Effects of species composition, management intensity, and shade tolerance on vertical distribution of leaf area index in juvenile stands in Maine, USA
2015
Nelson, Andrew S. | Wagner, Robert G. | Weiskittel, Aaron R. | Saunders, Michael R.
Leaf area index (LAI) affects forest-atmosphere fluxes and light interception rates and thus influences forest productivity. Early silvicultural treatments affect LAI partitioning among species of different shade tolerance in natural stands due to changes in composition and structure. We examined effects of species compositional objectives (conifer, hardwood, and mixedwood) and management intensity (low: thinning and/or release to 2,500 crop trees ha⁻¹, medium: thinning and/or release plus planting to 2,500 crop trees ha⁻¹, and a second year of vegetation control) on LAI and its vertical distribution in different shade tolerance groups over a 7-year period. Hardwood LAI increased by 242 and 318 % in the low and medium hardwood treatments, respectively, compared to a 123 % increase in the untreated control. Thinning possibly increased resource availability for upper stratum shade intolerant hardwoods, while also increasing light penetration through the canopy for midstory shade tolerant hardwoods. Conifer treatments substantially reduce overtopping hardwood LAI, facilitating an increase in conifer LAI by 281 and 378 % in the low and medium treatments, respectively. The height from the canopy base where LAI peaked increased between 29 and 80 % in the low mixedwood and medium hardwood treatments from pre-treatment through 7 years post-treatment. Comparatively, LAI at the peak increased by 16 and 36 % in the low and medium conifer treatments, respectively, with a minimal change in the height of the LAI peak. These contrasting responses were likely due to slower conifer reaction following treatment than hardwoods and stacking of conifer foliage within the middle portion of the canopy.
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