Physiological performance of three pine species provides evidence for gap partitioning

Forest Ecology and Management (Impact Factor: 2.66). 12/2008; 256(12). DOI: 10.1016/j.foreco.2008.08.003
Source: OAI

ABSTRACT Gradients of light and moisture availability peak at different positions within canopy gaps in northern latitudes providing the opportunity for niche partitioning in and around gaps based on differences in individual species' life history attributes. This gap partitioning offers potential for increasing diversity in forests impacted by gap-creating disturbances. We examined resource availability and the physiological performance of three Pinus species with varying tolerances for shade and moisture stress across large (0.3ha) canopy gaps to investigate relationships between gap position and species performance. Light availability was lowest in southern gap edges, while water availability was lowest in northern edges, and higher at gap interior positions than edges. Pinus banksiana seedlings had higher light-saturated CO₂ assimilation rates than P. resinosa or P. strobus seedlings at interior gap positions, and outperformed P. strobus at northern gap edges, but there were no differences between species at southern edges. Both transpiration and stomatal conductance were greatest for P. banksiana in gap centers, but showed few differences between species at edges. Foliar nitrogen concentrations were highest for P. banksiana, suggesting the dominance of this species in central gap locations may be due to a combination of high photosynthetic capacity and tight stomatal control to regulate moisture stress at drier gap positions. Our results suggest P. banksiana seedlings may be competitively superior in gap positions with high light and moisture availability, but P. resinosa and P. strobus become competitive under the drier conditions and moderate shade near gap edges. These findings support the concept of gap partitioning, and suggest silvicultural systems that incorporate patch cuttings could be used to promote diverse regeneration in northern pine forests.

Download full-text


Available from: Matt Powers, Jul 07, 2014
15 Reads
  • Source
    • "Thus, the positive relationship between d 18 O and basal area found in this study is most likely caused by a decline in E across the overstory basal area gradient associated with decreased g s . A previous study of niche partitioning within the gap environments at the same sites found light and soil moisture availability were lower in the partial canopy environment of gap edges than in gap interiors (Powers et al., 2008b), which would lead to decreased g s and E. While the declines in seedling gas exchange parameters observed from gap centers to gap edges in this previous study were not always statistically significant, they suggest the potential for declines in E across the larger range of overstory environments encompassed within our current study. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Overstory conditions influence understory microclimate and resource availability, leading to gradients in evaporative demand and moisture availability that influence seedling water relations. Partial canopies may either reduce seedling moisture stress by ameliorating environmental conditions, or increase moisture stress by reducing soil moisture availability. This study used stable isotope ratios of oxygen (δ¹⁸O) and carbon (δ¹³C) and mass-based foliar nitrogen concentrations to investigate changes in transpiration (E), stomatal conductance (g s) and intrinsic water use efficiency (iWUE) of pine seedlings across an overstory gradient from open canopy gap environments to closed canopy forest. Foliar δ¹⁸O increased sharply from basal areas of 0-10m² ha⁻¹ in Pinus banksiana, Pinus resinosa, and Pinus strobus seedlings, followed by a more gradual increase with further increases in basal area. Foliar δ¹³C followed a similar, but less pronounced pattern in P. banksiana and P. strobus seedlings, and had no apparent relationship with overstory basal area in P. resinosa seedlings. The slope of the δ¹⁸O:δ¹³C relationship was positive for every species. Foliar nitrogen concentrations were not correlated with overstory basal area. These results suggest seedling E declined as overstory basal area increased due to reductions in g s, while iWUE increased slightly from open gaps to partial canopy environments. Open gap environments appear to provide sufficient moisture to sustain high leaf-level gas exchange rates in the species we studied, while relatively small increases in overstory basal area apparently promote rapid declines in g s, leading to greatly reduced seedling water loss and small increases in iWUE.
    Forest Ecology and Management 09/2009; 258(7). DOI:10.1016/j.foreco.2009.06.040 · 2.66 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Itasca State Park, located in the northern central portion of Minnesota, is challenged with maintaining a pine forest covertype, yet regeneration failures may allow much of the park to succeed to northern hardwoods. Efforts to improve pine regeneration and growth have included deer exclosures and prescribed burning to reduce competing vegetation. We revisited Itasca's Mary Lake deer exclosure 66 years after establishment to compare stand development, structure, and white pine (Pinus strobus L.) regeneration and growth with that of adjacent plots that have been: (1) untreated and (2) recently repeatedly under-burned. Overstory structure and composition was similar among all three treatments, and mid- and understory structures were similar in the treatments subject to deer browse. Sapling and midstory white pine were only present in the exclosure. White pine regeneration was present in all treatments and most abundant in the burned treatment, but was restricted to the smallest height class and consistently overtopped by the shrub layer. Regeneration, sapling, and midstory layer tree densities were highest within the deer exclosure, as was white pine height growth. The untreated plot lacked young pine and will likely succeed to northern hardwoods with a shrub understory. The three-fire sequence of the burned treatment increased the abundance of white pine regeneration at this site, but may require additional measures to control competing vegetation to allow that regeneration to ascend into the sapling layer.
    Natural Areas Journal 04/2009; 29(Apr 2009):157-166. DOI:10.3375/043.029.0208 · 0.66 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Variable retention harvesting (VRH) is promoted for enhancing biodiversity and ecosystem processes in managed forests, but regeneration responses to the complex stand structures that result from VRH are poorly understood. We analyzed foliar stable carbon isotope ratios (delta(13)C), oxygen isotope ratios (delta(18)O), light-saturated photosynthetic rates (A(max)), stomatal conductance (g(s)) and sizes of pine seedlings in Pinus resinosa stands treated with VRH systems that created different spatial patterns of overstorey retention. Pinus banksiana, P. resinosa and Pinus strobus seedlings in dispersed retention, aggregated retention between small gaps and aggregated retention between large gaps treatments had greater delta(13)C, A(max), g(s), diameter and height than seedlings in unharvested treatments, but seedling performance was similar among VRH treatments when averaged across stands. There were no significant differences in delta(18)O associated with any treatment. These results indicate seedling photosynthetic capacity, water relations and growth were improved by VRH, but the spatial pattern of retention had surprisingly little impact on average performance in the first 4 years after harvesting. This suggests retention treatments that produce different residual stand structures can promote similar mean rates of early seedling development when performance is averaged across all of the neighbourhood environments within each treatment.
    Forestry 02/2010; 84(1):13-22. DOI:10.1093/forestry/cpq038 · 2.09 Impact Factor
Show more