Stem Counts Research Articles

Habitat Associations of Bottomland Bats, With Focus on Rafinesque's Big-Eared Bat and Southeastern Myotis

ABSTRACT Bottomland forests in the eastern United States are used by bat populations for both roosting and foraging. To quantify habitat characteristics important to bat presence in the Mississippi River alluvial valley, we measured forest habitat variables and related them to bat captures obtained in six management areas located near Jonesboro, Arkansas. Forest measurements included species composition, stem count, canopy height, basal area, canopy coverage and percent vegetative ground coverage for trees found in 120 0.03-ha circular plots from 12 bat capture sites. Principal component analysis was conducted on habitat data, and compared to bat captures by use of multiple regression analysis. Interaction effects due to the nested structure of the sampling design were measured with mixed linear models. We found significant correlations between total bat captures, composed of all captures for eight species and forests of high stem count and vegetative ground cover. Mixed model analysis revealed that Rafin...

Interpretation and topographic compensation of conifer canopy self-shadowing

The self-shadowing of conifer canopies results from the size and arrangement of trees within a stand and is a first-order term controlling radiance from forested terrain at common pixel scales of tens of meters. Although self-shadowing is a useful attribute for forest remote-sensing classification, compensation for the topographic effects of self-shadowing has proven problematic. This study used airborne canopy LiDAR measurements of 80 Pacific Northwest, USA conifer stands ranging in development stage from pre-canopy closure to old-growth in order to model canopy self-shadowing for four solar zenith angles (SZA). The shadow data were compared to physical measurements used to characterize forest stands, and were also used to test and improve terrain compensation models for remotely sensed images of forested terrain. Canopy self-shadowing on flat terrain strongly correlates with the canopy's geometric complexity as measured by the rumple index (canopy surface area/ground surface area) ( R 2 = 0.94–0.87 depending on SZA), but is less correlated with other stand measurements: 95th percentile canopy height ( R 2 = 0.68), mean diameter at breast height (dbh) ( R 2 = 0.65), basal area ha − 1 ( R 2 = 0.18), and canopy stem count ha − 1 ( R 2 = 0.18). The results in this paper support interpretation of self-shadowing as a function of canopy complexity, which is an important ecological characteristic in its own right. Modeling of canopy self-shadowing was used to assess the accuracy of the Sun-Canopy-Sensor (SCS) topographic correction, and to develop a new empirical Adaptive Shade Compensation (ASC) topographic compensation model. ASC used measured shadow (as an estimate of canopy complexity) and the SCS term (to describe the illumination geometry) as independent variables in multiple regressions to determine the topographic correction. The ASC model provided more accurate radiance corrections with limited variation in results across the full range of canopy complexities and incidence angles.

Long-term dynamics of leafy spurge ( Euphorbia esula) and its biocontrol agent, flea beetles in the genus Aphthona

Three flea beetle species ( Aphthona spp.), first introduced into North America in 1988, have come to be regarded as effective biological control organisms for leafy spurge ( Euphorbia esula). The black flea beetles ( Aphthona lacertosa and A. czwalinae) in particular have been shown to cause reductions in leafy spurge stem counts in the northern Great Plains, while the brown flea beetle ( A. nigriscutis) has persisted and spread, but has not been found to be as effective at controlling leafy spurge. The ability of black flea beetles to control leafy spurge in any given year, however, has been found to vary. To better understand the long-term effects of flea beetle herbivory on leafy spurge, we monitored stem counts of leafy spurge and numbers of black and brown flea beetles at three sites on two National Wildlife Refuges in east-central North Dakota, USA, from 1998 to 2006. Brown flea beetle numbers were observed to be negligible on these sites. Over the 9 years of the study, black flea beetles were seen to spread over the three study sites and leafy spurge stem counts declined substantially on two of the three sites. Even at low densities of spurge, black flea beetle populations persisted, a necessary prerequisite for long-term control. We used structural equation models (SEM) to assess the yearly effects of black flea beetles, soil texture, and refuge site on leafy spurge stem counts over this time period. We then used equations developed from the SEM analysis to explore flea beetle–leafy spurge dynamics over time, after controlling for soil texture and refuge. Yearly effect strength of black flea beetles on leafy spurge was found to be modest, largely owing to substantial spatial variability in control. However, simulation results based on prediction coefficients revealed leafy spurge to be highly responsive to increases in flea beetle populations on average.

Cooling and Long-day Lighting Influences Growth and Flowering of Phlox paniculata L. ‘Ice Cap’ Used for Cut Flowers

In two studies, rooted cuttings of Phlox paniculata L. ‘Ice Cap’ (summer phlox) were cooled for 0, 4, 8, 12, or 16 weeks. Plants were forced in a glasshouse averaging 18 °C nights under extended-day and night-interruption lighting from incandescent lamps providing a minimum of 14 μmol·s−1·m−2 at plant level or continuous lighting from metal halide (HID) lamps providing a minimum of 400 μmol·s−1·m−2 at plant level. The influence of cooling duration on forcing days to flower, flowering stem counts, and flowering stem length was evaluated. Cooling plants promoted longer stems, higher flowering stem yields, and decreased days to flower when forced under long days provided by incandescent lamps, but when forced under HID lamps, days to flower for cooled plants were similar to those of noncooled plants regardless of cooling duration. Phlox forced in extended daylighting flowered in fewer days, had longer stems, and produced more flowering stems than those forced in night-interruption lighting. With continuous HID lighting, stem lengths and stems harvested per plant increased in a linear manner as cooling increased from zero to 16 weeks. Stem lengths ranged from 63.6 cm for noncooled plants to 96.3 cm for those receiving 16 weeks cooling, and flowering stem yields ranged from seven stems per plant for noncooled plants to 13 for those cooled 16 weeks. Phlox forced under HID lights flowered in substantially fewer days and had longer stems than those forced under incandescent lamps.

Multi-temporal analysis of high spatial resolution imagery for disturbance monitoring

Mountain pine beetle red attack damage has been successfully detected and mapped using single-date high spatial resolution (< 4 m) satellite multi-spectral data. Forest managers; however, need to monitor locations for changes in beetle populations over time. Specifically, counts of individual trees attacked in successive years provide an indication of beetle population growth and dynamics. Surveys are typically used to estimate the ratio of green (current) attack trees to red (previous) attack trees or G:R. In this study, we estimate average stand-level G:R using a time-series of QuickBird multi-spectral and panchromatic satellite data, combined with field data for three forested stands near Merritt, British Columbia, Canada. Using a ratio of QuickBird red to green wavelengths (Red–Green Index or RGI), the change in RGI (ΔRGI) in successive image pairs is used to estimate red attack damage in 2004, 2005, and 2006, with true positive accuracies ranging from 89 to 93%. To overcome issues associated with differing viewing geometry and illumination angles that impair tracking of individual trees through time, segments are generated from the QuickBird multi-spectral data to identify small groups of trees. These segments then serve as the vehicle for monitoring changes in red attack damage over time. A local maxima filter is applied to the panchromatic data to estimate stem counts, thereby allowing an indication of the total stand population at risk of attack. By combining the red attack damage estimates with the local maxima stem counts, predictions are made of the number of attacked trees in a given year. Backcasting the current year's red attack damaged trees as the previous year's green attack facilitates the estimation of an average stand G:R. In this study area, these retrospective G:R values closely match those generated from field surveys. The results of this study indicate that a monitoring program using a time series of high spatial resolution remotely sensed data (multi-spectral and panchromatic) over select sample locations, could be used to estimate G:R over large areas, facilitating landscape level management strategies and/or providing a mechanism for assessing the efficacy of previously implemented strategies.

Estimating Cephus cinctus Wheat Stem Cutting Damage – Can We Cut Stem Counts?

Abstract In the last decade, the wheat stem sawfly [Cephus cinctus Norton (Hymenoptera: Cephidae)] has resurged as an important pest of wheat in the Canadian prairies and continues to be a chronic pest in the Northern Great Plains of the USA. Ecological and management studies to determine egg and larval infestation, damage and parasitoid attack rates, require laborious dissections of stems collected at various spatial scales. We used a statistical simulation study to determine the minimum number of stems required to estimate these response variables at the level of a sub-sample (e.g., within a plot). The number of stems required to estimate sawfly cutting damage and parasitoid attack to larvae was strongly and negatively related with the response variable. At moderate to high levels of sawfly pressure where the stems cut by larvae exceeds 40%, it is possible to reduce stem counts to 50 stems; however, in the 10% cutting range, up to 200 stems are needed for accurate estimates. These values were similar fo...

Using Stem Count as a Decision Aid in Turning Over Alfalfa Stands

Using Stem Count as a Decision Aid in Turning Over Alfalfa Stands

Using Stem Count as a Decision Aid in Turning Over Alfalfa Stands

Alfalfa stem density can be an indicator of when alfalfa stands no longer have potential for high yield. Studies were conducted at University of Wisconsin Arlington Research Station and River Falls Farm where areas of differing plant density were selected within 1-, 2- and 3-year-old fields of differing varieties each year, for three years. Stem density and yield were determined on the same plot areas for each cutting and plant density was determined at the end of the season. Plant density and stems per plant had little relationship to yield. Stem density below 40 stems/ft² had reduced yield potential.

Short-term disruption of a leafy spurge (Euphorbia esula) biocontrol program following herbicide application

Integrated pest management (IPM) for invasive plant species is being advocated by researchers and implemented by land managers, but few studies have evaluated the success of IPM programs in natural areas. We assessed the relative effects of components of an IPM program for leafy spurge (Euphorbia esula), an invasive plant, at Theodore Roosevelt National Park, North Dakota. Effects of herbicides on leafy spurge abundance and on dynamics of flea beetles (Aphthona spp.) used to control leafy spurge were evaluated over three field seasons following herbicide application. We monitored leafy spurge-infested plots with established flea beetle populations that had received picloram plus 2,4-D in September 1997 or 1998, imazapic in September 1998, versus those with no chemical treatment. Mature stem counts did not differ significantly between treated and untreated plots in 2001, suggesting that leafy spurge stands had recovered from herbicide treatment. Flea beetles were less abundant on plots with a history of herbicide treatment. Structural equation models indicated that in 2000 negative correlations between relative abundances of the two flea beetle species were greater on plots that had received herbicide treatments than on those that had not, but by 2001 no differences were apparent between treated and untreated plots. These results suggest that the most effective component of IPM for leafy spurge at this site is biological control. All herbicide effects we observed were short-lived, but the increased negative correlation between flea beetle relative abundances during 2000 implies that herbicide application may have temporarily disrupted an effective biological control program at this site.

Spatial analysis enhances modelling of a wide variety of traits in forest genetic trials

Spatial analysis of progeny trial data improved predicted genetic responses by more than 10% for around 20 of the 216 variables tested, although, in general, the gains were more modest. The spatial method partitions the residual variance into an independent component and a two-dimensional spatially autocorrelated component and is fitted using REML. The largest improvements in likelihood were for height. Traits that exhibit little spatial structure (stem counts, form, and branching) did not respond as often. The spatial component represented up to 50% of the total residual variance, usually subsuming design-based blocking effects. The autocorrelation tended to be high for growth, indicating a smooth environmental surface, it tended to be small for measures of health, indicating patchiness, and otherwise the autocorrelation was intermediate. Negative autocorrelations, indicating competition, were present in only 10% of diameter measurements for the largest diameter square planted trials, and between nearest trees with rectangular planting at smaller diameters. Bimodal likelihood surfaces indicate that competition may be present, but not dominant, in other cases. Modelling of extraneous effects yielded extra genetic gain only in a few trials with severely asymmetric autocorrelations. Block analysis of resolvable incomplete-block or row–column designs was better than randomized complete-block analysis, but spatial analysis was even better.

Estimating Arundo donax shoot biomass

We developed an equation for estimating Arundo donax shoot dry weight from shoot length. The equation, shoot dry weight (g) = 14.254 (standard error = ±0.275) × shoot height 2 (m), was as effective at explaining a high proportion of total variation in shoot dry weight ( R 2 = 0.90) as more complicated equations containing additional morphometric parameters. Tested against two independent datasets, the equation provided accurate estimates of dry weight for shoots ranging from 0.3 to 7.06 m height (dataset 1, P < 0.0001, R 2 = 0.87, N = 29; dataset 2, P < 0.0001, R 2 = 0.82, N = 192). The equation provides aboveground biomass estimates from stem counts and heights more rapidly than harvest methods.

Growth of Phragmites australis and Phalaris arundinacea in constructed wetlands for wastewater treatment in the Czech Republic

Common reed ( Phragmites australis) and reed canarygrass ( Phalaris arundinacea) are two most commonly used plant species in constructed wetlands for wastewater treatment in the Czech Republic. Growth characteristics of both plants (biomass, stem count, and length) have been measured in 13 horizontal sub-surface flow constructed wetlands since 1992. The results revealed that while Phalaris usually reaches its maximum biomass as early as during the second growing season, Phragmites usually reaches its maximum only after three to four growing seasons. The maximum biomass of both species varies widely among systems and the highest measured values (5070 g m −2 for Phragmites and 1900 g m −2 for Phalaris) are similar to those found in eutrophic natural stands. The shoot count of Phragmites decreases after the second growing season while length and weight of individual shoots increases over time due to self-thinning process. Number of Phalaris shoots is the highest during the second season and then the shoot count remains about the same. Also the shoot length remains steady over years of constructed wetland operation.

Poor recovery of woody vegetation on sand and gravel mines in the Darwin region of the Northern Territory

Summary Sand sheets near Darwin support a distinct heathland vegetation type which includes the habitat of several threatened species. Sand and gravel are extracted from shallow mines in this region. Woody vegetation recovery in 31 small, shallow former sand or gravel mine sites near Darwin that were up to 27 years old was assessed and compared to paired unmined control sites. Recovery in vegetation structure within each mine was calculated as the percentage of that in the control site. Mined sites recovered about 50% of their stem count and canopy cover, but only about 10% of basal area and mature tree count. Gravel mines showed poorer recovery than sand mines. Time since mining had no significant effect on the extent of recovery, but deeper mines had significantly poorer recovery. Only 35% of woody species in sand controls were present in mine sites, and 41% of gravel control species were present in former mine sites. It is unlikely that recovery will significantly improve in coming decades. Sand mining affects about 40 ha of land per year in this region, but is likely to increase in the future. If Darwin expands to a population of 1 million people, and mine sites are not fully rehabilitated, all of the sand‐sheet vegetation in the region could be removed in the next 100 years. Improved rehabilitation and protection is crucial for the conservation of heathland vegetation in this region.

Harvest Recovery of Goldenseal, Hydrastis canadensis L

Goldenseal, Hydrastis canadensis L., is a herbaceous understory plant of the eastern deciduous forest that is harvested from natural populations due to its medicinal value. The objectives of this study were to determine if regrowth from harvest varies between patches and also to relate regrowth to pre-harvest leaf and patch size. We used data from three experimentally harvested natural patches and data on recovery of an illegally harvested patch harvested at the end of the growing season. We found variation in patch regrowth which suggests harvest technique and timing may be important. Experimental rhizome removal during mid-summer resulted in slower recovery of leaf size relative to the patch that was illegally harvested. We found a trend for reduced leaf area 2 y post-harvest relative to that pre-harvest. We also found variation in stem count between patches in response to harvest, which may be due to the pre-harvest size of ramets. The patch with larger pre-harvest ramets showed compensatory growth in the year immediately after harvest while the patches comprised of smaller ramets did not. Our results indicate that response to, and recovery from, harvest varies between patches and that individual ramet leaf size may be a better predictor of patch recovery than stem count. Because regrowth may be affected by harvest timing, an established harvest season may alleviate some harvest pressure on H. canadensis.

Vegetative and structural characteristics of agricultural drainages in the Mississippi Delta landscapes

Agricultural drainage ditches in the Mississippi Alluvial Delta landscape vary from edge-of-field waterways to sizeable drainages. Ditch attributes vary with size, location and maintenance and may aid in mitigation of contaminants from agricultural fields. The goal of this study was to better understand how vegetative characteristics affect water quality in conveyance structures in the context of ditch class and surrounding land use. Characterization of 36 agricultural ditches included presence of riparian buffer strips, water depth, surrounding land use, vegetative cover, and associated aqueous physicochemical parameters. Vegetation was assessed quantitatively, obtaining stem counts in a sub-sample of ditch sites, using random quadrat method. Physical features varied with ditch size and vegetative diversity was higher in larger structures. Polygonum sp. was the dominant bed vegetation and was ubiquitous among site sizes. Macrophytes varied from aquatic to upland species, and included Leersia sp. and upland grasses (Poaceae family) in all drainage size classes. Percent cover of bed and bank varied from 0 to 100% and 70 to 100%, respectively, and highest nutrient values were measured in sites with no buffer strips. These conveyance structures and surrounding buffer zones are being ranked for their ability to reduce excess nutrients, suspended solids, and pesticides associated with runoff.

Temporal dynamics of leafy spurge (Euphorbia esula) and two species of flea beetles (Aphthona spp.) used as biological control agents

The goal of this study was to evaluate the biological control program of leafy spurge (Euphorbia esula) in a large natural area, Theodore Roosevelt National Park, western North Dakota, USA. Aphthona lacertosa and Aphthona nigriscutis have been released at more than 1800 points in the 18,600-ha South Unit of the park beginning in 1989; most releases have occurred since 1994. We established permanent vegetation plots throughout the infested area of the park and determined stem counts and biomass of leafy spurge and abundance of the two flea beetle species at these plots each year from 1999 to 2001. Both biomass and stem counts declined over the 3 years of the study. Both species of flea beetle are well established within the park and have expanded into areas where they were not released. A. nigriscutis was more abundant than A. lacertosa in the grassland areas we surveyed, but in all other habitats abundances were similar. Using structural equation models, only A. lacertosa could be shown to have a significant effect on counts of mature stems of leafy spurge. A. nigriscutis numbers were positively correlated with stem counts of mature stems. Previous year’s stem counts had the greatest influence on change in stem counts over each 2-year time step examined with structural equation models.

Influence of Fusing Lidar and Multispectral Imagery on Remotely Sensed Estimates of Stand Density and Mean Tree Height in a Managed Loblolly Pine Plantation

Abstract Stereo aerial photography has long been used to measure tree density and height photogrammetrically. Recent attempts have been made to locate and measure trees automatically in high-resolution digital imagery. This study used small-footprint lidar (1.057 µm, 1 mrad divergence, 0.67 m footprint) and high-resolution (0.61 m) multispectral (550, 675, 700, and 800 nm) data sets to estimate stem counts and tree heights in 15-yr-old loblolly pine stands. A data fusion process was used to combine the datasets. Tree identification accuracy and mean height estimation derived from the separate and fused data sets were compared against field data. Tree identification was more accurate using spectral data (78.6% and 92.4%) than lidar data (64.7% and 87.3%) within the two planting densities, respectively. The fused dataset improved accuracy of tree identification over the single-dataset approaches (83.5% and 94.8%). Plot-level mean height of lidar-located trees provided the best estimates of mean field height (average difference = 0.15 m). Missed trees for all methods were shorter than mean field height by up to 3.03 m (fused data). These results indicate fusion of spectral and lidar data will likely improve estimates of mean tree height and stem density. Increased lidar posting density is identified as a key factor to improve tree recognition and measurement. FOR. SCI.49(3):457–466.

Use of Native Forest and Eucalyptus Plantations by Eleutherodactylus Frogs

We examined population densities, movements, and habitat use of common coqui (Eleutherodactylus coqui), the most common and widespread species of frog in Puerto Rico, in native forest and eucalyptus plantations in 2 forest reserves of the Cordillera Central between July 1997 and June 1998. We established 4 grids of bamboo retreat sites on stands of native forest and eucalyptus plantations in each reserve. We established sampling points within trapping grids to quantify vegetation and determine habitat use. Sampling was conducted during the wet and dry seasons. We used mark-recapture for population estimation. Population estimates and maximum distances moved were determined using program CAPTURE. During the dry season, common coqui population densities were similar in 3 of the 4 study grids, but 1 eucalyptus site had significantly lower densities. We found no differences in adult frog density among study sites during the wet season. Horizontal movements differed between forests, albeit not significantly. Our results indicate that plant species richness did not affect common coqui density. Coqui density was influenced more by vegetation structure than by plant species composition. Five habitat variables (midstory epiphyte load, midstory stem count, ground-cover stem count, total epiphyte load, total basal area) were correlated with adult common coqui density. Eucalyptus plantations in montane regions of Puerto Rico provide suitable habitat for the common coqui. However, suitability may be linked to threshold basal area levels of 18-28 m 2 /ha.

Structural change detection in a disturbed conifer forest using a geometric optical reflectance model in multiple-forward mode

Geometric optical reflectance models provide a physical linkage between image data and forest structure. We developed a "multiple-forward-mode" pseudoinversion modeling approach to produce structural lookup tables for Landsat Thematic Mapper images before and after 1993 partial harvests in New Brunswick, Canada. Modeling results validated for stand density, crown radius, and stem counts enabled simple forest structural change detection.

Generalized additive modelling and zero inflated count data

This paper describes a flexible method for modelling zero inflated count data which are typically found when trying to model and predict species distributions. Zero inflated data are defined as data that has a larger proportion of zeros than expected from pure count (Poisson) data. The standard methodology is to model the data in two steps, first modelling the association between the presence and absence of a species and the available covariates and second, modelling the relationship between abundance and the covariates, conditional on the organism being present. The approach in this paper extends previous work to incorporate the use of Generalized Additive Models (GAM) in the modelling steps. The paper develops the link and variance functions needed for the use of GAM with zero inflated data. It then demonstrates the performance of the models using data on stem counts of Eucalyptus mannifera in a region of South East Australia.