The quadrat method presented an interaction between time and thin. Total fuel load consumption was significant only in 2018 and 1000-hr sound fuel was the only fuel affected by thinning.