摘要:

Seed dispersal ofArceuthobiumpusillumPeck onPiceamariana(Mill.) B.S.P. was studied at two locations in Minnesota from 1974–1980. Seed dispersal began as early as August 23 and was observed as late as September 27. Most seeds were dispersed in the mornings between 0400 and 0900. The mean annual distance of dispersal ranged from 1.0 to 2.3 m. The density of seeds trapped on the plots ranged from 4.2 to 16.7 seeds/m2. At both locations, the number of seeds trapped outside the stand decreased logarithmically with distance from the source trees. Within stands, seeds were more frequently trapped 1–4 m from source trees than under them. Most seed dispersal occurred 1-3 days after rain. Seeds were dispersed normally on 23 of 30 days when minimum temperatures were less than 0 °C. Fruit abortion was noted on four occasions. Insects were not found to carry dwarf mistletoe seeds.

ISSN:0045-5067    

DOI:10.1139/x86-001

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Laboratory studies with two leaf litter and one forest floor substrate showed that the herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), a 50:50 mixture of these, and glyphosate all had toxic thresholds at which they reduced decomposition. However, in all cases, the thresholds were > 50 times higher than residue concentrations that occur in the field after silvicultural herbicide treatments. In a field study at one site, no measurable 1-year postspray effects on litter decomposition were found among treatment plots sprayed at 0.0, 3.4 or 6.7 kg 2,4,5-T/ha.

ISSN:0045-5067    

DOI:10.1139/x86-002

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Sapling sugar maple (AcersaccharumMarsh.) trees were defoliated artificially at 10-day intervals beginning May 27 and ending August 5, 1981. Refoliation, terminal bud and shoot development, and xylem starch and sap sugar concentration were observed in defoliated and control trees. All defoliated trees refoliated, but decreasingly with later defoliation. Defoliation caused an acceleration in the rate of primordia initiation in terminal shoot apices. After early season defoliations, the developing buds in the axils of the removed leaves abscissed, but axillary and terminal buds on the refoliated terminal shoots survived through winter. In late season defoliation, most buds of refoliated shoots did not survive and the next year's growth depended on axillary buds formed prior to defoliation. Thus, when progressing from early to late defoliations, the next year's shoot growth depended decreasingly on the last-formed and increasingly on the first-formed portions of the previous year's shoot. Early October starch concentration in xylem decreased with later defoliation and was nearly absent in shoots and roots of trees defoliated in late July. There was not, however, a corresponding decrease in sap sugar concentration. Mortality occurred only in late defoliated trees and was associated with starch depletion.

ISSN:0045-5067    

DOI:10.1139/x86-003

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Various precipitation data, collected over a 13-year period, from different softwood and hardwood stands located at the Acadia Forest Experiment Station in central New Brunswick are evaluated to demonstrate differences between stands in their ability to alter the acidity of rainwater. In the soil organic horizons, retention and exchange processes are shown to be effective in altering the acidity of rainwater. Significant species effects in the quantities of water retained by the organic horizons are recognizable owing to differences in the quantities of organic materials accumulated under each stand and their moisture-retention characteristics. In turn, differences in the quantities of liquid retained in the organic horizons affect the residence time of the acid components of rain reaching the mineral soil. Major differences in chemical characteristics such as cation-exchange capacity, percent base saturation, and pH of the organic horizons suggest that the interactions of acid components of wet and dry deposition of air pollutants can be significantly different depending upon the species composition of stands.

ISSN:0045-5067    

DOI:10.1139/x86-004

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

To provide a method of quantifying brush competition in coastal Douglas-fir (Pseudotsugamenziesii(Mirb.) Franco) plantations, data from 124 planted trees, 1–5 years old, were used to derive a competition index for predicting changes in tree vigour measured as a relative production rate. The index, including measures of brush proximity, relative height, and percent ground cover, appears to act as a measure of light interception around the tree crown. Tree vigour was found to be largely a function of the age of the tree from planting and the competition index (r2 = 0.71). Foliage-based measures of growth vigour were more strongly related to the index than basal area or height measures. The index has potential for assessing interspecific competition problems in young Douglas-fir plantations.

ISSN:0045-5067    

DOI:10.1139/x86-005

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Four sites from two forests were examined to determine the effect of various levels of infection byArceuthobiumdouglasiion the growth ofPseudotsugamenziesiiin precommercially thinned stands. We found less than 1% mortality among the trees that we examined. Changes in level of infection did occur; we estimate that changes to levels of infection sufficient to cause significant reductions in diameter growth occurred among 19% of the infected trees that we studied. Height growth was significantly reduced in both forests, while diameter growth was reduced by infection in one forest. Trees of lower infection rating (dwarf mistletoe rating 0–2) showed a significant increase in radial growth following thinning in both forests, while more heavily infected trees (dwarf mistletoe rating 5 and 6) did not. Trees that were heavily infected and had spike tops consistently showed significant reductions in diameter growth in both forests.

ISSN:0045-5067    

DOI:10.1139/x86-006

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Nutritional problems, deficiencies of B and Zn in particular, have been tentatively identified as the cause of specific distorted growth symptoms in several young stands of Douglas-fir (Pseudotsugamenziesii(Mirb.) Franco), western hemlock (Tsugaheterophylla(Raf.) Sarg.), and Pacific silver fir (Abiesamabilis(Dougl.) Forbes) in southwestern coastal British Columbia. The most common symptoms associated with these apparent micronutrient deficiencies include leader dieback and discolouration, multileadered and bushy crowns, and, in severely deficient trees, swollen and distorted stems. Visual symptoms of apparent B deficiency become obvious when foliar concentrations are <5.0 ppm; visual symptoms of apparent Zn deficiency are less easily recognized, usually occurring when foliar Zn levels are less than approximately 9.0 ppm. Low foliar concentrations of B were often associated with low levels of Ca and Mg. Foliar B concentration was also correlated with total foliar S. Temporal variation in foliar nutrient levels, examined over 3 years, was quite high with an apparent strong relationship to growing season precipitation. This suggests that deficiencies of B and (or) Zn may be acute rather than chronic, with the appearance of periodic acute deficiencies being influenced by growing season soil moisture supply.

ISSN:0045-5067    

DOI:10.1139/x86-007

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

The response of root systems of four conifer species (Pinusstrobus,Pinusresinosa,Piceaglauca, andPiceamariana) to saturated soil conditions was examined in growth chamber experiments using 2- to 4-year-old nursery transplants potted into Plexiglas cylinders using a soil-containing mix. None of the conifers appeared adapted to grow roots into flooded soil, with the deepest roots of any species reaching only 10 cm below a water table after allowing time for maximum growth (30 days, 23 °C). Accordingly, anatomical observations of root cross sections indicated that none of the species had a significant internal air-filled pore space. There was a major difference between the pine and spruce genera in the response of aerobically grown roots to flooding. In both spruce species, no root tips survived flooding treatments longer than 1 day, whereas in both pine species, 35% or more tips survived even the longest (7-day) treatment. This difference could not be readily related to differences between these species in drainage preference in the field. Despite the much greater loss of root tips in the spruces, the postdrainage recovery of transpiration, after a depression during flooding, was as rapid in the spruces as in the pines.

ISSN:0045-5067    

DOI:10.1139/x86-008

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

Field experiments were conducted at a rural site in Millbrook, NY, to measure effects of ambient ozone on saplings ofPopulustremuloidesMichx. Over a 3–year period, four clones representing a range of pollutant sensitivities were exposed to charcoal-filtered and ambient air in open-top chambers. Ambient ozone significantly reduced (12–24%) aboveground dry-matter production and modified tree morphology, root/shoot ratios, and rates of leaf senescence. For two clones, biomass was reduced without visible foliar symptoms. This response raises the possibility of widespread, asymptomatic depression of forest productivity under ambient air pollutant conditions.

ISSN:0045-5067    

DOI:10.1139/x86-009

出版商:NRC Research Press    

年代:1986

数据来源: NRC

摘要:

A model of forest development has been adapted for the Pacific Northwest. The regeneration, growth, and death of individual trees are tracked for simulated 0.2 ha plots and tree attributes are aggregated to provide stand measures. The model includes the influence of temperature, soil moisture, light tolerance, and competition on tree growth. Long-term simulations for Douglas-fir dominated forests on the western Olympic Peninsula show that the stand is eventually dominated by western hemlock with silver fir being codominant. Even after 1200 years of subsequent stand development, silver fir fails to replace western hemlock indicating that this is a self-replicating and stable community. Fire, windthrows, insect disturbance, and clear-cut logging followed by replanting are incorporated into the model as single-event disturbances to a 500-year-old forest. For those cases where large Douglas-fir survive the disturbance, stand biomass and leaf area patterns are not significantly impacted until the death of the last large Douglas-fir. The projections were all carried out to the time when the forest is dominated by western hemlock and silver fir. At that time, the differential effect of the earlier disturbance is not apparent from the forest composition, biomass, or leaf area patterns except for the insect disturbance. Following the removal of all Douglas-fir by an insect, leaf area fluctuates regularly with a period of 600 years.

ISSN:0045-5067    

DOI:10.1139/x86-010

出版商:NRC Research Press    

年代:1986

数据来源: NRC