AUSTRALIA — Of all the things you might amass, trees would have to be one of the most unwieldy. They take up space and they soak up time. It’s not a pursuit for the restless. But it’s hard to keep a good tree collector from grouping trunks and canopies, foliage and flowers. Their plantations spill over hectares and change with the seasons. In 1838 the pioneering Scottish botanist and garden designer John Claudius Loudon came up with a name for such a collection: “arboretum”. The term stuck. …Max Bourke, a Canberra-based arboreta enthusiast, will this month give an online talk about Loudon’s role in the evolution of tree collecting. Bourke says hundreds or arboreta have been planted in Australia, with their roles having varied over time. …He says arboreta are increasingly being established, at least in part, to preserve trees that are endangered in the wild.