Chaparral is an evergreen shrub vegetation that dominates the rocky slopes of southern and central California. It forms a nearly continuous cover of closely spaced shrubs 6 to 12 feet (2 to 4 meters) tall, with intertwining branches that make the vegetation nearly impenetrable to humans. Herbaceous vegetation (grasses and wildflowers) is generally lacking, except after fires, which are frequent throughout the range. Because of complex patterns of topographic, soil, and climatic variations, chaparral may form a mosaic pattern in which patches of oak woodland, grassland, or coniferous forest appear in sharp juxtaposition. Fire frequency and soil are major factors that determine these patterns. Chaparral is replaced by grassland on frequently burned sites, especially along the more arid borders at low elevations (where shrub recovery is more precarious due to drought) and on deeper clay soils and alluvial plains, and by oak woodland on more moist slopes (where fires are less frequent...