Cross-sectional versus longitudinal research: a case study of trees with hollows and marsupials in Australian forests

How different are insights based on cross-sectional studies from those of longitudinal investigations? We addressed this question using a detailed case study encompassing a rare suite of inter-connected cross-sectional and longitudinal investigations that have spanned the past two decades and included work on (1) the decay and collapse of large cavity forest trees (termed trees with hollows), (2) populations of a suite of species of arboreal marsupials which are reliant on trees with hollows as nesting and denning sites, and (3) relationships between the abundance, type and condition of trees with hollows and the presence, abundance and species richness of these animals. Our case study was from the montane ash eucalypt forests of the Central Highlands of Victoria, south-eastern Australia. Our longitudinal studies led to new insights that either would not have been possible from a cross-sectional study or which were unexpected because they did not conform, or only partially conformed, to...