Net Rate Of Change Research Articles

Resilient adaptive event‐triggered synchronization control of piecewise‐homogeneous Markov jump delayed neural networks under aperiodic DoS attacks

SummaryUnder the aperiodic Denial‐of‐service (DoS) attacks, this paper studies the resilient adaptive event‐triggered synchronization control problem for a class of Piecewise‐Homogeneous Uncertain Markov Jump Neural Networks (PHUMJNNs) with time‐varying delays. First of all, a new way of carving DoS attacks is given from the defenders' perspective, that is, aperiodic DoS attacks based on fixed detection periods. Then, under such attacks, a new Resilient Adaptive Event‐triggered Communication (RAETC) is designed between sensor and controller, which has a threshold function based on the net change rate and is real‐time updated depending on the present sampling state. Next, a single functional is used in the construction of the Lyapunov‐Krasovskii functional, while a new looped functional is introduced that makes full use of the state information of the current instant , the trigger instant and the next trigger instant . Based on the constructed single functional, under the framework of the input delay method and the linear matrix inequality technique, the exponential mean square stabilization criterion of the error system is obtained, which makes the master system and the slave system synchronized. In the end, three simulation examples are used to illustrate the validity of the obtained results.

Monitoring forest dynamics in Africa during 2000–2020 using a remotely sensed fractional tree cover dataset

ABSTRACT Africa is covered with extensive woodlands, savannas and rainforests. The tree cover of these biomes has been undergoing substantial changes in recent decades. However, the dynamics of forests in Africa are currently unclear, particularly in the woodlands and savanna areas covered by sparse trees. Here, we assessed the spatio-temporal trend of African forests from 2000 to 2020, using a 250-m resolution fractional tree cover product that can capture the variation of forest density in the widespread mixed vegetation landscapes of the continent. The tree cover trends, interannual change and hotspots of forest gain and loss were evaluated. Results showed that the African forest area increased at a rate of 3.59 million ha/year over the study period, reaching 589 million ha in 2020. Considerable forest gain and loss both occurred in Africa. The net change rate in woodlands’ forest area was the fastest (2.28 million ha/year), followed by rainforests (0.80 million ha/year) and savannas (0.34 million ha/year). Hotspots of forest gain were concentrated in the north belt of woodlands and savannas, while forest loss primarily clustered in East and South Africa. This work would help African countries to monitor forest change and promote forest management to achieve the Sustainable Development Goals.

Extreme Weather Events and Internal Migration: Evidence from Mongolia

This article examines the effects of extreme weather events on internal migration in Mongolia. Our focus is on dzuds, extremely harsh winters characterized by very cold temperature, snowfall anomalies, and/or storms causing very high livestock mortality. We exploit exogenous variation in the intensity of extreme winter events across time and space to identify their causal impacts on permanent domestic migration. Our database is a time series of migration and population data at provincial and district level from official population registries, spanning the 1992-2018 period. Results obtained with a two-way fixed effects panel estimator show that extreme winter events cause significant and sizeable permanent out-migration from affected provinces for up to two years after an event. These effects are confirmed when considering net change rates in the overall population at the district level. The occurrence of extreme winter events is also a strong predictor for declines in the local population of pastoralist households, the socio-economic group most affected by those events. This suggests that the abandonment of pastoralist livelihoods is an important channel through which climate affects within-country migration.

A Pseudo‐Lagrangian Transformation to Study a Chlorophyll‐a Patch in the Ría de Vigo (NW Iberian Peninsula)

AbstractBecause of the difficulties in tracking a water mass over time and conducting synoptic surveys over large spatial scales, measurements of biological variables in the ocean are often restricted to isolated Eulerian observations. Here a proof‐of‐concept of a pseudo‐Lagrangian transformation was applied to a time series of chlorophyll‐a profiles acquired at a single fixed station to diagnose the shape of a phytoplankton patch, and its physical‐biological rates of transformation. During August 2013, a 27‐hr time series of observations of horizontal currents, hydrographic properties, turbulent mixing and chlorophyll‐a was acquired at a central station of the Ría de Vigo (NW Iberian Peninsula). A chlorophyll‐a patch, tilted upward toward the inner part of the Ría, was observed moving back and forth past the sampling station. Its shape and position during the sampling period were modulated by the semi‐diurnal (M2) tidal currents and the vertically sheared upwelling circulation. The pseudo‐Lagrangian transformation allowed estimation of chlorophyll‐a net rates of change. These rates were positive between 12 and 14 m depth, and negative elsewhere, with a mean value of −0.001 ± 0.449 days−1 within the patch maximum. After accounting for the effects of diffusion and sinking, the mean net biological production rate in the upper 15 m (0.53 ± 0.25 days−1) was comparable with in vitro estimates of the balance between phytoplankton growth and mortality obtained from dilution experiments carried out under similar conditions (0.2 ± 0.7 days−1). This pseudo‐Lagrangian transformation is complementary to traditional analyses for the quantification of ecological processes and biogeochemical budgets.

Aspects regarding the trend of the average annual, seasonal and monthly drainage of river water from the Căliman Mountains in the period 1950-2010

The Căliman Mountains are the highest volcanic mountains in Romania, being positioned on the western side of the Eastern Carpathians, between their central strip (north and east), south – the Harghita Mountains, and west – the Transylvanian Depression. This positioning gives special features of the water drainage, with both spatial and temporal differentiations. This paper analyzed the trend of average drainage from rivers in the studied group for the period 1950-2010, both multi-annually and seasonally and in the extreme months; the months taken into account being those with the lowest flows (January), respectively the largest (May). To evaluate the mentioned parameters, we used the help of Excel MAKESENS (Mann-Kendall test for trend and Sen’s slope estimates), which identified the type of drainage trend (positive or negative), and using the Sen nonparametric method to estimate the slope of the trend. Based on the type of trend obtained, 9 trend classes were obtained, and with the help of the slope, the net change rate was obtained.

Performance of a dynamic cobble berm revetment for coastal protection, under increasing water level.

In a changing climate, sea level rise and projected regional–scale changes in storminess may increase the vulnerability of sandy coastlines to coastal erosion and flooding. As a result, there is increased interest in the development of adaptable, sustainable and effective coastal protection measures to protect these highly variable sandy coastlines. One such example is a dynamic cobble berm revetment; a “soft–engineering” solution (i.e., not fixed) consisting of a cobble berm constructed around the high tide wave runup limit, that has the potential to stabilise the upper beach, provide overtopping protection to the hinterland and translate with water level rise. However, there have been limited applications of dynamic cobble berm revetments to date, and there is a lack of understanding about the efficacy of this coastal protection to current and changing waves and water levels. This study details a prototype–scale experiment conducted to test the behaviour and performance of a dynamic cobble berm revetment as a form of coastal protection against erosive waves and water level increase. Results from the experiment showed that the revetment was “dynamically stable” under wave action as a consistent global shape was retained even though individual cobbles were mobilised under every swash event. Although the front slope and the crest responded to the incident wave condition, the net rate of change was always an order of magnitude lower than the gross rate of change. Tracking of individual cobbles using Radio Frequency Identification (RFID) technology showed that stability of the revetment was likely maintained by rollover transport of cobbles onto the crest, as the revetment moved upward and landward under water level rise. The presence of the revetment reduced the vertical and horizontal runup as well as the retreat of the upper beach. The experimental results presented suggest that a dynamic cobble berm revetment could be a cheap, efficient and low environmental impact engineering solution for protecting sandy coastlines in a changing climate. Some preliminary design guidelines for coastal engineers are also drawn from this experiment.

The changing patterns in the distribution of red and grey squirrels in the North of England and Scotland between 1991 and 2010 based on volunteer surveys

In the UK, alien grey squirrels have been replacing the native red squirrel for >100 years and by the turn of the century the distribution of grey squirrels had extended to most of central and southern England and Wales (apart from some islands), and large parts of Scotland and Ireland. To understand how this species replacement may continue into the future, we explore 20 years of squirrel records (1991-2010) collected in an unsystematic way by volunteers in northern England and Scotland. To aid analysis, we standardised the data to one record of squirrel presence per 4 km square per year in each of six geographic regions, two in northern England and four in Scotland. Over the 20 years and across all regions, the number of 4 km squares that returned the presence of squirrels increased from 23% to 80%. The evolving distribution pattern of red and grey squirrels differed among the regions and was complex with occupancy records for many 4 km squares changing from red to grey squirrel from one year to the next, but also some changing from grey to red squirrel. The net rate of change, however, was from red to grey squirrel with the exception of the more recent years, 2007-2010, when this trend became less distinct. Estimates of the complete loss of red squirrels assuming current trends, varied from the 2020s in northern England to 2104 in North East Scotland. The recent incertitudes in the replacement of red by grey squirrels may, at least in part, result from increasing efforts to control grey squirrels in these regions. Although the volunteer data presented are valuable, monitoring aims must be clearly defined and sampling designs involving volunteers and professionals must be systematic and of sufficient effort to obtain reliable information on changes in distribution and population trends. Download the complete issue.

Nature and stability of atoll island shorelines: Gilbert Island chain, Kiribati, equatorial Pacific

AbstractIslands rimming Pacific atolls typically form narrow, low‐lying lands that are commonly perceived to be particularly vulnerable to global changes such as sea‐level rise. As these, low islands form the only habitable land for many island nations, understanding the character of shorelines, and the rates and controls that operate to bring about changes, is an issue of central importance. The purpose of this study is to unravel the characteristics of coastal change on atoll islands of the Gilbert Island chain of the equatorial Pacific nation of Kiribati, especially as they relate to autogenic shoreline processes and El Niño/Southern Oscillation variability. Integration of field observations, differential global positioning system data, historical aerial photographs and ultra‐high resolution remote sensing images demonstrates the nature, spatial patterns and rates of change from 17 islands on Maiana and Aranuka atolls. The results illustrate that, between 2005 and 2009, ca 50% of the shorelines on these islands displayed a discernable shift in position; some shorelines were accretionary (at net rates up to ca 8 m year−1) and others were erosional (up to ca 18 m year−1). Long‐term net rates of change on Maiana between 1969 and 2009 were lower than short‐term net rates measured between 2005 and 2009. Both short‐term and long‐term observations illustrate some of the greatest change occur near terminations of the largest, north–south oriented islands, associated with longshore movement of coarse sand and gravel. Direct hits by tropical depressions and marked seasonality, factors interpreted as being essential in island growth and shoreline dynamics elsewhere, do not directly impact these equatorial atolls and can be eliminated as fundamental controls on shoreline dynamics. Similarly, observations over four years suggested that shoreline variability probably is not influenced directly by marked sea‐level change, although a recent increase in the rates of shoreline change could reflect instability related to the cumulative effect of a long‐term increase in the rate of sea‐level rise. Within this framework of global change, local anthropogenic effects, autogenic shoreline processes and El Niño/Southern Oscillation‐influenced wind and wave variability control many aspects of these dynamic shorelines. These results provide quantitative insights into the character and variability of rates of shoreline change, information essential for evaluating and mitigating the vulnerability of island nations such as Kiribati.

Variation of an indicator ofEscherichia colipersistence from surface waters of mixed-use watersheds, and relationship with environmental factors

Escherichia coli is an indicator of fecal pollution used to mandate recreational and drinking water quality. Concentrations of culturable E. coli following contamination of surface water are determined by three factors: dilution; cell attachment to particulate material and settling or resuspension in the water column; and the net rate of change in viability. This study evaluated the variability in the latter parameter, and how predictive variation in death rate was of culturable population densities at the time of sampling. Water samples (N =232) with varying levels of E. coli contamination were collected from 46 discrete locations in four watersheds across Canada over a three-month period and enumerated for culturable E. coli by membrane filtration plate counting (T0EC ). Water samples were again enumerated following a laboratory 24 h holding period at 30°C in the dark, and the difference considered the death rate (ΔEC ). Relationships of T0EC and ΔEC with environmental and water chemistry factors were explored using step-wise multiple regression. The model predicting T0EC indicated that stream order, total rainfall seven days in advance of sampling day, total phosphorus, and ΔEC were the most significant contributors. The model predicting ΔEC indicated that turbidity and NH3 +NH4 were the most important contributors. A model suggests that the persistence factor is less important than dilution (i.e. stream order) in describing E. coli densities, followed by factors that influence the loading of E. coli into watersheds.

Evolution in Fossil Lineages: Paleontology andThe Origin of Species

Of all of the sources of evidence for evolution by natural selection, perhaps the most problematic for Darwin was the geological record of organic change. In response to the absence of species-level transformations in the fossil record, Darwin argued that the fossil record was too incomplete, too biased, and too poorly known to provide strong evidence against his theory. Here, this view of the fossil record is evaluated in light of 150 years of subsequent paleontological research. Although Darwin's assessment of the completeness and resolution of fossiliferous rocks was in several ways astute, today the fossil record is much better explored, documented, and understood than it was in 1859. In particular, a reasonably large set of studies tracing evolutionary trajectories within species can now be brought to bear on Darwin's expectation of gradual change driven by natural selection. An unusually high-resolution sequence of stickleback-bearing strata records the transformation of this lineage via natural selection. This adaptive trajectory is qualitatively consistent with Darwin's prediction, but it occurred much more rapidly than he would have guessed: almost all of the directional change was completed within 1,000 generations. In most geological sequences, this change would be too rapid to resolve. The accumulated fossil record at more typical paleontological scales (10(4)-10(6) years) reveals evolutionary changes that are rarely directional and net rates of change that are perhaps surprisingly slow, two findings that are in agreement with the punctuated-equilibrium model. Finally, Darwin's view of the broader history of life is reviewed briefly, with a focus on competition-mediated extinction and recent paleontological and phylogenetic attempts to assess diversity dependence in evolutionary dynamics.

The Dynamics of Secondary Forest Landscapes in the Lower Mekong Basin

Secondary forests in the Lower Mekong Basin (LMB) are increasingly recognized as a valuable component of land cover, providing ecosystem services and benefits for local users. A large proportion of secondary forests in the LMB, especially in the uplands, are maintained by swidden cultivation. In order to assess the regional-scale status and dynamic trends of secondary forests in the LMB, an analysis of existing regional land cover data for 1993 and 1997 was carried out and forms the basis of this paper. To gain insight into the full range of dynamics affecting secondary forests beyond net-change rates, cross-tabulation matrix analyses were performed. The investigations revealed that secondary forests make up the largest share of forest cover in the LMB, with over 80% located in Laos and Cambodia. The deforestation rates for secondary forests are 3 times higher than the rates for other forest categories and account for two-thirds of the total deforestation. These dynamics are particularly pronounced in the less advanced countries of the LMB, especially in Laos, where national policies and the opening up of national economies seem to be the main drivers of further degradation and loss of secondary forests.

Phycoerythrin-containing picocyanobacteria in the Arabian Sea in February 1995:

Abstract The abundance of phycoerythrin-containing picocyanobacteria in the surface mixed layer was measured both along-shore and offshore between 8 and 23 February 1995 in the Northwestern Arabian Sea. Water samples from 3 m depth were taken at 2-h intervals and picocyanobacterial abundance and frequency of dividing cells were determined by epifluorescence microscopy. Cell counts showed an average diel change from a mid-day minimum of ∼50×10 3 cells ml −1 to an evening maximum of ∼180×10 3 cells ml −1 . The diel change was greater than the differences observed between physically and spatially discrete water masses. By counting the frequency of dividing cells (FDC) and using a novel approach to estimating the length of time required to complete cell division, growth and loss rates were both estimated to be ∼2.9 d −1 with daily turnover being 140% of the mean standing stock. If differences in the intrinsic population growth rate ( μ ) and the net rate of change in cell number ( r ) are assumed to be due to grazing, then grazing occurred throughout the day at a relatively constant rate (reflecting phytoplankton loss rates of ∼0.12 h −1 ). Cell division rates peaked in the late afternoon and early evening. FDC decreased throughout the night, suggesting that dark-inhibition of cell division is weak or nonexistent in the picocyanobacteria we studied. While all cell types included in this study would be identified as Synechococcus by flow cytometry because they were small unicells with bright phycoerythrin fluorescence, morphological variability suggests that the community was actually taxonomically diverse and included cells other than Synechococcus , including Synechocystis . Despite this diversity, the strong diel patterns we observed persisted throughout the study region, suggesting that great care should be taken when interpreting picocyanobacterial survey data and experimental results that do not account for the effects of time-of-day.

Markov Models of Inertia and Dynamism on Two Contiguous Ohio Landscapes

This study examined landcover change during 1940–1988 in two contiguous landscapes of approximately 12,400 hectares in central Ohio, USA: an inertial till plain area and a more dynamic moraine area. Agriculture dominated both landscapes throughout, however, the cover of natural vegetation and urban‐suburban development increased over time on the moraine while natural vegetation decreased and agriculture increased on the till plain. Markov process models for landcover change were constructed for three 14–17‐year time intervals and for the entire forty‐eight‐year study period. Probabilities of self‐replacement for agricultural lands (0.91–0.97) were higher and those for forests (0.54–0.65) lower than those reported for other landscapes. Predictions of landcover percentages for fifty years in the future were made using Markov process models derived from actual cover changes in 1940–1957, 1971–1988, and 1940–1988. All three models produced similar predictions for the inertial till plain area. In contrast, the three models' predictions differed considerably for the moraine area. Only the 1971–1988 transition matrix was sensitive to increases in urbanization and reforestation which began on the moraine in the 1970s. These results indicate that reliance on lengthy study intervals and net rates of change can obscure spatial and temporal patterns of landcover change that are caused by natural and socioeconomic factors operating on shorter time scales.

On the symmetric circulation of a moving hurricane

The evolution of the symmetric circulation of a moving hurricane-scale vortex on a beta-plane is investigated and interpretations of this investigation are given in terms of vorticity fluxes. the study, which is fundamental to understanding vortex motion, is based largely on numerical integrations of the barotropic vorticity equation, using a finite-difference method. In the absence of any large-scale flow, the north-westward drift of an initially symmetric, cyclonic vortex in the northern hemisphere is accompanied by a decrease in the tangential circulation at most radii, and a consequent deceleration of the azimuthally averaged tangential velocity. This behaviour is not simply a consequence of the increase in the Coriolis parameter over the domain of the cyclone as is often supposed, but may be explained as the sum of three effects: the outwards radial flux of relative vorticity associated with the asymmetric component of flow, the corresponding flux of planetary vorticity, and the rate of change in planetary vorticity due to the meridional displacement of the vortex. In particular, the net rate of change in absolute vorticity, the sum of the last two effects, makes the largest contribution to the circulation changes. the flux of absolute vorticity is associated, inter alia, with the generation of Rossby waves by the vortex. the behaviour is different from that in recent calculations by Carr and Williams in which the flux of planetary vorticity was omitted. It is pointed out that in the analytic theory for vortex motion developed by the first author and co-workers, an initially symmetric vortex with zero net relative circulation at large radial distances subsequently develops a finite negative relative circulation whose strength increases linearly with time; this is because the net flux of planetary vorticity at large radial distances is finite. In contrast, in the numerical model the flux is close to zero so that the symmetric circulation decays more rapidly with radius than the 1/(radius) decay rate in the analytic model. At inner radii there is good qualitative agreement between the predictions of the two methods, even though there are quantitative differences between them. It is noted that the occurrence of the finite circulation in the analytic theory violates a theorem of Flierl et al. and that it represents a limitation of the long-term validity of the theory.

On the symmetric circulation of a moving hurricane

AbstractThe evolution of the symmetric circulation of a moving hurricane‐scale vortex on a beta‐plane is investigated and interpretations of this investigation are given in terms of vorticity fluxes. the study, which is fundamental to understanding vortex motion, is based largely on numerical integrations of the barotropic vorticity equation, using a finite‐difference method. In the absence of any large‐scale flow, the north‐westward drift of an initially symmetric, cyclonic vortex in the northern hemisphere is accompanied by a decrease in the tangential circulation at most radii, and a consequent deceleration of the azimuthally averaged tangential velocity. This behaviour is not simply a consequence of the increase in the Coriolis parameter over the domain of the cyclone as is often supposed, but may be explained as the sum of three effects: the outwards radial flux of relative vorticity associated with the asymmetric component of flow, the corresponding flux of planetary vorticity, and the rate of change in planetary vorticity due to the meridional displacement of the vortex. In particular, the net rate of change in absolute vorticity, the sum of the last two effects, makes the largest contribution to the circulation changes. the flux of absolute vorticity is associated, inter alia, with the generation of Rossby waves by the vortex. the behaviour is different from that in recent calculations by Carr and Williams in which the flux of planetary vorticity was omitted.It is pointed out that in the analytic theory for vortex motion developed by the first author and co‐workers, an initially symmetric vortex with zero net relative circulation at large radial distances subsequently develops a finite negative relative circulation whose strength increases linearly with time; this is because the net flux of planetary vorticity at large radial distances is finite. In contrast, in the numerical model the flux is close to zero so that the symmetric circulation decays more rapidly with radius than the 1/(radius) decay rate in the analytic model. At inner radii there is good qualitative agreement between the predictions of the two methods, even though there are quantitative differences between them. It is noted that the occurrence of the finite circulation in the analytic theory violates a theorem of Flierl et al. and that it represents a limitation of the long‐term validity of the theory.

Application of an Electrochemical Quartz Crystal Microbalance to a Study of the Anodic Deposition of PbO2 and Bi ‐ PbO2 Films on Gold Electrodes

The net rate of change in surface mass measured with respect to faradaic charge is calculated for electrodeposited films from the slopes of plots of frequency vs. charge . Abrupt changes in observed early in the deposition of and some films correspond to the transition from two‐dimensional island growth to one‐dimensional growth of the continuous films. Further, these changes in are a consequence of differences in the surface hydration of the deposited films in comparison with the substrate. XPS data indicate that Bi/Pb ratios in films correspond approximately to the [Bi3+]/[Pb2+] ratios in the deposition solutions. Further, voltammetric data for oxidation of dimethylsulfoxide indicate the catalytic activity of the films increases with the increased Bi/Pb ratios in these films. Nevertheless, limiting values of are virtually identical for the deposition of the films containing variable Bi/Pb ratios. The precision of the EQCM data does not allow designation of exact compositions of these various films. Nevertheless, we speculate that the EQCM data indicate the deposition of Bi3+ as Bi(V) with some Bi(IV), and the incorporation of in the films. Limiting values of for thick lead oxide films deposited in the absence of Bi3+ are within experimental error of the theoretical value of 1.24 mg C−1 for pure , and we conclude there is no evidence from the EQCM data for incorporation of and/or supporting electrolyte into these films.

High-frequency ventilation attenuation of hypoxic pulmonary vasoconstriction. The role of prostacyclin.

In order to determine the effects of high-frequency ventilation on the pulmonary vascular response to hypoxia, we assessed pulmonary vascular resistance at 2 levels of inspired oxygen tension (PlO2), 200 and 30 mmHg, during conventional and high-frequency ventilation in the isolated, blood-perfused lungs of 10 sheep, 5 treated with indomethacin (40 micrograms/ml of perfusate) and 5 untreated. Resistance was assessed by measuring pulmonary artery pressure-flow curves generated over a wide range of flows (20 to 140 ml X min-1 X kg body wt-1). Conventional ventilation was provided by an animal ventilator at a rate of 10 min-1 and a tidal volume of 10 ml X kg body wt-1. High-frequency ventilation was provided by a flow interrupter at a rate of 1,200 min-1 and a tidal volume less than 1.5 ml X kg body wt-1. In the 5 untreated lungs, the normoxic pressure-flow curve was unaltered by high-frequency ventilation, but the hypoxic pulmonary vasoconstrictor response was significantly attenuated. Furthermore, the net rate of change of 6-keto-prostaglandin F1 alpha concentration in the perfusate during hypoxia was significantly greater with high-frequency ventilation (65.4 +/- 8.9 pg X ml-1 X min-1) than with conventional ventilation (2.8 +/- 18.7 pg X ml-1 X min-1). In the 5 indomethacin-treated lungs, production of 6-keto-prostaglandin F1 alpha was markedly depressed, and the attenuation of the hypoxic vasoconstrictor response by high-frequency ventilation was abolished.(ABSTRACT TRUNCATED AT 250 WORDS)

Litter Accumulation in Selected Forests of the Republic of Panama

Accumulated litter was collected from primary and secondary tropical moist forests, and from a primary, premontane wet forest in Panama during June to August 1967 (wet-season months), and in January 1968 (a dry-season month). Weights of litter and caloric contents were greatest in the premontane wet forest. Litter accumulation and energy content increased during the dry season in two secondary, tropical moist forests. THE NET RATE of change in energy stored in an ecosystem or its parts equals the rate of income minus the rate of loss (Olson 1963). These rates may be expressed for various trophic levels or species and also for accumulated organic matter. In forests, both living and dead material accumulate large reservoirs of energy. A substantial fraction, often one-third to one-half or more of the energy and carbon annually fixed in forests, is present on the forest floor as litter. Because litter is generally related to the amount of photosynthetic machinery in the system, it can be a useful index of ecosystem productivity. Since litter fall can serve as an indicator of forest production, it is feasible that the energy content of litter accumulated on the forest floor can be used to compare levels of productivity in various forest types. Calorimetric methods, which involve measuring the amount of heat liberated by combustion of samples in oxygen-filled bombs, have been used frequently as a means of deriving energy contents of organic materials. The purpose of this paper is to report the amounts of litter collected from several selected forests in the Republic of Panama and calorimetric analyses of the material.