Systematic assessment of terrestrial biogeochemistry in coupled climate–carbon models

With representation of the global carbon cycle becoming increasingly complex in climate models, it is important to develop ways to quantitatively evaluate model performance against in situ and remote sensing observations. Here we present a systematic framework, the Carbon‐LAnd Model Intercomparison Project (C‐LAMP), for assessing terrestrial biogeochemistry models coupled to climate models using observations that span a wide range of temporal and spatial scales. As an example of the value of such comparisons, we used this framework to evaluate two biogeochemistry models that are integrated within the Community Climate System Model (CCSM) – Carnegie‐Ames‐Stanford Approach′ (CASA′) and carbon–nitrogen (CN). Both models underestimated the magnitude of net carbon uptake during the growing season in temperate and boreal forest ecosystems, based on comparison with atmospheric CO₂ measurements and eddy covariance measurements of net ecosystem exchange. Comparison with MODerate Resolution Imaging Spectroradiometer (MODIS) measurements show that this low bias in model fluxes was caused, at least in part, by 1–3 month delays in the timing of maximum leaf area. In the tropics, the models overestimated carbon storage in woody biomass based on comparison with datasets from the Amazon. Reducing this model bias will probably weaken the sensitivity of terrestrial carbon fluxes to both atmospheric CO₂ and climate. Global carbon sinks during the 1990s differed by a factor of two (2.4 Pg C yr^?1 for CASA′ vs. 1.2 Pg C yr^?1 for CN), with fluxes from both models compatible with the atmospheric budget given uncertainties in other terms. The models captured some of the timing of interannual global terrestrial carbon exchange during 1988–2004 based on comparison with atmospheric inversion results from TRANSCOM (r=0.66 for CASA′ and r=0.73 for CN). Adding (CASA′) or improving (CN) the representation of deforestation fires may further increase agreement with the atmospheric record. Information from C‐LAMP has enhanced model performance within CCSM and serves as a benchmark for future development. We propose that an open source, community‐wide platform for model‐data intercomparison is needed to speed model development and to strengthen ties between modeling and measurement communities. Important next steps include the design and analysis of land use change simulations (in both uncoupled and coupled modes), and the entrainment of additional ecological and earth system observations. Model results from C‐LAMP are publicly available on the Earth System Grid.     

The effect of soil compaction on germination and early growth of Eucalyptus albens and an exotic annual grass

Most agricultural land has been compacted to some degree by heavy machinery or livestock trampling. This legacy is expected to influence the success of tree seedling recruits in farmland areas where natural regeneration is being encouraged. We investigated the impact of soil compaction on seedlings of a woodland eucalypt (Eucalyptus albens) and an annual grass competitor (Vulpia myuros) in a laboratory experiment. Replicate soil cores were created at five bulk density levels; 1.0, 1.1, 1.2, 1.3 or 1.4 Mg m^?3 with a soil water content of 20%. The depth of root penetration declined linearly with increasing bulk density, resulting in a decrease in root depth of around 75% in the most compacted soil compared with the least compacted soil for both species. Shoot length and primary root length did not vary between soil bulk density levels for either species, but seedlings responded to increasing levels of compaction with oblique (non‐vertical) root growth. Results suggest that young seedlings of both E. albens and V. myuros will be more susceptible to surface drying in compacted than uncompacted soils and therefore face a greater risk of desiccation during the critical months following germination. Any competitive advantage that V. myuros may have over E. albens is not evident in differential response to soil compaction.     

A test for Allee effects in the self‐incompatible wasp‐pollinated milkweed Gomphocarpus physocarpus

It has been suggested that plants that are good colonizers will generally have either an ability to self‐fertilize or a generalist pollination system. This prediction is based on the idea that these reproductive traits should confer resistance to Allee effects in founder populations and was tested using Gomphocarpus physocarpus (Asclepiadoideae: Apocynaceae), a species native to South Africa that is invasive in other parts of the world. We found no significant relationships between the size of G. physocarpus populations and various measures of pollination success (pollen deposition, pollen removal and pollen transfer efficiency) and fruit set. A breeding system experiment showed that plants in a South African population are genetically self‐incompatible and thus obligate outcrossers. Outcrossing is further enhanced by mechanical reconfiguration of removed pollinaria before the pollinia can be deposited. Self‐pollination is reduced when such reconfiguration exceeds the average duration of pollinator visits to a plant. Observations suggest that a wide variety of wasp species in the genera Belonogaster and Polistes (Vespidae) are the primary pollinators. We conclude that efficient pollination of plants in small founding populations, resulting from their generalist wasp‐pollination system, contributes in part to the colonizing success of G. physocarpus. The presence of similar wasps in other parts of the world has evidently facilitated the expansion of the range of this milkweed.     

Stakeholder Norms Toward Beaver Management in Massachusetts

ABSTRACT In Massachusetts, USA, both human and beaver (Castor Canadensis) population levels are increasing, beaver damage complaints are escalating, and beaver management options are restricted by the 1996 Wildlife Protection Act. We looked at the public's norms toward beavers in Massachusetts. In 2002 we sent a mail-back questionnaire to a random sample of 5,563 residents in 3 geographic regions in Massachusetts and to residents who submitted a beaver complaint to Massachusetts Division of Fisheries and Wildlife (MassWildlife) in 1999–2000 (47.3% overall response rate). Respondents supported some form of beaver management. As severity of beaver damage was perceived to increase, respondents were more willing to accept lethal management and control of beavers. These results emphasize the importance of how tolerance and acceptability of wildlife are influenced by the type of activity the animal is engaged in, the type of management action that is proposed, the positive or negative perception of a species in the eye of the public, and the public's preference for future population levels. A full understanding of these 4 points will help tailor management accordingly, because this knowledge can define a threshold of acceptance by the public for anticipated management actions. Restoration of full beaver management authority to the cognizant wildlife management agency would facilitate application of normative information to determine appropriate management response for minimizing conflicts between humans and beavers.     

Galápagos' Opuntia (prickly pear) cacti: extensive morphological diversity, low genetic variability

Due to the pronounced morphological variation and geographical distribution of Galápagos' Opuntia cacti, numerous hypotheses have been advanced regarding their radiation, diversification, and classification. The currently accepted classification is based on morphology and recognizes six species and fourteen varieties, but the plasticity of many of the characteristics renders any morphological taxonomy problematic. Our analysis of previously published morphological data agrees only partially with the current classification. We present the first molecular phylogeny of these plants. Multiple DNA sequences indicate little genetic distinction among the currently identified species, despite restricted gene flow and limited long distance dispersal within the archipelago. No clear relationship exists between morphological and genetic differences. These results suggest that both molecular and morphological data should be used in conservation planning.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 451–461.     

ROTATORY COLONIES OF THE CORALS SIDERASTREA RADIANS AND SOLENASTRAEA SSP. (CNIDARIA, SCLERACTINIA), FROM THE PLEISTOCENE BERMONT FORMATION, SOUTH FLORIDA, USA

Abstract:  Study of corallum shape in Siderastrea and Solenastraea colonies collected from Pleistocene Bermont strata in western Palm Beach County, Florida, indicates that the corals are rotatory, formed by rolling during growth on the Pleistocene sea floor. Growth of a radial and centrifugal nature away from the corallum centre suggests that rolling was sufficiently frequent and energetic to maintain the health of individual polyps along the skeleton's entire spherical surface with no evidence of growth stoppage. Post-mortem sponge boring accompanied by that of sipunculid worms and boring by the bivalves Gastrochaena and Lithophaga during coral colony life is common. Colonization by cirripeds (barnacles) on some live colonies also occurred, but these are most commonly overgrown. Boring of rotatory coralla decreased the mass of the skeleton and probably increased the ease and frequency of rolling. Comparison with modern rotatory specimens of S. radians from Rodriguez Bank indicates that the Pleistocene corals were not greatly modified during diagenesis, given their comparable densities. Diameters of both groups of corals are utilised to calculate levels of shear velocities necessary to move them, based on hydrodynamics of rounded sediment of comparable size. The presence of these rotatory coralla, by analogy, strongly suggest that Bermont sediments in the study area accumulated on shallow shelf areas populated by numerous other free-living corals along with fewer fixed corals, accompanying a diverse molluscan assemblage, all indicative of a Thalassia (turtle-grass) community. Nearshore, wave data recorded along Florida's present-day east coast, in contrast to conditions along the west coast, indicate that sufficient wave-generated velocities are present to cause regular rotation of Siderastrea and Solenastraea , and would likely have done so during the Pleistocene.     

Restoring lakes by using artificial plant beds: habitat selection of zooplankton in a clear and a turbid shallow lake

1. Return of large‐bodied zooplankton populations is of key importance for creating a shift from a turbid to a clear‐water state in shallow lakes after a nutrient loading reduction. In temperate lakes, recovery is promoted by submerged macrophytes which function as a daytime refuge for large zooplankton. However, recovery of macrophytes is often delayed and use of artificial plant beds (APB) has been suggested as a tool to enhance zooplankton refuges, thereby reinforcing the shift to a clear‐water state and, eventually, colonisation of natural plants. 2. To further evaluate the potential of APB in lake restoration, we followed the day–night habitat choices of zooplankton throughout summer in a clear and a turbid lake. Observations were made in the pelagic and littoral zones and in APB in the littoral representing three different plant densities (coverage 0%, 40% and 80%). 3. In the clear lake, the zooplankton (primarily Daphnia) were mainly found in the pelagic area in spring, but from mid‐May they were particularly abundant in the APB and almost exclusively so in mid‐June and July, where they appeared in extremely high densities during day (up to 2600 ind. L⁻¹). During night Daphnia densities were overall more equally distributed between the five habitats. Ceriodaphnia was proportionally more abundant in the APB during most of the season. Cyclopoids were more abundant in the high APB during day but were equally distributed between the five habitats during night. 4. In the turbid lake, however, no clear aggregation was observed in the APB for either of the pelagic genera (Daphnia and Bosmina). This may reflect a higher refuge effect in the open water due to the higher turbidity, reduced ability to orient to plant beds and a significantly higher fish density (mainly of roach, Rutilus rutilus, and perch, Perca fluviatilis) in the plant beds than in the clear lake. Chydorus was found in much higher proportions among the plants, while cyclopoids, particularly the pelagic Cyclops vicinus, dominated in the pelagic during day and in the pelagic and high density plants during night. 5. Our results suggest that water clarity is decisive for the habitat choice of large‐bodied zooplankton and that introduction of APB as a restoration measure to enhance zooplankton survival is only a useful tool when water clarity increases following loading reduction. Our results indicate that dense APB will be the most efficient.     

Unravelling complexities in benthic food webs using a dual stable isotope (hydrogen and carbon) approach

1. Stable carbon isotope studies have been an essential component of research regarding the contribution of methane (CH₄)-derived carbon to freshwater food webs and results have suggested that benthic macroinvertebrates in billabongs, streams and lakes may be partially, and in some instances, significantly 'fuelled' by methanotrophic biomass. However, the singular use of carbon isotopes can lead to ambiguous interpretations concerning the origin of carbon, especially in systems where phototrophs are likely to be using carbon respired sources and hence show more ¹³C-depleted values.
2. These uncertainties can be further resolved by the inclusion of additional isotopic data. Stable hydrogen isotopes are being increasingly used in food web studies with a marked advantage that sources may be isotopically distinct by one or two orders of magnitude greater than stable carbon or nitrogen, the isotopes most commonly used to delineate trophic interactions. By using hydrogen as a second biogeochemical tracer we provide further supportive evidence for the assimilation of methanotrophic microbial biomass by chironomid larvae.
3. Moreover, the hydrogen and carbon isotope values we found in chironomid tissues appear to reflect the original substrate used during methanogenesis; either acetate fermentation or carbonate reduction. Use of the former tends to result in relatively heavy carbon and light hydrogen isotope values due to kinetic isotope effects, whereas use of the latter results in relatively lighter carbon and heavier hydrogen isotope values.
4. We provide preliminary evidence to suggest that hydrogen and carbon isotope values in macroinvertebrates may be used to distinguish between CH₄ formation pathways and help to explain inter-depth and inter-specific differences between co-existing chironomid species found in the same lake.