摘要:

Model-based ideas in finite-population sampling have received renewed discussion in recent years.Their relationship to the classical ideas in sampling theorydo not appear to be universally well understood by samplers in applied disciplines such as forestry, and ecology more broadly.The two inferential paradigms are constrasted, andexplanations are supplemented with examples of discrete aswell as continuously distributed populations. The treatment of spatial structureis examined, also.

ISSN:0045-5067    

DOI:10.1139/x98-166

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Each day, forest fire managers must deploy airtankers at initial attack bases to minimize initial attack response times. They must decide how many airtankers to deploy at each base and the initial attack range of each airtanker. We develop a daily airtanker simulation model and use it to investigate how airtanker system performance varies as a function of initial attack range, fire arrival rates, and time of day. Our results indicate that the optimal initial attack range decreases as the daily fire load increases. Fire managers can use this information to design airtanker dispatch policies that will minimize initial attack response times.

ISSN:0045-5067    

DOI:10.1139/x98-127

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Throughfall concentrations and fluxes were examined in an oak-hickory forest on the western ecotone of the eastern deciduous forest biome during 1989. Throughfall chemistry from event-based sampling of three stands was compared with the chemistry of incident precipitation. During the dormant season, only one of eight elements had significantly higher flux under the forest canopy relative to precipitation. During the growing season, six elements had significantly higher flux in throughfall relative to incident precipitation, and nitrogen had a significantly lower flux. Rates of dry deposition of pedogenically derived elements were high relative to forests further to the east, while rates of deposition of anthropogenically derived elements were low in comparison to these same forests. About 50% of the inorganic nitrogen in precipitation was taken up by the canopy, the highest value reported for an eastern deciduous forest. There were significant differences in throughfall chemistry among the three stands, possibly due to differences in canopy structure and (or) species composition. Multiple regression analysis of the throughfall patterns showed significant correlations of throughfall chemistry with the length of the antecedent dry period and rainfall quantity for all elements examined.

ISSN:0045-5067    

DOI:10.1139/x98-121

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Secondary ion mass spectroscopy and synchrotron X-ray fluorescence analysis have been used to document the changes in metal content across the ring system of trees from northern Canada. The results show a seasonal qualitative variation in the uptake of Na, Al, K, Ca, Cr, Mn, Fe, Cu, and Zn. Diffusional models show that locally elevated concentrations of selected metals are sufficiently stable within individual rings that variations in content among rings remain at detectable levels for at least a century.

ISSN:0045-5067    

DOI:10.1139/x98-131

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The soil seed bank of the low-value, pioneer tree pin cherry (Prunus pensylvanicaL.f.) appears to increase markedly after multiple, large-scale disturbance events, which may result in interference with the growth of high-value species. Seven northern hardwood forest sites of varying age and disturbance history in the White Mountains of New Hampshire were examined to quantify the patterns of accumulation and depletion of the pin cherry soil seed bank. The pin cherry seed bank accumulated in a predictable fashion based on pin cherry stem abundance. High- and low-density populations accumulated approximately 440 and 1900 viable seeds per pin cherry stem, respectively. Depletion of the seed bank appeared to be negligible in stands between age 40 and 60, and moderate (30% loss over 20 years) in stands between age 95 and 115. Short (e.g., 60-year) harvest rotation times may triple the size of the pin cherry soil seed bank, causing proliferation of this species with consequences for ecosystem and community dynamics, whereas longer rotation times of 120 years may allow enough depletion of the seed bank to stabilize population sizes.

ISSN:0045-5067    

DOI:10.1139/x98-133

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

The paper provides a framework to approach price and quantity determination in the roundwood market from a new perspective. In the spirit of the trade union literature, a model of timber price determination is formulated according to which the forest owners' association determines timber prices and then forest firms unilaterally decide on the timber to be used. The novelty here is to incorporate investment decisions of firms as a strategic factor into the model. The structure of the model is the following. The game is played in two stages. First, the forest owners' association and the firms in the forest industry decide on timber price and capital stock, respectively. In the second stage, the firms determine timber demand conditional on the timber price - capital stock game, so that the equilibrium concept is the subgame perfect Nash equilibrium. This game-theoretic model is applied to the annual data from the Finnish pulp and paper industry over the period 1960-1992. Estimation and testing results concerning the price and quantity determination of timber as well as capital stock behavior are generally favorable for the hypotheses presented. In particular, diagnostics and various test procedures indicate that these equations outperform conventional specifications derived from the theory of the demand for factors of production.

ISSN:0045-5067    

DOI:10.1139/x98-105

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Riparian forest strips are usually protected from logging for their buffer effect on aquatic habitats. However, their value to terrestrial wildlife species such as snowshoe hare (Lepus americanusErxleben) is unknown. From 1990 to 1996, we compared habitat characteristics (shrubs and saplings 0.25-2.25 m high), hare browsing, and hare pellet densities in five types of experimental riparian forest strips (20, 40, 60, and >300 m wide intact strips, and 20 m wide thinned strips), in a humid boreal balsam fir (Abies balsamea(L.) Mill.) landscape managed primarily for timber harvesting in Quebec. Based on coniferous and deciduous shrub densities, all riparian forest strips and adjacent clearcuts remained low-quality habitats for hare over 6 years following clear-cutting. Only 103 shrubs were browsed in a 1500-m2area sampled over 3 years, of which only 33 had >20% of browsed stems. Nevertheless, pellet data revealed a low but sustained use of all strips each summer and winter, and there were no changes over 6 years (mean 280 pellets/ha per month;P> 0.05). Whether hare populations are cyclic or not in our region remains an open question. However, they show some fluctuations and timber harvesting coincided with "high" hare populations in our study area. Sampling in "low" years might show that fewer hares occupy the forest strips. Further work is required to determine the influence of regional and local perturbations on the use of riparian forest strips by snowshoe hares.

ISSN:0045-5067    

DOI:10.1139/x98-110

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Amodel was developed to predict the severity of dwarf mistletoe (Arceuthobium tsugense(Rosendahl) G.N. Jones) in western hemlock trees (Tsuga heterophylla(Raf.) Sarg.) that developed within forests of Southeast Alaska that experienced near-catastrophic windthrow in the late 1800s. The model suggests that the degree of dwarf mistletoe severity on western hemlock trees was significantly and positively correlated with levels of dwarf mistletoe infection and basal area (m2/ha) in large and small residual trees that survived the wind disturbance. No significant relationships were found between severity level and any other factors, including site productivity, density of coexisting Sitka spruce (Picea sitchensis(Bong.) Carr.), or slope. The model demonstrates the overriding importance of infected residual trees to predict future severity of dwarf mistletoe; greater size and infection level of residual trees results in greater dwarf mistletoe levels on regenerating hemlock crop trees. The model, derived from 76 plots on Kuiu Island, was tested in 18 plots on Chichagof Island, providing a preliminary validation. Slower rates of dwarf mistletoe spread and intensification in forests of southeastern Alaska, as compared with similar coastal forests south of Alaska, provide an opportunity for managers to manipulate the parasite to desired levels in managed forests.

ISSN:0045-5067    

DOI:10.1139/x98-132

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Conventional top height estimates are biased if the area of the sample plot differs from that on which the definition is based. Sources of bias include a sampling selection effect and spatial autocorrelation. The problem was studied in relation to the use of data sets with varying spatial detail for modelling Douglas-fir (Pseudotsuga menziesii(Mirb.) Franco) plantation growth. Improved top height estimators, developed taking into account the selection effect, eliminated the bias. Bias was reduced, but not eliminated completely, when the estimators were tested using more highly autocorrelated eucalypt data.

ISSN:0045-5067    

DOI:10.1139/x98-128

出版商:NRC Research Press    

年代:1998

数据来源: NRC

摘要:

Conversion of natural broad-leafed evergreen forests into pure and mixed plantation forests in a subtropical area in China is a common practice in forest management. We investigated the effects of this conversion on litterfall, litter decomposition, and nutrient cycling. Monthly deposition of total N, P, K, Ca, and Mg through throughfall, stemflow, and various components of litterfall was investigated and compared over 3 consecutive years from January 1989 to December 1991 for both forests. The total annual fine litterfall over 3 years of observation was 4.8 t/ha in a pure plantation conifer forest of Chinese-fir (Cunninghamia lanceolata), 7.1 t/ha in a mixed plantation forest of Chinese-fir andSchima superba, and 13.3 t/ha in a natural broad-leafed evergreen forest ofCastanopsis kawakamii, respectively. The contributions of litterfall to the total nutrient fluxes were greater than those of throughfall and stemflow for all five nutrient elements in two contrasting forests of Chinese-fir andC. kawakamii. The results of this study demonstrate that natural broad-leafed evergreen forest has a greater capability of nutrient return, coupled with higher rates of litter decomposition and nutrient release, larger soil nutrient pools, and higher nutrient availability, than pure forest, suggesting that conservation of a natural forest is a necessary measure for maintaining woodland soil quality and primary productivity.

ISSN:0045-5067    

DOI:10.1139/x98-173

出版商:NRC Research Press    

年代:1998

数据来源: NRC