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.