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We characterized structural and functional attributes along hillslope gradients in headwater catchments. We endeavored to identify parameters that described significant transitions along the hillslope. On each of four catchments, we installed eight 50 m transects perpendicular to the stream. Structural attributes included woody and herbaceous vegetation; woody debris and forest floor mass, nitrogen (N) and carbon (C); total soil C and N; litterfall amount and quality by species; and microclimatic conditions. Functional attributes included litter decomposition, soil microarthropods, soil [CO.sub.2] evolution, soil solution chemistry, and soil extractable N. Forest floor mass, N and C, and soil depth increased with distance from the stream and transitioned between 10 and 20 m. In contrast, litterfall N rate (kilograms of nitrogen per hectare per day), downed woody debris, soil A-horizon C and N, and soil solution [NO.sub.3] concentration all decreased with distance, and exhibited significant transitions. Certain overstory species were more abundant in the uplands than near the stream. Herbaceous diversity and richness were similar across the hillslope, but species distributions varied in response to hillslope moisture content. Taken together, these results suggest that at 10-20 m from the stream, transitions occur that separate riparian from upland conditions and may provide valuable insight into riparian zone definition. Resume: Nous avons caracterises les attributs structuraux et fonctionnels le long de gradients de pente dans des bassins versants de tete. Nous avons tente didentifier les parame tres qui caracterisent les zones de transition importante le long des pentes. Dans chacun de quatre bassins versants, nous avons installe huit transects de 50 m perpendiculaires au cours d'eau. Les attributs structuraux incluaient la vegetation ligneuse et herbacee, la teneur en N et C ainsi que la masse des de-bris ligneux et de la couverture morte, la quantite totale de C et N dans le sol, la quantite et la qualite de la chute de litiere par espece et les conditions microclimatiques. Les attributs fonctionnels incluaient la decomposition de la litiere, les microarthropodes du sol, l'evolution du [CO.sub.2] dans le sol, les caracteristiques chimiques de la solution du sol et la quantite de N extractible dans le sol. La teneur en N et C ainsi que la masse de la couverture morte et la profondeur du sol augmentaient avec la distance depuis le cours d'eau et subissaient une transition a une distance de 10 a 20 m. Par contre, le taux de N (kg N*[ha.sup.-1]*[j.sup.-1]) dans la chute de litiere, les debris ligneux au sol, la quantite de C et N dans l'horizon A du sol et la concentration de [NO.sub.3] dans la solution du sol diminuaient avec la distance et connaissaient d'importantes transitions. Certaines especes de letage dominant etaient plus abondantes en terrain eleve qua proximite des cours d'eau. La diversite et la richesse des especes herbacees etaient semblables le long de la pente mais leur distribution variait en fonction de la teneur en humidite le long de la pente. Globalement, ces resultats indiquent qua 10 a 20 m du cours d'eau, des zones de transition separent les conditions riveraines des conditions en terrain eleve et peuvent donner un apercu interessant de la definition de la zone riveraine. [Traduit par la Redaction], Introduction Forested riparian areas mediate a number of terrestrial--aquatic linkages (Karr and Schlosser 1978) through their influence on physical, chemical, and biological dimensions of streams. Riparian zones are three-dimensional areas [...]

An integrated management approach is needed to maintain eastern hemlock ( Tsuga canadensis (L.) Carrière) in eastern North America and to minimize tree damage and mortality caused by the invasive hemlock woolly adelgid ( Adelges tsugae Annand). This study examined the hypothesis that chemical control with low rates of insecticide and biological control can be combined in the same stand to impact adelgid populations, prolong crown health, and allow predator proliferation. Sixty T . canadensis trees in northern Georgia were individually treated via soil injection with 0%, 10%, or 25% of the label rate of imidacloprid insecticide, and the biological control predator Laricobius nigrinus Fender was released in the stand, two and four years later. By year seven, hemlocks treated with the 25% imidacloprid rate lost their insecticide protection, had significantly better crown health and higher adelgid densities than untreated trees, and supported as many Laricobius predator larvae as untreated trees. In year seven, no residues of imidacloprid were detected in Laricobius larvae feeding on previously-treated hemlocks. Most (77%) of the predators collected on study trees were identified as L . nigrinus , 12% were the native congener Laricobius rubidus LeConte, and 11% were hybrids between the introduced and native species. The hybridization rate remained stable over time. The density of undisturbed A . tsugae ovisacs was twice as high on branches protected from predators as compared with branches exposed to predators. Results suggest that chemical and biological control of A . tsugae can be successfully integrated to help prolong hemlock health, although additional predators may be necessary to protect hemlock trees in the southern Appalachians. [ABSTRACT FROM AUTHOR]

This study explored the effects of canopy gaps and gap size on leaf litter microarthropod abundance at five sites within the experimental forest of the Coweeta Hydrologic Laboratory, in the Nantahala Mountain Range of western North Carolina. In March, 2002, five canopy gaps were formed by pulling over trees, to mimic natural disturbances. Two of the gaps measured 20m in diameter and three measured 40m. At each of the five gap sites we placed four experimental plots under canopy gaps and two control plots under closed canopy located just outside the gaps. Microarthropods were collected using 15cm2 mesh bags filled with two grams of leaf litter. Litter bags were placed in a three-by-four pattern at each plot on February 1, 2004. Litter bags and soil data were collected every other month for two years. A generalized linear mixed model was used to investigate effects of canopy gap presence and size on the populations of collembola, oribatid mites, prostigmatid mites, and mesostigmatid mites. Microarthropod counts were typically significantly greater in control plots than in gaps, with no significant effect due to gap size. [ABSTRACT FROM AUTHOR]