Composite Site Productivity Index (CSPI) v3.1.0: North American extension with a continent-wide ESI surface (CONUS + Canada)

Version 3.1.0 extends the CSPI release across North America. It inherits all v3.0.0 CONUS products (ESI v7, Asym v9 corrective surface, parent material overlay, component layers) and adds a continent-wide site-index (ESI) surface spanning the conterminous United States and Canada. New in v3.1.0: (1) NorthAmerica_ESI.tif, a ~4 km climate-model site-index surface covering CONUS and Canada wall-to-wall (median 26.5 m), from the North America ClimateNA model trained on the joint compilation including ~16,000 Canadian site-index plots (within-Canada cross-validated R^2 = 0.85, RMSE 5.1 m; CONUS CV RMSE ~3.7 m). (2) NorthAmerica_ESI_uncert90.tif, a quantile-regression-forest 90% PREDICTION interval half-width: it reflects plot-to-plot variation in site index within a climate neighborhood (wide, median ~22 m, because climate explains only part of plot-level site index) and is NOT a confidence bound on the mapped mean; the surface's validated accuracy is the cross-validated RMSE above, and a calibrated per-pixel confidence interval is deferred to a future version. (3) NorthAmerica_ESI_borealmask.tif flags pixels above 55 N where the training envelope thins and predictions warrant added caution. (4) Acadian_ESI.tif, a 1 km cross-border detail surface for Maine and New Brunswick. (5) The revised North American manuscript. Scope note: the surface is a climate-based site-index product, not a biomass or composite product; the Canadian biomass-growth and asymptotic-biomass components await true-coordinate inventory remeasurement. The Canadian analysis uses the open Multi-Agency Ground Plot (MAGPlot) Database; Canadian plot-level outputs are keyed by site identifier with coordinates withheld. License CC-BY-4.0.