Indeed, some biologists feel that western clones could be as old as 1 million years (Barnes 1966, 1975). In the semi-arid western United States, some argue that widespread seedling establishment has not occurred since the last glaciation, some 10,000 years ago (Einspahr and Winton 1976, McDonough 1985). tremuloides in eastern North America are very common, but generally less than 0.1 ha in size, while in areas of Utah, groups as large as 80 ha have been observed (Kemperman and Barnes 1976). According to an Organisation for Economic Co-operation and Development (OECD) report in 2000:Д¬lonal groups of P. While Pando is the largest known aspen clone and its age has received considerable attention, other large and old clones exist. Rogers and Jan Е ebesta surveyed other vegetation within Pando besides aspen in 2019, finding additional support for their 2018 conclusion interactions between browsing and past and ongoing management have had adverse effects on Pando's long-term resilience to change. Paul Rogers and Darren McAvoy, also with Utah State University, completed the first comprehensive assessment of Pando's status in 2018 and stressed the importance of reducing herbivory by mule deer to conserving Pando for the future. Genetic sampling and analysis in 2008 by Jennifer DeWoody, Carol Rowe, Valerie Hipkins, and Karen Mock of Utah State University and the University of Southampton confirmed the earlier analyses and increased the clone's estimated size from 43.3 to 43.6 ha. Both teams of researchers described Pando as a single asexual reproduction organism based on its morphological characteristics. Michael Grant, Jeffrey Mitton, and Yan Linhart of the University of Colorado at Boulder re-examined the clone in 1992, naming it Pando and claiming it to be the world's largest organism by weight. Pando was identified in 1976 by Jerry Kemperman and Burton Barnes. 4.1 Additional references from OECD quote in history section.This decline in recruitment of young stems began in the 1980s and has been attributed primarily to mule deer ( Odocoileus hemionus), though Pando also undergoes restricted grazing by domestic cattle ( Bos taurus) and is potentially browsed by elk ( Cervus canadensis). In areas of Pando lacking adequate protective fencing, grazing animals have prevented Pando from developing enough young stems to fully replace existing older stems as they die. The Western Aspen Alliance is studying the tree in an effort to save it in collaboration with the United States Forest Service. Pando's long-term survival is uncertain due to a combination of factors including drought, human development, grazing, and fire suppression. The root system of Pando is estimated to be several thousand years old, placing Pando among the oldest known living organisms. Pando occupies 43.6 hectares (108 acres) and is estimated to weigh collectively 6,000,000 kilograms (6,600 short tons), making it the heaviest known organism. The plant is located in the Fremont River Ranger District of the Fishlake National Forest at the western edge of the Colorado Plateau in south-central Utah, United States, around 1 mile (1.6В km) southwest of Fish Lake. Pando ( Latin for 'I spread'), also known as the trembling giant, is a clonal colony of an individual male quaking aspen ( Populus tremuloides) determined to be a single living organism by identical genetic markers and assumed to have one massive underground root system. Pando aspen grove at Fishlake National Forest