Ecological dynamics

This site is represented by a California red fir-Jeffrey pine (Abies magnifica-Pinus jeffreyi respectively) forest with pinemat manzanita (Arctostaphylos nevadensis) in the canopy openings. Western white pine (Pinus monticola) replaces Jeffrey pine at the upper elevations of this site. In its natural condition this forest has relatively low canopy cover from large old growth California red fir and Jeffrey pine. The understory cover is moderate with a mix of shrubs, forbs and grasses.

The dominance of California red fir (Abies magnifica) in this forest type increases with elevation and northern aspects. California red fir is a tall, long-lived conifer with short branches and a narrow crown. It produces single 0.8 to 1.4 inch needles that are distributed along young branches. Firs produce upright cones that open and fall apart while still attached to the tree, so cones are not often seen on the forest floor unless cut by squirrels or chipmunks in fall. California red fir cones are about 9 inches long. California red fir prefers cold wet winters in areas with deep snow accumulation, followed by warm summers. The young trees have thin bark and are very susceptible to fire, but as the trees mature the bark thickens and fire resistance increases.

Jeffrey pine (Pinus jeffreyi) is commonly co-dominant with California red fir in this ecological site. Jeffrey pine produces 3 to 8 inch needles in bundles of three. The female seed cones range from 4.7 to 12 inches in length. Trees produce deep taproots and extensive lateral roots (Gucker, 2007) that are intolerant of wet conditions. Jeffrey pine looks similar to ponderosa pine but has a vanilla-like odor in the bark, which is not as yellow. They are shade intolerant and can be replaced over time by white fir or California red fir if fire is excluded from the system. Older Jeffrey pines are somewhat adapted to fire because their bark is thick enough to provide protection from moderate intensity fires. Additionally, their branches tend to thin along the lower portion of the tree trunk, leaving the crown 20 to 30 meters above the forest floor.

A study on conifer growth phenology in the Sierra Nevada describes the timing and growth period for several conifer species. The initial growth of California red fir is faster than its associated conifer species, then returns to a slower growth. Temperature is critical in initiating conifer growth after snowmelt. In the study, trees generally started stem growth about 2 weeks after snow melt, a delay that may be related to the warming of soils and roots. If the snow melt was unusually early, the trees did not begin annual growth until specific air temperatures were reached. It was hypothesized that heavy shrub cover delayed the start of annual growth because shade kept the soil from warming as fast as needed. The pines in the study began leader growth when the air temperatures reached -4 degrees C (24.8 degrees F), and the firs responded after temperatures reached 2 to 3 degrees C (35.6 to 37.4 degrees F). Pines have heavily insulated terminal buds, whereas the terminal buds of fir trees are less insulated and more susceptible to frost damage. The length of the leader growth is predetermined by growth conditions of the prior year. Primordia of fir needles and pine fascicles are developed the year before leader growth. The internode length between fir needles or pine fascicles is determinate, the leader length is determined by the number of primordia developed. It appears that some conifers will not start leader growth until a specific photoperiod (a ratio of light hours to dark hours during one 24 hour period) is met, even if the snow has melted and the temperatures are warm enough. If drought conditions set in before the leader has reached its determinate length, growth will be terminated prematurely. If precipitation comes after the snow has melted, the growing season can be prolonged. Conifer growth ceases with the onset of drought conditions and the decline of water potentials (Royce and Barbour, 2001). This study shows that precipitation and soil and air temperatures are critical for annual growth, with each species having specific tolerance zones. This site is within the tolerance range of California red fir and Jeffrey pine. Western white pine finds appropriate conditions for growth at the upper elevations of this site, and white fir is adapted at the lower elevations.

This site receives 42 inches average annual precipitation, mostly in the form of snow in winter. As the snow melts it fills macropores in the soil with water. Soil characteristics such as depth and texture determine how much water the soil can hold and how long it will remain before filtering through, evaporating away, or being lost to evapotranspiration. The soils associated with this site have very low to low water holding capacities. Under the same climatic conditions, drought would come earlier to these soils than those with higher water holding capacities. As this site experiences early drought conditions, these trees have a short growing season.

In the year 2000 Alan Taylor published a report on the historic fire regimes of several forest types in relation to aspect on Prospect Peak. A large portion of this ecological site is located on the south and south-eastern side of Prospect Peak between the Jeffrey pine-white fir forests at the lower elevations and the red fir-western white pine forests at the upper elevations. In Taylor’s report fire regimes were determined by dating wood cross sections from fire scarred trees or by examining radial growth changes in tree cores. Between the years of 1546 and 1903, the point fire return interval for Jeffrey pine-white fir forests ranged from 15.5 to 38 years, with a mean of 29.8. The point fire return interval for red fir-western white pine forests between the years of 1685 and 1937 ranged from 26 to 109, with a mean of 70 (Taylor, 2000). Fire return intervals were shorter on the eastern slopes than on the southern and western slopes. Data was not analyzed for the northern slopes, which extend beyond the park boundary. Some of the variation in the fire return interval was attributed to the un-vegetated areas of Fantastic Lava Beds, Painted Dunes and Cinder Cone, which lie to the south. These formations do not provide fuel sources and act as a fire barrier. This red fir-Jeffrey pine ecological site probably has a fire return interval between the means listed above (30 to 70 years) or shorter, if on an eastern aspect. In a separate study, Beaty and Taylor report that fire return intervals are longer on north facing slopes than on south facing slopes. This report also states that stand replacing fire is more common on the upper slopes, while low to moderate intensity fires occur only along the lower slopes. This is probably due to the tendency of fire to burn upslope, preheating the fuels as it goes. Large fires and multiple small fires in the same season are associated with dry and very dry years (Beaty and Taylor, 2001). Fire size on Prospect Peak between the years of 1627 and 1904 ranged from 39 to 1537 ha, with a mean of 457 ha. The larger fires generally occurred in the Jeffrey pine forests (Taylor, 2000).

Taylor reports a significant drop in fire frequency and a corresponding increase in understory fuels and canopy cover after 1905. This change developed more quickly in the lower Jeffrey pine-white fir forests than in the upper elevation red fir-western white pine forests. Natural fire regimes reflect the time it takes for forests to naturally develop fuels sufficient to carry fire. At the upper elevations in a red fir dominated forest, fuel accumulation is slower, more compact, and the fuels remain moist for longer during the summer, thereby reducing the risk of fire. Red fir seedlings develop slower than white fir seedlings due to physiographic characteristics and climatic variables, so ladder fuels take longer to develop in red fir forests. If a natural fire regime is 70 years (as for red fir-western white pine forests) then the impact of missing 1 fire cycle in 100 years will be less significant than a forest with a 30 year fire regime that has missed 3 fire cycles. If fire cycles continue to be passed, stand density and fuel loads will increase to levels that put forests at risk of disease and severe canopy fire. The suppression of fire cycles can also create a change in species composition by allowing fire intolerant and shade tolerant firs to increase in cover and density, eventually out-competing fire tolerant and shade intolerant pines (Taylor and Solem, 2001).

Most of the forest within the present park boundary was never logged, but fire suppression has created a change in the stand structure and composition. With a natural fire regime an open forest and the presence of Jeffrey pine or western white pine is encouraged. Low to moderate intensity fires maintain an open forest, with patches of montane shrubs and forbs in the canopy openings. In the absence of fire, California red fir continues to regenerate in the understory, increasing forest density and fuels.

Tree pathogens and insect infestations can have significant impacts on the composition and structure of mid and upper montane coniferous forests. Small infestations may affect just a few trees but large outbreaks may kill the dominant trees over large areas of forest, creating large canopy openings and stand regeneration. Most of these pathogens are a natural cycle of regulation and can push the closed forest types into more open forest types. Large outbreaks are often associated with drought years or overstocked forests. Fuel loads are frequently high after outbreaks, creating ideal conditions for high intensity fires.

Jeffrey Pine is susceptible to several diseases and insect infestations, especially in periods of drought or when overcrowded. Pathogens that affect Jeffrey pine in this area are the dwarf mistletoe (Arceuthobium campylopodium), root disease (Phaeoleus schweinitzii), needle cast (Elytroderma deformans), Jeffrey pine bark beetle (Dendroctonus jeffreyi), Red turpentine beetle (D. valens), and pine engravers (Ips species). The most threatening of these are the dwarf mistletoe and the Jeffrey pine bark beetle (Bohne, 2006; Jenkinson, 1990).

The major pathogens that affect California red fir in this area are red fir dwarf mistletoe (Arceuthobium abietinum f. sp. magnificae), fir broom rust (Melampsorella caryophyllacearum), annosus root rot (Heterobasidium annosum), and the fir engraver (Scolytus ventralis) (Murphy et al., 2000). Other diseases that can affect red fir are the heart rots yellow cap fungus (Pholiota limonella) and Indian paint fungus (Echinodontium tinctorium). Insects that can affect red fir are cone maggots (Earomyia spp.), several chalcids (Megastigmus spp.) and cone moths (Barbara spp. and Eucosma spp.) (Burns, et al., 1990).

The reference state consists of the most successionally advanced community phase (numbered 1.1) as well as other community phases which result from natural and human disturbances. Community phase 1.1 is deemed the phase representative of the most successionally advanced pre-European plant/animal community including periodic natural surface fires that influenced its composition and production. Because this phase is determined from the oldest modern day remnant forests and/or historic literature, some speculation is necessarily involved in describing it.

All tabular data listed for a specific community phase within this ecological site description represent a summary of one or more field data collection plots taken in communities within the community phase. Although such data are valuable in understanding the phase (kinds and amounts of ground and surface materials, canopy characteristics, community phase overstory and understory species, production and composition, and growth), it typically does not represent the absolute range of characteristics nor an exhaustive listing of species for all the dynamic communities within each specific community phase.