Recruitment of Swiss stone pine (Pinus cembra) at short- and long-distance seed caching sites of spotted nutcrackers (Nucifraga caryocatactes)

Abstract Plants whose seeds are dispersed by animals are highly dependent on the behavior of seed dispersers to place seeds in micro-sites suitable for germination and establishment. In landscapes with complex topography, variation in micro-site selection is therefore a key determinant of plant recruitment. Differences in seed dispersal distance and deposition sites lead to seeds encountering different micro-environmental conditions. Yet, few studies connect individual disperser behavior to subsequent plant recruitment. In this study, we investigated plant recruitment at seed caching sites of spotted nutcrackers ( Nucifraga caryocatactes ), the primary seed disperser of Swiss stone pine ( Pinus cembra ). Specifically, we compared micro-environmental conditions and pine abundances between seed caching sites located at short and at long distances from seed harvesting sites. We also tested which local environmental factors, as well as elevational differences, explain pine occurrence at both short- and long-distance seed caching sites. We found that short-distance seed caching sites were characterized by higher soil moisture and higher shrub cover, and were located at higher elevations than long-distance seed caching sites. Additionally, the abundance of Swiss stone pine was higher at short-distance caching sites, compared to long-distance sites. Our results indicate that seeds are more likely to recruit at short dispersal distances and with low canopy cover. Hence, potential upward shifts of Swiss stone pine appear to be enabled primarily by short- rather than long-distance dispersal. These insights have important implications for the current and future recruitment potential of Swiss stone pine and emphasize the importance of seed disperser behavior for plant population dynamics.