ALBERT

Description: Light regimes beneath closed canopies and tree-fall gaps are compared for five temperate and tropical forests using fish-eye photography of intact forest canopies and a model for calculating light penetration through idealized gaps. Beneath intact canopies, analyses of canopy photographs indicate that sunflecks potentially contribute 37–68% of seasonal total photosynthetically active radiation. In all of the forests, potential sunfleck duration is brief (4–6 min), but the frequency distributions of potential sunfleck duration vary because of differences in canopy geometry and recent disturbance history. Analysis of the photographs reveals that incidence angles for photosynthetically active radiation beneath closed canopies are not generally vertical for any of the forests, but there was considerable variation both among and within sites in the contribution of overhead versus low-angle lighting. Calculations of light penetration through idealized single-tree gaps in old growth Douglas-fir – hemlock forests indicate that such gaps have little effect on understory light regimes because of the high ratio of canopy height to gap diameter. However, single-tree gaps in the other four forest types produce significant overall increases in understory light levels. There is also significant spatial variation in seasonal total radiation in and around single-tree gaps. Our results demonstrate that there can be significant penetration of light into the understory adjacent to a gap, particularly at high latitudes. As gap size increases, both the mean and the range of light levels within the gap increases, but even in large gaps (ca. 1000 m2) the potential duration of direct sunlight is generally brief (

Description: The effects of gap formation on solar radiation, soil and air temperature, and soil moisture were studied in mature coniferous forests of the Pacific Northwest, U.S.A. Measurements were taken over a 6-year period in closed-canopy areas and recently created gaps in four stands of mature (90140 years) and old-growth (〉400 years) Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forest in the western Cascade Range of central Oregon and southern Washington. Gap sizes ranged from 40 to 2000 m2. Summer solar radiation levels and soil temperatures differed significantly among gap sizes and positions within gaps and were driven primarily by patterns of direct radiation. Nevertheless, effects on air temperature were slight. Soil moisture was more abundant in gaps than in controls, was most abundant in intermediate gap sizes, and tended to decline during the growing season in single-tree gaps and on the north edges of large gaps. However, there was substantial variation in moisture availability within individual gaps, primarily related to the variety of organic substrates present. Moisture in gaps declined over multiple years, likely caused by encroachment of vegetation within and around gaps. Low light levels probably limit filling of natural gaps in these forests, but the variety of microenvironments in large gaps may facilitate diverse plant communities.

Description: This research evaluates the utility of several remote sensing data types for the purpose of mapping forest structure and related attributes at a regional scale. Several sensors were evaluated, including (i) single date Landsat Thematic Mapper (TM); (ii) multitemporal Landsat TM; (iii) Airborne Data Acquisition and Registration (ADAR), a sensor with high spatial resolution; (iv) Airborne Visible-Infrared Imaging Spectrometer (AVIRIS), a sensor with high spectral resolution; and (v) Scanning Lidar Imager Of Canopies By Echo Recovery (SLICER), a lidar sensor that directly measures the height and canopy structure of forest vegetation. To evaluate the ability of each of the sensors to predict stand structure attributes, we assembled a data set consisting of 92 field plots within the Willamette National Forest in the vicinity of the H.J. Andrews Experimental Forest. Stand structure attributes included age, basal area, aboveground biomass, mean diameter at breast height (DBH) of dominant and codominant stems, mean and standard deviation of the DBH of all stems, maximum height, and the density of stems with DBH greater than 100 cm. SLICER performed better than any other remote sensing system in its predictions of forest structural attributes. The performance of the imaging sensors (TM, multitemporal TM, ADAR, and AVIRIS) varied with respect to which forest structural variables were being examined. For one group of variables there was little difference in the ability of the these sensors to predict forest structural attributes. For the remaining variables, we found that multitemporal TM was as or more effective than either ADAR or AVIRIS. These results indicate that multitemporal TM should be investigated as an alternative to either hyperspectral or hyperspatial sensors, which are more expensive and more difficult to process than multitemporal Landsat TM.

Description: Types and rates of mortality were measured and canopy gap formation rates were estimated from 5- to 15-year records of mortality in 34 permanent plots in mature (100- to 150-year-old) and old-growth (〉200-year-old) Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco)/western hemlock (Tsugacanadensis (Raf.) Sarg.) forests in western Oregon and Washington. Gap surveys were conducted in a mature and an old-growth stand, and characteristics of 40 gaps and regeneration were measured. Most canopy trees died without disrupting the forest in both mature (87.6%) and old-growth stands (73.3%). The amount of forest area per year representing new gaps was 0.7% in mature stands and 0.2% in old-growth stands. The gap survey found a higher proportion of gaps in the mature stand than in the old-growth stand. Most regeneration (〉 1 m tall) in gaps was western hemlock; Douglas-fir regeneration did not occur. The ratio of seedling density in gaps to density under canopies was about 3 for the mature stand and about 9 for the old-growth stand. Seedling density was correlated with measures of gap age but not gap size. The study suggests that gap disturbances and vegetative responses are important processes in the dynamics of these forests. However, gap formation rates and vegetative responses appear to be slow relative to other forest types. In addition to gap size, canopy structure and disturbance severity are important determinants of gap response.

Description: Using a landscape simulation model, we examined ecological and economic implications of forest policies designed to emulate the historical fire regime across the 2 × 106 ha Oregon Coast Range. Simulated policies included two variants of the current policy and three policies reflecting aspects of the historical fire regime. Policy development was guided by the management intentions of four owner groups: forest industry, nonindustrial private, state, and federal. Fire severity was emulated with green-tree retention standards; fire frequency was emulated with annual harvestable area restrictions; and fire extent was emulated with harvest-unit size regulations. Simulated disturbance-based policies produced age-class distributions closer to the estimated historical range than those created by the current policy. Within 100 years, proportions of younger forests were within the historical range, while older forests moved closer to, but remained below, historical conditions. In the near term, disturbance-based policies produced annual harvest volumes 20%60% lower than those produced by the current policy. However, relative costs of disturbance-based policies diminished over time. Our results suggest that if expediting a return to historical age-class distributions at a provincial-scale was a goal, then public lands would be needed to provide large patches of old forest. In addition, this experiment illustrated that distributing costs and benefits of conservation policies equitably across multiple private landowners is a significant challenge.

Description: An ecological method of multifactor ecosystem classification was applied in the Sylvania Recreation Area, an 8500-ha tract of old-growth northern hardwood – conifer forests in upper Michigan. The uplands and wetlands were subjectively classified into 25 ecosystems by a method combining reconnaissance, plot sampling, data analysis, and ecosystem mapping. Each ecosystem was a characteristic combination of physiography, ecological species groups (ground vegetation), and soil. Discriminant analysis was used to evaluate the distinctness of the upland ecosystems and to compare the discriminating abilities of different ecosystem components (physiography, ground vegetation, and soil). The classification was corroborated in the multivariate analyses. The lowest estimated error rate (9.4%) in discriminant analysis was obtained by a model based on a combination of physiographic and soil characteristics and ecological species groups. The estimated error rates based on the species groups alone and physiography and soil alone were 42.2 and 25.0%, respectively. The discriminant analyses indicate that neither vegetation alone nor physiography and soil alone could be used with high reliability in classifying and mapping ecosystems. An additional discriminant analysis of the three ecosystem components indicated that the ecosystems could be distinguished by field characteristics without information from soil laboratory analyses. This analysis also demonstrated the particular value of the vegetation component as a readily observed, acceptable substitute for soil laboratory data in identifying and mapping ecosystem units.

Description: Understanding the relative importance of landscape history, topography, vegetation, and climate to dead wood patterns is important for assessing pattern–process relationships related to dead wood and associated biodiversity. We sampled dead wood at four topographic positions in two landscapes (1400–2100 km2) that experienced different wildfire and salvage histories in coastal Oregon. Study objectives were to (i) determine whether and how the landscapes differed in dead wood amounts and characteristics and (ii) evaluate relationships between dead wood characteristics and potentially related biophysical variables associated with historical and current vegetation, topography, climate, soils, and ecoregion. Despite differences in history, the two landscapes differed little in total dead wood volume; however, they differed in dead wood volume by structural type, decay class, and source (legacy/nonlegacy). Dead wood varied by topographic position, and topography was of greatest importance compared with other factors. In this mountainous region, upper topographic positions may be source areas for dead wood and riparian areas and streams sinks for dead wood. Climate explained more variance in dead wood in the landscape that burned earlier and was not salvaged. Landscape-scale patterns of dead wood are evident in landscapes with different disturbance histories and despite finer-scale variation in topography, vegetation, and other biophysical attributes.

Description: The historical range of variability (HRV) in landscape structure and composition created by natural disturbance can serve as a general guide for evaluating ecological conditions of managed landscapes. HRV approaches to evaluating landscapes have been based on age-classes or developmental stages, which may obscure variation in live and dead stand structure. Developing the HRV of stand structural characteristics would improve the ecological resolution of this coarse-filter approach to ecosystem assessment. We investigated HRV in live and dead wood biomass in the regional landscape of the Oregon Coast Range by integrating stand-level biomass models and a spatially explicit fire simulation model. We simulated historical landscapes of the region for 1000 years under pre-Euro-American settlement fire regimes and calculated biomass as a function of disturbance history. The simulation showed that live and dead wood biomass historically varied widely in time and space. The majority of the forests historically contained 500–700 Mg·ha–1 (50–70 kg·m–2) of live wood and 50–200 Mg·ha–1 (5–20 kg·m–2) of dead wood. The current distributions are more concentrated in much smaller amounts for both biomass types. Although restoring the HRV of forest structure is not necessarily a management goal for most landowners and managing agencies, departure from the reference condition can provide relative measure to evaluate habitat conditions for managers seeking to use forest structure as a means to maintain or restore ecosystem and species diversity.

Description: Zero-order basins, where hillslope topography converges to form drainages, are common in steep, forested landscapes but we know little about their ecological structure. We used indirect gradient analysis to characterize gradients in plant species composition and cluster analysis to characterize groups of plant species associated with specific geomorphic areas. We sampled vegetation within 63 randomly selected zero-order basins in the southern Coast Range of Oregon and collected data on herb, shrub, and overstory tree cover, as well as environmental conditions. Zero-order basin overstories were similar in tree composition to both first-order riparian and upland plant assemblages, but were intermediate in tree density. Shrubs in zero-order basins included both species associated with dry upland conditions and species associated with riparian conditions. Results suggest that understory plant species composition in zero-order basins follows gradients in geomorphic and overstory conditions. Furthermore, it appears that zero-order basins have distinctive geomorphology and fluvial regimes. These distinctive features appear to support both plant species associated with riparian conditions and species associated with upland conditions. Zero-order basins represent the farthest upstream extension of riparian plant species into upland areas, increasing plant species diversity in steep, forested landscapes.