Biomass Regrowth Research Articles

Disentangling the effects of predator hunting mode and habitat domain on the top-down control of insect herbivores

1. Polyphagous predatory invertebrates play a key role in the top-down control of insect herbivores. However, predicting predation risk for herbivores is not a simple function of predator species richness. Predation risk may be reduced or enhanced depending on the functional characteristics predator species. We predict that where predator species spatially overlap this will reduce predation risk for herbivores by allowing negative inter-specific interaction between predators to occur. Where increased predation risk occurs, we also predict that this will have a cascading effect through the food chain reducing plant growth. 2. We used a substitutive replicated block design to identify the effect of similarity and dissimilarity in predator hunting mode (e.g. 'sit and wait', 'sit and pursue', and 'active') and habitat domain (e.g. canopy or ground) on the top-down control of planthoppers in grasslands. Predators included within the mesocosms were randomly selected from a pool of 17 local species. 3. Predation risk was reduced where predators shared the same habitat domain, independent of whether they shared hunting modes. Where predators shared the same habitat domains, there was some evidence that this had a cascading negative effect on the re-growth of grass biomass. Where predator habitat domains did not overlap, there were substitutable effects on predation risk to planthoppers. Predation risk for planthoppers was affected by taxonomic identity of predator species, i.e. whether they were beetles, spiders or true bugs. 4. Our results indicated that in multi-predator systems, the risk of predation is typically reduced. Consideration of functional characteristics of individual species, in particular aspects of habitat domain and hunting mode, are crucial in predicting the effects of multi-predator systems on the top-down control of herbivores.

Greenhouse Gas Budget of a Cool-Temperate Deciduous Broad-Leaved Forest in Japan Estimated Using a Process-Based Model

A terrestrial ecosystem model, called the Vegetation Integrative Simulator for Trace gases model (VISIT), which fully integrates biogeochemical carbon and nitrogen cycles, was developed to simulate atmosphere–ecosystem exchanges of greenhouse gases (CO2, CH4, and N2O), and to determine the global warming potential (GWP) taking into account the radiative forcing effect of each gas. The model was then applied to a cool-temperate deciduous broad-leaved forest in Takayama, central Japan (36°08′N, 137°25′E, 1420 m above sea level). Simulations were conducted at a daily time step from 1948 to 2008, using time-series meteorological and nitrogen deposition data. VISIT accurately captured the carbon and nitrogen cycles of this typical Japanese forest, as validated by tower and chamber flux measurements. During the last 10 years of the simulation, the model estimated that the forest was a net greenhouse gas sink, having a GWP equivalent of 1025.7 g CO2 m−2 y−1, most of which (1016.9 g CO2 m−2 y−1) was accounted for by net CO2 sequestration into forest biomass regrowth. CH4 oxidation by the forest soil made a small contribution to the net sink (11.9 g CO2-eq. m−2 y−1), whereas N2O emissions were a very small source (3.2 g CO2-eq. m−2 y−1), as expected for a volcanic soil in a humid climate. Analysis of the sensitivity of GWP to changes in temperature, precipitation, and nitrogen deposition indicated that warming temperatures would decrease the size of the sink, mainly as a result of increased CO2 release due to increased ecosystem respiration.

A novel knotted cotton-thread carrier: its potential use in achieving the biomass renewal of Phanerochaete chrysosporium in an immobilized growth system

In order to achieve an innovative strategy to renew the biomass of Phanerochaete chrysosporium in an immobilized growth system which can maintain white-rot fungi biomass, a novel knotted cotton-thread carrier was designed and made. By using a high-speed stirring apparatus under the conditions of 1400 r/min stirring speed for 6 min, mycelia immobilized on the knotted cotton-thread carriers were exfoliated completely and homogenized to a proper size. Furthermore, the homogenized mycelia from the immobilized mycelia can resume their growth on the knotted cotton-thread carriers in agitated flask cultures. The average regrowth biomass on the new carriers and the reused carriers was 0.0171 g/carrier and 0.0314 g/carrier, respectively. It proves that the knotted cotton-thread carrier performs perfectly in homogening the immobilized mycelia to achieve the biomass renewal of P. chrysosporium in an immobilized growth system.

Use of multitemporal SAR data for monitoring vegetation recovery of Mediterranean burned areas

Remote sensing in the optical band is a well-established tool for monitoring changes in forested areas, although it can suffer from limitations, especially where frequent cloud cover occurs. The increased availability of space-borne radar imagery offers additional means for assessing the state of forests and monitoring their dynamics. In this study, the potential of multi-temporal space-borne SAR data for monitoring vegetation recovery over burned areas next to the Mediterranean coast is investigated. In particular, the study considers a set of ERS-SAR images, C-band and VV polarization, taken over the Castel Fusano pinewood, located near Rome, Italy, devastated in summer 2000 by a fire that burned about 350 ha of the wood. Starting from the analysis of the information contained in the variations, both in burnt and unburnt areas, of the inter annual multitemporal backscattering signatures, the study presents two different approaches, one more qualitative, the other one more quantitative, for the retrieval of the biomass re-growth after the fire. In the quantitative case, the inversion procedure computes the biomass re-growth rate by means of simulations carried out with the Tor Vergata scattering model. The obtained results are satisfactory as they are in agreement with simultaneous analysis based on optical data and in-situ measurement campaigns.

Differential herbivory tolerance of dominant and subordinate plant species along gradients of nutrient availability and competition

We tested whether differences in the herbivory tolerance of plant species is related to their abundance in grassland communities and how herbivory and nutrient availability affect competitive balances among plant species through changes in their tolerance. The experimental approach involved a simulated grazing treatment (clipping) of two competitive grass species (Arrhenatherum elatius and Holcus lanatus) and two subordinate forb species (Prunella vulgaris and Lotus corniculatus) along a gradient of nutrient availability and under conditions of competition. Total standing, aboveground, root, and regrowth biomass were evaluated at the end of the experiment as an estimate of the capacity to compensate for twice removing aboveground biomass at different nutrient levels (NPK). Although clipping had a more pronounced negative effect on dominant plant species (Arrhenatherum and Holcus) than on subordinate species, the negative effects on dominant species were offset by the application of fertilizer. The combined effect of fertilizer and competition had more negative effects on the performance of Lotus and Prunella than on the dominant species. In terms of competition, the regrowth ability of Arrhenatherum and Holcus increased with the application of fertilizer, while the opposite pattern was observed for Lotus and Prunella. The addition of fertilizer has a positive effect on both grass species in terms of growth in clipped pots and competition, while subordinate species did not respond to the addition of fertilizer to the clipped pots and were negatively affected by competition with both grass species. The results suggest (1) that species replacement towards subordinate species as a function of herbivory is partially dependent on the herbivory tolerance of that species, (2) competitive relations between competitive grass species and subordinate forb species change under different environmental conditions, and (3) although grazing disturbance significantly influences competitive relations in favor of less competitive species, increasing nutrient levels counteract the negative effect of grazing on dominant competitive plant species.

Allometric growth, disturbance regime, and dilemmas of controlling invasive plants: a model analysis

Disturbed communities are observed to be more susceptible to invasion by exotic species, suggesting that some attributes of the invaders may interact with disturbance regime to facilitate invasion success. Alternanthera philoxeroides, endemic to South America, is an amphibious clonal weed invading worldwide. It tends to colonize disturbed habitats such as riparian zones, floodplain wetlands and agricultural areas. We developed an analytical model to explore the interactive effects of two types of physical disturbances, shoot mowing and root fragmentation, on biomass production dynamics of A. philoxeroides. The model is based on two major biological assumptions: (1) allometric growth of root (belowground) vs. shoot (aboveground) biomass and (2) exponential regrowth of shoot biomass after mowing. The model analysis revealed that the interaction among allometric growth pattern, shoot mowing frequency and root fragmentation intensity might lead to diverse plant ‘fates’. For A. philoxeroides whose root allocation decreases with growing plant size, control by shoot mowing was faced with two dilemmas. (1) Shoot regrowth can be effectively suppressed by frequent mowing. However, frequent shoot mowing led to higher biomass allocation to thick storage roots, which enhanced the potential for faster future plant growth. (2) In the context of periodic shoot mowing, individual shoot biomass converged to a stable equilibrium value which was independent of the root fragmentation intensity. However, root fragmentation resulted in higher equilibrium population shoot biomass and higher frequency of shoot mowing required for effective control. In conclusion, the interaction between allometric growth and physical disturbances may partially account for the successful invasion of A. philoxeroides; improper mechanical control practices could function as disturbances and result in exacerbated invasion.

Influence of nutrient availability on the mechanisms of tolerance to herbivory in an annual grass, Avena barbata (Poaceae)

Tolerance, or the capacity of a genotype to survive and reproduce following herbivore damage, varies widely across the plant kingdom. One proximate cause of this variation is resource availability, which can influence tolerance through mechanisms such as growth rate and photosynthesis. We examined the effect of high and low soil nutrient levels on the relationship between tolerance and two of its underlying mechanisms, biomass regrowth and photosynthetic upregulation, among genotypes of the Mediterranean annual grass Avena barbata. Although defoliated plants did not reach the same biomass as controls, biomass regrowth was higher at high nutrients. However, increased seed abortion at high nutrients caused tolerance to be the same in both nutrient treatments. Increased seed abortion also uncoupled biomass regrowth from tolerance at high nutrients. We found no evidence for photosynthetic upregulation in defoliated compared to control plants in either nutrient treatment. However, tolerance was positively correlated with predefoliation photosynthetic efficiency at high nutrients. Thus, constitutive photosynthetic efficiency may be a better predictor of tolerance than photosynthetic responses following herbivory in A. barbata. More generally, our results highlight the possibility that the mechanisms of tolerance can differ across resource environments even if tolerance is the same.

Biomass Inventory and Regrowth Rate of Harvestable Tree and Shrub Moss in the Oregon Coast Range

Abstract The commercial moss harvest industry is at a crossroads. Concerns about the sustainability of harvest have led to moratoria on moss harvest from public lands, limiting access to this nontimber forest resource in most of the highest production regions of the United States. Resumption of legal harvest depends on improved knowledge about resource inventory and yield, which will enable the development of appropriate management scenarios. We present here the results of an inventory of current readily available legally harvestable moss and of a 10-year biomass regrowth study from the Coast Range of western Oregon. Harvestable tree and shrub moss was removed from 21 sites on the Siuslaw National Forest, using typical harvest methods and following the Forest's standards and guidelines for commercial moss harvest. Biomass across these sites averaged only 19 kg/ha (fresh weight). Only 52% of sites bore any harvestable moss, and only 38% had commercial quantities. Moss mats regrowing on experimentally stripped vine maple (Acer circinatum) shrub stems accumulated mass at a mean rate of 3.0 g/m-stem/year across six sites. At this rate, moss mats of equivalent biomass to the originally harvested mats would require approximately 27 years to develop. These data provide estimates of input parameters needed to develop schedules for commercial moss harvest.

Utilization Characteristics and Importance of Woody Biomass Resources on the Rural-Urban Fringe in Botswana

This article examines the utilization characteristics and importance of woody biomass resources in the rural-urban fringe zones of Botswana. In the literature for Africa, attention has been given to the availability and utilization of biomass in either urban or rural environments, but the rural-urban fringe has been neglected. Within southern Africa, this neglect is not justified; the rural-urban fringe, not getting the full benefits available in urban environments in Botswana, has developed problems in woody biomass availability and utilization that require close attention. In this article, socioeconomic data on the importance of woody biomass in the Batlokwa Tribal Territory, on the rural-urban fringe of Gaborone, Botswana, were collected together with ecologic data that reveal the utilization characteristics and potential for regrowth of woody biomass. The analysis of these results show that local woody biomass is very important in the daily lives of communities in the rural-urban fringe zones and that there is a high level of harvesting. However, there is no effort in planning land use in the tribal territory to either conserve this resource or provide alternatives to its utilization. The future of woody biomass resources in Botswana's rural-urban fringe is uncertain. The investigators recommend that a comprehensive policy for the development of the rural-urban fringe consider the importance of this resource. The neglect of this resource will have far-reaching implications on the livelihoods of residents as well as the environment in this zone.

Management of below-ground biomass of Typha angustifolia by harvesting shoots above the water surface on different summer days

A dynamic model of regrowth in Typha angustifolia after cutting shoots above the water surface was formulated by characterizing the phenology and mobilization of resources from below-ground to above-ground organs after the cutting. The model parameters were determined by two cutting experiments to investigate the different strategies with flowering and non-flowering shoots after cutting in 2001 and by four cutting experiments to elucidate the regrowth characteristics after cutting on different days from June to September in 2002. A difference was evident both for flowering and non-flowering shoots and for each cutting day. From June to August, non-flowering shoots regrew immediately after cutting, but flowering shoots did not. The shoot regrowth height, number of leaves and shoot biomass were higher with the earlier cutting. The model was validated using the below-ground biomass observed in December 2002 and below-ground dynamics observed in 2003. In the low-flowering shoot zone of the stands, in which the percentage of flowering shoots was small (around 10%), the decrease in below-ground biomass became larger from June (20%) to August (60%). Cutting the high-flowering shoot zone (flowering shoots: 78%) in July 2001, just 1 week after peduncle formation, decreased the below-ground biomass by about 50%. In the low-flowering shoot zone, cutting just before senescence is better for decreasing below-ground biomass with a smaller rate of flowering shoots. The difference of below-ground biomass reduction in non-flowering shoots is mainly due to the decrease in downward translocation (DWT) of above-ground material to below-ground organs during senescence, because of the decrease in regrowth biomass. As for flowering shoots, the decrease in the photosynthate transportation from above-ground to below-ground organs and that of DWT are closely related because they cannot grow again within the season.

Deflocculation effects due to chemical perturbations in sequencing batch reactors

Toxic shock-induced deflocculation was examined for activated sludge exposed to six different classes of industrially relevant chemical toxins: an electrophilic solvent (1-chloro-2,4-dinitrobenzene, CDNB), a heavy metal (cadmium), a hydrophobic chemical (1-octanol), an uncoupling agent (2,4-dinitrophenol, DNP), alkaline pH, and weakly complexed cyanide. The concentrations required to inhibit respiration by 50% were used to shock sequencing batch reactors (SBRs) containing a nitrifying (10-day solids retention time (SRT)) and a non-nitrifying (2-day SRT) biomass. Effluent total suspended solids (TSS) and soluble potassium were monitored to examine deflocculation caused by a bacterial stress response mechanism called glutathione-gated potassium efflux (GGKE). Reactors were monitored for recovery over a period of 3 SRTs or less. At the concentrations tested, CDNB, cadmium and pH 11 were found to cause significant increases in effluent TSS concentrations and showed elevated levels of potassium. In contrast, octanol, DNP and cyanide did not induce severe deflocculation and showed moderate increases in effluent potassium levels. Recovery of effluent TSS and potassium concentrations to control levels generally did not correlate, supporting the hypothesis that reflocculation requires regrowth of biomass. These results suggest that different chemicals induce deflocculation in SBRs, but deflocculation is not necessarily caused by the GGKE mechanism in all cases.

FIRE EFFECTS ON PLANT DIVERSITY IN SERPENTINE VS. SANDSTONE CHAPARRAL

Fire contributes to the maintenance of species diversity in many plant communities, but few studies have compared its impacts in similar communities that vary in such attributes as soils and productivity. We compared how a wildfire affected plant diversity in chaparral vegetation on serpentine and sandstone soils. We hypothesized that because biomass and cover are lower in serpentine chaparral, space and light are less limiting, and therefore postfire increases in plant species diversity would be lower than in sandstone chaparral. In 40 pairs of burned and unburned 250-m2 plots, we measured changes in the plant community after a fire for three years. The diversity of native and exotic species increased more in response to fire in sandstone than serpentine chaparral, at both the local (plot) and regional (whole study) scales. In serpentine compared with sandstone chaparral, specialized fire-dependent species were less prevalent, mean fire severity was lower, mean time since last fire was longer, postfire shrub recruitment was lower, and regrowth of biomass was slower. Within each chaparral type, the responses of diversity to fire were positively correlated with prefire shrub cover and with a number of measures of soil fertility. Fire severity was negatively related to the postfire change in diversity in sandstone chaparral, and unimodally related to the postfire change in diversity in serpentine chaparral. Our results suggest that the effects of fire on less productive plant communities like serpentine chaparral may be less pronounced, although longer lasting, than the effects of fire on similar but more productive communities.

Importance of tolerance to herbivory for plant survival in a British grassland

Abstract Question: Is plant capacity to regrow under different herbivore treatments related to herbivore increaser/decreaser plant status? Location: Grassland in Southeast England (GR 41/944691). Methods: A field experiment was established in order to understand the role of plant tolerance to herbivory in explaining the abundance of nine grassland species previously known as herbivore increasers or decreasers. Tolerance was measured as a plant's capacity to regrow after exposure to herbivores. The experiment was designed to measure the impact of rabbits, molluscs, insects and clipping (artificial damage). Plants were propagated by stolons, exposed to different treatments in the field and then allowed to recover in the greenhouse for a month Results: Previous studies have stated that plants that are able to persist in a herbivore environment could be tolerant or resistant, in agreement with the later our results showed that rabbit increaser plants were tolerant to herbivory in terms of biomass regrowth. No...

Biomass growth and element uptake by young trembling aspen in relation to site treatments in Northern Ontario, Canada

A second-growth boreal mixedwood, consisting mainly of trembling aspen and balsam fir, with white spruce, balsam poplar and white birch admixed, defoliated in part by spruce budworm, was harvested in late autumn 1992 by conventional cut-and-skid, whole-tree logging. Four blocks, subdivided into 10-m by 10-m plots, separated by buffer strips, were laid out. The objective of the study was to compare the efficacy and environmental implications of screefing (i.e. organic layer removal) versus high-speed mixing (using a prototype forestry rototiller), both applied in strips and across whole plots, versus no treatment (cut control) in terms of regrowth biomass production and nutrient uptake. All plots were quickly occupied by a verdant herbaceous regrowth and, depending upon treatment, hardwood shoots. Screefing generally increased numbers of hardwood shoots relative to the control, whereas mixing generally reduced numbers. Above-ground standing crops including tree and non-tree species by the middle of 1997 ranged from 9500 kg ha −1 on cut control plots to 4400 kg ha −1 on whole-area mixed plots. Nutrient contents in the aboveground vegetation varied commensurately, ranging up to 91 kg ha −1 for N, 11 for P, 79 for K, 94 for Ca, 18 for Mg and 8 for S. Leafy matter recovery on the most responsive treatment (harvest with no further site preparation) was ca. 70% complete within five years and the N, P, K, Ca, Mg, and S contents therein had reached or almost reached the same levels as the precut stand. This implies that nutrient cycling largely resumes within five years of harvest.

Volunteer biomass production between multipurpose tree hedgerows after two years of fallow in southern Cameroon

The ability of multipurpose hedgerow tree species to out-compete undesired regrowth during fallow phases was examined. Biomass and spatial distribution of grass and broad leaf volunteers was measured after two years of fallow, in two alley cropping systems planted at six m interrow distance, at the Humid Forest Ecoregional Centre Research Station, Mbalmayo, southern Cameroon. The two experiments had been continuously cropped for five and six years previously. In the experiment cropped for six years, the presence of Senna spectabilis [(DC.) Irwin and Barnaby] hedgerows reduced the biomass of the volunteer regrowth from 9.2 to 4.3 Mg ha−1. Tillage during the previous cropping phase increased the broad leaf biomass from 3.0 to 4.4 Mg ha−1, reduced the biomass of grasses from 3.4 to 2.7 Mg ha−1 but had no effect on the total volunteer biomass. Volunteer biomass was significantly lower within 1.5 m of the S. spectabilis hedgerows than at positions further away. In the experiment cropped for five years, S. spectabilis reduced the volunteer regrowth biomass significantly. Two other hedgerow species, Dactyladenia barteri [(Hook f ex Oliv.) Engl.] and Flemingia macrophylla [(Willd.) Merrill] had no effect on the total amount of volunteer regrowth but did reduce volunteer biomass within 0.5 m of the hedgerows. S. spectabilis caused a stronger reduction of volunteer biomass than D. barteri and F. macrophylla at almost all distances from the hedgerows. The competitiveness of D. barteri and F. macrophylla is insufficient and their growth habit is unsuitable to out-compete undesired species in this alley cropping system.

The impact of biomass harvesting on phosphorus uptake by wetland plants

Two species of macrophytes, Baumea articulata and Schoenoplectus mucronatus, were examined for their capacity to remove phosphorus under nutrient-rich conditions. Forty large bucket systems with the two different species growing in two types of substrate received artificial wastewaters for nine months, simulating a constructed wetland (CW) under high loading conditions. Half of the plants growing in the topsoil and gravel substrates were periodically harvested whereas the other half remained intact. Plant tissue and substrate samples were regularly analysed to determine their phosphorus concentrations. With respect to phosphorus uptake and removal, the Schoenoplectus in the topsoil medium performed better than the Baumea. Biomass harvesting enhanced P uptake in the Schoenoplectus, however the effect was not significant enough to make an improvement on the overall P removal, due to the slow recovery of plants and regrowth of biomass after harvesting. From P partitioning, it was found that the topsoil medium was the major P pool, storing most of total P present in the system. Plant parts contributed only minor storage with approximately half of that P stored below ground in the plant roots. The overall net effect of harvesting plant biomass was to only remove less than 5% of total phosphorus present in the system.

Nutrient Dynamics of Rangeland Burns in Southeastern Arizona

Burning of vegetation generally increases surface runoff and erosion and potentially can change the nutrient dynamics of an ecosystem with loss of nutrients. Nitrogen, phosphorus, and potassium nutrient status of soil and aboveground biomass were determined before fall and spring burns and 1 year later at 2 different soil and vegetation type locations in southeastern Arizona. The evaluations were repeated in subsequent years to evaluate a year effect. Potential nutrient loss in surface runoff and sediment was assessed with rainfall simulations conducted immediately after prescribed burns and after a second burn one year later. Nutrient loss in the runoff water and sediment from burned areas was compared to paired unburned. The soil contained >98% of the total nutrient and was not significantly influenced by the burn treatment. The nutrient concentrations in the regrowth biomass were generally greater. Immediately after the first burn, nutrient loss in surface runoff and sediment was not affected by the burn treatment, but one location was greater than the other. After 1 year and a second burn, nutrient losses on the burn treatment were significantly greater than the unburned treatment and similar between locations. The nutrient loss in surface runoff was primarily associated with the sediment and influenced by an interaction between biomass and soil. The nutrient loss in runoff and sediment was small compared to the nutrient in the aboveground biomass and insignificant compared to the soil nutrient. The implication is that increased surface nutrient loss from burning could take place for many years before a significant amount of nutrient would be lost from the large soil pool and change the nutrient status of the ecosystem. Year and season were also important factors influencing nutrients in the soil, biomass, and in runoff and sediment losses, irrespective of a burn treatment effect.

Regrowth of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) following defoliation

Effects of defoliation of crested wheatgrass (Agropyron cristatum [L.] Gaertn.) on the amount of time required to reach peak regrowth, the lag period for regrowth to begin, regrowth biomass, tiller survival and replacement, and carryover effects of defoliation the following year were investigated. Regrowth of crested wheatgrass was determined during the summers of 1990, 1991 and 1992 in central Saskatchewan following a single defoliation to a 5-cm stubble height at eight stages of growth. Crested wheatgrass regrew 54–130 g m−2 of biomass when defoliated tillers had ≤3.6 leaves. Regrowth began accumulating within 3–53 growing degree-days (GDD) and peaked in 705–875 GDD. Rates of leaf development after defoliation (218–252 GDD phyllochron−1) equaled or were faster than control (218–330 GDD phyllochron−1). Regrowth biomass accounted for 35–76% of total annual production. Total annual production was greatest when plants were defoliated during vegetative growth or at peak growth. In 1991 and 1992, etiolated growth in the spring following defoliation was reduced by defoliation in the previous year. Tiller replacement was not affected by defoliation and averaged 1.2 tillers tiller−1 (SE = 0.1) in 1991 and 1.5 tillers tiller−1 (SE = 0.1) in 1992. Two periods of grazing can be expected from crested wheatgrass if it is grazed when tillers have ≤3.6 leaves; however, the impacts of a second grazing must be determined. If crested wheatgrass is grazed late in the growing season, only one period of grazing can be expected, and production will likely be less the following growing season, necessitating a rest period for plants to regain their production potential. Key words: Crested wheatgrass, defoliation, grazing management, growing degree-days, phyllochron, regrowth

Applications of imaging radar data in Earth science investigations

Synthetic aperture radar (SAR) data provide unique information about the Earth's surface and biodiversity, including critical data for natural hazards and resource assessments. The ability to calculate the cross-section of a scatterer for any transmit and receive polarisation combination provides detailed information about vegetation for assessing changes in land cover, biomass and forest regrowth. Unique SAR interferometric measurements, predominantly large-scale surface change at fine resolution, are used to generate topographic data sets, monitor surface topographic change, and measure glacier ice velocity. The LightSAR mission, planned for launch in 2002 will be optimised for polarimetric and interferometric data acquisition in order to provide long-term observations of the Earth's changing conditions.

Biomass production and species composition change in a tallgrass prairie ecosystem after long‐term exposure to elevated atmospheric CO2

AbstractTo determine the long‐term impact of elevated CO2 on primary production of native tallgrass prairie, we compared the responses of tallgrass prairie at ambient and twice‐ambient atmospheric CO2 levels over an 8‐year period. Plots in open‐top chambers (4.5 m diameter) were exposed continuously (24 h) to ambient and elevated CO2 from early April to late October each year. Unchambered plots were monitored also. Above‐ground peak biomass was determined by clipping each year in early August, and root growth was estimated by harvesting roots from root ingrowth bags. Plant community composition was censused each year in early June. In the last 2 years of the study, subplots were clipped on 1 June or 1 July, and regrowth was harvested on 1 October. Volumetric soil water content of the 0–100 cm soil layer was determined using neutron scattering, and was generally higher in elevated CO2 plots than ambient. Peak above‐ground biomass was greater on elevated CO2 plots than ambient CO2 plots with or without chambers during years with significant plant water stress. Above‐ground regrowth biomass was greater under elevated CO2 than under ambient CO2 in a year with late‐season water stress, but did not differ in a wetter year. Root ingrowth biomass was also greater in elevated CO2 plots than ambient CO2 plots when water stress occurred during the growing season. The basal cover and relative amount of warm‐season perennial grasses (C4) in the stand changed little during the 8‐year period, but basal cover and relative amount of cool‐season perennial grasses (C3) in the stand declined in the elevated CO2 plots and in ambient CO2 plots with chambers. Forbs (C3) and members of the Cyperaceae (C3) increased in basal cover and relative amount in the stand at elevated compared to ambient CO2. Greater biomass production under elevated CO2 in C4‐dominated grasslands may lead to a greater carbon sequestration by those ecosystems and reduce peak atmospheric CO2 concentrations in the future.