Importance of regional species pools and functional traits in colonization processes: predicting re-colonization after large-scale destruction of ecosystems.
Large-scale destruction of ecosystems caused by surface mining provides an opportunity for the study of colonization processes starting with primary succession. Surprisingly, over several decades and without any restoration measures, most of these sites spontaneously developed into valuable biotope mosaics with many endangered plant species. Investigations were carried out in 10 open-cast mined sites. Data from extensive floristic mapping of mined sites and their surroundings were combined with functional traits. Using binary logistic regression, we showed that eight variables have a significant influence on the probability of the occurrence of particular plant species in mined sites. The regional species pool explained the highest proportion of variance. Further significant variables were distance of source populations, abundance in the habitat species pool, capacity for long-distance dispersal by wind and birds, terminal velocity of seeds and requirements for light and nitrogen. In the 10 study mine sites, 143 establishing events of Red List species have been recorded. For 40% of these establishing events, the nearest recorded seed source is 3-10 km away, while for 19%, the distance to the nearest seed source exceeds 10 km. This study showed for the first time that the abundance of species up to a distance of at least 17 km plays an important role in colonization processes following large-scale destruction of ecosystems. In large-scale, nutrient-deficient, open sites, an accumulation of plant species, including rare species, can be expected in time frames amenable to planning (several decades), because the sites acted as huge seed traps in the landscape. Synthesis and applications. The floristic colonization probability of restoration sites is higher if large-scale, open and nutrient-poor habitats are available. In regions where such habitats have become highly fragmented, restoration planning of derelict land (e.g. surface mines, quarries, landfills) that supports the creation of such conditions can contribute to the regional survival of rare pioneer species. In future restoration planning, a new protocol must be established that combines the utilization of site potential with spontaneous colonization processes.