Estimating woody and herbaceous vegetation cover from time series satellite observations

In this paper we test a method to estimate the tree and grass vegetation cover over Australia from satellite-derived normalized difference vegetation index (NDVI) time series (monthly 1981–91, ≈5 km pixels) observations. The evergreen cover is assumed to track along the base of the NDVI time series, which is assumed to be equivalent to the woody vegetation cover. The base of the NDVI time series is estimated using modifications to a classical econometric model (i.e. time series is the sum of trend, seasonal and random components). Estimates of the average evergreen component during 1982–85 and 1986–89 were generally consistent with known vegetation distributions. Changes in evergreen cover were largely restricted to the south-west and south-east of Australia. Those changes were largely the result of differences in rainfall between the two periods. The proposed method for estimating woody vegetation cover is found to be generally robust. However, there are some regions where the grass (or pasture) is mostly evergreen. Some possible refinements are proposed to handle such cases.     

Hydro-sedimentology of the Johnstone River estuary

This paper examines the physical consequences of increased catchment sediment yields on the sediment budget and the hydrodynamic setting of the South Johnstone River estuary in North Queensland. A combined study involving hydrological monitoring, assessment of sediment sources, estimation of riverine sediment budget and hydro-sedimentological numerical modelling for estuarine sediment transport is currently underway. Initial field and laboratory observations indicate that the sediment delivery from highly erosion-prone sugar cane cultivations in the tropical catchment has increased dramatically during the last 10 years. This has subsequently given rise to elevated flood levels in both the lower and upper catchment areas, as well as significant modifications to the river bed morphology.     

数学模型与自然保护科学

日益加剧的人类干扰和景观破碎化已危及全球的生物多样性。自然保护成为人类所面临的最重要也最富有挑战性的任务。指导这一实践的理论和原则极为需要。本文试图综述与自然保护科学有关的几个学科在理论和实际研究(尤其是模型)方面的近期成果以及发展趋势,从而提出自然保护模型的发展方向。文中涉猎基于不同方法论、不同组织水平的模型,并对数学模型在自然保护科学中的作用和实用性加以讨论。     

缀块性和缀块动态:Ⅱ.描述与分析

在生态学中,“缀块”(patch)的概念早已在植被群落和海洋生态系统中浮游动植物空间分布研究中广泛应用。A.S.Watte早在1947年就强调缀块在植物群落结构分析中的重要性。实际上,缀块存在于地球的任何地方。森林可     

Mathematical modelling of primary production in Green Bay (Lake Michigan,USA), a phosphorus-and light-limited system

Application of mathematical models in the design and evaluation of lake restoration programmes must include due consideration of three basic concepts of model development; 1) that the model framework is appropriately matched to the intended management use, 2) that selection of the proper degree of model complexity is fundamental to the achievement of model credibility and 3) that field and laboratory studies must be designed and interpreted with the aid of the model to insure development of a comprehensive, integrated tool.These concepts are demonstrated for the case of lake restoration efforts in Green Bay (Lake Michigan, USA). Striking gradients in water quality (transparency, algal standing crop, hypolimnetic oxygen depletion) and trophic state occur along the major axis of the bay in response to phosphorus loaded from the Fox River. A simple model for gross primary production is developed to permit calculation of the relative importance of internal carbon production to the total organic carbon budget of the bay. Primary production varies from high rates over a limited photic depth in the turbid, phosphorus-rich waters of the eutrophic portions of the bay to low rates over an extensive photic depth in the transparent, phosphoruspoor reaches of the oligotrophic regions. Internal production accounts for approximately 90% of the total organic carbon loaded to the system over the summer growing season. Water quality management strategies must address the stimulation of primary production by phosphorus loaded from the Fox River in any attempt to lower the standing crop of nuisance algae, improve water clarity, and reduce rates of hypolimnetic oxygen depletion in Green Bay.     

Three-dimensional finite element stress analysis of the dentate human mandible.

The biomechanical events which accompany functional loading of the human mandible are not fully understood. The techniques normally used to record them are highly invasive. Computer modelling offers a promising alternative approach in this regard, with the additional ability to predict regional stresses and strains in inaccessible locations. In this study, we built two three-dimensional finite element (FE) models of a human mandible reconstructed from tomographs of a dry dentate jaw. The first model was used for a complete mechanical characterization of physical events. It also provided comparative data for the second model, which had an increased vertical corpus depth. In both cases, boundary conditions included rigid restraints at the first right molar and endosteal cortical surfaces of the articular eminences of temporal bones. Groups of parallel multiple vectors simulated individual masticatory muscle loads. The models were solved for displacements, stresses, strains, and forces. The simulated muscle loads in the first model deformed the mandible helically upward and toward its right (working) side. The highest principal stresses occurred at the bite point, anterior aspects of the coronoid processes, symphyseal region, and right and left sides of the mandibular corpus. In general, the observed principal stresses and strains were highest on the periosteal cortical surface and alveolar bone. At the symphyseal region, maximum principal stresses and strains were highest on the lower lingual mandibular aspect, whereas minimum principal stresses and strains were highest on its upper labial side. Subcondylar principal strains and condylar forces were higher on the left (balancing or nonbiting) side than on the right mandibular side, with condylar forces more concentrated on the anteromedial aspect of the working-side condyle and on the central and lateral aspects of the left. When compared with in vivo strain data from macaques during comparable biting events, the predictive strain values from the first model were qualitatively similar. In the second model, the reduced tensile stress on the working-side, and decreased shear stress bilaterally, confirmed that lower stresses occurred on the lower mandibular border with increased jaw depth. Our results suggested that although the mandible behaved in a beam-like manner, its corpus acted more like a combination of open and closed cross sections due to the presence of tooth sockets, at least for the task modelled.(ABSTRACT TRUNCATED AT 400 WORDS)     

Numerical modelling of large-scale circulation in Lakes Onega and Ladoga

The results of numerical modelling of large-scale circulation in Lakes Onega and Ladoga are presented, with primary emphasis on the temporal variability of currents with time scales of days. Some typical circulation patterns have been inferred from model calculations. They reflect the existence of different dynamic regimes in the lakes, namely, forced and free circulation regimes. The forced circulation regime is the well-known wind-induced double-gyre circulation accompanied by coastal upwelling and downwelling. A case of double-gyre circulation in Lake Onega was investigated in particular detail. The second dynamic regime is a free response (or a relaxation) of the stratified lake to wind cessation, and is connected closely with the evolution of wind-induced upwelling and thermal front propagation. Diagnostic calculations demonstrate that the regime of relaxation supports the restoration of cyclonic circulation in Lake Onega. Barotropic circulation patterns in Lake Ladoga were calculated with the emphasis on prevailing winds from west to south-east. Our calculations show that the bottom relief of Lake Ladoga causes asymmetry in the double-gyre circulation patterns. In particular, approximately equal cyclonic and anticyclonic circulation cells appearing in the case of southerly wind transform to a single dominant cyclonic cell and several small anticyclonic cells in the case of westerly wind. We also found especially strong sensitivity of the sense of rotation of the largest gyre to the east-west components of the wind vector.     

Mathematical model for the ecosystem response of Lake Ladoga to phosphorus loading

The ecosystem response model described in this paper combines an ecosystem model and a three-dimensional circulation model of Lake Ladoga developed earlier by the authors. The ecosystem model describes the process of Lake Ladoga eutrophication, and its biological submodel describes changes in the phyto- and zooplankton. In the earlier model version, lake circulation was determined using a two-dimensional hydrodynamical model which was not completely adequate. The present model allows calculation of the distributions of phyto- and zooplankton and mineral phosphorus and nitrogen. One of its main advantages is that reliable computations of the ecosystem dynamics over an extended period of time are possible. The response of the ecosystem to different levels of phosphorus pollution loading and to weather conditions is studied.     

Measurement and modelling of photosynthetic response of pearl millet to soil phosphorus addition

There have been no studies of the effects of soil P deficiency on pearl millet (Pennisetum glaucum (L.) R. Br.) photosynthesis, despite the fact that P deficiency is the major constraint to pearl millet production in most regions of West Africa. Because current photosynthesis-based crop simulation models do not explicitly take into account P deficiency effects on leaf photosynthesis, they cannot predict millet growth without extensive calibration. We studied the effects of soil addition on leaf P content, photosynthetic rate (A), and whole-plant dry matter production (DM) of non-water-stressed, 28 d pearl millet plants grown in pots containing 6.00 kg of a P-deficient soil. As soil P addition increased from 0 to 155.2 mg P kg^–1 soil, leaf P content increased from 0.65 to 7.0 g kg^–1. Both A and DM had maximal values near 51.7 mg P kg^–1 soil, which corresponded to a leaf P content of 3.2 g kg^–1. Within this range of soil P addition, the slope of A plotted against stomatal conductance (g_s) tripled, and mean leaf internal CO₂ concentration ([CO₂]_i) decreased from 260 to 92 L L^–1, thus indicating that P deficiency limited A through metabolic dysfunction rather than stomatal regulation. Light response curves of A, which changed markedly with P leaf content, were modelled as a single substrate, Michaelis-Menten reaction, using quantum flux as the substrate for each level of soil P addition. An Eadie-Hofstee plot of light response data revealed that both K_M, which is mathematically equivalent to quantum efficiency, and V_max, which is the light-saturated rate of photosynthesis, increased sharply from leaf P contents of 0.6 to 3 g kg^–1, with peak values between 4 and 5 g P kg^–1. Polynomial equations relating K_M and V_max, to leaf P content offered a simple and attractive way of modelling photosynthetic light response for plants of different P status, but this approach is somewhat complicated by the decrease of leaf P content with ontogeny.