Ecological dynamics

A number of large rockfall avalanches have tumbled down the slopes from Chaos Crags, primarily during 3 distinct episodes. The area is called Chaos Jumbles. The oldest event was the largest and has been roughly dated to 1,500 years ago. The middle event was smaller than the first, occurring approximately 750 years ago. The smallest and most recent event occurred around 300 years ago. Because the more recent events were consecutively smaller, the older rockfall avalanche deposits were not completely buried (Heath, 1967) and different stages of soil and forest development are visible. The hummocky rock-strewn debris from the youngest event is very noticeable and remains exposed across the landscape. Now 300 years after the event, scattered conifers, forbs, and sub-shrubs are slowly going through the process of primary succession. The hummocky landform from older deposits is still present, but the surface has smoothed and a mineral soil has formed due to physical weathering, microbial activity, and organic matter accumulation. These older rockfall avalanche deposits are further along in forest development, the oldest exhibiting well-developed Jeffrey pine-white fir forests. All the tree species established in Lassen Volcanic National Park are found within the Chaos Jumbles, except whitebark pine.

The initial colonization of plants on newly exposed parent material initiates a wide range of processes. Nitrogen fixation is commonly one of the first processes to be initiated by pioneering plant species and microorganisms. It converts atmospheric nitrogen gas into ammonia (NH4+) through chemical and biological reactions. The resultant ammonia is converted to nitrate (NO3-) by microorganisms via nitrification. In this process, plants assimilate inorganic nitrogen in the form ammonia and nitrate. As plants continue to establish on the new substrate, they absorb CO2 from the atmosphere and convert it to plant carbon through the process of photosynthesis. The carbon is sequestered as either above-ground or below-ground biomass, or as soil carbon. Soil organisms are responsible for the decomposition of plant material. When soil organisms die and decompose, nutrients are processed back into the soil. Plant material and dead soil organisms provide the bulk of organic matter in soil. The process of CO2 production and the accumulation of organic matter begin to transform freshly exposed parent material by providing nutrients and creating better water availability for plants and microorganisms, affecting pH and weathering minerals. Over time, as these organisms eat, grow and move through the soil, they transform it into a more vibrant biologic substrate. Most of these processes are concentrated in the upper A horizon of the soil. The B horizon, located directly below, is influenced by the leaching of acids and other products from the A horizon.

Living and dead plant material stabilize the soil surface by physically buffering raindrop impact and impeding surface runoff. Within the soil, plants, animals and microbes bind the soil together as aggregates with roots, hyphae, fecal pellets and decomposed organic matter. The micro-structure formed by the combined processes of buffering and binding increases soil stability, porosity, water infiltration and water holding capacity (NRCS, 2010).

Trees and burrowing animal activity produce rather large pores and mix soil on a greater scale than processes provided by buffering and binding. Ants and gophers transport soil material by depositing subsoil on the surface as they build tunnels and nests. Dead tree roots produce macropores that often accumulate surface material and incorporate organic matter deeper into the profile (NRCS, 2010).

Many of the trees in the center of this site are chloritic because they lack available plant nutrients. A variety of conifer species are present, some being outside their usual elevation range. Sierra lodgepole pine (Pinus contorta var. murrayana) is generally the dominant tree species during primary succession, but Jeffrey pine (Pinus jeffreyi), white fir (Abies concolor), California red fir (Abies magnifica), sugar pine (Pinus lambertiana), western white pine (Pinus monticola), and mountain hemlock (Tsuga mertensiana) are also present in small amounts. Commonly associated plants are western needlegrass (Achnatherum occidentale), rockcress (Arabis sp.), pinemat manzanita (Arctostaphylos nevadensis), greenleaf manzanita (Arctostaphylos patula), carex (Carex sp.), bush chinquapin (Chrysolepis sempervirens), buckwheats (Eriogonum spp.), and oceanspray (Holodiscus microphyllus).

Conifers are rarely documented as the initial colonizers during primary succession. More common is a forb and grass phase with species that are able to fix nitrogen. An interesting study was conducted on an ectomycorrhizal association of the blue staining slippery jack fungi (Suillus tomentosus) with a variety of lodgepole pine (Pinus contorta var. latifolia) found north of California and extending into Canada and Alaska. Lodgepole pine (Pinus contorta var. latifolia) formed tuberculate ectomycorrhizae (TEM) with Suillus tomentosus, and the nitrogen-fixing bacteria Paenibacillus amylolyticus and Methylobacterium mesophilicum were shown to reside within the TEM (Paul, 2002). The results of the study indicate high nitrogenase activity, which was attributed to the TEM association. This indicates a symbiotic relationship similar to that of alder (Alnus spp.) and lupine (Lupinus spp.), wherein nitrogen fixing bacteria (Frankia spp. and Rhizobium spp. respectively) are found within root nodules. Several studies indicate a direct correlation between nitrogen fixation and nitrogen demand that varies depending upon season, soil chemistry, and stand age (Paul et al., 2007). The study of the symbiotic relationship between lodgepole pine (Pinus contorta var. latifolia) and Suillus tomentosus may not apply directly to this area, or to the Sierra lodgepole pine (Pinus contorta var. murrayana) variety; however, Suillus tomentosus is a common mushroom throughout the area and is documented in lodgepole pine forests in northern California and the Sierra Nevada (Arora, 1986).

Once the forest develops it has the same successional pattern as other Jeffrey pine-white fir forests. Sierra lodgepole pine and Jeffrey pine are shade intolerant species which dominate after disturbances. Jeffrey pine is generally a taller and longer-lived species than Sierra lodgepole pine, and will eventually overtop and shade it out. White fir will eventually establish in the understory in the absence of fire.

Sierra lodgepole pine grows tall and narrow with short branches. Needles are 1.2 to 2.4 inches long in fascicles of 2. Although its thin bark and shallow root system make Sierra lodgepole pine susceptible to fire, it is the only non-serotinous lodgepole pine. Therefore it does not need fire to open its cones to release seeds. The roots of Sierra lodgepole pine are generally shallow, which enable it to grow on this site. Sierra lodgepole pine produces a taproot that can atrophy or grow horizontally in cases of a high water table or a root restrictive layer. Sierra lodgepole pine is shade intolerant and is an early successional species on this site. Though it often reproduces abundantly after fire, it is unknown if it will dominate this site after fire.

Jeffrey pine dominates this site after the early stages of primary succession, and through later succession with reoccurring understory burns. Jeffrey pine produces 3 to 8-inch needles in bundles of 3. The female seed cones range from 4.7 to 12 inches in length. Jeffrey pine produces a deep taproot 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. Jeffrey pine is shade intolerant and can be replaced over time by white 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 65 to 100 feet above the forest floor.

White fir is common in the later successional stages if there is an absence of fire. White fir produces single needles 1.2 to 2.8 inches long that are distributed along young branches. The female cones open and fall apart while still attached to the tree, so cones are not often seen on the forest floor. White fir tends to develop a shallow root system that can graft to other white fir roots and spread root rots (Zouhar, 2001).

Fire regime studies based on tree rings and fire scars report historic median fire return intervals in Jeffrey pine-white fir forests of 14, 18.8, and 70 years (Bekker and Taylor; Skinner and Chang; Taylor and Solem respectively). Beaty and Taylor report that fire frequency and intensity is additionally associated with slope position, aspect, and climatic fluctuations. Fire return intervals are longer on north facing slopes than on south facing slopes. Stand-replacing fire is more common on upper slopes, while low to moderate intensity fires occur only along lower slopes. This is probably due to the tendency of fire to burn upslope, preheating the fuels as it goes (Beaty and Taylor, 2001). In July and August, thunderstorms are common in Lassen Volcanic National Park and the summer drought conditions begin, initiating the fire season. Large fires and multiple small fires in the same season are associated with dry and very dry years (Beaty and Taylor, 2001). Beaty and Taylor report that after a stand-replacing fire, evenly aged forests are formed. The current management practice of fire suppression has shifted forest density and composition by allowing the fire intolerant and shade tolerant firs to increase in cover and density, eventually out-competing the fire tolerant and shade intolerant pines (Taylor and Solem, 2001).

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 can kill the dominant trees over significant tracts of forest, creating large canopy openings and stand regeneration. Most of these pathogens are natural cycles of regulation that can push 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 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).

Pathogens that affect white fir are dwarf mistletoe (Arceuthobium abietinum f. sp. concoloris), Cytospora canker (Cytospora abietis), broom rust (Melampsorella caryophyllacearum), annosus root disease (Heterobasidium annosum), armillaria root disease (Armillaria sp.), trunk rot (Echinodontium tinctorium) and fir engravers (Scotylus ventralis). The most threatening of these is the combination of the fir engraver and annosus root disease. These pathogens can kill large areas of white fir (Bohne, 2006; Laacke, 1990).

The most serious pest for Sierra lodgepole pine is the mountain pine beetle (Dendroctonus ponderosae). It is a natural pest that can kill a significant portion of the larger trees in a stand. Infestations can last for several years and often return in 20 to 40-year cycles (Cope, 1993). Prominent among the other insects to affect Sierra lodgepole pine is the Ips beetle (Ips spp.), which commonly develops in moist, shaded logging slash. Prompt slash disposal is an effective control measure. Ips also can build up in windthrows. Fungal diseases that affect lodgepole pine productivity include the stem cankers caused by atropelius canker (Atropellis piniphilia), comandra blister rust (Cronartium comandrae), and western gall rust (Peridermium harknessii). The honey mushroom (Armillaria mellea) and annosus root disease (Heterobasidion annosum) are sources of root rot, and wood decay is caused by such fungi as red rot (Phellinus pini) and red heart wood stain (Peniophora pseudo-pini). Dwarf mistletoe (Arceuthobium americanum) is a common parasite that affects large areas of lodgepole pine (Lotan and Critchfield, 1990).

The reference state consists of the anticipated 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 plant/animal community including periodic natural surface fires that would influence its composition and production. Because this phase is estimated from historic literature and other nearby similar sites that have gone through secondary succession, 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.