Estimate Biomass Production Research Articles

Is ring width a reliable proxy for stem-biomass increment? A case study in European beech

The relationship between basal-area increment and stem-volume increment or biomass annual production was investigated in 30 dominant European beech (Fagus sylvatica L.) in northeastern France. The trees were sampled at four heights along the stem for dendrochronological and densitometric measurements. Annual stem-volume and stem-biomass increments were computed from the measurements and were not obtained by applying allometric relationships. A comparison of the ring-area increments at the four stem heights indicated that the vertical distribution of annual growth fluctuates at an interannual time step and is influenced by climate during the growing season, particularly drought events. Ring-area increments were more strongly reduced at breast height than in the upper parts of the tree during dry years. Relationships between basal-area increment and volume or annual biomass production were very strong, but the residuals of these relationhips contained up to 50% climate information. The amplitude of the breast-height radial-growth response to drought is much larger than the volume and biomass-production responses. Variations of wood density in this diffuse-porous species are not large enough to consistently modify the estimates of annual stem biomass production. Breast-height series are a valuable tool for dendrochronological investigations, but as they are more sensitive to drought, they greatly underestimate tree biomass increments during drought episodes.

Rangeland Resources Assessment with Satellite Imagery: An Operational Tool for National Planning in Namibia

The Namibian authorities endeavour to implement a rangeland resources management policy at national level. The first line of action is the allocation of livestock marketing priorities to the most drought‐affected areas. Another potential application is the estimation of land value in terms of grazing capacity, as a base for land purchase and redistribution for private land taxation. Accurate and up‐to‐date information on the resources, which are very variable in time and space, is indispensable for rational and efficient decision‐making. In this regard, low‐resolution satellite imagery appears to be a practical and suitable source of data for non‐biased and reasonably accurate estimation of forage production over the whole country. Using 17 years of AVHRR and VEGETATION satellite data over Namibia, seasonal biomass production estimates were obtained with a simple but operational vegetation production model known as the Monteith model. The accuracy of the products was assessed by comparison to field measurements carried out between 1999 and 2001, showing good correspondence and a residual error of approximately 25% of the average. Long‐term averages of biomass production from all available satellite data (17 growing seasons) give an indication of the “normal” potential of the land in terms of grazing. This can be used for marketing priority allocations, the comparison of the production of the current season to the long‐term average allowing to identify the most problematic zones and to quantify the severity of a crisis. The long‐term average is also a good base for land value assessment, although complementary processing is required. The products are integrated in a GIS environment to be used with complementary geographic information. The potential of such a system for decision making within the Namibian range resources management policy is discussed.

Estimating Chlorophyll-a Vertical Profiles from Satellite Data and the Implication for Primary Production in the Kuroshio Front of the East China Sea

An algorithm was evaluated for estimating primary production in the Kuroshio front of the East China Sea. The algorithm involves three principal inputs: chlorophyll-a (Chl-a) vertical profile, water column photosynthetic parameter and underwater irradiance parameter. We construct empirical models for estimating those three inputs from sea surface variables accessible by means of satellite remote sensing. Types of Chl-a vertical profile were closely associated with water mass features, and sea surface temperature seemed to be a potential variable to distinguish profile types. The consequence of the deep Chl-a maximum (DCM) presence was investigated by comparing the vertically non-uniform Chl-a profile against the uniform Chl-a profile in terms of the integrated biomass and primary production estimates. Since the DCM in the frontal region occurred in a relatively shallow layer with relatively high light level, allowing intensive photosynthetic processes to take place in the DCM layer. In contrast, as the DCM in the Kuroshio region occurred in the low-light, deep layer, it contributed less to the integrated primary production. We inferred that the DCM formation is more important in the frontal region than in the Kuroshio region, as they potentially contributed within 30.9% (±9.1%) and 20.9% (±5.4%) to the integrated primary production in the frontal and the Kuroshio regions, respectively. Such different degrees in the DCM contribution was then revealed by the higher integrated primary production in the frontal region than in the Kuroshio region.

Fine Root Production and Turnover in a Norway Spruce Stand in Northern Sweden: Effects of Nitrogen and Water Manipulation

Fine root length production, biomass production, and turnover in forest floor and mineral soil (0–30 cm) layers were studied in relation to irrigated (I) and irrigated-fertilized (IL) treatments in a Norway spruce stand in northern Sweden over a 2-year period. Fine roots (<1 mm) of both spruce and understory vegetation were studied. Minirhizotrons were used to estimate fine root length production and turnover, and soil cores were used to estimate standing biomass. Turnover was estimated as both the inverse of root longevity (RTL) and the ratio of annual root length production to observed root length (RTR). RTR values of spruce roots in the forest floor in I and IL plots were 0.6 and 0.5 y−1, respectively, whereas the corresponding values for RTL were 0.8 and 0.9 y−1. In mineral soil, corresponding values for I, IL, and control (C) plots were 1.2, 1.2, and 0.9 y−1 (RTR) and 0.9, 1.1, and 1 y−1 (RTL). RTR and RTL values of understory vegetation roots were 1 and 1.1 y−1, respectively. Spruce root length production in both the forest floor and the mineral soil in I plots was higher than in IL plots. The IL-treated plots gave the highest estimates of spruce fine root biomass production in the forest floor, but, for the mineral soil, the estimates obtained for the I plots were the highest. The understory vegetation fine root production in the I and IL plots was similar for both the forest floor and the mineral soil and higher (for both layers) than in C plots. Nitrogen (N) turnover in the forest floor and mineral soil layers (summed) via spruce roots in IL, I, and C plots amounted to 2.4, 2.1, and 1.3 g N m−2 y−1, and the corresponding values for field vegetation roots were 0.6, 0.5, and 0.3 g N m−2 y−1. It was concluded that fertilization increases standing root biomass, root production, and N turnover of spruce roots in both the forest floor and mineral soil. Data on understory vegetation roots are required for estimating carbon budgets in model studies.

Remote sensing capabilities to estimate pasture production in France

Pastures constitute an important terrestrial ecosystem. In France, pastures occupy 21% of the total area. A big effort is being made to develop a real-time systematic approach to estimate biomass production at a national level, focusing on spatial and seasonal variability in relation to drought. The absence of indirect low-cost methods that could be applied to large areas contributes to this situation. Advances in remote sensing and crop models offer new methodological and operative possibilities to solve this problem. In this paper, 13 forage regions (FR) in France were selected on the basis of their different geomorphologic, climatic and soil conditions with regard to pastoral production. Images from Système Probatoire de l'Observation de la Terre (SPOT) 4-VEGETATION were used to forecast productive variables estimated by the STICS-Prairie simulation model. In general terms, both satellite and productive data agreed properly. Particularly, the relationship between the middle infrared based vegetation index (SWVI) and the Leaf Area Index (LAI) demonstrated the best results whatever the FR. Results obtained confirm the capabilities of remote sensing data as an accurate predictor of productive variables estimated as from simulation models. Differences between satellite information and model estimations of pasture systems, especially during the harvesting periods, could be good indicators to improve model estimations at a regional scale as well.

Assessing the biomass dynamics of Andean bofedal and totora high-protein wetland grasses from NOAA/AVHRR

Biomass measurements of totora and bofedal Andean wetland grasses in the Bolivian Northern Altiplano were correlated over a growing season to vegetation indices derived from 1-km visible and near-infrared bands of the advanced very high resolution radiometer (AVHRR) instrument flown on the NOAA-14 polar-orbiting meteorological satellite. This article discusses the potential and limits of these indices for the assessment of the spatial and temporal variation of biomass and of the fraction of the photosynthetic active radiation absorbed by these herbaceous native forages growing in water-saturated environments. Bidirectional reflectance distribution function (BRDF) normalization was also investigated based on simple kernel-driven models. BRDF normalized difference vegetation index (NDVI) performed the best for both totorales and bofedales vegetation associations, followed by the uncorrected maximum-value composite NDVI. BRDF normalized NDVI was shown to be sensitive to the green leaf or photosynthetically active biomass. Estimation of biomass production after Kumar and Monteith (1982) was used to determine the efficiency of solar energy conversion into biomass ( ε b) for the main phenological periods, corresponding to the rainy and dry seasons. Two approaches were investigated for the biomass production estimation: the first one is based on monthly field biomass measurements; the second one is based on estimates from the regression computed previously using Roujean's BRDF normalized NDVI. The values found for these efficiencies for the rainy season agree with those of the literature for grasslands of temperate regions. For the dry season, more accurate information on totora and bofedal senescence and on animal consumption is required to get a reasonable efficiency value. This is not surprising, as other workers have reported biomass estimation with remotely sensed data to be most relevant to the growing season.

Water use in a Grevillea robusta–maize overstorey agroforestry system in semi-arid Kenya

Abstract Novel approaches involving a combination of sap flow measurements of transpiration and allometric estimates of biomass production were used to determine seasonal water use by trees and crops in agroforestry systems. The results were used to test the hypothesis that agroforestry may improve productivity by capturing a greater proportion of annual rainfall than annual crops. Grevillea robusta A. Cunn., which is reputed to have a deep rooting habit, was grown in semi-arid Kenya either as sole stands or in combination with maize (Zea mays L.). Water use by individual trees and maize plants was determined using constant temperature heat balance gauges and scaled to provide stand-level estimates of transpiration based on linear relationships (r2>0.70) between sap flow and leaf area across a range of tree ages and environmental conditions. Maximum stand-level transpiration rates for grevillea ranged from 2.6 to 4.0 mm per day, consistent with previous studies in similar environments. Biomass production by grevillea was closely correlated with stand-level transpiration (r2>0.69–0.74), suggesting that non-destructive estimates of biomass increments can be used to provide reliable estimates of seasonal transpiration. Cumulative water use by grevillea over the 4.5-year observation period was comparable in the sole tree and agroforestry treatments, reaching a maximum utilisation of annual rainfall of 64–68% 3–4 years after planting. Approximately 25% of the water transpired by the trees was used during the dry season, indicating that they were able to utilise off-season rainfall, comprising 16% of the total annual rainfall, and residual water remaining in the soil profile after the cropping period. During the 1995 long rains, when 221 mm of rain was received, transpiration by sole maize was

Biomass development for intensively managed loblolly pine plantations growing on Spodosols in the southeastern USA

Few published studies exist for intensively managed loblolly pine stands that document both above- and below-ground biomass accumulation over time. Site-specific biomass estimation equations (i.e., above-ground, above-ground+taproot, total tree including taproot, coarse roots and fine roots) for plantation-grown loblolly pine ( Pinus taeda L.) were developed from 13 intensively managed stands (1–4 yr) established on a common soil type (Spodosols) on the lower Coastal Plain of southern Georgia, USA. Extensive areas of pine plantations have been established on seasonally wet Spodosols, a dominant soil type in this region. Covariance analyses indicated that a single regression equation could be used to predict either above-ground or total tree biomass for 1- and 2-yr-old or 3- and 4-yr-old stands across all locations. Variations in the allometric relationships among sites were perhaps reduced because of the intensive understory competition control and fertilizer treatments that were applied to enhance growth. Leaf area accretion rates for these developing stands were rapid and largely sigmoidal, reaching a high of approximately 10.5 (all-sided) after three growing seasons. Total biomass increment ranged from about 2.0 Mg ha −1 yr −1 at age 1 yr to 10 Mg ha −1 yr −1 at ages 2 and 3 yr (total standing crop biomass at age 3 yr=22.8 Mg ha −1 ). The largest increase in total biomass increment, approaching 25 Mg ha −1 yr −1, occurred during the fourth growing season (total standing crop biomass=48.1 Mg ha −1 ). Roots (tap, coarse and fine) accounted for 32% of total biomass production at age 4 yr. Estimates of net annual biomass production documented in this study approach the upper limits of biological potential previously reported for this species within its native range. With the advent of advanced silvicultural systems that have combined genotype deployment, density control, and increased nutrient availability, differences between actual production and biological potential have become much narrower for loblolly pine over the last two decades.

Real-time monitoring of vegetation biomass with NOAA-AVHRR in Etosha National Park, Namibia, for fire risk assessment

Estimates of biomass production are important in a wildlife reserve such as Etosha National Park, Namibia, for assessment of fire risk and subsequent selection of sites for controlled burning. We present methodology for using locally acquired NOAA-AVHRR images to make estimates of biomass in near-to-realtime. To this end, techniques for rapid measurement of the biomass of herbaceous and woody vegetation were developed using a rising disc pasture meter and individual plant dimensions. A field sampling methodology is presented to make biomass estimates which were compatible with the scale of AVHRR spatial resolution and sufficiently close to the time of satellite overpasses to enable correlation with the NDVI from single images. Initial results show high correlations of biomass with NDVI for individual vegetation cover classes, which appear to be temporally stable. There seem to be different regression equations for the different savanna vegetation types although more field observations are needed to confirm this. The results were exploited to illustrate the potential application of this work for fire management. The combination of rapid field methods and real time image acquisition developed in this work provides a sound basis for biomass monitoring at local level.

Growth monitoring of a photosynthetic micro-organism (Spirulina platensis) by pressure measurement

An on-line measurement technique for estimating biomass production rate in a photosynthetic micro-organism culture was developed and tested experimentally. The technique is based on monitoring O2 production from the increase in pressure inside a closed photobioreactor. The data obtained by this method correlated with the direct measurement of the biomass concentration. A material balance on the components in the system allows the validity domain of the method to be defined. The method was applied to batch cultures of the cyanobacterium, Spirulina platensis, in a cylindrical photobioreactor validating existing physiological and light energy models.

Biomass equations for determining fractions of common and grey alders growing on abandoned farmland and some practical implications

A study was conducted in order to construct functions for above-ground biomass of fractions of young common alders ( Alnus glutinosa (L.) Gaertn.) and grey alders ( Alnus incana (L.) Moench.). The constructed functions were designed to be used to predict the amount of biofuel produced from small areas. Biomass production was estimated in 10 stands of common alder and 15 stands of grey alder, growing on abandoned farmland. The common alder stands were located in Sweden at latitudes ranging from 58° to 60° N, and their total age varied from 4 to 36 years. Grey alder stands were located at latitudes ranging from 60° to 66° N, and their total age varied from 5 to 35 years. A modified ‘mean tree technique’ was used to estimate biomass production, i.e. the tallest tree was chosen for sampling. The mean total dry weight above the stump level for common alder stands was 39 tonnes ha −1 with a range of 5 to 140 d.w. ha −1 and 61 tonnes ha −1 with a range of 3 to 140 tonnes d.w. ha −1 for grey alder stands. The mean annual increment for common alder stands was 3.11 tonnes ha −1 y −1 (0.50–7.71) and 4.38 tonnes ha −1 y −1 (0.66–9.32) for grey alder stands. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and leaf area index (LAI), among other measures, were estimated. The mean LAI for common alder stands was 3.16 and 2.03 for grey alder stands. The specific leaf area per tree for common alder was 16.1 m 2 kg −1 and 14.4 m 2 kg −1 for grey alder. Practical implications of the findings are discussed.

In situ versus laboratory estimations of length–weight regression and growth rate of Daphnia magna (Branchiopoda, Anomopoda) from an aerated waste stabilization pond

The present paper questions the adequacy of using length–weight regressions and growth rates calculated in the laboratory under constant physico-chemical and food conditions for the estimation of biomass and secondary production of animals living in a variable environment from the physico-chemistry and food availability point of view. Length–weight regressions (LWR) and growth rate of Daphnia magna were determined in situat five key periods of the year. In parallel, LWR and growth rate were determined in laboratory incubators at temperature adjusted to the mean temperature measured during the in situexperiments. LWR estimated from pond daphnids collected during the in situ experiments were, on the whole, not significantly different from LWR established during laboratory experiments, indicating that the food availability was globally similar in the laboratory and in situexperiments, even though food items were substantially different between the experiments. In situ algal biomass was indeed low compared to the algal biomass in laboratory experiments, but high biomasses of bacteria, protozoa and detritus were available for daphnid feeding in the tubes incubated in situ. Growth rate of D. magnawas monitored in situusing 50-ml tubes closed with Nylon net (mesh size = 80 μm) and in the laboratory using 50-ml glass flasks. The physico-chemical, bacteriological and algological variables were checked to be similar in the tubes and in the pond. Growth rates varied according to the size of the animal and according to the water temperature. The maximum growth rates were observed for juveniles at 20.2 °C. Growth rates were also determined in the laboratory at temperature corresponding to the mean temperature recorded in the pond during the in situ growth experiments. Differences between in situ and laboratory body length–growth rate regressions (LgR) were observed for the experiments conducted at 15.6 °C and 23.6 °C. Due to differences in LWR and LgR between in situ and laboratory experiments, biomass and daily production estimated from laboratory cultures were found to be significantly, but not severely, higher than biomass and daily production estimated on the basis of in situ experiments. It has been, therefore, concluded that, when the constraints linked to the realization of in situ growth experiments are too strong, the laboratory approach is fully justified.

Biomass equations for determining fractions of European aspen growing on abandoned farmland and some practical implications

A study was conducted in order to construct functions for aboveground biomass of fractions of young European aspens ( Populus tremula L.). The constructed functions were designed to be used for predicting the amount of biofuel produced from small areas. Biomass production was estimated in 11 stands of European aspen growing on abandoned farmland. The stands were located in Sweden at latitudes ranging from 65° to 60° N, and their total age varied from 5 to 24 years. A modified “mean tree technique” was used to estimate biomass production; i.e. depending on the plot area size, the number of sampled trees was chosen. The mean total dry weight above stump level for aspen stands was 78 tonnes ha −1 with a range of 14–162 d.w. ha −1. Mean annual increment for the stands was 5.56 tonnes ha −1 year −1 (2.86–9.15). Aspens growing on silt soils produced more than on fine sand soils. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and LAI, among other measures, were estimated. The mean LAI was 2.58 and the specific leaf area was 9.4 m 2 kg −1. Some practical implications are given.

Biomass equations for determining fractions of pendula and pubescent birches growing on abandoned farmland and some practical implications

Biomass production was estimated in 10 stands each of pendula birch ( Betula pendula Roth) and pubescent birch ( Betula pubescens Ehrh.) growing on abandoned farmland. The pendula birch stands were located in Sweden at latitudes ranging from 66° to 58°N, and their total age varied from 8 to 32 years. Pubescent birch stands were located at latitudes ranging from 66° to 60°N, and their total age varied from 6 to 20 years. A modified “mean tree technique” was used to estimate biomass production; i.e. the tallest tree was chosen for sampling. The actual mean total dry weight above stump level was 71 tonnes ha −1 (range, 6 to 175 tonnes d.w. ha −1) for pendula birch stands and 27.3 tonnes ha −1 (range, 7 to 61 tonnes d.w. ha −1) for pubescent birch stands. In addition to estimating conventional dry weights of trees and tree components, specific leaf area, total surface area and LAI, among other measures, were estimated.

Fertilization of Earth Ponds. III: Effects on Benthic Macro Invertebrates and Ecological Inter-Relationship with Aquatic Macrophytes

Organic fertilizers in form of cow and chicken manure were applied in oligotrophic or unproductive pond water over a period of one year to stimulate the production of benthic macro invertebrates for the benefit of trout culture, while maintaining adequate water quality. Development of aquatic macrophytes during both inorganic and organic fertilization in all the ponds was also evaluated with respect to the mutually beneficial relationship or `trade off' between the macrophytes and benthos. For the organic fertilization, replicate ponds were treated with low and high chicken manure (LC, HC), combination of high chicken and cow manure (HCC) and untreated controls (CTRL). The results showed that the application of HC and combination of HCC gave the highest numbers and biomass of benthos. The dominant groups encountered were in the order: Oligochaeta > Chironomidae > Asellidae > Sialidae > Hirudinea > Mollusca. Total abundance, biomass and dry weight production estimates of the benthos during the culture period were in the range, 3.5 - 134.0 x 103 ind. m-2; 26.0 - 113. gm-2 and 14.7 - 70.0g dry wt m-2 respectively. Throughout the inorganic and organic fertilization trials, pond 2, which was at various times treated with high phosphorus (HP) fertilizer and HCC had the most abundant macrophytes, with Elodea canadensis, Lemna mino, Glyceria fluitans and Alisma plantago-aquatica dominating, especially in the warm summer periods of July - August. The development of aquatic macrophytes in some ponds favoured production of some benthos, presumably due to greater foliage surface area that influenced plankton development, which are good sources of diet for the benthos. The results are discussed with respect to the mutually beneficial relationship or `trade-off' between the macrophytes and benthos, nutrient circulation and pond ecosystem stability. Journal of Aquatic Sciences Volume 14, April 1999, pp. 19-28 KEY WORDS: Fertilization, earth pond, macro invertebrates, macrophytes and ecological inter-relationship

Biomass production of Norway spruce (Picea abies (L.) Karst.) growing on abandoned farmland

Biomass production of forests has been studied for at least a century. Tree biomass is used in Sweden both as industrial raw material and an energy source. Few studies dealing with biomass yield from Norway spruce (Picea abies (L.) Karst.) growing on farmland are published. Practical recommendations are sparsely. The aim of this study was to construct dry weight equations for Norway spruce growing on farmland. Dry weight equations for fractions of Norway spruce trees were made. Biomass production was estimated in 32 stands of Norway spruce growing on abandoned farmland. The stands were located in Sweden at latitudes ranging from 58° to 64° N, and their total age varied from 17 to 54 years. A modified ‘mean tree technique’ was used to estimate biomass production; i.e. the tallest tree was chosen for sampling. The actual mean total dry weight above stump level for the 32 stands was 116 ton ha–1, with a range of 6.0 to 237.4 ton d.w. ha–1. When previous thinning removals were included, the mean biomass value was 127 ton ha–1 (6.0–262.8). In addition to estimating conventional dry weights of trees and tree components, basic density, specific leaf area, total surface area and leaf area index, among other measures, were estimated. Norway spruce biomass yields on plots subjected to different thinning were compared. The total harvested biomass was 75–120 ton d.w. ha–1 in heavy thinnings from below. Stands were thinned four to five times, with the first thinning at 23–27 years and the last at 51–64 years. The harvested biomass obtained in the first thinning was 18–38 ton d.w. ha–1. Total biomass production was 178–305 ton d.w. ha–1. Stands thinned from above supplied 71–130 ton d.w. ha–1 in total and 17–42 ton d.w. ha–1 in the first thinning. The total biomass supply was 221–304 ton d.w. ha–1. Unthinned stands produced a total of 155–245 ton d.w. ha–1.

Estimation of standing stock of chlorophylla and primary production from remote-sensed ocean color in the Oyashio region, the Western subarctic Pacific, during the spring bloom in 1997

In order to examine the applicability of remotely-sensed ocean color for the estimation of phytoplankton biomass and primary production in the Oyashio region, the western subarctic Pacific, vertical distributions of chlorophylla concentration and primary production were observed in April and May 1997. Spring bloom was observed in both April and May, and the surface concentration of chlorophylla exceeded 40 mg m−3. The relationship between the standing stocks of chlorophylla within the layer from the sea surface to one optical depth (0–1/k layer) and the surface chlorophylla concentration is expressed as a Michaelis-Menten equation. The mean ratio of the standing stock of chlorophylla in the euphotic layer to that in the 0–1/k layer was 4.41, this ratio did not significantly differ from 4.61 which was obtained at homogeneous distribution of chlorophylla within the euphotic layer. These facts suggest that the distribution of chlorophylla could be assumed to be homogeneous in the euphotic layer during the spring bloom. Results of primary production measurements by simulatedin situ method were compared with those by an algorithm with two variables; chlorphylla and non-spectral PAR. Daily primary production in the euphotic layer estimated by the algorithm varied in a range of 38–274% of that estimated by incubation, although the primary productions by the algorithm agreed with those by the incubation at a half of stations. Primary production within the euphotic layer calculated using simply the surface data was the same as that estimated using vertical distribution of chlorophylla. These results show that the primary production in the euphotic layer may be estimated from the remote sensed measurements during the spring bloom in the Oyashio region.

The integration of a satellite spectral analysis into a heather moorland management model (HMMM): The case of Moidach More, northeast Scotland, U.K.

In this paper, high resolution, remotely-sensed data are investigated as a source of management information for moorland vegetation communities on a hypothetical farm in a marginal farming area of Scotland. A hybrid technique for vegetation mapping is adopted. This involves unsupervised machine classification of spectral variation in digitally enhanced air photographs and satellite imagery, together with visual interpretation of the imagery in both the laboratory and the field. This technique enables relative estimates of annual gross biomass production, for a range of vegetation types, to be obtained. The data are integrated into a simple heather moorland management model (HMMM), to produce potential sheep-stocking capacities under a range of management scenarios, the possible financial implications of these scenarios are also assessed.

Estimation of biomass and utilization of three perennial range grasses in Saudi Arabia

Most range management decisions are based on quantitative measurements of production and utilization of key range plant species. A study was conducted to estimate biomass production and utilization of three perennial grasses using dimension analysis and height–weight profiles. Plant height, basal diameter and canopy diameter were highly correlated with biomass ofLasiurus sindicus. Plant biomass ofPennisetum divisumandStipagrostis drariiwas correlated to basal and canopy diameters. The three variables were evaluated for predicting biomass of the three grass species using best subset regression approach. From a practical point of view, basal and canopy diameters would be good predictors ofL. sindicusandS. drariibiomass. ForP. divisum, all three dimension measurements are needed for satisfactory results. Height–weight profiles were developed for each species to assess utilization based on estimation of percentage of height removed in relation to percentage weight removed. Although good correlation was found between height and weight, it is likely that light grazing will be underestimated. However, this would not limit the use of height–weight profiles as defoliation thresholds are never approached under long-term light grazing.

Virtual plants—integrating architectural and physiological models

Recent advances in computer technology have made it possible to create virtual plants by simulating the details of structural development of individual plants. Software has been developed that processes plant models expressed in a special purpose minilanguage based on the Lindenmayer system formalism. These models can be extended from their architectural basis to capture plant physiology by integrating them with crop models, which estimate biomass production as a consequence of environmental inputs. Through this process, virtual plants will gain the ability to react to broad environmental conditions, while crop models will gain a visualisation component. This integration requires the resolution of the fundamentally different time scales underlying the approaches. Architectural models are usually based on physiological time; each time step encompasses the same amount of development in the plant, without regard to the passage of real time. In contrast, physiological models are based in real time; the amount of development in a time step is dependent on environmental conditions during the period. This paper provides a background on the plant modelling language, then describes how widely-used concepts of thermal time can be implemented to resolve these time scale differences. The process is illustrated using a case study.