Over the last several decades, incentive-based restoration efforts were undertaken across the southern U.S aimed at afforesting former bottomland hardwood forests with high-value species such as oaks (Quercus spp.). The majority of these initial restoration efforts targeted mainly ecological goals, particularly habitat improvement. Several studies have evaluated early growth and survival of oaks in afforested bottomland stands of 10-20 years old, which has yielded insights on early stand dynamics. However, few studies have addressed the growth dynamics of afforested oak stands beyond age 20 and we lack research on post-establishment treatment options (e.g., thinning) for these planted stands. Landowners who have participated in federal programs, like CRP and WRP, could benefit from an improved knowledge of silvicultural treatments for enhancing oak growth for economic benefits. This study evaluated basal area increment (BAI) of four oak species (cherrybark, swamp chestnut, Nuttall, and water) in relation to silvicultural treatments (spacing and thinning) and an index of neighborhood competition (CI) in a 41-year Arkansas bottomland hardwood plantation. Both BAI and CI were measured using data obtained from individual trees, and silvicultural treatments were evaluated using two levels of spacing (12' x 12' and 8' x 8') and thinning (thinned and unthinned plots).
Results/Conclusions
Of the species studied, cherrybark and Nuttall oaks represented the highest and lowest BAI (23.0 ± 2.1 and 14.8 ± 1.7 cm-2 year-1, respectively), which were significantly different. In contrast, swamp chestnut and water oaks had similar BAI: 18.3 ± 2.3 and 18.9 ± 1.4 cm-2 year-1, respectively. These results indicate that cherrybark oak may be more favorable over other oaks in similar bottomland plantings from an individual-tree growth perspective. BAI varied significantly with both CI and species. In particular, BAI decreased with CI, but the CI-by-species interaction term had no relationship with BAI, suggesting that the decrease in BAI with CI did not differ across species. Spacing and thinning did not affect BAI across species. This suggests the influence of these earlier silvicultural treatments on oak growth may not persist in older plantations. However, our data were based on only two spacings and a single thinning to 50% stocking, hence we are unable to conclude definitively on the effects of spacing and thinning regimes. Nevertheless, this study provides new knowledge on suitability of oaks and consequences of silviculture for establishing and tending bottomland oak plantations, which could prove critical for landowners and incentive-based programs for sustaining hardwood afforestation efforts.