Restoration of the 1936 statewide forest survey of Minnesota: Data description and comparisons with 2014 forest conditions

Long-term forest plot datasets have proven invaluable for understanding the changing conditions and ecology across Minnesota’s 17.3 million acres of forestland. Data from past and present USDA Forest Service (USFS) Forest Inventory and Analysis (FIA) program efforts are of high quality and are informed by thousands of field plot observations for each survey. Unfortunately, only the data from 1977 to the present is available in electronic format with full detail; the earlier plot records have been lost. The aim of this study was to locate historic forest records for Minnesota, identify useful data, and develop methodologies for digitizing and restoring data to a usable format. Over 300 stand and stock tables and summary of volume tables for Minnesota
were restored from the first FIA Lake States forest survey conducted between 1930 and 1938. The level of detail of the data varied, but included area of forest cover types and stand size classes, and number of trees and volumes per acre by individual species. This report is primarily intended as a reference for describing how the data was located, restored, digitized and compared with current FIA data, including overcoming limitations in the available data.

Included with this documentation is a set of comparisons of various forest conditions over an eighty-year period using the restored dataset and FIA data for Minnesota from 1977 and 2014 inventories. The results showed that overall statewide comparisons using the historic data were most complete and more dependable than comparisons made at survey unit and per-acre scales. Total forest area in Minnesota increased by 1.8 million acres during the eighty-year period, much of that due to the recovery of lands categorized as brush lands in the 1930s. The stand size class distribution in the 1930s was also dominated by an abundance of young stands, and pine forests were more common than hardwood stands across the state. Today the situation is somewhat reversed, with older forest common over large areas, less conifer acreage and much increased standing volume and hence biomass. Both merchantable volume and total cubic volume have increased three-fold since 1936. Additionally, ownership has shifted by nearly five-million acres to more public ownership today than eighty years ago. Historic volume summary tables have provided sufficient detail to develop meaningful comparisons with current FIA data, establishing linkage to the 1977 and more recent reports.