Mountain maple and balsam fir early response to partial and clear-cut harvesting under aspen stands of northern Quebec

This study is a component of the Sylviculture et am

Mixed-severity fire regimes: Lessons and hypotheses from the Klamath-Siskiyou Ecoregion

Although mixed-severity fires are among the most widespread disturbances influencing western North American forests, they remain the least understood. A major question is the degree to which mixed-severity fire regimes are simply an ecological intermediate between low- and high-severity fire regimes, versus a unique disturbance regime with distinct properties. The Klamath-Siskiyou Mountains of southwestern Oregon and northwestern California provide an excellent laboratory for studies of mixed-severity fire effects, as structurally diverse vegetation types in the region foster, and partly arise from, fires of variable severity. In addition, many mixed-severity fires have occurred in the region in the last several decades, including the nationally significant 200,000-ha Biscuit Fire. Since 2002, we have engaged in studies of early ecosystem response to 15 of these fires, ranging from determinants of fire effects to responses of vegetation, wildlife, and biogeochemistry. We present here some of our important early findings regarding mixed-severity fire, thereby updating the state of the science on mixed-severity fire regimes and highlighting questions and hypotheses to be tested in future studies on mixed-severity fire regimes. Our studies in the Klamath-Siskiyou Ecoregion suggest that forests with mixed-severity fire regimes are characterized primarily by their intimately mixed patches of vegetation of varied age, resulting from complex variations in both fire frequency and severity and species responses to this variation. Based on our findings, we hypothesize that the proximity of living and dead forest after mixed-severity fire, and the close mingling of early- and late-seral communities, results in unique vegetation and wildlife responses compared to predominantly low- or high-severity fires. These factors also appear to contribute to high resilience of plant and wildlife species to mixed-severity fire in the Klamath-Siskiyou Ecoregion. More informed management of ecosystems with mixed-severity regimes requires understanding of their wide variability in space and time, and the particular ecological responses that this variability elicit

Ponderosa pine of the Willamette Valley, Western Oregon

Ponderosa pine (Pinus ponderosa) is an overlooked component of the historical vegetation in the Willamette Valley of western Oregon, USA. Pollen, historical, and field data show that ponderosa pine has been a component of both lowland/floodplain and upland/foothill vegetation. In the latter, it was an important constituent of the savanna and open oak woodland vegetation that was widespread in the early 1800s. Much of the historical range of ponderosa pine has been converted to other land uses, such as agriculture, or changed by ecological succession to a closed forest dominated primarily by Douglas-fir (Pseudotsuga menziesii). Efforts to understand past Willamette Valley vegetation or to restore historical ecosystems in the Valley should recognize the important ecological position once held by ponderosa pine

Ponderosa pine of the Willamette Valley, Western Oregon

Ponderosa pine (Pinus ponderosa) is an overlooked component of the historical vegetation in the Willamette Valley of western Oregon, USA. Pollen, historical, and field data show that ponderosa pine has been a component of both lowland/floodplain and upland/foothill vegetation. In the latter, it was an important constituent of the savanna and open oak woodland vegetation that was widespread in the early 1800s. Much of the historical range of ponderosa pine has been converted to other land uses, such as agriculture, or changed by ecological succession to a closed forest dominated primarily by Douglas-fir (Pseudotsuga menziesii). Efforts to understand past Willamette Valley vegetation or to restore historical ecosystems in the Valley should recognize the important ecological position once held by ponderosa pine.Hibbs et al "Ponderosa pine of the Willamette Valley, Western Oregon." Northwest Science. 2002; 76(1): 80-8

Reaction of thiones with dihalogens: comparison of the solid state structures of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione-diiodine, -dibromine and -iodine monobromide

Reaction of 4,5-bis(methylsulfanyl)-1,3-dithiole-2-thione 1 with diiodine or iodine monobromide in CH2Cl2 resulted in the formation of molecular charge-transfer complexes 1 . I-2 and 1 . IBr respectively. Both complexes have been characterised crystallographically and contain a linear S-I-X (X = I or Br) moiety with the sulfur adopting a tetrahedral geometry taking into account the stereochemically active lone pairs. The S-I [2.716(3)] and I-I [2.808(3) Angstrom] bond lengths in 1 . I-2 are similar to those reported for diiodine complexes of related thione donors. The adduct 1 . IBr is the first crystallographically characterised thione-iodine monobromide charge-transfer complex. The S-I distance [2.589(2) Angstrom] is shorter than that in 1 . I-2, consistent with IBr being a stronger acceptor than I-2. The I-Br distance [2.7138(11) Angstrom] is lengthened with respect to that in unco-ordinated IBr, but within bonding distance when compared to the sum of the van der Waals radii for iodine and bromine (3.75 Angstrom). Treatment of 1 with dibromine under identical conditions resulted in the formation of the adduct 1 . Br-2 and the dithiolylium salt [C5H6S4Br][Br-3]. 1/2Br(2) 2. Treatment of 1 with Br-2 in toluene led to the isolation of 1 . Br-2 only. The crystal structure of 1 . Br-2 shows the compound to contain a linear Br-S-Br moiety with the sulfur in a T-shaped or Psi-trigonal bipyramidal environment (taking into account the stereochemically active lone pairs). The structure of 2 reveals a three component system consisting of the [C5H6S4Br](+) cation, the [Br-3](-) anion and a molecule of Br-2 in a 2:2:1 ratio. These components are held in the lattice by a series of weak intermolecular interactions which link the tribromide ions and dibromine molecules into zigzag chains