Seedling Stands Research Articles

Seed physiological traits and environmental factors influence seedling establishment of vegetable soybean (Glycine max L.).

Edamame (Glycine max (L.) Merr.), a specialty soybean prized for its nutritional value and taste, has witnessed a surge in demand within the U.S. However, subpar seedling stands have hindered its production potential, necessitating increased inputs for farmers. This study aims to uncover potential physiological factors contributing to low seedling emergence in edamame. We conducted comprehensive assessments on thirteen prominent edamame genotypes alongside two food-grade and two grain-type soybean genotypes, focusing on germination and emergence speed in both laboratory and field settings. Additionally, we employed single electrical conductivity tests and identified and quantified seed leachate components to distinguish among soybean types. Furthermore, using a LabField™ simulation table, we examined seed emergence across a wide soil temperature range (5°C to 45°C) for edamame and other soybean types. All seeds were produced under the same environmental conditions, harvested in Fall 2020, and stored under uniform conditions to minimize quality variations. Our findings revealed minimal divergence in emergence percentages among the seventeen genotypes, with over 95% germination and emergence in laboratory conditions and over 70% emergence in the field. Nonetheless, edamame genotypes typically exhibited slower germination speeds and higher leachate exudates containing higher soluble sugars and amino acids. Seed size did not significantly impact total emergence but was negatively correlated with germination and emergence speed, although this effect could be mitigated under complex field conditions. Furthermore, this study proposed differences that distinguish edamame from other soybean types regarding ideal and base temperatures, as well as thermal time. The finds offer valuable insights into edamame establishment, potentially paving the way for supporting local edamame production in the U.S.

Understorey structural complexity mediated by plantation management as a driver of predation events on potential eucalypt pests

Current forest management aims to reduce the economic and environmental impact of pests on forest ecosystem productivity and to develop sustainable control approaches. The enemies hypothesis states that more diverse plant communities support a greater number and diversity of predators and parasitoids leading to a reduction in pest damage via top-down control. In forests, research on the enemies hypothesis typically focuses on tree species diversity. Here, we modify this hypothesis to determine how structural complexity of the forest understorey, as mediated by management, influences the abundance of predators and predation events on potential forest insect pests. To test this, we studied Eucalyptus sp. plantations managed under two approaches of tree establishment, hypothesising that those managed under the less disturbed system of regrowth (regeneration from clear cut stumps) will have greater vegetation structural complexity, predator abundance and predation events (as an indirect measure of predation rate) than the more disturbed seedling planting system. In six stands of each management type, we measured vegetation understorey layers (ground-, shrub- and sub-canopy cover), predator abundance (insectivorous birds, spider web counts) and predation events (artificial larvae attacks, spider web prey items).Vegetation structural complexity, abundance of insectivorous birds and spider webs, and artificial larvae attacks and web prey items were all greater in the regrowth than in the seedling stands. Path analysis evidenced direct support for our modified enemies hypothesis for birds, the regrowth management with low disturbance levels after clearcutting promotes both predator abundance and predation events via increased vegetation structural complexity. However, for spiders the increase in web abundance and predation events was directly and positively associated with regrowth management, but there was no indirect link via vegetation structural complexity, suggesting other factors driven by forest management are important.Manipulative experiments explicitly exploring the cause-and-effect relationship between predation rates and herbivory rates and consideration of the economic implications of the different approaches are required before changes to management are implemented. Our study agrees with the overarching paradigm in sustainable forest management that promotion of structural complexity will be beneficial to biodiversity, ecosystem function and resilience.

First report of seedling damping off in forage ryegrass caused by Pythium aphanidermatum and P. periilum in Japan.

Italian ryegrass (Lolium multiflorum Lam.) and perennial ryegrass (L. perenne L.) are important for hay fields and grazing lands across Japan, with nearly 70,000 ha production, the largest share in forage grass cultivation. In August 2018, damping off of seedlings of both species was observed about 2wk after seeding in Tochigi Prefecture, central region of Japan. Roots were brown and decayed drastically with browning of basal stem. Nearly 90% of the row seedling stands were eradicated in some fields, especially ones seeded from August to early September, when the soil and air temperatures were around 25-30 ˚C. Six Pythium-like isolates were obtained by isolation from surface-sterilized diseased hypocotyls (1-2cm) placed on water agar. Six isolates were purified as single hyphal tips and deposited at the NARO genebank (https://www.gene.affrc.go.jp/index_en.php), with accession no. MAFF101946-101951. Two of them, MAFF101946 and 101948 were used for detailed study. The isolates were grown in the dark on clarified V8 juice agar for 10 days to produce oogonia. The oogonia of MAFF101946 were globose, colorless, smooth, 21 to 30 µm in size, and had 1(- 2) antheridia. Oospores were mostly aplerotic, and oogonia walls were 1.1 to 2.3 µm thick. The oogonia of MAFF101948 were globose, colorless, smooth, 19 to 27 µm in size, and had 2-5 antheridia. Oospores were mostly plerotic, and oogonia walls were 1.7 to 4.2 µm thick. The morphology of the MAFF101946 matched that of P. aphanidermatum (Edson) Fitzp.(abbr. PA) and the MAFF101948 matched P. periilum Drechsler (abbr. PP) (Van der Plaats-Niterink, 1981). DNA sequences of cox1 (Robideau et al, 2011) and rDNA-ITS regions (White et al,1990) of each isolate were analyzed. The cox1 sequences of the MAFF101946 and 101948 (GenBank Accession No. LC548774 and LC548775) matched 100% (680/680 bp) with that of PA (HQ708486) and PP (HQ708781), respectively. The rDNA-ITS sequence of the MAFF101946, LC592700, matched PA (772/777 bp; HQ643439), and the MAFF101948 (LC592701) matched PP (HQ643740), with 99% similarity (764/773 bp). The optimal growth temperature was 35 ˚C for both. Their pathogenicity was confirmed by seeding two Italian (cv. Inazuma and Minamiaoba) and perennial (cv. Yatsuyutaka and Natsugoshi-pere) ryegrasses cultivars in cell trays containing commercial potting mixture inoculated with the isolates. Barley grains autoclaved with a half volume of water and incubated with each isolate at 25 ˚C for about 2 wk were added to inoculate the potting mixture (5%, v/v). Separate trays were used for each isolate to avoid cross-contamination, sown with 60 seeds were sown per cv. and the trays were placed in a light thermostat chamber under the daily cycle of 16 hr light at 30 ˚C and 8 hr dark at 25 ˚C. About 3 wk later, seedlings on the inoculated soil exhibited the symptoms, but not in control (no inoculum) plots. Both inoculated organisms were re-isolated from the diseased plants to confirm their pathogenicity. PA was more aggressive with grater percent damping off compared to PP. Both species are known as pathogens of diverse plants including grasses and legumes (Abad et al, 1994; Ao et al, 2018), but to our knowledge, this is the first report of seedling damping off caused by these Pythium species in forage ryegrass in Japan. With the increased duration of hot, humid condition across temperate regions due to global warming, the damping off may become a problem in hay fields and pasture and resistance breeding for these pathogens may be needed.

Using Leaf-Off and Leaf-On Multispectral Airborne Laser Scanning Data to Characterize Seedling Stands

Information from seedling stands in time and space is essential for sustainable forest management. To fulfil these informational needs with limited resources, remote sensing is seen as an intriguing alternative for forest inventorying. The structure and tree species composition in seedling stands have created challenges for capturing this information using sensors providing sparse point densities that do not have the ability to penetrate canopy gaps or provide spectral information. Therefore, multispectral airborne laser scanning (mALS) systems providing dense point clouds coupled with multispectral intensity data theoretically offer advantages for the characterization of seedling stands. The aim of this study was to investigate the capability of Optech Titan mALS data to characterize seedling stands in leaf-off and leaf-on conditions, as well as to retrieve the most important forest inventory attributes, such as distinguishing deciduous from coniferous trees, and estimating tree density and height. First, single-tree detection approaches were used to derive crown boundaries and tree heights from which forest structural attributes were aggregated for sample plots. To predict tree species, a random forests classifier was trained using features from two single-channel intensities (SCIs) with wavelengths of 1550 (SCI-Ch1) and 1064 nm (SCI-Ch2), and multichannel intensity (MCI) data composed of three mALS channels. The most important and uncorrelated features were analyzed and selected from 208 features. The highest overall accuracies in classification of Norway spruce, birch, and nontree class in leaf-off and leaf-on conditions obtained using SCI-Ch1 and SCI-Ch2 were 87.36% and 69.47%, respectively. The use of MCI data improved classification by up to 96.55% and 92.54% in leaf-off and leaf-on conditions, respectively. Overall, leaf-off data were favorable for distinguishing deciduous from coniferous trees and tree density estimation with a relative root mean square error (RMSE) of 37.9%, whereas leaf-on data provided more accurate height estimations, with a relative RMSE of 10.76%. Determining the canopy threshold for separating ground returns from vegetation returns was found to be critical, as mapped trees might have a height below one meter. The results showed that mALS data provided benefits for characterizing seedling stands compared to single-channel ALS systems.

Modelling the effect of moose Alces alces population density and regional forest structure on the amount of damage in forest seedling stands.

BACKGROUNDMoose (Alces alces L.) populations and moose damage in forests are debated in Nordic countries with dense moose populations. Moose populations and food resources vary greatly, both spatially and temporally, and reliable data covering both variables simultaneously at the same scale have seldom been available. We modelled the effect of moose population density and forest resources on the area of moose damage at regional scale, referring to moose management areas (MMA). Forest data and moose damage data originated from the Finnish National Forest Inventory, and the moose population data came from a Bayesian moose model. For modelling, average values of moose population, damage and forest variables were calculated for the periods 2004–2008 and 2009–2013 for each MMA. The MMAs were further classified into one of four larger geographical zones. The area of moose damage was used as a dependent variable, and the proportions of different types of forests and moose population densities per land area or area of seedling stands as explanatory variables. The relationships were modelled with a linear mixed‐effects model with an exponential spatial correlation structure.RESULTSThe area of moose damage was best explained by total forest area, proportions of plantations and mature forests, and moose population density per land area or the proportion of plantations. There were differences among the biogeographical zones in how different variables explained the amount of damage.CONCLUSIONThe results provide tools for analyzing the regional effects of moose population density and the amount of food resources on the amount of moose damage. This information can be used in reconciling sustainable moose population levels and the amount of damage.

Productivity in Mechanizing Early Tending in Spruce Seedling Stands

According to National Forest Inventory data, there is an urgent need for tending seedling stands of at least 700,000 ha and a need for 1 million ha in the next few years in Finland. The motivation for forest owners to conduct pre-commercial silvicultural operations is low due to the associated high costs. Especially the costs of tending and clearing operations after the regeneration of the stand have been increasing. In addition, the availability of labor is a restricting factor due to the high seasonality of silvicultural works. In the 2000s, several solutions for the mechanization of tending have been proposed. These are based on the use of harvester or a forwarder as a base machine. Typically, light weight base machines are favored to reduce the hourly cost of operations and the impacts on the remaining seedlings. There have been challenges with the high speed of the cutting device, which increases the risk of damages to the head and the ignition of forest fires when the circular saw or chain hits stones, for example. In addition, the chain can become dislocated due to bending forces caused by stumps. Cutlink has presented a low RPM solution based on rotating cone-shaped shears that cut 50–100 cm wide corridors between and around seedlings. In this study, the productivity of mechanized tending with Cutlink´s device compared to manual tending was evaluated in spruce seedling stands in central Finland. The productivity, fuel consumption and quality of the seedling stand after the operation were measured. In early tending, the productivity of motor manual tending was notably better than when using the Cutlink device. Crucial factors for the competitiveness of a mechanized alternative include the annual working hours and finding suitable working areas for the machine. Additional work for the device and base machine can also be found in the clearing of forest road sides.

Characterizing Seedling Stands Using Leaf-Off and Leaf-On Photogrammetric Point Clouds and Hyperspectral Imagery Acquired from Unmanned Aerial Vehicle

Seedling stands are mainly inventoried through field measurements, which are typically laborious, expensive and time-consuming due to high tree density and small tree size. In addition, operationally used sparse density airborne laser scanning (ALS) and aerial imagery data are not sufficiently accurate for inventorying seedling stands. The use of unmanned aerial vehicles (UAVs) for forestry applications is currently in high attention and in the midst of quick development and this technology could be used to make seedling stand management more efficient. This study was designed to investigate the use of UAV-based photogrammetric point clouds and hyperspectral imagery for characterizing seedling stands in leaf-off and leaf-on conditions. The focus was in retrieving tree density and the height in young seedling stands in the southern boreal forests of Finland. After creating the canopy height model from photogrammetric point clouds using national digital terrain model based on ALS, the watershed segmentation method was applied to delineate the tree canopy boundary at individual tree level. The segments were then used to extract tree heights and spectral information. Optimal bands for calculating vegetation indices were analysed and used for species classification using the random forest method. Tree density and the mean tree height of the total and spruce trees were then estimated at the plot level. The overall tree density was underestimated by 17.5% and 20.2% in leaf-off and leaf-on conditions with the relative root mean square error (relative RMSE) of 33.5% and 26.8%, respectively. Mean tree height was underestimated by 20.8% and 7.4% (relative RMSE of 23.0% and 11.5%, and RMSE of 0.57 m and 0.29 m) in leaf-off and leaf-on conditions, respectively. The leaf-on data outperformed the leaf-off data in the estimations. The results showed that UAV imagery hold potential for reliably characterizing seedling stands and to be used to supplement or replace the laborious field inventory methods.

Assessing spectral measures of post-harvest forest recovery with field plot data

Information regarding the nature and rate of forest recovery is required to inform forest management, monitoring, and reporting activities. Delayed establishment or return of forests has implications to harvest rotations and carbon uptake, among others, creating a need for spatially-explicit, large-area, characterizations of forest recovery. Landsat time series (LTS) has been demonstrated as a means to quantitatively relate forest recovery, noting that there are gaps in our understanding of the linkage between spectral measures of forest recovery and manifestations of forest structure and composition. Field plots provide a means to better understand the linkage between forest characteristics and spectral recovery indices. As such, from a large set of existing field plots, we considered the conditions present for the year in which the co-located pixel was considered spectrally recovered using the Years to Recovery (Y2R) metric. Y2R is a long-term metric of spectral recovery that indicates the number of years required for a pixel to return to 80% of its pre-disturbance Normalized Burn Ratio value. Absolute and relative metrics of recovery at 5 years post-disturbance were also considered. We used these three spectral recovery metrics to predict the stand development class assigned by the field crew for 284 seedling plots with an overall accuracy of 73.59%, with advanced seedling stands more accurately discriminated (omission error, OE = 15.74%) than young seedling stands (OE = 49.84%). We then used field-measured attributes (e.g. height, stem density, dominant species) from the seedling plots to classify the plots into three spectral recovery groups, which were defined using the Y2R metric: spectral recovery in (1) 1–5 years, (2) 6–10 years, or (3) 11–15 years. Overall accuracy for spectral recovery groups was 61.06%. Recovery groups 1 and 3 were discriminated with greater accuracy (producer’s and user’s accuracies > 66%) than recovery group 2 (< 50%). The top field-measured predictors of spectral recovery were mean height, dominant species, and percentage of stems in the plot that were deciduous. Variability in stand establishment and condition make it challenging to accurately discriminate among recovery rates within 10 years post-harvest. Our results indicate that the long-term metric Y2R relates to forest structure and composition attributes measured in the field and that spectral development post-disturbance corresponds with expectations of structural development, particularly height, for different species, site types, and deciduous abundance. These results confirm the utility of spectral recovery measures derived from LTS data to augment landscape-level assessments of post-disturbance recovery.

Instrumental analysis of health status of Quercus petraea stands in the Carpathian Basin

Abstract Numerous prognoses indicate that climate change will manifest itself in extreme climatic conditions. Therefore, it will be of high importance to know in what extent can plant communities and certain species adapt to altering environmental conditions. Our examinations were implemented in stands of sessile oak common in the Carpathian Basin. The reason behind it has been that, according to climatic models, the realized niche of this species can be reduced by 80% in some regions by 2050. Examinations were made in 3 points of an approximately 400 km long (East-West) transsect crossing the Carpathian Basin: 3 submontane regions of a subatlantic, a continental and a subcarpathian mountain were involved with 5 age groups in each regions. Health status examinations of sessile oaks have been completed by using FAKOPP 3D acoustic tomograph. Among the three venues trees of the subatlantic area were the healthiest; here, the 100 years old age group showed the lowest deterioration, only 0.68%. The most severely deteriorated stands occur in the continental region where the value in the 60 years old age group reached 4.24%. It seems that, besides annual precipitation, the method of planting also influences the health status of stands, since considerable differences could be observed between coppice and seedling stands.

Efficacy of bio-agents against damping off in solanaceous crops under nursery conditions

The study was conducted to assess efficacy of Trichoderma harzianum and Pseudomonas fluorescens against damping off in tomato and brinjal seedlings during Kharif season. The investigation was performed as on farm trials on farmers’ field over three years viz., 2013-14, 2014-15 and 2015-16. T. harzianum and P. fluorescens were applied in combination of soil+seed treatment. Talc based formulation of both bio control agents were used @ 10 g kg -1 in seed treatment and 100 g m -2 in soil treatment. Results indicated that the combination of soil+seed treatment with T. harzianum was gives maximum seedling stands (84.15%) with minimum mortality (15.85%) in brinjal followed by soil+seed treatment with mixture of T. harzianum and P. fluorescens (78.30%) and soil+seed treatment with P. fluorescens alone (69.68%) whereas, in control plot treated with Carbendazim 50 WP (soil+seed) recorded less seedling stand (41.50%). In case of tomato, application of T. harzianum as soil+seed gave the maximum seedling stand (80.32%) followed by soil+seed treatment with combination of T. harzianum and P. fluorescens (73.45%) and P. fluorescens alone (58.64%) while seed+soil treatment with Carbendazim 50 WP given minimum seedling stand (42.01%). Consortium of T. harzianum and P. fluorescens significantly increased the growth and yield attributes of brinjal and tomato crops i.e. plant height, number of branches plant -1 , number of fruit plant -1 and fruit yield ha -1 followed by along Trichoderma and Pseudomonas. The study showed that T. harzianum and P. fluorescens are the potential bio control agents as compare to Carbendazim 50 WP and can be used effectively for the management of damping off in seedlings in nursery.

Detection of the need for seedling stand tending using high-resolution remote sensing data

Seedling stands are problematic in airborne laser scanning (ALS) based stand level forest management inventories, as the stem density and species proportions are difficult to estimate accurately using only remotely sensed data. Thus the seedling stands must still be checked in the field, which results in an increase in costs. In this study we tested an approach where ALS data and aerial images are used to directly classify the seedling stands into two categories: those that involve tending within the next five years and those which involve no tending. Standard ALS-based height and density features, together with texture and spectral features calculated from aerial images, were used as inputs to two classifiers: logistic regression and the support vector machine (SVM). The classifiers were trained using 208 seedling plots whose tending need was estimated by a local forestry expert. The classification was validated on 68 separate seedling stands. In the training data, the logistic model’s kappa coefficient was 0.55 and overall accuracy (OA) 77%. The SVM did slightly better with a kappa = 0.71 and an OA = 86%. In the stand level validation data, the performance decreased for both the logistic model (kappa = 0.38, OA = 71%) and the SVM (kappa = 0.37, OA = 72%). Thus our approach cannot totally replace the field checks. However, in considering the stands where the logistic model predictions had high reliability, the number of misclassifications reduced drastically. The SVM however, was not as good at recognizing reliable cases.

Capercaillie (Tetrao urogallus) habitat characteristics in north-boreal Finland

This study aimed to identify tools for taking capercaillie habitats into consideration in forest management. This would provide new alternatives for ecologically more sustainable forest management. Capercaillie summer and winter locations, from wildlife monitoring counts (1998–2004) in northern Finland, and reference, non-capercaillie locations were combined with forest planning data, and the area proportions of different landscape classes in an 800-m radius circle surrounding capercaillie and reference locations were compared. Thinning stands (in summer and winter) and spruce mires (in summer) were more abundant in capercaillie habitats than in reference landscapes, whereas e.g. seedling stands, mature stands and waste land areas were less abundant. The relative habitat use was highest in mean tree diameter (DBH) classes from 10.5 to 14.5 cm in summer habitats of adult capercaillie in heath forests, whereas in peatland forests, in brood habitats and in winter habitats it peaked in diameter classes 14.5 to 18.5 cm. The tree layer density was positively associated with the relative habitat use. A trend of lower habitat use was detected in the largest diameters (17–40 cm) in comparison to middle-sized diameters (10–16 cm) in heath forests, but not in peatland forests. Relatively young managed forests (age 30–40 years or more) can form suitable capercaillie habitats in north-boreal forests. However, this suitability is not necessarily permanent. Understorey management, longer rotations and multicohort forest management are suitable tools for capercaillie habitat management, because they can increase the available cover close to the ground, canopy cover, overall forest cover at the landscape scale and bilberry cover.

Short- and long-term effects of site preparation, fertilization and vegetation control on growth and stand development of planted loblolly pine

Short- and long-term effects of high and low site preparation intensity, fertilization at planting and vegetation control on growth and stand development were examined in a study that was established on six sites in southeastern USA. The study was established in 1979–1980, and growth after the 18th growing season is reported. The high-intensive site preparation improved long-term stand volume growth. Evidence suggests that the main long-term effect of the intensive site preparation was a reduction in competition from hardwoods. Herbicide treatment improved seedling establishment and early growth, but growth during the last period of measurements (14–18 years after planting) were lower in the herbicide-treated plots as compared to plots without herbicide treatment when herbicides were combined with intensive site preparation. Fertilization at planting, in combination with high-intensive site preparation, improved volume growth during the first 10 years after planting, while fertilization at planting in combination with low-intensive site preparation had little effect on volume growth. The hypothesis that low variability in the seedling stage due to intensive site preparation will lead to low variability in the mature stands with a subsequent reduction in self-thinning was examined. The low site preparation intensity had higher coefficient of variations of stem volumes, and higher mortality. However, the difference in mortality was probably partly a result of differences in competition from hardwoods, and it was not possible to separate the importance of reduced variability from reduced competition from hardwoods. Fertilized plots had lower variability than non-treated control plots but there was no significant difference in mortality between the two treatments. Therefore, it was concluded that reduced variability in the seedling stands, as a result of intensive regeneration methods that reduces environmental heterogeneity, reduces the variability in the mature stands. However, it could not be inconclusively proved that lower variability in the mature stands will result in reduced or postponed self-thinning.

Efficacy of resistance inducers, free‐radical scavengers and an antagonistic strain of Pseudomonas fluorescens for control of Rhizoctonia solani AG‐4 in bean and cucumber

Sixteen chemicals from different groups of known resistance inducers were tested as a soil drench in a humosoil : sand mix infested with an isolate of Rhizoctonia solani AG‐4. Among these, 5‐nitrosalicylic acid (2 mM aqueous solution), o‐acetylsalicylic acid (2 mM), 2,6‐dichloroisonicotinic acid (0.25 mM), 2‐aminoisobutyric acid (2 mM) and lichenin (2 mM) controlled pre‐emergence damping‐off and post‐emergence seedling mortality of bean cv. Dufrix, but gave little or weak and variable disease control in cucumber cv. Delikatess. Two‐component mixtures of these five chemicals controlled the disease effectively in bean, mixtures containing 2‐aminoisobutyric acid being the most effective, with seedling stands of up to 94% in infested soil. As none of these five chemicals (≤ 2 mM) reduced mycelial growth of R. solani on PDA plates, induced resistance in seedling tissues is implied in their disease control. Control was augmented in both hosts when any one of the five inducers was applied in a mixture with a cell suspension (1 × 109 cells mL−1) of an antagonistic fluorescent strain of Pseudomonas fluorescens; these mixtures showed additive effects and provided much better disease control in bean than in cucumber. The free‐radical scavengers (antioxidants) ascorbic acid, benzoic acid, gluconic acid lactone and thiourea inhibited R. solani growth in vitro and efficiently controlled both pre‐emergence damping‐off and post‐emergence seedling mortality of bean; ascorbic acid and benzoic acid also offered significant protection in cucumber. However, disease control values were reduced substantially when inducers were applied with antioxidants, because of strong antagonistic interactions in most of these mixtures. Probable mechanisms of disease control by 5‐nitrosalicylic acid, o‐acetylsalicylic acid, 2,6‐dichloroisonicotinic acid, 2‐aminoisobutyric acid and lichenin and their interactions with P. fluorescens and antioxidants are discussed.

Tree Size Dependence of Litter Production, and Above-ground Net Production in a Young Hinoki (Chamaecyparis obtusa) stand

The study was carried out in a 9-year-old hinoki cypress (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.), stand over a span of three years from July 1992 to June 1995, primarily to predict litter production from exteral tree dimensions by combining open-top clothtrap and clipping methods. Litter production was virtually concentrated in October and November. Stem cross-sectional area at the crown base was proved to be the reliable predictor of litter production, and that single regression model was evolved irrespective of year. The regression model had proportional constants of 2.696 × 10−2 and 3.540 × 10−2 kg cm−2 year−1 for leaf litter and total litter production, respectively. Utilizing the model, leaf litter production of the stand was assessed to be 5.04, 5.12, and 4.99, and total litter production to be 6.48, 6.58, and 6.40 Mg ha−1 year−1 for the first, second and third year, respectively. Biomass increment was 6.67, 7.80, and 7.70, tree mortality was 0.15, 0.13, and 0.41, and insect grazing was 0.09, 0.05, and 0.002 Mg ha−1 year−1 for the first, second and third year, respectively. Above-groud net production was therefore 13.39, 14.55, and 14.51, Mg ha−1 year−1, and biomass accumulation ratio (biomass/net production) was 1.86, 2.21, and 2.76 year for the first, second and third year, respectively. Considering data from earlier studies and the results of this study, biomass accumulation ratio, BAR (year), of hinoki stands was best related to above-ground biomass, y (Mg ha−1), using the power function: BAR=0.112 y 0.936. Excluding seedling stands, leaf efficiency (above-ground net production per unit leaf mass) of hinoki stands was 0.91±0.02 (SE) Mg Mg−1 year−1, irrespective of stand biomass or age.

Photosynthetic response of loblolly pine and sweetgum seedling stands to elevated carbon dioxide, water stress, and nitrogen level

Seedling stands of loblolly pine (Pinustaeda L.) and sweetgum (Liquidambarstyraciflua L.) were grown in monoculture or mixed stands for two growing cycles in controlled-environment chambers. Treatments consisted of ambient (408 ppm) and elevated (806 ppm) CO2, concentrations, water-stressed and well-watered conditions, and low (20 kg N/ha) and high (215 kg N/ha) nitrogen application rates. Photosynthesis rates were measured under ambient and elevated cuvette CO2 concentrations for both whole stands and individual seedlings from these stands. Significant interactions between CO2 and water suggested that elevated CO2 concentration compensated for low water availability in individually measured loblolly pine and in whole seedling stands regardless of stand type. Expressing photosynthesis on a soil area versus a leaf-mass basis influenced the photosynthetic rankings of the three stand types relative to one another. Net photosynthetic rates per unit leaf mass were 390 and 880% higher in individually measured seedlings than in whole monoculture stands for loblolly pine and sweetgum, respectively. Lower photosynthetic contributions from lower canopy leaves in whole seedling stands compared with the upper canopy leaves used in individual-seedling measurements were thought to be responsible for lower photosynthetic rates in seedling stands. These results suggest that photosynthetic response is influenced by canopy dynamics that are unaccounted for by individual-seedling measurements of photosynthesis. Differences in photosynthetic response between loblolly pine and sweetgum stands and individuals are thought to be largely due to species-specific differences in canopy light extinction characteristics.

Interference Interactions in Simulated Pine-Hardwood Seedling Stands

Abstract A multiresource factor approach, using biomass allocation patterns and resource-use efficiencies, was employed to investigate interference mechanisms in mixed species tree seedling stands. Seedling mixtures of loblolly pine (Pinus taeda L.) with one of two hardwood tree species, black locust (Robinia pseudoacacia L.) or red maple (Acer rubrum L.), were grown together at close spacing under well-watered and water-stressed conditions in a greenhouse. Pure stands of each species were included as controls. Greatest biomass growth increment was observed in pure hardwood stands, while pure pine stands had the lowest increments. Interference in mixed stands was highly one-sided, with hardwoods suppressing pine growth. Mechanisms or attributes accounting for interference outcomes included higher relative growth rates, increased below-ground allocation of photosynthate, effective display of foliage, and higher resource-use efficiencies of hardwood species. Interference strategies differed for hardwood species. Black locust could be classified as an uptake specialist with a high relative growth rate and a low root:shoot ratio. Red maple was a resource-use specialist, exhibiting high internal resource-use efficiencies for light, soil moisture, and nitrogen. FOR. SCI. 39(2):383-395.

Establishment of Bottomland Oak Plantations on the Yazoo National Wildlife Refuge Complex

Abstract Stocking, height and diameter growth, and invasion of both herbaceous and woody plant species are reported for 5 direct seeded and 5 planted seedling stands of bottomland oaks, all of which were between 4 and 8 years old. Stocking was generally higher in the planted seedling stands. Both height and diameter growth were substantially higher in the planted seedling stands. Low stocking and poor growth, especially for the direct seeded stands, was associated with medium-textured soils and a heavy cover of Johnson grass (Sorghum halepense) and goldenrod (Solidago altissima). Invasion of woody species was heavily dominated by light-seeded species, and was highest in stands close to mature trees. South. J. Appl. For. 14(4):206-210.

A Simple Competition Assessment System Associated with Intensive Competition Control in Natural Loblolly-Shortleaf Pine Seedling Stands

Abstract A simple competition assessment system was evaluated as part of an intensive competition control study in a natural, even-aged stand of loblolly-short-leaf pine (Pinus taeda L.- P. echinata Mill.) seedlings in southern Arkansas. Four levels of competition control were maintained annuallyfor 3 years as follows: (1) no competition control, (2) woody competition control, (3) herbaceous competition control, and (4) total control of nonpine vegetation. The competition assessment system is based on a correlation of total height to groundline diameter (gld) for loblolly pine seedlingsthat are less than 6 ft tall. The correlation indicated that if seedling gld's are not within + 10 mm of total seedling height (in feet) multiplied by 10, then the seedlings would most likely show a positive growth response to competition control. South. J. Appl. For. 13(1):8-12.

A tentative model for describing the effects of some regenerative process on the properties of natural seedling stands.

A tentative model for describing the effects of some regenerative process on the properties of natural seedling stands.