Mean Fire Return Interval Research Articles

Above-ground biomass and structure of pristine Siberian Scots pine forests as controlled by competition and fire.

The study presents a data set of above-ground biomass (AGB), structure, spacing and fire regime, for 24 stands of pristine Siberian Scots pine (Pinus sylvestris) forests with lichens (n = 20) or Vaccinium/mosses (n = 4) as ground cover, along four chronosequences. The stands of the "lichen" site type (LT) were stratified into three chronosequences according to stand density and fire history. Allometric equations were established from 90 sample trees for stem, coarse branch, fine branch, twig and needle biomass. The LT stands exhibited a low but sustained biomass accumulation until a stand age of 383 years. AGB reached only 6-10 kgdw m-2 after 200 years depending on stand density and fire history compared to 20 kgdw m-2 in the "Vaccinium" type (VT) stands. Leaf area index (LAI) in the LT stands remained at 0.5-1.5 and crown cover was 30-60%, whereas LAI reached 2.5 and crown cover was >100% in the VT stands. Although nearest-neighbour analyses suggested the existence of density-dependent mortality, fire impact turned out to have a much stronger effect on density dynamics. Fire scar dating and calculation of mean and initial fire return intervals revealed that within the LT stands differences in structure and biomass were related to the severity of fire regimes, which in turn was related to the degree of landscape fragmentation by wetlands. Self-thinning analysis was used to define the local carrying capacity for biomass. A series of undisturbed LT stands was used to characterise the upper self-thinning boundary. Stands that had experienced a moderate fire regime were positioned well below the self-thinning boundary in a distinct fire-thinning band of reduced major axis regression slope -0.26. We discuss how this downward shift resulted from alternating phases of density reduction by fire and subsequent regrowth. We conclude that biomass in Siberian Scots pine forests is strongly influenced by fire and that climate change will affect ecosystem functions predominantly via changes in fire regimes.

Comment-Reverse cumulative standing age distributions in fire-frequency analysis

Fire-frequency (FF) analysis is used to derive, from empirical data, parameters that describe the frequency of fires in a system; the time-since-fire distribution; the age-specific probability of fire; and other summary statistics such as the natural fire rotation, the mean fire-return interval, and the fire cycle (Heinselman 1973, 1981; Romme 1981; Agee 1993; Johnson and Gutsell 1994). Results of FF analyses have been used to identify changes in conditions affecting fires in the past (Heinselman 1973; Alexander 1980; Stokes and Dieterich 1981; Hemstrom and Franklin 1982; Mastrogiuseppe et al. 1983; Johnson et al. 1990; Johnson and Larsen 1991; McCune 1983; Romme 1982; Swetnam 1993), to model landscapes produced by natural or altered fire regimes (Baker 1992), and to predict the amount of old forests expected in natural fire-dominated landscapes (B.C. Ministry of Forests and B.C. Environment 1995; Johnson et al. 1995; Martell 1995; Lesica 1996). The ecosystem-management paradigm of mimicking natural disturbances in managed ecosystems (Hunter 1993; Grumbine 1994) or containing the effects of management within the range of natural disturbances (Attiwill 1994) has recently increased the influence of FF models in informing planning decisions in forest management (Mutch et al. 1993; B.C. Ministry of Forests and B.C. Environment 1995) and in protected areas management (Brown et al. 1995). Unfortunately, a common method of applying empirical data on stand ages to FF analysis is incorrect, producing incorrect results and interpretations in published studies. We demonstrate the mistake by examining the derivation of FF models, comparing them to their analogue in population ecology, static life-table (SLT) analyses.

The structure and dynamics of Abies magnifica forests in the southern Cascade Range, USA

AbstractAbies magnifica (Red fir) forests in the Cascade Range and Sierra Nevada of California are composed of groups, or patches, of even‐sized individuals that form structurally complex stands. Patches may be even‐aged, resulting from synchronous post‐disturbance establishment, or multi‐aged, reflecting continuous recruitment of seedlings moderately tolerant of shade. We analyze the population structure (i.e. age, size, and spatial patterning) of A magnifica, and associated A concolor, White fir, and reconstruct the disturbance history of two mature to old‐growth A. magnifica forests in order to determine the relationship between disturbance and forest structure.Within both stands examined, the distributions of A. magnifica seedlings, saplings, and small understory trees were clumped, with clump sizes corresponding to the area of canopy gaps. Gaps were created by frequent wildfire (mean fire return interval of 41 yr) and by windstorms. Severe fire initiated mass establishment of Abies magnifica, whereas gaps created by windthrowreleasedalreadyestablishedindividuals. Lowinten‐sity fire stimulated little recruitment, but Red fir established continuously during fire‐free intervals. Thus, the complex age and structures of Red fir forests reflect both episodic and continuous recruitment, as determined by the type and severity of natural disturbance.

Forest fire history of Desolation Peak, Washington

Forests in the vicinity of Desolation Peak, Washington, are of special ecological interest because of their transitional nature between coastal and interior forest types. The area is west of the Cascade Mountain crest but in the rainshadow of mountains farther to the west. Fire return intervals were hypothesized to be shorter than typical for coastal forest types, such as those dominated by western hemlock and Pacific silver fir, and longer than typical for interior forest types, such as ponderosa pine, owing to the close juxtaposition of these types at Desolation Peak. Seven forest community types were defined, and a 400-year fire history was developed for this 3500-ha area. The average natural fire rotation was 100 years; this varied by a factor of two by century and by topographic aspect. Forest types typical of coastal regions, such as Douglas-fir, – western hemlock and mountain hemlock – Pacific silver fir, had mean fire return intervals (108–137 years) much lower than in other western Washington areas. The most interior forest type, ponderosa pine – Douglas-fir, had a higher mean fire return interval (52 years) than reported for similar forest types east of the Cascades. Historically, fire has created structural and landscape diversity on Desolation Peak and may be an important process in the maintenance of such diversity into the future.

Fire history and vegetation pattern of coniferous forests in Jasper National Park, Albert

Periodicity, location, extent, and severity of fires from 1665 to 1975 were determined for a 43 200-ha area of Jasper National Park using fire-scar dendrochronology. Before fire suppression began in 1913, there were 46 fires with a mean fire return interval (MFRI) of 5.5 years. Twenty-four fires each covered more than 500 ha and had a MFRI of 8.4 years. Fires covering more than 50% of the area had a MFRI of 65.5 years. Present forests originated primarily after the fires of 1889, 1847, and 1758. Most fires between 1665 and 1913 were low to medium intensity, but higher intensities did occur. Interaction of fire periodicity, intensity, and extent determined age, size, density, crown height, and temporal frequency of forest patches. Stands varied from even-age- to multiple-age-classes intermingled over short distances. Multiple-aged stands dominated lower elevations and were maintained by frequent removal, by fire, of low organic matter accumulations. Large, continuous, even-aged forests occurred at mid to high elevations where mesic moisture regimes allowed greater fuel accumulations, and consequently, more intense fires during droughts. Fire periodicity and extent have declined since 1913, accompanied by reduced structural heterogeneity of the forests.