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Historically, the goal of forest inventories has been to determine the extent of the timber resource. Predictions of how the resource was changing were made by comparing differences between successive inventories. The general view of the associated sample design was with selection probabilities based on land area observed at a discrete point in time. Time was not considered to be part of the sample design because it was not considered to be an element of the sampled population. Over the last few decades, the general goal of many national-scale forest inventories has been changing to monitoring the dynamic forest ecosystem. Here, we explore the inferential advantages of replacing the two-dimensional areal probability paradigm with a three-dimensional spatiotemporal probability paradigm. Our general discussion is augmented with a simulated example for estimating annual growth by diameter classes. Two assumptions of temporal indifference and remeasurement interval length indifference, which arose because of the two-dimensional view, are investigated through a simulation. The simulation compares and contrasts five estimators that differ in their reliance on those assumptions to make annual estimates. The results of the simulations often show those assumptions to be bias inducing. [ABSTRACT FROM AUTHOR]

Simple methods for estimating the proportion of land changing from forest to nonforest are developed. Variance estimators are derived to facilitate significance tests. A power analysis indicates that 400 inventory plots are required to reliably detect small changes in net or gross forest loss. This is an important result because forest certification programs may require additional precautions when wood from areas where forestland area loss is occurring is harvested or purchased. Net and gross forest area loss must be clearly differentiated to avoid confusion. Estimates of gross forest cover loss from satellite data should not be equated with net forest area loss, which can be better determined from remeasured forest inventory plots. Simultaneous tests of net and gross forest area loss should use multiple comparison procedures to ensure that overall error rates are correct. Examples of applications demonstrate how to properly perform these tests. A simulated example is used to verify that the variance estimators are reliable. An application to USDA Forest Service inventory data indicates that neither net nor gross forest loss at the state level was statistically significant for states that had sufficien remeasured plot data publicly available when this analysis was done. [ABSTRACT FROM AUTHOR]

Wildlife studies to determine preferred habitat often involve sampling used sites and making comparisons with unused background sites. We apply these data to a somewhat different purpose, which is to assess the spatial distribution of important habitat variables relative to spotted owl nest sites. It is necessary to compare habitat characteristics of used and unused sites to understand habitat preferences. However, ecological literature provides little guidance for selection of appropriate background sites necessary for such an analysis. We apply propensity score matching to telemetry gathered samples of spotted owl habitat for the purpose of weighting the selected background sites. This helps to ensure that important covariates have similar distributions in the used and unused habitat samples. We propose a two-stage process where propensity score matching of used and unused sites results in weights that are applied in the second stage modelling process. The objective is to quantify how wildlife responses to important variables change with distance from a nest, den site or other central location. The expectation is that this will strengthen guidance to managers who wish to protect or to improve wildlife habitat on their forest land. Example applications using spotted owl telemetry data demonstrate how to apply the methods and show the potential to elucidate habitat characteristics. [ABSTRACT FROM AUTHOR]

The transitioning of land from forest to other uses is of increasing interest as urban areas expand and the world's population continues to grow. Also of interest, but less recognized, is the transitioning of land from other uses into forest. In this paper, we show how rates of conversion from forest to non-forest and non-forest to forest can be estimated in the US from a continuously improving publicly available annual forest inventory database, under varying definitions of conversion. Two estimation approaches are considered and contrasted. The approaches are a simple ratio estimator and the weighted maximum likelihood estimator. The latter involves a statistical procedure that incorporates the binomial nature of the indicator variables, the transition of mapped plot conditions and an intuitively appealing way to combine data from varying remeasurement periods for a temporally dependent variable. [ABSTRACT FROM PUBLISHER]

Line transects are commonly used for sampling coarse woody debris (CWD). The USDA Forest Service Forest Inventory and Analysis programme uses a variant of this method that involves sampling for CWD along transects that radiate from the centre of a circular plot-like spokes on a wheel. A new approach for analysis of data collected with spoked transects is developed. This approach does not attempt to mimic traditional analysis methods for line transects, which do not readily apply to spoked transects. The method developed here generalizes to any number of spokes. We also demonstrate that there is a close relationship between spoked transects and a particular fixed plot design for sampling CWD. [ABSTRACT FROM AUTHOR]

The use of fixed-area plots for sampling down coarse woody debris is reviewed. A set of clearly defined protocols for two previously described methods is established and a new method, which we call the ‘sausage’ method, is developed. All methods (protocols) are shown to be unbiased for volume estimation, but not necessarily for estimation of population density in terms of number of down pieces. The new sausage method performs best overall in terms of minimum variance criteria. This review should also help establish a description of the major fixed-area plot sampling methods that will allow unambiguous application and description in future studies. [ABSTRACT FROM AUTHOR]

Forest certification is designed to assure consumers that the wood products they purchase come from sustainably managed forests. Certified forests must meet certain standards that vary with the certification scheme. However, certification generally promotes environmental objectives by restricting forest management options in ways that may reduce wood and fibre production and increase the cost of delivering wood to market. For example, some aspects of certification programmes can discourage creation of new forest plantations and application of herbicide and fertilizer. These restrictions have costs which often are difficult to quantify. Bounds on the opportunity costs of restricting silvicultural options are explored by comparing a natural pine regime to plantation management regimes with and without herbicide using some basic economic criteria. In this analysis, a plantation regime with herbicide had nearly four times the land expectation value (LEV) of a natural pine regime and almost double the LEV of a plantation without herbicide treatment. [ABSTRACT FROM PUBLISHER]

In the past decade, the United States Department of Agriculture Forest Service's Forest Inventory and Analysis Program (FIA) has replaced regionally autonomous, periodic, state-wide forest inventories using various probability proportional to tree size sampling designs with a nationally consistent annual forest inventory design utilizing systematically spaced clusters of fixed-area plots. This has resulted in significant changes in the spatial-temporal distribution of observations on the nation's forest resource. This paper discusses the resulting changes in the observation of the distribution of tree diameters measured at 1.37 m above ground level. We show that in three of the four FIA regions, a significant portion of the upper end of the diameter distribution has thus far gone unobserved by the new inventory design. We conclude that the reason is not that the larger diameter trees have become less common but rather that there is a low enough probability of observing these trees that they are not being observed. This postulate is supported by the observation that large-diameter trees are not missing from the data acquired by the fourth FIA region (the Pacific Northwest), which uses an additional sampling mechanism for large-diameter trees. We explore the implications of this effect in addition to potential solutions. [ABSTRACT FROM PUBLISHER]

Mapped plots are used for the national forest inventory conducted by the US Forest Service. Mapped plots are also useful for single ownership inventories. Mapped plots can handle boundary overlap and can provide less variable estimates for specified forest conditions. Mapping is a good fit for fixed plot inventories where the fixed area plot is used for both mapping and tree sampling. However, mapping can be done with a colocated fixed area plot even though the tree inventory uses variable plots. In fact, the tree measurement plots can be completely decoupled from the plots used for measuring condition proportions, although this is not recommended. [ABSTRACT FROM AUTHOR]

A volume change index is suggested that is derived from growth components that can be estimated from remeasured plots. The new index incorporates more information than the traditional growth over removals ratio. The new index directly indicates whether the standing volume will be increasing or decreasing if current conditions persist, whereas the ratio of growth over removals obscures the impact of mortality. The details of estimating the components of growth are discussed with regard to interpreting the new index. The effect of spatial scale on the index is explored and a variance estimator is suggested. The new index is estimated from US Department of Agriculture Forest Service annual inventory data for two example applications. The first application looks at spatial trends in the index. The second application applies the index to a mill working circle. [ABSTRACT FROM AUTHOR]

Alternative definitions for growth and removals from a forest being monitored over time are discussed. It is shown that the definitions that are used in practice may not be what one would expect and estimates can vary substantially under alternative definitions. This can result in conclusions about forest sustainability that may be misleading. Alternative definitions are applied to selected states using US Department of Agriculture Forest Service inventory data. Standard errors of growth over removals ratios are used to indicate potential sustainability problems for selected forest types. [ABSTRACT FROM AUTHOR]

A region can conceptually be tessellated into polygons at different scales or resolutions. Likewise, samples can be taken from the region to determine the value of a polygon variable for each scale. Sampled polygons can be used to estimate values for other polygons at the same scale. However, estimates should be compatible across the different scales. Estimates are often required for zones within a region, where a region might be a state and counties could be the zones. A method is developed for estimating high-resolution (pixel) values that are constrained to be compatible with results for lower resolution values. The high-resolution values are constrained to sum to totals for zones within a region, where the totals are being simultaneously estimated from measurements taken at a different scale. If the zone estimates are unbiased, then the pixel-based estimates for the zone will be less biased. Sums of pixels in arbitrary polygons are thereby constrained to approach unbiased estimates. Approximate variance estimators are developed for the summed pixel estimates. Two example applications are provided. The first example is based on simulated data and verifies that the proposed variance estimators give reasonable results. The second example estimates the volume in a circle around a possible mill site in North Carolina. This example uses publicly available US Forest Service inventory data and simulated inventory data that the mill would provide. [ABSTRACT FROM AUTHOR]