Barriers to white pine regeneration: Predation and substrate

Unsuccessful reproduction can be due to a variety of factors. I estimated pre-dispersal predation, post dispersal predation, and influence of substrate on establishment of white pine seedlings. In September, 2005, 200 seed were sown in a nested design in a mature  forest with ~ 30% canopy.  The whole plot (1m x 1m) factor was caging (n=4 per treatment).  Nested within were 3 seed bed treatments – bare soil, clipped vegetation, and control.  Five spots 10 cm in diameter were sown with five seeds per treatment. In the fourth sub-plot, a Petri dish was set flush with ground line.  The fate of these seeds was evaluated in June, 2006.   In July, 2006, 49 fully-formed EWP cones were collected and examined for evidence of pre-dispersal predation.  The exclosures significantly increased the number of intact seeds (6.9 vs. 1.8/plot) and the number of seedlings (3.8 vs. 0.3/plot).  They also significantly reduced the number of seed lost to predation.  The disappearance of 23.5% of seed in the Petri dishes inside exclosures corroborates the importance of predation.  Total predation was 86% in the OPEN plots and 53% in the EXCLOSURES.  Bare mineral soil increased (3.5X) germination by June, but seed predation was also notably higher (2.5X).  59.2 % of the cones were predated.  In Sept., 2006, the experiment was repeated with a larger sample size (12 treatment quadrats and 1200 seed/substrate).  I tentatively conclude that germination rate, and pre- and post-dispersal predation are important limitations, and that the net effect of bare soil is slightly positive.