Long-term spatial and structural dynamics in Acadian mixedwood stands managed under various silvicultural systems

Abstract

Using inventory data from a long-term silviculture experiment in east-central Maine, spatial models were developed to analyze 28 years (1974–2002) of stand structural dynamics. Differences in spatial pattern, species mingling, height differentiation, and relative stand complexity index (rSCI) were compared among five treatments: commercial clear-cutting, fixed diameter-limit, 5 year single-tree selection, three-stage shelterwood (both with and without precommercial thinning), and unharvested natural areas. Regardless of treatment, regeneration events (whether induced by natural breakup of the overstory or by harvesting) increased aggregation in spatial pattern and reduced species mingling, more so in the commercial clearcut and fixed diameter-limit treatments where hardwood densities were highest. Regular spatial patterns were rare. Height differentiation values for individual trees and stand-level mean rSCI were generally highest in untreated natural areas and 5 year selection treatments, intermediate in commercial clearcut and fixed diameter-limit treatments, and lowest in three-stage shelterwood treatments. After a brief adjustment period, precommercial thinning in a shelterwood treated stand generally increased species mingling, height differentiation, and rSCI. Two untreated natural areas exhibited divergent pathways of structural development. Dynamics in uneven-aged selection treatments more closely resembled that of the untreated natural areas than did the shelterwood, commercial clearcut, or fixed diameter-limit treatments.

Changes in the structure and composition of two Pinus nigra subsp. salzmannii forests over a century of different silvicultural treatments

“…The selection method usually produces more complex forest structures than those generated by the shelterwood method and, additionally, better resembles the dynamics found in untreated natural areas (Saunders and Wagner, 2008). Similarly, the diameter distributions found in Navahonda should be considered better models in the search for a sustainable silviculture able to maintain biodiversity in Pinus nigra stands.…”

Do partial cuts create forest complexity? A new approach to measuring the complexity of forest patterns using photographs and the mean information gain

“…In previous research by Proulx and Parrot (2008), the most complex patterns were shown to be represented by intermediate values of MIG. Traditionally, digital cameras record pictures in RGB (Red Green Blue) format, but for a more direct link to the actual colour of objects and effects of light, our photographs were converted to HSB images (Hue Saturation Brightness) following the method proposed by Smith (1978). Each pixel in the image thus bears three values respectively defining its colour (hue), the intensity of the colour (saturation) and the quantity of light it received (brightness).…”

“…Instead, earlier studies have looked at the relationship between species and structural diversity. Years of study have thus led to knowledge of the response of specific structures such as living trees (Crow et al 2002, Brais et al 2004, Saunders and Wagner 2008, dead wood, (McGee et al 1999) and understory plants (Roberts 2007) to different types of harvesting. On the other hand, the effects of partial cuts on the spatial distribution of structure and habitat heterogeneity have also been studied for different animal taxa (Suzuki and Hayes 2003, Loehle et al 2005, AguilarAmuchastegui and Henebry 2007.…”

Do natural processes at the juvenile stage of stand development differentiate the spatial structure of trees in artificially established forest stands?

“…In natural stands, where human activity is limited to the minimum, this diversity is usually much greater than in commercial forests, which are often even-aged and a single species. In the latter, diversity can be shaped indirectly by using proper treatments (Pretzsch 1996(Pretzsch , 1999Hanewinkel 2004;Saunders, Wagner 2008;Jaworski 2013). There is, of course, no option to abandon precommercial treatments in these forests, but one can discuss methods applied depending on the species and commercial purposes.…”