Long-term patterns in the decay, collapse, and abundance of trees with hollows in the mountain ash (Eucalyptus regnans) forests of Victoria, southeastern Australia

2010 ◽  
Vol 40 (1) ◽  
pp. 48-54 ◽  
Author(s):  
David B. Lindenmayer ◽  
Jeff T. Wood
Keyword(s):  
Population Dynamics ◽  
Structural Complexity ◽  
Time Dependent ◽  
Old Growth ◽  
Eucalyptus Regnans ◽  
Southeastern Australia ◽  
Large Trees ◽  
Mountain Ash ◽  
Over Time

Large trees with hollows are an important component of stand structural complexity worldwide. Understanding their population dynamics is needed to manage cavity-dependent biota. We quantified long-term rates of collapse of 302 measured trees with hollows in 1939-aged regrowth mountain ash ( Eucalyptus regnans F. Muell.) forest in southeastern Australia. We identified time-dependent dynamics in which the collapse rates of trees slowed from ∼4% annually between 1983 and 1993 to ∼2.2% between 1993 and 2007. Transitions of trees between different decay states (forms) also slowed over time. Nevertheless, during the 24-year period of our study, over half of our marked and measured trees had fallen, but there was no recruitment of new trees with hollows. Under current projections, few trees with hollows will occur on our field sites by ∼2050, although more had been forecast in earlier investigations. Such a paucity of trees with hollows in extensive areas of regrowth mountain ash forests will lead to a shortage of nesting and sheltering sites for cavity-dependent biota. We suggest a short–medium (10- to 100-year) focus on the conservation of old growth and multi-aged stands will be needed to maintain populations of those species strongly associated with trees with hollows in mountain ash forests.

scholarly journals The dynamics of questing ticks collected for 164 consecutive months off the vegetation of two landscape zones in the Kruger National Park (1988–2002). Part II. Rhipicephalus appendiculatus and Rhipicephalus zambeziensis

2011 ◽  
Vol 78 (1) ◽  
Author(s):  
Arthur M. Spickett ◽  
Gordon J. Gallivan ◽  
Ivan G. Horak
Keyword(s):  
Population Dynamics ◽  
Relative Humidity ◽  
National Park ◽  
Rhipicephalus Appendiculatus ◽  
Kruger National Park ◽  
Large Herbivore ◽  
Questing Ticks ◽  
Over Time

The study aimed to assess the long-term population dynamics of questing Rhipicephalus appendiculatus and Rhipicephalus zambeziensis in two landscape zones of the Kruger National Park (KNP). Ticks were collected by dragging the vegetation monthly in three habitats (grassland, woodland and gully) at two sites in the KNP (Nhlowa Road and Skukuza) from August 1988 to March 2002. Larvae were the most commonly collected stage of both species. More R. appendiculatus were collected at Nhlowa Road than at Skukuza, with larvae being most abundant from May to August, while nymphs were most abundant from August to December. Larvae were most commonly collected in the gullies from 1991 to 1994, but in the grassland and woodland habitats from 1998 onwards. Nymphs were most commonly collected in the grassland and woodland. More R. zambeziensis were collected at Skukuza than at Nhlowa Road, with larvae being most abundant from May to September, while nymphs were most abundant from August to November. Larvae and nymphs were most commonly collected in the woodland and gullies and least commonly in the grassland (p < 0.01). The lowest numbers of R. appendiculatus were collected in the mid-1990s after the 1991/1992 drought. Rhipicephalus zambeziensis numbers declined after 1991 and even further after 1998, dropping to their lowest levels during 2002. The changes in numbers of these two species reflected changes in rainfall and the populations of several of their large herbivore hosts, as well as differences in the relative humidity between the two sites over time.

scholarly journals Progression of mild cognitive impairment to dementia: a challenge to current thinking

2006 ◽  
Vol 189 (5) ◽  
pp. 399-404 ◽  
Author(s):  
Anja Busse ◽  
Matthias C. Angermeyer ◽  
Steffi G. Riedel-Heller
Keyword(s):  
Cognitive Impairment ◽  
Mild Cognitive Impairment ◽  
Community Sample ◽  
Neuropsychological Testing ◽  
Time Dependent ◽  
Current Thinking ◽  
Conversion Rates ◽  
Over Time ◽  
Long Term Studies

BackgroundStudies of conversion from mild cognitive impairment to dementia suggest a linear progression over time. Conversion rates during lifetime may extend to 80–90%.AimsThis study examines the time-dependent evolution from mild cognitive impairment to dementia. Current assumptions regarding yearly and lifetime conversion rates are challenged.MethodA community sample of 1045 dementia-free individuals aged 75 years and over was examined by neuropsychological testing based on 6 years of observation.ResultsApproximately 60–65% of people with mild cognitive impairment develop clinical dementia during their life. Progression from mild cognitive impairment to dementia appears to be time dependent, occurring primarily within the initial 18 months.ConclusionsFurther long-term studies are needed to examine the time-dependent evolution from mild cognitive impairment to dementia and to establish age-specific conversion rates during lifetime.

Long-term performance and herbivory of tree seedlings planted into primary and secondary forests of Central Amazonia

2013 ◽  
Vol 29 (4) ◽  
pp. 301-311 ◽  
Author(s):  
Julieta Benítez-Malvido ◽  
Miguel Martínez-Ramos
Keyword(s):  
Secondary Forest ◽  
Tree Seedlings ◽  
Secondary Forests ◽  
Old Growth ◽  
Old Growth Forest ◽  
Central Amazonia ◽  
One Year ◽  
Term Performance ◽  
Over Time

Abstract:Plant survival and growth in tropical rain forest are affected by different biotic and abiotic forces. As time elapses and plants grow the relative importance of such forces as regeneration inhibitors and/or facilitators may change according to habitat and species. To detect within- and among-species divergences in performance over time in different habitats we followed, for nearly a decade, the survival, growth and herbivory of seedlings of the native tree species: Chrysophyllum pomiferum, Micropholis venulosa and Pouteria caimito. In Central Amazonia, young seedlings were planted into old-growth and secondary forests dominated by Vismia spp. One year after planting, C. pomiferum ranked first (i.e. fast growth, fewer dead and less herbivory) for both habitats, followed by M. venulosa and P. caimito. Initial trends changed over time. In the long term, M. venulosa ranked first for both habitats, followed by C. pomiferum and P. caimito ranked consistently lowest. Within-species divergences in growth and herbivory were greater in secondary forest. Initial seedling responses cannot always be used to predict species persistence in the long term. Contrary to previous estimations, old-growth-forest species can persist under Vismia spp. stands, at least when planted.

scholarly journals Older eastern white pine trees and stands sequester carbon for many decades and maximize cumulative carbon

2020 ◽  
Author(s):  
Robert T. Leverett ◽  
Susan A. Masino ◽  
William R. Moomaw
Keyword(s):  
New England ◽  
Carbon Storage ◽  
Safety Net ◽  
White Pine ◽  
Eastern White Pine ◽  
Old Growth ◽  
Old Growth Forest ◽  
Large Trees ◽  
Natural Climate

AbstractPre-settlement New England was heavily forested, with some trees exceeding 2 m in diameter. New England’s forests have regrown since farm abandonment and represent what is arguably the most successful regional reforestation on record; the region has recently been identified as part of the “Global Safety Net.” Remnants and groves of primary “old-growth” forest demonstrate that native tree species can live for hundreds of years and continue to add to the biomass and structural and ecological complexity of forests. Forests are an essential natural climate solution for accumulating and storing atmospheric CO2, and some studies emphasize young, fast-growing trees and forests whereas others highlight high carbon storage and accumulation rates in old trees and intact forests. To address this question directly within New England we leveraged long-term, accurate field measurements along with volume modeling of individual trees and intact stands of eastern white pines (Pinus strobus) and compared our results to models developed by the U.S. Forest Service. Our major findings complement, extend, and clarify previous findings and are three-fold: 1) intact eastern white pine forests continue to sequester carbon and store high cumulative carbon above ground; 2) large trees dominate above-ground carbon storage and can sequester significant amounts of carbon for hundreds of years; 3) productive pine stands can continue to sequester high amounts of carbon for well over 150 years. Because the next decades are critical in addressing the climate crisis, and the vast majority of New England forests are less than 100 years old, and can at least double their cumulative carbon, a major implication of this work is that maintaining and accumulating maximal carbon in existing forests – proforestation - is a powerful near-term regional climate solution. Furthermore, old and old-growth forests are rare, complex and highly dynamic and biodiverse, and dedication of some forests to proforestation will also protect natural selection, ecosystem integrity and full native biodiversity long-term. In sum, strategic policies that grow and protect existing forests in New England will optimize a proven, low cost, natural climate solution for meeting climate and biodiversity goals now and in the critical coming decades.

Flexible Design of Systems Considering Time-Dependent Reliability

2015 ◽  
Author(s):  
Vijitashwa Pandey ◽  
Zissimos P. Mourelatos ◽  
Annette Skowronska
Keyword(s):  
Time Dependent ◽  
Time Varying ◽  
Repairable Systems ◽  
Flexible Design ◽  
Change Over Time ◽  
New Approach ◽  
Hydrokinetic Turbine ◽  
The Future ◽  
Over Time

Many repairable systems degrade with time and are subjected to time-varying loads. Their characteristics may change over time considerably, making the assessment of their performance and hence their design difficult. To address this issue, we introduce in this paper the concept of flexible design of repairable systems under time-dependent reliability considerations. In flexible design, the system can be modified in the future to accommodate uncertain events. As a result, regardless of how uncertainty resolves itself, a modification is available that will keep the system close to optimal provided failure events have been properly characterized. We discuss how flexible design of repairable systems requires a fundamentally new approach and demonstrate its advantages using the design of a hydrokinetic turbine. Our results show that long-term metrics are improved when time-dependent characteristics and flexibility are considered together.

scholarly journals Within and among-population variation in vital rates and population dynamics in a variable environment

2015 ◽  
Author(s):  
Simone Vincenzi ◽  
Marc Mangel ◽  
Dusan Jesensek ◽  
John Carlos Garza ◽  
Alain J Crivelli
Keyword(s):  
Population Dynamics ◽  
Population Density ◽  
Debris Flows ◽  
Life Histories ◽  
Population Variation ◽  
Population Differences ◽  
Vital Rates ◽  
Marble Trout ◽  
Over Time

Understanding the causes of within- and among-population differences in vital rates, life histories, and population dynamics is a central topic in ecology. To understand how within- and among-population variation emerges, we need long-term studies that include episodic events and contrasting environmental conditions, data to characterize individual and shared variation, and statistical models that can tease apart population-, shared-, and individual contribution to the observed variation. We used long-term tag-recapture data and novel statistical and modeling techniques to investigate and estimate within- and among-population differences in vital rates, life histories and population dynamics of marble trout Salmo marmoratus, a endemic freshwater salmonid with a narrow range. Only ten populations of pure marble trout persist in headwaters of Alpine rivers in western Slovenia. Marble trout populations are also threatened by floods and landslides, which have caused the extinction of two populations in recent years. We estimated and determined causes of variation in growth, survival, and recruitment both within and among populations, and evaluated trade-offs between them. Specifically, we estimated the responses of these traits to variation in water temperature, density, sex, early life conditions, and the occurrence of extreme climatic events (e.g., flash floods and debris flows). We found that the effects of population density on traits were mostly limited to the early stages of life and that individual growth trajectories were established early in life. We found no clear effects of water temperature on survival and recruitment. Population density varied over time, with flash floods and debris flows causing massive mortalities and threatening population persistence. Apart from flood events, variation in population density within streams was largely determined by variation in recruitment, with survival of older fish being relatively constant over time within populations, but substantially different among populations. Marble trout show a fast to slow continuum of life histories, with slow growth associated with higher survival at the population level, possibly determined by food conditions and age at maturity. Our work provides unprecedented insight into the causes of variation in vital rates, life histories, and population dynamics in an endemic species that is teetering on the edge of extinction.

scholarly journals Time-Dependent Apparent Increase in dd-cfDNA Percentage in Clinically Stable Patients Between One and Five Years Following Kidney Transplantation

2020 ◽  
Vol 66 (10) ◽  
pp. 1290-1299 ◽  
Author(s):  
Ekkehard Schütz ◽  
Thomas Asendorf ◽  
Julia Beck ◽  
Verena Schauerte ◽  
Nina Mettenmeyer ◽  
...  
Keyword(s):  
Kidney Transplantation ◽  
Digital Pcr ◽  
Time Dependent ◽  
Cross Sectional ◽  
Apparent Increase ◽  
Cell Counts ◽  
White Blood Cell Counts ◽  
Over Time ◽  
Observation Period

Abstract Background Donor-derived cell-free DNA (dd-cfDNA) is reportedly a valuable tool for graft surveillance following kidney transplantation (KTx). Possible changes in dd-cfDNA(%) reference values over time have not been evaluated. For long-term monitoring after KTx, changes in host cfDNA might represent a biasing factor in dd-cfDNA(%) determinations. Methods Plasma samples were obtained (n = 929) 12–60 months after engraftment in a cross-sectional cohort of 303 clinically stable KTx recipients. Total cfDNA(copies/mL), dd-cfDNA(%), and dd-cfDNA(copies/mL) were determined using droplet-digital PCR. Stability of threshold values in these stable KTx recipients over time was assessed by 80th, 85th, and 90th quantile regression. Results Upper percentiles of total cfDNA showed a significant decline of −1902, −3589, and −4753 cp/mL/log(month) (P = 0.014, &lt;0.001, and 0.017, respectively), resulting in increasing dd-cfDNA(%) percentiles by 0.25, 0.46, and 0.72%/log(month) (P = 0.04, 0.001, and 0.002, respectively), with doubling of the 85th percentile value by 5 years. In contrast, dd-cfDNA(cp/mL) was stable during the observation period (P = 0.52, 0.29, and 0.39). In parallel increasing white blood cell counts and decreasing tacrolimus concentrations over time were observed. After 5 years, the median total cfDNA was still 1.6-fold (P &lt; 0.001) higher in KTx recipients than in healthy controls (n = 135) and 1.4-fold (P &lt; 0.001) higher than patients with other medical conditions (n = 364). Conclusions The time-dependent decrease of host cfDNA resulted in an apparent increase of dd-cfDNA fraction in stable KTx patients. For long-term surveillance, measurement of absolute dd-cfDNA concentrations appears to be superior to percentages to minimize false positive results.

A method for predicting the spatial distribution of arboreal marsupials

1995 ◽  
Vol 22 (4) ◽  
pp. 445 ◽  
Author(s):  
DB Lindenmayer ◽  
K Ritman ◽  
RB Cunningham ◽  
JBD Smith ◽  
D Horvath
Keyword(s):  
Spatial Distribution ◽  
Kernel Smoothing ◽  
Eucalyptus Regnans ◽  
Field Surveys ◽  
Probability Of Occurrence ◽  
Predicted Probability ◽  
Arboreal Marsupials ◽  
Large Trees ◽  
Mountain Ash ◽  
Smoothing Procedure

A method is described for predicting the spatial distribution of arboreal marsupials. The approach is demonstrated using a statistical habitat association model for the greater glider (Petauroides volans), developed in the mountain ash (Eucalyptus regnans) forests of the central highlands of Victoria. The method is applied to predict the spatial distribution of P. volans in the Ada Forest Block, using forestinventory data on the values of the two significant variables in the statistical model (the age of a stand of forest and the abundance of large trees with hollows in a 3-ha area). The application of the model enabled values for the estimated probability of occurrence of P, volans (with a 95% confidence interval) to be generated for each of approximately 2200 3-ha pixels in the Ada Forest Block. A kernel smoothing procedure was then applied to allow for the spatial dependence implicit in these data. The standard measures of statistical uncertainty employed in our analysis revealed substantial variation in the predicted probability of occurrence of P. volans, even though the terms in the statistical relationship were highly significant. However, whilst the model is unable to reliably predict the occurrence of P. volans at any given 3-ha site, tests of the performance of the model showed that it performed well when the results of field surveys were aggregated over many sites. The results of our analysis emphasise the importance of including measures of uncertainty in spatial predictions generated from statistical models.

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