In this paper, we provide a short proof for the Hopf bifurcation theorem in the Gurtin-MacCamy’s population dynamics model. Here we use the Crandall and Rabinowitz’s approach, based on the implicit ...function theorem. Compared with previous methods, here we require the age-specific birth rate to be slightly smoother (roughly of bounded variation), but we have a huge gain for the length of the proof.
Alpine grasslands are distributed widely on high-elevated ranges and plateaus from the wet tropics to polar regions, accounting for approximately 3% of the world's land area. The Qinghai-Tibetan ...Plateau (QTP) is the highest and largest plateau in the world, and approximately 60% of the plateau consists of alpine grassland, which is used mainly for grazing animals. Livestock structure was determined in Guinan (GN), Yushu (YS) and Maqu counties (MQ) on the QTP by interviewing 235 local pastoralists. Based on data collected from GN, the livestock carrying capacity was calculated using herbage dry matter biomass intake (LCCm) by the livestock, and the metabolizable energy yield (LCCe) and digestible crude protein (LCCp) available in pasture. The pasture area per household differed among the regions of the QTP, which was the main reason for the difference in livestock stocking rate. The householders raised the appropriate proportion of breeding females and young yaks and sheep in GN and MQ, but not in YS, to maintain a constant turnover. Most pasture in YS was used at the community level, especially in summer. The calculated carrying capacities based on metabolizable energy yield (LCCe) of the pasture and dry matter biomass (LCCm) were similar in most months except for August, when the value of LCCe was higher than LCCm. Based on the digestible protein of the pasture, the calculated livestock carrying capacity overestimated the actual carrying capacity during the herbage growing season from May to September. Appropriate practices should be taken in different regions of QTP, such as providing supplementary feed, especially protein, during the forage non-growing season. Livestock carrying capacity should be adjusted dynamically, and calculated by a number of parameters. The stocking rate should be controlled to optimize livestock production and curb or minimize grassland degradation to generate a sustainable system. This study examined the grasslands and LCC on the QTP, but the results could be applied to grasslands worldwide.
•Maintaining old yaks is the main reason for high stocking rate on the grassland.•Livestock turnover rate is faster in lowland than highland of the Tibetan Plateau.•Using forage digestible protein overestimates pasture carrying capacity in summer.•It is recommended to use dry matter biomass to estimate pasture carrying capacity.
Abstract
Background and Objectives
The co-occurring trends of population aging and climate change mean that rising numbers of U.S. older adults are at risk of intensifying heat exposure. We estimate ...county-level variations in older populations’ heat exposure in the early (1995–2014) and mid (2050) 21st century. We identify the extent to which rising exposures are attributable to climate change versus population aging.
Research Design and Methods
We estimate older adults’ heat exposure in 3,109 counties in the 48 contiguous U.S. states. Analyses use NASA NEX Global Daily Downscaled Product (NEX-GDDP-CMIP6) climate data and county-level projections for the size and distribution of the U.S. age 69+ population.
Results
Population aging and rising temperatures are documented throughout the United States, with particular “hotspots” in the Deep South, Florida, and parts of the rural Midwest. Increases in heat exposure by 2050 will be especially steep in historically colder regions with large older populations in New England, the upper Midwest, and rural Mountain regions. Rising temperatures are driving exposure in historically colder regions, whereas population aging is driving exposure in historically warm southern regions.
Discussion and Implications
Interventions to address the impacts of temperature extremes on older adult well-being should consider the geographic distribution and drivers of this exposure. In historically cooler areas where climate change is driving exposures, investments in warning systems may be productive, whereas investments in health care and social services infrastructures are essential in historically hot regions where exposures are driven by population aging.
The aging of the population represents one of the dominant characteristics of the demographic development of Serbia in the second half of the 20th century. The aging process was especially ...intensified during the last decade of the last century, which resulted in the fact that the population of Serbia today is among the oldest in the world. The main cause of population aging is the declining and low fertility and negative migration balance of the young and younger middle-aged population. Demographic aging is a comprehensive process that has affected all municipalities, districts and regions of the country and takes place simultaneously from the top of the age pyramid (increasing the share of the old population) and from the base of the age pyramid (decrease in the share of youth). A clear spatial polarization of demographic age has been established within the Republic of Serbia. On the one hand, there are large cities that have improved the age structure and raised fertility rates through immigration, while on the other hand, there are depopulated municipalities of eastern and southern Serbia and the municipalities of the inner city core of Belgrade. During the first half of the 21st century, a continuation of low fertility and a further decrease in mortality are expected, which will lead to an increase in life expectancy. The depopulation tendencies could be stopped only due to a sudden increase in fertility and a positive migration balance. The aging process will be continuous and continue to be very intense. The aging of the elderly will be especially pronounced. The contingent of the population over 80 years old will increase significantly and will represent a quarter of the total number of old people. All of the above points to a seriously deteriorated age structure, which further leads to an imbalance in the relationship between the able-bodied and dependent part of the population, primarily the elderly. The effects will be reflected on the financing of social programs related to the elderly population, that is, on the pension and health systems.
This review summarizes the evidence from cross-country, macro-level studies on the way demographic factors and processes—specifically, population, age structure, household size, urbanization, and ...population density—influence carbon emissions and energy consumption. Analyses employing time-variant data have produced great variance in population elasticity estimations—sometimes significantly greater than one, sometimes significantly less than one; whereas, cross-sectional analyses typically have estimated population elasticities near one. Studies that have considered age structure typically have used standard World Bank definitions and mostly have found those variables to be insignificant. However, when researchers have considered levels of disaggregation that approximate life-cycle behavior like family size, they have uncovered relationships that are complex and nonlinear. Average household size has a negative relationship with road energy use and aggregate carbon emissions. Urbanization appears positively associated with energy consumption and carbon emissions. Higher population density is associated with lower levels of energy consumption and emissions.
Fire is recognized as a keystone process in dry mixed-conifer forests that have been altered by decades of fire suppression. Restoration of fire disturbance to these forests is a guiding principle of ...resource management in the U.S. National Park Service. Policy implementation is often hindered by a poor understanding of forest conditions before fire exclusion, the characteristics of forest changes since excluding fire, and the influence of topographic or self-organizing controls on forest structure. In this study the spatial and temporal characteristics of fire regimes and forest structure are reconstructed in a 2125-ha mixed-conifer forest. Forests were multi-aged, burned frequently at low severity and fire-return interval, and forest structure did not vary with slope aspect, elevation, or slope position. Fire exclusion has caused an increase in forest density and basal area and a compositional shift to shade-tolerant and fire-intolerant species. The median point fire-return interval and extent of a fire was 10 yr and 115 ha, respectively. The pre-Euro-American settlement fire rotation of 13 yr increased to 378 yr after 1905. The position of fire scars within tree rings indicates that 79% of fires burned in the midsummer to fall period. The spatial pattern of burns exhibited self-organizing behavior. Area burned was 10-fold greater when an area had not been burned by the previous fire. Fires were frequent and widespread, but patches of similar aged trees were <0.2 ha, suggesting small fire-caused canopy openings. Managers need to apply multiple burns at short intervals for a sustained period to reduce surface fuels and create small canopy openings characteristic of the reference forest. By coupling explicit reference conditions with consideration of current conditions and projected climate change, management activities can balance restoration and risk management.
This article investigates the influence of age structure on CO2 emissions from household road transport by using an extended STIRPAT model plus data from 380 Norwegian municipalities for 2009, 2011 ...and 2013. After controlling for population, household income, age structures, household size, and different urban forms (urbanization, urban density, housing type, building density), the paper reveals that the age group responsible for the highest CO2 emissions is 50–69, followed by 20–34 and 35–49. Moreover, compared with other groups, the road transport activities of age group 35–49 are highly constrained by household income. The paper also shows that there is an inverted U-shape relationship between household CO2 road-related emissions and building densities. However, it indicates certain limitations on city planners when it comes to reducing household CO2 road-related emissions by bringing the downtown area closer. Moreover, the paper also identifies a so-called compensatory mechanism supporting the hypothesis that building densities have positive effects. Furthermore, the coefficient of low-density housing is positive and significant, implying that the private gardens of low-density housing might not be the reason for the hypothesized compensatory mechanism. However, this remains a question worth investigating.
•The extended STIRPAT model covers data from 380 Norwegian municipalities.•The highest CO2 emissions group is age 50–69, followed by ages 20–34, and ages 35–49.•The net elasticity of income is negative.•There is an inverted U-shape relationship between household CO2 emissions on the road and the building density.
Large‐scale disturbances, such as megafires, motivate restoration at equally large extents. Measuring the survival and growth of individual plants plays a key role in current efforts to monitor ...restoration success. However, the scale of modern restoration (e.g., >10,000 ha) challenges measurements of demographic rates with field data. In this study, we demonstrate how unoccupied aerial system (UAS) flights can provide an efficient solution to the tradeoff of precision and spatial extent in detecting demographic rates from the air. We flew two, sequential UAS flights at two sagebrush (Artemisia tridentata) common gardens to measure the survival and growth of individual plants. The accuracy of Bayesian‐optimized segmentation of individual shrub canopies was high (73–95%, depending on the year and site), and remotely sensed survival estimates were within 10% of ground‐truthed survival censuses. Stand age structure affected remotely sensed estimates of growth; growth was overestimated relative to field‐based estimates by 57% in the first garden with older stands, but agreement was high in the second garden with younger stands. Further, younger stands (similar to those just after disturbance) with shorter, smaller plants were sometimes confused with other shrub species and bunchgrasses, demonstrating a need for integrating spectral classification approaches that are increasingly available on affordable UAS platforms. The older stand had several merged canopies, which led to an underestimation of abundance but did not bias remotely sensed survival estimates. Advances in segmentation and UAS structure from motion photogrammetry will enable demographic rate measurements at management‐relevant extents.
Mixing peculiar socioeconomic conditions and demographic contexts, urban decline in Mediterranean Europe was less extensively documented than in other regions of the continent. Urbanization without ...industrialization or, more frequently, a ‘late and light’ industrialization prevented a specific interpretation of metropolitan dynamics in Mediterranean basin according with the paradigm of ‘industrial shrinkage’. For the first time in the recent history, the great recession was a factor leading to metropolitan decline in Southern Europe and, after more than one decade, its outcomes can be investigated considering sufficiently long time series of demographic indicators that assess natural population growth and migration rates. Benefiting from quantitative information derived from official statistics, the present study describes medium- and short-term demographic transformations in a large metropolitan region (Attica, Greece) in response to the great recession. After an uninterrupted growth lasting more than one century, the last decade (2010–2019) has provided a dynamic representation of regional population decline based on the interplay of long-term factors (aging, low fertility) and concomitant short-term disturbances (counter-urbanization and crisis-driven emigration). By delineating the most relevant socio-demographic mechanisms at the base of recent urban decline, our study contributes to (re)formulate short-term development scenarios in large metropolitan regions, shedding further light on crisis-driven shrinkage in Southern Europe.
•Urban decline in Mediterranean Europe was poorly documented up to now.•The 2007 recession was a leading factor of metropolitan decline in Southern Europe.•Demographic indicators were used to test shrinkage in a representative Mediterranean city.•Both long-term and short-term factors were important drivers of shrinkage dynamics.•Our study contributes to (re)formulate short-term development scenarios in large cities.
PDF
