Abstract
Cluster planting of shortleaf pine, along with various site preparation and release treatments, were tested to restore mixed shortleaf pine (Pinus echinata Mill.)–hardwood stands in areas where the shortleaf pine has diminished in recent years. Shortleaf pine–hardwood mixtures were once a common forest type throughout the Cumberland Mountains and Plateau physiographic regions of the southeastern United States. Knowledge of how to restore shortleaf pine–hardwood mixtures is limited throughout shortleaf pine’s large native range. The objectives of this study were to compare planted shortleaf pine and natural hardwood regeneration survival, growth, and composition following various site preparation and early release treatments. Cluster planting and partial timber harvesting were used to reintroduce shortleaf pine and create two-aged stands in the Cumberland Mountains of Tennessee, USA. Results indicated that shortleaf pine survival, basal diameter, and height growth did not differ following four growing seasons among treatments. Natural regeneration stem densities and heights within shortleaf pine clusters did not differ significantly by treatment. Natural regeneration stem densities differed by species group and height class across the site, while the treatment × species interaction term was also significant. At this early stage of stand development, the brown-and-burn treatment appears poised for greater shortleaf pine growth rates than the other treatments. The herbicide treatment had the fewest regenerating hardwoods per hectare and the most desirable hardwood species composition.
Highlights
Mixed shortleaf pine–hardwood forest types are defined as forests that contain approximately25% to 75% pine species and 25% to 75% hardwood species as a percent of total stocking [1,2]
Restoration of shortleaf pine in current mixed hardwood stands, with the intent to create two-age mixed shortleaf pine–hardwood stands, is still possible with current shortleaf pine survival rates, yet the results indicated that overtopping understory hardwood competition may be an issue across all treatments on this site
Shortleaf pine can endure competition during the establishment and stem exclusion phase of stand development from some hardwood species, but on the best sites where species such as red maple and yellow-poplar occur, shortleaf pine may not be successful at reaching overstory positions [62]
Summary
Mixed shortleaf pine–hardwood forest types are defined as forests that contain approximately25% to 75% pine species and 25% to 75% hardwood species as a percent of total stocking [1,2]. In the southeastern United States, these forest types occur more frequently on low productivity dry to xeric sites that have a history of frequent disturbance associated with mixed severity fire, logging, or wind events [3,4,5]. Successful regeneration of shortleaf pine requires disturbances that increase light levels and expose bare mineral soil [6]. Without regular disturbance, these sites will transition to mixed hardwoods over time [7,8]. Appalachian Mountain regions, a variety of hardwood and pine species occur with shortleaf pine to form mixed stands. Associated species include: black oak (Quercus velutina Lam.), scarlet oak
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