Plant Biomass Distribution Research Articles

Predicting sub‐continental fuel hazard under future climate and rising atmospheric CO2 concentration

Abstract Bushfire fuel hazard is determined by the type, amount, density and three‐dimensional distribution of plant biomass and litter. The fuel hazard represents a biological control on fire danger and may change in the future with plant growth patterns. Rising atmospheric CO2 concentration (Ca) stimulates plant productivity (‘fertilisation effect’) but also alters climate, leading to a ‘climatic effect’. Both effects have impacts on future vegetation and thus fuel hazard. Quantifying these effects is an important component of predicting future fire regimes and evaluating fire management options. Here, we combined a machine learning algorithm that incorporates the power of large fine spatial resolution (i.e. 90 m) datasets with a novel optimality model that accounts for the climatic and fertilisation effects on vegetation cover. We demonstrated the usefulness and practicality of this framework by predicting fuel hazard across the state of Victoria in Australia. We fitted and evaluated the models with long‐term (i.e. 20 years), ground‐based fuel observations. The models achieved strong agreement with observations across the fuel hazard range (accuracy >65%). We found fuel hazard increased more in dry environments due to future climate and Ca. The contribution of the ‘fertilisation effect’ to future fuel hazard varied spatially by up to 12%. The predictions of future fuel hazard are directly useful to inform fire mitigation policies and as a reference for climate model projections to account for fire impacts. Synthesis and applications: Climate change and rising Ca have profound impacts on vegetation and thus fuel load. Operational fire management and future fire risk forecasts will benefit from our realistic fuel load prediction framework that incorporates plant responses and fine soil and terrain attributes.

Recent above-ground biomass changes in central Chukotka (Russian Far East) using field sampling and Landsat satellite data

Abstract. Upscaling plant biomass distribution and dynamics is essential for estimating carbon stocks and carbon balance. In this respect, the Russian Far East is among the least investigated sub-Arctic regions despite its known vegetation sensitivity to ongoing warming. We representatively harvested above-ground biomass (AGB; separated by dominant taxa) at 40 sampling plots in central Chukotka. We used ordination to relate field-based taxa projective cover and Landsat-derived vegetation indices. A general additive model was used to link the ordination scores to AGB. We then mapped AGB for paired Landsat-derived time slices (i.e. 2000/2001/2002 and 2016/2017), in four study regions covering a wide vegetation gradient from closed-canopy larch forests to barren alpine tundra. We provide AGB estimates and changes in AGB that were previously lacking for central Chukotka at a high spatial resolution and a detailed description of taxonomical contributions. Generally, AGB in the study region ranges from 0 to 16 kg m−2, with Cajander larch providing the highest contribution. Comparison of changes in AGB within the investigated period shows that the greatest changes (up to 1.25 kg m−2 yr−1) occurred in the northern taiga and in areas where land cover changed to larch closed-canopy forest. As well as the notable changes, increases in AGB also occur within the land-cover classes. Our estimations indicate a general increase in total AGB throughout the investigated tundra–taiga and northern taiga, whereas the tundra showed no evidence of change in AGB.

Influence of discrete-pulse energy input on the distribution of plant biomass

Influence of discrete-pulse energy input on the distribution of plant biomass

Uniconazole and diethyl aminoethyl hexanoate increase soybean pod setting and yield by regulating sucrose and starch content.

Uniconazole (S3307) and diethyl aminoethyl hexanoate (DA-6) are known plant growth regulators (PGRs). However, it is unknown if their regulation of sucrose and starch content can affect pod setting and yield in soybean. Herein, S3307 and DA-6 were foliar sprayed on soybean Hefeng50 and Kangxian6 at the beginning of the bloom cycle in field tests conducted over two years. PGRs promoted the accumulation and distribution of plant biomass and significantly improved leaf photosynthetic rates. Sucrose and starch content increased after PGR treatment across organs and varieties. Accumulation and allocation of sucrose and starch content in soybean source organs are enhanced by PGRs, which supply high levels of assimilate to sink organs. Moreover, sucrose and starch contents in source and sink organs are positively correlated. S3307 and DA-6 also significantly increased pod setting rates and reduced flower and pod abscission rates, leading to increased yield. S3307 and DA-6 promoted the accumulation and availability of sucrose and starch content in source organs and increased sucrose and starch content in flowers and pods or seeds, thereby maintaining the balance between source and sink organs and contributing to increased pod setting rates and soybean yield. © 2018 Society of Chemical Industry.

Tundra plant above-ground biomass and shrub dominance mapped across the North Slope of Alaska

Arctic tundra is becoming greener and shrubbier due to recent warming. This is impacting climate feedbacks and wildlife, yet the spatial distribution of plant biomass in tundra ecosystems is uncertain. In this study, we mapped plant and shrub above-ground biomass (AGB; kg m−2) and shrub dominance (%; shrub AGB/plant AGB) across the North Slope of Alaska by linking biomass harvests at 28 field sites with 30 m resolution Landsat satellite imagery. We first developed regression models (p < 0.01) to predict plant AGB (r2 = 0.79) and shrub AGB (r2 = 0.82) based on the normalized difference vegetation index (NDVI) derived from imagery acquired by Landsat 5 and 7. We then predicted regional plant and shrub AGB by combining these regression models with a regional Landsat NDVI mosaic built from 1721 summer scenes acquired between 2007 and 2016. Our approach employed a Monte Carlo uncertainty analysis that propagated sampling and sensor calibration errors. We estimated that plant AGB averaged 0.74 (0.60, 0.88) kg m−2 (95% CI) and totaled 112 (91, 135) Tg across the region, with shrub AGB accounting for ~43% of regional plant AGB. The new maps capture landscape variation in plant AGB visible in high resolution satellite and aerial imagery, notably shrubby riparian corridors. Modeled shrub AGB was strongly correlated with field measurements of shrub canopy height at 25 sites (rs = 0.88) and with a regional map of shrub cover (rs = 0.76). Modeled plant AGB and shrub dominance were higher in shrub tundra than graminoid tundra and increased between areas with the coldest and warmest summer air temperatures, underscoring the fact that future warming has the potential to greatly increase plant AGB and shrub dominance in this region. These new biomass maps provide a unique source of ecological information for a region undergoing rapid environmental change.

LiDAR‐derived canopy structure supports the more‐individuals hypothesis for arthropod diversity in temperate forests

Despite considerable progress in the ability to measure the complex 3‐D structure of forests with the improvement of remote‐sensing techniques, our mechanistic understanding of how biodiversity is linked to canopy structure is still limited. Here we tested whether the increase in arthropod abundance and richness in beech forest canopies with increasing canopy complexity supports the more‐individuals hypothesis or the habitat‐heterogeneity hypothesis. We used fogging to collect arthropod samples from 80 standardized plots from canopies of single‐ to multi‐layered mature montane European beech stands. Tree height and an independent measure of vertical heterogeneity – the vertical distribution ratio – on each arthropod sampling plot were derived from high‐resolution full‐waveform airborne laser scanning data. Mixed‐model path analysis based on almost 20 000 specimens of 762 species from 11 orders provided support for the more‐individuals hypothesis, with higher arthropod abundance but not higher species richness in stands with a more equal vertical distribution of plant biomass. By contrast, we found no support for the habitat‐heterogeneity hypothesis. The increase in the number of individuals with increasing vertical distribution of biomass might be caused either by increasing leaf area, as indicated by higher space filling and productivity in multi‐layered stands, or by higher persistence of arthropod populations owing to better shelter, reduced competition and more refuges under harsh conditions, or by both. High‐resolution airborne laser scanning, with its ability to penetrate dense canopies under leaf‐on conditions, has proved suitable for measuring vertical structures as a predictor for canopy diversity. Expanding combinations of remote‐sensing and canopy‐biodiversity data opens many avenues for improving our understanding of the link between diversity and forest structures.

Aboveground biomass in reforestation with native species established by means of Taungya agroforestry system

ABSTRACT The mitigation of CO2 emission through high-productivity systems associated with restoration of degraded sites have been increasingly common, highlighting the importance of estimates of the amount and distribution of plant biomass in different ecosystems and under different management systems. The aim of this study was to investigate the influence of planting and soil characteristics and the type of management performed over the aboveground biomass accumulation in two reforestation projects with native species, implanted through Taungya agroforestry system. The differences in aboveground biomass accumulation were probably influenced by agroforestry management, since these variations showed to be independent of age (considered within the age range in this study), the spacing, the species composition, and soil fertility. The values of aboveground biomass are similar to those reported in the literature for other reforestation projects with native species of similar ages.

Do sheep grazing patterns affect ecosystem functioning in steppe grassland ecosystems in Inner Mongolia?

Overgrazing has driven degradation and desertification of semi-arid grasslands in Northern China over recent decades. Selective grazing by sheep influences sward structure by inducing heterogeneous vegetation patterns comprising overgrazed hotspots and areas rejected by grazing sheep. In this study, we examined the effects of grazing intensity (ungrazed, light and heavy grazing in 2008 and 2010) and grazing system (a mixed system involving continuous grazing alternating annually with hay making vs. a continuous system involving continuous utilization of the same area for grazing) on plant biomass distribution and ecosystem functioning after 4 years and 6 years of controlled grazing in a semi-arid steppe of Inner Mongolia, China. The spatial biomass distribution was determined by sward height measurements converted to biomass and afterwards visualized in biomass distribution semivariograms. Within each of the different areas: grazed (i.e., areas frequently grazed by sheep), rejected (i.e., areas largely avoided by grazing sheep) and fenced (i.e., areas from which grazing had been excluded by fencing), plant species and soil parameters were sampled in order to analyze the mechanisms and effects of grazing patterns on ecosystem functioning. The results revealed a more homogeneous biomass distribution in the ungrazed and heavily grazed plots compared to lightly grazed plots, in which heterogeneous biomass distribution patterns included both overgrazed hotspots and rejected areas. The patch vegetation patterns were consistent between years only under light grazing intensity. However, patch vegetation patterns in the continuous system did not necessarily indicate negative effects on grassland ecosystem functioning. Within the 6 years of grazing experiment, it appears that patchy structure rather than homogeneous patterns showed higher biodiversity, significant variations in litter, soil water content and soil temperature and smaller effects on belowground biomass and carbon storage. Therefore, heterogeneous patchy vegetation patterns are likely to moderate grassland recovery and optimize ecosystem functioning by forming resource islands with sufficient water and nutrients in the short run.

Using imaging spectroscopy to predict above‐ground plant biomass in alpine grasslands grazed by large ungulates

AbstractAimsImaging spectroscopy enables measurement of vegetation optical properties to predict vegetation characteristics that are important for a wide range of ecological applications. Our aim was to predict fresh above‐ground biomass of heterogeneous alpine grasslands in two areas and at two ecological scales. We assessed model plausibility for an intensively studied alpine grassland site (plant community scale) having distinct biomass and ungulate grazing patterns.LocationAlpine grasslands in the Swiss National Park.MethodsBiomass data were collected in 51 plots and combined with imaging spectroscopy data to establish simple ratio models. We analysed the predictive power and transferability of models developed in two areas (Val Trupchun, Il Fuorn) and at two ecological scales (regional, local). In a next step, we compared our results to the broadband normalized difference vegetation index (NDVI). Finally, we assessed the correlations between model predictions and plant biomass distribution at the plant community scale.ResultsThe best local simple ratio models yielded a model fit of R2 = 0.60 and R2 = 0.30, respectively, the best regional model a fit of R2 = 0.44. NDVI model performance was weaker for the regional and one local area, but slightly better for the other local area. However, at the plant community scale only the local model showed a significant positive correlation (RS = 0.39) with the known biomass distribution. Further, predictive power decreased when models were transferred from one local area to another or from one ecological scale to another.ConclusionsOur study demonstrated that imaging spectroscopy is generally useful to predict above‐ground plant biomass in alpine grasslands with distinct grazing patterns. Site‐specific local models based on simple ratio indices performed better than the NDVI or regional models, suggesting that standardized approaches might not be adequate, particularly in heterogeneous grasslands inhabited by large ungulates. We emphasize the importance of collecting ground reference data covering the expected range of productivity and plant species composition. Moreover, plant community‐scale data from a previous study proved to be extremely valuable to test model plausibility.

Influence of some landscape factors on the belowground plant biomass distribution in mountain ecosystems of Armenia

Presented are the results from investigating the belowground biomass of grass associations as an important factor of functional stability of mountain ecosystems. Field investigations were conducted in plant communities of the dry-steppe, meadow-steppe and alpine belts of Armenia at altitudes of 1200–3250 m above the sea level. It is shown that the conditions of vertical belts, topography and the slope aspect of the mountain landscapes under investigation have influence on belowground biomass accumulation and distribution in the profile of the root layer of soils.

Winter Soil Respiration from Different Vegetation Patches in the Yellow River Delta, China

Vegetation type and density exhibited a considerable patchy distribution at very local scales in the Yellow River Delta, due to the spatial variation of soil salinity and water scarcity. We proposed that soil respiration is affected by the spatial variations in vegetation type and soil chemical properties and tested this hypothesis in three different vegetation patches (Phragmites australis, Suaeda heteroptera and bare soil) in winter (from November 2010 to April 2011). At diurnal scale, soil respiration all displayed single-peak curves and asymmetric patterns in the three vegetation patches; At seasonal scale, soil respiration all declined steadily until February, and then increased to a peak in next April. But, the magnitude of soil respiration showed significant differences among the three sites. Mean soil respiration rates in winter were 0.60, 0.45 and 0.17 μmol CO(2) m(-2) s(-1) for the Phragmites australis, Suaeda heteroptera and bare soil, respectively. The combined effect of soil temperature and soil moisture accounted for 58-68 % of the seasonal variation of winter soil respiration. The mean soil respiration revealed positive and linear correlations with total N, total N and SOC storages at 0-20 cm depth, and plant biomass among the three sites. We conclude that the patchy distribution of plant biomass and soil chemical properties (total C, total N and SOC) may affect decomposition rate of soil organic matter in winter, thereby leading to spatial variations in soil respiration.

Predictive models for transient protein expression in tobacco (Nicotiana tabacum L.) can optimize process time, yield, and downstream costs

The transient expression of recombinant biopharmaceutical proteins in plants can suffer inter-batch variation, which is considered a major drawback under the strict regulatory demands imposed by current good manufacturing practice (cGMP). However, we have achieved transient expression of the monoclonal antibody 2G12 and the fluorescent marker protein DsRed in tobacco leaves with ∼ 15% intra-batch coefficients of variation, which is within the range reported for transgenic plants. We developed models for the transient expression of both proteins that predicted quantitative expression levels based on five parameters: The OD(600 nm) of Agrobacterium tumefaciens (from 0.13 to 2.00), post-inoculation incubation temperature (15-30°C), plant age (harvest at 40 or 47 days after seeding), leaf age, and position within the leaf. The expression models were combined with a model of plant biomass distribution and extraction, generating a yield model for each target protein that could predict the amount of protein in specific leaf parts, individual leaves, groups of leaves, and whole plants. When the yield model was combined with a cost function for the production process, we were able to perform calculations to optimize process time, yield, or downstream costs. We illustrate this procedure by transferring the cost function from a production process using transgenic plants to a hypothetical process for the transient expression of 2G12. Our models allow the economic evaluation of new plant-based production processes and provide greater insight into the parameters that affect transient protein expression in plants.

Aluminum-based winter wheat biomass and grain yield spatial variability in arable soils: concept and field test

The paper outlines a concept related to selecting a site for experimental purposes. Selection of an experimental plot most frequently relies on performing visual evaluation of a given site, followed by the establishment of a field trial. In general, the question of geochemical variability is ‘intentionally’ postponed! Verification of this approach has been undertaken, testing such parameters as soil pH and exchangeable aluminum (Alex) versus spatial (investigated area, 12 672 m2) and downward (sampling depths, i.e., 0-20, 20-40 and 40-60 cm) distribution. Winter wheat biomass at tillering (BBCH29) and grain yield at harvest (BBCH99) were additionally considered. The results have revealed that pH values fluctuated between 3.6 and 4.4 with respective coefficients of variation (CV) ranging from 3.10 to 5.92%. The concentrations of Alex ranged from 38.0 to 144.9 mg kg –1, corresponding to CV within 28.34 and 44.03%. The variograms and geostatistical maps have demonstrated the spatial as well as downward variability of these parameters. The spatial distribution of plant biomass followed quite closely the exchangeable aluminum (Alex) levels, which implies that natural soil parameters such as Alex are not easily compensated for by agricultural practices, for instance nitrogen application. The spatial grain yield – Alex dependence which emerged at harvest confirmed the variability observed at tillering (BBCH29). Thus, the spatial variability of pH, Alex and wheat biomass as well as grain yields (BBCH99) verified the approach to selecting an experimental site. It was demonstrated that selection of a research site on the basis of its appearance and shape alone may lead to misinterpretation of experimental results.

The Effects of Plant-Soil-Enzyme Interactions on Plant Composition, Biomass and Diversity of Alpine Meadows in the Qinghai-Tibetan Plateau

Four different alpine meadow communities were studied to examine the effects of plant-soil-enzyme interactions on plant composition and diversity. Enzyme activities differed by meadow type, and in general were higher in the upper soil layers (0–10 and 10–20 cm) than in the 20–40 cm layer. Community differences in plant composition or functional group composition were reflected in plant biomass distribution. The identity of a species (or a functional group) was a greater determinant of ecosystem function than the number of plant species. A significant correlation was found between the coverage per functional group and the aboveground biomass of functional groups in four alpine meadows. Soil microbial biomass carbon (Cmic) and enzyme activity were each affected by both functional group biomass andCABin the different meadow types. The negative correlation between diversity andCABin theKTSmay be influenced by a high soil nutrients input as a result of a higher litter input because of high aboveground biomass. Soil enzyme activities have been related to soil physio-chemical characters and plant primary production to change in vegetation. The original soil conditions, plant community composition, and community productivity are very important in regulating plant community productivity and microbial biomass and activity.

Potential for Sudden Shifts in Transient Systems: Distinguishing Between Local and Landscape-Scale Processes

Thorough understanding of the potential for threshold dynamics and catastrophic shifts to occur in natural systems is of great importance for ecosystem conservation and restoration. However, verifying the presence of alternative stable states, one of the theoretical explanations for sudden shifts in natural systems, has proven to be a major challenge. We examine processes on local and landscape scales in salt-marsh pioneer zones, to assess the presence of alternative stable states in this system. To that end, we investigated the presence of typical characteristics of alternative stable states: bimodality and threshold dynamics. We also studied whether vegetation patches remained stable over long time periods. Analysis of false-color aerial photographs revealed clear bimodality in plant biomass distribution. By transplanting Spartina anglica plants of three different biomass classes on three geographically different marshes, we showed that a biomass threshold limits the establishment of Spartina patches, potentially explaining their patchy distribution. The presence of bimodality and biomass thresholds points to the presence of alternative stable states and the potential for sudden shifts, at small, within-patch scales and on short time scales. However, overlay analysis of aerial photographs from a salt marsh in The Netherlands, covering a time span of 22 years, revealed that there was little long-term stability of patches, as vegetation cover in this area is slowly increasing. Our results suggest that the concept of alternative stable states is applicable to the salt-marsh pioneer vegetation on small spatio-temporal scales. However, the concept does not apply to long-term dynamics of decades or centuries of heterogeneous salt-marsh pioneer zones, as landscape-scale processes may determine the large-scale dynamics of salt marshes. Hence, our results provide the interesting perspective that threshold dynamics may occur in systems with, on the long term, only a single stable state.

On the use of sediment fertilization for seagrass restoration: a mesocosm study on Zostera marina L.

The use of nitrogen and phosphorus sediment fertilization for seagrass restoration is explored. Special attention was given to the effects of nitrogen sediment fertilization. The sediment fertilization treatment combined different levels of nitrogen (0, 30, 500 mg N g DW −1) with sufficient phosphorus to avoid P-limitation (fertilizer N:P ratio<0.25). Using indoor mesocosms, we studied the effects of sediment fertilization, and its interactions with light availability (55, 200 μmol m −2 s −1) and sediment redox conditions (300, −100 mV), on Zostera marina L. We assessed (1) treatment effects on growth and plant biomass distribution, (2) the capacity of Z. marina roots to meet the plant nutrient demand, (3) plant tolerance to high nutrient porewater concentration, and (4) pro’s and con’s of use NH 4NO 3 as the N source in sediment fertilization for seagrass restoration. Plant biomass, growth and leaf turnover rate were stimulated by light and sediment fertilization. Biomass partitioning was not affected by light availability, whereas the relative root production was decreased in fertilized sediments. Root uptake following fertilization met nutrient plant demand. After high sediment fertilization, ammonium porewater concentration was high (30 mM) regardless of redox conditions. On the other hand, nitrate availability was also high, but 80% lower in reduced sediments (0.7–4 mM) compared to non-reduced ones (20 mM). Plants of Z. marina exhibited a remarkable tolerance to high N+P sediment fertilization. However, plant inhibition (reduction in plant weight, leaf growth and leaf turnover rate) was detected when porewater N concentrations exceeded 30 mM. The effects of phosphorus and ammonium toxicity were discarded because availability was similar for both inhibited and non-inhibited plants. We attributed the Z. marina inhibition to the extra porewater nitrogen available as nitrate (20 mM). Experimental treatments did not inhibit the photosynthetic apparatus of Z. marina. The mechanisms of inhibition might be related with deficiencies in energy or C-skeletons, since inhibitory effects were buffered when saturating irradiance and/or nitrate levels decreased in reduced sediments. In conclusion, we consider that the combined N+P sediment fertilization, with NH 4NO 3 as N source and high P supply, is highly beneficial for Z. marina restoration. This species has positive response to N+P sediment fertilization, high tolerance to the extensive porewater enrichment, and bacterial metabolism may reduce the porewater nitrate availability in anoxic seagrass sediments. However, for adequate sediment fertilization for restoration purposes, several precautions are suggested.

Estimating the biodiversity of hay meadows in north-eastern Switzerland on the basis of vegetation structure

Biological diversity is a major criterion in evaluating the effectiveness of measures to enhance the ecological quality of rural areas. Assessments of biodiversity based on selected groups of indicator organisms, including both animal and plant groups, are time-consuming and require a high level of expert knowledge: simpler methods are therefore needed. The biodiversity of 18 hay meadows in north-eastern Switzerland (Schaffhauser Randen, Canton Schaffhausen) was investigated using three indicator groups (angiosperms, spiders and true bugs). Simple structural parameters describing the vegetation canopy were investigated in terms of their usefulness as surrogates for biodiversity measures. Eighteen sites varied widely in terms of species richness, diversity and abundance for all indicator groups. Numbers of angiosperm species varied from 21 to 57, spiders 25 to 45, and true bugs 12 to 37. Species numbers of the three indicator groups were significantly correlated with each other (angiosperms versus spiders: r=0.53, P=0.02; angiosperms versus true bugs: r=0.59, P=0.01; true bugs versus spiders: r=0.61, P=0.01). Management had a strong influence on species richness, the sites under extensive management showing the highest species number and diversity. The strongest correlations were those between true bugs and the two other indicator groups. However, the number of angiosperm species per 120 m 2, which was easy to assess, was also an acceptable predictor of the other two indicator groups. Several parameters of the vegetation canopy were significantly related to species numbers and multiple regression models based on these parameters explained 25–60% of the variance in species richness and composition. Canopy density, plant biomass distribution and plant height were the most important parameters for all indicator groups. The results indicate that parameters describing the structure of the vegetation provide useful information about the relative species richness of sites. In combination with parameters describing the surrounding land-use and an inventory of the angiosperms present, they offer a promising method for assessing biodiversity on a large scale.

Shifting the carbon balance

Christopher S. Potter (BioScience 49: 769-778) addresses an issue of funda­ mental importance for the future of our planet. The global distribution of plant biomass, and the net primary production (NPP) that produces the biomass, has implications not only for the global carbon cycle, deforestation, and the greenhouse effect but also for environmental sustainability, biodiver­ sity, and the health and wealth of human society. We are concerned that the comput­ er- and satellite-based estimates in Table 2 of Potter's article are signifi­ cantly larger than estimates derived from ground-based measurements (Olson et al. 1983) for total terrestrial carbon, and for the biomass and NPP of tropical forests in particular. Potter's estimates for total carbon are actually greater than the 15% difference with Olson et al.'s number for total carbon indicates, because Olson's numbers include carbon in both above- and belowground biomass, whereas Pot­ ter's numbers include carbon in above­ ground biomass only. Potter's numbers, if correct, sub­ stantially alter the estimated global dis­ tribution of both biomass and plant productivity, producing a dramatic shift in plant resources from the devel­ oped countries of the temperate lati­ tudes to the less-developed countries of the tropics. Potter's estimate (in his Table 2) of 61 % of global plant carbon in the two major tropical ecosystems (broadleaf evergreen forest and wood­ ed grassland and shrubland) represents a nearly 50% increase from Olson et al.'s (1983) estimate of 42.8% of the global total in these ecosystems, with a concomitant decrease in temperate zone biomass~ There is an equivalent latitudinal shift in Potter's estimated distribution of NPP carbon. This shift has profound implications for our understanding of global-scale ecological patterns, as well as for the distribu­ tion of natural resources, wealth, and political responsibilities among nations. Unfortunately, it is currently impos­ sible to determine which set of esti­ mates is most accurate. The global dis­ tribution and quality of measurements of the biomass and productivity of the earth's ecosystems is woefully inade­ quate for to day's scientific and political needs. Most of the existing ground­ based data were collected 30 years ago during the International Biological Program, and current global carbon models are being compared against compilations of these old data (e.g., www-eosdis.ornl.gov/NPP/npp_ home.html) because there has been no systematic program to collect addi­ tional data since then. If we are to make rational decisions about protect­ ing and managing our biosphere, we must make a greater investment in actually measuring the properties of the plants and animals distributed over the surface of the earth.

Monitoring Water Stress Induced Variation in the Remotely Sensed Biomass Pattern of Sardinia (Italy) with Variograms

ABSTRACT In Mediterranean climates, the most important ecological factor for natural vegetation as well as for crops is low summer rainfall coinciding with a period of maximum temperatures creating a more or less prolonged period of intense drought. During the summer, water stress enhances the differences between adjacent landscape elements in terms of plant biomass distribution giving way to increased vegetation cover heterogeneity. The aim of this article is to use variogram analysis to quantitatively estimate water stress‐induced oscillations in remotely sensed biomass spatial distribution of Sardinia (Italy).

Why Are Parts of the World Green? Multiple Factors Control Productivity and the Distribution of Biomass

This paper evaluates the multiple factors that determine the production of plant biomass and its distribution among producers and various trophic groups of con_ ?^)^ Osumers. In rough order of their importance, water and nutrient availability, factors 0*S that deter herbivores (plant defenses, environmental heterogeneity and disturbance, nutrient stoichiometry), and consumption by herbivores appear to be the most universal determinants of the production and distribution of plant biomass. In some times and places, indirect effects from enemies of herbivores (predators, parasites, parasitoids and pathogens) propagate through the food web to influence plant biomass, in a manner somewhat consistent with green world and exploitation ecosystem mechanisms. I discuss why such food web dynamics appear to be much more important in water than on land. The only demonstrated cases of communitylevel trophic cascades occur in water. Although species-level cascades are moderately frequent on land, community-level cascades rarely or never occur.