Wildﬁre activity and land use drove 20th-century changes in forestcover in the Colorado front range

Rodman, Kyle; Veblen, Thomas; SARACENI, SARA; CHAPMAN, TERESA

Recent shifts in global forest area highlight the importance of understanding the causes andconsequences of forest change. To examine the inﬂuence of several potential drivers of forest cover change,we used supervised classiﬁcations of historical (1938–1940) and contemporary (2015) aerial imagery cover-ing a 2932-km2study area in the northern Front Range (NFR) of Colorado and we linked observed changesin forest cover with abiotic factors, land use, and ﬁre history. Forest cover in the NFR demonstrated broad-scale changes 1938–2015 and overall cover increased 7.8%, but there was notable spatial variability andmany sites also experienced Forest Loss. Recent (1978–2015) wildﬁre was the largest single driver of ForestLoss, with ﬁres burning 14.3% of the total study area. Recently burned areas showed net losses of 36.9%forest cover. Reasons for Forest Gain were more complex, with elevation, past mining density, ﬁre history,and topographic heat load index being the strongest predictors of increases in forest cover. Historical min-ing activity is one of the dominant anthropogenic impacts in ecosystems in the NFR and it had a complex,non-linear relationship with 20th-century changes in forest cover. Subalpine stands originating after stand-replacing ﬁres circa mid-1800s to early 1900s showed some of the greatest gains in forest cover, indicativeof slow and continuous post-ﬁre recovery through the 20th century. We also investigated factors such asland ownership, road density, forest management activities, and development intensity, which playeddetectable, but more minor roles in observed change. Twentieth-century changes in forest cover through-out the NFR are a result of ecological disturbances and anthropogenic inﬂuences operating at varying time-scales and overlaid upon variability in the abiotic environment.