East Coast of North America, as its fast growth rate and tolerance for air pollution make it widely adaptable and able to thrive where other species might suffer. This species tends to struggle without irrigation in arid climates such as the American West unless planted directly on or adjacent to a body of water such as a pond or stream. This species is also highly susceptible to damage from contact with heavy amounts of winter de-icing salt. In the 1980s, it was discovered that many of the second-generation trees in cultivation suffered from inbreeding depression (extremely low genetic variability), which could lead to increased susceptibility to disease and reproductive failure. Many sources claim that the original 1947 seedlots came from as few as one tree; however, this has proven to be false. The original seeds did have a wide range of source trees, and the inbreeding depression is more likely to come from self-pollination by isolated trees. However, the total cultivated population still had less genetic variation than the wild ones, and more widespread seed-collecting expeditions in China in the 1990s sought to resolve this problem and restore genetic diversity to cultivated M. glyptostroboides. In China Pizhou, Jiangsu has the longest dawn redwood avenue in the world. The avenue is approximately 60 km long with over one million trees. The Water Forest in Xinghua, Jiangsu is named after the many dawn redwood trees found there in the park. In the United Kingdom The dawn redwood is frequently encountered across the UK. Growth has been fastest in the south-east, but it is believed the tree may have a longer future in the more humid western regions. The first dawn redwood to be planted out in the UK was at the Cambridge University Botanic Garden. The seed was not from the Arnold expedition, but came to Cambridge directly. The Botanic Garden's Annual Report for 1949 declares: ‘Seeds of Metasequoia glyptostroboides, sent by Dr Silow from China to Professor F T Brooks, germinated freely. Three of the seedlings have been planted out: one in the Yard at the back of the Range and two beside the Pond (now called the Lake).' The tree on the south-west side of the Lake is still living, as at July 2019. Seed distributed in the 1940s to Hillier Gardens near Winchester, UK, have thrived and are now the emblem of the gardens. The TROBI Champions are at