Can deadwood be preferred to soil? Vascular plants on decaying logs in different forest types in Central Europe

Deadwood is known to be an irreplaceable substrate for various groups of organisms but its importance for vascular plants is still unclear. To examine which deadwood characteristics promote its colonization by vascular plants and whether species can prefer this substrate to mineral soil (or vice versa), we used regression modeling and ordination methods to analyze an extensive data set of vegetation records from more than 1800 pieces of lying deadwood and 200 control plots on soil. Data were collected in four old-growth forest sites ranging from lowland alluvial to mountain spruce forests. Colonization of deadwood of all decay classes, including freshly fallen logs, was frequent at all study sites. The density of colonizers differed between deadwood species, increased with deadwood decomposition stage and was higher when deadwood was exposed to light. On average, about 40% of observed species showed a preference for either deadwood or soil substrate with preference for soil usually being more common. Species that preferred deadwood to soil were typically early successional species, while those with preference for soil were often hygrophytes or typical understorey species. Most species responded consistently to substrate across multiple sites. With its unique microsite conditions and specific composition of plant colonizers, we highlight the importance of deadwood for herb layer species composition. Deadwood retention should be encouraged not only in protected but also in commercial forests.