Annual Aboveground Biomass Production Research Articles

Allometric models for estimating aboveground biomass of young Norway spruce trees in the Western Carpathians, Slovakia

Abstract In the period of climate change, it is necessary to have biomass models for trees of all sizes to make precise estimations of biomass forest stocks to quantify carbon sequestration by forest cover. Therefore, we created allometric models of aboveground biomass in young Norway spruce (Picea abies [L.] Karst.) trees including main components, i.e. stem, branches and needles. The models used 200 sampled trees from 10 sites located in the central part of the Western Carpathians in Slovakia. The models, i.e. allometric regression relations implemented stem base diameter (diameter d0) and/or tree height. Moreover, using the derived allometric relations and a constant annual diameter increment of 10 mm, we calculated quasi-annual aboveground biomass production with regard to diameter d0. While stem had the largest contribution to aboveground biomass, followed by needles and branches, a different situation was revealed for the annual aboveground biomass production with the largest share of needles followed by stem and branches. Finally, we implemented the allometric models in a specific forest stand, where repetitive measurements were performed within 14 consecutive years. The results showed for example nearly 650 kg of the aboveground biomass per 102 m2 at the stand age of 10 years. The new biomass models can be applied to estimate the aboveground biomass stock in Norway spruce dominating stands in the Western Carpathians. Since the models are based on both diameter d0 and tree height a user can choose which variable is more suitable for particular conditions.

Alternative Grazing Management Strategies Combat Invasive Grass Dominance

Changes in historical disturbance regimes have increased the susceptibility of Great Plains ecosystems to various threats, including invasive species. Kentucky bluegrass (Poa pratensis; hereafter bluegrass) invasion in the northern Great Plains is displacing native species and has created novel ecosystems with no historical precedent to guide management. Traditional season-long (SL) grazing management increases bluegrass abundance, so we conducted a field experiment to determine if alternative early-intensive (EI) and patch-burn (PB) grazing management strategies can elicit more desirable outcomes in bluegrass-invaded pastures. Alternative EI grazing involved a triple of the stock density, compared to SL and PB stock density, for the first third of the grazing season while PB grazing incorporated SL grazing with prescribed burns. We randomly assigned treatments to 16-ha pastures with three replicates per treatment (n = 3). We conducted vegetation cover surveys and collected aboveground biomass samples to analyze plant community dynamics and production at study initiation and after 4 y of treatment. The SL grazing treatment increased bluegrass abundance by approximately 20% after 4 y of treatment while the alternative EI and PB grazing maintained its abundance at study initiation levels. Compositional differences also indicated increased native plant species cover with alternative management. Annual aboveground biomass production was not affected by management, but has the potential to become less variable with PB grazing in bluegrass-dominated pastures. Our results provide promising evidence that alternative grazing management may help combat bluegrass invasion by preventing additional increases in its abundance in the northern Great Plains.

Current status of grassland degradation and measures for grassland restoration in northern China

Grasslands in northern China are traditionally important bases for livestock production and ecological barriers for China. However, these grasslands degraded extensively due to global climatic change and poor management during the past half century. Such grassland degradation leads to dramatic declines in multiple ecosystem functions. Here we first analyzed the current status of these grasslands, with emphasizing on production and ecological functions. In general, the capability of annual aboveground biomass production in these grasslands has been greatly impaired in comparison with that in 1980s and not recovered to normal level despite application of some restoration measures. As indicated by large inter-annual variation in grasses production, the capability of feedback regulation to buffer the negative impacts of climatic change was greatly eroded. Carrying capability for animals of grasslands at the national level displayed an increasing trend in recent years, while the actual stocking capacity remained higher than its potential. Total water resources in these grasslands have declined greatly as evidenced by rapid losses of lakes and drying up of rivers. We next reviewed the major measures for restoration and management of grasslands in northern China during the past decades and analyzed their advantages and constrains, respectively. Fencing (prohibition of grazing) has been used in some area, but was difficult to extend to a larger area mainly due to economic reasons. Seasonal grazing and rotational grazing have been recommended by local governments. However, the outcomes of these measures are limited. Tillage and harrowing have also been suggested for restoration of the degraded grasslands, but it has rarely been largely used due to higher costs and inconsistent results. Reseeding grasses and/or legumes in natural grasslands are potentially useful for grassland restoration, but frequent droughts limit its application. Rotational mowing is a good measure for hey production system. Moreover, the yearly shift between grazing and mowing is much better than successive grazing or mowing. Fertilization has often been used in grassland management in most developed countries. However, this measure has not been widely applied in China due mainly to the lack of information on the types, rates and applied methods. Finally, based on our long-term studies on grassland ecology and practices in grassland restoration, especially the demonstration work in Hulunbuir grasslands, we propose some proposition on policy making and development of technical measures related to sustainable management of the grasslands in northern China. Ecological monitoring and evaluation of native grasslands should be done, and local farmers should be compensated for based on the evaluation results. Establishing cultivated pastures with high productivity and quality of forage grasses are key measures for protection and restoration of the degraded natural grasslands. As above-mentioned measures on grassland restoration usually take long time (from several years to decades) to restore the natural grasslands, new technical measures to restore the degraded natural grasslands are urgently needed. This review has important implications for improving the production and ecological functions of natural grasslands in general and for the sustainability of grass-based animal husbandry in particular.

Carbon saturation and assessment of soil organic carbon fractions in Mediterranean rainfed olive orchards under plant cover management

Abstract Olive groves are undergoing a marked change in the way that inter-row land is managed. The current regulation and recommendation encourages the implementation of plant cover, mainly to improve soil fertility and reduce erosion. However, there is no quantitative information on the dynamics and pools of soil organic carbon (SOC) fractions of different protection levels of the plant-residue-derived organic carbon (OC). This study was conducted to provide a range of annual OC inputs in commercial olive oil groves under natural plant cover, to assess the influence of the annual application of aboveground plant cover residues on unprotected and physically, chemically and biochemically protected SOC. In addition, we tested the carbon saturation hypothesis under plant cover. Ten olive oil orchards under plant cover management (PC), together with five comparable bare soil olive oil orchards (NPC) were selected and annual aboveground natural plant residues and SOC pools were sampled and quantified. Annual aboveground plant cover biomass and OC production in PC olive orchards averaged 1.48 t dry-weight (DW) ha −1 and 0.56 t C DW ha −1 , respectively with a great variability among sites (coefficient of variation of about 100%). SOC concentration in PC orchards was, on average, 2.8 (0–5 cm soil) and 2.0 (5–15 cm) times higher than in bare soils of NPC, and the pool of protected SOC in the top 15 cm was 2.1 times higher in the PC (17.9 mg C g −1 ± 5.7) (±standard deviation) compared to NPC (8.5 mg C g −1 ± 2.9) olive orchards. Linear or saturation type relationships between each SOC fraction and total SOC content for the range of SOC of the commercial olive oil orchards were statistically indistinguishable, and thus linear models to predict SOC accumulation due to plant cover in olive orchards are suitable, at least for the studied range of SOC. Overall, at regional scale where olive oil groves represent a very high proportion of the agricultural land, the use of plant cover appears to be a promising practice that promotes protection of the SOC, thus improving SOC sequestration.

Managing peatland vegetation for drinking water treatment.

Peatland ecosystem services include drinking water provision, flood mitigation, habitat provision and carbon sequestration. Dissolved organic carbon (DOC) removal is a key treatment process for the supply of potable water downstream from peat-dominated catchments. A transition from peat-forming Sphagnum moss to vascular plants has been observed in peatlands degraded by (a) land management, (b) atmospheric deposition and (c) climate change. Here within we show that the presence of vascular plants with higher annual above-ground biomass production leads to a seasonal addition of labile plant material into the peatland ecosystem as litter recalcitrance is lower. The net effect will be a smaller litter carbon pool due to higher rates of decomposition, and a greater seasonal pattern of DOC flux. Conventional water treatment involving coagulation-flocculation-sedimentation may be impeded by vascular plant-derived DOC. It has been shown that vascular plant-derived DOC is more difficult to remove via these methods than DOC derived from Sphagnum, whilst also being less susceptible to microbial mineralisation before reaching the treatment works. These results provide evidence that practices aimed at re-establishing Sphagnum moss on degraded peatlands could reduce costs and improve efficacy at water treatment works, offering an alternative to ‘end-of-pipe’ solutions through management of ecosystem service provision.

Production and Economic Parameters of a Poplar (J 105) Coppice Plantation with Different Length of the First Rotation in the Conditions of the Bohemian-Moravian Highlands

The paper analysed production and economic effectiveness of a short-rotation coppice plantation, namely J 105, after the first rotation period of 7 and 8 years respectively. The plantation is located in the region of the Bohemian-Moravian Highlands with an annual precipitation of 497 mm and mean air temperature of 8.6 °C. To assess the productivity, the trees were selected according to stem diameter at a height of 10 cm above the ground level and classified into three categories: I) 0–3.0 cm; II) 3.1–7.0 cm and III) > 7.0 cm. Sample trees were selected in each year. The economic effectiveness of the plantation was assessed as the difference between profits and costs for both rotation cycles. The mean annual above-ground biomass production for the 7-year rotation (2012) was 3.15 t/ha and 3.30 t/ha for the 8-year rotation (2013). The low productivity of poplar was due to slow growth (approx. 0.5 m in height) and drought in the first year after the plantation was established. The economic effectiveness for the 7-year rotation was CZK −5,300/ha and CZK +17,500/ha for the 8-year rotation. It was due to current total aboveground dry mass increment in the 8th year of rotation.

Estimating the Annual Above-Ground Biomass Production of Various Species on Sites in Sweden on the Basis of Individual Climate and Productivity Values

The literature contains a large number of bioclimate, climate and biometric models for estimating the production of different species or stands under specific conditions on a defined site or models giving the distribution of a single species. Depending on the model used, the amount of input data required varies considerably and often involves a large investment in time and money. The purpose of this study was to create a model to estimate the annual above-ground biomass production of various species from site conditions defined by mean annual temperature and mean annual precipitation. For this approach, the Miami model of Lieth was used as a base model with some modifications. This first version of the modified model was restricted to sites in Sweden, where changes in the soil and groundwater level were relatively small, and where the growth of land vegetation was mostly dependent on temperature. A validation of this model has shown that it seems possible to use the Miami model to estimate the annual above-ground biomass production of various species, and that it was possible to compare the annual above-ground biomass production of different species on one site, as well as the annual above-ground biomass production of different species on different sites using the modeled data.

Field‐quantified responses of tropical rainforest aboveground productivity to increasing CO2 and climatic stress, 1997–2009

AbstractA directional change in tropical‐forest productivity, a large component in the global carbon budget, would affect the rate of increase in atmospheric carbon dioxide ([CO2]). One current hypothesis is that “CO2 fertilization” has been increasing tropical forest productivity. Some lines of evidence instead suggest climate‐driven productivity declines. Relevant direct field observations remain extremely limited for this biome. Using a unique long‐term record of annual field measurements, we assessed annual aboveground net primary productivity (ANPP) and its relation to climatic factors and [CO2] in a neotropical rainforest through 1997–2009. Over this 12 year period, annual productivity did not increase, as would be expected with a dominant CO2 fertilization effect. Instead, the negative responses of ANPP components to climatic stress far exceeded the small positive responses associated with increasing [CO2]. Annual aboveground biomass production was well explained (73%) by the independent negative effects of increasing minimum temperatures and greater dry‐season water stress. The long‐term records enable a first field‐based estimate of the [CO2] response of tropical forest ANPP: 5.24 g m−2 yr−1 yr−1 (the summed [CO2]‐associated increases in two of the four production components; the largest component, leaf litterfall, showed no [CO2] association). If confirmed by longer data series, such a small response from a fertile tropical rainforest would indicate that current global models overestimate the benefits from CO2 fertilization for this biome, where most forests' poorer nutrient status more strongly constrains productivity responses to increasing [CO2]. Given the rapidly intensifying warming across tropical regions, tropical forest productivity could sharply decline through coming decades.

High Resilience in Heathland Plants to Changes in Temperature, Drought, and CO2 in Combination: Results from the CLIMAITE Experiment

Climate change scenarios predict simultaneously increase in temperature, altered precipitation patterns and elevated atmospheric CO2 concentration, which will affect key ecosystem processes and plant growth and species interactions. In a large-scale experiment, we investigated the effects of in situ exposure to elevated atmospheric CO2 concentration, increased temperature and prolonged drought periods on the plant biomass in a dry heathland (Brandbjerg, Denmark). Results after 3 years showed that drought reduced the growth of the two dominant species Deschampsia flexuosa and Calluna vulgaris. However, both species recovered quickly after rewetting and the drought had no significant effect on annual aboveground biomass production. We did not observe any effects of increased temperature. Elevated CO2 stimulated the biomass production for D. flexuosa in one out of three years but did not influence the standing biomass for either D. flexuosa or the ecosystem as more litter was produced. Treatment combinations showed little interactions on the measured parameters and in particular elevated CO2 did not counterbalance the drought effect on plant growth, as we had anticipated. The plant community did not show any significant responses to the imposed climate changes and we conclude that the two heathland species, on a short time scale, will be relatively resistant to the changes in climatic conditions.

Competitive ability of Rhinanthus minor L. in relation to productivityin the Rengen Grassland Experiment

Rhinanthus minor (yellow-rattle) can be used for restoration of species-rich grasslands but is vulnerable to competitive exclusion from high total aboveground biomass production of vascular plants. We asked (1) whether there is a threshold limit for total annual aboveground biomass production of vascular plants above which R. minor cannot establish viable population in grasslands and (2) how is cover of R. minor in grassland related to standing biomass of bryophytes. Data were collected in the Rengen Grassland Experiment (RGE) established in Germany in 1941 with following fertilizer treatments: unfertilized control, application of Ca, CaN, CaNP, CaNPKCl and CaNPK<sub>2</sub>SO<sub>4</sub>. Cover of R. minor and total annual aboveground biomass production of vascular plants were determined from 2005 to 2009. Further relationship between standing biomass of bryophytes and cover of R. minor was analyzed in 2006. Mean cover of R. minor over five years ranged from 0.7% to 12.3% in CaNPK<sub>2</sub>SO<sub>4</sub> and control treatments, respectively. Cover of R. minor was significantly negatively related to total annual aboveground biomass production of vascular plants and cover of R. minor was below 3% in all plots with total annual aboveground dry matter biomass production of vascular plants higher than 5 t/ha. Although cover of R. minor was markedly reduced in highly productive plots in the RGE, high standing biomass of bryophytes (1.8 t/ha) in low productive control was not an obstacle for establishment of its viable population. We concluded, that viable population of R. minor can be established in grasslands only if total annual aboveground dry matter biomass production of vascular plants is below 5 t/ha regardless on standing biomass of bryophytes.

Production and decomposition in floating soils of the Iberá wetlands (Argentina)

Floating soils grow due to the deposition of dead material onto their surface as well as the increment in belowground biomass. The imbalance between biomass production and decomposition is the source of organic matter accumulation. The Esteros del Ibera wetland (Argentina) features extensive areas of floating soils, locally known as “embalsados”. The annual aboveground biomass production, decomposition rate, and changes in nitrogen content in Thalia multiflora, a common species of Ibera, were determined in order to assess the organic matter addition and the nitrogen dynamics in the floating soils dominated by this species. The aboveground net primary production was estimated by measuring the standing crop at the peak registered during the sampling period. The decomposition rates of leaves and stems were determined by the litterbag method. The litterbags were collected periodically during a year. The annual organic matter addition was estimated from the relation between aboveground production and the amount of mass lost in a year. The maximum aboveground biomass was 1368 g/m 2 (± 271 SD), 71 % stems and 29 % leaves. The loss of weight in the sampling period (399 days) corresponds to 78 % of the initial mass: the total biomass exponential decay coefficient was significantly (ANCOVA; p<0.001) lower in stems (k = 0.0036) than in leaves (k = 0.0040). Both the decomposition rate value as well as the P/D ratio = 1.37, indicate that in T. multiflora stands the organic matter incorporated to the floating soil’s surface is small when compared to other peatlands. Initial nitrogen concentration in leaves and stems was 1.07 % and 0.32 %, respectively, this value increased to 1.76 % and 1.25 % in both substrates. Immobilization was observed in intermediate stages; by day 399, when leaves and stems lost nearly 2/3 of their initial weight, N values were similar to the initials, in agreement with the low nutrient availability that is characteristic of peatlands.

Soil, biomass, and management of semi-natural vegetation. I. Interrelationships

The interrelationships between biomass characteristics and soil properties (including in situ annual nitrogen mineralization) were statistically investigated in a descriptive study using a broad range of plant communities in unfertilized road verges. Not only the dependence of biomass characteristics on soil properties, but also the possibility of inferring soil nutrient availability from biomass characteristics was investigated. Possible effects of vegetation management (mowing) and overstory trees (shading) were accounted for. Annual aboveground biomass production was mainly explained by annual N mineralization, average soil moisture content, shading intensity, and soil pH (optimum at pH-CaCl2 5.7). Average tissue nutrient concentrations were primarily explained by mowing frequency, shading intensity, the availability of the corresponding soil nutrient, and pH (optima between 5.5 and 6.0). Results also implied that making hay twice per year removes more nutrients than a single cut at the end of the season. N mineralization may be inferred from the aboveground biomass production, but only across sites with equal moisture and shading conditions (partial r=0.74). In general, it is concluded that nutrient availability can only be deduced from biomass characteristics if sites with similar moisture content are compared. The only exception to this general rule is K availability. The latter was mainly indicated by the K concentration in vegetation biomass (partial r=0.80), and the confounding effect of other factors was small (bivariate r was still 0.71). Soil available P could not be satisfactorily indicated, even across sites with equal moisture and shading conditions. Also, different nutrients appeared to interact, and should not be considered in isolation. K was the only element with a strong relationship between its soil and tissue concentration. For the other nutrients, tissue concentrations did not depend predominantly on the soil availability. It seems most likely that the species occurring in semi-natural vegetation are adapted to the local fertility by means of their physiology or growth rate. It is concluded that, with the possible exception of K, simple relationships between soil properties and biomass characteristics cannot be expected over wide environmental gradients.

Studies on biomass production, partitioning and allometry of different bamboo (Bamboo spp.) plant species grown in bamboosetum in Arunachal Pradesh

The biomass production and partitioning of 30 bamboo species were evaluated at ICAR Research Complex for NEH Region, Arunachal Pradesh Center, Basar located in the humid sub-tropic. Bamboo species were planted in a bamboosetum on the hill with 25% slope at planting density of 2l8 clumps/ha. On the basis of mean annual aboveground biomass production and annual culms production, all the species were grouped into five distinct clusters at average linkage distance of 0.6. Bamboo species grouped in cluster III viz. B. bambos, B. balcooa, D. giganteus, B. cacharensis, B. pallida type I, B. nutans, B. tulda, D. sikkimensis, D. hookeri were the highest annual biomass producer (494.67 260.36 t/ha). Culms constituted more than 90% of total biomass in Arundinaria hirsuta, A. mannii, B. bambos and B. balcooa. Leaves and branches constitute 45% of the total biomass in Schizostachyum polymorphum. Biomass production in bamboo had significant (p &lt; 0.01) positive correlation with culms height (0.835), rind thickness (0.654), leaf length (0.0.659) and number of internodes/culms (0.716). Culms height, rind thickness and leaf length fitted into multiple linear regression models predicted 79% variability in the annual total biomass. Culms height, rind thickness and leaf length culms spacing explained about 90% variability in single culms weight of different species.

Bedload and Nearbed Detritus Transport in a Tidal Saltmarsh Creek

Bedload and nearbed transport of coarse (>1 mm) detritus particles were investigated in a tidal creek of a salt marsh in the Westerschelde estuary (south-west Netherlands). Using a fyke net positioned on the creek bottom, hourly transport through the creek was measured during 14 flood–ebb cycles in 1990 and 1991. Transport was bidirectional with flood imports varying between 32 and 2601 g dry weight (DW), and ebb exports varying between 0 and 4737 g DW. In nine of 14 tidal cycles, the creek was functioning as a net exporting system. The material that was exported with the ebb consisted mainly of macrophyte material. The annual loss of coarse organic matter by bedload plus nearbed transport through the creek was estimated to be less than 0·2% of the estimated annual above-ground plant biomass production in the drainage area of the creek. Therefore, it is concluded that this type of detritus transport is probably insignificant for the carbon balance of the salt marsh.

The effects of water and nutrient addition on annual aboveground biomass production ofChenopodium petiolareH.B.K. (Chenopodiaceae) in a north-central Chilean old field

Abstract:The effects of water and nutrient supplementation on the annual aboveground biomass production of Chenopodium petiolare H.B.K. were measured in an old field of north-central Chile by simulating rainfall events of 5 mm per month and by adding fertilizers to experimental quadrats in two years with different precipitation levels. In irrigated quadrats, the biomass of C. petiolare was higher than in non-irrigated quadrats. In the nutrient supplementation experiment, the only fertilizer that elicited a plant response was nitrogen. Biomass yield in the nitrogen-supplemented quadrats was over twice that in the control quadrats. As expected from experimental results, biomass in the wet year (1991) was twice as high as the biomass yield during the dry year (1990). Observations on the spatial distribution of C. petiolare elsewhere support our experimental results.

Above- and below-ground biomass and fine roots of 4-year-old hybrids of Populustrichocarpa × Populusdeltoides and parental species in short-rotation culture

Mean annual aboveground leafless biomass production averaged 14.8, 11.4, and 24.3 Mg•ha−1•year−1 at harvest at 4 years of age for Populustrichocarpa Torr. &amp; Gray, Populusdeltoides Marsh., and P. trichocarpa × P. deltoides hybrids, respectively. These trees were planted at 1 × 1 m spacing on a medium- to coarse-textured alluvial soil in western Washington. Branches accounted for 13.2–20.3% of the aboveground weight. Total weight of stumps and coarse roots at harvest varied from 12.3 to 29.6 Mg•ha−1, or 22–33% of the weight of aboveground leafless biomass. Small and fine roots sampled to a depth of 3.17 m using soil cores amounted to an additional 6.6–11 Mg•ha−1 of roots. Stumps and all roots as a ratio of aboveground biomass (root/shoot ratio) ranged from 0.34 to 0.42, with hybrids accounting for the entire range of values present. Mass of the fine roots (less than 0.5 mm diameter) ranged from 4.0 to 6.5 Mg•ha−1, or an average of 6.8% of the aboveground biomass. The smallest of the fine roots measured 0.06 mm in diameter. Specific root length of fine roots averaged 50.7 m•g−1 for P. deltoides, 42 m•g−1 for P. trichocarpa, and 30–47 m•g−1 for hybrids. Total length of fine roots to a depth of 3.17 m ranged from 179 000 to 284 000 km•ha−1. Density of fine roots by length per unit soil volume was greatest at the surface with the range of means for clones in the top 0.18 m being 2.4–6.3 cm•cm−3; at 1.0–3.17 m soil depth, density was 0.02–0.6 cm•cm−3. For two of the hybrid clones, the density of fine roots at the soil surface was half that of the other clones. The distribution of fine roots in the stratified soil profile was correlated with soil depth, Kjeldahl N, and organic matter, with the latter two parameters showing the highest coefficients of determination (0.73 and 0.71, respectively). In the more sandy but layered subsoil (0.36–3.17 m depth), soil depth, Kjeldahl N, and sand content were most strongly correlated with fine root density, with depth and sand content giving the highest coefficients of determination (0.32 and 0.31, respectively). Roots in sandy subsoil were coarser and much less branched than in adjacent finer textured layers.

Effects of thinning and nitrogen fertilization on growth of Scots pine trees: total annual biomass increment, needle efficiency, and aboveground allocation of biomass increment

The effects of thinning and nitrogen fertilization, singly and in combination, on growth of 45-year-old Scots pine (Pinussylvestris L.) trees in northern Sweden were examined for 5 years after treatment. Annual examination of trees determined height growth, diameter growth, crown development, annual biomass increment, aboveground biomass allocation, and needle efficiency in relation to treatments. Nitrogen fertilization increased total dry matter production. The combination of thinning and nitrogen fertilization increased total dry matter production per tree more than the additive effects of thinning and nitrogen fertilization singly. Dry matter production per hectare was increased by nitrogen fertilization. Needle efficiency, i.e., total annual aboveground biomass production per unit of needle mass, was also increased by nitrogen fertilization. The increased aboveground production after nitrogen fertilization resulted from both an increase in biomass of needles and from the increased needle efficiency. The allocation pattern indicated that an increased production of stemwood was a result of a larger biomass of needles. An increase in cone production of the control trees was associated with a decrease in needle efficiency.

Comparison of atmospheric carbon dioxide concentration and metabolic activity in Boreal Forest ecosystems

The increasing seasonal amplitude of atmospheric CO 2 concentrations may reflect biotic influences such as increased photosynthesis due to higher CO 2 concentrations or increased winter respiration due to warmer temperatures. Boreal forests have a large role in the seasonal dynamics of atmospheric CO 2 in the Northern Hemisphere, and if terrestrial ecosystems contribute to the greater amplitude, such a signal should appear in the metabolic activity of boreal forests. Analyses in which a mechanistic model of photosynthesis, respiration, and decomposition was driven with the observed annual increase in atmospheric CO 2 concentration and observed daily air temperature and precipitation show that from 1974 to 1982 the seasonal amplitude in metabolic activity in boreal forests near Fairbanks, Alaska, increased by 0.52 ± 0.03% year -1 . The increasing amplitude was due to increased tree photosynthesis as CO 2 concentration increased. However, the increase in annual aboveground biomass production was so small (3 g m -2 year -1 year -1 ) that it is undetectable given field sampling errors. The small biomass growth increase indicates that a larger seasonal amplitude of atmospheric CO 2 can occur without large changes in net primary production, nutrient availability, or nutrient use efficiency. The increase in CO 2 concentration that produced the higher biomass production was also small (1.1 ppm year -1 ), suggesting more attention should be paid to the ecological effects of small changes in CO 2 concentrations. DOI: 10.1034/j.1600-0889.1992.t01-2-00002.x

Par Absorption and Its Relation to Above-Ground Dry Matter Production of Sitka Spruce

(1) The annual amounts of PAR absorbed were measured for six Sitka spruce (Picea sitchensis) plots with different thinning and fertilizer treatments in Central Scotland, and related to the annual above-ground biomass production estimated for four consecutive years. It was found that the above-ground dry matter production was proportional to the amount of PAR absorbed, irrespective of treatments. (2) Based on the radiation data collected from these six plots, amounts of PAR absorbed were estimated for the other twenty-four experimental plots in the same stand. The quotients of above-ground dry matter produced and PAR absorbed were 0-43gmol-1 for nitrogen-fertilized plots and 0 33gmol-1 for the other plots. (3) The annual photosynthetic efficiency of Sitka spruce was estimated to be c. 3% using a physiological processes-based model, MAESTRO, and the upper limit of biomass production of a Sitka spruce stand in Scotland was estimated to be 36thayear-1

Seasonal dynamics and leaf growth of Zostera noltii hornem., A perennial intertidal seagrass

From May to October 1983, seasonal dynamics and leaf growth of Zostera noltii Hornem, were studied in three permanent quadrats (PQ) in the Zandkreek (SW Netherlands). Dense Z. noltii beds covered 100 ha of tidal flats together with occasional patches of Zostera marina L. Leaf growth was estimated weekly using a modified leaf-marking method. Seasonal curves for biomass and shoot-density development were identically shaped for all plots but had different timing, with a strong incline in biomass increase in PQ 1 in the middle of June, in PQ 2 at the end of July and in PQ 3 at the end of August. Vigorous growth occurred above a shoot density of 1000–2000 m −2. Mean shoot density of PQ 2 and 3 in May did not differ much (300–400 m −2) but distribution in PQ 2 was patchy while PQ 3 was homogeneous. It is hypothesized that mutuality is the cause of this difference in timing. Above a threshold density, patches may suffer less from uprooting by currents. Total leaf growth of Z. noltii shows maxima in spring and late summer (0.06g g −1 ash-free dry weight day −1), a more or less constant summer level (0.04g g −1 day −1) and declining values in autumn (≤0.03 g g −1 day −1). A comparison of aboveground biomass increase in PQ 1 and net leaf growth rates revealed no significant difference, thus validating the leaf-marking method applied. Total leaf production of Z. noltii was 135 g m −2 during the study period, including leaf loss (51% of the production). Estimated annual aboveground biomass production of Z. noltii was 230 g m −2.