Ecology of El Dorado County
Why is El Dorado County so diverse?
First, we live in a botanically rich area; with over 7,000 plants, the California Floristic Province1 is one of the top 25 plant biodiversity hotspots in the world.
Second, the county is topographically varied; west-slope elevation increases from 450 to over 10,000 feet above sea level, and the 70 mile-long slope is bisected by the south and middle forks of the American River, and their tributaries, creating riverine valleys, slopes, and peaks. Millions of years ago the Sierra Nevada was uplifted, a process that continues today, due to plate tectonics. The uplift created elevational climatic zones that support seven distinct plant communities each containing 100s of native plants (see Table 6 below).
Third, our area contains a diversity of soil types, also due to plate tectonics, including several that have botanical significance. Specifically, we have areas with serpentine soils and those with gabbro soil, both of which create harsh or unusual growing conditions for plants. The result is that unique plant assemblages have developed in these areas. El Dorado County is home to almost 200 species of plants that can thrive on serpentine (see Traverse Creek Botanical Special Interest Area). There are only 5 federally listed plant species in El Dorado County and they all occur on the gabbro soil area of Pine Hill (see Pine Hill Ecological Reserve).
What grows here?
The plant list for El Dorado County includes over 100 trees, almost 300 shrubs, and over 1,900 grass-like plants and forbs (Table 1). The most common trees are conifers (31 species, Table 2), including 15 pine trees (Table 3), and oaks (15 kinds, Table 4), with several willows (9 tree species) growing near creeks and in wet meadows. There is a diversity of California lilacs, manzanitas, and currents and gooseberries in our shrub flora. The sunflower/daisy family is particularly well-represented with almost 300 species, mostly forbs, occurring in the county, as is the grass family with 160 species (Table 5).
Where do the plants grow?
Seven distinct plant communities are encountered driving up the “hill” from El Dorado Hills in the west to the mountain passes in the east due to plant adaptations to elevational climatic zones (see Table 6 below and Figure 1 at right). Precipitation, both amount and kind (rain or snow), and the length of the growing season determine these zones. Precipitation increases as moist air masses ascend the slope, cool, and shed their moisture as rain (lower down) or snow (higher up), and growing season decreases from several months to as short as 7 weeks at the highest peaks. Grassland, dominated by annual plants, extends from the Central Valley into El Dorado Hills. Woodlands, distinguished by blue oak and gray pine, occur on cooler north-facing slopes with chaparral on warmer south slopes as one ascends to Shingle Springs. Woodland gives way to widespread Mixed Coniferous Forest from Placerville to beyond Kyburz. Ponderosa Pine, with its jigsaw-puzzle-like bark, is the characteristic tree here, but this community has the highest plant diversity in the county with over 1,100 species, including hardwoods like black oak and big-leaf maple. Lodgepole Pine-Red Fir forest extends from 5,000 to 7,000 feet and is our “snow forest,” receiving 50 feet of snow in typical years past. Above this forest is Subalpine Forest, composed of conifers, apparently arising out of granite and adapted to shallow soils and a short growing season. Above tree line is the Alpine community dominated by perennial grasses and forbs that put on spectacular wildflower displays during the short summer.