Using historic maps and citizen science to investigate the survival of old survey 'blaze' trees

Large old trees often possess important biodiversity and heritage values. This study investigated the occurrence and condition of survey reference trees in temperate woodland remnants in southern New South Wales, Australia. A citizen science method, in conjunction with a systematic examination of historic land maps, was carried out to locate historic survey reference trees for subsequent field survey of their biophysical attributes. 81 survey trees were found in a combined study area ~5000 km2, where an estimated 1.3–2.6% of the original number surveyed remain. Tree markings (‘blazes’) ranged 14 – 140 years in age, where most were 120 – 130 years old, and predominately Eucalyptus species. Blaze age was strongly correlated to the thickness of bark overgrowth. Types of reference trees identified included several PM (permanent marker) trees, a cemetery marker, a trig station and 15 benchmark (BM) trees used for watercourse surveys in the mid-1800s. Eleven BM trees located were related to 1928—1932 irrigation surveys and were previously undocumented. Many reference trees were found in roadside vegetation or in conjunction with clumps of other large trees on farms. Being a form of living heritage, our results show that survey trees are succumbing to the ravages of time.