Supplementary introduction
THE STUDY SYSTEM: DEADWOOD-DEPENDENT FOREST FUNGI
Forest-living, deadwood-dependent decomposer fungi are an excellent system for testing the performance of different kinds of predictive models, including occupancy versus colonisation-extinction modelling, and the effects of spatial modelling scale and resource resolution on species projection performance. Wood-decomposer fungi are sessile species that may respond to environmental change with a delay (Gu et al. 2002, Paltto et al. 2006, Sverdrup-Thygeson et al. 2014). Snapshot occupancy data on wood-decomposer fungi are abundant, but in the current study we also utilize a large dataset on colonization-extinction dynamics collected over a wide ecological gradient. The resource units of the wood-decomposer fungi are dynamic in the sense that they have a lifespan of years to decades and even centuries (depending on tree species, tree size and environmental conditions). Wood-decomposer fungi must therefore balance extinctions from resource units with colonisations elsewhere to ensure metapopulation persistence (Gourbiere and Gourbiere 2002). In production forests, and especially for rare species, rates of local colonisation are expected to be lower and rates of local extinction higher than in natural-like forests, because production forests have much less deadwood (<10%) than natural-like forests (Jonsson et al. 2016) and the quality of the deadwood present usually does not meet the requirements of specialised species (Nordén et al. 2013). In more common species, the differences in colonisation and extinction rates between production and natural-like forests can be assumed to be smaller, and therefore the bias in projection when using occupancy models instead of colonization-extinction models can be assumed to be smaller. As deadwood rich set-aside forests are typically small in area and few in the landscape, many species of wood-decomposer fungi have small local populations and appear to be limited by dispersal (Edman et al. 2004, Norros et al. 2012). Furthermore, these fungi occur in hierarchically structured systems: they are restricted to resource units (dead trees) located in forest patches (Fig. 1 in the main text). Empirical data have usually been collected in sample plots of varying size, i.e. survey data that usually cover only a part of each forest patch. The fungi are to a varying extent specialised with respect to resource-unit characteristics, such as deadwood tree species, size, type and stage of decomposition (Nordén et al. 2013), and this gives an opportunity to test the effects of resource resolution on population projections.