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Snag retention is increasingly being incorporated into forest management guidelines. Questions remain, however, in northern hardwood systems regarding factors affecting retention in actively managed stands, the effectiveness of snag creation, and the net effects of snag creation and timber harvesting on snag numbers and sizes. To address some of these questions, we examined the dynamics of natural and created snags within mature, even-aged northern hardwood forests under seven different management scenarios: three Harvest Only treatments, three Harvest Plus (created) Snags treatments, and one untreated Control. We found tree diameter, tree species, and stand treatment status (i.e., managed or Control) to be related to the retention of natural snags, created snags, or both. Snags were less likely to remain standing if they had smaller diameters, were species with relatively rapid decay rates, or were found in stands that had been logged. We found girdling trees to be an effective method of dead wood creation, although trees took longer to die than we expected. At least 84% of girdled trees had died in most stands within 4.5 years of girdling, and 30–77% of girdled trees were still standing 5.5 years after treatment. Comparison of net effects of snag creation and timber harvesting among treatments showed that managed stands, on average, experienced net snag losses compared to untreated Controls. These losses were statistically significant for all snag sizes, but not for large snags alone (i.e., dbh ⩾25.4 cm). Active management prescriptions that included snag creation demonstrated the potential to mitigate snag losses, with the extent of mitigation varying with the type of management. Surprisingly, mitigation was primarily driven by significantly greater natural snag recruitment in Plus Snags treatments, potentially due to competition from girdled trees that had not yet died. Our results may help inform the development of snag management guidelines in even-aged, second-growth northern hardwood systems for forest managers who are interested in enhancing the structural complexity of these forests.

The widespread availability of satellite imagery and image processing software has made it relatively easy for ecologists to use satellite imagery to address questions at the landscape and regional scales. However, as often happens with complex tools that are rendered easy to use by computer software, technology may be misused or used without an understanding of some of the limitations or caveats associated with a particular application. The results can be disappointment when maps are less accurate than expected or incorrect decisions when they are treated as truth. In this paper, we discuss several key issues which are critical to ensuring the effectiveness and value of remote sensing products, but which are also sometimes sources of confusion: (1) direct versus indirect models of land surface properties and processes, (2) differences between class-based and continuous mapping models, (3) scale, and (4) accuracy assessment. We illustrate our points with examples from the application of satellite imagery to forest management issues in the Pacific Northwest, USA. While our examples focus largely on Landsat image data, the issues we discuss have broad relevance across sensor data types, land cover properties, and geographic locations.

Active management techniques that emulate natural forest disturbance and stand development processes have the potential to enhance species diversity, structural complexity, and spatial heterogeneity in managed forests, helping to meet goals related to biodiversity, ecosystem health, and forest resilience in the face of uncertain future conditions. There are a number of steps to complete before, during, and after deciding to use active management for this purpose. These steps include specifying objectives and identifying initial targets, recognizing and addressing contemporary stressors that may hinder the ability to meet those objectives and targets, conducting a pretreatment evaluation, developing and implementing treatments, and evaluating treatments for success of implementation and for effectiveness after application. In this report we discuss these steps as they may be applied to second-growth northern hardwood forests in the northern Lake States region, using our experience with the ongoing managed old-growth silvicultural study (MOSS) as an example. We provide additional examples from other applicable studies across the region.

Mapping and monitoring of leaf area index (LAI) is important for spatially distributed modeling of vegetation productivity, evapotranspiration, and surface energy balance. Global LAI surfaces will be an early product of the MODIS Land Science Team, and the requirements for LAI validation at selected sites have prompted interest in accurate LAI mapping at a more local scale. While spectral vegetation indices (SVIs) derived from satellite remote sensing have been used to map LAI, vegetation type, and related optical properties, and effects of Sun–surface–sensor geometry, background reflectance, and atmospheric quality can limit the strength and generality of empirical LAI–SVI relationships. In the interest of a preliminary assessment of the variability in LAI–SVI relationships across vegetation types, we compared Landsat 5 Thematic Mapper imagery from three temperate zone sites with on-site LAI measurements. The sites differed widely in location, vegetation physiognomy (grass, shrubs, hardwood forest, and conifer forest), and topographic complexity. Comparisons were made using three different red and near-infrared-based SVIs (NDVI, SR, SAVI). Several derivations of the SVIs were examined, including those based on raw digital numbers (DN), radiance, top of the atmosphere reflectance, and atmospherically corrected reflectance. For one of the sites, which had extreme topographic complexity, additional corrections were made for Sun–surface–sensor geometry. Across all sites, a strong general relationship was preserved, with SVIs increasing up to LAI values of 3 to 5. For all but the coniferous forest site, sensitivity of the SVIs was low at LAI values above 5. In coniferous forests, the SVIs decreased at the highest LAI values because of decreasing near-infrared reflectance associated with the complex canopy in these mature to old-growth stands. The cross-site LAI–SVI relationships based on atmospherically corrected imagery were stronger than those based on DN, radiance, or top of atmosphere reflectance. Topographic corrections at the conifer site altered the SVIs in some cases but had little effect on the LAI–SVI relationships. Significant effects of vegetation properties on SVIs, which were independent of LAI, were evident. The variability between and around the best fit LAI–SVI relationships for this dataset suggests that for local accuracy in development of LAI surfaces it will be desirable to stratify by land cover classes (e.g., physiognomic type and successional stage) and to vary the SVI.

It has been suggested that a feedback exists between the vegetation and soil whereby fertile (vs infertile) sites support species with shorter leaf life spans and higher quality litter which promotes rapid decomposition and higher soil nutrient availability. The objectives of this study were to (1) characterize and compare the C and N dynamics of dominant upland forest ecosystems in north central Wisconsin, (2) compare the nutrient use efficiency (NUE) of these forests, and (3) examine the relationship between NUE and site characteristics. Analyzing data from 24 stands spanning a moisture / nutrient gradient, we found that resource-poor stands transferred less C and N from the vegetation to the forest floor, and that N remained in the forest floor at least four times longer than in more resource-rich stands. Analyzing data by leaf habit, we found that less N was transferred to the forest floor annually via litterfall in conifer stands, and that N remained in the forest floor of these stands nearly three times longer than in hardwood stands. NUE did not differ among forests with different resource availabilities, but was greater for conifers than for hardwoods. Vitousek's (1982) index of nutrient use efficiency (INUE1 = leaf litterfall biomass / leaf litterfall N) was most closely correlated to litterfall specific leaf area and percent hardwood leaf area index, suggesting that differences in species composition may have been responsible for the differences in NUE among our stands. NUE2, defined as ANPP / leaf litterfall N, was not closely correlated to any of the site characteristics included in this analysis.

Habitat type classification is a natural classification system that uses the co-occurrence of ground flora and tree species to formulate taxa that can be used to identify sites which support similar plant communities or associations at climax. In 1988 a habitat type classification was developed for northern Wisconsin forests, but scientists have yet to determine whether important soil and vegetation characteristics are similar within a habitat type and if they exhibit consistent differences among habitat types. We compared the soil and vegetation characteristics of 24 sites from the 6 major habitat types in north central Wisconsin. Total soil nitrogen and organic matter concentrations, soil available potassium, soil silt fraction, and soil water-holding capacity all generally increased in the order: Quercus-Acer/Epigaea (QAE) < Acer-Quercus/Vaccinium (AQV) < Pinus/Maianthemum-Vaccinium (PMV) < Acer/Vaccinium-Viburnum (AVVib) < Acer-Tsuga/Dryopteris (ATD) < Acer/Viola-Osmorhiza (AViO). In addition, we observed positive trends (QAE < AQV < PMV < AVVib < ATD < AViO) in leaf area index (leaf area per unit ground area )and forest net primary productivity, both of which are expressions of total resource availability. North. J. Appl. For. 15(2):69-76.

Leaf area index (LAI) is an extremely important structural characteristic of vegetation because it is directly related to the exchange of energy, CO2 and mass from plant canopies at a variety of scales. Research investigating the relationship between forest LAI and satellite data for hardwood and mixed conifer-hardwood forests is lacking, however. The objective of this study was to explore the utility of Landsat-5 Thematic Mapper (TM) data for accurately estimating the LAI of conifer, hardwood, and mixed conifer-hardwood forests in north central Wisconsin. Individual bands and vegetation indices (VIs) calculated from satellite measures of exoatmospheric reflectance were related to the litterfall-estimated LAI of 24 stands. The results showed that individual bands or VIs containing at least one infrared (IR) band (either near- or mid-infrared) or a strong IR component divided data into at least two groups, with each group requiring a different regression line. The primary division was between conifer-dominated and hardwood-doin inated stands. Of the individual bands and VI.s considered, seven were strongly correlated to the LAI of conifer stands (r2=0.69–0.73). For the hardwoods, the best individual band or VI was Green/mid-IR#1 (r2=0.35), although an additional individual band and two VIs did much better using re subset of lower LAI stands (r2=0.60–0.75). For individual bands and VIs not requiring a conifer-hardwood distinction, the sixth Tasseled Cap component was most closely related to LAI (r2=0.60). Multiple-variable models (using LAI as the dependent variable) were found to offer substantial improvement over single-variable models, especially for hardwood stands. We recommend for further consideration a four-variable model for the conifers, and one four-variable and two eight-variable models for the hardwoods.

Measurement of foliage surface area index (foliage SAI) is prominent in studies of terrestrial ecosystems because it is an important determinant of water, carbon, and energy exchange at the stand, landscape, and global scales, yet is very time consuming and labor intensive to measure directly. The objectives of this study were to 1) compare the resolution and accuracy of the Ceptometer, LAI-2000, and DEMON which measure a vegetation area index (VAI; includes branches, stems, cones, etc. in addition to leaves) optically using light interception, 2) examine the utility of logarithmic versus linear averaging and a correction factor proposed by Gower and Norman (1991), and 3) determine if there is a ‘universal’ regression relating optical and direct estimates of SAI across the range of foliage areas for most North American forests (and if one exists, how it relates to individual site regressions). For our analysis, data collected in open canopy natural ponderosa pine (Pinus ponderosa Dougl. ex Laws) forests and closed canopy red pine (Pinus resinosa Ait.) plantations were combined with data from previous studies which used one or more of the instruments. We found all instruments generally underestimated SAI when compared with direct estimates. Logarithmic averages of light transmittance reduced this problem, especially for conifer forests with foliage clumped at the shoot and canopy levels. The DEMON, using logarithmically averaged data, provided the most accurate optical estimates of SAI. We did not find the clumping correction factor suggested by Gower and Norman (1991) to be useful and suggest an alternative correction technique that is based on hemisurface area index (HSAI) and includes a shoot shape factor along with a clumping factor. Across a broad range in foliage SAI, all instruments provided optical estimates of SAI that were strongly correlated to direct estimates but the optical estimates were biased. The LAI-2000 (R2 = 0.93) and the DEMON logarithmic (R2 = 0.93) had the best fits. Because of the small size of the data sets evaluated, we strongly recommend the collection of larger data sets across a wider range of foliage SAIs to better test the strength of ‘universal’ regressions relating optical estimates of SAI to direct estimates.

The objective of this study was to examine the effect of fertilization on the allometric relations for red pine (Pinusresinosa Ait.) and ponderosa pine (Pinusponderosa Dougl. ex Laws.) growing in contrasting climates. After 2 years of treatment, fertilization did not significantly affect the allometric relations between stem or branch mass and stem diameter for either species. For a similar-diameter tree, current foliage mass and area and new twig mass were significantly greater for fertilized than for control red pine and ponderosa pine. The significant increase in new foliage mass and area occurred in the upper and middle canopy for red pine and middle and lower canopy for ponderosa pine. For a similar-diameter tree, projected (one-sided) leaf area and total foliage mass were significantly greater for fertilized than for control red pine. However, leaf area and total foliage mass did not differ between similar-diameter fertilized and control ponderosa pine because fertilization decreased leaf longevity. The ratios of leaf area/sapwood cross-sectional area measured at breast height (1.37 m) were 0.14 and 0.11 for control plus fertilized red pine and ponderosa pine, respectively, and were greater (but not significantly) for fertilized than for control trees, while the ratios of leaf area/sapwood cross-sectional area measured at the base of live crown were significantly greater for fertilized than for control red pine and ponderosa pine.