Direct Environmental Control Research Articles

Improved process representation of leaf phenology significantly shifts climate sensitivity of ecosystem carbon balance

Abstract. Terrestrial carbon cycle models are routinely used to determine the response of the land carbon sink under expected future climate change, yet these predictions remain highly uncertain. Increasing the realism of processes in these models may help with predictive skill, but any such addition should be confronted with observations and evaluated in the context of the aggregate behavior of the carbon cycle. Here, two formulations for leaf area index (LAI) phenology are coupled to the same terrestrial biosphere model: one is climate agnostic, and the other incorporates direct environmental controls on both timing and growth. Each model is calibrated simultaneously to observations of LAI, net ecosystem exchange (NEE), and biomass using the CARbon DAta-MOdel fraMework (CARDAMOM) and validated against withheld data, including eddy covariance estimates of gross primary productivity (GPP) and ecosystem respiration (Re) across six ecosystems from the tropics to high latitudes. Both model formulations show similar predictive skill for LAI and NEE. However, with the addition of direct environmental controls on LAI, the integrated model explains 22 % more variability in GPP and Re and reduces biases in these fluxes by 58 % and 77 %, respectively, while also predicting more realistic annual litterfall rates due to changes in carbon allocation and turnover. We extend this analysis to evaluate the inferred climate sensitivity of LAI and NEE with the new model and show that the added complexity shifts the sign, magnitude, and seasonality of NEE sensitivity to precipitation and temperature. This highlights the benefit of process complexity when inferring underlying processes from Earth observations and representing the climate response of the terrestrial carbon cycle.

Fungal community composition and genetic potential regulate fine root decay in northern temperate forests.

Understanding how genetic differences among soil microorganisms regulate spatial patterns in litter decay remains a persistent challenge in ecology. Despite fine root litter accounting for ~50% of total litter production in forest ecosystems, far less is known about the microbial decay of fine roots relative to aboveground litter. Here, we evaluated whether fine root decay occurred more rapidly where fungal communities have a greater genetic potential for litter decay. Additionally, we tested if linkages between decay and fungal genes can be adequately captured by delineating saprotrophic and ectomycorrhizal fungal functional groups based on whether they have genes encoding certain ligninolytic class II peroxidase enzymes, which oxidize lignin and polyphenolic compounds. To address these ideas, we used a litterbag study paired with fungal DNA barcoding to characterize fine root decay rates and fungal community composition at the landscape scale in northern temperate forests, and we estimated the genetic potential of fungal communities for litter decay using publicly available genomes. Fine root decay occurred more rapidly where fungal communities had a greater genetic potential for decay, especially of cellulose and hemicellulose. Fine root decay was positively correlated with ligninolytic saprotrophic fungi and negatively correlated with ECM fungi with ligninolytic peroxidases, likely because these saprotrophic and ectomycorrhizal functional groups had the highest and lowest genetic potentials for plant cell wall degradation, respectively. These fungal variables overwhelmed direct environmental controls, suggesting fungal community composition and genetic variation are primary controls over fine root decay in temperate forests at regional scales.

Resolving the intricate role of climate in litter decomposition.

With approximately 60 Pg of carbon (C) released as CO2 annually, the decomposition of dead organic matter feeds the major terrestrial global CO2 flux to the atmosphere. Macroclimate control over this critical C flux facilitates the parametrization of the C cycle in Earth system models and the understanding of climate change effects on the global C balance. Yet, the long-standing paradigm of climate control was recently challenged by the so far underestimated environmental heterogeneity at local scales, questioning the conceptual framework of thousands of decomposition studies and accuracy of current predictive models. Using three complementary decomposition experiments at a European scale, we showed that macroclimate and litter characteristics largely control plant litter decomposition, reaffirming the role of macroclimate as an integrative decomposition driver through direct environmental control and by influencing co-evolving local plant and decomposer communities. Neglecting this latter indirect effect, commonly used standard litter types overrated micro-environmental control and failed to predict local decomposition of plot-specific litter. Our data help clarify a key question on the regulation of the global C cycle by identifying the relative role of control factors over decomposition and the scales at which they matter and by highlighting sources of confusion in the literature.

Environmental control of carbon allocation matters for modelling forest growth.

We aimed to evaluate the importance of modulations of within-tree carbon (C) allocation by water and low-temperature stress for the prediction of annual forest growth with a process-based model. A new C allocation scheme was implemented in the CASTANEA model that accounts for lagged and direct environmental controls of C allocation. Different approaches (static vs dynamic) to modelling C allocation were then compared in a model-data fusion procedure, using satellite-derived leaf production estimates and biometric measurements at c. 104 sites. The modelling of the environmental control of C allocation significantly improved the ability of CASTANEA to predict the spatial and year-to-year variability of aboveground forest growth along regional gradients. A significant effect of the previous year's water stress on the C allocation to leaves and wood was reported. Our results also are consistent with a prominent role of the environmental modulation of sink demand in the wood growth of the studied species. Data available at large scales can inform forest models about the processes driving annual and seasonal C allocation. Our results call for a greater consideration of C allocation drivers, especially sink-demand fluctuations, for the simulations of current and future forest productivity with process-based models.

The dynamic of the annual carbon allocation to wood in European tree species is consistent with a combined source–sink limitation of growth: implications for modelling

Abstract. The extent to which wood growth is limited by carbon (C) supply (i.e. source control) or by cambial activity (i.e. sink control) will strongly determine the responses of trees to global changes. Nevertheless, the physiological processes that are responsible for limiting forest growth are still a matter of debate. The aim of this study was to evaluate the key determinants of the annual C allocation to wood along large soil and climate regional gradients over France. The study was conducted for five tree species representative of the main European forest biomes (Fagus sylvatica, Quercus petraea, Quercus ilex, Quercus robur and Picea abies). The drivers of stand biomass growth were assessed on both inter-site and inter-annual scales. Our data set comprised field measurements performed at 49 sites (931 site-years) that included biometric measurements and a variety of stand characteristics (e.g. soil water holding capacity, leaf area index). It was complemented with process-based simulations when possible explanatory variables could not be directly measured (e.g. annual and seasonal tree C balance, bioclimatic water stress indices). Specifically, the relative influences of tree C balance (source control), direct environmental control (water and temperature controls of sink activity) and allocation adjustments related to age, past climate conditions, competition intensity and soil nutrient availability on growth were quantified. The inter-site variability in the stand C allocation to wood was predominantly driven by age-related decline. The direct effects of temperature and water stress on sink activity (i.e. effects independent from their effects on the C supply) exerted a strong influence on the annual stand wood growth in all of the species considered, including deciduous temperate species. The lagged effect of the past environmental conditions (e.g. the previous year's water stress and low C uptake) significantly affected the annual C allocation to wood. The C supply appeared to strongly limit growth only in temperate deciduous species. We provide an evaluation of the spatio-temporal dynamics of the annual C allocation to wood in French forests. Our study supports the premise that the growth of European tree species is subject to complex control processes that include both source and sink limitations. The relative influences of the growth drivers strongly vary with time and across spatial ecological gradients. We suggest a straightforward modelling framework with which to implement these combined forest growth limitations into terrestrial biosphere models.

Topographic separation of two sympatric palms in the central Amazon – does dispersal play a role?

Despite broadly overlapping geographic distributions in the central Amazon basin, two congeneric palm species (Attalea attaleoides and Attalea microcarpa) have topographically separated distributions on a local scale in Reserva Ducke near Manaus. Our aim here was to determine if this local scale separation can be linked to (1) seedling stage specialization to different habitat conditions of the two species, and/or (2) environmentally-controlled seed dispersal. We assessed the role of these potential drivers by mapping the local distribution of the two species over a 25-km2 grid and testing for correlation to seed removal and seed germination patterns using seed sowing experiments. 360 seeds of each species were sown in 30 uniformly distributed plots (12 seeds of each species in each plot), and seed removal and germination were subsequently monitored. Adult populations of the two species showed opposite distribution patterns linked to topography. However, there was little evidence for specialization to different habitat conditions at the seedling stage: after 11 months, 26.1% of seeds of A. microcarpa had germinated along the entire topographic gradient, albeit with a tendency toward higher germination in more inclined areas. For A. attaleoides, only 2.2% seeds had germinated, and again along the entire topographic gradient. In contrast, there was evidence for environmentally-controlled seed dispersal: for both species, seed removal was higher in flat areas. Presence of adults did not affect germination or seed removal. Our results suggest that topographically differentiated distributions of A. attaleoides and A. microcarpa may be reinforced by steep slope avoidance by their seed dispersers. A direct environmental control mechanism remains to be identified to explain the consistent topographic associations, but our results show that this mechanism does not work at the seed germination stage.

Advances in Spring but Variable Autumnal Trends in Timing of Inland Wader Migration

Advancement of spring migration in response to recent global climate change is well documented for a variety of bird species, but the pattern for autumn migration is rather equivocal. During a 42-year period (1964–2005) the changes in timing of spring and autumn migration of eight wader species were studied at multiple inland sites in Central Europe (Czech Republic and Slovakia) using ringing data. While a clear pattern was found for the advancement of the spring passage, there were variable trends in the timing of the autumn passage. Three species significantly advanced (Wood Sandpiper, Common Sandpiper and Dunlin), three species delayed (Ruff, Snipe and Little Ringed Plover), and two species did not change the timing of the autumn passage (Little Stint and Green Sandpiper). Earlier studies had predicted that long-distance migrants wintering south of the Sahara would advance the timing of autumn migration, while short-distance migrants would postpone it. However, our findings do not fully conform to these predictions. Across species, the timing of both the spring and autumn passages was negatively associated with the winter North Atlantic Oscillation (NAO) index, suggesting that even in long-distance migrants the timing of migration might be under direct environmental control. In conclusion, phenological responses of birds to recent changes in climate are quite coherent for the early phenological phases; however, the responses to later phases are not so straightforward, and the present study contributes to this diverse pattern.

Destructive interjurisdictional competition: Firm, capital and labor mobility in a model of direct emission control

A theoretical exception to a regional race to the bottom contends that, if decentralized environmental policy is comprised of direct controls on each firm—emissions standards are set too high relative to a centralized optimum, provided populations are immobile. Herein, we relax population immobility within a ‘purely competitive’ interjurisdictional model of direct environmental controls. By generalizing previous models, we show that the race is likely to be on when local land incomes are important and firms respond grudgingly to changes in direct emission controls.

Static mental representations in recurrent neural networks for the control of dynamic behavioural sequences

What enables an organism to perform behaviour we would call cognitive and adaptive, like language? Here, it is argued that an essential prerequisite is the ability to build up mental representations of external situations to uncouple the behaviour from direct environmental control. Such representations can be realized by building up cell assemblies. The recurrent neural network presented to cope with this task has been used for generation of action but can also be utilized as a basis for mental representations due to its attractor characteristics. In this context, a new learning algorithm (Dynamic Delta Rule) is proposed, which leads to a self-organized weight distribution yielding stable states on the one hand and which, on the other hand, only activates subpopulations of larger networks that code for the respective situation. In a second step, ways are shown of how the static information of these internal models can be transformed into time-dependent behavioural sequences.

δ 13C variation in scallop shells: Increasing metabolic carbon contribution with body size?

We examined δ 13C values of shallow and deep-water scallop shells as well as δ 13C of dissolved inorganic carbon (DIC) from the Bay of Brest in western Brittany. Time series of shell calcite δ 13C do not reflect seasonal variation in seawater δ 13C, but rather show a consistent pattern of decreasing δ 13C with age, suggesting a metabolic effect rather than direct environmental control. This δ 13C trend reflects an increasing contribution of metabolic CO 2 to skeletal carbonate throughout ontogeny, although this respired CO 2 does not seem to be the major source of skeletal carbon (contribution of only 10% over the first year of life). We propose a model of this effect that depends on the availability of metabolic carbon relative to the carbon requirements for calcification. A ratio of “respired to precipitated carbon” is calculated, and represents the amount of metabolic carbon available for calcification. Interestingly, this ratio increases throughout ontogeny suggesting a real increase of metabolic carbon utilization into the skeleton relative to carbon from seawater DIC. This ratio allows us to separate two different populations of Pecten maximus of different water depth. It is therefore suggested that shell δ 13C might be used to track differences in the metabolic activity of scallops from different populations.

On Environmental Federalism and Direct Emission Control

A theoretical exception to the race to the bottom contends that if decentralized environmental policy is comprised of direct controls on each firm, emissions standards are set too high when compared to a centralized optimum. Herein we examine potential distortions in decentralized decision-making by reconciling two recent views of direct environmental controls. We show that differences in direct control policy can arise from differences in the number of symmetric jurisdictions in an economy. Our results suggest the race is on once the number of jurisdictions competing for a fixed number of firms increase; we see the race is off when few jurisdictions can exploit their form of environmental market power.

CONTROL OF GERMINATION OF ALEXANDRIUM TAMARENSE (DINOPHYCEAE) CYSTS FROM THE LOWER ST. LAWRENCE ESTUARY (CANADA)

Cysts of the toxic dinoflagellate Alexandrium tamarense (Lebour) Balech 1992 from the lower St. Lawrence estuary were used in a test of the following hypotheses: (1) cyst germination is triggered by a change in temperature, and (2) germination rate varies throughout the year and is controlled by a circannual internal biological clock. Results show that cyst germination was not affected significantly by temperature of incubation over the range 1°–16° C, and light showed no significant stimulation of germination. This is supported by the lack of effect of cyst incubation conditions during evaluation of the seasonal changes in germination rate (two temperatures: 4° and 15° C, and two light conditions: darkness and 150 μmol photons·m−2·s−1). Thus, direct environmental control through short-term increases in temperature and exposure to light has no effect on the germination of the cysts tested. The rate of germination, observed monthly over a 16-month period, showed low germination (<20%) over most of the period tested, except for a maximum reaching more than 50% germination in August to October of the second year of the experiment. This pattern was observed for cysts both from monthly field collections and from laboratory-stored cysts kept under constant environmental conditions (4° C, in the dark). The peak in germination observed under constant environmental conditions (in the laboratory), the almost coincidental increase in cyst germination observed for the field-collected cysts, and the absence of effects of temperature and light during incubation could be explained either by a temperature-controlled cyst maturation period (the time-temperature hypothesis of Huber and Nipkow 1923) or by the presence of an internal biological clock. However, the large decline in the rate of germination 2 months after the maximum provides strong support for the biological clock hypothesis. The ca. 12-month maturation (dormancy) period observed for the laboratory-stored cysts is the longest reported for this species to our knowledge; this might be related to the low storage temperature (4° C), which is close to bottom temperatures generally encountered in this environment (0° to 6° C). Similar field and laboratory storage temperatures could explain the coincidental increase in germination rate in the fall of the second year if cyst maturation is controlled by temperature. A fraction of the laboratory-stored cysts did not follow a rhythmic pattern: A rather constant germination rate of about 20% was observed throughout the year. This continuous germination of likely mature cysts may supplement the local blooms of this toxic dinoflagellate, as these often occur earlier than peak germination observed in late summer. It seems that two cyst germination strategies are present in the St. Lawrence: continuous germination after cyst maturation, with temperature controlling the length of the maturation period, and germination controlled by a circannual internal rhythm.

HUMAN AND ENVIRONMENTAL INFLUENCES ON FOREST COMPOSITION OF A TENNESSEE LOESS BLUFF

Prior investigations of forests on Mississippi River loess bluffs suggest that their composition is regionally distinct, attributing mesophytic species abundance to atypical physical conditions or Pleistocene history. Owing to the widespread anthropogenic impacts on this landscape, this study examines the relative importance of human and natural factors influencing bluff forest composition. Within the mosaic of former agricultural fields and uncleared areas on the Third Chickasaw Bluff of southwestern Tennessee, 10 transects were placed along the gradient from bottomlands to ridgetops, stratified by former land use. Ordination indicates that the greatest compositional distinction exists between bottomlands and upland positions. Treated separately, the uplands are organized along two primary dimensions: the first distinguishes formerly cleared ridgetops from all other habitats, the second represents a moisture gradient. Three species groups respond differently to these upland conditions: (1) recently disturbed sites favor sweetgum/tulip poplar; (2) sites likely to have been disturbed in the more distant past are oak dominated; (3) mesophytic species prefer undisturbed habitats. The disturbance-related characteristics of each habitat, rather than their direct environmental controls, are a major determinant of bluff composition. The ubiquity of anthropogenic disturbance throughout the region gives rise to the seeming uniqueness of the atypical bluff sites that escaped disturbance. [Key words: human impacts, ordination, vegetation-environment relationships, forest ecology, Tennessee.]

Modeling methane emissions from rice paddies

The quantification of methane (CH4) emissions from global rice paddies is still highly uncertain. The extrapolation of CH4 release rates from point measurements to regional level or empirically correlating methane emission rates with a few factors (e.g., temperature and rice primary production) is unlikely to yield reliable results. Reducing the uncertainties in estimates of current CH4 emission and predicting its future change require a process model to simulate CH4 emissions from various paddyland environments. CH4 emission is an ecosystem process closely coupled to plant growth and soil organic matter decomposition. In this study a methane emission model was developed based on supplies of carbon substrate for methanogens by rice primary production and soil organic matter degradation, direct environmental controls on methanogenesis, and the balance between CH4 production and consumption by methanotrophic oxidation. A validation of the model indicated its reasonable ability to calculate CH4 emission rates and their seasonal variations. The model, when coupled with supporting data sets, would complement spatial and dynamic analysis of CH4 emissions from rice paddies in the framework of climate‐plant‐soil interactions.

Environmental Control Costs and U.S. Effective Rates of Protection

This study investigates the impact of U.S. environmental control costs on the Abstract effective rates of protection given to U.S. industrial sectors in 1977. The effective rate of protection equation is modified in order to quantify the loss of protection due to environmental control costs and compare it to the protection afforded by the tariff structure. Results are presented for the following two cases: (1) only direct environmental control costs influence the net level of protection, and (2) direct environmental control costs and environmental control costs borne by inputs influence the net level of protection. For the case with direct environmental control costs and environmental control costs borne by inputs, the loss ofprotection due to environmental control costs is 19.67% of the protection afforded by the U.S. tariff structure.

PETROLEUM AND THE ENVIRONMENT

Energy is the base for industrialization. Petroleum is not only the major source of energy but also has the greatest growth rate amongst the more important energy sources.With industrialization has come urbanization, and with urbanization has come a recognition of conservation. The Torrey Canyon and the Santa Barbara incidents have focussed this public recognition on the oil industry.When we speak of environment, we must include such things as the automobiles we drive and the plastics we use. We must consider our total environment and control its development for the good of all mankind - that is what conservation is about.Conservation is the watchword of most of the Petroleum Industry. Esso spends in excess of five million dollars per year on direct environmental control research. The American Petroleum Institute spent three million dollars on Air and Water Conservation research in 1969, and 1970 will see an expanded budget.At present 13 per cent of U.S.A.'s production of oil and gas comes from the seabed of the Gulf and Californian coasts where some 13 thousand million dollars have been invested. Of the 8,000 wells that have been drilled in Federal waters, only 16 have blown out — 12 gas and 4 oil — and only one of the latter has resulted in significant pollution — Santa Barbara. Contrary to emotional statements, informed sources have so far concluded that little detrimental effect has been sustained on marine life, whales, seals and commercial fish. Long-term effects are now being studied.Australia this year should see the first substantial reduction in oil imports due in the main to oil from offshore sources — what effect will this have on our environment?Techniques used in oil exploration today from seismic surveys to the drilling and production phases of the industry are preplanned, using all the data that can be gathered. Safety factors are built in to every phase of the plan including casing programmes, mud systems, and blow-out preventors and crude oil loading equipment. As an additional conservation measure, procedures for handling emergencies are also planned.It is evident that the Oil Industry stands ready to do its share: are we as individuals doing ours?