Techniques for reducing edge bias are discussed and a new approach, termed the linear expansion method, is presented. This method is applicable to a wide variety of plot shapes and sizes and is unbiased under very general assumptions about the forest tree spatial pattern. The accuracy and efficiency of the linear expansion method were compared with (i) no edge bias correction and (ii) corrections by plot image translation techniques for several forest stands and spatial patterns. Results indicated translation and the linear expansion method behaved equally well on square plots 0.08 ha in size. As the plot size diminished or its shape deviated from square, the linear expansion method provided greater accuracy and lower bias than translation techniques. The linear expansion method also provided useful accuracy on circular plots where translation was not feasible.

To see if the Holocene optimum (4600 to 6000 yr before present) is an analogue for predicted future climate, a comparison was made between Sibenan paleovegetation for this Late Atlantic Period and predicted Siberian vegetation under climate change. S~berian paleovegetation is also compared to a current landscape map of Siberia. The Siberian Vegetation Model was used to estimate Siberian vegetation under climate change scenarios resulting from CO2 doubling. Both visual and statistical analysis of the maps indicate that the warm period known as the Holocene optimum does not provide a good analogy to predicted future warming. Although the predicted rise in temperature with future warming is similar to the Holocene optimum, the predicted precipitation is much less, resulting in much more temperate forest-steppe vegetation than the forest vegetation found in the past. Comparison of past and present vegetation revealed that most vegetation zones have not changed greatly in size or location, although species composition is quite different. Dark-needled species were widespread In the Northern and Middle T a~g a in the Holocene opt~mum, while light-needled species now dominate these zones. Temperate broad-leaved species were a component in the Subtalga In the mid-Holocene, whereas today they have disappeared. Tundra has greatly expanded since the Holocene optimum. These changes indicate that the current climatic regime is cooler and more severe than 4600 to 6000 yr ago.

We demonstrate the methods and results for broad-scale mapping of forest site productivity for the Canadian province of Alberta. Site index (SI) data were observed for lodgepole pine (Pinus contorta var. latifolia) based on stem analysis (observed height at an index breast height age of 50 years). A total of 2624 trees at nearly 1000 site locations were available for the analysis. Mapping methods were based on ANUSPLIN, Hutchinson's thin-plate smoothing spline in four dimensions (latitude, longitude, elevation, site index). Although this approach is most often used for modelling climatic surfaces, the high density of the site productivity network in Alberta made this an appropriate application of the method. Maps are presented for lodgepole pine, the major forest species of Alberta. Although map patterns were highly complex, predicted SI decreased regularly and continuously as elevation increased from the parklands, through the foothills, to the mountains, conforming to field observations and a shorter growing season. In the high mountains, SI predictions were the lowest (<10 m), again conforming to field observations. Thus, the map correctly represents the inverse relationship between SI and elevation exhibited in the data. Analysis of residuals revealed no bias in the predictions. Furthermore, residuals were homogeneous and had no apparent pattern. The standard deviation of the observed site index values was 3.23 m, and the root mean squared error of the spline surface predictions was 1.16 m.