Seed Dispersal and Recruitment Limitation Across Spatial Scales in Temperate Forest Fragments

Abstract

Despite increasing evidence of seed limitation in forest ecosystems, data remain sparse on spatial patterns of seed rain at large (Ͼ1 ha) spatial scales. We monitored seed rain (28.5 m 2 ) throughout five northern hardwood forest fragments (27 ha sampled across 14-km 2 area) in southeastern Michigan over two years. Four fragments were nearest neighbors (300-700 m), yet varied in species composition, providing the opportunity to detect landscape-scale seed exchange. Of the 37 species of woody plants present in the seed rain (98 032 mature seeds), only three (Betula papyrifera, Ostrya virginiana, and Ulmus americana) had widespread seed dispersions within all fragments containing resident sources (seed in Ͼ70% of traps in each fragment). Seed dispersions, measured as the percentage of traps within a fragment receiving seed, differed among species using different dispersal vectors with animal-dispersed species arriving in a lower percentage of seed traps than wind-dispersed seeds. At a given source density, seed dispersions increased with decreasing seed mass. Light-seeded, fecund species such as Betula or Tsuga required lower source densities to saturate fragments with seed compared to heavy-seeded species (Acer, Fraxinus, Tilia). Heavy-seeded wind-and animal-dispersed species also displayed the strongest evidence of seed limitation, with seedling presence significantly associated with presence of seed for Carpinus caroliniana, Fagus grandifolia, Prunus avium, and Tilia americana. Of 17 species, landscape-scale seed exchange was detected for only four disturbance-associated species (Acer negundo, Betula papyrifera, Celastrus scandens, Eleaganus umbellata). No exchange was detected for Acer rubrum, Betula alleghaniensis, or Tsuga canadensis, despite broad seed dispersions (Ͼ50%) in fragments with resident sources, suggesting the potential for seed limitation for these species at larger spatial scales. Seed encounter probabilities suggest that potential seed competitors often fail to simultaneously colonize microsites. We suggest that all dominant species in northern hardwood forests can be seed limited at some spatial scale and that results are consistent with ''winning by forfeit'' scenarios of diversity maintenance in forest ecosystems.

Functional diversity and management mediate aboveground carbon stocks in small forest fragments

“…Damschen et al (2006) found a net positive effect on native plant species richness in patches connected by corridors, compared to patches isolated by 150 m. Additionally, surrounding forests may have the potential to buffer existing forest fragments from microclimatic edge effects; in tropical forests, landscape level influences such as increasing forest cover and structural connectivity influenced microclimatic differences between forest fragments and the surrounding matrix, with air temperature and moisture in larger and more connected fragments deviating less from the surrounding matrix (Pinto et al 2010). However, the majority of forest fragmentation studies focus primarily on summary metrics such as species richness and composition (Estades and Temple 1999, Honnay et al 1999, Petit et al 2004, Uezu et al 2005, Damschen et al 2006, Echeverría et al 2007, and dispersal of organisms (Tewksbury et al 2002, McEuen and Curran 2004, Kolb and Diekmann 2005, Pardini et al 2005, and rarely make the link to ecosystem functions or services (but see Billings and Gaydess 2008).…”

Distribution of vascular plant species in woodland patches of Ojców National Park (southern Poland) in relation to seed dispersal

“…According to the findings of various authors, zoochores are the best colonizers (fastest and spreading over largest distances), endozoochores first, followed by epizoochores; anemochores are slightly poorer, with autochores, myrmecochores, and barochores closing the list as the poorest colonizers [7,12]. Distances covered by diaspores of anemochorous woodland species are short compared to the species of non-woodland communities spreading in the same way; additionally, wind force and direction play a lesser role in this case, though they facilitate a higher migration rate and a more even distribution of these plants [58]. If winds blow in a particular direction, they only enhance species colonization in that direction [59].…”

Diversity of woody plant seedling banks under closed canopy in fragmented coppice forests

“…III). Seed dispersal limitation of forest trees can emerge, indeed, at various spatial scales (e.g., from stand to landscape) (Clark et al, 1998;McEuen and Curran, 2004). For species with limited dispersal capacities (oaks in our case), recruitment limitation may occur at the stand scale, whereas for species with higher dispersal capacities such as bird-dispersed species (P. avium, for example), it may occur at the landscape scale (Grashof-Bokdam, 1997;Hewitt and Kellman, 2002).…”

“…IV). This suggests that recruitment in these temperate forests could be limited by dispersal (McEuen and Curran, 2004). Harmer and Morgan (2007) also observed that since acorns are heavy, many fall directly beneath their parent trees, although they can be dispersed by birds and small mammals over several kilometres (Gomez, 2003).…”

“…For the seedling bank under closed canopy, stand characteristics may partly determine seedling density and community composition by affecting seed availability through the proximity of conspecific adults (Frey et al, 2007). The dependence of seedling establishment on adult presence and/or abundance may vary between plant species according to their dispersal abilities (vector type and/or seed mass) (Grashof-Bokdam, 1997;Hewitt and Kellman, 2002;McEuen and Curran, 2004).…”