Tree survival and growth in the highlands of central Argentina: Impact of wildfires and land management

Abstract

High-mountain forests of subtropical and tropical South America are dominated by Polylepis trees. Forest fragmentation is believed to result from human-caused wildfires, livestock grazing and deforestation. Since the 1900s, management of Polylepis forests has included the establishment of conservation areas. We assessed survival and growth of P. australis trees in central Argentina, examining wildfires and land management effects. We monitored 880 trees over 15 years (2003–2018) in 139 plots distributed across conservation and ranching areas. Tree survival rate was 99.2 % yr− 1, net height growth 1.4 cm yr− 1, and crown dieback 17 %. Fire affected 16 % of plots in ranching areas and 25 % in conservation areas. Compared to unburned plots, fire damage resulted in a 3 % yr− 1 reduction in survival rate, a 4 cm yr− 1 reduction in height growth, and a 15 % increase in crown dieback. Land management did not affect survival, growth, or crown dieback when controlling for wildfire incidence. However, survival rate and net growth were 0.3 % and 0.6 cm lower in the conservation areas than in ranching areas when wildfire incidence was considered. Plot tree cover was not linked to survival but was positively associated with net growth, elevation was positively associated with survival and negatively with net growth, and tree height was negatively associated with both survival and growth. No logging evidences were observed. We conclude that wildfires are the primary human-induced impact on P. australis trees; therefore, strengthening fire reduction policies is crucial.