Seed dispersal of anemochoric Abies alba Mill.: lessons learned from seed tracking, seed trap experiments and genetic parentage assignment of seedlings

Abstract

Several methods are used to estimate the spatial pattern of seed dispersal. However, each method has specific shortcomings that limit the accuracy and reliability of the resulting dispersal models. In this study we compared seed shadows of the anemochoric species Abies alba Mill. obtained from (1) phenomenological models derived from seed trapping data and inverse modelling, (2) ballistic models based on wind speed at canopy height and an exponential wind profile and (3) empirical models parameterised from seed-tracking data. In addition, we checked whether the empirical model coupled with multiannual wind characteristics provides a dispersal pattern concordant with the gene shadow obtained from parentage assignment between seedlings and overstorey trees. The seed trap and seed-tracking experiments were conducted in 2013 and 2015 with contrasting wind conditions in five study plots located in the Krynica Forest Experimental Station in southern Poland. Genetic data originated from 16 mature stands with dominant A. alba . The study revealed that the distances reached by single seeds strongly vary at the same wind speed at canopy height. The ballistic model overestimated the flight distances of A. alba seeds. Similarly, the empirical model calibrated on data that disregarded seeds trapped in the crowns of neighbouring conifer trees predicted longer flight distances than those derived from the seed trap experiments. The gene shadow obtained from the parentage analysis suggests dispersal patterns concordant with those anticipated by the empirical model based on the seed-tracking experiments, with a possible shift towards an increased proportion of seeds landing close to the source. It was concluded that in dense canopies collisions with canopy elements during seed flight and secondary dispersion of seeds trapped in the canopy zone may considerably shorten the travel distances of A. alba seeds .