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1.
Two new density estimators for k-tree distance sampling are proposed and their performance is assessed in simulated distance sampling from 22 stem maps representing
a wide range of natural to semi-natural forest tree stands with random to irregular (clustered) spatial distribution of trees.
The new estimators are model-based. The first (Orbit) computes density as the inverse of the average of the areas associated
with each of the k-trees nearest to a sample location. The area of the k-th tree is obtained as a prediction from a linear regression model while the area of the first is obtained via a Poisson probability
integral. The second (GamPoi) is based on the expected distribution of distance to the k nearest tree in a forest where the local distribution of trees is random but the stem density varies from sample location
to sample location as a gamma distribution. In a comprehensive assessment with 17 promising reference estimators, a subset
composed of Morisita’s, Persson’s, Byth’s, Kleinn’s, Orbit, and GamPoi was significantly better, in terms of relative root
mean square error (RRMSE), than average. GamPoi emerged as the better estimator for sample sizes larger than or equal to 30.
For smaller sample sizes, both Kleinn’s and Morisita’s appear attractive. 相似文献
2.
A new composite k-tree estimator of stem density 总被引:1,自引:1,他引:0
Steen Magnussen 《European Journal of Forest Research》2012,131(5):1513-1527
This study presents a generally applicable and robust k-tree composite estimator of density. We propose to estimate stem density by a weighted average $ \left( {\hat{\lambda }_{\text{aic}} } \right) $ of 16 individual density estimators. The weights given to individual estimators are inversely proportional to the relative fit (Akaike’s corrected information criterion) of each estimator to the assumed distribution of observed k-tree distances. The performance of the proposed estimator is evaluated in simulated simple random sampling with k?=?3 and 6 in 58 forest stands (54 actual and 4 simulated) and 600 replications. Sample sizes were 15 and 30 locations per stand. Eleven estimators were novel, including three designed for regular spatial patterns. Absolute stand-level bias with k?=?6 varied from 0.1 to 8.1% (mean 1.8%), and a bias larger than 6% was limited to 3 stands with either pronounced density gradients or a strong clustering of stem locations. Root mean squared errors were approximately 16% (k?=?6 and n?=?15) versus 12% for sampling with comparable fixed-area plots. Coverage of computed 95% confidence intervals ranged from 0.72 to 0.99 (median?=?0.98 with n?=?15 and 0.95 with n?=?30), with 98% of all intervals achieving a coverage of 0.85 or better. In seven stands used in an assessment of a novel spatial point pattern reconstruction k-tree density estimator (RDE) by Nothdurft et al. (Can J For Res 40:953–967, 2010), the average absolute bias of $ \hat{\lambda }_{\text{aic}} $ with k?=?6 was 1.5 versus 0.7% for $ \hat{\lambda }_{\text{RDE}} $ . 相似文献
3.
A generalized difference, a model-calibrated (MC), and a pseudo-empirical likelihood (PEMLE) kNN estimator of a population mean and its sampling variance was assessed with simulated simple random (SRS) and one-stage cluster sampling (CLU) from three artificial and one actual multivariate populations. The number of nearest neighbors (k) for imputing values of a target variable varied from one to eight. The design-based MC estimator had the lowest bias, but bias varied among populations and target variables. In terms of root mean squared errors (RMSEs), the estimators had similar performance, yet RMSEs of MC and PEMLE were less variable. Results were uneven across populations and target variables. The value of k had little effect on RMSE suggesting an advantage of choosing a low value that retains most of the attribute variance in a map. Nominal confidence intervals computed from MC estimators of variance achieved overall the best coverage rate. Rankings of the estimators in SRS and CLU designs were similar. We recommend MC for practical kNN applications in forest inventories for pixel-level predictions and derived estimates. 相似文献
4.
Forest inventory relies heavily on sampling strategies. Ratio estimators use information of an auxiliary variable (x) to improve the estimation of a parameter of a target variable (y). We evaluated the effect of measurement error (ME) in the auxiliary variate on the statistical performance of three ratio
estimators of the target parameter total τ
y
. The analyzed estimators are: the ratio-of-means, mean-of-ratios, and an unbiased ratio estimator. Monte Carlo simulations
were conducted over a population of more than 14,000 loblolly pine (Pinus taeda L.) trees, using tree volume (v) and diameter at breast height (d) as the target and auxiliary variables, respectively. In each simulation three different sample sizes were randomly selected.
Based on the simulations, the effect of different types (systematic and random) and levels (low to high) of MEs in x on the bias, variance, and mean square error of three ratio estimators was assessed. We also assessed the estimators of the
variance of the ratio estimators. The ratio-of-means estimator had the smallest root mean square error. The mean-of-ratios
estimator was found quite biased (20%). When the MEs are random, neither the accuracy (i.e. bias) of any of the ratio estimators
is greatly affected by type and level of ME nor its precision (i.e. variance). Positive systematic MEs decrease the bias but
increase the variance of all the ratio estimators. Only the variance estimator of the ratio-of-means estimator is biased,
being especially large for the smallest sample size, and larger for negative MEs, mainly if they are systematic. 相似文献
5.
The spruce bark beetle, Ips typographus, is one of the most extensively studied European forest pests. Gaps exist in the knowledge about second generation breeding
performance in bivoltine populations. In this study, the breeding performance of the second generation was evaluated in three
bivoltine populations of I. typographus in the SE Alps. Length of the maternal galleries (from 40.5 to 44.8 mm), population growth rate (PGR; from 0.7 to 3.6), and
emerged adults per m2 (from 669 to 1,570 insects/m2) varied among populations and were negatively correlated with bark colonisation density. Pheromone traps set up in the three
investigated forests differed in the number of trapped beetles, with mean captures ranging between 5,310 and 19,850 insects
per trap. The populations giving the highest captures in the traps showed the lowest bark colonisation density (248 vs. 489
maternal galleries per m2) and the best breeding performance. The populations of parasitoids and predators corresponded to just 1–9 and 2–10% of the
emerging I. typographus adults, respectively, and phloem temperature never reached thresholds lethal to I. typographus. Interspecific competition was negligible, whereas intraspecific competition was found to be the main factor affecting the
breeding performance of the second generation, although with different intensity according to the colonisation density. It
is hypothesised that competition with the first generation and spring precipitation influence the number of suitable hosts
available to the second generation. 相似文献
6.
Matthias Scheuber 《European Journal of Forest Research》2010,129(5):825-832
The k-nearest-neighbour (knn) method is known as a robust nonparametric method. It is used to estimate unknown values of data sets by means of similarity
to reference data sets with known values. The spectral information of satellite remote sensing data can be used to provide
the common characteristics in the knn estimation process. In forest sciences, the knn method is studied for its application potential. Some application examples are: (1) the estimation of parameters such as
basal area, stem volume, number of trees per diameter class and tree species; (2) the estimation of forest debris and non-wood
goods and services; (3) the production of wall-to-wall information for modelling, risk management and logistics. On the other
hand, different limitations with respect to methodological characteristics as well as the selection of suitable parameters
must be taken into consideration. The scope of this article concentrates on the discussion of the application potential and
limits of the knn method in forestry with particular emphasis on management planning needs. The study is based on data taken from a forest
inventory (FI) covering a test site near Rottenburg, in southwest Germany. Analysis results are compared with the traditional
outcome of inventory data analysis and partly presented in thematic maps, which show identical spatial distribution patterns.
For the map of six tree species, a map accuracy of 52.2% was found. The user’s accuracy for the prevailing tree species was
between 52.6% for Picea abies and 69.4% for Quercus sp. A timber volume map for Quercus sp. clearly visualises the bias at the extreme ends of the volume distribution. The root mean square error (RMSE) for the
total timber volume estimate was 30.9% for k = 5 and could be reduced to 22.6% for k = 20. For Quercus sp., however, the respective RMSE values were between 106.5 and 84.8%. Significant differences between FI and knn estimates
were mainly found for rare classes with minor representation in the reference data. 相似文献
7.
Lukáš Varga Peter J. Fedor Martin Suvák Jozef Kiseľák Ekrem Atakan 《Journal of pest science》2010,83(3):319-327
Numerous occurrence of Echinothrips americanus Morgan, 1913, a relatively newly established pest in European greenhouses, on a wide spectrum of cultivated plants throughout
Slovakia has encouraged us to present current data on its food ecology. Analysing 1,650 plant species, the poinsettia thrips
was found on 106 species (48 families) including 19 showing sporadic, 75 moderate and 17 high infestation. Larvae were detected
on 25 plant taxa from 13 families, most of them being new hosts. Mature clusters of Acalypha hispida, showing moderate to high infestation level and carrying both larvae and adults, were selected for more detailed statistical
evaluation. Preference of adults for upper and lower leaf surface tends to be without statistical significance, the larvae
on the contrary were strongly related to the lower side (Pearson’s χ2 = 13.3552, P = 0.0013). Concerning the age, increased occurrence was apparent on younger leaves for both larvae and adults. For larvae
the nonparametric test gives the statistical difference between three age categories of leaves with the following values:
Kruskal–Wallis χ2 = 6.6384, P = 0.03618. The statistical significance of age seems to be more crucial for younger shoots, as proved by the statistics for
both larvae (Kruskal–Wallis χ2 = 8.4852, P = 0.0144) and adults (Kruskal–Wallis χ2 = 7.1049, P = 0.0287). Different food preferences of larvae and adults may result in specific approach when applying an effective biological
or chemical control. Narrower tolerance of larvae could make them more manageable target in plant protection instead of efforts
to control the whole thrips population. 相似文献
8.
Steen Magnussen 《Journal of Forest Research》2014,19(1):194-204
A new species richness estimator applicable to probability sampling with fixed-area (a) plots in a finite-area (A) population is presented and tested in simulated sampling from three stem-mapped forest compartments, and from six large collections of forest inventory data. The estimator of richness is the average number of species per plot times the sum—over the N = A/n plots in a population—of the probability (p m ) of observing a new species in the mth plot (m = 1,…, N). A Cauchy distribution function is used to capture trends in p m . The parameters of the Cauchy distribution were estimated by optimizing a weighted maximum likelihood function. In comparison to five presumed best alternative estimators, the new estimator was ‘average’ with respect to bias, but best in terms of average root mean squared error. Taking the average of the estimates of richness produced by the five alternate and the new estimator would, generally, keep bias below 15 %. With relatively large sample sizes, the bias is moderately small (<10 %). 相似文献
9.
Since the end of the glacial age, Picea koyamae has been sparsely distributed in Japan as a relict species and is presently threatened with extinction. We investigated the
population structure and genetic structure of nine populations of P. koyamae. Population size was assessed at 9–135 individuals in habitats ranging from 0.5 to 11.5 ha, and seedlings and saplings were
observed in all but one particular population, which had a Sasa-type (bamboo grass) forest floor. The effective number of alleles per locus (N
e) within peripheral populations in the Yatsugatake Mountains was 1.8–2.7, much lower than that of core populations in the
Akaishi Mountains (2.8–4.3) using five nuclear simple sequence repeat loci. This finding suggests that genetic variation in
these populations has been reduced by isolation from other populations. The standardized genetic differentiation among populations
(G′
st
) was 0.410 and higher than that found in other Japanese conifers, suggesting that isolation and inbreeding have progressed
in this species. In two isolated populations at the Yatsugatake Mountains, the fixation index (F
is
) was 0.315–0.354, much higher than the values determined for the other populations (−0.188 to 0.263). This suggests that
these two populations have survived several generations while increasing the degree of inbreeding. However, the highest seedling
density was in a population with low genetic variation and high F
is
. The most serious problems at present appear to be the declining number of mature trees and the deterioration of suitable
environments for seedling establishment. 相似文献
10.
Sofia Leal Vicelina B. Sousa Sofia Knapic José Luís Louzada Helena Pereira 《European Journal of Forest Research》2011,130(6):1023-1029
Cork oak (Quercus suber L.) has a dense wood that allows high-quality uses. In the present work, we study the influence of vessel characteristics,
measured through image analysis and optical microscopy, on wood density, measured using X-ray microdensitometry, on 40-year-old
trees. Vessel area increases with cambial age (5403–33064 μm2), while wood density decreases (1.229–0.836 g/cm3). The number of vessels is relatively constant at 6 vessels/mm2, while vessel proportion in cross-section increases from 3.3% near the pith to 20.5% near the bark. In growth rings closest
to the pith, with high wood density and low vessel area, the relationship between the two variables is linear (R
2 = −32.1%, P < 0.01) but with increasing tree age and vessel size, the wood density remains rather constant, suggesting that decreases
in density might compromise mechanical support of the tree at a stage when the increase in cross-sectional area alone might
not provide mechanical stability. Other anatomical characteristics not considered in this study, like large xylem rays that
increase with cambial age, may be responsible for the constant density. 相似文献
11.
Soil properties under an exotic plantation (Pinus caribaea) and an indigenous plantation (Podocarpus imbricatus) were compared with adjacent secondary forests and abandoned land in the tropical forest areas of Jianfengling National Nature
Reserve in Hainan province, southern China. The surface soil (0–0.2 m) under Pi. caribaea has higher bulk density, lower soil organic carbon, total N, total K, available N, microbial biomass carbon, and smaller
soil microbial communities (as indicated by soil Biolog profiles) than under Po. imbricatus. Both land use types showed negative cumulative soil deterioration index (DI) compared to secondary forests. However, compared
to abandoned land (DI = –262), the soil quality of Po. imbricatus showed improvement (DI = –194) while that of Pi. caribaea showed deterioration (DI = –358). These results demonstrated that these exotic pine plantations can significantly and negatively
influence soil properties. By contrast, our results showed that adoption of indigenous species in plantations, or natural
regeneration, can improve soil quality. 相似文献
12.
India is the largest grower of Eucalyptus with an area of 3.943 million hectares under plantations and E. tereticornis is the predominant species in the plains of southern India with an average productivity of 12–25 m3 ha−1 year−1. With the aim to establish seedling seed orchards of the species, seed lots of fifteen provenances were imported from Australia
and a trial was laid. In the present study the genetic diversity existing in the seed orchard was estimated using ISSR–PCR.
Seven ISSR primers amplified 663 amplicons in the size ranging from 255 to 2,711 bp. The total number of polymorphic bands
varied from 59 to 123 with 100% polymorphic banding profiles. The average gene diversity (Hj) of all the provenances ranged from 0.0589 to 0.1109 and the total gene diversity estimated was low (H
T = 0.130) when compared to the earlier reports from other eucalypts species. Analysis of Molecular Variance partitioned the
ISSR variation into inter and intra population components. The inter population component accounted for 55.2% of the variation
and the intra population component accounted for 46.3% (P < 0.001). A neighbour-joining analysis was done using the dissimilarity matrix to determine the aggregation of the individuals
into clusters. Existence of population structure among the populations was revealed in STRUCTURE analysis but geographical
region based clustering was not observed. The assessment of intra and inter genetic variation documented in the present study
suggests that, along with the phenotypic traits, knowledge about genetic diversity measured at the DNA level in individuals
of seed orchards provide an objective guide for selective culling of trees for maintaining optimal diversity for enhanced
genetic gains. 相似文献
13.
A simultaneous estimation procedure for the parameters of two functions, i.e., the maximum size–density line and the self-thinning
curve, is presented to predict stand development for fast-growing tropical species. This procedure assumes that the rate of
periodic reduction in stand density with increasing quadratic mean diameter on a logarithmic scale (r) will increase inversely proportionally to the distance from the maximum size–density line and consequently equals the slope
of the line at distance 0. Under this assumption, the maximum size–density line can be incorporated into the self-thinning
curve to form an integrated equation with three parameters: k and m, the slope and constant of the maximum size–density line, and a, the rate of reduction of r of the self-thinning curve. These parameters are estimated simultaneously using measurement data on stand density, quadratic
mean diameter, and the corresponding r. This procedure was evaluated by application to two data sets: 186 measurements of Acacia mangium and 95 measurements of Paraserianthes falcataria, for which the parameters k and m have previously been calculated. The parameters estimated using this procedure were in good agreement with previous ones
based on the A. mangium data set, and the differences found for the P. falcataria data set were also small, within the error variances. Therefore, it is concluded that the proposed procedure would give almost
the same estimates from a single calculation step as the previous procedure that required two separate calculation steps. 相似文献
14.
Dhiraj Naik Durgeshwer Singh Varsha Vartak Sharayu Paranjpe Sujata Bhargava 《New Forests》2009,38(1):99-115
Gmelina arborea is an important timber-yielding tree that grows naturally in the tropical and subtropical regions of Southeast Asia and has
also been introduced as a plantation species outside these regions. Genetic diversity in this tree species was observed in
stone/seed-related traits and in vitro responses of cultured nodal segments from plants of eight different populations representing
natural forests, fragmented forests and plantations. Variance analysis showed significant differences between populations
for these traits. However, it was not possible to separate the different populations using these traits by multivariate analysis,
even after environmental variation was reduced over six subcultures. Genetic diversity was therefore analysed using molecular
markers. Inter-simple sequence repeat (ISSR) primers yielded 95% polymorphic loci among the eight populations and UPGMA analysis
enabled separation of these populations on the basis of their genetic distances. Diversity was also analyzed using population
genetics parameters like Nei’s genetic diversity and gene differentiation. Nei’s genetic diversity was 0.29 between populations
and 0.11 within populations. AMOVA analysis indicated 41 and 59% within- and between-population genetic diversity, respectively.
Mantel test suggested that genetic differentiation between six Indian populations was positively correlated to geographic
distance (r = 0.626, P = 0.029). Assessment of the genetic variation in G. arborea populations is an important step in selection of conservation strategies for this species since diversity forms the basis
for species adaptation. 相似文献
15.
The extent of genetic variation in seed and seedling traits of Trigonobalanus doichangensis, a rare and endangered tree in southwest China, was evaluated at the population level. Seeds were collected from four natural
populations in the south and southwest Yunnan province, China. Significant differences (P < 0.05) between populations were observed in seed length, seed weight and seedling morphological characters. The analyses
revealed that none of the seed and seedling traits had significant correlations with the geo-climatic variables of the populations.
Among seed and seedling traits, significant correlations (P < 0.05) were discovered among seed length, seed weight and height of 30-day-old seedlings. Significant correlation (r = 1.00, P < 0.01) occurred also between the height and root collar diameter of 4-year-old seedlings. With the exception of seed width
and seed germination percentage, 51–96% of total variation in other seed and seedling related traits was attributed to population
effect, as determined by the broad sense heritability. In conclusion, these observations on variation in seed and seedling
traits should be a reference point, when considering seed collection of this species for ex situ conservation and species
restoration. 相似文献
16.
Priscila Ambrósio Moreira Walter Steenbock Nivaldo Peroni Mauricio Sedrez dos Reis 《Agroforestry Systems》2011,83(2):245-256
Bracatinga (Mimosa scabrella) is a legume tree species common in the early stages of succession in Araucaria angustifolia forests in southern Brazil. Bracatinga can form high-density monospecific stands called bracatingais. Its traditional management for charcoal production involves maintenance of the seed bank. Our objective was to analyze the
genetic diversity and structure of bracatingais to understand the mechanisms by which intraspecific diversity of M. scabrella is created and maintained in landscapes managed by family farmers in their agroforestry mosaics. We analyzed 14 bracatingais using 8 allozyme loci. We compared parental and progeny generation indices (7 loci) and described the mating system (9 loci)
of two progenies. Overall diversity was high: A = 2.69, H
o = 0.257, H
e = 0.382 and similar between populations. Overall fixation (F = 0.364) was similar to the fixation index (f = 0.329). The genetic divergence among populations was low (Θp = 0.052) but significant. The progenies’ genetic diversity values were similar to those of the previous generation (H
e pop11 = 0.342 vs. 0.420/H
e pop10 = 0.432 vs. 0.400). Progenies were compatible with half-sib and full-sib crossing expectations (θ
xy
= 0.204 and 0.194). Our data showed that there is a tendency for genetic structuring caused not only by the reproductive
system but also by genetic drift. It is very likely that the high genetic diversity is amplified by internal migration within
each bracatingal. This study showed that current landscape management can contribute to maintaining high levels of bracatinga genetic diversity, which contributes to its regional conservation. 相似文献
17.
The two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), and the onion thrips, Thrips tabaci Lind. (Thysanoptera: Thripidae), are significant field pests of potato in the Ardabil region of Iran. Orius niger (Wolf.) and O. minutus (L.) (Hemiptera: Anthocoridae) are locally the predominant natural enemies of these pests. This study compared the functional
responses of O. niger and O. minutus to female mites and second instar thrips larvae across a range of prey densities (5, 10, 20, and 40 prey/arena) under controlled
conditions of 24 ± 1°C, 50 ± 5% RH and 16:8 h (L:D). The resulting data were appropriately fit to Type II functional response
models in four predator–prey interactions, including: (1) O. niger to second instar thrips larvae (a = 0.009 h−1; and T
h = 1.62 h); (2) O. niger to females mites (a = 0.006 h−1 and T
h = 1.28 h); (3) O. minutus to second instar thrips larvae (a = 0.008 h−1 and T
h = 1.93 h) and (4) O. minutus to females mites (a = 0.01 h−1 and T
h = 1.1 h). The number of second instar thrips larvae attacked by O. niger was greater than that by O. minutus (P ≤ 0.01); conversely, the number of females mites attacked by O. minutus was greater than that by O. niger (P ≤ 0.01). These results confirm the potential for both O. niger and O. minutus to make valuable contributions to a biological control program against onion thrips and the two-spotted spider mites infesting
potato fields in this region. 相似文献
18.
Allometric models for estimation of aboveground carbon stocks in improved fallows in eastern Zambia 总被引:2,自引:1,他引:1
This paper presents allometric functions for estimation of C stocks in aboveground tree biomass in 2-year-old improved fallows
in eastern Zambia. A total of 222 individual trees representing 12 tree species were destructively harvested for C analysis
by LECO CHN-1000 analyzer. Allometric models relating collar diameter (D10) and total tree height (H) to stem and total aboveground C stocks were developed using data from tree fallows. Logarithmically
transformed power functions displayed a good ability to stabilize variance of aboveground C stocks and showed a good fit (84 < R
2 < 99) with a bias of 0.7–3.6%. D10 alone and in combination with H explained most of the variability in total aboveground C stocks. Validation of the species-specific
and generalized models with field data indicated that they accurately predicted aboveground tree C stocks. Generalized C estimation
functions were also validated and described 73–97% of variability in aboveground C stocks with an average unsigned deviation
of 1.5–4.9%. The C functions will serve as a vital tool for predicting and monitoring C pool sizes in long-term studies and
agroforestry projects, especially where destructive sampling is not possible. 相似文献
19.
Heat-induced colour changes of pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) wood 总被引:4,自引:0,他引:4
Bruno Esteves António Velez Marques Idalina Domingos Helena Pereira 《Wood Science and Technology》2008,42(5):369-384
Heat treatment of Pinus pinaster and Eucalyptus globulus wood was carried out by hot air in an oven for 2–24 h at 170–200°C and by steam in an autoclave for 2–12 h at 190–210°C.
The colour parameters L*, a* and b* were determined by the CIELAB method on radial, tangential and transverse sections of untreated and treated wood, and their
variation with regard to the treatment (ΔL*, Δa* and Δb*) were calculated in percent. For untreated eucalypt wood, lightness (L*) varied between 54.1 and 63.8% with a* between 7.4 and 8.5, and b* between 15.7 and 19.9. For untreated pine wood, L* varied between 67.3 and 76.1%, a* between 6.9 and 7.6 and b* between 16.3 and 24.1. Oven heat-treated wood became darker (ΔL* about 50% for 4% mass loss), and this was more for eucalypt wood under the same treatment conditions. In general, the contribution
of red (a*) and yellow (b*) colour decreased with heat treatment. The transverse section of the two species darkened less for both the treatments with
small differences between radial and tangential sections. Lightness decrease was related to chemical changes; with good correlations
with glucose (R
2 = 0.96), hemicelluloses (R
2 = 0.92) and lignin (R
2 = 0.86). As regards colour, the heat treatments showed an interesting potential to improve the wood quality for solid timber
products from pine and eucalypt. 相似文献
20.
E. Shibata 《Journal of Forest Research》2003,8(2):0123-0126
To establish a sampling procedure for estimating the density of bamboo galls induced by Aiolomorphus rhopaloides Walker (Hymenoptera: Eurytomidae) in a stand of bamboo Phyllostachys heterocycla (Carr. Mitf.) (Monocotyledoneae: Gramineae), 5–12 bamboo culms were cut at random in late March of each year during 1998–2001
just before gall-maker emergence. The number of galls on the branches of each bamboo culm was counted. The spatial patterns
of the galls on the culms in the stand and on the branches within each culm were measured by Iwao's patchiness regression.
Galls were distributed contagiously both on culms and on branches. Current bamboo culms that emerged the previous summer did
not require sampling because no galls were observed on them. Except for this, there was no difference in gall density on young
and old culms, suggesting that it is not necessary to distinguish them. There were few (<4%) galls above 6 m height during
the 4 years. There was no significant difference in gall density up to 4 m and above 4 m, suggesting that branches up to 4 m
can be sampled with confidence. Kuno's two-stage sampling method at different precision levels showed that the number of culms
to be sampled varied with gall density. For example, at mean density m = 1.0 per branch when the number of sampled branches per culm is 10, a total of 24 culms is required to estimate gall number
at a precision level of D = 0.2, where D is the ratio of standard error to mean.
Received: July 10, 2002 / Accepted: November 25, 2002
Acknowledgments I thank Dr. K. Kamijo for insect identification. Thanks are also due to the members of the Laboratory of Forest Protection
for their kind help with the fieldwork. This study was supported in part by a Grant-in-Aid for Scientific Research (No. 11460068)
from the Ministry of Education, Culture, Sports, Science and Technology, Japan. 相似文献