An artificial regeneration system for establishing northern red oak on dry-mesic sites in the Lake States, USA

Artificial regeneration of northern red oak is difficult to achieve in the Lake States, USA. A replicated study was established in northern Wisconsin in 1990 to determine the effect of overstory density and understory competition on the performance of bareroot and containerized northern red oak seedlings on dry-mesic sites. The relationship between seedling performance and the number of first-order lateral roots on the seedlings was also tested. Seedling performance was evaluated under 3 overstory densities (each 0.3 ha) — a clearcut, 25%, and 50% crown covers in combination with (and without) understory vegetation control with herbicide. Height growth was greater for containerized seedlings than bareroot stock after 2 and 3 growing seasons. After 2 yr seedling growth was greatest in the sprayed clearcut plots, but was only slightly greater than the unsprayed plots under the 25% crown cover (bareroot 25.5 vs 23.8 cm, and containerized 33.0 vs 31.2 cm, respectively). After 3 yr seedling height growth was significantly greater in the unsprayed plots under the 25% crown cover for both the bareroot and containerized seedlings when compared to all other overstory/understory treatment combinations examined in the study. Early performance results suggest that the light shelterwood silvicultural method (ie 25% crown cover) without chemical control of vegetation is preferred for establishing northern red oak on dry-mesic sites, when compared to the more traditional management schemes.Une technique de régénération artificielle pour l'installation du chêne rouge dans les stations sèches de la région des lacs (États-Unis). La régénération artificielle du chêne rouge est difficile à réaliser dans la région des lacs (États-Unis). Une expérimentation a été mise en place en 1990 dans le Nord Wisconsin, afin de déterminer les effets de la densité du couvert et de la compétition du sous-étage sur les performances de plants de chêne rouge (à racines nues ou en containers) plantés dans des stations sèches. Les relations entre les performances des plants et le nombre de leurs racines latérales d'ordre 1 ont aussi été étudiées. Les performances des plants furent évaluées sous 3 densités de couvert : 0%, 25% et 50% (placettes de 0,3 ha) en combinaison avec (ou sans) un sous-étage contrôlé par herbicide. Après 2 et 3 saisons de végétation, la croissance en hauteur des plants a été supérieure pour les plants en containers par rapport à ceux à racines nues. Après 2 ans, la croissance des plants était supérieure dans les placeaux coupés à blanc et traités par herbicides, mais seulement un peu plus élevée que dans les traitements non contrôlés par herbicides avec un couvert de 25% (plants à racines nues 25,5 et 23,8 cm, plants en containers 33,0 et 31,2 cm, respectivement). Après 3 ans, sous un couvert de 25% (avec ou sans sous-étage), la croissance en hauteur des plants était significativement plus élevée dans les traitements sans herbicides pour les plants à racines nues comme pour ceux élevés en containers, par rapport à l'ensemble des autres traitements sous couvert de cette étude. Les résultats initiaux laissent à penser qu'une méthode de sylviculture par abris légers (25% de couvert) et sans contrôle chimique de la végétation est préférable pour l'introduction du chêne rouge sur les stations sèches, par rapport aux méthodes plus traditionnelles des aménagements sylvicoles

Volatile organic compound emission rates from mixed deciduous and coniferous forests in Northern Wisconsin, USA

Biogenic emissions of volatile organic compounds (VOC) from forests play an important role in regulating the atmospheric trace gas composition including global tropospheric ozone concentrations. However, more information is needed on VOC emission rates from different forest regions of the world to understand regional and global impacts and to implement possible mitigation strategies. The mixed deciduous and coniferous forests of northern Wisconsin, USA, were predicted to have significant VOC emission rates because they are comprised of many genera (i.e. Picea, Populus, Quercus, Salix) known to be high VOC emitters. In July 1993, a study was conducted on the Chequamegon National Forest near Rhinelander, WI, to identify and quantify VOC emitted from major trees, shrubs, and understory herbs in the mixed northern forests of this region. Emission rates were measured at various scales - at the leaf level with cuvettes, the branch level with branch enclosures, the canopy level with a tower based system, and the landscape level with a tethered balloon air sampling system. Area-average emission rates were estimated by scaling, using biomass densities and species composition along transects representative of the study site. Isoprene (C5H8) was the primary VOC emitted, although significant quantities of monoterpenes (C10H16) were also emitted. The highest emission rates of isoprene (at 30°C and photosynthetically active radiation of 1000 μmol m-2 s-1) were from northern red oak (Quercus rubra, > 110 μg(C) g-1 h-1); aspen (Populus tremuloides, > 77); willow (Salix spp., > 54); and black spruce (Picea mariana, > 10). Emission rates of hybrid poplar clones ranged from 40 to 90 μg(C) g-1 h-1 at 25°C; those of Picea provenances were generally < 10, and emission rates of a hybrid between North American and European spruces were intermediate to parental rates. More than 30 species of plants were surveyed from the sites, including several from previously unstudied genera such as Alnus, Chamaedaphne, Ledum, Tilia, Rubus, and Sphagnum. Based on the measured isoprene concentrations in the daytime atmospheric surface layer and mixed layer, area-averaged fluxes of isoprene were estimated to be about 1 mg(C)m-2 h-1. This estimate agrees reasonably well with model predictions. Our results indicate that mixed forests in the Lake States region of the USA are a significant source of reactive VOC to the atmosphere. Accurate estimates of these emissions are required for determining appropriate regulatory air pollution control strategies. Future studies are needed to extrapolate these estimates to other landscapes and to better understand the factors controlling observed variations in VOC emissions