摘要:

The15N-enrichment technique for estimating biological nitrogen fixation inCasuarinaequisetifoliaJ.R. & G. Forst. was evaluated under field conditions in single-species and mixed-species plantings (with a nonfixing reference species,Eucalyptus×robustaJ.E. Smith) between ages 6 and 24 months in Puerto Rico. Trenched and untrenched quadrats within the plantations were labelled at 6-month intervals with15N-enriched ammonium sulfate at a rate of 0.2 g15N•m−2•year−1(2.0 g N•m−2•year−1). Analyses of foliar and whole-tree (weighted average) N-isotope ratios, based on periodic nondestructive and whole tree harvests, were used to estimate the proportion of nitrogen derived from biological dinitrogen fixation (PNDFA) and total nitrogen derived from fixation (TNDFA) inCasuarina. These results were compared with those obtained using the nitrogen difference method. The15N-enrichment technique yielded consistent estimates of biological nitrogen fixation inCasuarinawhen either foliar or whole-tree N-isotopic data were used to calculate PNDFA and TNDFA. Estimates of PNDFA inCasuarinawere similar for trenched monoculture and mixed-species quadrats, and in trenched and untrenched quadrats where the reference species (Eucalyptus) was interplanted with the N-fixing species. However, the results indicate that eucalyptus grown in small, untrenched monoculture quadrats is an inappropriate reference for estimating PNDFA inCasuarina. During the first 2 years after plantation establishment,Casuarinaobtained from 48 to 67% of its nitrogen from the atmosphere based on foliar and whole-tree sampling. This amounted to between 82 and 94 kg•ha−1•year−1in the monoculture treatment and between 39 and 62 kg•ha−1•year−1in the mixed stands withEucalyptus. These results also were in close agreement with estimates made using an N-difference method.

ISSN:0045-5067    

DOI:10.1139/x94-030

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The 5-year height and diameter growth response of a frost-tolerant species, (lodgepole pine,Pinuscontortavar.latifoliaDougl. ex Loud.) and a frost-susceptible species (hybrid spruce,Piceaglauca(Moench) Voss ×Piceasitchensis(Bong.) Carr.) to different vegetation-control site-preparation treatment and timing combinations was examined using a factorial experiment. The site chosen for the experiment is subject to frequent summer growing season frosts. The vegetation control treatments were: an untreated control, manual cutting, and glyphosate applied at the rates of 1.4 and 2.1 kg active ingredient (a.i.) per hectare. Each vegetation-control treatment was applied at four dates (timing) that covered the active growing season of the vegetation on the study area. Vegetation-control method had a major impact on the growth of the planted seedlings. The influence of timing of control treatments on growth was found to be minor. Fifth-year height and diameter in the manual cutting and control treatments were equally poor. Growth was significantly improved by both levels of chemical vegetation control and after 5 years, no differences were apparent between the two. Pine height and diameter and spruce diameter continually improved as the level of thimbleberry (RubusparviflorusNutt.) was reduced. Below 5% thimbleberry cover, this growth increased dramatically, suggesting a response threshold. As vegetation cover was lowered, however, spruce seedlings were damaged by frost, resulting in reduced total height. In this case, better height growth was associated with either very low or moderately high thimbleberry cover than with moderate to low levels.

ISSN:0045-5067    

DOI:10.1139/x94-031

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

This research measures technical efficiency among methods of pulpwood harvesting in the southern United States in 1979 and 1987. An econometric frontier production function is modeled using analysis of covariance methods, which results in consistent estimates of method effects. Employed efficiency measures isolate economies of scale from what can be termed pure technical efficiency. Harvesting methods utilizing either extremely low or high capitalization levels were the most technically efficient. Longwood grapple skidder systems were the most efficient, and intermediate systems least efficient. This suggests a noncontinuous improvement in harvesting technology that has investment implications for small producers interested in upgrading low capitalization systems. Scale economies represented only a small percentage of the total efficiency effect, the rest being attributed to efficiency of method. Thus, too much emphasis may be placed on the impacts of scale economies when analyzing structural change in the industry. Efficiency measures correlate well with the observed evolution of the industry over the period and conform with the predictions of economic theory.

ISSN:0045-5067    

DOI:10.1139/x94-032

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Age and size structures were determined in 40 stands of black spruce (Piceamariana(Mill.) B.S.P.) growing on peatlands and transitional peatlands in northeastern Ontario, Canada. Natural and second-growth stands representing several site types were examined. The age structure of natural black spruce stands varied from even aged in young stands (<160 years) to uneven aged in older stands. Uneven-aged black spruce stands on nutrient-poor peats appear to be self perpetuating in the absence of intense disturbance. Natural stands on more fertile peats or on transitional peatlands are less likely to escape disturbance and more likely to undergo succession to other species. Second-growth stands, which originated after forest harvesting 50–70 years ago, were uneven-aged, although a high frequency of stems commonly occurred in the age-class associated with the time of harvesting. The age and size structures of second-growth stands currently differ from that of natural stands, but will likely become similar to natural stands over time.

ISSN:0045-5067    

DOI:10.1139/x94-033

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A 2 × 4 set of factorial treatments of stump removal in combination with nitrogen fertilization was applied to 0.04-ha circular plots within a clearcut on the west slope of the Cascade Range (44°21′N, 122°39′W). Treatments included stump removal (either all stumps removed or the plot left undisturbed) and broadcast fertilization with ammonium nitrate (0, 336, 672, or 1345 kg N•ha−1). Diameter at breast height and height of Douglas-fir (Pseudotsugamenziesii(Mirb.) Franco) seedlings, planted 4 months after treatment, were recorded five and nine seasons after outplanting. Soil bulk density in the upper 20 cm was measured with a single-probe neutron densimeter. Stump removal reduced the number of seedlings killed by laminated root rot (Phellinusweirii(Murr.) Gilb.) but had no significant effect on seedling growth. Stump removal increased soil bulk density only 7% as measured 9.7 years after treatment. Fertilization increased the growth in diameter at breast height, and height growth of the seedlings. Elevated total soil nitrogen could still be detected on fertilized, nonstumped plots 9.7 years after treatment.

ISSN:0045-5067    

DOI:10.1139/x94-034

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The relative preferences of snowshoe hares for native and exotic tree species and the relationship of these preferences to nutritional constituents and phenols have important forestry management implications. Thus, feeding preferences of confined snowshoe hares (LepusamericanusErxleben) for Siberian larch (Larixsibericus(Endl.) Sabine ex Trautv.), Norway spruce (Piceaabies(L.) Karst.), white spruce (Piceaglauca(Moench) Voss), and black spruce (Piceamariana(Mill.) B.S.R) were examined under two experimental ad libitum feeding conditions. At the end of experiment 1, two-year-old Siberian larch and Norway spruce were equally selected by hares. Twigs and stems of Siberian larch, however, were browsed almost exclusively during the first few days of the experiment, while white spruce was browsed very little at all. Siberian larch was richer in crude protein and lower in fiber than white spruce and Norway spruce, whereas Norway spruce was lower in condensed tannins and total phenols than the other two species. In experiment 2, twigs and stems of 4-year-old black spruce were preferred to those of white spruce. Black spruce contained significantly higher concentrations of crude protein, calcium, and phosphorus and lower concentrations of cellulose and total phenols than white spruce. Overall, white spruce was most resistant to hare damage, though the lack of preference was not reflected in either low nutrient or high tannin values. In fact, concentrations of condensed tannins and total phenols had no antifeedant effects.

ISSN:0045-5067    

DOI:10.1139/x94-035

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Forest inventory data collected in 1987 from the Kenai Peninsula, Alaska, were used to explore whether or not such data can be used to evaluate dynamics of a spruce bark beetle (Dendroctonusrufipennis(Kirby)) infestation there. The utility of the inventory data as an evaluation tool is shown by performing analyses equivalent to those performed by other researchers in smaller scale studies conducted on the Kenai Peninsula and comparing results. Analyses showed that extensive forest inventory data can be used to estimate areas of infestation and to establish relations among tree diameter, recent radial growth, tree stocking, state of beetle attack, and stage of infestation. Understanding of spruce bark beetle infestation dynamics on broad, regional scales, can be achieved while also obtaining extensive forest inventory data.

ISSN:0045-5067    

DOI:10.1139/x94-036

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Crown class, site class, and breast-height age were incorporated into Kozak's variable-exponent taper equation (A. Kozak. 1988. Can. J. For. Res. 18: 1363–1368) for three species: Douglas-fir (Pseudotsugamenziesii(Mirb.) Franco), western red cedar (ThujaplicataDonn), and aspen (PopulustremuloidesMichx.). For lodgepole pine (PinuscontortaDougl.), crown ratio, breast-height age, and quadratic mean diameter were incorporated into Kozak's taper equation. The effects of adding these variables to the exponent part of the taper equation on the prediction abilities of the taper model were assessed for prediction of diameter inside bark along the stem, total tree volume, and tree merchantable height. It was found that apart from the use of crown ratio for lodgepole pine, the additional variables resulted in only marginal improvements to the published version of Kozak's taper function. Therefore, the cost of measuring these additional variables is not justifiable.

ISSN:0045-5067    

DOI:10.1139/x94-037

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Vegetation and aboveground biomass and nutrient capital (N, P, K, Ca, and Mg) were examined in a 22-stand, 75-year chronosequence within an angiosperm-dominated forest in Nova Scotia. Stands 20 years old and younger originated with clear-cutting, whereas older stands originated with wildfire. Early successional, ruderal species of vascular plants were prominent for ca. 5 years after clear-cutting, but they occurred as a part of a diverse, species-rich community dominated by more-tolerant species, many of which survived the disturbance of clear-cutting. The rate of accumulation of aboveground biomass averaged 2.2 t•ha−1•year−1during the first 11 years after clear-cutting, 4.7 t•ha−1•year−1between 11 and 30 years, and then decreased to 1.5 t•ha−1•year−1between 30 and 75 years. Foliage biomass recovered to a quantity typical of mature stands within only 3–5 years of disturbance, as a result of the vigorous growth of both ground vegetation and stump sprouts of certain tree species. The patterns of accumulation of N, P, K, and Mg were similar to that of biomass, except that initially their relative rates of accumulation were faster because of the large proportion of nutrient-rich foliage in young stands. The accumulation of Ca was relatively slower, because of its large concentration in tree bark, a tissue whose proportion in the aboveground biomass reached a maximum much later than did foliage.

ISSN:0045-5067    

DOI:10.1139/x94-038

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

An extensive rhizome system is an important aspect of the morphology and architecture of salmonberry (RubusspectabilisPursh) and of its potential for regrowth following disturbance. Seasonal activity of the rhizome system was studied by collecting rhizome segments monthly from February through October 1988 and February 1989 from four sites. Total nonstructural carbohydrate content was determined and segments were incubated in a growth chamber to determine periodicity of shoot and root production. The number and dry weight of shoots peaked in February and March, declined from April through June when aboveground shoot growth was greatest and were generally low through the dry summer months. Root production was highest from August through October and generally lower the rest of the year. Total nonstructural carbohydrate content was highest during the dormant season and dropped to the lowest level in midsummer. Shoot production was more closely associated with total nonstructural carbohydrate content than was root production. The significant reduction in shoot production potential suggests a time in the annual growth cycle when the species capacity for regrowth following disturbance is at a relatively low level.

ISSN:0045-5067    

DOI:10.1139/x94-039

出版商:NRC Research Press    

年代:1994

数据来源: NRC