Analysis Of Age Structure Research Articles

Timing of Sprouting in Hamabiwa (Litsea japonica Juss.) Growing in a Coastal Dwarf Forest

Morphology, age structure and growth of sprouts in Hamabiwa (Litsea jufionica Juss.) growing in a coastal dwarf forest in northern Kyushu were investigated, and timing of sprouting was discussed in relation to activities of terminal buds. Sprouts of Hamabiwa were collected and n~orphology of sprouts and their prilnordia were observed. On the stem surfaces of Hamabiwa, there were numerous suppressed buds with vascular traces connected to the pith. Similar vascular traces were observed at the base of sprouting positions. So, the priinordia of sprouts in Hamabiwa were assumed to be suppressed buds. 67 sprouts from six clumps were randomly sampled for age structure analysis, Although there were large fluctuations in the frequency distributioil of sprout age, sprouts existed in most age classes. The frequency distribution showed a gentle inverse-J shape indicating a high survival rate of sprouts. Disks of stems of one clump with 7 sprouts were sampled for stem growth and sprouting analysis. Sprouting was observed in years when the height growth rate declined or in the following years. This result suggested that sprouting was closely related to the activity of terminal buds. However, there was no significant relationship between sprouting and volume or radial growth rates. From these results, it was suggested that Hamabiwa growing in a coastal dwarf forest flushes sprouts constailtly due to stress at terminal buds, and maintains their

Régénération après feu de l'épinette noire (Piceamariana) et du pin gris (Pinusbanksiana) dans la forêt boréale, Québec

Age structure analysis was performed in black spruce (Piceamariana (Mill.) B.S.P.) and jack pine (Pinusbanksiana Lamb.) stands following fire (i) to determine if there is a time lag between black spruce and jack pine establishment and (ii) to compare the composition of the regeneration with regard to the original stand. The study was conducted in an area burnt in 1983, 100 km northwest of Lake Saint-Jean, Quebec. Five years after fire, the age structure of the regeneration shows an early establishment of jack pine and black spruce, with more than 95% of the seedlings established during the first three growing seasons after fire (excluding the year of fire). The age structures were similar in mature stands and in the regeneration for the jack pine while they differed for black spruce. Errors in age determination due to suppression of adult trees sampled or other causes could explain the difference in the establishment pattern of young and mature black spruces. Compared with the mature stand, the postfire regeneration had an increased proportion of jack pine. The study concludes that both species can regenerate shortly after fire, but in somewhat varying proportions.

Analysis of the standing age distribution and age-specific recruitment rate of the George River and Beverly barren-ground caribou populations

The primary advantage of the standing age distribution of a population is that it can be sampled. Analysis of the age frequencies for estimates of survival rates and determinations of population status by life table construction depend heavily on assumption that require additional data to evaluate. The analysis of age structures for the George River (Messier et al., 1988) and Beverly (Thomas and Barry, 1990a,b) caribou herd was reviewed. An alternativ method of estimating age specific survival rates was explored. The dependence of the life tables produced by the analysis of Messier et al. (1988) and Thomas and Barry (1990a,b) on tenuous and untestable assumptions regarding population growth rate over the life span of the oldest animals, stability of the standing age distribution, and constancy of life table parameters was emphasized. Although the life tables produced by Messier et al. (1988) for the George River herd and Thomas and Barry (1990a,b) for the Beverly herd are probably the best available for barren-ground caribou, they should be used with caution, particularly for management decisions.

Accumulation of fluorescent age pigments in a laboratory population of Antarctic krill Euphausia superba Dana

Age-class separation by morphometric means has proved difficult for Antarctic krill Euphausia superba because the size of the animals does not necessarily relate to their age in any predictable fashion. The measurement of temporal increases in quantities of fluorescent age-pigments has been suggested as a method which obviates the problems associated with size-related measures of age. In this study, a laboratory population of Antarctic krill exhibited a clear increase in the mean amount of fluorescent age-pigment per animal over a period of 1 yr. At the same time the mean weight of the animals in the population decreased markedly — body shrinkage. Analyses of fluorescence- and weight-frequency plots from samples taken a year apart demonstrated that the fluorescence technique could successfully discriminate the two year groups and determine their correct temporal sequence whereas the weight frequency analysis was less successful at discriminating the two peaks and placed them in an incorrect temporal sequence. On the basis of these results it is suggested that age-pigment fluorescence may now be a useful tool in the analysis of age-structure in populations of Antarctic krill.

The Response of Subalpine Forests to Spruce Beetle Outbreak in Colorado

Spruce beetle (Dendroctonus rufipennis Kirby) outbreaks are important disturbances affecting subalpine forests of Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), and lodgepole pine (Pinus contorta) in the southern Rocky Mountains. However, little is known about the influences of these outbreaks on overall forest dynamics. We used age—structure analyses and dendrochronological techniques to investigate the effects of a major spruce beetle outbreak on stand composition, dominance, tree age and size structures, radial growth, and succession in subalpine forests in Colorado. This outbreak, which occurred in the 1940s, caused a shift in dominance from spruce to fir and a reduction in average and maximum tree diameters, heights, and ages. The outbreak did not favor new seedling establishment of the seral lodgepole pine. Thus, in seral stands spruce beetle outbreak accelerates succession towards the shade—tolerant tree species. The predominant response to the outbreak was the release of previously suppressed small—diameter spruce (not attacked by the beetle) and subalpine fir (a non—host species). Following the 1940s outbreak, growth rates of released trees remained high for >40 yr. The relative increases in growth rates were similar for both species. Both spruce and fir will continue to codominate the affected stands. The predominance of accelerated growth following a spruce beetle outbreak, instead of new seedling establishment, is a major contrast to the pattern of stand development following fire. In some Colorado subalpine forests the effects of disturbance by spruce beetle outbreaks appear to be as great as those due to fire.

Historical Biogeography of Picea abies (L.) Karst. at Its Subarctic Limit in Northern Sweden

Late Holocene behaviour of the spruce (Picea abies (L.) Karst.) at its forest-limit in northem Sweden was assessed from age structure analyses and comparison of present-day distribution with older geobotanical surveys. At a landscape scale, spruce has maintained a dynamic equilibrium with climate during recent centuries. On very short time scales (years to decades), non-equilibrium responses are perceivable. Thus, for example, a recent episode of canopy dieback due to severe ground cooling has occurred. Ground frost may be part of the mechanism which limits further expansion of spruce against the westward/elevational gradient. Pulses of population growth, mainly in pre-existing stands, were inferred for the 1830s40s and the 1940s-60s, which reasonably related to shortterm climatic variability. Regeneration lagged slightly behind thermal optima. Possibly, instant responses to warming were precluded since generative processes presupposed a short period of vegetative recovery after cold episodes. Additionally, the peaking of precipitation after the temperature may be of some importance for this delay.

The significance of life history strategies in the developmental history of mixed beech (Nothofagus) forests, New Zealand

Size and age structure analysis, dated past disturbances, treefall replacement patterns, and spatial pattern analysis were used to reconstruct the developmental history of two old-growth Nothofagus fusca/N. menziesii stands, South Island, New Zealand. Diameter and height class distributions suggested that N. menziesii was replacing N. fusca, however, stand history reconstruction analysis showed that both species had regenerated intermittently after small-scale disturbances. Although large-scale disturbances such as blowdowns may occasionally generate even-aged stands, gap-phase regeneration maintains the forests in compositional equilibrium. In the absence of other competing tree species and understorey plants the two species appear to coexist by way of different life history strategies, where one species (N. menziesii) has low juvenile mortality and the other (N. fusca) has faster height growth rates and greater longevity and adult survivorship.

Comparison of Actual and Predicted Blue Oak Age Structures

There is increasing interest in understanding the role of management on the current lack of blue oak (Quercus douglasii H. & A.) recruitment on California foothill rangelands. Age structure analysis has been suggested to relate when and how much recruitment occurred under past management as an indication of current management effects on recruitment. Previous estimates of blue oak age structure were based on unquantified correlations between age and diameter. Using regression analysis we found that diameter at breast height (DBH) accounted for 42-71% of the variation in tree age at 2 sites. Actual age structures were significantly different than age structures predicted from all regression equations at both sites. We suggest that the use of age structures to infer the role of management on blue oak population dynamics requires direct age measurement.

Recent Vegetation Changes along the Forest/Steppe Ecotone of Northern Patagonia

Abstract In northern Patagonia over a west-to-east distance of approximately 50 km, the vegetation changes from Nothofagus rainforests through woodlands of Austrocedrus chilensis to steppe dominated by bunchgrasses and shrubs. Analysis of tree population age structures and photographic comparisons of the forest/steppe margin over the past century indicate an expansion of trees into the steppe. Throughout northern Patagonia, Austrocedrus chilensis and other trees began invading the steppe 75 to 100 years ago. During the early decades of the twentieth century, there was also a shift in dominance from bunchgrasses towards spiny shrubs in the steppe near the forest margin. Cessation of frequent burning of the steppe by Indians hunting guanacos at the end of the nineteenth century appears to have permitted the tree invasion. Severe overgrazing by sheep and livestock during the early decades of the present century was the main factor in the shift in dominance from bunchgrasses towards shrubs. European settlemen...

The regeneration process in a mixed forest in central Hokkaido, Japan

The regeneration process in a mixed forest was investigated in Nopporo National Forest, Hokkaido. The analysis of age structure in an 80 m×80 m plot revealed that almost all of the species regenerated intermittently. In eleven gaps observed in the plot, the regeneration of a boreal conifer (Abies sachalinensis) was seldom observed. Temperate hardwoods, even climax species (Acer mono, Quercus mongolica var. grosseserrata, Tilia japonica), regenerated vigorously in the gaps. The age structure in ten additional plots scattered all over the forest showed that Abies tended to regenerate synchronously. From previous records, regeneration of Abies could be ascribed to catastrophic storms causing serious windfalls. On the other hand, regeneration of the temperate hardwoods was not synchronous but independent in different places within the forest. They could regenerate not only after those catastrophic storms but also after less severe disturbances which caused the death and fall of one or several trees. It is concluded that the coexistence of boreal coniferous species and temperate deciduous broad-leaved species in mixed forests may be maintained not only by the difference in habitat but also by the balance between the less frequent large disturbances, and the more frequent smaller ones.

Conifer regeneration failure in New Zealand: dynamics of montane Libocedrus bidwillii stands

Size and age structure analysis were used to reconstruct the population dynamics of six apparently old and stable stands dominated by the conifers Libocedrus bidwillii and/or Dacrydium biforme in Camp Creek, West land, New Zealand. All stands contained relatively even-aged groups of Libocedrus that had probably originat ed after either mass movement or windthrow. The age distributions of stands reflected the effects of distur bances 200-400 yr ago. There was no evidence to support synchronous failure of regeneration of Libocedrus and Dacrydium bi forme. Between 1600 and 1800 A.D., the period of the postulated conifer regeneration gap, over 70% of trees of these species had established. A lack of Libocedrus regeneration over the last 200 yr reflects a lack of distur bance over that time. Because of the dominating influence of disturbances and other factors it may be inap propriate to use tree population structures alone to substantiate or refute claims of recent climate change.

Survivorship of adult females in a northern population of common snapping turtles, Chelydra serpentina

Survivorship of adult female snapping turtles (Chelydra serpentina) in a marked population in Algonquin Provincial Park, Ontario, was estimated using recapture records and catch-curve analysis of age structure. Known mortality was less than 1% per year, and a 13-year average of survivorship was 96.6% per year. Even the conservatively biased catch-curve estimate (92.9% per year) was among the highest yet reported for any turtle population. We compared two hypotheses to account for these high values. Although not at variance with our results, we rejected Rubner's proximal "rate of living" hypothesis because of lack of any other evidence that this process operates in reptiles. The second hypothesis was that high survivorship was the consequence of specific demographic features in a bet-hedging life-history strategy. Females would be more successful, given the high and stochastic clutch mortality and lack of predation on adults in this northern population, if they produced smaller clutches over many years than if they produced larger clutches over fewer years. This suite of characteristics may have allowed for the establishment of this northern population, or the high survivorship of adult females in this population may be an evolved response in the direction predicted by bet-hedging theory.

Vegetation Pattern and Diversity in S.E. Labrador, Canada: Betula Papyrifera (Birch) Forest Development in Relation to Fire History and Physiography

(1) The Betula papyrifera (paper birch) forest of the wilderness of south-eastern Labrador is described. (2) B. papyrifera forests range in size from less than 1 ha to several kM2, display sharp borders with the adjoining conifer forests and are restricted to steep slopes that have burned in the previous 110 years. (3) Floristically, the B. papyrifera community is distinguished from conifer forests by the presence of fourteen differential species, by the scarcity of terrestrial cryptogams and by the development of a diverse understorey of vascular plants. (4) Three minimum conditions are necessary for B. papyrifera forest development: (i) moist and well-drained soils, (ii) a nearby seed source, and (iii) an open site. (5) The nearly exclusive restriction of B. papyrifera forest to areas that have burned in the last 110 years indicates that the open-site conditions necessary for stand initiation are largely created by lightning fires. (6) Age-structure analysis demonstrates that, following fire, regeneration by B. papyrifera is rapid and results in the formation of an even-aged overstory. Gradual invasion of canopy openings by Picea mariana and Abies balsamea results in the progressive conversion to conifer forest. (7) Fire maintains B. papyrifera and other early post-fire communities in a mosaic pattern and increases regional vegetation diversity. The pattern is not random, but is controlled by species autecologies, the pattern of fires and physiography. The vegetation of south-eastern Labrador is in a state of dynamic equilibrium.

A demographic analysis of the Wisconsin Regional Primate Center rhesus colony, 1962-1982.

A detailed demographic analysis was made of the Wisconsin Regional Primate Research Center rhesus colony from vital statistics recorded over a 20-year period. Techniques used were based on demographic and epidemiological methods developed for human populations, which provide the potential for making standardized measurements within captive primate colonies. A life table based on 1,086 deaths showed an abnormally high survivorship at the older ages, probably caused by a tendency to retain especially robust animals for breeding purposes. During the period of study, 2,194 animals were removed for sale or research. Removal rates were relatively uniform across ages. Age-specific fertility rates based on 1,616 births occurring during the second decade showed a relatively rapid increase in births from about age 2 through age 12, with peak fertility persisting until about age 20. Vital events showed significant seasonality, with a birth peak in April and May. Analysis of the stable age structure (excluding removal) showed an intrinsic growth rate of 6.3%. With removal rates added, the growth rate dropped to -0.3%. Although the use of these methods is probably warranted onlyby the level of detail found in captive colony records, analysis of captive colonies can provide information relevant to the demography of wild primates.

ANTHROPOGENIC DISTURBANCE AND RECOVERY PATTERNS IN MONTANE FORESTS, COLORADO FRONT RANGE

Extensive logging and burning in association with the mining booms of the latter half of the 19th century severely disturbed the montane forests of Boulder County in the Colorado Front Range. Repeat photography of 68 historical photographs and age structure analysis of 24 stands were used to investigate patterns of stand development following disturbance. The data set of nearly 1300 tree ages revealed highly variable patterns of development of stands dominated mainly by ponderosa pine (Pinus ponderosa), Douglas fir (Pseudotsuga menziesli), lodgepole pine (Pinus contorta), limber pine (Pinus flexilis), and subalpine fir (Abies lasiocarpa). In most cases, forest succession followed an “initial floristics” pattern in which both early and late successional (or climax) species established more or less synchronously. Less commonly, and always on less favorable sites, forest succession followed a “relay floristics” pattern in which the late successional species did not establish until several decades after initi...

Presettlement Regeneration Patterns in a Southwestern Ponderosa Pine Stand

Tree stems @>106 yr old (i.e., established before significant European influence in this area) in a 7.3—ha old—growth ponderosa pine (Pinus ponderosa) forest in northern Arizona were aged and mapped. Age structure analysis showed that successful establishment of ponderosa pine was infrequent. The periods without successful establishment could be quite long, as suggested by four consecutive decades in which only two surviving trees were established. The stems were strongly aggregated, as measured with nearest neighbor analysis, and groups were visually distinct in the field. Most of the stems occurred in groups of three or more, with group size ranging from 3 to 44 stems and area occupied by a group ranging from 0.02 to 0.29 ha. Ages of stems within groups were variable, the most homogeneous group having a range of 33 yr and the least having a range of 268 yr. The data are not consistent with the commonly held view that southwestern ponderosa pine occurs in even—aged groups and that each group became established following the demise of the group previously occupying the site. Instead, it seems more likely that seedlings became established when one or two trees within the group died, the additional fuel surrounding the dead trees causing an intensely burned spot in the otherwise low—intensity fires that were frequent in the area. The hot spot would create a potential seedbed for pine by eliminating, at least temporarily, the competing grasses on that small area. This decreased competition, in conjunction with adequate seed production and favorable moisture conditions in the spring and early summer, may well have been critical for ponderosa pine establishment. The relative infrequency of all these events occurring in the necessary sequence could explain the erratic age structure data from this area.

Age and Size Structure Analyses of Engelmann Spruce, Ponderosa Pine, Lodgepole Pine, and Limber Pine in Colorado

Ages and diameters were measured in mature stands for each of 507 ponderosa pine, 541 lodgepole pine, 141 limber pine, and 217 Engelmann spruce trees in the Colorado Front Range of the Rocky Mountains, USA. Cumulative age distributions were statistically different for each species. The spruce and ponderosa pine age distributions each exhibited a strong infection point at °210 and 125 yr, respectively, while neither lodgepole nor limber pine showed such a sharp inflection point. We suggest that the presence of this inflection point may be indicative of climax type in mature stands and interpret the age distributions of these species as reflective of their climax, colonizing and fugitive ecological patterns, respectively. Diameter distribution curves exhibited patterns markedly different from the age patterns. Ponderosa pine and Englemann spruce showed almost identical distribution despite widely disparate age structure. We interpret this result to simply that to the complex of forces which influence size distributions in forest trees is very similar in ponderosa pine and spruce although they form very different ecological communities. Lodgepole and limber pine diameter distributions were quite different. Our conjectures that the presence of a sharp inflection point in cumulative age distributions indicates a climax stand and that climax species will often have coincident diameter distributions, are offered as empirically testable hypotheses.

The pattern of invasion and establishment of Piceamariana (Mill.) BSP. into the subcanopy layers of Pinusbanksiana Lamb. dominated stands

Stand age-structure analysis is used to determine whether establishment of Piceamariana (Mill.) BSP. in the subcanopy of Pinusbanksiana Lamb. dominated stands takes the form of a gradual influx or a sudden event. Twenty-six P. banksiana dominated stands were investigated of which 15 contained P. mariana trees at moderate to high densities. Postfire ages ranged from 46 years to 132 years for the oldest P. banksiana cohort in each stand. The 26 stands were subjectively assigned to one of seven groups on the criterion of age-structure histogram appearance. A multivariate test of the hypothesis that such age-structure differences could be due to soil differences was not significant. Three patterns of P. mariana influx were indicated, (i) Gradual influx over a long time span in the oldest stands. (ii) Contemporaneous postfire reestablishment of both P. banksiana and P. mariana on a site. (iii) Invasion of P. mariana cohorts following surface fire activity as evidenced by fire scar dates. Results from a P. mariana seedling survival experiment indicated that depth of burn is of critical importance for black spruce seedling establishment in these stands. However, circumstantial evidence suggests that P. mariana seed supply may also be limiting to establishment success. These observations are discussed briefly in relation to models of forest succession.

Animal community structure and energy budget calculations of a Daphnia magna (straus) population in relation to the rock pool environment

The fauna and environmental conditions in a freshwater rock pool ecosystem were followed by a weekly quantitative sampling program from April to August, 1974. The rock pool, situated on a small island in the northern Baltic Sea, was heavily eutrophicated by droppings from the surrounding colony of sea birds. The intermittent flushing of the pool with rainwater and the input of bird droppings, as well as the biological activity, contributed to the large seasonal variations in nutrients and organic matter that were observed. A dense algal bloom of flagellates occurred in April but vanished when the animal population started to increase in the middle of May. During the rest of the summer, most of the photosynthetic pigments were found in the bottom sediment, mostly as degraded phaeo-pigments due to intensive grazing by the animals in the pool. Very few animal taxa were found and the phyllopod Daphnia magna (Straus) dominated throughout the whole sampling period. D. magna contributed to more than 50% of the total biomass, except in late July when chironomid larvae were most abundant. The total biomass in the pool increased from about 15 mg (dry weight) l −1 in May to a maximum of about 60 mg l −1 at the end of June. There were few carnivores in the system, except during the spring when the water bug Deronectes griseostriatus (de Geer) was common. Analyses of size, age and sex structure and calculations of birth and death rates of the D. magna population showed large seasonal variations, correlated with the volume fluctuations and flushings of the pool which stimulated both the algal production and the growth and reproduction of Daphnia. Data from the extensive literature that exists on D. magna and other species of the same genus were used, together with field and experimental data from the rock pool population, in a numerical model describing the energy budget of this species. The model describes variations in weight-specific growth, reproduction, moulting, feeding and respiration rates in relation to temperatures and food concentrations. Energy budget relationships that maximise the chances for survival and utilisation of the available energy for a population exposed to varying food concentrations are predicted by the model. The energy budget model was also used to estimate the secondary production of the rock pool population of D. magna. The total production between April and August was 203 mg (dry weight) l −1 and the average production per biomass ratio was 0.094 day −1. The average net production efficiency was 42%, very close to other values reported for D. magna from other biotopes. The relative importance of different factors controlling the production was also analysed with the model. Production per biomass ratio was calculated, assuming a constant temperature and/or food concentration for the whole sampling period. The varying food concentrations in the rock pool had the most pronounced influence, greater than that of temperature and size structure variations in the population.

The age structure of a striped maple population

Cohort and population age structure analysis showed that, after the initially high mortality rates of the 1st year (87.5%), striped maple seedlings (Acerpensylvanicum L.) underwent practically no mortality until the age of 15. Annual mortality was up (3.8%) between the ages of 16 and 40, then dropped to a lower level (1.6%). Mortality was age dependent and generally density independent. The survivorship curve agrees well with a pattern that could be expected of a species whose strategy is gap phase replacement.