Stocking rate mediates responses of mid-rotation loblolly pine in west-central Arkansas. 1. Growth

摘要

Further study is needed on 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 in trees ha−1 [TPH]) at mid-rotation (14 years old). Survival, diameter at 1.3 m above soil surface (dbh), height, basal area (BA), and volume (V) were measured in unthinned plantations ranging from 490 to 2,300 TPH. Stocking rate was positively correlated with BA (r ≥ 0.67) and V (r ≥ 0.55) and negatively correlated with survival (r ≤ −0.83) and dbh (r ≤ −0.83). Plantations with ≥2,000 TPH had closed canopies and excessively high BA and V at mid-rotation. The 4- and 5-row plantations (≥12 m alley spacing) had small dbh (≤17.5 cm). Single-row plantations with ≥3.6 m within row spacing and ≤700 TPH, and the 3-row multiple-row plantations (1,200 TPH), had acceptable BA (29.4–33.2 m2 ha−1) and V (127–136 m3 ha−1). Basal area was ≥30 m2 ha−1 in most plantations indicating thinning is needed to optimize individual tree 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 production at ≥1,800 TPH, and alley cropping or silvopasture in single-row (≤1,000 TPH) and multiple-row plantations (<1,400 TPH).