Understory vegetation, resource availability, and litterfall responses to pine thinning and woody vegetation control in longleaf pine plantations

Abstract

In six 8-to 11-year-old plantations of longleaf pine (Pinus palustris Mill.) near Aiken, S.C., responses of understory vegetation, light, and soil water availability and litterfall were studied in relation to pine thinning (May 1994), herbicidal treatment of nonpine woody vegetation (1995)(1996), or the combined treatments (treatment responses described below are in absolute units). Treatment differences in fifth-year (1998) herbaceous species density were as follows: pine thinning > woody control = combined treatments > untreated (33, 30, 30, and 25 species per 40 m 2 , respectively). Forb and grass covers were 13 and 8% greater, respectively, after pine thinning and 7 and 9% greater after woody control. Pine thinning stimulated a large increase in third-year gap fraction (0.26), short-term increases in soil water content (1%), and a reduction in pine litterfall by half (-120 g·m -2 per year). Woody control had no effect on gap fraction, decreased litterfall of nonpine woody vegetation (-32 g·m -2 per year), and stimulated season-long increases in soil water content (1-2%). The ranking of factors affecting herbaceous vegetation responses was as follows: light > soil water > herbicides > litterfall. Herbaceous species density and cover can be promoted in longleaf pine plantations by intensive thinning of pines and herbicidal control of non-pine woody vegetation.Résumé : Dans six plantations de pin des marais (Pinus palustris Mill.) âgées de 8 à 11 ans et situées près de Aiken en Caroline du Sud, aux États-Unis, la réaction de la végétation de sous-bois, la disponibilité de la lumière et de l'eau du sol, de même que la chute de litière ont été étudiées en fonction de l'éclaircie (mai 1994), de la répression des autres espèces ligneuses à l'aide d'herbicides (1995)(1996) et des traitements combinés (les réactions aux traitements sont présentées en unités absolues). Les différences de densité des espèces herbacées attribuables aux traitements après 5 ans étaient : éclaircie des pins > répression des espèces ligneuses = traitements combinés > témoin (respectivement 33, 30, 30 et 25 espèces par 40 m 2 ). La couverture des graminées et celle des autres espèces herbacées étaient respectivement supérieures de 8 et 13% après l'éclaircie et de 9 et 7% après la répression des espèces ligneuses. L'éclaircie a stimulé une forte augmentation de la proportion de trouées à la troisième année (0,26), des augmentations à court terme du contenu en eau du sol (1%) et une réduction de moitié de la chute de litière de pin (-120 g·m -2 par année). La répression des espèces ligneuses n'a pas eu d'effet sur la proportion de trouées, a réduit la chute de litière des autres espèces ligneuses (-32 g·m -2 par année), et a provoqué des augmentations saisonnières du contenu en eau du sol (1-2%). La classification des facteurs influençant la réaction de la végétation herbacée était : lumière > eau du sol > herbicides > chute de litière. La densité et la couverture des espèces herbacées peuvent être augmentées dans les plantations de pin des ma...

Light availability and understory vegetation four years after thinning in a Larix leptolepis plantation of central Korea

“…Therefore, it appeared that the increases in understory biomass after thinning resulted from the enhanced light condition in the forest floor. Our results were consistent with the conclusions of the other recent studies for Pinus palustris plantations (Harrington and Edwards 1999) and Nothofagus pumilio forest (Martinez Pastur et al 2002) that light is the principal environmental factor determining understory production. Also it was known that Larix spp., which generated light shade, supported a large ground vegetation compared to other coniferous species such as Abies spp., Picea spp., and Tsuga spp.…”

“…These results were consistent with previous findings of positive effects of thinning on species richness based on relatively short-term investigations (Bailey et al 1998;Thomas et al 1999; but see He and Barclay 2000). Light intensity was also considered to be the strongest single influence on the ground vegetation by Harrington and Edwards (1999) and Hill (1979). Increases in species richness with management intensity have been reported for other forests (Brunet et al 1996).…”

“…Other studies reported that cover and frequency of grasses and sedges increased in thinned Pseudotsuga menziesii (Bailey et al 1998) and Pinus palustris Mill. (Harrington and Edwards 1999) stands compared to unthinned stands. The floral composition generally shifts following intensive forest management (Moore and Allen 1999).…”

“…However, it is not clear whether these effects would still be similar in the longer term (Battles et al 2001;Ito et al 2003;Harrington and Edwards 1999;He and Barclay 2000). In particular, it is possible that there would be a lag between environmental changes after thinning and changes in understory vegetation (Thomas et al 1999).…”

“…Thinning is commonly prescribed to concentrate growth on high-value trees, and it has been known for some time that thinning influences resource availability, understory vegetation, soil properties, and nutrient cycling in forest ecosystems (Breda et al 1995;Harrington and Edwards 1999;He and Barclay 2000;Prescott 1997;Thomas et al 1999;Velazquez Martinez and Perry 1997). Larix leptolepis Gord.…”