Effective Seed Dispersal Across a Fragmented Landscape

Abstract

The role of seed dispersal in maintaining genetic connectivity among forest fragments has largely been ignored because gene flow by pollen is expected to predominate. By using genealogical reconstruction, we investigated gene flow after establishment of seeds in a wind-pollinated, wind-dispersed tree. Our data show that seed dispersal is the main vector of gene flow among remnants and that long-distance dispersal is common across a chronically fragmented landscape. The relative importance of seed-mediated gene flow may have been underemphasized in other fragmented systems, and diagnosing the response of forest trees to current anthropogenic disturbances requires the assessment of phenomena after establishment.

Spruce colonization at treeline: where do those seeds come from?

“…Genetic methods seem particularly appropriate to provide more accurate LDD data (Alsos et al 2007), although studies based on parentage analysis that can provide LDD estimates at the population level, are still scarce (Nathan, 2006). By means of parentage analysis on established juveniles, Troupin (2005) found in Pinus halepensis colonization events over 500 m long, and Bacles et al (2006) recorded individuals established up to 1.4 Km from their mother tree in a fragmented population of F. excelsior. Long-distance dispersal and establishment events were also detected in other tree species by Goto et al (2006) and Hardesty et al (2006) using the same approach.…”

“…In Fraxinus excelsior, a wind dispersed species with seeds one order of magnitude heavier than P. abies, Bacles et al (2006) estimated seed immigration rate ranging from 50 to 70% in three remnants in an extended fragmented landscape (900 ha). Our results are also similar to those obtained in earlier studies on P. abies.…”

“…The proportion of juveniles with no identified parents and with only one identified parent represent, respectively, an estimate of seed and pollen gene flow from outside the study area (Bacles et al, 2006). Then, we used the assumptions postulated by Dow and Ashley (1996) to determine pollen and seed movements inside the sampling area.…”

“…The theory was first proposed by Janzen (1970) and Connell (1971) ('J-C recruitment pattern model'), and recently modelled by Nathan and Casagrandi (2004). In addition, parentage analysis seems to be a promising technique to assess the scale and the quality of long-distance dispersal (LDD) events (Wang and Smith, 2002;Bacles et al, 2006). The study of LDD is crucial for understanding how plants can respond to global environmental changes (Trakhtenbrot et al, 2005).…”

Constraints to and conservation implications for climate change adaptation in plants

“…The landscape does not necessarily need to be continuous, but distances between populations or fragments need to be short enough to enable successful dispersal. For example, scattered trees in fragmented landscapes have been identified as having a key role to play in aiding migration , and provide a connective link between remnant vegetation via seed dispersal (Bacles et al 2006;Sork and Smouse 2006).…”