SOIL SEED BANKS IN 4 LOWER MONTANE FORESTS OF MEXICO

Soil seed banks from four Mexican lower montane forests were studied. These forests are in the transition zone between neartic and Neotropical floristic regions. Soil seed bank characteristics were biased toward the dominant - temperate or tropical - phytogeographical affinity. The northern site (El Cielo Biosphere Reserve, Tamaulipas) had the lowest seed density, 720 seeds m-2. The eastern (Rancho La Mesa, Veracruz), western (Sierra de Manantlan Biosphere Reserve, Jalisco) and southern (El Triunfo Biosphere Reserve, Chiapas) sites all had much higher seed densities (2291, 2901, and 2341 seeds m-2, respectively). Germinated tropical species seeds were more abundant than temperate species seeds at all four sites, and were higher for southern and intermediate sites when compared with the northern site. On the basis of family, El Cielo appears to be different. The tropical family Melastomataceae was absent from this northern site, whereas it represented >30% of total germinated seeds at the other three sites. Trees were the most abundant life form at the southern site but were particularly poorly represented in the eastern and northern sites. Herbs were very abundant in the eastern, western and northern sites but were poorly represented in the seed bank of the southern site. The four seed banks differ between themselves and resemble seed banks of neither temperate deciduous nor tropical forests. In some ways they are unique, at least with respect to floristic composition, seed density, and life form representation.