J. S. Singh

PLANT DECOMPOSITION AND SOIL RESPIRATION IN TERRESTRIAL ECOSYSTEMS

SummaryThis review deals with methodological approaches, measured rates, and environmental control of two major interdependent processes regulating the structure and function of terrestrial ecosystems, viz., plant decomposition and soil respiration.Both these processes have been evaluated through indirect assessments as well as through direct measurements under the field conditions. The techniques used suffer in general from difficulties in creating conditions of natural environment during the process of measurement. Generalizations regarding the magnitude of rates in different ecosystems are difficult because of limited results or non-comparability of results from different methods.Temperature and moisture and their interactions markedly influence both the processes. The surface feeders and soil animals have a marked influence on the decomposition. Partitioning of soil respiration into components due to live roots, microbes, and soil fauna has eluded a satisfactory solution so far.SommaireCette revue traite des approches méthodologiques, des vitesses mesurées et du contrôle des environs de deux procédés interdépendants principaux qui règlent la structure et la fonction des écosystèmes terrestes, viz, la décomposition des plantes et de la respiration du sol.Ces deux procédés ont été évalués par des méthodes indirectes aussi bien que par des mesures directes sous le terrain. Les techniques employées souffrent en géneral des difficultés dans la création des conditions de l’environnement naturel pendant mesure. Des généralisations en ce qui concerne la grandeur des vitesses dans les différents écosystèmes sont difficiles parce que les différentes méthodes ne peuvent pas être comparées que d’une façon limitée ou non-comparable.La température et l’humidité et leurs interactions ont une très grande influence sur les deux procédés. Les animaux et les plantes qui se nourrissent sur la surface et les animaux dans la terre ont une très grande influence sur la décomposition. La séparation de la respiration du sol en composantes causée par des microbes des racines vivantes et de la faune du sol a echappé à une solution satisfaite jusqu’à présent.

The structure and function of ten Western North American grasslands: III. Net primary production, turnover and efficiencies of energy capture and water use

(1) Levels of net primary production and the efficiencies of energy capture and water use were investigated in six grassland types encompassing ten western North American grasslands. Emphasis was placed on between-site analysis to show the importance of abiotic variables in the functioning of the ecosystem at the producer level. (2) Above-ground primary production (ANP) ranged from 54 to 523 g m -2 yr -1 . Average ANP for grazed grasslands was 212 compared to 236 g m -2 yr -1 for ungrazed grasslands (P ≤ 0.05). (3) There was an apparent linear increase in ANP with increasing precipitation up to approximately 500 mm yr-1. Likewise, ANP increased linearly with increases in both growing-season and annual actual evapotranspiration. (4) Net root production (RP) ranged from 148 to 641 g m -2 yr -1 . The RP was significantly higher on grazed treatments compared to ungrazed grasslands. In general, RP increased with decreasing levels of long-term mean annual temperature. (5) Total net primary productivity (TNP) ranged from 225 to 1425 g m -2 yr -1 . Approximately 46% and 58% of the variability in TNP were explained by annual precipitation in ungrazed and grazed grasslands, respectively. (6) Generally, the warmer grasslands had higher rates of turnover of crown material than did cooler grasslands. As annual usable incident solar radiation and annual actual evapotranspiration increased, so the rate of crown-turnover increased. (7) The average rate of turnover of root material was 0.18, 0.30 and 0.49 for the mixed-grass, tallgrass and shortgrass prairies, respectively. There was a positive curvilinear relationship between root turnover and total annual usable incident solar radiation. (8) Efficiency of energy capture in TNP ranged from 0.12% to more than 1.4% for both ungrazed and grazed grasslands. It appears that plant communities dominated by cool-season species were comparable to or more efficient in energy capture than the communities dominated by warm-season plants. Grasslands having higher efficiencies of water use for TNP also had greater efficiency of energy capture. Consequently, these two important functional properties of the producer system are positively related.

Forest vegetation of the Himalaya

This review deals with the forest vegetation of the Himalaya with emphasis on: paleoecological, phytogeographical, and phytosociological aspects of vegetation; structural and functional features of forest ecosystem; and relationship between man and forests.The Himalayan mountains are the youngest, and among the most unstable. The rainfall pattern is determined by the summer monsoon which deposits a considerable amount of rain (often above 2500 mm annually) on the outer ranges. The amount of annual rainfall decreases from east to west, but the contribution of the winter season to the total precipitation increases. Mountains of these dimensions separate the monsoon climate of south Asia from the cold and dry climate of central Asia. In general, a rise of 270 m in elevation corresponds to a fall of 1°C in the mean annual temperature up to 1500 m, above which the fall is relatively rapid.Large scale surface removals and cyclic climatic changes influenced the course of vegetational changes through geological time. The Himalayan ranges, which started developing in the beginning of the Cenozoic, earlier supported tropical wet evergreen forests throughout the entire area (presently confined to the eastern part). The Miocene orogeny caused drastic changes in the vegetation, so much so that the existing flora was almost entirely replaced by the modern flora. Almost all the dominant forest species of the Pleistocene continue to maintain their dominant status to the present. Presently the Himalayan ranges encompass Austro-Polynesian, Malayo-Burman, Sino-Tibetan, Euro-Mediterranean, and African elements. While the Euro-Mediterranean affinities are well represented in the western Himalayan region (west of 77°E long.), the Chinese and Malesian affinities are evident in the eastern region (east of 84°E long.). However, the proportion of endemic taxa is substantial in the entire region.A representation of formation types in relation to climatic factors, viz., rainfall and temperature, indicates that boundaries between the types are not sharp. Formation types often integrate continuously, showing broad overlaps. Climate does not entirely determine the formation type, and the influence of soil, fire, etc., is also substantial. The ombrophilous broad leaf forests located in the submontane belt (< 1000 m) of the eastern region are comparable to the typical tropical rain forests. On the other extreme, communities above 3000 m elevation are similar to sub-alpine and alpine types. From favorable to less favorable environments, as observed with decreasing moisture from east to west, or with decreasing temperature from low to high elevations, the forests become increasingly open, shortstatured and simpler, with little vertical stratification. Ordination of forest stands distributed within 300–2500 m elevations of the central Himalaya, by and large indicates a continuity of communities, with scattered centers of species importance values in the ordination field. Within the above elevational transect, sal (Shorea robusta) and oak (Quercus spp.) forests may be designated as the climax communities, respectively, of warmer and cooler climates. The flora of a part of the central Himalayan region is categorized as therohemigeophytic and that of a part of the western Himalayan region as geochamaephytic.An analysis of population structure over large areas in the central Himalaya, based on density-diameter distribution of trees, suggests that oldgrowth forests are being replaced by even-aged successional forests, dominated by a few species, such asPinus roxburghii. Paucity of seedlings of climax species, namelyShorea robusta andQuercus spp. over large areas is evident.The Himalayan catchments are subsurface-flow systems and, therefore, are particularly susceptible to landslips and landslides. Loss of water and soil in terms of overflow is insignificant.Studies on recovery processes of forest ecosystems damaged due to shifting cultivation or landslides indicate that the ecosystems can recover quite rapidly, at least in elevations below 2500 m. For example, on a damaged forest site, seedlings of climax species (Quercus leucotrichophora) appeared only 21 years after the landslide.In the central Himalaya, the biomass of a majority of forests (163-787 t ha−1) falls within the range (200-600 t ha−1) given for many mature forests of the world, and the net primary productivity (found in the range of 11.0–27.4 t ha−1 yr−1) is comparable with the range of 20–30 t ha−1 yr−1 given for highly productive communities of favorable environments. In most of the forests of this region, the litter fall values (2.1-3.8 t C ha−1 yr−1) are higher than the mean reported for warm temperate forests (2.7 t C ha−1 yr−1). Of the total litter, the tree leaves account for 54–82% in the Himalayan forests.The rate of decomposition of leaves in some broadleaf species of submontane belt (0.253-0.274% day−1) are comparable with those reported for some tropical rain forest species. Because of the paucity of microorganisms and microarthropods in the forest litter and soil, high initial C:N ratio and high initial lignin content in leaves, the rate of leaf litter decomposition inPinus roxburghii is markedly slower than in other species of the central Himalaya. The fungal species composition of the leaf litterof Pinus roxburghii is also distinct from those of other species.A greater proportion of nutrients is accumulated in the biomass component of the Himalayan forests than in the temperate forests. Although litter fall is the major route through which nutrients return from biomass to the soil pool, a substantial proportion of the total return is in the form of throughfall and stemflow. Among the dominant species of the central Himalaya, retranslocation of nutrients from the senescing leaves was markedly greater inPinus roxburghii than inQuercus spp. andShorea robusta. Consequently, the C:N ratio of leaf litter is markedly higher inPinus roxburghii than in the other species. Immobilization of nutrients by the decomposers of the litter with high C:N ratio is one of the principal strategies through whichPinus roxburghii invades other forests and holds the site against possible reinvasion by oaks.Observations on the seasonality of various ecosystem functions suggest that Himalayan ecosystems are geared to take maximum advantages of the monsoon period (rainy season).Most of the human population depends on shifting-agriculture in the eastern region and on settled agriculture in the central and western regions. Either of these is essentially a forest-dependent cultivation. Each unit of agronomic energy produced in the settled agriculture entails about seven units of energy from forests. Consequently, forests with reasonable crown cover account for insignificant percentage of the land. Tea plantations and felling of trees for timber, paper pulp, etc., are some of the major commercial activities which adversely affected the Himalayan forests.RésuméCette revue concerne la végétation forestière de l’Himalaya. Elle précise l’information concernant la paléoécologie, la phytogéographie, la phytosociologie, le structure et le fonctionnement des écosystèmes et le rapport entre l’homme et la forêt.Les montagnes de l’Himalaya sont les plus jeunes et parmi les plus instables. La pluviométrie dépend surtout de la mousson d’été et les chaînes extérieures sont bien arrosées (>2500 mm par an). Les précipitations annuelles décroissent de l’Est vers l’Ouest tandis que la composante hivernale augmente. Ces montagnes séparent les climats de mousson de l’Asie du Sud des climats froids et secs de l’Asie Centrale.L’érosion du sol sur une grand étendue et des changemenets cycliques du climat ont déterminé des changements dans le couvert végétal tout au long des temps géologiques. Les chaînes Himalayennes qui ont commencés leur soulèvement au commencement du coenozoïque étaient entièrement couvertes d’une forêt ombrophile tropicale. (Ce type se trouve encore de nos jours dans la partie orientale de l’Himalaya.) L’orogénie miocène provoqua de tels changements dans la végétation que la flore de cette époque a été entièrement remplacée par la flore moderne. Les espèces forestières dominantes du pleistocène gardent leur importance dans les forêts actuelles.Des éléments floraux Austro-Polynésiens, Malais-Birmans, Sino-Tibetains, Euro-Méditerranéens et Africains sont actuellement présents sur les montagnes himalayennes. Tandis que les affinités Euro-Mediterranéennes sont bien représentées dans l’Himalaya occidental (à l’Ouest du 77° Est), les affinités Chinoises et Malaises sont évidentes dans la partie orientale (à l’Est de 84°E). Cependant la proportion des éléments endémiques est importante dans toute la région.La relation entre les types de formations et les facteurs climatiques (pluviosité, température) indique que les limites entre les types sont approximatives. D’ailleurs, le climat lui même ne détermine pas exclusivement les types et les effets du sol, du feu, etc., peuvent être importantes. Les forêts feuillues ombrophiles localisées dans l’étage sous-montagnard (< 1000 m) de la région orientale sont comparables aux forêts ombrophiles tropicales typiques. A l’opposé les communautés qui se trouvent au-dessus de 3000 m d’altitude sont comparables aux types subalpins et alpins. En allant des conditions favorables vers le moins favorables soit par exemple d’Est en Ouest le long de l’axe de diminution des précipitations soit en suivant les gradient altitudinal de baisse des températures les forêts deviennent de plus en plus ouvertes, basses et structurellement simples avec peu de stratification verticale. L’ordination des peuplements forestières situés entre 300–2500 m dans l’Himalaya central indique une continuité des communautés avec des centres de valeurs d’importance des espèces dispersés dans le champ d’ordination. Dans ce transect altitudinal, les forêts à sal (Shorea robusta) et à chêne (Quercus spp.) peuvent

The Structure and Function of Ten Western North American Grasslands: I. Abiotic and Vegetational Characteristics

(1) Data collected from coordinated comparative studies on the structure and function of ten central and western United States grasslands are presented and analysed. The ten study areas encompassed six major grassland types: mountain grassland, northwest bunchgrass, mixed-grass prairie, shortgrass prairie, tallgrass prairie and desert grassland. Experimental design at each location included two replications of ungrazed (i.e. long-term absence of grazing by large domestic herbivores) and grazed treatments. (2) Structural characteristics studied included quantities of cool- and warm-season plants at each site, and magnitude and seasonality of primary producer compartments. (3) The environmental variables measured at each site were precipitation, temperature and solar radiation. These variables were calculated as both annual and growing-season values, along with annual and growing-season potential and actual evapotranspiration. (4) The seasonal mean live biomass averaged 94 g m -2 for the ten grasslands, with a mean of 98 g m -2 on ungrazed grasslands and 89 g m -2 for grazed grasslands. Ungrazed grasslands averaged about 160 g m -2 of recent and old dead plant material, compared to approximately 70 g m -2 on grazed grasslands. Ungrazed grasslands had about 50 and 150% more recent and old dead material, respectively, than grazed grasslands. Generally, grazing in previous seasons decreased the standing crop of dead material across the grasslands. (5) The mean total shoot standing crop averaged 203 g m -2 for all grasslands across all treatments; ungrazed grasslands averaged 245 g m -2 , compared to 161 g m -2 for grazed grasslands. The magnitude of litter corresponded in general to the amount of total shoot standing crop. (6) Generally, the shortgrass prairie had the maximum amount of crown material, followed by the mixed-grass prairie, with the tallgrass prairie least. Crown material averaged c. 275 g m -2 for the mixed- and shortgrass prairie, compared to c. 200 g m -2 for the tallgrass prairie. Although grazing did not significantly influence the amount of crown material, crown material tended to increase under grazing in mixed-grass and shortgrass prairies. (7) Root biomass ranged from 156 g m -2 in the desert grassland to as much as 2000 g m -2 in the mixed-grass prairie, while other grasslands were intermediate between these two extremes. (8) There was an inverse relationship between root biomass and dynamics and mean annual temperature. Grazing generally resulted in an increase in the root/shoot ratios, particularly on the cooler grasslands.

Ecology of seed and seedling growth for conservation and restoration of tropical dry forest : a review

Dry forests are among the most threatened ecosystems and have been extensively converted into grasslands, secondary forest, savanna or agricultural land. Knowledge of seed germination and seedling establishment is required for the success of efforts on restoration of these forests. This review focuses on the ecological requirements at seed and seedling stages, and collates the current knowledge of seed viability, dormancy, germination pattern and seedling behaviour of dry tropical tree species. The spatio-temporal variations within the tropical dry forest biome in soil moisture, light, temperature, nutrients and intensity of predation, significantly affect the seed and seedling traits of component species. The majority of dry tropical species possess orthodox seeds which are characterized by dormancy, while a few have recalcitrant seeds which possess little or no dormancy. Seed coat dormancy, which can be overcome by mechanical or acid scarification or sometimes by transit through animal guts, is most prevalent in the dry tropical forest species. Persistent species dominating the undisturbed portions of the forest have bigger seeds compared to those that mostly occur in disturbed regions and require shade for the survival of their seedlings. Shade demand is associated with drought endurance, and may be absolute in species such as Guettarda parviflora and Coccoloba microstachya, or facultative as in Plumeria alba and Bursera simaruba. The fluctuation in temperature significantly affects seed germination in several species of dry Afromontane forest trees of Ethiopia. Seedling mortality is primarily a function of moisture stress during the dry period. Adaptive responses of seedlings to drought stress include increased chlorophyll content, for example in Acacia catechu, and root biomass, as in several dry forest species (for example Drypetes parvifolia, Teclia verdoornia) of Ghana. Mulching, application of fertilizers, interplanting of leguminous species and mycorrhizal inoculation are useful tools for promoting seedling establishment in nutrient-poor dry tropical soils. Periodic forest fires, and predation affect recruitment and seedling development according to their intensity. Many species experiencing frequent fires have evolved thick seed coats, produce fire-hardy seedlings, or escape the effect by temporal separation of seed dispersal and fire events. Predation may result in abortion of fruits or may enhance germination and recruitment by scarification and dispersal, as in most species of the Guanacaste dry forest. Exposure to elevated CO2 has increased relative growth rate, total leaf area and water use efficiency in most of the dry tropical seedlings tested, but the magnitude of the effect has varied markedly among species. Due to the availability of a large source of energy, large seeds show higher germination percentage, greater seedling survival and increased growth. Seeds originating from different provenances exhibit differences in germination and seedling growth (for example Prosopis cineraria, Albizia lebbeck, Eucalyptus camaldulensis and Acacia mangium), efficiency of nodulation (for example Acacia nilotica, A. auriculiformis), and stress resistance (for example Populus deltoides, Dalbergia sissoo). The review points out the need for coordinated, long-term, field-based studies for identification of multiple cues and niches for germination, on seed and seedling dynamics in response to fire, and on within-species genetic variability for selection of suitable provenances. Field-based studies at species and community levels are also needed to permit manipulations of biotic components to augment the recruitment of desired species and to suppress that of undesirable species.

Tree species composition, dispersion and diversity along a disturbance gradient in a dry tropical forest region of India

Forest inventory data were collected in 1998–2000 from fifteen 1 ha permanent plots along a disturbance gradient in a dry tropical forest region of India. A total of 4033 stems, 49 species, 44 genera and 24 families of adult trees (� 30 cm CBH), occurred in the 15 ha of forest area. The study indicated that the dry tropical forest is characterised by a patchy distribution of species and individuals with mixed species composition, and the sites are represented by different combinations of the dominants and co-dominant species. A PCA ordination indicated that the variation in species composition of the sites is explained by the variation in soil nitrogen as well as the degree of disturbance. About half the analysed species showed changing nature in dispersion along the disturbance gradient. The distribution of Boswellia serrata, Holarrhena antidysenterica and Lannea coromandelica changed from clumped to uniform and the distribution of Butea monosperma, Cassia fistula and Elaeodendron glaucum changed from uniform to clumped as the degree of disturbance increased. The mean stem density was highest (419 stems ha � 1 ) at the least disturbed site and lowest (35 stems ha � 1 ) at the highly disturbed site, and for basal area, the highest value (13.78 m 2 ha � 1 ) was for the second least disturbed forest site and the lowest value (1.30 m 2 ha � 1 ) was for the most disturbed site. The total number of stems, indices of species richness, evenness and a-diversity decreased with disturbance. A strong influence of number of species per individual on b-diversity suggests that for resisting change in floristics due to disturbance, a site must have low species-individual ratio. # 2003 Elsevier B.V. All rights reserved.

Review and assessment of various techniques for estimating net aerial primary production in grasslands from harvest data

SummaryMethodology for calculating aboveground net production (ANP) has progressed from a single estimate of total standing crop at the end to an evaluation of multiple categories of biomass (viz. live, recent dead, old dead) by species and considering, with statistical constraints, each peak during the growing season.We have reviewed the published methods for calculating ANP with the purpose of critically comparing them with each other and with current understanding of primary productivity.As a further comparison of methods we have calculated net aboveground production by 13 methods on sets of harvest data collected by the US/IBP Grassland Biome. The data represent a grazed and ungrazed treatment on 10 sites of six grassland types. One to three years of data were available for each site.A hierarchical cluster analysis showed that all methods except one were significantly correlated (r < -0.61). Analysis of variance indicated that although all methods were significantly correlated, there were significant differences among the methods in terms of usefulness as discriminators of sites, years, or treatments.For various utilitarian and theoretical reasons the numbers of methods were reduced to two groups of “best estimators”. One group consisted of two methods involving summation of species peaks, the first utilizing live biomass, the second live + recent dead biomass. The second group comprised three methods using troughpeak analysis on live, live + recent dead, and live + recent dead + old dead biomass. Analysis for linear relations between the “best estimator” methods and 15 abiotic variables showed many significant relationships.RésuméLa méthologie pour calculer la production nette au-dessus du sol (ANP) a évolué depuis un seul calcul de la récolte totale fixe à la fin de la saison jusqu’ à l’évolution de multiples catégories de poids des plantes (c’est-à-dire des plantes vivantes, mortes récemment, mortes depuis longtemps) pour chaque espèce et en tenant compte de chaque maximum pendant la saison de croissance dans les limites statistiques.Nous avons analysé les méthodes de calcul ANP qui ont été publiées avec l’intention de les comparer les unes avec les autres avec soin et avec une connaissance actuelle de la production primaire.Afin de faire une comparaison de méthodes plus poussée, nous avons calcule la production nette au-dessus du sol à l’aide de treize méthodes à partir de données de séries de récolte rassemblées par la US/IBP Grassland Biome. Les données représentent un traitement de broutage et de non-broutage sur dix emplacements de six types de prairies. Des données datant de un à trois ans étaient disponibles pour chaque emplacement.Une analyse hiérarchique de groupe a montré que toutes les méthodes, à l’exception d’une seule, correspondaient de manière significative (r < -0.61). L’analyse de variance a indiqué que, bien que toutes les méthodes aient correspondu de manière significative, il y avait des différences d’importance parmi les méthodes quant à leur utilité en tant qu’éléments discriminatoires des emplacements, des années ou des traitements.Pour des raisons diverses, utilitaires et théoriques, les nombres des méthodes ont été réduits à deux groupes de “meilleurs estimateurs.” Un groupe consistait en deux méthodes entraînant l’addition des maximums des espèces, la première utilisant un poids de plantes vivantes, l’autre un poids de plantes vivantes et de plantes mortes récemment. Le deuxième groupe comportait trois méthodes utilisant l’analyse du point le plus bas de la courbe sur un poids de plantes vivantes, vivantes + mortes récemment et vivantes + mortes récemment + mortes depuis longtemps.L’analyse pour les relations linéaires entre les méthodes de “meilleur estimateur” et quinze variables abiotiques ont montré beaucoup de rapports d’importance.

A phytosociological analysis of woody species in forest communities of a part of Kumaun Himalaya

This paper reports on a detailed phytosociological analysis of forests in the NW catchment of the Gola River in Kumaun Himalaya, 29°19′–29°27′N and 79°32′–79°42′E. Fourteen sites and 56 stands at elevations ranging from 1200 to 2523 m and covering the following five forest types were investigated: Pinus roxburghii, mixed, Quercus leucotrichophora, Q. lanuginosa, and Q. floribunda. The basal cover of the forests differed according to slope position and aspect. The three oak forests had more basal cover than the other two, and Q. lanuginosa had the most. The performance of individual tree and shrub species and the number of saplings and seedlings differed according to slope position and aspect. The mixed forest had the greatest tree diversity, and among the others diversity increased with increasing basal cover. The diversity of trees, saplings, and herb layer was greatest on aspects with intermediate temperature and moisture conditions; whereas that of shrubs and seedlings increased towards the cooler (and wetter) and warmer (and drier) exposures. There was a positive relation between the diversity of shrubs plus seedlings and trees plus saplings in P. roxburghii and mixed forests; whereas this relationship was inverse in the three oak forests. In general, the dominance-diversity curves for the tree layer followed a geometric series conforming to the niche pre-emption situation in communities of low diversity. Among the forests, the regeneration was best in Q. lanuginosa and worst in Q. leucotrichophora.

Microbial C, N and P in dry tropical forest soils: Effects of alternate land-uses and nutrient flux

Abstract The effects of alternate land-uses (savanna, cropfield and mine spoil) on microbial C, N and P in dry tropical forest soil of India were studied. The mean microbial C, N and P, respectively, in the four major systems ranged from 250 to 609 μg C g −1 , 27 to 65 μg N g −1 and 12 to 26 μg P g −1 . The microbial biomass in these systems was characterized by a mean C:N:P ratio of 23:2:1. The microbial C, N and P were positively related to root biomass and total plant biomass (aboveground + root biomass). The derived ecosystems (savanna, cropland and mine spoil) have changed from the original forest ecosystems in terms of soil features and microbial biomass. The conversion of forest into other land-uses resulted in remarkable decline in the amounts of soil nutrients and microbial C, N and P. The microbial nutrients in this dry tropical environment are sensitive to land-use changes. The calculated flux of N and P through the microbial biomass ranged from 27 to 64 kg N ha −1 yr −1 and 13 to 26 kg P ha −1 yr −1 . Thus, in this dry tropical environment the microbial biomass appears to contribute substantially to the N and P requirements of higher plants.

The Structure and Function of Ten Western North American Grasslands: II. Intra-Seasonal Dynamics in Primary Producer Compartments

(1) Intra-seasonal dynamics of the various above-ground and below-ground primary producer compartments for ten central and western North American grassland sites are presented. (2) The seasonal peak values of the primary producer compartments are examined, as indicative of the net accumulation of organic material, and the relationships of these peak values to various abiotic regimes at the sites are investigated. (3) Seasonal live biomass followed either a unimodal or a bimodal growth pattern. In general, grasslands with only cool-season or only warm-season plants showed a unimodal pattern, while grasslands dominated by both cool- and warm-season species had a bimodal seasonal growth pattern. There were no significant differences between grazed and ungrazed treatments in seasonal live biomass, although there was a significant site × treatment interaction. (4) Peak live biomass ranged from 84 to 336 g m -2 , and showed a linear increase with increasing amounts of growing-season precipitation up to 450 mm; at higher values of precipitation increases in live biomass tended to level out. (5) Maximum rates of accumulation of live biomass ranged from 0.4 to 6.5 g m -2 day -1 . Ungrazed grasslands had a peak rate of 4.2 g m -2 day -1 compared with 3.2 g m -2 day -1 for grazed grasslands. (6) Generally the recent-dead compartment showed maximum values soon after the peak in the live compartment. Material in the old-dead compartment, however, was at a maximum early in the growing season, and a general decline in the standing crop of old dead material followed as material was transferred to the litter compartment. (7) Litter dynamics responded closely to precipitation events, and showed a rather erratic pattern. (8) Root biomass generally reached a maximum about midway through the growing season. On the cooler grasslands, grazed treatments typically had a larger peak in root biomass; in contrast, the warmer grasslands did not show a marked response in root biomass to grazing.