Influence of Herbaceous Interference on Growth and Biomass Partitioning in Planted Loblolly Pine (Pinus taeda)

Abstract

Three herbaceous regimes were established, using herbicides, to examine the effects of interference on growth and biomass partitioning in loblolly pine (Pinus taedaL.). Trees were sampled near Auburn and Tallassee, AL. Trees at the Auburn site grown with low weed interference (LWI) had 4, 10, 10, 8, and 4 times greater total aboveground biomass than did trees with high weed interference (HWI) for ages one through five, respectively. Medium weed interference (MWI, Auburn site only) resulted in three times greater biomass the first 4 yr and two times greater total biomass by the fifth year compared to trees grown with HWI. Trees growing with LWI were 5, 8, 10, and 6 times larger than those with HWI for ages one through four, respectively, at the Tallassee site. At all levels of interference, the percentage of total biomass in foliage decreased, and stem and branch components increased, with increasing tree size at both sites. Trees growing with HWI had a lower percentage of total biomass in foliage and a greater percentage of total biomass in stem than those growing with LWI when compared over a common size. Growth efficiency per tree, expressed as annual increase in stem biomass per unit leaf area (g m−2), was slightly greater for trees growing with LWI compared to HWI when leaf area index (LAI3, total surface) was less than 0.2. For LAI values greater than 0.2 the relationship was reversed. The latter contradicts the idea that growth efficiency can be used as a measure of vigor for young loblolly pine. Changes in carbon partitioning to the development of leaf area are suggested to be driving the accelerated growth responses associated with a reduction of weed interference.

Effects of annual fertilization and complete competition control on current annual increment, foliar development, and growth efficiency of different aged Pinus taeda stands

“…The benefits of fertilization and competition control on stem biomass growth and foliage development have been documented numerous times (e.g., Zutter et al 1986;Vose and Allen 1988;Allen et al 1990;Britt et al 1990;Colbert et al 1990;Jokela and Martin 2000;Borders and Bailey 2001). The unique aspect of our study was that throughout, fertilization was applied annually, and interspecific competition was completely eliminated to remove growth limitations due to competing vegetation and nutrition.…”

“…), interspecific competition control shifted biomass partitioning from belowground to aboveground tree components (Shan et al 2001). Changes in partitioning or size-mediated differences in GE (Britt et al 1990) probably drive the differences in GE related to competition control.…”

“…Fertilization acts by increasing the amount of foliage (e.g., Vose and Allen 1988;Colbert et al 1990;Jokela and Martin 2000), sometimes increasing photosynthetic capacity (e.g., Sheriff et al 1986;Evans 1989;Thomas et al 1994;Murthy et al 1996), and may increase biomass partitioning to stem (Colbert et al 1990;Johnson 1990). Competition control increases stem growth primarily by increasing foliage of crop trees (e.g., Zutter et al 1986;Britt et al 1990;Colbert et al 1990;Green et al 1991;Jokela and Martin 2000) but may also increase the amount of biomass partitioned to the stem (Colbert et al 1990). In loblolly pine (Pinus taeda L.), an important component of natural stands and the most important commercial forest species in the southeastern United States, photosynthetic capacity generally is not affected by silvicultural treatments (Green et al 1991;Zhang et al 1997;Samuelson 1998;Tang et al 1999;Samuelson et al 2001;Will et al 2001).…”

“…Inefficiencies associated with higher leaf areas, such as greater self-shading, increased water stress, or greater respiratory carbon losses may decrease GE of fertilized stands and negate the potentially positive impacts of fertilization on GE (Vose and Allen 1988). Competition control also can affect GE, but the impact depends on leaf area and stand age (Britt et al 1990;Colbert et al 1990;Jokela and Martin 2000).…”

Imperata cylindrica, an alien invasive grass, maintains control over nitrogen availability in an establishing pine forest

“…Weed control experiments have been conducted on many crop tree species throughout the world, showing that reduction in competing vegetation promoted the growth of the tree species (Britt et al 1990;Cain 1991;Miller et al 1991;Morris et al 1993;Martin and Jokela 2004). Supplementing nutrients through fertilization can have similar effects as vegetation control, suggesting that competition with other vegetation for nutrients plays a major role in limiting tree growth.…”