Decomposition and Fragmentation of Coarse Woody Debris: Re-visiting a Boreal Black Spruce Chronosequence

We re-visited a seven-stand boreal chronosequence west of Thompson, Manitoba, Canada, in which coarse woody debris (CWD) and its instantaneous decomposition were measured in 2000. New CWD measurements were performed in 2007, and tree inventories updated to provide mortality and snag failure data. These data were used to model CWD changes, compare methods of estimating decomposition, and infer possible fragmentation rates. Measured CWD was between 9.7 (in both the 77- and 43-year-old stands) and 80.4 (in the 18-year-old stand) Mg ha⁻¹ in 2007. Spatial variability was high; at most stands CWD levels had not changed significantly from 2000 to 2007. Tree mortality was a significant flux only in older stands, whereas snag fall rate varied by an order of magnitude, from 2.9% y⁻¹ (0.2 Mg ha⁻¹ y⁻¹) in the 9-year-old stand to 9.8% y⁻¹ (2.3 Mg ha⁻¹ y⁻¹) in the 12-year-old stand. A one-pool model based on these inputs underestimated actual 2000–2007 CWD decomposition in the younger stands, suggesting that fragmentation could be an important part of the carbon flux exiting the CWD pool. We compared three independent measures of annual decomposition (k): direct measurements of CWD respiration, rates based on the 7-year re-sampling effort described here, and rates inferred from the chronosequence design itself. Mean k values arrived at via these techniques were 0.06 ± 0.03, 0.05 ± 0.04, and 0.05 ± 0.05 y⁻¹, respectively. The four-pool model suggested that the transition rate between decay classes was 0.14–0.19 y⁻¹; the model was most sensitive to initial CWD values. Although the computed k values implied a problem with chronosequence site selection for at least one site, the overall CWD trend was consistent with a larger number of sites surveyed in the region.     

Nitrogen dynamics of a boreal black spruce wildfire chronosequence

This study examined the nitrogen (N) dynamics of a black spruce (Picea mariana (Mill.) BSP)-dominated chronosequence in Manitoba, Canada. The seven sites studied each contained separate well- and poorly drained stands, originated from stand-killing wildfires, and were between 3 and 151 years old. Our goals were to (i) measure total N concentration ([N]) of all biomass components and major soil horizons; (ii) compare N content and select vegetation N cycle processes among the stands; and (iii) examine relationships between ecosystem C and N cycling for these stands. Vegetation [N] varied significantly by tissue type, species, soil drainage, and stand age; woody debris [N] increased with decay state and decreased with debris size. Soil [N] declined with horizon depth but did not vary with stand age. Total (live + dead) biomass N content ranged from 18.4 to 99.7 g N m⁻² in the well-drained stands and 37.8–154.6 g N m⁻² in the poorly drained stands. Mean soil N content (380.6 g N m⁻²) was unaffected by stand age. Annual vegetation N requirement (5.9 and 8.4 g N m⁻² yr⁻¹ in the middle-aged well- and poorly drained stands, respectively) was dominated by trees and fine roots in the well-drained stands, and bryophytes in the poorly drained stands. Fraction N retranslocated was significantly higher in deciduous than evergreen tree species, and in older than younger stands. Nitrogen use efficiency (NUE) was significantly lower in bryophytes than in trees, and in deciduous than in evergreen trees. Tree NUE increased with stand age, but overall stand NUE was roughly constant (∼ ∼150 g g⁻¹ N) across the entire chronosequence.     

Natural 15N abundance of soil N pools and N2O reflect the nitrogen dynamics of forest soils

Natural ¹⁵N abundance measurements of ecosystem nitrogen (N) pools and ¹⁵N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ¹⁵N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ¹⁵N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ¹⁵N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand: 5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in ¹⁵N of all soil N pools. Denitrification represented the main N₂O-producing process in the mixed forest stand as we detected a significant ¹⁵N enrichment of its substrate NO₃⁻ (3.6 ± 4.5‰) compared to NH₄⁺ (−4.6 ± 2.6‰) and its product N₂O (−11.8 ± 3.2‰). In a ¹⁵N-labelling experiment in the spruce stand, nitrification contributed more to N₂O production than denitrification. Moreover, in natural abundance measurements the NH₄⁺ pool was slightly ¹⁵N-enriched (−0.4 ± 2.0 ‰) compared to NO₃⁻ (−3.0 ± 0.6 ‰) and N₂O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N₂O. The more positive δ¹⁵N values of N₂O in the spruce stand than in the mixed stand point to extensive microbial N₂O reduction in the spruce stand. Combining natural ¹⁵N abundance and ¹⁵N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.     

Primary production in papyrus (<Emphasis Type="Italic">Cyperus papyrus</Emphasis> L.) of Rubondo Island,Lake Victoria,Tanzania

Above- and below-ground production and morphological characteristics of papyrus wetlands were measured at monthly intervals from July 2005 to June 2006 at Rubondo Island, Lake Victoria, Tanzania. The average value of live culm biomass (5,789 ± 435 g DW m⁻²) was higher than that of umbel biomass (2,902 ± 327 g DW m⁻²) by 50%. Root to rhizome means biomass value ratio was 1:1.8, rhizome biomass (4,144 ± 452 g DW m⁻²) being higher than roots biomass (2,254 ± 314 g DW m⁻²) by 45%. Direct proportion was observed between shoot density and culm–unit (culms and umbels) biomass. The average value of detritus/litter biomass (1,306 ± 315 g DW m⁻²) was less than total aerial biomass by 86%. The values of biomass are average of 12 sampling months from July 2005 to June 2006.     

Nitrogen uptake in a Norway spruce stand following ammonium sulphate application,fertigation, irrigation,drought and nitrogen-free-fertilisation

The above-ground accumulation of N,N uptake and litter quality resulting from improved or deteriorated availability of water and nutrients in a 25 year old Norway spruce stand in SW Sweden (as part of the Skogaby project) is presented. Treatment include irrigation; artificial drought; ammonium sulphate addition; N-free-fertilisation and irrigation with liquid fertilisers including a complete set of nutrients according to the Ingested principle (fertigation). At start of the experiment the stand contained 86.5 t dry mass and 352 kg N ha⁻¹. The following three years the annual N uptake in untreated trees was 32 kg N ha⁻¹ to be compared with the annual N throughfall of 17 kg ha⁻¹. Simultaneously, the treatment with ammonium sulphate and liquid fertilisation resulted in 48 and 56 kg ha⁻¹ y⁻¹, respectively, in treatment specific N-uptake following an application of 100 kg N ha⁻¹ y⁻¹. Addition of a N-free fertiliser resulted in improved N-uptake by 19 kg N ha⁻¹ y⁻¹ and irrigation by 10 kg N ha⁻¹ y⁻¹, compared to control. A linear relation between total above-ground dry mass production and N-uptake was found for trees growing with similar water availability. Dry mass production increased with increased water availability given the same N-uptake. It is concluded that the studied stand this far is not N saturated', as N fertilisation resulted in both increased N uptake and increased growth. Addition of a N-free-fertiliser resulted in increased uptake of N compared to the control, indicating an increased mineralisation rate or uptake capacity of the root system. The linear relation between N uptake and biomass production shows that at this study site N is a highly limiting factor for growth.     

Future Spruce Budworm Outbreak May Create a Carbon Source in Eastern Canadian Forests

Spruce budworm (Choristoneura fumiferana Clem.) is an important and recurrent disturbance throughout spruce (Picea sp.) and balsam fir (Abies balsamea L.) dominated forests of North America. Forest carbon (C) dynamics in these ecosystems are affected during insect outbreaks because millions of square kilometers of forest suffer growth loss and mortality. We tested the hypothesis that a spruce budworm outbreak similar to those in the past could switch a forest from a C sink to a source in the near future. We used a model of ecosystem C to integrate past spruce budworm impact sequences with current forest management data on 106,000 km² of forest in eastern Québec. Spruce budworm-caused mortality decreased stand-level merchantable C stocks by 11–90% and decreased ecosystem C stocks by 2–10% by the end of the simulation. For the first 13 years (2011–2024), adding spruce budworm significantly reduced ecosystem C stock change for the landscape from a sink (4.6 ± 2.7 g C m⁻² y⁻¹ in 2018) to a source (−16.8 ± 3.0 g C m⁻² y⁻¹ in 2018). This result was mostly due to reduced net primary production. The ecosystem stock change was reduced on average by 2 Tg C y⁻¹ for the entire simulated area. This study provides the first estimate that spruce budworm can significantly affect the C sink or source status of a large landscape. These results indicate that reducing spruce budworm impacts on timber may also provide an opportunity to mitigate a C source.     

Biometric Based Carbon Flux Measurements and Net Ecosystem Production (NEP) in a Temperate Deciduous Broad-Leaved Forest Beneath a Flux Tower

Biometric based carbon flux measurements were conducted over 5 years (1999–2003) in a temperate deciduous broad-leaved forest of the AsiaFlux network to estimate net ecosystem production (NEP). Biometric based NEP, as measured by the balance between net primary production (including NPP of canopy trees and of forest floor dwarf bamboo) and heterotrophic respiration (RH), clarified the contribution of various biological processes to the ecosystem carbon budget, and also showed where and how the forest is storing C. The mean NPP of the trees was 5.4 ± 1.07 t C ha⁻¹ y⁻¹, including biomass increment (0.3 ± 0.82 t C ha⁻¹ y⁻¹), tree mortality (1.0 ± 0.61 t C ha⁻¹ y⁻¹), aboveground detritus production (2.3 ± 0.39 t C ha⁻¹ y⁻¹) and belowground fine root production (1.8 ± 0.31 t C ha⁻¹ y⁻¹). Annual biomass increment was rather small because of high tree mortality during the 5 years. Total NPP at the site was 6.5 ± 1.07 t C ha⁻¹ y⁻¹, including the NPP of the forest floor community (1.1 ± 0.06 t C ha⁻¹ y⁻¹). The soil surface CO₂ efflux (RS) was averaged across the 5 years of record using open-flow chambers. The mean estimated annual RS amounted to 7.1 ± 0.44 t C ha⁻¹, and the decomposition of soil organic matter (SOM) was estimated at 3.9 ± 0.24 t C ha⁻¹. RH was estimated at 4.4 ± 0.32 t C ha⁻¹ y⁻¹, which included decomposition of coarse woody debris. Biometric NEP in the forest was estimated at 2.1 ± 1.15 t C ha⁻¹ y⁻¹, which agreed well with the eddy-covariance based net ecosystem exchange (NEE). The contribution of woody increment (Δbiomass + mortality) of the canopy trees to NEP was rather small, and thus the SOM pool played an important role in carbon storage in the temperate forest. These results suggested that the dense forest floor of dwarf bamboo might have a critical role in soil carbon sequestration in temperate East Asian deciduous forests.     

Spatial and temporal patterns of aboveground net primary productivity (ANPP) along two freshwater-estuarine transects in the Florida Coastal Everglades

We present here a 4-year dataset (2001–2004) on the spatial and temporal patterns of aboveground net primary production (ANPP) by dominant primary producers (sawgrass, periphyton, mangroves, and seagrasses) along two transects in the oligotrophic Florida Everglades coastal landscape. The 17 sites of the Florida Coastal Everglades Long Term Ecological Research (FCE LTER) program are located along fresh-estuarine gradients in Shark River Slough (SRS) and Taylor River/C-111/Florida Bay (TS/Ph) basins that drain the western and southern Everglades, respectively. Within the SRS basin, sawgrass and periphyton ANPP did not differ significantly among sites but mangrove ANPP was highest at the site nearest the Gulf of Mexico. In the southern Everglades transect, there was a productivity peak in sawgrass and periphyton at the upper estuarine ecotone within Taylor River but no trends were observed in the C-111 Basin for either primary producer. Over the 4 years, average sawgrass ANPP in both basins ranged from 255 to 606 g m⁻² year⁻¹. Average periphyton productivity at SRS and TS/Ph was 17–68 g C m⁻² year⁻¹ and 342–10371 g C m⁻² year⁻¹, respectively. Mangrove productivity ranged from 340 g m⁻² year⁻¹ at Taylor River to 2208 g m⁻² year⁻¹ at the lower estuarine Shark River site. Average Thalassia testudinum productivity ranged from 91 to 396 g m⁻² year⁻¹ and was 4-fold greater at the site nearest the Gulf of Mexico than in eastern Florida Bay. There were no differences in periphyton productivity at Florida Bay. Interannual comparisons revealed no significant differences within each primary producer at either SRS or TS/Ph with the exception of sawgrass at SRS and the C−111 Basin. Future research will address difficulties in assessing and comparing ANPP of different primary producers along gradients as well as the significance of belowground production to the total productivity of this ecosystem.     

Responses of sawgrass and spikerush to variation in hydrologic drivers and salinity in Southern Everglades marshes

Aboveground net primary production (ANPP) by the dominant macrophyte and plant community composition are related to the changing hydrologic environment and to salinity in the southern Everglades, FL, USA. We present a new non-destructive ANPP technique that is applicable to any continuously growing herbaceous system. Data from 16 sites, collected from 1998 to 2004, were used to investigate how hydrology and salinity controlled sawgrass (Cladium jamaicense Crantz.) ANPP. Sawgrass live biomass showed little seasonal variation and annual means ranged from 89 to 639 gdw m⁻². Mortality rates were 20–35% of live biomass per 2 month sampling interval, for biomass turnover rates of 1.3–2.5 per year. Production by C. jamaicense was manifest primarily as biomass turnover, not as biomass accumulation. Rates typically ranged from 300 to 750 gdw m⁻² year⁻¹, but exceeded 1000 gdw m⁻² year⁻¹ at one site and were as high as 750 gdw m⁻² year⁻¹ at estuarine ecotone sites. Production was negatively related to mean annual water depth, hydroperiod, and to a variable combining the two (depth-days). As water depths and hydroperiods increased in our southern Everglades study area, sawgrass ANPP declined. Because a primary restoration goal is to increase water depths and hydroperiods for some regions of the Everglades, we investigated how the plant community responded to this decline in sawgrass ANPP. Spikerush (Eleocharis sp.) was the next most prominent component of this community at our sites, and 39% of the variability in sawgrass ANPP was explained by a negative relationship with mean annual water depth, hydroperiod, and Eleocharis sp. density the following year. Sawgrass ANPP at estuarine ecotone sites responded negatively to salinity, and rates of production were slow to recover after high salinity years. Our results suggest that ecologists, managers, and the public should not necessarily interpret a decline in sawgrass that may result from hydrologic restoration as a negative phenomenon.     

Seasonal growth and biomass ofTrapa japonica Flerov in Ojaga-Ike Pond,Chiba, Japan

In order to determine the seasonal growth and biomass ofTrapa japonica Flerov, field observations were carried out at Ojaga-ike Pond, Chiba, Japan, during 1979 and 1980. In spring, the plant showed exponential growth (c. 0.080 g g⁻¹ day⁻¹) and shoot elongation was as rapid as 10 cm day⁻¹. The plant attained its maximum biomass (380.5±35.1 g m⁻²) in late August, and about 50% of this was concentrated in the topmost 30-cm stratum (645.7±33.1 g m⁻³); maximum total stem length exceeded 6m. The plant produced large (500–800 mg per fruit), but small numbers of nut-like fruit (maximum, 5 fruits per rosette). Defoliation occurred almost linearly with time at a rate of 30.6 leaves m⁻² day⁻¹; annual net leaf production was estimated to be about twice as large as the seasonal maximum leaf biomass. While the number of leaves per rosette showed moderate seasonal change, rosette density, rosette area and leaf dry weight changed considerably during the year. From the negative log-log correlation between mean total leaf dry weight per rosette and rosette density, density-dependent rosette growth was assumed. The cause of the wide spread of this species in aquatic habitats is briefly discussed in terms of its seed size and morphology.     

Soil Nutrients Limit Fine Litter Production and Tree Growth in Mature Lowland Forest of Southwestern Borneo

Efforts to improve models of terrestrial productivity and to understand the function of tropical forests in global carbon cycles require a mechanistic understanding of spatial variation in aboveground net primary productivity (ANPP) across tropical landscapes. To help derive such an understanding for Borneo, we monitored aboveground fine litterfall, woody biomass increment and ANPP (their sum) in mature forest over 29 months across a soil nutrient gradient in southwestern Kalimantan. In 30 (0.07 ha) plots stratified throughout the watershed (∼340 ha, 8–190 m a.s.l.), we measured productivity and tested its relationship with 27 soil parameters. ANPP across the study area was among the highest reported for mature lowland tropical forests. Aboveground fine litterfall ranged from 5.1 to 11.0 Mg ha⁻¹ year⁻¹ and averaged 7.7 ± 0.4 (mean ± 95 C.I.). Woody biomass increment ranged from 5.8 to 23.6 Mg ha⁻¹ year⁻¹ and averaged 12.0 ± 2.0. Growth of large trees (≥60 cm dbh) contributed 38–82% of plot-wide biomass increment and explained 92% of variation among plots. ANPP, the sum of these parameters, ranged from 11.1 to 32.3 Mg ha⁻¹ year⁻¹ and averaged 19.7 ± 2.2. ANPP was weakly related to fine litterfall (r ² = 0.176), but strongly related to growth of large trees at least 60 cm dbh (r ² = 0.848). Adjusted ANPP after accounting for apparent “mature forest bias” in our sampling method was 17.5 ± 1.2 Mg ha⁻¹ year⁻¹.Relating productivity measures to soil parameters showed that spatial patterning in productivity was significantly related to soil nutrients, especially phosphorus (P). Fine litterfall increased strongly with extractable P (r ² = 0.646), but reached an asymptote at moderate P levels, whereas biomass increment (r ² = 0.473) and ANPP (r ² = 0.603) increased linearly across the gradient. Biomass increment of large trees was more frequently and strongly related to nutrients than small trees, suggesting size dependency of tree growth on nutrients. Multiple linear regression confirmed the leading importance of soil P, and identified Ca as a potential co-limiting factor. Our findings strongly suggest that (1) soil nutrients, especially P, limit aboveground productivity in lowland Bornean forests, and (2) these forests play an important, but changing role in carbon cycles, as canopy tree logging alters these terrestrial carbon sinks. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China

The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N₂O, CO₂ and CH₄ soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N₂O emission in these regions on a landscape level. The mean N₂O emission at site PF was 6.0 ± 0.1 SE μg N m⁻² h⁻¹. Fluxes of N₂O increased from <5 μg N m⁻² h⁻¹ during dry season conditions to up to 24.5 μg N m⁻² h⁻¹ with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N₂O were measured in the SF and RP sites, where mean N₂O emissions were 7.3 ± 0.7 SE μg N m⁻² h⁻¹ and 4.1 ± 0.5 SE μg N m⁻² h⁻¹, respectively. The dependency of N₂O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N₂O emission peaks, not the total amount of N₂O emitted. For all sites, significant positive correlations existed between N₂O emissions and both soil moisture and soil temperature. Mean CH₄ uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m⁻² h⁻¹), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m⁻² h⁻¹) and lowest for the RP site (−5.7 ± 0.5 SE μg C m⁻² h⁻¹). At all sites, CH₄ uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N₂O emissions, CH₄ uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO₂ emissions at the PF site increased significantly from 50 mg C m⁻² h⁻¹ up to 100 mg C m⁻² h⁻¹ (mean value 68.8 ± 0.8 SE mg C m⁻² h⁻¹), whereas CO₂ emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m⁻² h⁻¹ (SF) and 34.9 ± 1.1 SE mg C m⁻² h⁻¹ (RP). A dependency of soil CO₂ emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO₂ emissions as compared to control chambers. Correlation of CO₂ emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified.     

Aboveground Net Primary Production and Leaf-Area Index in Early Postfire Vegetation in Yellowstone National Park

Aboveground net primary production (ANPP) and leaf-area index (LAI) of lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.) saplings and aboveground productivity of herbaceous vegetation components were determined 9 years after the 1988 fires in Yellowstone National Park (YNP). Measurements were made in four sites representing a wide range of early postfire vegetation present in YNP, including high-density lodgepole pine, low-density lodgepole pine, and two nonforest stands. LAI of the pine saplings and total ANPP (trees plus herbs) generally increased with increasing sapling density, from 0.002 m² m^{− 2} and 0.25 Mg ha^{− 1} year^{− 1} in the infertile nonforest stand (100 pine saplings ha^{− 1}) to 1.8 m² m^{− 2} and 4.01 Mg ha^{− 1} year^{− 1} in the high-density pine stand (62,800 saplings ha^{− 1}). Aboveground herbaceous productivity was not strongly correlated with sapling density, but appeared to be influenced by soil fertility. In the high-density pine stand, tree ANPP and LAI were within the lower range of values reported for similar mature coniferous forests. This finding suggests that at least some ecosystem processes (related to ANPP and LAI) may have nearly recovered after only 9 years of postfire succession, in at least some of the young forests developing after the 1988 Yellowstone fires. Received 7 April 1998; accepted 1 December 1998.     

Estimation of fungal biomass in the decaying cones ofPinus densiflora

Fungal biomass in the decaying cones ofPinus densiflora was investigated. Leaching, immobilization and mobilization phases were recognized in the decomposition process of cones. Fungal biomass was estimated by the agar-film technique, using a conversion factor of 0.62 mg dry wt. mm⁻³ of hyphal volume to biomass and a factor of 2.5 for in-efficiencency of homogenization. The fungal biomass was 4.9±2.1 (mean±S.D.) mg dry wt. g⁻¹ dry matter in the cones on the tree, 11±6 mg g⁻¹ in the leaching phase, 19±7 mg g⁻¹ in the immobilization phase and 30±15 mg g⁻¹ in the mobilization phase. It significantly increased after cones had lain on the forest floor, and also in the immobilization phase. The latter result suggests that the fungal biomass contributed to the immobilization of nitrogen in the decomposition process. The ratio of ergosterol content to fungal biomass in the cones was 2.9–8.8 μg mg⁻¹ dry wt., lying in the range of 2–16 μg mg⁻¹ reported for mycelia. This suggested that the estimate of fungal biomass was reasonable. Reduction in this ratio with the dry weight loss in the cones suggested that the proportion of relatively active fungal biomass decreased with the progress of decomposition.     

Variation in fine root biomass of three European tree species: Beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.)

Abstract

Fine roots (<2 mm) are very dynamic and play a key role in forest ecosystem carbon and nutrient cycling and accumulation. We reviewed root biomass data of three main European tree species European beech, (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.), in order to identify the differences between species, and within and between vegetation zones, and to show the relationships between root biomass and the climatic, site and stand factors. The collected literature consisted of data from 36 beech, 71 spruce and 43 pine stands. The mean fine root biomass of beech was 389 g m^?2, and that of spruce and pine 297 g m^?2 and 277 g m^?2, respectively. Data from pine stands supported the hypothesis that root biomass is higher in the temperate than in the boreal zone. The results indicated that the root biomass of deciduous trees is higher than that of conifers. The correlations between root biomass and site fertility characteristics seemed to be species specific. There was no correlation between soil acidity and root biomass. Beech fine root biomass decreased with stand age whereas pine root biomass increased with stand age. Fine root biomass at tree level correlated better than stand level root biomass with stand characteristics. The results showed that there exists a strong relationship between the fine root biomass and the above-ground biomass.     

The influence of ultraviolet-B radiation on the growth, pigment production and chlorophyll fluorescence of Norway spruce seedlings

Norway spruce (Picea abies (L.)Karst.) from seven seed sources was grown in a greenhouse with 8.3 and 14.7 kJ·m⁻²·d⁻¹ m UV-B_BE (biologically effective UV-B: 280–320 nm) irradiation, and with no supplemental irradiation as control. The seedlings total biomass (dry weight) and shoot growth decreased with high UV-B treatment but spruce from low elevation seed sources were more affected. The seedlings grown at the highest UV-B irradiance (14.7 kJ·m⁻²·d⁻¹) showed from 5 to 38% inhibition of total biomass and 15 to 70 % shoot growth inhibition. Norway spruce populations from higher altitude seed sources manifested greater tolerance to UV-B radiation compared to plants from low altitudes. Changes in phospholipids and protective pigments were also determined. The plants grown at the lower UV-B irradiance (8.3 kJ·m⁻²·d⁻¹) showed greater ability to concentrations UV-B-absorbing pigments then control plants. Chlorophyll a fluorescence parameter R_fd, (R_fd=(F_m-F_s)/F_s) showed a significant decrease in needles of UV-B treated plants and this correlated with the altitude of seed source. Exposure to UV-B affect levels of the ratio of variable to maximum fluorescence (F_v/F_m). Results from this study suggest that the response to increased levels of UV-B radiation is depended upon the ecotypic differentiation of Norway spruce and involved changes in metabolites in plant tissues.     

Subsurface CO<Subscript>2</Subscript> Dynamics in Temperate Beech and Spruce Forest Stands

Rates of soil respiration (CO₂ effluxes), subsurface pore gas CO₂/O₂ concentrations, soil temperature and soil water content were measured for 15 months in two temperate and contrasting Danish forest ecosystems: beech (Fagus sylvatica L.) and Norway spruce (Picea abies [L.] Karst.). Soil CO₂ effluxes showed a distinct seasonal trend in the range of 0.48–3.3 μmol CO₂ m⁻² s⁻¹ for beech and 0.50–2.92 μmol CO₂ m⁻² s⁻¹ for spruce and were well-correlated with near-surface soil temperatures. The soil organic C-stock (upper 1 m including the O-horizon) was higher in the spruce stand (184±23 Mg C ha⁻¹) compared to the beech stand (93±19 Mg C ha⁻¹) and resulted in a faster turnover time as calculated by mass/flux in soil beneath the beech stand (28 years) compared to spruce stand (60 years). Observed soil CO₂ concentrations and effluxes were simulated using a Fickian diffusion-reaction model based on vertical CO₂ production rates and soil diffusivity. Temporal trends were simulated on the basis of observed trends in the distribution of soil water, temperature, and live roots as well as temperature and water content sensitivity functions. These functions were established based on controlled laboratory incubation experiments. The model was successfully validated against observed soil CO₂ effluxes and concentrations and revealed that temporal trends generally could be linked to variations in subsurface CO₂ production rates and diffusion over time and with depths. However, periods with exceptionally high CO₂ effluxes (> 20 μmol CO₂ m⁻² s⁻¹) were noted in March 2000 in relation to drying after heavy rain and after the removal of snow from collars. Both cases were considered non-steady state and could not be simulated.     

Energy flow and subsidies associated with the complex life cycle of ambystomatid salamanders in ponds and adjacent forest in southern Illinois

Breeding adults and metamorphosing larval amphibians transfer energy between freshwater and terrestrial ecosystems during seasonal migrations and emergences, although rarely has this been quantified. We intensively sampled ambystomatid salamander assemblages (Ambystoma opacum,A. maculatum, and A. tigrinum) in five forested ponds in southern Illinois to quantify energy flow associated with egg deposition, larval production, and emergence of metamorphosed larvae. Oviposition by female salamanders added 7.0–761.4 g ash-free dry mass (AFDM) year⁻¹ to ponds (up to 5.5 g AFDM m⁻² year⁻¹). Larval production ranged from 0.4 to 7.4 g AFDM m⁻² year⁻¹ among populations in three ponds that did not dry during larval development, with as much as 7.9 g AFDM m⁻² year⁻¹ produced by an entire assemblage. Mean larval biomass during cohort production intervals in these three ponds ranged from 0.1 to 2.3 g AFDM m⁻² and annual P/B (production/biomass) ranged from 4 to 21 for individual taxa. Emergent biomass averaged 10% (range=2–35%) of larval production; larval mortality within ponds accounted for the difference. Hydroperiod and intraguild predation limited larval production in some ponds, but emerging metamorphs exported an average of 70.0±33.9 g AFDM year⁻¹ (range=21.0–135.2 g AFDM year⁻¹) from ponds to surrounding forest. For the three ponds where larvae survived to metamorphosis, salamander assemblages provided an average net flux of 349.5±140.8 g AFDM year⁻¹ into pond habitats. Among all ponds, net flux into ponds was highest for the largest pond and decreased for smaller ponds with higher perimeter to surface area ratios (r ² =0.94, P<0.05, n=5). These results are important in understanding the multiple functional roles of salamanders and the impact of amphibian population declines on ecosystems. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Biomass, carbonate standing stock and production of the mediterranean coralCladocora caespitosa (L.)

Summary The Mediterranean coralCladocora caespitosa often occurs in large beds, i.e. populations of hemispherical clonies with stock densities varying between 1.9 and 4 coloneis ·m⁻². Laboratory measurements of volume, skeleton weight, surface and number of corallites per colony, coupled with mean annual growth rates evaluated through sclerochronology, allowed for the estimation of biomass, skeleton bulk density, calcimass (carbonate standing stock) and secondary production (both organic and inorganic) of twoC. caespitosa beds at 4 and 9 m depth. The mean colony biomass varied between 0.73 and 0.99 kg dw ·m⁻², corresponding to a calcimass between 2 and 5 kg CaCO₃·m⁻². Organic secondary production was 215.5–305.4 g dw of polyps ·m⁻²·y⁻¹, while the potential (mineral) production was 1.1–1.7 kg CaCO₃·m⁻²·y⁻¹, for the year 1996–1997. These values show thatC. caespitosa is one of the major carbonate producers within the Mediterranean and one of the major epibenthic species originating stable carbonate frameworks both in recent and past times.     

Litterfall and fine root biomass contribution to nutrient dynamics in second- and old-growth Douglas-fir ecosystems

Litterfall and fine root production were measured for three years as part of a carbon balance study of three forest stands in the Pacific Northwest of the United States. A young second-growth Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stand, a second-growth Douglas-fir with red alder (Alnus rubra Bong.) stand, and an old-growth (∼550 years) Douglas-fir stand were monitored for inputs of carbon and nitrogen into the soil from litterfall and fine root production, as well as changes in soil C and N. Fine root production and soil nutrient changes were measured through the use of soil ingrowth bags containing homogenized soil from the respective stands. Litterfall biomass was greatest in the Douglas-fir-alder stand (527 g m⁻² yr⁻¹) that annually returned nearly three times the amount of N as the other stands. Mean residence time for forest floor material was also shortest at this site averaging 4.6 years and 5.5 years for C an N, respectively. Fine root production in the upper 20 cm ranged from 584 g m⁻² in the N rich Douglas-fir-alder stand to 836 g m⁻² in the old-growth stand. Fine root production (down to one meter) was always greater than litterfall with a below:above ratio ranging from 3.73 for the young Douglas-fir stand to 1.62 for the Douglas-fir-alder stand. The below:above N ratios for all three stands closely approximate those for biomass. Soil changes in both C and N differed by site, but the soil C changes in the old-growth stand mirrored those obtained in an ongoing CO₂ flux study. Results from the soil ingrowth bags strongly suggest that this method provides a simple, but sufficient device for measuring potential fine root biomass production as well as soil chemical changes.