摘要:

An algorithm for cross-dating tree rings based on dynamic programming is presented. The algorithm considers all possible combinations of missing and double rings while minimizing a squared error loss function in relation to a reference chronology. There is a provision for the user to increase the penalty associated with inserting missing or double rings. Therefore, the algorithm is not totally objective and depends on informed user interaction and repeated application to perform successfully. The end result is a list of years where the algorithm suggests that missing or double rings have occurred.

ISSN:0045-5067    

DOI:10.1139/x90-028

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Old-growth population dynamics ofPicearubensSarg. were studied in a montane spruce–fir forest in North Carolina and Tennessee. Size-class structure fit a semilogarithmic rotated sigmoid curve typical of a stable population. Although the population contained trees of all ages, a large proportion of the population was less than 100 years old; few trees were greater than 350 years old. Mortality rates were estimated from a 2-decade census and from population structure data. For trees above breast height, annual mortality was approximately 1% of the population. Small trees (<30 cm dbh) and large trees (>60 cm dbh) had mortality rates exceeding 0.7% per year. Intermediate-sized trees tended to have low mortality rates (<0.5% per year) and high radial growth rates. Growth in the 10-year interval preceding death tended to be slow for standing dead trees. Standing death of canopy trees was more prevalent than death by windfall. These findings emphasized the influence of stand dynamics on spruce growth and mortality.

ISSN:0045-5067    

DOI:10.1139/x90-029

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Monthly samples of ectomycorrhizal mat soils from a maturing Douglas-fir forest and adjacent nonmat soils were collected and analyzed for respiration, acetylene reduction activity, denitrification rates, extractable ammonium, nitrogen mineralization, microbial biomass, temperature, pH, percent moisture, total phosphate, nitrogen, and carbon. Seasonal patterns suggested complex interactions among the host tree, ectomycorrhizal fungus, and the mat microbial community as influenced by seasonal changes in moisture, temperature, and light availability. The most dramatic changes in rates were found during moisture-temperature transition periods in the spring and fall. Respiration within the mat community was highest during the period when tree growth is normally the greatest (in the spring and fall). In addition, there was a major respiration peak observed in the winter that we hypothesize was caused by the utilization of labile carbon by microheterotrophs. Differences were also observed between mat and nonmat soils in respiration rates, microbial biomass carbon, acetylene reduction activity, and levels of mineralizable nitrogen, which were all generally higher in the mat soils, and pH and denitrification rates, which were generally lower in nonmat soils. There is also evidence that suggests that nitrogen is very tightly coupled within the mat communities.

ISSN:0045-5067    

DOI:10.1139/x90-030

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Long-term fire, climate, and vegetation data were used together with simulation models to estimate the effects of 20th century climate change and fire suppression on fire regime and organic-matter accumulation in mixed-conifer stands of Itasca State Park, northwestern Minnesota. Spatial and temporal patterns of fire occurrence and forest composition over the last 150 years determined by stratigraphic charcoal, fire-scar, tree-ring, and pollen analyses in separate studies provide evidence for vegetation and fire relationships. Water balances constructed from temperature and precipitation data collected since 1840 were used to model fire probability and intensity of burn before fire suppression which began in 1910. Existing patterns of biomass accumulation in forest-floor, herb, shrub, and tree components were compared with fire history and topographic variability to provide a spatial perspective on fire effects. Simulation models used these relationships to estimate (i) how accumulation of organic matter had changed through the past under the different fire regimes that prevailed on different topographic aspects, (ii) the changes brought about by fire suppression in 1910, and (iii) the fire regimes and their effects that would have prevailed since fire suppression with the warm–dry climate of the 20th century. Humus, litter, shrubs, and herb cover were less abundant and more variable spatially and temporally before fire suppression. Spatial variability in forest-floor organic matter, which resulted from different fire frequencies in different vegetation and topographic settings before fire suppression, was largely gone by 1920 as a result of fire suppression. Had fire suppression not been instituted in 1910, fire frequency would have increased by 20–40% in the 20th century because of warmer and drier conditions. Forest-floor oganic matter would have been largely depleted by frequent and severe fires exposing mineral soils, particularly during the drought years of the 1930s. Herb biomass would have increased, shrubs would have been more variable, and tree seedling establishment would have been substantially altered. Time required for buildup of fuels limits the extent to which increased moisture deficits increase fire frequency.

ISSN:0045-5067    

DOI:10.1139/x90-031

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Water relations, stem girth, and crown vigour were measured in jarrah (EucalyptusmarginataDonn ex Sm.) trees in adjoining areas of healthy and dieback-affected forest. The soil-borne fungusPhytophthoracinnamomiRands was recovered from soils in the dieback areas, but not from neighbouring healthy forest. Trees on dieback sites were found to be more water stressed (with lower dawn water potentials and daytime stomatal conductances) than healthy trees on nearby areas free ofP.cinnamomi. Severe water stress usually preceded crown deaths by several weeks to months. Dawn water potential and midday stomatal conductance were the most useful nondestructive indicators of dieback severity in declining trees. Subjective assessment of crown form was slightly less reliable than water relations as a separator of dieback and healthy trees. Changes in trunk girth were the least sensitive indicators of dieback severity. Midday stomatal conductance is recommended as a useful tool for monitoring short-term changes in vigour of dieback-affected trees.

ISSN:0045-5067    

DOI:10.1139/x90-032

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Robiniapseudoacaciastem annual growth rings from 1958 to 1987 were analyzed for14C content. The radioactivity of annual rings was found to be strongly correlated with14C concentration in the atmosphere, which showed a very sharp rise until 1963 due to nuclear weapon tests followed by a regular decrease from then on. Taking into account seasonal variations in both atmospheric14C concentration and CO2assimilation slightly improved the relation between14C in wood and the atmosphere. A predictive curve that gives the year of wood formation as a function of radioactivity with a 5% confidence interval is shown. These results can be used to analyze wood for which traditional analysis is impossible, for example, trees with false rings or missing rings, or wood from stumps or roots.

ISSN:0045-5067    

DOI:10.1139/x90-033

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Container-grownLarixlaricina(Du Roi) K. Koch seedlings were inoculated with the ectomycorrhizal fungusLaccarialaccata(Scop, ex Fr.) Berk and Br. and grown under two levels of slow-release fertilizer (Osmocote) or two levels of soluble fertilizer (N–P–K). Nonmycorrhizal seedlings grew better under high fertility regimes, whereas no significant differences were observed between low and high fertility levels for the mycorrhizal seedlings. Mycorrhizal seedlings had significantly greater root length, total biomass, and a lower shoot:root ratio under all fertility treatments. Ectomycorrhizal development was excellent regardless of fertilizer treatment. Nitrogen, P, K, Ca, and Mg concentrations were significantly higher in the mycorrhizal seedlings than in the nonmycorrhizal seedlings under all fertility regimes.

ISSN:0045-5067    

DOI:10.1139/x90-034

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

not available

ISSN:0045-5067    

DOI:10.1139/x90-035

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

We classified red spruce (PicearubensSarg.) sites from northern Maine by radial growth release history. Two major releases were apparent for a majority of the sites. The first was a reduction and subsequent increase in radial increment in 1920. The second was an increase in radial increment from 1935 to 1955. Red spruce radial growth reduction in the 1960s is apparent only for sites released from 1935 to 1955 (approximately 54% of the sites in this study). These sites are now approaching the radial growth rates of the unreleased stands. Birch dieback is suggested as a probable contributor to the 1935–1955 red spruce growth increase and subsequent 1960s growth reduction.

ISSN:0045-5067    

DOI:10.1139/x90-036

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A simple protocol for the extraction of total DNA from minute amounts of tissues and subsequent amplification of specific sequences by polymerase chain reaction is presented. The method is applicable to a wide variety of vegetative tissues such as leaves, single needles and rootlets, cell suspensions, and also single sexual embryos and megagametophytes derived from a variety of gymnosperms and perennial angiosperms. Amplification of DNA is shown using pairs of primers specific to genes that encode the small ribosomal subunit.

ISSN:0045-5067    

DOI:10.1139/x90-037

出版商:NRC Research Press    

年代:1990

数据来源: NRC