Rapid digitization to reclaim thematic maps of white-tailed deer density from 1982 and 2003 in the conterminous US

Abstract

Background Despite availability of valuable ecological data in published thematic maps, manual methods to transfer published maps to a more accessible digital format are time-intensive. Application of object-based image analysis makes digitization faster. Methods Using object-based image analysis followed by random forests classification, we rapidly digitized choropleth maps of white-tailed deer (Odocoileus virginianus) densities in the conterminous US during 1982 and 2001 to 2005 (hereafter, 2003), allowing access to deer density information stored in images. Results The digitization process took about one day each per deer density map, of which about two hours was computer processing time, which will differ due to factors such as resolution and number of objects. Deer were present in 4.75 million km2 (60% of the area) and 5.56 million km2 (70%) during 1982 and 2003, respectively. Population and density in areas with deer presence were 17.15 million and 3.6 deer/km2 during 1982 and 29.93 million and 5.4 deer/km2 during 2003. Greatest densities were 7.2 deer/km2 in Georgia during 1982 and 14.6 deer/km2 in Wisconsin during 2003. Six states had deer densities ≥9.8 deer/km2 during 2003. Colorado, Idaho, and Oregon had greatest increases in population and area of deer presence, and deer expansion is likely to continue into western states. Error in these estimates may be similar to error resulting from differential reporting by state agencies. Deer densities likely are within historical levels in most of the US. Discussion This method rapidly reclaimed informational value of deer density maps, enabling greater analysis, and similarly may be applied to digitize a variety of published maps to geographic information system layers, which permit greater analysis.

Regaining the History of Deer Populations and Densities in the Southeastern United States

“…Overall in the southeastern United States, white‐tailed deer population size increased from a minimum of <215,000 during 1915–1930 (Blackard 1971) to 304,000 by 1940 (Newsom 1969), 476,000 by 1950, 2.41 million by the 1960s (Newsom 1969), 2.94 million to 4.12 million by approximately 1970 (Blackard 1971), 6.17 million by 1982, to 10.79 million or about 12 million by approximately 2003 (for 2005 in Adams and Ross 2015 and Southeast Deer Study Group 2002–2006; Tables 1 and 2). Please note that similar results during 1982 and 2003 for the continental United States, including the southeastern states, are presented in Hanberry and Hanberry (2020). Mean deer densities in the southeastern United States increased from 0.22 deer/km 2 during 1940 (Newsom 1969), 0.35 deer/km 2 during 1950 (1950 map), 2.2 to 3.1 deer/km 2 during approximately 1970 (Blackard 1971, 1970 map), 4.6 deer/km 2 during 1982 (1982 map), to 8 deer/km 2 or 9 deer/km 2 during about 2003 (for 2005 in Adams and Ross 2015 and Southeast Deer Study Group 2002–2006).…”

“…Population estimates from distribution maps overall were similar to estimates from other sources, and may be no worse, considering the uncertainty involved. Nationwide estimates also matched well with other sources of estimates (Hanberry and Hanberry 2020). For the Southeast Deer Study Group (2002–2006), reported mean deer densities typically ranged considerably from year to year or did not change at all.…”

“…The 1950 (A), 1970 (B), 1982 (C), and 2003 (D; 2001 to 2005) mean statewide deer densities (deer/km 2 ) in the southeastern United States (modified from Hanberry and Hanberry 2020). …”

“…Following the methodology of Hanberry and Hanberry (2020), to estimate population numbers from the densities and distributions, we applied an approximate continental United States population estimate of 30 million at year 2000 to calibrate population estimates for the 2003 United States map (Webb 2014). To produce this value from the 2003 map, we used the least value for each density class (i.e., 5.8, 11.6, 17.4 deer/km 2 ), except we used a value of 1.85 deer/km 2 for the low density class.…”

Effects of white‐tailed deer exclusion on the plant community composition of an upland tallgrass prairie ecosystem

“…Because bison herbivory reduces C 4 grass dominance it offsets the effects of fire on plant species richness (Hartnett et al, 1996; Collins et al, 1998; Knapp et al, 1999; Fuhlendorf and Engle, 2004; Spasojevic et al, 2010). However, with the decline of historical bison populations (Lott, 2002) and the increase of woody encroachment and fragmentation in these grasslands (Briske, 2017), browsers such as white‐tailed deer ( Odocoileus virginianus ; hereafter deer) have increased in density (Hanberry and Hanberry, 2020). The shift in herbivore pressure from the grazing pressure of bison to the browsing pressure of deer could be playing a large role in restructuring the plant community composition in present‐day North American tallgrass prairie.…”