>Anyone out there have some input on this? Naturally. .... The amount of available soil oxygen and water (what is bizarrely characterized as “drainage” in horticulture) is a determining factor. Possibly the determining factor. Conifers, the dominant tree type in the Rockies just west of here, grow on more highly-oxygenated, porous soils than do grasses and meadow plants. Bacteria and fungus probably play a minimal role. Water is more readily available to plant roots in coarse soils; water penetrates more deeply, binds less clingingly to the soil particles, and is less subject to evaporation. It takes a prolonged period of higher-than-normal precipitation for conifers to be able to populate heavier soils. (The increase in the frequency of precipitation allows for greater water penetration in heavier soils.) Hence the migration of Pinus edulis to heavier, clay-type soils during a period of much higher precipitation about 600 years ago. Bob Nold Denver, Colorado, USA _______________________________________________ pbs mailing list pbs@lists.ibiblio.org http://pacificbulbsociety.org/list.php http://pacificbulbsociety.org/pbswiki/