Basal Area Factor Research Articles

Comparison of three sampling methods in estimating stand parameters for a tropical forest

Three methods — fixed-area plot sampling using 100 × 7-m, 70 × 10-m, 50 × 14-m, 28 × 25-m, and 26.45 × 26.45-m plots; angle-count sampling based on the corners of these plots with a basal area factor of 9.3; and horizontal-line sampling using the long axis of the fixed-area plots with a diameter factor of 6.0 — are compared in terms of statistical efficiency in a sampling simulation study of a 60-ha forest in Surinam. For each method, 1000 iterations of ten sample locations with an expected number of 7.94 trees per location are used to estimate number of trees, sum of tree diameters, average tree diameter, total basal area, and frequencies of trees by 10-cm diameter classes. Fixed-area plot sampling is most efficient for number of trees; horizontal-line sampling for total basal area, sum of tree diameters, and average tree diameter. The angle-count method is best for number of trees by diameter class for the larger diameter classes; the fixed-area plot method is best for the smallest trees. All three methods are most efficient with sample locations based on square sample plots. A count sampling method combining the three methods using a long rectangular plots is recommended for practical purposes if interest is in all parameters except frequencies by diameter class, so that tree diameters do not need to be measured. If interest is in frequencies by diameter class, the angle-count sample trees should be measured to give the most reliable results.

Biomass Estimation for Four Common Grass Species in Northern Arizona Ponderosa Pine

Vegetation allometric relations were examined for 4 important grass species in southwestern ponderosa pine (Pinusponderosa). Logarithmic regressions were developed relating aboveground biomass to basal area, height, and number of seedheads, as well as 3 factors: overstory type (pole, yellow pine), burning treatment (unburned, prescribed burn 2-, 5-, and 7-yr previously), and site (3 locations). Basal area was defined as longest basal diameter multiplied by the widest perpendicular diameter. Of the metric variables, basal area proved to be the best predictor of biomass. Height and number of seedheads did little to increase Rl values. Burning treatment was a significant factor for Sitanion longejolium and Muhlenbe&a mon&na. Overstory type significantly affected Poa fenderiana and Festuca ankonica equations. Site effects were important for all but SuMion lonsefolfum When biomass regressions are used for species such as these, sampling efficiency can be improved by including factors such as overstory type, burning history, and locale. Final regression equations relating biomass of each species to basal area and significant factors were significant at 60.05 and had adjusted Rz values ranging from 0.81 to 0.87. A validation test using 20% of the data not used in developing the regressions indicated that these equations are adequate predictors. When used with double sampling, weight prediction based on basal area indices should provide a more objectively measured predictor than percent cover. Allometric relationships are often used to estimate understory biomass (e.g., Brown and Marsden 1976, Ohmann et al. 1981, Olson and Martin 1981). When compared with harvesting, the application of regression equations based on these relationships can result in lower sampling costs (or higher precision) due to relatively greater sampling efficiency (Reese et al. 1980). Most understory biomass equations are developed using fairly subjective ocular estimates of percent cover as the independent variable. Ocular estimates have the disadvantage of varying between observers as well as over time for a single observer, introducing unknown, but potentially substantial, error into the biomass estimates. We felt that using some combination of basal area, plant height, or number of seedheads might overcome these problems. A recent study of the effect of prescribed burning on understory production in northern Arizona (Andariese 1982), provided us with the opportunity to test this technique for a ponderosa pinebunchgrass type and to determine if overstory conditions, site, or burning treatment significantly alter the allometric relationship.

Evaluation of Methods for Sampling Gypsy Moth (Lepidoptera: Lymantriidae) Egg Mass Populations and Development of Sequential Sampling Plans

Plots of 0.01 ha and 0.04 ha (fixed-radius) and 10-prism and 20-prism basal area factor (BAF) (fixed- and variable-radius) were evaluated in relation to their efficiency for sampling gypsy moth, Lymantria dispar (L.), egg masses (GMEM) in 14 predominantly oak woodlots on the Eastern Shore of Maryland. Relative order of reliability for each sampling method varied with GMEM density. No difference in precision was seen between 10- prism and 20-prism BAF plots; however, the 20 BAF plot required 40% less time to survey. An analysis of cost and precision showed the 0.01-ha plots to be clearly superior to the other sampling methods throughout the range of GMEM densities evaluated. Based on a sample unit size of 0.01 ha, GMEM dispersion patterns were analyzed by Iwao's regression technique. Analysis indicated that egg masses were contagiously distributed, with single egg masses forming the basic component of the population. Parameters for the mean crowding and mean density regression were used to develop research-oriented and pest management-oriented sequential sampling plans with fixed levels of precision.

How much space does a seedling need?

A method is described to identify canopy trees which significantly affect regeneration at a given point, estimate the effect of these trees on the growth and survival of seedlings, and determine the maximum density of the canopy trees compatible with successful regeneration. All this information is obtained using point sampling done with several basal area factors from the same point. An example of the method's application is provided.

Distance to point-sampled trees and their diameters

The expected mean distance to point-sampled trees, E( r) , is a function of their average diameter, d , and the basal area factor F : E ( r) = d/(3√F) . This distance is independent of the diameter distribution of the sampled trees and of any other factor. The relation can be applied for comparison of circular plot and point sampling, investigation of stand structure, and competition among trees.

Evaluation of a Roadside Survey Procedure for Dwarf Mistletoe on Ponderosa Pine in Colorado

Tentative study areas were randomly Merrill, L. M., Hawksworth, F. G., and Johnson, D. W. 1985. Evaluation of a roadside survey chosen on the basis of the amount of procedure for dwarf mistletoe on ponderosa pine in Colorado. Plant Disease 69:572-573. dwarf mistletoe infection observed. A survey of dwarf mistletoe intensity on ponderosa pine (Pinusponderosa) was conducted along Presence or absence of dwarf mistl roadsides and on adjacent plots in the Roosevelt, Pike, and San Juan national forests in Colorado. was recorded for each 0.1 km of a strip Presence of dwarf mistletoe (Arceuthobium vaginatum subsp. cryptopodum) was recorded along one chain (20 m) wide and 1.6 km long on roads for each 0. 1 km of a strip one chain (20 m) wide and 1.6km long. Plots were then established the right side of the road in each study at 100-m intervals 40 m from and parallel to the same surveyed portion of the road. Regression of area. The study areas were grouped into plot data on roadside data was highly significant (R 2 = 0.88 for all national forests combined). The incidence categories by visual estimation roadside survey procedure can be reliable for estimating the proportion of ponderosa pine stands of the percentage of ponderosa pine with dwarf mistletoe if the road network provides a representative sample of the stands being infested with dwarf mistletoe: 1) none r surveyed. no visible infection, 2) low = fewer than one-third of the trees infected, 3) medium = one-third to two-thirds of the trees Dwarf mistletoes (Arceuthobium spp.) compared with results obtained from infected, and 4) high = more than twoare highly specialized, dicotyledonous more intensive surveys. Hawksworth (6) thirds of the trees infected. pathogens that damage many North found that incidence estimated from a Thirty-five study areas were estabAmerican conifers, including ponderosa roadside survey of ponderosa pine on the lished: three study areas in each dw pine (Pinus ponderosa Laws.). South- Mescalero Apache Reservation (New mistletoe incidence category in each of western dwarf mistletoe (Arceuthobium Mexico) was within 5% of that estimated the three national forests. (Only vaginatum (Willd.) Presl. subsp. crypto- from an intensive plot survey (9). Data study areas in the high-incidence category podum (Engelm.) Hawksw. & Wiens) is from an earlier roadside survey of were established in the San Juan National distributed throughout the central Rocky lodgepole pine (P. contorta Dougl.) Forest.) Within each study area, a row of Mountains and the Southwest (8). The conducted by Hawksworth in 1958 (7) plots (on the surveyed side of the road) pathogen causes extensive losses in were compared with those from a 1977 was established at 100-m intervals 40 m ponderosa pine stands through growth roadside/plot survey conducted by from and parallel to the road. At each reduction, mortality, tree deformity, and Johnson et al (10) in the Medicine Bow plot center, a fixed 0.004-ha circular plot reduction in cone and seed crops (13). National Forest in Wyoming. Estimates and a variable plot (basal area factor 2.3 Dwarf mistletoe also weakens its host, of incidence were 59% in 1958 and 60.5% m 2 /ha.) were established. Depending on increasing susceptibility to other pests in 1977. In addition, there was only 0.5% the curvature of the road, 13-17 plots (8). Information on dwarf mistletoe difference between the incidence observed intensity and distribution and estimates from the roadside (60.5%) and that wer loated infestudy area. of losses caused by dwarf mistletoes are observed in plots (60%) in the 1977 infected tree was present. Litne needed to assist the land manager in survey. Although the roadside survey regression analyses of the data were used making sound management decisions (2). technique is reliable where the forest type to compare the incidence of dwarf Dwarf mistletoe surveys have routinely is relatively continuous, the accuracy of combined plot survey information, this technique in discontinuous forest found in the plots 40 m from the road. designed to estimate volume loss, with types (i.e., ponderosa pine) was unknown. Data from each national forest were roadside reconnaissance surveys to Thus, this study was made to evaluate the analyzed separately. Data were also determine incidence and severity of the accuracy of roadside surveys for gopdacrigt h wr iteo

Is BAF 10 a Good Choice for Point Sampling?

Abstract The use of basal-area-factor (BAF)-5 and BAF-10 when point sampling in an Appalachian hardwood forest caused serious underestimation of sawtimber volume BAF's of 20 and 40 gave appropriate volume estimates and smallest mean-square errors. We recommend that BAF's 20 to 40 be used for sawtimber cruises. North. J. Appl. For. 2:23-24, June 1984.

Sampling Proportional to Size with Bitterlich's Mirror Relascope

SYNOPSIS A sampling study was carried out in four stands of Pinus radiata to test the accuracy and efficiency of Sampling Proportional to Size (SPS) with Bitterlich's mirror relascope. Basal area estimates derived from SPS-sampling were compared with those obtained in fixed radius sample plots of comparable size and indicated the occurrence of a positive bias. Additional studies were carried out in which the observed distance between the instrument and a test target at the position of coincidence served as study variable. They confirmed the existence of operator-bias for one of the two operators. Computer studies were carried out in stands with known co-ordinate positions of all trees and their diameters at breast height. The studies did not reveal bias associated with the location of the sampling point. Time studies indicated that measuring times for a basal area factor of k=4 are 53% of those for k=2. Walking times between sampling points were 67% of measuring times for k=4 and 35% of measuring times fo...

The Relative Efficiency of Some Forest Growth Estimators

The relative efficiencies of permanent-plot and point sampling estimators of forest volume growth are derived for completely random and clustered random tree spatial distributions. The relative efficiencies are found to be dependent on the spatial distribution and the relationship between tree volume growth and basal area. However, the relative efficiencies are independent of the area of the sample plot, the basal area factor of the sample point, and the average number of trees per unit land area. The plot sampling estimator is always more efficient if tree volume growth is independent of, or tends to vary inversely with, basal area. If tree volume growth tends to vary in proportion to basal area, there exists a critical coefficient of correlation that determines which estimator is more efficient. The point sampling estimator is more efficient if and only if the coefficient of correlation between tree volume growth and basal area exceeds the critical coefficient. The critical coefficient, which is always greater than zero and less than one, approaches zero as the spatial distribution becomes more clustered.

Comparison of Five Metric Basal Area Factors

Abstract Five metric basal area factors (1, 2, 2.5, 3, and 4) were compared at three sampling intensities (10, 20, and 40 points) for a 16.14-hectare pine-hardwood stand in Arkansas. Only 5 of the 15 possible combinations of basal area factors and sample intensities appeared to provide reasonable estimates of the true basal area distribution. These were factors 1, 2, 2.5, and 3 at 40 points each, and factor 1 at 20 points.

Aspects of statistical bias due to the forest edge: horizontal point sampling

A tree-concentric procedure is presented to eliminate edge effect statistical bias for horizontal point sampling. For known forest populations, the exact mean of the unbiased (adjusted for edge effect) and biased (unadjusted for edge effect) estimators of a forest characteristic can be determined along with the exact bias. Edge-effect bias is investigated for three forests that vary in area, four basal area factors (BAF), and three forest characteristics. Exact and estimated results based on 5000 random points were compared. Edge effect bias increases as the BAF decreases and varies with forest size, size and spatial distribution of trees, percentage of edge trees, and forest characteristic. The variance of the biased estimator was always smaller than the variance of the unbiased estimator. Using mean square errors, the biased estimator was found to be, in general, more accurate and the distortion of probability statements caused by the bias negligible for small to moderate sample sizes, especially for larger BAF's and certain forest characteristics.

Personal Bias in Forest Measurements

The assumption that measurement errors are negligible during a forest inventory was tested using forestry students. The magnitude of personal bias in measuring tree diameter at breast height (dbh), total height, and basal area per hectare was obtained. Bias was negligible in dbh measurements and the among-crew coefficient of variation (CV) was 8.16%. Heights were significantly underestimated and the among-crew CV was 21.86%. The percentage error in basal area per hectare determination was 4.09% at the 95% probability level, using a prism of basal area factor 6. Measurement errors are, in general, not negligible. Their magnitude should be estimated per inventory and included in the total error of the inventory estimate.

Selection of Basal Area Factor in Point Sampling

Abstract The basal area factor is preferably chosen by dividing the estimated stand basal area by the desired average tree count per sampling point. Bias may be introduced, generally in the form of overestimates, if the factor is varied from point to point in order to keep the count constant.

The Angle-Count Method

SUMMARY The basal area per acre at 77 sample points, estimated with Bitterlich's mirror relascope and with a wedge prism, has been compared with estimates derived from the conventional method of calipering trees in plots with fixed boundaries. Bitterlich's mirror relascope produced a negative bias of 4.5%, but unbiased estimates were obtained with a wedge prism, basal area factor 10.26. Bias was likely to be associated with the incorrect evaluation of borderline trees. Providing more contrast between the tree stems and the background did not improve the determination of the status of these doubtful trees and consequently did not serve a useful purpose. Random sampling in 5 stands showed that wedge sampling and calipering of trees in plots with a radius of 30 ft. both gave a coefficient of variation of 20% Time studies indicated that the time expended on calipering trees in 30 and 50 ft. plots increases curvilinearly with the number of trees per plot. For a given number of trees calipered, the average walk...