ECOSYSTEM MODELING OF A FORESTED RIVER BASIN1

ABSTRACT: A present concern in decision making processes for forest land use is the environmental effects of land use activities on water, air, and the land itself. Criteria for evaluating the magnitude and detriment of environmental impacts are not definite since it is often difficult to isolate a particular activity as the cause of a particular impact. Instead, interactions between various forest practices must be considered along with their integrated impacts. In order to provide an effective decision tool, the College of Forest Resources, University of Washington, is modeling the forest ecosystem of the Snohomish River Basin located in the Cascade Mountains of western Washington. The project consists of a general system model comprised of subsystem models dealing with product conversion processes, forest production processes, recreation supply processes, wildlife and fisheries supply processes, and the interactions of these processes with water and the atmosphere. The system model is interfaced with a computerized multiple player management game which enables land managers, manufacturing managers, and regulation agency personnel to make management decisions and respond to indications of lack of environmental control. Responses of the hydrologic system to various management decisions are simulated by the water subsystem model. The responses being considered include surface flow quantity and water quality. The model emphasizes the monitoring of non-point as well as point source impacts rather than predicting short-term hydrographs. The significance of impacts vary with land use patterns and the goals of the game player. Therefore, the model has flexible resolution and is able to predict hydrologic conditions for both large and small scale. The water subsystem model responds to management decisions by interpreting the effects of management options selected by game players for 40-acre cells within the Basin. The model then determines which streams are immediately affected, defines the watersheds contributing to these streams, and extracts from a resource data bank the information needed to define model parameters. Using these parameters and precipitation inputs, mean flow discharge on a montly and annual basis is calculated for the impactcd sub watersheds as well as 21 major watersheds of the Basin. Water quality responses predicted for these watersheds include suspended sediment concentration, temperature increases due to stream exposure, dissolved oxygen concentrations, the effects of fertilization on nitrogen content, biocide and herbicide effects, and residues from product conversion processes.     

A Review of Contributions to Disasters: 1977—1996

Since the first issue in 1977, Disasters has been one of the pre-eminent refereed journals on the study and reporting of disasters. This article reviews 703 articles and reports in the journal through 1996 to provide a snapshot of the nature of the journal throughout 20 years of publication. The results indicate the most common contributions: first, were research articles by authors from the North Atlantic; second, most often dealt with natural disaster relief or impact; and third, most frequently focused on Africa. These generalisations, however, do not reflect attention paid to food-related and political disasters and greatly understate the broad diversity of material presented in the journal. To improve the topical and geographic coverage of Disasters probably requires a proactive effort to close gaps in the journal's coverage of disasters.     

Pastoralists' responses to variation of rangeland resources in time and space.

We explore the response of pastoralists to rangeland resource variation in time and space, focusing on regions where high variation makes it unlikely that an economically viable herd can be maintained on a single management unit. In such regions, the need to move stock to find forage in at least some years has led to the evolution of nomadism and transhumance, and reciprocal grazing agreements among the holders of common-property rangeland. The role of such informal institutions in buffering resource variation is well documented in some Asian and African rangelands, but in societies with formally established private-property regimes, where we focus, such institutions have received little attention. We examine agistment networks, which play an important role in buffering resource variation in modern-day Australia. Agistment is a commercial arrangement between pastoralists who have less forage than they believe they require and pastoralists who believe they have more. Agistment facilitates the movement of livestock via a network based largely on trust. We are concerned exclusively with the link between the characteristics of biophysical variation and human aspects of agistment networks, and we developed a model to test the hypothesis that such a link could exist. Our model builds on game theory literature, which explains cooperation between strangers based on the ability of players to learn whom they can trust. Our game is played on a highly stylized landscape that allows us to control and isolate the degree of spatial variation and spatial covariation. We found that agistment networks are more effective where spatial variation in resource availability is high, and generally more effective when spatial covariation is low. Policy design that seeks to work with existing social networks in rangelands has potential, but this potential varies depending on localized characteristics of the biophysical variability.     

Assessing the carbon balance of circumpolar Arctic tundra using remote sensing and process modeling.

This paper reviews the current status of using remote sensing and process-based modeling approaches to assess the contemporary and future circumpolar carbon balance of Arctic tundra, including the exchange of both carbon dioxide and methane with the atmosphere. Analyses based on remote sensing approaches that use a 20-year data record of satellite data indicate that tundra is greening in the Arctic, suggesting an increase in photosynthetic activity and net primary production. Modeling studies generally simulate a small net carbon sink for the distribution of Arctic tundra, a result that is within the uncertainty range of field-based estimates of net carbon exchange. Applications of process-based approaches for scenarios of future climate change generally indicate net carbon sequestration in Arctic tundra as enhanced vegetation production exceeds simulated increases in decomposition. However, methane emissions are likely to increase dramatically, in response to rising soil temperatures, over the next century. Key uncertainties in the response of Arctic ecosystems to climate change include uncertainties in future fire regimes and uncertainties relating to changes in the soil environment. These include the response of soil decomposition and respiration to warming and deepening of the soil active layer, uncertainties in precipitation and potential soil drying, and distribution of wetlands. While there are numerous uncertainties in the projections of process-based models, they generally indicate that Arctic tundra will be a small sink for carbon over the next century and that methane emissions will increase considerably, which implies that exchange of greenhouse gases between the atmosphere and Arctic tundra ecosystems is likely to contribute to climate warming.     

“Alternative” mating behavior in the swordtails Xiphophorus nigrensis and Xiphophorus pygmaeus (Pisces: Poeciliidae)

Summary The swordtail Xiphophorus nigrensis exhibits three relatively discrete male body-size classes that derive from allelic variation at the Y-linked pituitary (P) locus. Previous studies have shown that larger males have greater relative reproductive success, and that females prefer large males. We describe the mating behavior utilized by males of each size class during individual encounters with females. Small males rely on chase behavior, similar to the alternative mating behavior classified as sneaker in small males of other species. Large males court and intermediate-sized males court or chase, depending on their body size. There is a strong correlation between P alleles for small size (s) and large size (L) with chasing and courting, respectively. The relationship between mating behavior of males of the genotype I is ambiguous. In the closely related species X. pygmaeus, males are of size similar to smaller X. nigrensis males. Paradoxically, these males do not show the courtship display that typifies larger male X. nigrensis and many other species of swordtails, but instead often employ chase behavior identical to the alternative mating behavior in small male X. nigrensis. We suggest that historical and genetic constraints, in addition to current selection forces, might be important factors in explaining the existence of alternative mating behavior in X. pygmaeus.     

Effect of the hard clam Mercenaria mercenaria on benthic fluxes of inorganic nutrients and gases

The effect of the hard clam Mercenaria mercenaria (L.) on the exchange of dissolved nutrients (silicate, phosphate, ammonium, nitrate+nitrite) and gases (oxygen, carbon dioxide) across the sediment-water interface was examined in 1983 and 1984 using experimental mesocosms (13 m³), designed to simulate a shallow coastal ecosystem, that allow for reciprocal biogeochemical interactions between water column (5 m) and bottom sediments (30 cm deep). Benthic, fluxes, measured during a spring-summer warming period, were compared for mesocosms maintained either with added M. mercenaria (16 per m², treatment) or without M. mercenaria (control) as a component of the benthic community. Fluxes were within the range observed for the (control) community in situ in mid-Narragansett Bay and exhibited the pattern of increasing flux with increasing temperature observed in nature. For dissolved inorganic (DIN=ammonia+nitrate+nitrite), analytical problems allowed comparison of fluxes only at the higher temperatures (17° to 22°C); average DIN fluxes were 57% higher in mesocosms with clams. Fluxes of other nutrients and gases were modelled as exponential functions of temperature (9° to 22°C) using a linear regression of the natural logarithm of flux upon temperature in both treatment and control situations. Differences between regression slopes and intercepts for conditions with and without clams were assessed by analysis of covariance. Slopes of the linearized temperature-flux relationships were not significantly different between treatments for any flux measured, suggesting that presence of the clams did not alter the basic relationship of flux and temperature normally observed with this community. For oxygen consumption and silicate production, the regression intercepts were significantly higher in the clam treatment, suggesting that the level of flux was generally elevated in the presence of M. mercenaria by about 20% (oxygen) and 86% (silicate) at any given temperature. Data for carbon dioxide and phosphate showed similar trends to oxygen and silicate, but the variance in fluxes was larger and regression intercepts for the two treatments were not significantly different.     

Transport of cadmium and other metals in the blood of the bivalve mollusc Mercenaria mercenaria

The distribution of metals (Ba, Cr, Cu, Fe, Mn, Ni and Zn) in the blood plasma and the circulating hemocytes was determined for a eulamellibranch bivalve, the quahog Mercenaria mercenaria (L.), collected from a relatively clean site at Falmouth, Massachusetts, USA. Whole blood volume was an exponential function of quahog length (Y=5.71×10^-5 X^3.0678; Y=ml of whole blood; X=mm length). Of this volume, 1.2±0.3% ( ) was attributable to blood cells. Total metal content (g metal, or g metal normalized per g of whole blood) was much higher in blood plasma than in hemocytes. In quahogs exposed in the laboratory to 100 ppb ¹⁰⁹Cd, 93.0% of the total accumulated blood Cd was in the plasma rather than in the circulating hemocytes (7.0%), irrespective of the length of exposure (1 h to 31 d). Less than 5% of the plasma Cd was either Cd²⁺, small inorganic Cd complexes or bound to organic molecules with a molecular weight smaller than 1 000. Cadmium was primarily bound to high molecular weight protein(s) (>60 000 daltons) within the plasma. This plasma protein-Cd complex has a low affinity constant (approximately 10⁴ M ^-1), indicating non-specific Cd binding, although the capacity for Cd-binding in the plasma is great (as high as 200 g Cd per ml of plasma). Blood plasma may be far more important in metal transport than has previously been realized.     

An Age-Structured Demographic Model for the Endangered Stephens' Kangaroo Rat

Effective conservation of endangered species often is hampered by inadequate knowledge of demography. We extracted information on survival and fecundity from an 18-month, live-trapping study of Dipodomys stephensi , and from this we developed an age-structured demographic model to assess population viability. Adult Stephens' kangaroo rats persisted longer than juveniles, and adult females persisted longer than adult males. Disappearance rates were high in the first months after initial capture. Thereafter, the fraction of animals persisting decreased slowly and in an approximately linear fashion on a semilogarithmic scale, suggesting age-independent mortality factors such as predation. Juvenile persistence did not differ substantially between two years of strikingly different rainfall. Onset of breeding followed the start of winter rains. Length of the breeding season, average number of litters per female, and the fraction of first-year females breeding were much greater in the year of higher rainfall. We propose a birth-pulse demographic model for D. stephensi that distinguishes juvenile and adult age classes. Temporal environmental variation can be modeled adequately with a constant survivorship schedule and variable fecundity determined by yearly precipitation. Several issues should be resolved, however, before conservation decisions are based on the model. Better estimates of juvenile survivorship are critical, the quantitative relationship between precipitation and fecundity must be determined, and the potential for density dependence and source-sink population dynamics must be evaluated.