bluuebunny/crossref_metadata_2025 huggingface dataset:
Enriched atmospheric CO2and defoliation: effects on tree chemistry and insect performance
Authors: Roth Sherry , Lindroth Richard L. , Volin John. C. , Kruger Eric. L.
Published: March 2003

We examined the effects of CO2and defoliation on tree chemistry and performance of the forest tent caterpillar, Malacosoma disstria. Quaking aspen (Populus tremuloides) and sugar maple (Acer saccharum) trees were grown in open‐top chambers under ambient or elevated concentrations of CO2. During the second year of growth, half of the trees were exposed to free‐feeding forest tent caterpillars, while the remaining trees served as nondefoliated controls. Foliage was collected weekly for phytochemical analysis. Insect performance was evaluated on foliage from each of the treatments. At the sampling date coincident with insect bioassays, levels of foliar nitrogen and starch were lower and higher, respectively, in high CO2foliage, and this trend persisted throughout the study. CO2‐mediated increases in secondary compounds were observed for condensed tannins in aspen and gallotannins in maple. Defoliation reduced levels of water and nitrogen in aspen but had no effect on primary metabolites in maple. Similarly, defoliation induced accumulations of secondary compounds in aspen but not in maple. Larvae fed foliage from the enriched CO2or defoliated treatments exhibited reduced growth and food processing efficiencies, relative to larvae on ambient CO2or nondefoliated diets, but the patterns were host species‐specific. Overall, CO2and defoliation appeared to exert independent effects on foliar chemistry and forest tent caterpillar performance.
Poa annuashows inter‐generational differences in response to elevated CO2
Authors: BEZEMER T. MARTIJN , THOMPSON LINDSEY J. , JONES T. HEFIN
Published: March 2003

Inter‐generational effects on the growth of Poa annua (L.) in ambient and elevated atmospheric CO2 conditions (350 and 550 μl l–1, respectively) were studied in two different experiments. Both experiments showed similar results. In a greenhouse experiment growth, measured as the numbers of tillers produced per week, was compared for plants grown from first and second generation seeds. Second generation seeds were obtained from plants grown for one whole generation in either ambient or elevated atmospheric CO2 (‘ambient’ and ‘elevated’ seeds, respectively). First generation plants and second generation ‘ambient’ plants did not respond to elevated CO2. Second generation ‘elevated’ plants produced significantly more tillers in elevated CO2. In the second experiment model terrestrial ecosystems growing in the Ecotron and which included Poa annua were used. Above‐ground biomass after one and two generations of growth were compared. At the end of Generation 1 no difference was found in biomass production while at the end of Generation 2 biomass increased in elevated CO2 by 50%. The implications for climate change research are discussed.
Effects of climatic variability on the annual carbon sequestration by a boreal aspen forest
Authors: Chen W. J. , Black T. A. , Yang P. C. , Barr A. G. , Neumann H. H. , Nesic Z. , Blanken P. D. , Novak M. D. , Eley J. , Ketler R. J. , Cuenca R.
Published: March 2003

To evaluate the carbon budget of a boreal deciduous forest, we measured CO2fluxes using the eddy covariance technique above an old aspen (OA) forest in Prince Albert National Park, Saskatchewan, Canada, in 1994 and 1996 as part of the Boreal Ecosystem‐Atmosphere Study (BOREAS). We found that the OA forest is a strong carbon sink sequestering 200 ± 30 and 130 ± 30 g C m–2y–1in 1994 and 1996, respectively. These measurements were 16–45% lower than an inventory result that the mean carbon increment was about 240 g C m–2y–1between 1919 and 1994, mainly due to the advanced age of the stand at the time of eddy covariance measurements. Assuming these rates to be representative of Canadian boreal deciduous forests (area ≈ 3 × 105km2), it is likely they can sequester 40–60 Tg C y–1, which is 2–3% of the missing global carbon sink.

The difference in carbon sequestration by the OA forest between 1994 and 1996 was mainly caused by the difference in leaf emergence date. The monthly mean air temperature during March–May 1994, was 4.8 °C higher than in 1996, resulting in leaf emergence being 18–24 days earlier in 1994 than 1996. The warm spring and early leaf emergence in 1994 enabled the aspen forest to exploit the long days and high solar irradiance of mid‐to‐late spring. In contrast, the 1996 OA growing season included only 32 days before the summer solstice. The earlier leaf emergence in 1994 resulted 16% more absorbed photosynthetically active radiation and a 90 g C m–2y–1increase in photosynthesis than 1996. The concomitant increase in respiration in the warmer year (1994) was only 20 g C m–2y–1. These results show that an important control on carbon sequestration by boreal deciduous forests is spring temperature, via the influence of air temperature on the timing of leaf emergence.
Effect of elevated atmospheric CO2 on mycorrhizal colonization, external mycorrhizal hyphal production and phosphorus inflow in Plantago lanceolata and Trifolium repens in association with the arbuscular mycorrhizal fungus Glomus mosseae
Authors: Staddon Philip L. , Fitter Alastair H. , Graves Jonathan D.
Published: March 2003

Plantago lanceolata and Trifolium repens were grown under ambient (400 μmol mol–1) and elevated (650 μmol mol–1) atmospheric CO2 conditions. Plants were inoculated with the arbuscular mycorrhizal fungus Glomus mosseae and given a phosphorus supply in the form of bonemeal. Six sequential harvests were taken in order to determine whether the effect of elevated CO2 on internal mycorrhizal colonization and external hyphal production was independent of the stimulatory effect of elevated CO2 on plant growth. At a given time, elevated CO2 increased the percentage of root length colonized (RLC), the total length of colonized root and the external mycorrhizal hyphal (EMH) density and decreased the ratio of EMH to total length of colonized root. When plant size was taken into account, the CO2 effect on RLC and total length of colonized root was greatly reduced (and only apparent for early harvests in T. repens) and the effects on the EMH parameters disappeared. Root tissue P concentration was unchanged at elevated CO2, but there was a decrease in shoot P at the later harvests. There was no direct effect of elevated CO2 on P inflow for the earlier period (< 50 d) of the experiment. However, over the last period, there was a significant negative effect of elevated CO2 on P inflow for both species, independent of plant size. It is concluded that elevated CO2 had no direct effect on mycorrhizal colonization or external hyphal production, and that any observed effects on a time basis were due to faster growing plants at elevated CO2. However, for older plants, elevated CO2 had a direct negative effect on P inflow. This decrease in P inflow coincides with the observed decrease in shoot P concentration. This is discussed in terms of downregulation of photosynthesis often seen in elevated CO2 grown plants, and the potential for mycorrhizas (via external hyphal turnover) to alleviate the phenomenon. The direction for future research is highlighted, especially in relation to carbon flow to and storage in the soil.
Elevated UV‐B radiation incident on Quercus robur leaf canopies enhances decomposition of resulting leaf litter in soil
Authors: Newsham K. K. , Greenslade P. D. , Kennedy V. H. , McLeod A. R.
Published: March 2003

We examined whether the exposure ofQuercus roburL. to elevated UV‐B radiation (280–315 nm) during growth would influence leaf decomposition rate through effects on litter quality. Saplings were exposed for eight months at an outdoor facility in the UK to a 30% elevation above the ambient level of erythemally weighted UV‐B radiation under UV‐B treatment arrays of fluorescent lamps filtered with cellulose diacetate, which transmitted both UV‐B and UV‐A (315–400 nm) radiation. Saplings were exposed to elevated UV‐A alone under control arrays of lamps filtered with polyester and to ambient radiation under unenergised arrays of lamps. Abscised leaves from saplings were enclosed in 1 mm2mesh nylon bags, placed in aQuercus–Fraxinuswoodland and were sampled at 0.11, 0.53, 1.10 and 1.33 years for dry weight loss, chemical composition and saprotrophic fungal colonization.

At abscission, litters from UV‐A control arrays had ≈ 7.5% higher lignin/nitrogen ratios than those from UV‐B treatment and ambient arrays (P< 0.06). Dry weight loss of leaves treated with elevated UV‐B radiation during growth was 2.5% and 5% greater than that of leaves from UV‐A control arrays at 0.53 and 1.33 years, respectively. Litter samples from UV‐B treatment arrays lost more nitrogen and phosphorus than samples from ambient arrays and more carbon than samples from UV‐A control arrays. The annual fractional weight loss of litter from UV‐B treatment arrays was 8% and 6% greater than that of litter from UV‐A control and ambient arrays, respectively. Regression analyses indicated that the increased decomposition rate of UV‐B treated litters was associated with enhanced colonization of leaves by basidiomycete fungi, the most active members of the soil fungal community, and that the frequency of these fungi was negatively associated with the initial lignin/nitrogen ratio of leaves.
The effect of termite biomass and anthropogenic disturbance on the CH4 budgets of tropical forests in Cameroon and Borneo
Authors: Macdonald J. A. , Jeeva D. , Eggleton P. , Davies R. , Bignell D. E. , Fowler D. , Lawton J. , Maryati M.
Published: March 2003

The exchange of CH4 between tropical forests and the atmosphere was determined by simultaneously measuring the net CH4 flux at the soil surface and assessing the flux contribution from soil‐feeding termite biomass, both within the soil profile and in mounds. In Cameroon the flux of CH4 ranged from a net emission of 40.7 ng m–2 s–1 to a net CH4 oxidation of –53.0 ng m–2 s–1. Soil‐inhabiting termite biomass was significantly correlated with CH4 flux. Termite mounds emitted up to 2000 ng s–1 mound–1. Termite‐derived CH4 emission reduced the soil sink strength by up to 28%. Disturbance also had a strong effect on the soil sink strength, with the average rate of CH4 oxidation, at – 17.5 ng m–2 s–1, being significantly smaller (≈ 36%) at the secondary forest site than the –27.2 ng m–2 s–1, observed at the primary forest site. CH4 budgets calculated for each site indicated that both forests were net sinks for CH4 at – 6.1 kg ha–1 y–1 in the near‐primary forest and – 3.1 kg ha–1 y–1 in the secondary forest.

In Borneo, three forest sites representing a disturbance gradient were examined. CH4 oxidation rates ranged from 0 to – 32.1 ng m–2s–1 and a significant correlation between the net flux and termite biomass was observed only in an undisturbed primary forest, although the biomass was insufficient to cause net emission of CH4. Rates of CH4 oxidation were not significantly different across the disturbance gradient but were, however, larger in the primary forest (averaging – 15.4 ng m–2 s–1) than in an old‐growth secondary forest (–13.9 ng m–2s–1) and a young secondary re‐growth (– 10.8 ng m–2s–1). CH4 flux from termite mounds ranged from net oxidation in an abandoned mound to a maximum emission of 468 ng s–1 mound–1. CH4 budgets calculated for each site indicated that CH4 flux from termite mounds had an insignificant effect on the budget of CH4 at the regional scale at all three forest sites. Annual oxidation rates were – 4.8, – 4.2 and – 3.4 kg ha–1 y–1 in the primary, secondary and young secondary forests, respectively.
Influence of precipitation seasonality on piñon pine cellulose δD values
Authors: Pendall Elise
Published: March 2003

The influence of seasonal to interannual climate variations on cellulose hydrogen isotopic composition (δD) was assessed by analysing tree rings and needles of piñon pine (Pinus edulis and P. monophylla). Sites spanned a gradient of decreasing summer precipitation, from New Mexico to Arizona to Nevada. Tree rings were divided into earlywood, latewood and whole‐year increments, and annual cohorts of needles were collected. The study period (1989–96) included two La Niña events (1989, 1996) and a prolonged El Niño event (1991–95). Winter and spring moisture conditions were strongly related to October–March Southern Oscillation Index (SOI) in New Mexico and Arizona, with above‐average precipitation occurring in El Niño years. Wood δD values at these sites were correlated with winter and spring moisture conditions. Needle δD values were correlated with summer moisture conditions in New Mexico and with winter moisture and SOI in Arizona. Low cellulose δD values observed from 1991 to 1993 in both wood and needles occurred during wet El Niño years, whereas high δD values in needles were present during the dry, La Niña years of 1989 and 1996. North‐eastern Nevada does not receive precipitation anomalies related to ENSO, and thus cellulose δD values did not reflect the ENSO pattern observed at the other sites. Cellulose δD values were strongly, inversely correlated with relative humidity variations at all sites, as predicted by a mechanistic model. Contrary to predictions from the same model and observations from more mesic areas, time series of cellulose δD values were not directly correlated with interannual or seasonal variations in precipitation δD values or temperature at any of the sites. On a regional basis, however, mean δD values in needles and wood were correlated with mean annual temperature and δD values of precipitation. This suggests that temporal averaging may bias relationships between biological systems and climate.
Effects of elevated atmospheric CO2 concentration on C and N pools and rhizosphere processes in a Florida scrub oak community
Authors: Schortemeyer Marcus , Dijkstra Paul , Johnson Dale W. , Drake Bert G.
Published: March 2003

The effect of elevated atmospheric CO2 concentration (Ca) on soil carbon and nitrogen accumulation and soil microbial biomass and activity in a native Florida scrub oak community was studied. The plant community, dominated by Quercus myrtifolia Willd. and Q. geminata Small, was exposed for 2 years to elevated Ca in open‐top chambers. Buried subsoil bags were retrieved after 1 year of exposure to elevated Ca. In addition, soil cores were taken twice from the chambers within two weeks in July 1998 (the first after a long dry spell and the second after 25 mm of rainfall) and divided into rhizosphere and bulk soil. Soil organic matter accumulation (excluding roots) into the buried subsoil bags was lower in elevated than in ambient Ca. Concentrations of soluble carbon and ninhydrin‐reactive nitrogen (Nninh) in the rhizosphere soil were reduced by elevated Ca for the first sampling date and unaffected for the second sampling date. Microbial activity, measured as fluorescein diacetate (FDA) hydrolysis, decreased in elevated Ca for the first sampling date. Microbial biomass carbon and nitrogen in the bulk soil were unaffected by elevated Ca. There was no effect of elevated Ca on bacterial numbers in the rhizosphere.
Climate‐driven changes in biomass allocation in pines
Authors: Delucia Evan H. , Maherali Hafiz , Carey Eileen V.
Published: March 2003

Future increases in air temperature resulting from human activities may increase the water vapour pressure deficit (VPD) of the atmosphere. Understanding the responses of trees to spatial variation in VPD can strengthen our ability to predict how trees will respond to temporal changes in this important variable. Using published values, we tested the theoretical prediction that conifers decrease their investment in photosynthetic tissue (leaves) relative to water‐conducting tissue in the stem (sapwood) as VPD increases. The ratio of leaf/sapwood area (AL/AS) decreased significantly with increasing VPD inPinusspecies but not inAbies, Pseudotsuga, Tsuga and Picea, and the averageAL/ASwas significantly lower for pines than other conifers (pines: 0.17 m2 cm−2; nonpines: 0.44 m2 cm−2). Thus, pines adjusted to increasing aridity by altering above‐ground morphology while nonpine conifers did not. The average water potential causing a 50% loss of hydraulic conductivity was −3.28 MPa for pines and −4.52 MPa for nonpine conifers, suggesting that pines are more vulnerable to xylem embolism than other conifers. ForPinus ponderosathe decrease inAL/ASwith high VPD increases the capacity to provide water to foliage without escalating the risk of xylem embolism. LowAL/ASand plasticity in this variable may enhance drought tolerance in pines. However, lowerAL/ASwith increasing VPD and an associated shift in biomass allocation from foliage to stems suggests that pines may expend more photosynthate constructing and supporting structural mass and carry less leaf area as the climate warms.
The net flux of carbon from agricultural soils in Canada 1970–2010
Authors: Smith W. N. , Desjardins R. L. , Pattey E.
Published: March 2003

Changes in soil organic carbon (SOC) in agricultural soils influence soil quality and greenhouse gas concentrations in the atmosphere. Land use, management practices, soil characteristics, and climate influence such changes. Using the Century model we estimated the rate of SOC change in agricultural soils of Canada for the period 1970 to 2010. This estimation was based on the estimated SOC change for 15% of the 1250 agriculturally designated soil landscape of Canada (SLC) polygons. Simulations were carried out for two to five crop rotations and for conventional and no‐tillage. The results indicate that the agricultural soils in Canada, whose SOC are currently very close to equilibrium, will stop being a net source of CO2 and will become a sink by the year 2000. Rates of carbon change for the years 1970, 1990, and 2010 were estimated to be −67, − 39, and 11 kgC ha−1. The rate of decline in the carbon content of agricultural soils in Canada has slowed considerably in the 1990s as a result of an increase in the adoption of no‐tillage management, a reduction in the use of summer fallowing, and an increase in fertilizer application. We estimate that the proportion of agricultural land storing SOC will have increased from 17% in 1990 to 53% by the year 2000.
The North Atlantic Oscillation and plankton dynamics in two European lakes –‐ two variations on a general theme
Authors: Straile Dietmar , Adrian Rita
Published: March 2003

Long‐term data on water temperature, phytoplankton biovolume,BosminaandDaphniaabundance and the timing of the clear‐water phase were compared and analysed with respect to the influence of the North Atlantic Oscillation (NAO) in two strongly contrasting lakes in central Europe. In small, shallow, hypertrophic Müggelsee, spring water temperatures andDaphniaabundance both increased more rapidly than in large, deep, meso/oligotrophic Lake Constance. Because of this, the clear‐water phase commenced approximately three weeks earlier in Müggelsee than in Lake Constance. In Müggelsee, the phytoplankton biovolume during late winter/early spring was related to the NAO index. In Lake Constance, where phytoplankton growth was inhibited by intense downward mixing during all years studied, this was not the case. However, in both lakes, interannual variability in water temperature, inDaphniaspring population dynamics and in the timing of the clear‐water phase, were all related to the interannual variability of the NAO index. TheDaphniaspring population dynamics and the timing of the clear‐water phase appear to be synchronized by the NAO despite large differences between the lakes in morphometry, trophic status and flushing and mixis regimes, and despite the great distance between the lakes (∼700 km). This suggests that a great variety of lakes in central Europe may possibly have exhibited similar interannual variability during the last 20 years.
Effects of elevated CO2, temperature and N fertilization on nitrogen fluxes in a temperate grassland ecosystem
Authors: Loiseau P. , Soussana J. F.
Published: March 2003

The soil nitrogen cycle was investigated in a pre‐established Lolium perenne sward on a loamy soil and exposed to ambient and elevated atmospheric CO2 concentrations (350 and 700 μL L−1) and, at elevated [CO2], to a 3 °C temperature increase. At two levels of mineral nitrogen supply, N– (150 kgN ha−1 y−1) and N+ (533 kgN ha−1 y−1), 15N‐labelled ammonium nitrate was supplied in split applications over a 2.5‐y period. The recovery of the labelled fertilizer N was measured in the harvests, in the stubble and roots, in the macro‐organic matter fractions above 200 μm in size (MOM) and in the aggregated organic matter below 200 μM (AOM). Elevated [CO2] reduced the total amount of N harvested in the clipped parts of the sward. The harvested N derived from soil was reduced to a greater extent than that derived from fertilizer. At both N supplies, elevated [CO2] modified the allocation of the fertilizer N in the sward, in favour of the stubble and roots and significantly increased the recovery of fertilizer N in the soil macro‐organic matter fractions. The increase of fertilizer N immobilization in the MOM was associated with a decline of fertilizer N uptake by the grass sward, which supported the hypothesis of a negative feedback of elevated [CO2] on the sward N yield and uptake. Similar and even more pronounced effects were observed for the native N mineralized in the soil. At N–, a greater part of the fertilizer N organized in the root phytomass resulted in an underestimation of N immobilized in dead roots and, in turn, an underestimation of N immobilization in the MOM. The 3 °C temperature increase alleviated the [CO2] effect throughout much of the N cycle, increasing soil N mineralization, N derived from soil in the harvests, and the partitioning of the assimilated fertilizer N to shoots. In conclusion, at ambient temperature, the N cycle was slowed down under elevated [CO2], which restricted the increase in the aboveground production of the grass sward, and apparently contributed to the sequestration of carbon belowground. In contrast, a temperature increase under elevated [CO2] stimulated the soil nitrogen cycle, improved the N nutrition of the sward and restricted the magnitude of the soil C sequestration.
Spatial and temporal dynamics of methane emissions from agricultural sources in China
Authors: Verburg Peter H. , Van Der Gon Hugo A. C. Denier
Published: March 2003

Agricultural activities contribute significantly to the global methane budget. Agricultural sources of methane are influenced by land‐use change, including changes in agricultural area, livestock keeping and agricultural management practices. A spatially explicit inventory of methane emissions from agriculture is made for China taking the interconnections between the different agricultural sources into account. The influence of land‐use change on methane emissions is studied by linking a dynamic land‐use change model with emission calculations. The land‐use change model calculates changes in rice area and livestock numbers for a base‐line scenario. Emissions are calculated for 1991 based on land‐use statistics and for 2010 based on simulated changes in land‐use patterns. Emissions from enteric fermentation and manure management are based on emission factors, while emissions from rice paddies involve the calculation of total organic carbon added to rice paddy soils and assume that a constant fraction is emitted as methane. Spatial patterns of emissions are presented for the different sources. For the land‐use scenario considered it is expected that total methane emissions from agricultural sources in China increase by 11% while the relative contribution of rice fields to the emission decreases. Emissions from manure management are expected to become more important. These results indicate that agencies should anticipate changes in source strengths as a consequence of land‐use changes when proposing mitigation strategies and future national greenhouse gas budgets.
Response of nitrogen cycling to simulated climate change: differential responses along a subalpine ecotone
Authors: Shaw M. Rebecca , Harte John
Published: March 2003

In situnitrogen (N) transformations and N availability were examined over a four‐year period in two soil microclimates (xeric and mesic) under a climate‐warming treatment in a subalpine meadow/sagebrush scrub ecotone. Experimental plots that spanned the two soil microclimates were exposed to anin situinfrared (IR) climate change manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, Colorado. Although the two microclimates did not differ significantly in their rates of N transformations in the absence of heating, they differed significantly in their response to increased IR. Under a simulated warming in the sagebrush‐dominated xeric microclimate, gross N mineralization rates doubled and immobilization rates increased by up to 60% over the first 2 years of the study but declined to predisturbance rates by the fourth year. This temporal pattern of gross mineralization rates correlated with a decline in SOM. Concurrently, rates of net mineralization rates in the heated plots were 60% higher than the controls after the first year. There were no differences in gross or net nitrification rates with heating in the xeric soils. In contrast to the xeric microclimate, there were no significant effects of heating on any N transformation rates in the mesic microclimate. The differing responses in N cycling rates of the two microclimate to the increased IR is most certainly the result of differences in initial soil moisture conditions and vegetation type and cover.
Responses to solar ultraviolet‐B radiation in a shrub‐dominated natural ecosystem of Tierra del Fuego (southern Argentina)
Authors: Rousseaux M. Cecilia , Scopel Ana L. , Searles Peter S. , Caldwell Martyn M. , Sala Osvaldo E. , Ballaré Carlos L.
Published: March 2003

A study was made of the effects of solar ultraviolet‐B radiation (UV‐B) on the growth of the dominant plant species of a shrub‐dominated ecosystem in Tierra del Fuego. This part of southern Argentina can be under the direct influence of the Antarctic ‘ozone hole’ during the austral spring and lingering ozone‐depleted air during the summer. The plant community is dominated by an evergreen shrub (Chiliotrichum diffusum) with an herbaceous layer of Gunnera magellanica and Blechnum penna‐marina in the interspaces between the shrubs. Inspections of ozone trends indicate that the springtime and summertime ozone column over Tierra del Fuego has decreased by 10–13% from 1978/9 to 1998/9. In a set of well‐replicated field plots, solar UV‐B was reduced to approximately 15–20% of the ambient UV‐B using plastic films. Polyester films were used to attenuate UV‐B radiation and UV‐transparent films (∼90% UV‐B transmission) were used as control. Treatments were imposed during the growing season beginning in 1996 and continued for three complete growing seasons. Stem elongation of the shrub C. diffusum was not affected by UV‐B attenuation in any of the three seasons studied. However, frond length of B. penna‐marina under attenuated UV‐B was significantly greater than that under near‐ambient UV‐B in all three seasons. Attenuation of solar UV‐B also promoted the expansion of G. magellanica leaves in two of the growing seasons. Differences between treatments in leaf or frond length in B. penna‐marina and G. magellanica did not exceed 12%. Another significant effect of UV‐B attenuation was a promotion of insect herbivory in G. magellanica, with a 25–75% increase in the leaf area consumed. Changes in plant phenology or relative species cover were not detected within the time frame of this study. The results suggest that the increase in UV‐B radiation associated with the erosion of the ozone layer might be affecting the functioning of this ecosystem to some degree, particularly by inhibiting the growth of some plant species and by altering plant–insect interactions.
Strategies to estimate national forest carbon stocks from inventory data: the 1990 New Zealand baseline
Authors: Hall Graeme M. J. , Wiser Susan K. , Allen Robert B. , Beets Peter N. , Goulding Chris J.
Published: March 2003

An estimate of live tree carbon stored in New Zealand forests at 1990 was made to partially satisfy New Zealand's international obligations under the Framework Convention for Climate Change. A national database was compiled of 4956 forest inventory plots measured as recently as possible to 1990. Plot biomass estimates were obtained by applying species allometric relationships derived from harvested stands. Forest areas and classes were taken from a 1987 national map of vegetation cover. Regularly spaced grids, based on an initial 1 km × 1 km grid, were overlaid on the total forest area and plots were tested for bias against site characteristics at the grid points. As grid point density and sample size increased, bias was minimal in regional sampling intensity and in total annual precipitation. Differences in mean elevation and annual temperature remained stable as grid point density increased, and showed little correlation with stem biomass. This sampling method gave a measure of precision not available from previous estimates.

An efficient sample size to estimate the mean within a 5% level of precision (at 95% probability) required a sample of 574 plots selected from a 4‐km grid. This strategy generated a mean estimate for the 1990 New Zealand forest carbon biomass of 179.3 ± 4.9 Mg ha−1(± SE), totalling 919.1 ± 25.1 Mt for the 5.1 million ha mapped forest area. The mean was 6–10% lower than previous estimates, and was within the range reported for other countries. Within forest classes, mean carbon biomass ranged from 105 Mg ha−1in pure podocarp forest to 215 Mg ha−1in mixed lowland podocarp–broadleaved–beech forest. Of the major taxa groups throughout the forest estate, beech (Nothofagus) contributed 60% of the national forest carbon biomass reservoir, 26.7% was in other hardwoods, 13.2% in conifers, and 0.1% in other taxa (e.g. tree ferns).
Carbon dioxide exchange of a Russian boreal forest after disturbance by wind throw
Authors: Knohl Alexander , Kolle Olaf , Minayeva Tatiana Y. , Milyukova Irina M. , Vygodskaya Natalja N. , Foken Thomas , Schulze Ernst‐Detlef
Published: March 2003

The exchange of carbon dioxide (CO2) between the atmosphere and a forest after disturbance by wind throw in the western Russian taiga was investigated between July and October 1998 using the eddy covariance technique. The research area was a regenerating forest (400 m × 1000 m), in which all trees of the preceding generation were uplifted during a storm in 1996. All deadwood had remained on site after the storm and had not been extracted for commercial purposes. Because of the heterogeneity of the terrain, several micrometeorological quality tests were applied. In addition to the eddy covariance measurements, carbon pools of decaying wood in a chronosequence of three different wind throw areas were analysed and the decay rate of coarse woody debris was derived.

During daytime, the average CO2uptake flux was −3 µmol m−2s−1, whereas during night‐time characterised by a well‐mixed atmosphere the rates of release were typically about 6 µmol m−2s−1. Suppression of turbulent fluxes was only observed under conditions with very low friction velocity (u* ≤ 0.08 ms−1). On average, 164 mmol CO2 m−2d−1was released from the wind throw to the atmosphere, giving a total of 14.9 mol CO2 m−2(180 g CO2 m−2) released during the 3‐month study period.

The chronosequence of dead woody debris on three different wind throw areas suggested exponential decay with a decay coefficient of −0.04 yr−1. From the magnitude of the carbon pools and the decay rate, it is estimated that the decomposition of coarse woody debris accounted for about a third of the total ecosystem respiration at the measurement site. Hence, coarse woody debris had a long‐term influence on the net ecosystem exchange of this wind throw area.

From the analysis performed in this work, a conclusion is drawn that it is necessary to include into flux networks the ecosystems that are subject to natural disturbances and that have been widely omitted into considerations of the global carbon budget. The half‐life time of about 17 years for deadwood in the wind throw suggests a fairly long storage of carbon in the ecosystem, and indicates a very different long‐term carbon budget for naturally disturbed vs. commercially managed forests.
An initial intercomparison of micrometeorological and ecological inventory estimates of carbon exchange in a mid‐latitude deciduous forest
Authors: Ehman J. L. , Schmid H. P. , Grimmond C. S. B. , Randolph J. C. , Hanson P. J. , Wayson C. A. , Cropley F. D.
Published: March 2003

The role of mid‐latitude forests in the sequestration of carbon (C) is of interest to an increasing number of scientists and policy‐makers alike. Net CO2exchange can be estimated on an annual basis, using eddy‐covariance techniques or from ecological inventories of C fluxes to and from a forest. Here we present an intercomparison of annual estimates of C exchange in a mixed hardwood forest in the Morgan‐Monroe State Forest, Indiana, USA for two years, 1998 and 1999. Based on eddy‐covariance measurements made at 1.8 times canopy height from a tower, C uptake by the forest was 237 and 287 g C m−2 y−1for 1998 and 1999, respectively. For the same time period, biometric and ecophysiological measures and modelled estimates of all significant carbon fluxes within deciduous forests were made, including: change in living biomass, aboveground and belowground detritus production, foliage consumption, and forest floor and soil respiration. Using this ecological inventory method for these same two time periods, C uptake was estimated to be 271 and 377 g C m−2 y−1, which are 14.3% and 31.4% larger, respectively, than the tower‐based values. The relative change between this method's annual estimates is consistent with that of the eddy‐covariance based values. Our results indicate that the difference in annual C exchange rates was due to reduced heterotrophic soil respiration in 1999.
Simulating climate change impacts on fire frequency and vegetation dynamics in a Mediterranean‐type ecosystem
Authors: Mouillot Florent , Rambal Serge , Joffre Richard
Published: March 2003

The impacts of climate change on Mediterranean‐type ecosystems may result from complex interactions between direct effects on water stress and subsequent modifications in flammability and fire regime leading to changes in standing biomass and plant species composition. We analysed these interrelations through a simulation approach combining scenarios of climate change developed from GCM results and a multispecies functional model for vegetation dynamics, SIERRA. A fire risk procedure based on weekly estimates of vegetation water stress has been implemented. Using climate data from 1960 to 1997, simulations of a typical maquis woodland community have been performed as baseline and compared with two climate scenarios: a change in the rainfall regime alone, and changes in both rainfall and air temperature. Climate changes are defined by an increase in temperature, particularly in summer, and a change in the rainfall pattern leading to a decrease in low rainfall events, and an increase in intense rainfall events. The results illustrate the lack of drastic changes in the succession process, but highlight modifications in the water budget and in the length of the drought periods. Water stress lower than expected regarding statistics on the current climate is simulated, emphasizing a long‐term new equilibrium of vegetation to summer drought but with a higher sensibility to rare events. Regarding fire frequency, climate changes tend to decrease the time interval between two successive fires from 20 to 16 years for the maquis shrubland and from 72 to 62 years in the forested stages. This increase in fire frequency leads to shrub‐dominated landscapes, which accentuates the yield of water by additional deep drainage and runoff.
Responses of leaf nitrogen concentration and specific leaf area to atmospheric CO2 enrichment: a retrospective synthesis across 62 species
Authors: Yin Xiwei
Published: March 2003

Knowledge of leaf responses to elevated atmospheric [CO2] (CO2 concentration) is integral to understanding interactions between vegetation and global change. This work deals with responses of leaf mass‐based nitrogen concentration (Nm) and specific leaf area (SLA). It assesses the statistical significance of factors perceived as influential on the responses, and quantifies how the responses vary with the significant factors identified, based on 170 data cases of 62 species compiled from the literature. Resultant equations capture about 41% of the variance in the data for percent responses of Nm and SLA, or about 95% of the variance for Nm and SLA at 57–320% normal [CO2]; these performance statistics also hold for leaf area‐based N concentration and specific leaf weight. The equations generalize that: (i) both Nm and SLA decline as [CO2] increases; (ii) proportional decline of Nm is greater with deciduous woody species and with plants of normally low Nm, increases with pot size in growth chamber and greenhouse settings and with temperature and photosynthetic photon flux density (PPFD), and is mitigated by N fertilization; and (iii) proportional decline of SLA depends on pot size and PPFD similarly to Nm, increases with leaf life span and water vapour pressure deficit in enclosed experiments, and decreases with prolonged exposure to elevated [CO2] among broadleaf woody species in field conditions. The results highlight great uncertainty in the percent‐response data and reveal the potential feasibility to estimate Nm and SLA at various magnitudes of elevated [CO2] from a few key plant and environmental factors of broad data bases.
Elevated atmospheric CO2 lowers herbivore abundance, but increases leaf abscission rates
Authors: Stiling Peter , Cattell Maria , Moon Daniel C. , Rossi Anthony , Hungate Bruce A. , Hymus Graham , Drake Bert
Published: March 2003

Increased levels of atmospheric carbon dioxide (CO2) are likely to affect the trophic relationships that exist between plants, their herbivores and the herbivores' natural enemies. This study takes advantage of an open‐top CO2 fertilization experiment in a Florida scrub oak community at Kennedy Space Center, Florida, consisting of eight chambers supplied with ambient CO2 (360 ppm) and eight chambers supplied with elevated CO2 (710 ppm). We examined the effects of elevated CO2 on herbivore densities and levels of leaf consumption, rates of herbivore attack by natural enemies and effects on leaf abscission. Cumulative levels of herbivores and herbivore damage were significantly lower in elevated CO2 than in ambient CO2. This may be because leaf nitrogen levels are lower in elevated CO2. More herbivores die of host plant‐induced death in elevated CO2 than in ambient CO2. Attack rates of herbivores by parasitoids are also higher in elevated CO2, possibly because herbivores need to feed for a longer time in order to accrue sufficient nitrogen (N), thus exposing themselves longer to natural enemies. Insect herbivores cause an increase in abscission rates of leaves throughout the year. Because of the lower insect density in elevated CO2, we thought, abscission rates would be lower in these chambers. However, abscission rates were significantly higher in elevated CO2. Thus, the direct effects of elevated CO2 on abscission are greater than the indirect effects on abscission mediated via lower insect densities. A consequence of increased leaf abscission in elevated CO2 is that nutrient deposition rates to the soil surface are accelerated.
Vulnerability of South African animal taxa to climate change
Authors: Erasmus Barend F. N. , Van Jaarsveld Albert S. , Chown Steven L. , Kshatriya Mrigesh , Wessels Konrad J.
Published: March 2003

The responsiveness of South African fauna to climate change events is poorly documented and not routinely incorporated into regional conservation planning. We model the likely range alterations of a representative suite of 179 animal species to climate change brought about by the doubling of CO2concentrations. This scenario is expected to cause a mean temperature increase of 2 °C. We applied a multivariate climate envelope approach and evaluated model performance using the most comprehensive bird data set. The results were encouraging, although model performance was inconsistent in the eastern coastal area of the country. The levels of climate change induced impacts on species ranges varied from little impact to local extinction. Some 17% of species expanded their ranges, 78% displayed range contraction (4–98%), 3% showed no response and 2% became locally extinct. The majority of range shifts (41%) were in an easterly direction, reflecting the east–west aridity gradient across the country. Species losses were highest in the west. Substantially smaller westward shifts were present in some eastern species. This may reflect a response to the strong altitudinal gradient in this region, or may be a model artifact. Species range change (composite measure reflecting range contraction and displacement) identified selected species that could act as climate change indicator taxa. Red‐data and vulnerable species showed similar responses but were more likely to display range change (58% vs. 43% for all species). Predictions suggest that the flagship, Kruger National Park conservation area may loose up to 66% of the species included in this analysis. This highlights the extent of the predicted range shifts, and indicates why conflicts between conservation and other land uses are likely to escalate under conditions of climate change.
Influence of elevated CO2 on interspecific interactions at higher trophic levels
Authors: Stacey David A. , Fellowes Mark D. E.
Published: March 2003

Abstract We report the results of a study investigating the influence of elevated CO2 on species interactions across three trophic levels: a plant (Brassica oleracea), two aphid herbivores (the generalist Myzus persicae and the specialist Brevicoryne brassicae), and two natural enemies (the coccinellid Hippodamia convergens (ladybird) and the parasitoid wasp Diaeretiella rapae). Brassica oleracea plants reared under elevated CO2 conditions (650 ppmv vs. 350 ppmv) were larger and had decreased water and nitrogen content. Brevicoryne brassicae reared on plants grown in elevated CO2 were larger and accumulated more fat, while there was no change in M. persicae traits. Fecundity of individual aphids appeared to be increased when reared on plants grown in elevated CO2. However, these differences were generally lost when aphids were reared in colonies, suggesting that such changes in plant quality will have subtle effects on aphid intraspecific interactions. Nevertheless, CO2 treatment did influence aphid distribution on plants, with significantly fewer M. persicae found on the shoots, and B. brassicae was only found on senescing leaves, when colonies were reared on plants grown in elevated CO2. We reared B. brassicae and M. persicae in competition on plants grown at both the CO2 concentration treatments. We found a significantly lower ratio of M. persicae: B. brassicae on plants grown under elevated CO2 conditions, strongly suggesting that increasing CO2 concentrations can alter the outcome of competition among insect herbivores. This was also reflected in the distribution of the aphids on the plants. While the CO2 treatment did not influence where B. brassicae were found, fewer M. persicae were present on senescing leaves under elevated CO2 conditions. Changes in plant quality resulting from the CO2 treatments did not appear to alter aphid quality as prey species, as the number consumed by the ladybird H. convergens, and the number parasitised by the parasitoid wasp D. rapae, did not change. To our knowledge, this study provides the first empirical evidence that changes in host plant quality mediated by increasing levels of CO2 can alter the outcome of interspecific competition among insect herbivores.
Response of two Antarctic bryophytes to stratospheric ozone depletion
Authors: Newsham K. K. , Hodgson D. A. , Murray A. W. A. , Peat H. J. , Smith R. I. Lewis
Published: March 2003

We report a study which measured changes to the radiative environment arising from stratospheric O3 depletion at Rothera Point on the western Antarctic Peninsula (67°S, 68°W) and subsequent associations between these changes and the pigmentation and maximum quantum yield of photochemistry (Fv/Fm) of two Antarctic bryophytes, the liverwort Cephaloziella varians and the moss Sanionia uncinata. We found a strong relationship between O3 column depth and the ratio of UV‐B to PAR irradiance (FUV‐B/FPAR) recorded at ground level. Weaker, but significant, associations were also found between O3 column depth and noon irradiances and daily doses of unweighted and biologically effective UV‐B radiation received at ground level. Regression analyses indicated that FUV‐B/FPAR and daily dose of unweighted UV‐B were best predictors for concentrations of total carotenoids and UV‐B screening pigments extracted from bryophyte tissues. Concentrations of these pigments were loosely but significantly positively associated with O3‐dependent irradiance parameters. HPLC analyses of carotenoids also suggested that both species increased the synthesis of neoxanthin during periods of O3 depletion. Violaxanthin, lutein, zeaxanthin and b,bββ‐carotene concentrations were also apparently influenced by O3 reduction, but not consistently across both bryophyte species. Concentrations of chlorophylls a and b were apparently unaffected by O3 depletion.

No direct associations between Fv/Fm and O3‐dependent irradiance parameters were found. However stepwise multiple regression analyses suggested that the production of UV‐B screening pigments conferred protection from elevated FUV‐B/FPAR on Fv/Fm in both species and that carotenoids conferred protection on Fv/Fm in Sanionia. Our data suggest that changes to the radiative environment associated with stratospheric O3 depletion influence the pigmentation of two Antarctic bryophytes, but that Fv/Fm is unaffected, at least in part because of rapid synthesis of protective pigments.
Intraspecific responses to climate inPinus sylvestris
Authors: Rehfeldt Gerald E. , Tchebakova Nadejda M. , Parfenova Yelena I. , Wykoff William R. , Kuzmina Nina A. , Milyutin Leonid I.
Published: March 2003

AbstractFive population‐specific response functions were developed from quadratic models for 110 populations ofPinus sylvestrisgrowing at 47 planting sites in Eurasia and North America. The functions predict 13 year height from climate: degree‐days > 5 °C; mean annual temperature; degree‐days < 0 °C; summer‐winter temperature differential; and a moisture index, the ratio of degree‐days > 5 °C to mean annual precipitation. Validation of the response functions with two sets of independent data produced for all functions statistically significant simple correlations with coefficients as high as 0.81 between actual and predicted heights. The response functions described the widely different growth potentials typical of natural populations and demonstrated that these growth potentials have different climatic optima. Populations nonetheless tend to inhabit climates colder than their optima, with the disparity between the optimal and inhabited climates becoming greater as the climate becomes more severe. When driven by a global warming scenario of the Hadley Center, the functions described short‐term physiologic and long‐term evolutionary effects that were geographically complex. The short‐term effects should be negative in the warmest climates but strongly positive in the coldest. Long‐term effects eventually should ameliorate the negative short‐term impacts, enhance the positive, and in time, substantially increase productivity throughout most of the contemporary pine forests of Eurasia. Realizing the long‐term gains will require redistribution of genotypes across the landscape, a process that should take up to 13 generations and therefore many years.