| Despite the rarity of island oak, Quercus tomentella, this research has demonstrated that it is growing on many different geologic substrates and soils, and is associated with many plant species and assemblages in the southern California Channel Islands. Field surveys show that this oak grows at a wide range of elevations, most frequently on steep northwest- and north-facing slopes. Associated soils have an A horizon that ranges in depth between 3-50 cm, contains 4-55% clay, and has a pH of 4-6.7. Soils adjacent had a bulk density in the B horizon much lower than soils far away from island oaks. Nonregenerating island oak populations grew on soils more acidic, with pH as low as 3.3.; Seventy-six percent of the higher plant species associated with island oak are native, and some may be useful for planting in order to facilitate the rebuilding of topsoil.; According to three models of island oak habitat, island oak is currently occupying only a tiny portion of its potential range. However, existing Torrey pine forest, closed cone pine forest, mixed woodland, and chaparral often overlap with the least restrictive model, according to GIS statistics. This finding corroborates field research on island oak plant communities, in which plots with island oak shared the most species in common with mixed chaparral, mixed woodland, and Torrey pine woodland, as well as grassland. If the island oak potential habitat model is used to estimate where woody species in general could thrive, 48% of the area of Santa Cruz and Santa Rosa islands could be good habitat for these woody plant species. According to the most restrictive model, 7% of the islands' area is suitable habitat for island oak. Island oaks currently occupy less than 1% of modelled core habitat, and much less than 1% of the islands' area, so there is great potential for the species' restoration. |
