Ground Cover Biomass Research Articles

CONIFEROUS LEAF-BEARING FOREST BIOMASS ASSESSMENT BY THE EXAMPLE OF THE EDUCATIONAL AND EXPERIMENTAL SOIL AND ECOLOGICAL CENTER OF LOMONOSOV MOSCOW STATE UNIVERSITY “CHASHNIKOVO”

The aim of the work was to assess the contribution of the following components - biomass and mortmass of tree stands, undergrowth, living ground cover, and forest litter - to the total organic matter’s pool of plant community. The object of the study was a territory of coniferous-deciduous forest located in Solnechnogorsk City District of the Moscow region, in which five permanent sample trial plots of 50·50 m were allocated. The greatest contribution to the total organic matter mass of studied plant communities was made by forest stand perennial parts (up to 87%) and forest stand mortmass (up to 14%), and phytomass of deciduous trees in stand containing 32 to 98%, which was connected with incompleteness of forest restoration succession process. The contribution of forest litter was no more than 3%; litter deposit was low (0,18-1,21 kg·m-2), which is not typical for spruce forests, as is the fact that all litter is of the destructive type. Living ground cover in terms of floristic composition and ecological-coenotic structure was typical for the subzone of coniferous-deciduous forests; its contribution to the overall productivity of forest biogeocenosis was insignificant. The spatial intrabiogeocenotic structure of litter reserves and living ground cover biomass distribution was disturbed compared to typical spruce forests due to the high proportion of deciduous species in the forest stand. Deciduous species inclusion in the tree tier, typical of the final stage of formation of a secondary coniferous forest during succession, caused a slight increase in the intensity of the biological cycle, which was indicated in this case by a decrease in the supply of litter and a simplification of their structure. Since the biomass and mortmass of tree stand make the greatest contribution to the sequestration of carbon by forest biogeocenoses, it is these components that require the most detailed assessment during monitoring observations, the purpose of which is to assess the carbon reserves of terrestrial ecosystems.

Responses of Soil Microbial Traits to Ground Cover in Citrus Orchards in Central China

A clear understanding of which factors play an important role in the development of the soil microbial community in orchards will benefit our understanding of ground cover impacts on soil nutrient cycling. Thus, in the present study, grass properties, soil properties, and soil microbial community structure were determined in a citrus orchard after 5 years of management with different types of ground cover (NG: natural grass, LP: monoculture of legumes, and NL: mixed culture of natural grasses and legumes) to evaluate how ground cover biomass and nitrogen-fixing ability drive soil physicochemical and microbial traits. Plant biomass carbon (BC) and nitrogen (BN) were significantly higher in LP and NL than NG and showed a significant (p < 0.01) positive relationship with soil total carbon (TC), NO3−-N (NN), and dissolved organic carbon (DOC) content. In addition, the amount of biologically fixed nitrogen (FixN) showed a significant positive relationship with soil total nitrogen (TN) (p < 0.05) and NH4+-N (AN) content (p < 0.01). We also observed a difference in the soil microbial community structure between plots with and without legumes. The TC and BN were the most influential factors driving bacterial and fungal communities, respectively. Nevertheless, FixN explained less than 9% of the differences in soil bacterial and fungal communities. Our results suggest that grass biomass and FixN are the strong drivers of soil chemical properties, whereas ground cover and soil properties both contribute significantly to the soil microbial community structure.

Multi-platform LiDAR approach for detecting coarse woody debris in a landscape with varied ground cover

ABSTRACT Coarse woody debris (CWD), or fallen logs, is known to be an essential habitat element for many organisms. CWD also supports ecosystem functioning through soil formation, nutrient cycling, and carbon storage. For these reasons, accurate assessments of CWD across landscapes are of interest to many ecologists and landscape managers, but traditional field-based measurements can be time-consuming and sampling strategies may not be representative of entire landscapes. Light detection and ranging (LiDAR) technologies may be able to provide a more rapid assessment of the number and volume of CWD across wide areas. However, most research using LiDAR for forest and woodland inventory assessment has focused on standing wood. Detection accuracy of CWD with LiDAR can be impacted by the point density of LiDAR data, ground layer vegetation, and sensor positioning relative to other vegetation or landscape structural features. We used a high-resolution terrestrial laser scanner (TLS), an unoccupied aerial vehicle (UAV) laser scanner (ULS), and a combination of data from both sensors (i.e. fused data, FLS) to estimate CWD in a grassy woodland ecosystem. The study area comprised plots with different types and amounts of vegetation cover and different types of CWD, both naturally occurring and introduced including dispersed, clumped, or a mixture of both types. This enabled a more detailed exploration of model performance across sensor types, vegetation types, and ground cover biomass. A random forest (RF) classification algorithm and noise removing operations on raster imagery were used to classify CWD. Completeness and correctness accuracy with the developed method were highly variable depending on the data and ground vegetation cover and ranged between 20% and 86%, and 12% and 96%, respectively, in comparison with field data. The LiDAR-derived digital surface model (DSM), surface roughness, and topographic position index were important variables for CWD detection. We found that the detection accuracy of CWD varied with the vegetation type, amount of ground vegetation cover, and LiDAR data. Ground cover density had a strong negative impact on accuracy, particularly for TLS and FLS data.

Ground Cover—Biomass Functions for Early-Seral Vegetation

Vegetation biomass is commonly measured through destructive sampling, but this method is time-consuming and is not applicable for certain studies. Therefore, it is necessary to find reliable methods to estimate vegetation biomass indirectly. Quantification of early-seral vegetation biomass in reforested stands in the United States Pacific Northwest (PNW) is important as competition between the vegetation community and planted conifer seedlings can have important consequences on seedling performance. The goal of this study was to develop models to indirectly estimate early-seral vegetation biomass using vegetation cover, height, or a combination of the two for different growth habits (ferns, forbs, graminoids, brambles, and shrubs) and environments (wet and dry) in reforested timber stands in Western Oregon, USA. Six different linear and non-linear regression models were tested using cover or the product of cover and height as the only predicting variable, and two additional models tested the use of cover and height as independent variables. The models were developed for six different growth habits and two different environments. Generalized models tested the combination of all growth habits (total) and sites (pooled data set). Power models were used to estimate early-seral vegetation biomass for most of the growth habits, at both sites, and for the pooled data set. Furthermore, when power models were preferred, most of the growth habits used vegetation cover and height separately as predicting variables. Selecting generalized models for predicting early-seral vegetation biomass across different growth habits and environments is a good option and does not involve an important trade-off by losing accuracy and/or precision. The presented models offer an efficient and non-destructive method for foresters and scientists to estimate vegetation biomass from simple field or aerial measurement of cover and height. Depending on the objectives and availability of input data, users may select which model to apply.

Carbon Sequestration Potentials of Man-made Grasslands under Different Pattern of Plantation Stands in West Bandung Regency, Indonesia

Alternatives of vegetations to store carbon need to be encouraged considering that forests are threatened by widespread destructions. One such vegetation is grasslands which have the potential for carbon storage and to reduce CO2 concentration in the atmosphere. At present, many enterprises have designed grasslands for many purposes. Grasslands at Cikalong Wetan and Little Farmers, West Bandung Regency were established under different pattern of plantation stands. The purpose of this research was to study the potential of carbon stock in grassland vegetation at these locations. Based on RaCSA method, the tree biomass was determined by nondestructive collection of density and basal area of trees, then calculated by an allometric equation. The ground cover biomass was determined by destructive collection of grass and roots. Total measured biomass was multiplied by 46% to obtain carbon storage. Based on the results, the potential of carbon stock in Little Farmers grassland (159,540 ton ha-1) is higher than in Cikalong Wetan (14,482 ton ha-1). Carbon stored in tree biomass gives the highest contribution to overall carbon stock potential in Little Farmers (94.84%) while carbon stored in below-ground understorey biomass gives the highest contribution in Cikalong Wetan (52.13 %). Different management of grasslands and pattern of plantation stands resulting a different contribution of carbon stock in every carbon pool. In order to maintain the carbon sequestration potentials of these locations, an agroforestry management such as agri-silviculture need to be encouraged. This study gives a comparison of the carbon sequestration potentials between two man-made grassland ecosystems. For many enterprises this study will aid in a management planning of man-made grassland in terms of ecosystem services, that is carbon sequestration.

Ratios between aboveground net primary production, litterfall and carbon stocks in scots pine stands (Russia)

Background: Forests are the main terrestrial regulators of greenhouse gas concentrations. However, estimates of carbon fluxes in them are characterized by large uncertainties. Therefore, the derivation of predictors for their assessment is an urgent task. The aim was to assess the carbon stocks in the biomass to characterize the intensity of aboveground net production and the amount of litterfall in Scots pine forests of different types on the North-East of the Europe. We estimated biomass and aboveground net primary production (ANPP) of stands using sample trees. For vegetation of ground cover biomass and primary production evaluating, we cut off all aboveground organs on an area of 625 cm2 and removed the first-year parts. Litterfall was collected over 3-6 years using litter traps. Results: Most of the carbon in the biomass of pine forests is concentrated in trees (Cstand) with dominating role of stem wood. However, in boggy forests, ground vegetation plays a significant role in carbon stocks, both in absolute and relative values. We estimated carbon fluxes in ANPP and stand litterfall. High contribution of needles was detected for these flows. The ratio between ANPP and Cstand varied from 0.018 to 0.056 but between Litterfal and Cstand ranged from 0.008 to 0.024. Conclusion: The biomass, ANPP and litterfall depended form forest type. Obtained ratios between them can be used for assessing carbon fluxes in large regions using remote data collection of forest biomass.

Potentials of Carbon Stored in Plant Biomass at Little Farmers Grassland Cisarua, West Bandung Regency

Alternatives of vegetations to store carbon need to be encouraged considering that forests are threatened by widespread destructions. One such vegetation is grasslands which have the potential for carbon storage and to reduce CO2 concentration in the atmosphere. At present, many enterprises have designed grasslands for animal feed. Grassland at Little Farmers, Cisarua, West Bandung was established for many purposes, i.e. recreation, education, and animal feed. The purpose of this research was to study the potential of carbon stock in grassland vegetation at this location. Based on RaCSA method, the tree biomass was determined by nondestructive collection of density and basal area of trees, then calculated by an allometric equation. The ground cover biomass was determined by destructive collection of grass and roots. Total measured biomass was multiplied by 46% to obtain carbon storage. Based on the results, the potential of carbon stock in Little Farmers grassland is 6,506.23 kg/m2 with the potential for carbon storage below the ground (0.129 kg / m2) was slightly higher than the carbon stored above the ground (0.101 kg / m2). Carbon stored in ground cover had been proven to be lower than woody plants (6,506 kg / m2). This study has pioneered in finding the carbon stocks potential of a man-made grassland, so it provides basis of an alternative land use that can be encouraged for carbon sequestration. For many enterprises, this study will aid in the conduct and management planning of grasslands with regards to ecosystem services preservation, such as carbon sequestration.

Thinning effects on soil and microbial respiration in a coppice-originated Carpinus betulus L. stand in Turkey

Abstract: Effects of thinning on soil respiration and microbial respiration were examined over a 2-year period (2010-2012) in a coppice-originated European hornbeam (Carpinus betulus L.) stand in Istanbul, Turkey. Four plots within the stand were selected; tree density was reduced by 50% of the basal area in two plots (thinning treatment), and the other two plots served as controls. The study focused on the main factors that affect soil respiration (RS) and microbial respiration on the forest floor (RFFM) and in soil (RSM): soil temperature (TS), soil moisture (MS), soil carbon (C), soil nitrogen (N), soil pH, ground cover biomass (GC), forest floor mass (FF), forest floor carbon (FFC) and nitrogen (FFN), and fine root biomass (FRB). Every 2 months, soil respiration was measured using the soda-lime method, and microbial respiration was measured with the incubation method separately for the soil and forest floor. Results were evaluated yearly and over the 2-year research period. During the first year after treatment, RS was significantly higher (11%) in the thinned plots (1.76 g C m-2 d-1) than in the controls (1.59 g C m-2 d-1). However, there were no significant differences in either the second year or the 2-year study period. In the thinned plots during the research period, RS was linearly correlated with GC, Ts and FRB. Thinning treatments did not affect RSM, but interestingly, they did affect RFFM, which was greater in the control plots than in the thinned plots. RSM had a significant and positive correlation with soil N and soil pH, while RFFM was linearly correlated with FFC and C/N ratio of the forest floor in both thinned and control plots during the research period.

Understory plant biomass dynamics of prescribed burned Pinus palustris stands

Longleaf pine (Pinus palustris Mill.) forests are characterized by unusually high understory plant species diversity, but models describing understory ground cover biomass, and hence fuel load dynamics, are scarce for this fire-dependent ecosystem. Only coarse scale estimates, being restricted on accuracy and geographical extrapolation, are available. We analyzed the dynamics of ground cover biomass under different prescribed burning regimes in longleaf pine stands in the southeastern United States. We developed a set of functions to simulate ground cover biomass dynamics in stands of varying age, basal area and fire management history. The subsequent models allow for estimation of ground cover biomass for unburned stands and living woody and herbaceous ground cover biomass for burned stands. Woody ground cover was highly reduced as fire frequency increased, and also affected by stand basal area when time since last burning was longer than two years. Herbaceous ground cover was affected little by burning frequency but was reduced as basal area increased. This novel model system is a useful tool that can be incorporated into fire management and carbon balance models.

Effects of thinning on soil respiration and microbial respiration of forest floor and soil in an oak (Quercus frainetto) forest

The effects of tree thinning on soil respiration and microbial respiration in a Hungarian oak (Quercus frainetto Ten.) forest were examined over a 2-year period (2010–12). Tree density was reduced to 50% of the basal area. The research focus was on the main factors influencing the soil respiration (RS) and microbial respiration in the forest floor (RFFM) and in the soil (RSM): soil temperature, moisture, carbon (C), nitrogen (N), and pH; groundcover biomass (GC); forest floor mass, carbon and nitrogen; and fine root biomass. RS was measured twice monthly with the soda-lime method, and the incubation method was used to measure RSM and RFFM separately. The results were evaluated annually and over the 2-year research period. Correlation and stepwise regression analyses were used for statistical evaluation. Annual mean RS was significantly higher in thinned plots (1.92 g C m–2 day–1) than in the control plots (1.79 g C m–2 day–1). Over the 2-year research period, RS was higher in the thinned plots, and had linear correlations with GC, soil temperature and fine root biomass. GC was found to be the main factor that determined RS. The control plots had significantly higher RSM in first year, whereas the thinned plots had significantly higher RSM in second year; no significant difference was found over the 2-year research period. RFFM was significantly higher in the control plots than in the thinned plots, by 84% in the second year and by 34% over the 2-year study period. RSM had a linear correlation with soil N content and soil pH, whereas RFFM had linear correlations with C concentration and the C : N ratio of the forest floor in the thinned plots.

Postfire recovery of the ground cover in pine forests of the Lower Angara region

This paper traces the dynamics of the living ground cover at the initial stage of pyrogenic succession (1–9 years) after different-intensity surface fires in the pine forests of the Lower Angara region. Depending on their intensities, fires have reduced the foliage cover and ground-cover biomass. The greatest changes occur in case of medium-intensity and high-intensity fires that change the horizontal structure of plant microgroups and lead to the death of moss-lichen layers.

Nitrogen Dynamics and Nutrient Budgets in Four Orchard Groundcover Management Systems

Excessive nitrogen (N) applications can increase surface and water contamination, and leaching losses may occur when N fertilizer rates are too high relative to crop demands and soil N availability. Quantifying nutrient inputs, cycling, and outputs from orchards provides a method to measure surplus of nutrients, particularly N, that may leach or runoff. We conducted a long-term study to develop N budgets based on observed nutrient dynamics under four groundcover management systems (GMSs) with and without N fertilization. Four GMS treatments were randomly assigned to 12 plots and maintained since 1992 in 2-m-wide strips within tree rows: pre-emergence residual herbicide (PreHerb), post-emergence herbicide (PostHerb), mowed-sod (Sod), and hardwood bark mulch (Mulch). We measured system N inputs in fertilizer, mulch biomass, rain, and irrigation water; N outputs in harvested fruit, surface runoff, and subsurface leaching; and internal N cycling from surface vegetation, soil mineralization, leaf fall, and pruned wood. For the year with N fertilizer (2005), the overall N balance was positive (inputs exceeded outputs) in all GMSs but greater in the PostHerb and Mulch treatments. In the year without N fertilizer (2007), the overall N balance was negative for PreHerb and PostHerb and positive for Mulch and Sod treatments. Soil mineralization and recycling groundcover biomass accounted for greater than 60% of internal N fluxes, and harvested fruit represented greater than 70% of N outputs from the system during both years. During the year with N fertilizer, N losses were 1% to 4% and 18% to 22% through surface runoff and subsurface leaching, respectively. During the year without fertilizer, surface runoff N losses were twice the subsurface leaching N losses in all GMSs.

English

There is growing interest in the reforestation of surface mined lands for various land uses including forest products and wildlife habitat. These objectives can be met by planting native tree species and seeding a ground cover to control erosion. However, many ground covers compete aggressively with tree seedlings in this region, preventing establishment. A research project was designed with two main objectives; to investigate the competitive effects of different ground cover species on the growth and survival of tree seedlings, and to identify the relationship between the growth and function of tree seedlings and microsite variables. Five tree species, native to the eastern hardwood forest surrounding the mine site, were planted in 2005: yellow poplar (Liriodendron tulipifera L.), sugar maple (Acer saccharum Marsh.), northern red oak (Quercus rubra L.), eastern redbud (Cercis canadensis L.), and Virginia pine (Pinus virginiana Mill.). Five different ground cover treatments were applied to the planted area. Two mixes consisted of native warm season grasses (NWSG), two standard reclamation mixes, and one control. Growth and survival, seedling transpiration, soil respiration, and groundcover biomass were analyzed. At each seedling, light measurements and percent herbaceous cover based on the Braun-Blanquet scale were collected. Seedling survival was related to size at planting, and to the density of ground cover. Survival was highest in moderate amounts of cover, although root collar diameter growth decreased with increasing cover in redbud and pine. Tree seedling growth and survival tended to be greatest in the native warm season grass treatments.

Community heterogeneity of Early Pennsylvanian peat mires

Reconstructions of Pennsylvanian coal swamps are some of the most common images of late Paleozoic terrestrial ecosystems. All reconstructions to date are based on data from either time-averaged permineralized peats or single-site collections. An erect, in situ Early Pennsylvanian forest preserved above the Blue Creek Coal, Black Warrior Basin, Alabama, was sampled in 17 localities over an area of .0.5 km 2 , resulting in the first temporally and spatially constrained Pennsylvanian mire data set. This three-tiered forest was heterogeneous. Lycopsid and calamitean trees composed the canopy, and lepidodendrids, Lepidophloios, and sigillarians grew together at most sites. More juvenile than mature lycopsid biomass occurs in the forest-floor litter, indicating a mixed-age, multicohort canopy. Pteridophytes (tree fern) and pteridosperms (seed fern) dominated as understory shrubs, whereas sphenophyllaleans, pteridophytes, and pteridosperms composed the ground-cover and liana tier. The proportion of canopy, understory, and ground-cover biomass varied across the forest. Low proportions of ground-cover and liana taxa existed where canopy fossils accounted for .60% of the litter. There is a distinct spatial clustering of sites with more or less understory (or ground cover) where canopy contribution was ,60%. Where canopy biomass was low (,50%), understory shrubs contributed more biomass, indicative of light interception and/or competition strategies. Sphenopteris pottsvillea, a ubiquitous ground-cover plant, is abundant in all sites except one, where pteridosperm creepers and lianas dominate the litter, interpreted to indicate total suppression of other ground-cover growth. Ecological wet-dry gradients identified in other Pennsylvanian swamps do not exist in the Blue Creek mire, with the interpreted wettest (Lepidophloios), driest (Sigillaria), and intermediate (Lepidodendron sensu latu) taxa coexisting in most assemblages.

Productivity and species richness across an environmental gradient in a fire‐dependent ecosystem

The fire-dependent longleaf pine-wiregrass (Pinus palustris Mill.-Aristida beyrichiana Trin. & Rupr.) savannas of the southeastern United States provide a unique opportunity to examine the relationship between productivity and species richness in a natural ecosystem because of the extremely high number of species and their range across a wide ecological amplitude (sandhills to edges of wetlands). We used a natural gradient to examine how plant species richness and plant community structure vary with standing crop biomass (which in this system is proportional to annual net productivity) as a function of soil moisture and nitrogen mineralization rates in a frequently burned longleaf pine-wiregrass savanna. Highest ground cover biomass and highest species richness were found at the same position along the gradient, the wet-mesic sites. Relative differences in species richness among site types were independent of scale, ranging from 0.01 m(2) to 100 m(2). Nitrogen availability was negatively correlated with species richness. Dominance of wiregrass (in terms of biomass) was consistent across the gradient and not correlated with species richness. Regardless of site type, the community structure of the savannas was characterized by many perennial species with infrequent occurrences, a factor in the low temporal heterogeneity (percent similarity between seasons and years) and high within-site spatial heterogeneity (percent dissimilarity of vegetation composition). The coexistence of numerous species is likely due to the high frequency of fire that removes competing hardwood vegetation and litter and to the suite of fire-adapted perennial species that, once established, are able to persist. Our results suggest that soil moisture is an important factor regulating both the number of species present and community production within the defined gradient of this study.

Orchard Groundcover Management Systems Affect Meadow Vole Populations and Damage to Apple Trees

Meadow vole (Microtus pennsylvanicus Ord) populations, feeding activity and damage to young apple (Malus ×domestica Borkh.) trees were monitored for several years in a New York orchard by direct observation, trap counts, and a feeding activity index in various groundcover management systems (GMSs). Meadow vole population density differed among GMSs, with consistently higher densities and more trees damaged in crown vetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.) turfgrass tree-row strips. Vole densities were high in autumn and low in spring each year. Anticoagulant rodenticides and natural predation did not adequately control voles in GMSs providing favorable habitat. Groundcover biomass per m2 was weakly correlated with vole densities in 2 of 3 years, while the percentage of soil surface covered by vegetation was not significantly correlated with vole populations. Applications of thiram fungicide in white latex paint were better than no protection, but less effective than 40-cm-high plastic-mesh guards for preventing vole damage to tree trunks. A combination of late-autumn trapping, close and consistent mowing of the orchard floor, trunk protection with mesh guards, contiguous habitat for vole predators, and herbicide applications within the tree rows provided effective control of meadow-vole damage to trees at this orchard during 3 years without applications of rodenticide baits. Chemical names used: Tetramethylthiuram disulfide (thiram)

Orchard Groundcover Systems Affect Meadow Vole Populations and Damage to Apple Trees.

Meadow vole (Microtus pennsylvanicus L.) populations, feeding activity, and damage to young apple (Malus domestica Borkh.) trees were monitored by direct observation, trap counts, and a feeding activity index in different groundcover management systems (GMSs) for five years in a New York orchard. Vole populations differed greatly among GMSs, with consistently higher populations and more damage to tree trunks in crownvetch (Coronilla varia L.), hay-straw mulch, and red fescue (Festuca rubra L.)sodgrass GMSs. Vole populations were highest in the fall and lowest during the spring seasons each year. Anticoagulant rodenticides and natural predation did not result in adequate control of voles in GMSs that provided favorable habitat for nesting and feeding of this pest. The percent of soil surface vegetation coverage was not, but the amount of groundcover biomass was, a significant predictor of vole populations and damage to trees, independent of groundcover vegetation species. Trunk applications of thiram fungicide were less effective than 40-cm-high plastic mesh trunk guards, but better than no protective measures for controlling vole depredation in groundcover management systems (GMSs) with high rodent populations. A combination of late fall vole trapouts, close and consistent mowing of orchard floor vegetation, tree trunk protection with mesh guards, ample surrounding habitat for natural predators of voles, and suppression of tree row groundcover species with herbicides provided adequate control of meadow voles without the use of rodenticides at this orchard.

Effect of Geographical Location on Species Composition, Vegetation Structure, Diversity and Phytoindicative Characteristics in Pine Forests

The subject of this study is the influence of geographical location on floristic composition, horizontal structure, biomass, species richness, species diversity and values of phytoindicators of the herb layer in pine and mixed pine forest communities along a climatic gradient. Geographical longitude was used as a synthetic measure of geographical position. Studies were conducted on 17 plots. The westernmost plot was located at 12°25′48″E and 53°6′7″N, the easternmost plot was situated at 32°37′37″E and 53°20′56″N. All study areas were representatives of the Dicrano–Pinion alliance and included two communities of pine forest ( Peucedano-Pinetum and Leucobryo-Pinetum) as well as the community of mixed pine forest ( Querco roboris-Pinetum). Plots fell into two geographical groups: suboceanic and subcontinental. Three types of ground flora were identified: one dominated by a cover of mosses, the second dominated by dwarf shrubs, and the third dominated by species of grass. The ground cover biomass on the west-east transect ranged from 49 to 544 g m −2. There is a statistically significant correlation between geographical longitude of the stand and biomass of mosses as well as of total biomass of the ground cover along the transect. On the basis of Ellenberg’s indices the vegetation on consecutive sample plots is not strongly differentiated. All sites on the transect occur on dry, strongly or slightly acidic soil, with low nitrogen content. Values for the index of continentality K reflect the climatic differentiation from west to east. The number of herb layer species increases eastward, and all diversity indices are strongly correlated with the longitude. The relative number of chamephytes and therophytes is positively correlated with the longitude. In pine forests there is a general tendency for the number of scleromorphic species to decrease (and of mesomorphic species to increase) westward. There is also a general tendency for meadow species to increase westward.

INFLUENCE OF ORCHARD-FLOOR VEGETATION MANAGEMENT ON APPLE TREE GROWTH, NUTRIENT UPTAKE AND LEAF TRANSPIRATION RATES

Eight vegetation management systems (VMS) were evaluated over four years in a newly planted apple site. VMS treatments included pre- and post-emergence herbicide strips, a close-mowed sodgrass, a growth-suppressed (maleic-hydrazide) sodgrass, a crownvetch “living mulch,” clean cultivation, and straw mulch. Soil moisture supply was highest under the straw mulch and lowest under crownvetch, and varied inversely with groundcover biomass. Leaf N was deficient in tress in both sodgrass VMS, and increased by the lequme “living mulch” only after four years. Leaf Cu was lowest, and appeared to limit tree growth in VMS with prolonged soil moisture deficits. No significant differences were observed in leaf transpiration over a broad range (10 to 700 kPa) of soil matric tension. Cumulative trunk crosssectional area was greatest in straw-mulched trees and least in sodgrass and crownvetch VMS. The optimal soil matric tension for nutrient uptake and tree growth appeared to be 175 to 200 kPa in this orchard. Increasing the width of glyphosate herbicide strips from 1.5 to 2.5 m in tree rows did not improve tree growth, nutritional status or fruit yield.

Biomass and nitrogen dynamics in an irrigated hybrid poplar plantation

A 3-year study measured the effects of ground cover treatments and N fertilization on biomass and nitrogen dynamics in an irridiated hybrid poplar ( Populus deltoides Bartr. X P. trichocarpa Torr. and Gray, clone NC-9922) plantation in northern Wisconsin, U.S.A. Annually fertilized (112 kg N ha −1 year −1) and unfertilized plots were maintained weed free (bare soil), allowed to revegetate with native weeds, or seeded to birdsfoot trefoil ( Lotus corniculatus L.). Biomass and N in trees and ground-cover vegetation were sampled before and after each growing season. Trees in bare-soil plots responded to fertilization primarily in the third growing season, but total biomass of 3-year-old trees was not increased by annual fertilization. In plots with a ground cover,fertilization increased tree growth but cover crop treatment had no effect. Ground cover biomass peaked during the second growing season, but declined thereafter, primarily due to reductions in below-ground biomass. Estimated recovery of fertilizer N was low in bare soil plots after 3 years, with 2% in the ‘perennial’ portion of the trees and 13% in the leaf litter. In contrast, recovery in the cover crop plots was 44%–51% in years 2–4. During that period, both biomass and N pool dominance shifted from primarily cover crop to primarily trees. The ground cover appeared to reduce tree growth in years 1–3, but total tree biomass after 4 years was greater in fertilized plots with ground cover (22.7 Mg/ha) than in fertilized bare soil plots (16.7 Mg/ha). Biomass production in fertilized trefoil plots in the fourth year (15.1 Mg ha −1 year −1, excluding leaves) exceeds that of local forests by 50%, and may be comparable to corn productivity in the area.