Competitive responses of seedlings and understory plants in longleaf pine woodlands: separating canopy influences above and below ground

Abstract

A trenching study was used to investigate above- and below-ground competition in a longleaf pine ( Pinus palustris P. Mill.) woodland. Trenched and nontrenched plots were replicated in the woodland matrix, at gap edges, and in gap centers representing a range of overstory stocking. One-half of each plot received a herbicide treatment to remove the understory. We monitored pine survival and growth, understory productivity, light level (gap fraction), and soil resources. The overstory facilitated pine seedling survival. Pine seedling growth was reduced as overstory stocking increased. Reduced growth of seedlings was also observed in gaps when the understory was left intact. Understory plants competed with seedlings by filling the root gaps that developed as a result of overstory disturbance. Hardwood growth increased in gaps, owing to decreased belowground competition with adult pines, while growth of herbaceous plants and pine seedlings increased with light availability. Large overstory gaps are not required to initiate regeneration in longleaf pine woodlands. Retaining overstory dispersed throughout the stand but variable in density, through single-tree selection approaches, may be an alternative to gap-based approaches. This approach would allow for the fuel continuity needed to sustain the frequent fire required to maintain the diversity characteristic of this type of woodland.

Effects of basal area on survival and growth of longleaf pine when practicing selection silviculture

“…Average RCD growth rates of the seedlings in this study were consistent with several studies in the literature (Gagnon et al, 2003;Dyson, 2010;Hu et al, 2012;Knapp et al, 2013). Longleaf pine seedling growth usually decreases as overstory stocking increases (Pecot et al 2007). Although the early growth of longleaf seedlings is quite slow, even under low levels of overstory RBA (Boyer, 1993), it is usually expected that higher rates of RCD growth would be observed under low RBA (Palik et al, 1997;Palik et al, 2003).…”

Leaf Physiological and Morphological Responses to Shade in Grass-Stage Seedlings and Young Trees of Longleaf Pine

“…Pecot et al [15] described two theories concerning mechanisms controlling longleaf pine seedling success in uneven aged systems. The first is that belowground competitive interactions between juvenile and mature trees rather than light limitations are most important in seedling establishment and larger gaps of up to 2 ha that increase the border distance between seedlings and mature trees are needed to reduce competition for nutrients and water [54].…”

“…Successful establishment and early growth of longleaf pine in even and uneven-aged management systems would be enhanced by a better understanding of leaf plasticity to light environment [15]. Shade tolerance is an important consideration in determining plantation density, gap sizes and gap shapes.…”

Carbon Dynamics of Pinus palustris Ecosystems Following Drought

“…The stands used for this study are approximately 90 years in age and were naturally regenerated. These stands have maintained their natural structure since they have been managed with single tree selection harvests using ecological forestry practices [29].…”