Woodlands and forest are both composed of various species of tree vegetation. However, trees in a forest habitat grow densely enough to produce a closed canopy of tree cover. Trees in a woodland grow less densely and are more open and sunlit, their canopies sometimes touching but rarely overlapping.
Woodlands within the county are typically comprised of a few dominant species. The coast live oak (Quercus agrifolia var. agrifolia), with cup shaped leaves, grows on the coast and in the foothills. The Engelmann oak (Quercus engelmannii) with bluish leaves grows in the foothills. Both the California black oak (Quercus kelloggii) with its deciduous lobed leaves, and the canyon live oak (Quercus chrysolepis) with shiny dark green leaves and big-capped acorns grow in the mountains. Oak woodlands often have an understory of poison oak (Toxicodendron diversilobum).
Oaks have evolved mechanisms to survive periodic burning. Moderate and even low-intensity fires can scorch all the leaves on woody plants. For most conifers such damage is usually lethal. Oaks, on the other hand, suffer little long-term damage from the burning of their foliage. If fire happens early in the growing season, the trees may regrow new leaves before autumn and by the end of the year it may be difficult to tell which trees were scorched in the fire. If fires occur in the summer the oaks usually will not produce a complete crop of new leaves until the following spring. Following such fires, the trees can appear dead, since all leaves are brown and brittle and the boles may be blackened. But many of these trees will survive and it is important that landowners understand this since some may want to cut these trees down, believing they will not recover. It is therefore generally a good practice to wait at least a year after the fire to determine if a tree has been killed and should be removed.
Pinyon - Juniper Woodland
Pinyon juniper woodland is dominated by four leaf pinyon pine (Pinus quadrifolia) and single leaf pinyon pine (Pinus monophylla). The other species that is dominant within this community is the California juniper (Juniperus californica).
Fire eliminates younger age classes of pinyon pines, but large seed-source trees may survive. Where pinyon trees have recently invaded sagebrush-grassland communities, young trees less than four feet tall are easily killed by fire. As tree dominance increases, understory is gradually suppressed. Understory fuels also decrease, and the potential for severe, stand-replacing fire is reduced. Prior to the 1940ís, there are indications that an extensive pinyon pine forest existed in the area near Jacumba. However, a large fire burned through the area and the trees were eliminated. California juniper is a nonsprouting, fire-sensitive species. It may depend on protected areas to survive fires. Frequency of fire in grasslands prevents California juniper from becoming a dominant species in those areas. Several years are required for nonsprouting species to set seed. In the pinyon-juniper type, fires are infrequent due to sparse understory growth.