Northern Hemisphere Ecosystems Research Articles

Deriving biomass conversion factors for southern temperate benthic fauna; analytical methods matter

Biomass is a fundamental ecological measure used to quantify ecosystem structure and function. It is costly to measure but can be estimated using conversion factors based on established relationships between different biomass measures, however such conversion factors may not be applicable across broad geographic regions. For temperate benthic fauna, currently available mass-to-mass conversion factors were largely established in Northern Hemisphere ecosystems. Here, we present conversion factors for temperate Australian benthic fauna typically found in microtidal coastal bays and estuaries (14 taxa encompassing five classes: Polychaeta; Bivalvia; Gastropoda; Crustacea; Insecta). We derived 126 conversion factors using two statistical techniques between several mass measures (e.g. wet mass, dry mass, ash-free dry mass, shell-free masses) with specimens from three preservation methods (ethanol, formalin, frozen). Our conversion factors were generally not congruent with those obtained from the literature. We also found that the choice of prediction method used to derive conversion factors can be a substantial source of error in biomass estimation that has largely been overlooked in mass-to-mass conversion. Log-linear ordinary least squares regression models provided substantially more accurate predictions than simple mean ratios. We outline an analytical approach for future use to derive more globally comparable conversion factors for estuarine benthic fauna.

Mycorrhizal symbioses in the Andean paramo.

The Andean paramo, hereafter "paramo", is a Neotropical high-mountain region between the treeline and permanent snowline (3500-4800m) and is considered the world's coolest biodiversity hotspot. Because of paramo's high humidity, solar radiation and temperature variation, mycorrhizal symbiosis is expected to be essential for plants. Existing theory suggests that replacement of arbuscular mycorrhizal (AM) by ectomycorrhizal (ECM) and then ericoid mycorrhizal plants (ERM) can be expected with increasing elevation. Previous findings also suggest that non-(NM) and facultatively mycorrhizal (FM) species predominate over obligatory mycorrhizal (OM) species at high elevations. However, these expectations have never been tested outside of the northern temperate zone. We addressed the distribution and environmental drivers of plant mycorrhizal types (AM, ECM and ERM) and statuses (NM, FM and OM) along the paramo's elevational gradient. We used vegetation plots from the VegParamo database, climatic and edaphic data from online repositories, and up-to-date observation information about plant mycorrhizal traits at species and genus level, the latter being proposed as hypotheses. AM plants were dominant along the entire gradient, and ERM plants were most abundant at the lowest elevations (2500-3000m). The share of FM plants increased and that of OM plants decreased with elevation, while NM plants increased above 4000m. Temperature and soil pH were positively related to the abundance of AM plants and negatively to ERM plants. Our results reveal patterns that contrast with those observed in temperate northern-hemisphere ecosystems.

Disturbance of eucalypt forests alters the composition, function, and assembly of soil microbial communities.

Forest disturbance has well-characterized effects on soil microbial communities in tropical and northern hemisphere ecosystems, but little is known regarding effects of disturbance in temperate forests of the southern hemisphere. To address this question, we collected soils from intact and degraded Eucalyptus forests along an east-west transect across Tasmania, Australia, and characterized prokaryotic and fungal communities using amplicon sequencing. Forest degradation altered soil microbial community composition and function, with consistent patterns across soil horizons and regions of Tasmania. Responses of prokaryotic communities included decreased relative abundance of Acidobacteriota, nitrifying archaea, and methane-oxidizing prokaryotes in the degraded forest sites, while fungal responses included decreased relative abundance of some saprotrophic taxa (e.g. litter saprotrophs). Forest degradation also reduced network connectivity in prokaryotic communities and increased the importance of dispersal limitation in assembling both prokaryotic and fungal communities, suggesting recolonization dynamics drive microbial composition following disturbance. Further, changes in microbial functional groups reflected changes in soil chemical properties-reductions in nitrifying microorganisms corresponded with reduced NO3-N pools in the degraded soils. Overall, our results show that soil microbiota are highly responsive to forest degradation in eucalypt forests and demonstrate that microbial responses to degradation will drive changes in key forest ecosystem functions.

Climate warming-induced phenology changes dominate vegetation productivity in Northern Hemisphere ecosystems

The climate change is expected to trigger changes in vegetation phenology, temperature, and soil moisture (SM), altering the productivity of ecosystems. Despite numerous existing efforts, however, their contradicting conclusions suggest that how vegetation productivity is impacted by these factors still remains unclear in the Northern Hemisphere ecosystems (≥25°N). This study used the optimal fingerprint (OFP) method and redundancy analysis (RDA) to attribute the importance of key drivers of vegetation productivity from 2001 to 2019 based on long-term remote sensing and FLUXNET observation data. The results showed that solar-induced chlorophyll fluorescence (SIF), gross primary productivity (GPP), and net primary productivity (NPP) were increased in 72.01% to 88.04% of the vegetation areas. We observed that the correlation between vegetation productivity and spring phenology, autumn phenology, growing season length (GSL), SM, temperature reached 99% significance level, where early spring phenology, delayed autumn phenology, extended GSL, increased SM, and elevated temperature all enhanced ecosystem productivity, with GSL being the most important factor driving vegetation productivity. In addition, the pixel-wise attribution analysis indicated that GSL, as the dominant driver, accounted for 30.24% of the vegetation productivity, followed by temperature (23.79%), spring phenology (19.56%), autumn phenology (14.09%), and SM (12.31%), all of which were dominated by positive effects (54.19% to 73.14%). The results from this study serve as important references that benefit our understanding of driving mechanisms of temperature-phenology-SM interactions on ecosystem productivity.

Widespread spring phenology effects on drought recovery of Northern Hemisphere ecosystems

The time required for an ecosystem to recover from severe drought is a key component of ecological resilience. The phenology effects on drought recovery are, however, poorly understood. These effects centre on how phenology variations impact biophysical feedbacks, vegetation growth and, ultimately, recovery itself. Using multiple remotely sensed datasets, we found that more than half of ecosystems in mid- and high-latitudinal Northern Hemisphere failed to recover from extreme droughts within a single growing season. Earlier spring phenology in the drought year slowed drought recovery when extreme droughts occurred in mid-growing season. Delayed spring phenology in the subsequent year slowed drought recovery for all vegetation types (with importance of spring phenology ranging from 46% to 58%). The phenology effects on drought recovery were comparable to or larger than other well-known postdrought climatic factors. These results strongly suggest that the interactions between vegetation phenology and drought must be incorporated into Earth system models to accurately quantify ecosystem resilience.

Genome-wide identification, phylogeny, and gene duplication of the epigenetic regulators in Fagaceae.

Epigenetic regulators are proteins involved in controlling gene expression. Information about the epigenetic regulators within the Fagaceae, a relevant family of trees and shrubs of the northern hemisphere ecosystems, is scarce. With the intent to characterize these proteins in Fagaceae, we searched for orthologs of DNA methyltransferases (DNMTs) and demethylases (DDMEs) and Histone modifiers involved in acetylation (HATs), deacetylation (HDACs), methylation (HMTs), and demethylation (HDMTs) in Fagus, Quercus, and Castanea genera. Blast searches were performed in the available genomes, and freely available RNA-seq data were used to de novo assemble transcriptomes. We identified homologs of seven DNMTs, three DDMEs, six HATs, 11 HDACs, 32 HMTs, and 21 HDMTs proteins. Protein analysis showed that most of them have the putative characteristic domains found in these protein families, which suggests their conserved function. Additionally, to elucidate the evolutionary history of these genes within Fagaceae, paralogs were identified, and phylogenetic analyses were performed with DNA and histone modifiers. We detected duplication events in all species analyzed with higher frequency in Quercus and Castanea and discuss the evidence of transposable elements adjacent to paralogs and their involvement in gene duplication. The knowledge gathered from this work is a steppingstone to upcoming studies concerning epigenetic regulation in this economically important family of Fagaceae.

Satellite observations reveal seasonal redistribution of northern ecosystem productivity in response to interannual climate variability

Interannual variability (IAV) in ecosystem productivity may reveal vulnerabilities of vegetation to climate stressors. We analyzed IAV of northern hemisphere ecosystems using several remote sensing datasets, including longstanding observations of the normalized difference vegetation index (NDVI) and more novel metrics for productivity including solar-induced chlorophyll fluorescence (SIF) and the near-infrared reflectance of vegetation (NIRv). Although previous studies have suggested SIF better tracks variations in ecosystem productivity at seasonal timescales, we found that satellite datasets (including SIF) and eddy covariance flux tower observations were subject to significant uncertainty when assessing IAV at fine spatial scales. Even when observations were aggregated regionally, IAV in productivity estimated by the various satellite products were not always well correlated. In response to these inconsistencies, we applied a statistical method on regionally aggregated productivity data in four selected North American ecoregions and identified two dominant modes of IAV—seasonal redistribution and amplification—that were consistent across satellite datasets. The seasonal redistribution mode, which played a stronger role at lower latitudes, associated high (low) spring productivity with warm (cold) spring and summer temperatures, but also with lower (higher) productivity and water availability in summer and fall, indicating that enhanced growth in spring may contribute to an earlier depletion of water resources. The amplification mode associated an increase (decrease) in productivity across the growing season with above-average (below-average) summer moisture conditions. Even though our statistical analysis at large spatial scales revealed meaningful links between terrestrial productivity and climate drivers, our analysis does suggest that IAV and long-term trends in presently available novel and more established satellite observations must be interpreted cautiously, with careful attention to the spatial scales at which a robust signal emerges.

Multi-Scale Phenology of Temperate Grasslands: Improving Monitoring and Management With Near-Surface Phenocams

Grasslands of the Australian Southern Tablelands represent a patchwork of native and exotic systems, occupying a continuum of C3-dominated to C4-dominated grasslands where composition depends on disturbance factors (e.g. grazing) and climate. Managing these complex landscapes is both challenging and critical for maintaining the security of Australia’s pasture industries, and for protecting the biodiversity of native remnants. Differentiating C3 from C4 vegetation has been a prominent theme in remote sensing research due to distinct C3/C4 seasonal productivity patterns (phenology) and high uncertainty about how C3/C4 vegetation will respond to a changing climate. Phenology is used in northern hemisphere ecosystems for a range of purposes but has not been widely adopted in Australia, where dynamic climate often results in non-repetitive seasonal vegetation patterns. We employed time-lapse cameras (phenocams) to study the phenology of twelve grassland areas dominated by cool season (C3) and warm season (C4), native or exotic grasses near Canberra, Australia. Our aims were to assess phenological characteristics of the functional types and to determine the drivers of phenological variability. We compared the fine-scale phenocam seasonal profiles with field sampling and MODIS/Landsat satellite products to assess paddock-to-landscape functioning. We found C3/C4 species dominance to be the primary driver of phenological differences among grassland types, with C3 grasslands demonstrating peak greenness in spring, and senescing rapidly in response to high summer temperatures. In contrast, C4 grasslands showed peak activity in Austral summer and autumn (January-March). Some sites displayed primary and secondary peaks dependent on rainfall and species composition. We found that the proportion of dead vegetation is an important biophysical driver of grassland phenology, as were grazing pressures and species-dependent responses to rainfall and temperature. The satellite and field datasets were in general agreement with the phenocam results. However, the higher temporal fidelity of the cameras captured changes in vegetation not observed in the coarser satellite or field results. Our phenocam data shows consistent periods of increasing and decreasing greenness over as little as five days. Applications for management of grasslands in temperate Australia include the identification of remnant native grasslands, tracking biosecurity issues, and assessing productivity responses to climate variability.

Palaeoecology: North-South recovery divide.

Plant–insect interactions reveal rapid recovery of terrestrial ecosystems in the Southern Hemisphere after the end-Cretaceous mass extinction, at more than twice the rate of contemporaneous Northern Hemisphere ecosystems.

First Draft Assembly and Annotation of the Genome of a California Endemic Oak Quercus lobata Née (Fagaceae).

Oak represents a valuable natural resource across Northern Hemisphere ecosystems, attracting a large research community studying its genetics, ecology, conservation, and management. Here we introduce a draft genome assembly of valley oak (Quercus lobata) using Illumina sequencing of adult leaf tissue of a tree found in an accessible, well-studied, natural southern California population. Our assembly includes a nuclear genome and a complete chloroplast genome, along with annotation of encoded genes. The assembly contains 94,394 scaffolds, totaling 1.17 Gb with 18,512 scaffolds of length 2 kb or longer, with a total length of 1.15 Gb, and a N50 scaffold size of 278,077 kb. The k-mer histograms indicate an diploid genome size of ∼720–730 Mb, which is smaller than the total length due to high heterozygosity, estimated at 1.25%. A comparison with a recently published European oak (Q. robur) nuclear sequence indicates 93% similarity. The Q. lobata chloroplast genome has 99% identity with another North American oak, Q. rubra. Preliminary annotation yielded an estimate of 61,773 predicted protein-coding genes, of which 71% had similarity to known protein domains. We searched 956 Benchmarking Universal Single-Copy Orthologs, and found 863 complete orthologs, of which 450 were present in > 1 copy. We also examined an earlier version (v0.5) where duplicate haplotypes were removed to discover variants. These additional sources indicate that the predicted gene count in Version 1.0 is overestimated by 37–52%. Nonetheless, this first draft valley oak genome assembly represents a high-quality, well-annotated genome that provides a tool for forest restoration and management practices.

Development of a Bioenergetics Model for the Threespine Stickleback

AbstractThe Threespine Stickleback Gasterosteus aculeatus is widely distributed across northern hemisphere ecosystems, has ecological influence as an abundant planktivore, and is commonly used as a model organism, but the species lacks a comprehensive model to describe bioenergetic performance in response to varying environmental or ecological conditions. This study parameterized a bioenergetics model for the Threespine Stickleback using laboratory measurements to determine mass‐ and temperature‐dependent functions for maximum consumption and routine respiration costs. Maximum consumption experiments were conducted across a range of temperatures from 7.5°C to 23.0°C and a range of fish weights from 0.5 to 4.5 g. Respiration experiments were conducted across a range of temperatures from 8°C to 28°C. Model sensitivity was consistent with other comparable models in that the mass‐dependent parameters for maximum consumption were the most sensitive. Growth estimates based on the Threespine Stickleback bioenergetics model suggested that 22°C is the optimal temperature for growth when food is not limiting. The bioenergetics model performed well when used to predict independent, paired measures of consumption and growth observed from a separate wild population of Threespine Sticklebacks. Predicted values for consumption and growth (expressed as percent body weight per day) only deviated from observed values by 2.0%. Our model should provide insight into the physiological performance of this species across a range of environmental conditions and be useful for quantifying the trophic impact of this species in food webs containing other ecologically or economically important species.

Comparative chemical sensitivity between marine Australian and Northern Hemisphere ecosystems: Is an uncertainty factor warranted for water‐quality–guideline setting?

The lack of Australian species data has pragmatically led to the use of toxicological data from the Northern Hemisphere to develop water-quality guidelines. However, it is unknown whether Australian species and ecosystems are equally as sensitive and if an uncertainty factor is warranted for Australian guideline setting. In the present study, it is hypothesized that an uncertainty factor is not required. This was tested by generating species sensitivity distributions by 2 parametric methods using marine Northern Hemisphere and Australian/New Zealand data. Sufficient acute data were found for only 3 compounds: 4-chlorophenol, phenol, and ammonia. For ammonia and 4-chlorophenol, the 95% species protection levels generated with Australian and Northern Hemisphere data were essentially the same. For phenol, protection levels derived from Australian data were approximately 10-fold higher. Therefore, the derived benchmark concentration from Northern Hemisphere data should be protective. It is tentatively concluded that there is no need for an uncertainty factor when deriving water-quality guidelines for marine Australian ecosystems using Northern Hemisphere data. It is, however, noted that this is based on only 3 compounds.

Do vascular plants and bryophytes respond differently to coniferous invasion of coastal heathlands?

Invasion by non-native conifers may pose a threat to local biodiversity, but knowledge about introduced conifer effects on Northern Hemisphere ecosystems is scarce. The coastal heathlands of north-west Europe are threatened by invasion of native and introduced tree species. We assess how spread of the introduced conifer Sitka spruce (Picea sitchensis (Bong.) Carr.) into European coastal heathlands affect two major functional groups; vascular plants and bryophytes, and how these effects relate to the environmental changes imposed by the developing tree canopies. We compared the impact of introduced Sitka spruce and native Scots pine (Pinus sylvestris L.) by analysing effects on species richness and turnover of vascular plants and bryophytes along fine-scale transects from individual tree stems into open heathland vegetation. Environmental impacts were assessed by measured environmental variables, and the responses of the two species groups were assessed by calculating changes in their respective mean Ellenberg indicator values. Species richness decreased beneath both conifers, related to decreased light and increased nitrogen and pH. Whereas vascular plants responded negatively to poor light conditions beneath dense and low Sitka spruce canopies, bryophytes were more negatively affected by the warmer and drier microclimates beneath Scots pine. Introduced Sitka spruce impacts the sub-canopy environment differently from the native Scots pine, and the two functional plant groups responded differently to these impacts. This suggests that future forests are likely to differ in species richness and composition, depending on whether succession is based on native or introduced coniferous trees.

Synthesizing lessons learned from comparing fisheries production in 13 northern hemisphere ecosystems: emergent fundamental features

Understanding the drivers of the productivity of marine ecosystems continues to be a globally important issue. A vast body of literature identifies 3 main processes that regulate the production dynamics of fisheries: biophysical, exploitative, and trophodynamic. Here, we synthe- size results from international workshops in which surplus production models were applied to 13 northern hemisphere ecosystems that support notable fisheries. The results are compared across systems, levels of species aggregation, and drivers. By applying surplus production models at sin- gle- species (SS), multi-species (MS), aggregated group, and full-system levels across ecosystems, we find that the different levels of aggregation provide distinct, but complementary, information. Further, it is clear that the triad of drivers contributes to fisheries productivity in each ecosystem, but the key drivers are system-specific. Our results also confirm that full-system yield is less than the sum of SS yields and that some MS and aggregate yields may lead to overharvest of some stocks if species groups are constructed without considering common productivity, inter-species, and en vironmental interactions. Several fundamental features emerge from this Theme Section including sigmoidal biomass accumulation curves across trophic levels, improvement of model fits by inclusion of environmental or ecological covariates, the inequality of system maximum sustain- able yield (MSY) versus aggregated sums and SS sums of MSY, a 1 to 5 t km �2 fishery yield rule of thumb, and the finding that tradeoffs among ocean use objectives may not be as harsh as origi- nally thought. These emergent features have the potential to alter our understanding of marine ecosystem dynamics and improve how we manage fisheries production.

Relative importance of fisheries, trophodynamic and environmental drivers in a series of marine ecosystems

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 459:169-184 (2012) - DOI: https://doi.org/10.3354/meps09805 Relative importance of fisheries, trophodynamic and environmental drivers in a series of marine ecosystems Caihong Fu1,*, Sarah Gaichas2, Jason S. Link3, Alida Bundy4, Jennifer L. Boldt1, Adam M. Cook4, Robert Gamble3, Kjell Rong Utne5, Hui Liu3, Kevin D. Friedland6 1Fisheries and Oceans Canada, Pacific Biological Station, Nanaimo, British Columbia V9T 6N7, Canada 2NOAA, National Marine Fisheries Service, Alaska Fisheries Science Center, Seattle, Washington 98115, USA 3NOAA, National Marine Fisheries Service, Northeast Fisheries Science Center, Woods Hole, Massachusetts 02543, USA 4Fisheries and Oceans Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia B2Y 4A2, Canada 5Institute of Marine Research, Nordnesgt 33, 5085 Bergen, Norway 6NOAA, National Marine Fisheries Service, Northeast Fisheries Science Center, Narragansett, Rhode Island 02882, USA *Email: caihong.fu@dfo-mpo.gc.ca ABSTRACT: Marine ecosystems are influenced by drivers that operate and interact over multiple scales, resulting in nonlinear or abrupt responses to perturbation. Because of the inherent complexity of marine ecosystems, progress towards an understanding of factors that affect fisheries production will be most efficient if researchers adopt a comparative approach across ecosystems using suites of indicators. The goals of this study were to explore a suite of biomass- and catch-based ecosystem response indicators for 9 northern hemisphere ecosystems relative to indices that capture the influence of fisheries, trophodynamic and environmental drivers, and to compare the relative influence of the triad of drivers. Partial least squares regression was used to explore relationships between the ecosystem response indicators and predictor drivers and to estimate the relative importance of each of the triad of drivers. Across ecosystems we have identified a few common observations: (1) environmental drivers, particularly temperature-related independent variables, are most likely related to total system biomass and biomass of specific biological groups (e.g. gadoid or clupeid fishes); (2) trophodynamic drivers are most relevant to the mean trophic level of community and the demersal-to-pelagic biomass ratio; and (3) fisheries drivers tend to be related to the catch-based indicators, such as fishing-in-balance and percent of primary production required to support fisheries. Overall, each of the triad of drivers was important for all ecosystems; however, the relative importance of each driver and the indicators they most affected varied among ecosystems, suggesting that an examination of a suite of indicators and drivers is required. A key finding is that fishing is categorically an important driver, but to explain biomass trends it is very important to consider environmental drivers as well. KEY WORDS: Marine ecosystems · Ecosystem indicators · Partial least squares regression · Multiple drivers Full text in pdf format Supplementary material PreviousNextCite this article as: Fu C, Gaichas S, Link JS, Bundy A and others (2012) Relative importance of fisheries, trophodynamic and environmental drivers in a series of marine ecosystems. Mar Ecol Prog Ser 459:169-184. https://doi.org/10.3354/meps09805 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 459. Online publication date: July 12, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Temperature response functions introduce high uncertainty in modelled carbon stocks in cold temperature regimes

Abstract. Models of carbon cycling in terrestrial ecosystems contain formulations for the dependence of respiration on temperature, but the sensitivity of predicted carbon pools and fluxes to these formulations and their parameterization is not well understood. Thus, we performed an uncertainty analysis of soil organic matter decomposition with respect to its temperature dependency using the ecosystem model LPJ-GUESS. We used five temperature response functions (Exponential, Arrhenius, Lloyd-Taylor, Gaussian, Van't Hoff). We determined the parameter confidence ranges of the formulations by nonlinear regression analysis based on eight experimental datasets from Northern Hemisphere ecosystems. We sampled over the confidence ranges of the parameters and ran simulations for each pair of temperature response function and calibration site. We analyzed both the long-term and the short-term heterotrophic soil carbon dynamics over a virtual elevation gradient in southern Switzerland. The temperature relationship of Lloyd-Taylor fitted the overall data set best as the other functions either resulted in poor fits (Exponential, Arrhenius) or were not applicable for all datasets (Gaussian, Van't Hoff). There were two main sources of uncertainty for model simulations: (1) the lack of confidence in the parameter estimates of the temperature response, which increased with increasing temperature, and (2) the size of the simulated soil carbon pools, which increased with elevation, as slower turn-over times lead to higher carbon stocks and higher associated uncertainties. Our results therefore indicate that such projections are more uncertain for higher elevations and hence also higher latitudes, which are of key importance for the global terrestrial carbon budget.

Recent climate forcing and physical oceanographic changes in Northern Hemisphere regions: A review and comparison of four marine ecosystems

As part of a project comparing the structure and function of four marine ecosystems off Norway and the United States, this paper examines the oceanographic responses to climate forcing, with emphasis on recent changes. The four Northern Hemisphere ecosystems include two in the Pacific Ocean (Bering Sea and Gulf of Alaska) and two in the Atlantic Ocean (Georges Bank/Gulf of Maine and the Barents/Norwegian Seas). Air temperatures, wind forcing and heat fluxes over the four regions are compared as well as ocean hydrography and sea-ice conditions where seasonal sea ice is found. The long-term interannual variability in air temperatures, winds and net heat fluxes show strong similarity between adjacent ecosystems and within subregions of an ecosystem, but no significant correlations between Pacific and Atlantic ecosystems and few across the Atlantic. In spite of the lack of correlation between climate forcing and ocean conditions between most of the ecosystems, recent years have seen record or near record highs in air and sea temperatures in all ecosystems. The apparent causes of the warming differ. In the Atlantic, they appear to be due to advection, while in the Pacific temperatures are more closely linked to air-sea heat exchanges. Advection is also responsible for the observed changes in salinity in the Atlantic ecosystems (generally increasing salinity in the Barents and Norwegian Seas and decreasing in the Gulf of Maine and Georges Bank) while salinity changes in the Gulf of Alaska are largely related to increased local runoff.

Ecosystem responses to recent oceanographic variability in high-latitude Northern Hemisphere ecosystems

As part of the international MENU collaboration, we compared and contrasted ecosystem responses to climate-forced oceanographic variability across several high latitude regions of the North Pacific (Eastern Bering Sea (EBS) and Gulf of Alaska (GOA)) and North Atlantic Oceans (Gulf of Maine/Georges Bank (GOM/GB) and the Norwegian/Barents Seas (NOR/BAR)). Differences in the nitrate content of deep source waters and incoming solar radiation largely explain differences in average primary productivity among these ecosystems. We compared trends in productivity and abundance at various trophic levels and their relationships with sea-surface temperature. Annual net primary production generally increases with annual mean sea-surface temperature between systems and within the EBS, BAR, and GOM/GB. Zooplankton biomass appears to be controlled by both top-down (predation by fish) and bottom-up forcing (advection, SST) in the BAR and NOR regions. In contrast, zooplankton in the GOM/GB region showed no evidence of top-down forcing but appeared to control production of major fish populations through bottom-up processes that are independent of temperature variability. Recruitment of several fish stocks is significantly and positively correlated with temperature in the EBS and BAR, but cod and pollock recruitment in the EBS has been negatively correlated with temperature since the 1977 shift to generally warmer conditions. In each of the ecosystems, fish species showed a general poleward movement in response to warming. In addition, the distribution of groundfish in the EBS has shown a more complex, non-linear response to warming resulting from internal community dynamics. Responses to recent warming differ across systems and appear to be more direct and more pronounced in the higher latitude systems where food webs and trophic interactions are simpler and where both zooplankton and fish species are often limited by cold temperatures.

Nitrous oxide and methane flux in Australian and New Zealand landscapes: measurements, modeling and mitigation

Nitrous oxide (N2O) and methane (CH4) represent around 25% of the increased radiative forcing in the earth’s atmosphere (Houghton et al. 2001). This may be half that represented by carbon dioxide (~50%), but nevertheless important enough to demand greater research into the sinks and sources of CH4 and N2O, the biogeochemical processes and factors involved, and ultimately to explore the management options available to mitigate emissions and enhance the sinks. Unlike carbon dioxide, the vast majority of the increase in the atmospheric concentrations of N2O and CH4 has been mediated by processes that occur naturally; in soils, sediments or animals within the landscape. N2O emissions are principally a product of microbial nitrification and denitrification in the soil (Firestone and Davidson 1989), whilst CH4 may be produced by methanogenic bacteria under anaerobic, anoxic conditions in the soils and sediments (Conrad 1996) and in the course of enteric fermentation by ruminant animals and termites. Predominantly, aerobic soils are an important CH4 sink (Dalal et al. 2008), greatest in well drained and undisturbed soils, such as many native forests (Price et al. 2004). However, human activities can have a profound effect on these processes: deforestation and land-clearing, agricultural intensification and increased use of fertilizers, ruminant animal domestication and livestock production have all contributed to enhanced emissions of N2O and modified exchange of CH4 between the soil and atmosphere. As such, understanding the ecosystem processes that mediate N2O and CH4 exchange between the landscape (soil–plant–animal) and the atmosphere is critical to enable a predictive understanding of how these landscapes will respond to a change in management, land-use or a change in the climate itself. Similarly, only with this process-level understanding can management options be successfully selected and applied to mitigate N2O and CH4 emissions and enhance available sinks. The measurement and understanding of greenhouse gas exchange in northern hemisphere ecosystems can not always be transferred to Australian or New Zealand ecosystems. Soils in Australia have generally very low nutrient concentrations (especially phosphorous) and atmospheric N deposition is very low. New Zealand’s greenhouse gas emissions inventory is dominated by N2O and CH4, because the economy and land management is dominated by agriculture. A Research Forum on ‘Non-CO2 greenhouse gas fluxes in Australian-New Plant Soil (2008) 309:1–4 DOI 10.1007/s11104-008-9674-5

Global environmental change and the uncertain fate of biodiversity

Global environmental change and the uncertain fate of biodiversity