Deciduous Stands Research Articles

Static and dynamic controls on fire activity at moderate spatial and temporal scales in the Alaskan boreal forest

AbstractWildfire, a dominant disturbance in boreal forests, is highly variable in occurrence and behavior at multiple spatiotemporal scales. New data sets provide more detailed spatial and temporal observations of active fires and the post‐burn environment in Alaska. In this study, we employ some of these new data to analyze variations in fire activity by developing three explanatory models to examine the occurrence of (1) seasonal periods of elevated fire activity using the number of MODIS active fire detections data set (MCD14DL) within an 11‐day moving window, (2) unburned patches within a burned area using the Monitoring Trends in Burn Severity fire severity product, and (3) short‐to‐moderate interval (<60 yr) fires using areas of burned area overlap in the Alaska Large Fire Database. Explanatory variables for these three models included dynamic variables that can change over the course of the fire season, such as weather and burn date, as well as static variables that remain constant over a fire season, such as topography, drainage, vegetation cover, and fire history. We found that seasonal periods of high fire activity are associated with both seasonal timing and aggregated weather conditions, as well as the landscape composition of areas that are burning. Important static inputs to the model of seasonal fire activity indicate that when fire weather conditions are suitable, areas that typically resist fire (e.g., deciduous stands) may become more vulnerable to burning and therefore less effective as fire breaks. The occurrence of short‐to‐moderate interval fires appears to be primarily driven by weather conditions, as these were the only relevant explanatory variables in the model. The unique importance of weather in explaining short‐to‐moderate interval fires implies that fire return intervals (FRIs) will be sensitive to projected climate changes in the region. Unburned patches occur most often in younger stands, which may be related to a greater deciduous fraction of vegetation as well as lower fuel loads compared with mature stands. The fraction of unburned patches may therefore increase in response to decreasing FRIs and increased deciduousness in the region, or these may decrease if fire weather conditions become more severe.

Satellite monitoring of the state of forest vegetation after fire impacts in the Zabaikal region

Based on the MODIS radiometer data, the level of disturbance of forest lands by fires has been estimated for southwestern areas of the Zabaikal region. A combined analysis of vegetation indices calculated by measuring reflected radiation in the near and mid-infrared wave ranges and the data of on-ground studies allowed us to identify sites with successful and poor reforestation. Based on the instrumental data, it is found that repeated fires prevent successful reforestation. An analysis of seasonal dynamics indicates that summer fires result in greater damages of forest vegetation than those caused by spring fires. Larch stands prevailing in the region cover the largest portion of fire-disturbed lands (and the largest area, where reforestation processes are hampered), while pine and deciduous stands are characterized by a higher frequency of fires.

Assessing the impacts of the decline of Tsuga canadensis stands on two amphibian species in a New England forest

AbstractDisturbances such as outbreaks of herbivorous insects and pathogens can devastate unique habitats and directly reduce biodiversity. The foundation tree species Tsuga canadensis (eastern hemlock) is declining due to infestation by the nonnative insect Adelges tsugae (hemlock woolly adelgid). The decline and expected elimination of hemlock from northeastern U.S. forests is changing forest structure, function, and assemblages of associated species. We assessed 10 years of changes in occupancy, detection probability, and relative abundance of two species of terrestrial salamanders, Plethodon cinereus (eastern red‐back salamander) and Notopthalmus viridescens viridescens (eastern red‐spotted newt), to the experimental removal in 2005 of T. canadensis at Harvard Forest. Salamanders were sampled under cover boards and using visual encounter surveys before (2004) and after (2005, 2013, 2014) canopy manipulations in replicate 0.81‐ha plots. In 2004, occupancy of P. cinereus was 35% lower in stands dominated by T. canadensis than that in associated mixed‐hardwood control stands, whereas detection probability and estimated abundance of P. cinereus were, respectively, 60% and 100% greater in T. canadensis stands. Estimated abundance of N. v. viridescens in 2004 was 50% higher in T. canadensis stands. Removal of the T. canadensis canopy increased occupancy of P. cinereus but significantly reduced its estimated detection probability and abundance. Estimated abundance of N. v. viridescens also declined dramatically after canopy manipulations. Our results suggest that ten years after T. canadensis loss due to either the adelgid or pre‐emptive salvage logging, and 50–70 years later when these forests have become mid‐successional mixed deciduous stands, the abundance of these salamanders likely will be <50% of their abundance in current, intact T. canadensis stands. This study adds to our understanding of how forest disturbance, directly and indirectly caused by invasive species, can contribute to declines in the relative abundance of amphibians.

Layer Stacking: A Novel Algorithm for Individual Forest Tree Segmentation from LiDAR Point Clouds

As light detection and ranging (LiDAR) technology advances, it has become common for datasets to be acquired at a point density high enough to capture structural information from individual trees. To process these data, an automatic method of isolating individual trees from a LiDAR point cloud is required. Traditional methods for segmenting trees attempt to isolate prominent tree crowns from a canopy height model. We here introduce a novel segmentation method, layer stacking, which slices the entire forest point cloud at 1-m height intervals and isolates trees in each layer. Merging the results from all layers produces representative tree profiles. When compared to watershed delineation (a widely used segmentation algorithm), layer stacking correctly identified 15% more trees in uneven-aged conifer stands, 7%–17% more in even-aged conifer stands, 26% more in mixedwood stands, and 26%–30% more (with 75% of trees correctly detected) in pure deciduous stands. Overall, layer stacking's commission error was mostly similar to or better than that of watershed delineation. Layer stacking performed particularly well in deciduous, leaf-off conditions, even those where tree crowns were less prominent. We conclude that in the tested forest types, layer stacking represents an improvement in segmentation when compared to existing algorithms.

Soil mercury distribution in adjacent coniferous and deciduous stands highly impacted by acid rain in the Ore Mountains, Czech Republic

Forests play a primary role in the cycling and storage of mercury (Hg) in terrestrial ecosystems. This study aimed to assess differences in Hg cycling and storage resulting from different vegetation at two adjacent forest stands - beech and spruce. The study site Načetín in the Czech Republic's Black Triangle received high atmospheric loadings of Hg from coal combustion in the second half of the 20th century as documented by peat accumulation rates reaching 100 μg m−2 y−1. In 2004, the annual litterfall Hg flux was 22.5 μg m−2 y−1 in the beech stand and 14.5 μg m−2 y−1 in the spruce stand. Soil concentrations and pools of Hg had a strong positive relation to soil organic matter and concentrations of soil sulfur (S) and nitrogen (N). O-horizon Hg concentrations ranged from 245 to 495 μg kg−1 and were greater in the spruce stand soil, probably as a result of greater dry Hg deposition. Mineral soil Hg concentrations ranged from 51 to 163 μg kg−1 and were greater in the beech stand soil due to its greater capacity to store organic carbon (C). The Hg/C ratio increased with depth from 0.3 in the O-horizon to 3.8 μg g−1 in the C horizon of spruce soil and from 0.7 to 2.7 μg g−1 in beech soil. The Hg/C ratio was greater at all mineral soil depths in the spruce stand. The organic soil Hg pools in beech and spruce stands (6.4 and 5.7 mg m−2, respectively) were considerably lower than corresponding mineral soil Hg pools (39.1 and 25.8 mg m−2). Despite the important role of S in Hg cycling, differences in soil Hg distribution at both stands could not be attributed to differences in soil sulfur speciation.

Assessment of forest soil contamination in Krakow surroundings in relation to the type of stand

The aim of the study was to determine the degree of soil pollution in different forest types around Krakow, using biochemical, chemical and magnetic methods. In assessing the degree of soil contamination, the impact of the forest species composition by comparing the surfaces of broadleaf and coniferous forest stands was taken into account. Enzymatic activity was related to other measures of pollution, i.e., heavy metal concentration, content of polycyclic aromatic hydrocarbons and level of magnetic susceptibility. The study was conducted in southern Poland. Krakow was the central point around which the test surfaces were designated. In soil samples pH, soil texture and organic carbon, nitrogen, base cation contents, dehydrogenase and urease activities were determined. Additionally, heavy metal concentration, polycyclic aromatic hydrocarbons (PAHs) content and magnetic susceptibility were recorded. The obtained results confirm the high diversity of forest soil pollution around Krakow agglomeration. Significant differences in both the content of heavy metals, polycyclic aromatic hydrocarbons and values of the magnetic susceptibility were observed in the soils of forest complexes located in different directions away from Krakow and at various distances from Krakow. The level of contamination is related to the historical and current deposition of industrial and urban dusts from Krakow and Silesia. The type of stand had a considerable influence on the content of polycyclic aromatic hydrocarbons. A higher content of aromatic hydrocarbons was observed in the soils of deciduous stands. A high level of magnetic susceptibility was observed in the soils of coniferous stands. The differences in enzymatic activity between the research plots result from different contents of PAHs and different amount of soil organic matter resulting from the species composition.

Apport Des Images Satellites MODIS Dans L’étude De L’évolution De La Végétation Forestière De l’Est Algérien

The monitoring of forest dynamics is needed to better quantify the intensity of climate change and their impacted on forest resources of Algeria. The NDVI (Normalized Difference Vegetation Index) was often used to take this step. It is considered a fluctuating parameter in space and in time, very used today to measure the physiological activity of plants and characterize the vigor of vegetation. In this study we tried to characterize the one hand the spatial and temporal variability of NDVI of forest ecosystems of eastern Algeria and also spatially identify via statistical calculations the stressed forest parcels where chlorophyll activity leaves shows fluctuations and anomalies. The data used are those of the spectral index NDVI MODIS sensor for detecting photosynthetic signal returned by the tree canopy. It appears from this study that the vegetative activity of the forest ecosystems of eastern Algeria is always strong in the coastal massifs and decreases according to a latitudinal gradient oriented approximately North-South. In terms of the ecosystems, this activity is greater for deciduous stands than for softwoods. Moreover, the mapping of the standard deviation of NDVI allowed us, first, to spatially discriminate stressed forest parcels that are considered priorities for the establishment of effective conservation strategy and, secondly, to identify the most threatened tree species that requires a rapid response and collaboration between the institutions concerned to protect it.

Sex-biased response in activity to light sources with different spectral composition in geometrid moths with flightless females (Lepidoptera: Geometridae)

Geometrid moths occurring in late autumn and early spring in temperate forest habitats are often harmful defoliators of deciduous stands. Their populations can cause locally cyclic outbreaks and thus preventive monitoring actions have been developed, mainly based on pheromone attraction of males. Females are mostly flightless with reduced or lost wings and reduced senses associated with flying. Males are standard flyers with well-developed eyes and must be able to deal with rapidly changing light conditions during their activity. Although such differences indicate sex-biased differences in reactions to light, this has been insufficiently tested. In conditions of an experimental arena and using light-emitting diodes, we tested the different reactions of the sexes for nine species to precisely defined short segments of the electromagnetic spectrum in the range 360-660 nm. Across all species, males preferred shorter wavelengths up to 500 nm, while females were nonselective and generally less active. The sexes differed by eye size and body mass, with males having significantly larger eyes and lower body mass. Between brachypterous and apterous females, the former had larger eye size, while body mass differences were statistically insignificant. There were differences between the sexes in move-to-light reactions and changes in eye size and body mass in line with wing reduction. While males preferred a relatively distinct range of shorter wavelengths, a method of attraction to lights with distinct narrow spectra could be used markedly to enhance the established methods of forest pest monitoring, either alone or in combination with chemical male attraction.

Imaging phenology; scaling from camera plots to landscapes

Abstract Information on the spatial and temporal patterns of plant phenology is important to develop a more comprehensive understanding of food availability and habitat for many animal species. The combination of broad scale, regional climatic, and more localized, site-level drivers presents a challenge when upscaling phenology from the plot to the region. Likewise, developing relationships between ground- or camera-based estimates and satellite imagery remains difficult due to the trade-off between temporal and spatial resolution. Landsat imagery, with its 16 day temporal resolution, is often thought of as being insufficient for timely observation of changes in vegetation throughout the year. However the free availability of the Landsat archive has enabled a major shift in the way Landsat imagery is processed moving towards pixel, rather than scene, based analyses. In this paper we build on previous research by examining the applicability and accuracy of Landsat derived phenology curves beyond deciduous stands into more mixed stands and conifer dominated forest types in the Rocky Mountains and foothills in Alberta, Canada. In addition, we discuss the application of these Landsat phenology curves to phenology of understorey species which are linked to habitat selection for free roaming wildlife, in particular grizzly bears. The agreement between Landsat- and camera-derived estimates of key phenological events was stronger for green-up (RMSE = 7 days) than for senescence (RMSE = 14 days). Our results show that yearly adjustment of green-up and senescence dates using available Landsat observations improved the agreement with camera-derived estimates when compared to average annual curves. Seasonal phenology transition dates accepted as valid ranged from 25% for alpine herbaceous pixels to 75% for closed deciduous, demonstrating the variable success of this approach across land cover types. Season transition dates were rejected if pixels lacked a strong enough green-up signal in Landsat spectral indices or if the estimated dates fell outside of the valid range. We conclude by investigating the spatial patterns of seasonal phenology at the Landsat scale, and assess the relative importance of regional vs. microsite conditions as well as the utility of these data for resource and wildlife management.

Influence of coniferous and deciduous vegetation on major and trace metals in forests of northern New England, USA

Climate change and land-use are predicted to shift coniferous stands to deciduous stands in northern New England. This change in vegetation type may modify plant-soil cycling of major and trace metals, potentially affecting soil fertility and contaminant transport. We studied eight pairs of adjacent coniferous- and deciduous-dominated forest stands across northern New England, USA. We estimated the mean residence time (MRT) of each metal in organic horizons using calculated litterfall from allometric equations and interpolated atmospheric deposition rates. Coniferous stands had 30–50 % smaller organic horizons pools of Ca, K, Mg, Mn, and Zn than deciduous stands. Mineral horizon metal pools were similar between vegetation types. Foliar metal concentrations and pools were smaller at coniferous stands than deciduous stands. The organic horizon MRT for Ca, Cd, Cu, K, Mg, and Mn was predicted to be 40–200 % longer for coniferous stands than deciduous stands. Based upon our findings, we conclude that a shift from coniferous to deciduous vegetation could decrease the accumulation and retention of major metals in the organic horizons. Further investigations into the effect of vegetation type on mineral horizons are needed to constrain regional changes.

Effects of nurse trees, spacing, and tree species on biomass production in mixed forest plantations

ABSTRACTGrowing concern about increasing concentrations of greenhouse gases in the atmosphere, and resulting global climate change, has spurred a growing demand for renewable energy. In this study, we hypothesized that a nurse tree crop may provide additional early yields of biomass for fuel, while in the longterm leading to deciduous stands that are believed to better meet the demands for other ecosystem services. Ten different species combinations were planted, with two different stocking densities, at three different sites in Denmark. Significant differences, with regard to biomass production, were observed among the different sites (P < .001) and species combinations (P < .001) after 12–13 growing seasons. Compared to pure beech stands, mixtures with beech and Japanese larch on average produced 4.4 t ha−1 yr−1 more biomass. The additional biomass production was similar to what was obtained in stands with conifers only (Sitka spruce, Douglas-fir and Japanese larch), which produced 4.9–6.1 t ha−1yr−1 more biomass than the pure beech stands. No effects of initial planting density (P = .19), or of initial weeding (P = .81), on biomass production were observed. Biomass production of the broadleaved crop was in most cases reduced due to competition. However, provided timely thinning of nurse trees, the qualitative development of the trees will allow for long-term timber production.

Land-cover patterns surrounding Caucasian grouse leks in Arasbaran region, East Azerbaijan, Iran

Context To create management strategies with the goal of sustaining a species such as Caucasian grouse (Lyrurus mlokosiewiczi), it is important to identify the habitat requirements of species, not just in terms of a correlation with a given habitat feature, but also the relationship between species presence and vegetation coverage, proximity to other habitat types, and importance at different spatial scales. Aims To predict the proportions and spatial configuration of major habitat types that are associated with high probabilities of Caucasian grouse lek occurrence. Methods Using minimum mapping-unit scale (i.e. grain) for land cover, we applied spatial analysis at three spatial extents (472-, 702- and 867-m-radius circles) to assess how the importance of different land-cover patterns and patch characteristics surrounding leks of Caucasian grouse changed with scale within the Arasbaran landscape (316.56 km2) in East Azerbaijan, Iran. A set of a priori models has been developed on the basis of landscape metrics linked to hypotheses that could explain the spatial pattern of Caucasian black habitat use at each scale. We used an information-theoretic approach based on Akaike’s information criterion (AIC) within a general additive models framework to model habitat selection, so as to compare the values of landscape metrics calculated for Caucasian grouse lek sites (n = 22) with those calculated for non-lek points (n = 44). Key results The probability of lek occurrence at each of the spatial scales increases with a larger amount of open, young forests in the landscape. At each scale, we could indicate the landscape composition and structure required to create an ideal habitat mosaic for Caucasian grouse. Such an ideal habitat mosaic within mountain forests of Arasbaran, for a 702-m-radius area around a potential lek site, would consist of non-square (i.e. more geometrically complex) patches of rangeland cover and deciduous stands with canopy cover of &lt;50%, which encompass over 30% of landscape. Conclusions Our results identified differences in black grouse requirements at several scales within the landscape. We believe this will help managers improve the habitat focusing on the area around existing or inactive leks, to adapt the landscape to species requirements, and to encourage targeting new sites. Implications These findings demonstrated that not only can we identify important landscape requirements at a range of scales, but by characterising landscape composition and structure across these scales, forest managers can help prioritise combinations of habitats that best serve the conservation of the target species.

The Importance of Spatiotemporal Heterogeneity for Biodiversity in Forest—Heathland Mosaics and Implications for Heathland Conservation

In biodiversity management, spatio-temporal heterogeneity is important to consider conserving high levels of habitat diversity and ecosystems. In this study, we investigated the relationship between landscape spatio-temporal heterogeneity and biodiversity in a mosaic-landscape, located in the Fontainebleau forest (France). The diversity of successional stages along a gradient from heathland to forest as well as the persistence of Calluna vulgaris (L.) Hull in different forest stands was examined in order to find how the numerous patches of European Heathland habitat embedded in this area should be maintained. The results indicated that in the areas of high spatio-temporal heterogeneity, a general increase is observed in species richness, in particular for vascular plants, bryophytes and carabids. C. vulgaris persisted in coniferous stands and young mixed stand but decreased under deciduous trees and old mixed stands. The Ellenberg’s values for light, nutrients and acidity, show the persistence of favorable enviromental conditions for heathland vegetation under coniferous stands and young mixed stands. These results enable us to offer recommendations to better manage mosaic-landscape biodiversity, and in particular, the heathland semi-natural habitats in the Fontainebleau forest and elsewhere in Europe.

Seasonal Differences in Forest Height Estimation From Interferometric TanDEM-X Coherence Data

This paper demonstrates the use of X-band bistatic synthetic aperture radar (SAR) interferometric coherence for retrieving tree height of coniferous and deciduous forests during leaf-off season in early spring and leaf-on period in summer. TerraSAR-X add-on for Digital Elevation Measurements (TanDEM-X) HH and VV polarization channel coherence images were studied for over 249 ha of forests in Estonia and compared against light detection and ranging (LiDAR) and forest registry field inventory data. Strong correlation was found between interferometric coherence magnitude and LiDAR measured average tree height, especially for winter period. The regression models show the strongest correlation between pine stand heights and single-polarization interferometric coherence, where the correlation coefficients ( ${{\text{r}}^{2}}$ ) range between 0.75 and 0.97. The highest correlation for mixed deciduous tree stands was found during leaf-off period with ${{\text{r}}^{2}}$ ranging from 0.87 to 0.94, whereas leaf-on period resulted in ${{\text{r}}^{2}}$ from 0.58 to 0.75. Strong correlations were also found for spruce trees with ${{\text{r}}^{2}}$ between 0.54 and 0.83. Moreover, a simple semiempirical model based on random volume over ground model framework was constructed to describe the relation between the forest height and interferometric coherence. Also, the seasonal variability of the correlation was studied. Our results demonstrate that under Northern-European conditions, seasonal changes have a significant effect for deciduous trees as standard deviations dropped from 1.34–1.78 m during leaf-off conditions to 2.22–3.16 m for leaf-on conditions. Thus, height estimation of deciduous stands requires leaf-off conditions for accurate coherence-based height retrieval. Correlation coefficients for pine stands were unvarying across different weather conditions and least affected by the season. The observed strong sensitivity of interferometric coherence to forest height makes it feasible for estimating canopy height for boreal and deciduous forests in both summer and winter conditions. The estimation algorithm works best for coniferous forests.

Mercury in coniferous and deciduous upland forests in northern New England, USA: implications of climate change

Abstract. Climatic changes in the northeastern US are expected to cause coniferous stands to transition to deciduous stands over the next hundred years. Mercury (Hg) sequestration in forest soils may change as a result. In order to understand potential effects of such a transition, we studied aboveground vegetation and soils at paired coniferous and deciduous stands on eight mountains in Vermont and New Hampshire, USA. Organic horizons at coniferous stands accumulated more total Hg (THg; 42 ± 6 g ha−1) than deciduous stands (30 ± 4 g ha−1). Total Hg pools in the mineral horizons were similar for coniferous (46 ± 8 g ha−1) and deciduous stands (45 ± 7 g ha−1). Soil properties (C, % clay, and pH) explained 56 % of the variation in mineral soil Hg concentration when multiply regressed. Foliar and bole wood Hg concentrations were generally greater for coniferous species than deciduous species. Using allometric equations, we estimated that aboveground accumulation of Hg in foliage and woody biomass was similar between vegetation types but that coniferous stands have significantly smaller annual litterfall fluxes (0.03 g ha−1 yr−1) than deciduous stands (0.24 g ha−1 yr−1). We conclude that organic horizon Hg accumulation is influenced by vegetation type but mineral horizon Hg accumulation is primarily controlled by soil properties. Further investigations into the effect of vegetation type on volatilization, atmospheric deposition, and leaching rates are needed to constrain regional Hg cycling rates.

Edge effects on the lichen genus Lobaria in Atlantic Canadian Forests

Clear-cut or mosaic forestry practices are known to reduce biodiversity in harvested areas, but the biodiversity in the remaining adjacent forests is also affected. Interior parts of the forest that become edge have increased light, wind, and temperature, and a decrease in moisture. Species with a narrow range of tolerance to environmental change are most affected. To better understand this ‘edge effect’ in the Acadian Forest, 20 mature deciduous stands in northeastern New Brunswick were examined that were adjacent to clear-cuts ranging from 6–11 years old. We used lichens as our bioindicators and selected the genus Lobaria because it is particularly sensitive to disturbance, but also common in mature deciduous forests of this region. Three Lobaria species that are known to occur in the Acadian Forest were examined: L. pulmonaria, L. quercizans, and L. scrobiculata. Canopy closure, temperature, and presence data were recorded at the forest edge and at the first occurrence of any of these three species alo...

Transforming Abandoned Farm Fields to Conifer Plantations Reduces Ruffed Grouse Density

Abstract Natural forests likely will be unable to fulfill society’s needs sustainably for wood fiber in the near future. In an attempt to meet increasing demands while protecting intact forests, producers have increasingly considered alternative sources of timber, such as intensively managed plantations. In regions that are economically dependent on forest harvesting, abandoned farm fields are often targeted for conversion to intensive coniferous plantations. These sites are generally in an early successional stage that is dominated by deciduous stands, which provide an important habitat type for several game species, including ruffed grouse (Bonasa umbellus). Therefore, conversion could represent a loss of habitat for this species and several others that are associated with early successional deciduous stages. We conducted grouse drumming surveys in northwestern Quebec, Canada to evaluate the effects of transforming old fields into conifer plantations on ruffed grouse by comparing densities between two habitat types: abandoned farm fields (n = 22) and old fields converted to conifer plantations (n = 19). To correct any audibility bias between habitat types, we located all drumming males that were heard at each site. We then analyzed the number of individuals that were detected in the sites with repeated count models. Our results show that overall drumming males avoided plantations. Overhead cover increased drumming male densities in both habitat types, whereas lateral cover increased drumming grouse densities only in plantations. The density of deciduous stems and fruit-bearing stems also had a tendency to increase drumming male densities, but their effects were marginal. Most ruffed grouse in abandoned farm fields used piles of woody debris on the ground as drumming structures rather than large logs or rock outcrops. Our results suggest that plantations do not have the vegetative cover and quantity of food stems necessary to support high ruffed grouse densities during the drumming season and that conversion of abandoned farm fields to coniferous plantations may exert negative cascading effects for reproduction and population growth.

Monitoring seasonal and diurnal changes in photosynthetic pigments with automated PRI and NDVI sensors

Abstract. The vegetation indices normalized difference vegetation index (NDVI) and photochemical reflectance index (PRI) provide indicators of pigmentation and photosynthetic activity that can be used to model photosynthesis from remote sensing with the light-use-efficiency model. To help develop and validate this approach, reliable proximal NDVI and PRI sensors have been needed. We tested new NDVI and PRI sensors, "spectral reflectance sensors" (SRS sensors; recently developed by Decagon Devices, during spring activation of photosynthetic activity in evergreen and deciduous stands. We also evaluated two methods of sensor cross-calibration – one that considered sky conditions (cloud cover) at midday only, and another that also considered diurnal sun angle effects. Cross-calibration clearly affected sensor agreement with independent measurements, with the best method dependent upon the study aim and time frame (seasonal vs. diurnal). The seasonal patterns of NDVI and PRI differed for evergreen and deciduous species, demonstrating the complementary nature of these two indices. Over the spring season, PRI was most strongly influenced by changing chlorophyll : carotenoid pool sizes, while over the diurnal timescale, PRI was most affected by the xanthophyll cycle epoxidation state. This finding demonstrates that the SRS PRI sensors can resolve different processes affecting PRI over different timescales. The advent of small, inexpensive, automated PRI and NDVI sensors offers new ways to explore environmental and physiological constraints on photosynthesis, and may be particularly well suited for use at flux tower sites. Wider application of automated sensors could lead to improved integration of flux and remote sensing approaches for studying photosynthetic carbon uptake, and could help define the concept of contrasting vegetation optical types.

Atmospheric inputs and nitrogen saturation status in and adjacent to Class I wilderness areas of the northeastern US.

Atmospheric inputs of N and S in bulk deposition (open collectors) and throughfall (beneath canopy collectors) were measured in and adjacent to two Class 1 wilderness areas of the northeastern US. In general, atmospheric S inputs followed our expectations with throughfall S fluxes increasing with elevation in the White Mountains, New Hampshire and throughfall S fluxes being greater in coniferous than deciduous stands in both sites. In contrast, throughfall N fluxes decreased significantly with elevation. Throughfall NO3 (-) fluxes were greater in coniferous than deciduous stands of Lye Brook, Vermont, but were greater in deciduous than coniferous stands of the White Mountains. We found overlap in the range of values for atmospheric N inputs between our measurements and monitoring data [National Atmospheric Deposition Program (NADP) and Clean Air Status and Trends Network (CASTNET)] for wet and total (wet + dry) deposition at Lye Brook. However, our measurements of total S deposition in the White Mountains and bulk (wet) deposition at both Lye Brook and the White Mountains were significantly lower than NADP plus CASTNET, and NADP data, respectively. Natural abundance (18)O in throughfall and bulk deposition were not significantly different, suggesting that there was no significant biological production of [Formula: see text] via nitrification in the canopy. NO3 (-) concentrations in streams were low and had natural abundance (18)O values consistent with microbial production, demonstrating that atmospheric N is being biologically transformed while moving through these watersheds and that these forested watersheds are unlikely to be N saturated.

Structural and Spatial Characteristics of Old-Growth Temperate Deciduous Forests at Their Northern Distribution Limit

Relic old-growth forests are unique witnesses of long-term forest dynamics that can be used as reference conditions for ecosystem-based forest management. In temperate deciduous forests, catastrophic stand-replacing disturbances are rare, and stand dynamics are controlled by endogenous tree-by-tree replacement. Processes might be different at the northern distribution limit of temperate deciduous forests, because of differences in climate and disturbance regimes. We studied tree species composition, diameter, age, and spatial structures of 11 old-growth temperate deciduous stands across an age gradient. Stand characteristics differed from expectation, based on previous studies that were conducted in the central region of the range of temperate deciduous forests. Instead of increasing with age, tree species richness was higher in stands <120 years old because of the presence of relatively short-lived species such as Abies balsamea and Acer rubrum. All diameter distributions followed a two- or three-parameter Weibull model, instead of a rotated sigmoid. Some age structures showed recruitment pulses, contrary to the expectation of constant recruitment, and the spatial distribution of living trees was mostly random with regard to age and species at assessed distances (<14 m). In the context of ecosystem-based forest management, our results suggest that harvest levels should vary across harvesting blocks and selection silviculture should occasionally include larger, multiple-tree gaps in addition to single-tree gaps.