Submitted to: Agroforestry Systems
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/2/2010
Publication Date: 6/17/2011
Citation: Burner, D.M., Dwyer, J., Godsey, L. 2011. Stocking rate-mediated responses of mid-rotation loblolly pine in west-central Arkansas 2. Growth. Agroforestry Systems. 81(3):287-293. Interpretive Summary: Loblolly pine is the predominant timber species on 45% of the commercial forest land in the southern US, but adoption of pine-based agroforestry practices has been slow because of the lack of scientific, socio-economic, and technology transfer support systems. For example, the value of pine straw, a landscaping product, has been so poorly appreciated that large areas in the southern US have little or no commercial industry. To address this deficiency, researchers at ARS-Booneville and University of Missouri, Columbia measured loblolly pine growth and agroforestry implications when trees were planted in 13 plantation designs. The various designs differed in number of trees per acre, which affected growth. As is common for similarly aged (14-year-old) plantations, most of the stands had too many trees per acre which reduced tree growth and survival. Landowners could use this information to plan for companion products along with timber. Plantations with trees in rectangular designs, or those with trees in multiple row sets separated by wide alleys, generally had acceptable rates of timber production when there were less than 600 trees per acre. These designs tended to be best for timber, alley cropping, or silvopasture. Conversely, designs with more trees per acre might be better for bioenergy or pine straw production. Landowners should design plantations according to anticipated end products.
Technical Abstract: Relatively few studies have compared loblolly pine (Pinus taeda L.) growth in a systematic array of plantation designs or stocking rates commonly used in temperate forestry and agroforestry practices. Our objective was to determine loblolly pine growth responses and agroforestry implications of 13 plantation designs (i.e., stocking rates) at mid-rotation (14-yr-old). Survival, diameter at breast height (dbh), height, basal area (BA), and volume (V) were measured in unthinned plantations ranging from 490 to 2300 trees/ha (TPH). Stocking rate was positively correlated with BA (r greater than or equal to 0.67) and V (r greater than or equal to 0.55) and negatively correlated with survival (r less than or equal to -0.83) and dbh (r less than or equal to -0.83). Plantations with greater than or equal to 2000 TPH had closed canopies and excessively high BA and V at mid-rotation. The 4- and 5-row plantations (alley width greater than or equal to 12 m) had small dbh (less than or equal to 17.5 cm). Single-row plantations with greater than or equal to 3.6 m within row spacing and less than or equal to 700 TPH, and the 3-row multiple-row plantations (1200 TPH), had acceptable BA (29.4 to 33.2 m2/ha) and V (127 to 136 m3/ha). Basal area tended to be too high in most plantations (greater than or equal to 30 m2/ha), indicating thinning was needed to optimize growth. Besides timber, an array of design-dependent agroforestry and forestry products should drive the selection of any one of these plantation designs: pine straw or biomass feedstock at greater than or equal to 1800 TPH, alley cropping or silvopasture in wide alleys of 4- and 5-row plantations, and alley crop or livestock for single-row (less than or equal to 1000 TPH) and multiple-row plantations (less than 1400 TPH).