Elfin forest refers to several similar ecosystems, found in coastal temperate regions and montane tropical regions. Elfin forests are usually at high elevations, and are host to communities of dwarf plants, invertebrates, vertebrates, and a significant presence of epiphytes. There are two different elfin forest ecosystem types, involving different species and environmental characteristics.
Elfin forests should be more commonly found on isolated mountains due to the Massenerhebung effect. The Massenerhebung effect is a phenomenon where treelines are typically higher among mountains in close proximity to other mountains. The mountains in close proximity affect the rate of wind and heat retention, decreasing the negative effect of climate. When the treeline is lower, on isolated mountains, the climatic effects are more severe.
Coastal temperate elfin forest
Californian elfin forest is expansive, and covers most of the mountains in the southern half of California, extending into Mexico, Nevada, and Arizona. Other expanses of elfin forest are found throughout the state, in the northern and central regions.
In northern California, Henry Cowell Redwoods State Park is home to an elfin forest with Mendocino cypress (Cupressus pigmaea), and Sargent's cypress (Cupressus sargentii), which is partially within a section of the Zayante Sandhill Area. On the Central Coast of California, on the southeastern shore of Morro Bay, Los Osos contains the El Moro Elfin Forest Natural Area. The area is approximately 90 acres. It derives the “elfin forest” title from the short California live oaks, which range in height from 4 – 20 feet, compared to the typical 30–80 feet. This region also contains the federally endangered Morro shoulderband snail (Helminthoglypta walkeriana). At a higher altitude, on Cuesta Ridge, the Land Conservancy of San Luis Obispo County manages the San Luis Obispo Elfin Forest of dwarf cypresses (Cupressus)
Factors such as soil moisture, solar radiation, and rockiness of soil influence species composition along an elevational gradient, resulting in certain shrub species, such as Adenostoma fasciculatum and Arctostaphylos glauca, being present in elfin forest habitats.
Fire occurs at low-moderate frequency with high severity. Many plants have adapted to this by having serotinous seeds that open to germinate only under high heat. Because of this, they are often the first to colonize a new area.
Given that chaparral areas can be waterlogged in the winter, and arid and desert-like in the summer, native plants in these dry elfin forests have adapted accordingly, and are generally much shorter, smaller, and compact than related plants elsewhere. Diminutive plants commonly found in Californian elfin forests include Portulacaceae such as Mount Hood pussypaws (Cistanthe umbellata) and Alkali heath (Frankenia salina), and species of Aeonium and bird's-foot trefoil (Lotus). Trees and shrubs, such as chamise (Adenostoma fasciculatum), manzanita (Arctostaphylos), ceanothus, sumac (Rhus), sage (Salvia officinalis), and scrub-oak (Quercus berberidifolia) rarely grow more than 20 ft (7m) tall in these communities.[clarification needed]
Californian elfin forest fauna includes many species of deer mouse (Peromyscus spp.), harvest mouse (Reithrodontomys spp.), California vole (Microtus californicus), California pocket mouse (Chaetodipus californicus), kangaroo rat (Dipodomys spp.), and several species of spiny lizards (Sceloporus spp.), along with other small vertebrates. Invertebrates include the common scorpion (Scorpiones spp.), burrowing scorpion (Opistophthalmus spp.), and various species of spider (Araneae) and tick (Parasitiformes).
The California elfin forests usually exhibit wet winters and dry summers. Variation in these patterns can cause devastating damage to numerous plant communities. Plants found in elfin forests have adapted to grow during winter months, and become dormant during the summer due to drought stress. Plant communities deal with low, seasonal rainfall by relying on fog interception and taking in moisture from the air.
High-altitude tropical elfin forest
High-altitude tropical locations in cloud forests contain mossy wet elfin forests due to high-altitude precipitation. These regions are characterized by low rainfall, with most of the water in the form of mist and fog. The water supplied is primarily available during the night, when clouds move from the ocean over the mountains, and are intercepted by the vegetation. During the day, water demands are increased as clouds rise over the mountain peaks without dissipating into available forms of precipitation.
The forests are characterized by small trees (5-8m), with shallow root systems, and abundant epiphytes. The epiphytes make up a large portion of the canopy, with greater abundances in high-altitude tropical elfin forests than what is found in other, non-elfin, tropical forests.
Within these elfin forests, there are relatively few species with a small number of dominant species that make up a large portion of the population. Low, horizontally branching, shrub-like plants, and dense populations of moss, lichen, and liverworts are found due to high wind speeds, low temperatures, and light reduction from persistent clouds/fog, which limit the growth of large/tall plants. The high wind speeds act as the determining factor of the stature in elfin forest flora, especially on ridges and slopes. A low stature increases the structural stability of the plants. Wind-exposed trees invest more of their resources to increasing strength than to growth, compared to non-wind exposed trees. The increased focus on strengthening leads to thicker trunks and twigs, which increases the ability of the trees to withstand greater wind stresses near the ridgecrest (where the majority of wind-exposed trees are found). A large percentage of energy is also allocated to growing and maintaining heavy and extensive root structures, further strengthening the tree, and increasing its resistance to high winds.
Plants have leaves with moisture-tolerant characteristics, such as drip tips and waxy cuticles. They also have a slow rate of transpiration and metabolism due to low temperatures and low radiation penetration.
A large percentage of plants possess alkaloids and other biochemicals, likely to combat a high amount of herbivory from insects. This may also account for the low leaf surface area, and low transpiration rates of the plants. One study showed that leaves of 10 plant species had approximately 70-98% of all leaves damaged by insects.
Elfin forests occur at high elevations which are generally associated with low vertebrate biodiversity. Hummingbirds and bats make up large proportion of vertebrates in this area, usually as altitudinal migrants during seasonal shifts, such as for reproduction, or in response to food abundance. Other vertebrate species mostly include small rodents.
Rainfall tends to be highly seasonal, sparse, and far between, therefore fog interception is a significant water source during dry seasons. Throughout the year, wind speed, temperature, and humidity are fairly consistent, with humidity usually greater than 90%. At one study site in the Guajira Peninsula, dry season precipitation ranged from 1–4 days per month, while in the wet season, although increased, it was still a relatively low 4 to 12 days per month, supporting the idea that the majority of the water in this region is held in low cloud cover and fog interception. Sunshine duration is distributed bimodally and correlates with evaporation rates.
In the high-altitude Antilles elfin forests, low water use by vegetation due to reduced solar radiation, vapor deficit, canopy wetting, and low evapotranspiration rates marks an important water supply function. With climate change, and the introduction of invasive species into elfin forests, this function may be lost with the degradation of the forests.
Elfin forests in California serve important roles in regulating stream flow, preventing soil erosion, and preventing evaporation by shading the ground, which keeps the soil moist during dry summer months. Clear cutting for agricultural and economic development, amongst other things, may disrupt these environmental services.
- Pygmy forest — overlap in terms
- Krummholz - corresponding term for cool-temperate regions (particularly in the Alpide belt)
- Pedology (soil study)
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