Daniel B. Tinker

Surprises and lessons from the 1988 Yellowstone fires

The size and severity of the fires in Yellowstone National Park in 1988 surprised ecologists and managers alike. Much has been learned about the causes and consequences of crown fires from studies of the Yellowstone fires, and some results were surprising. Plant cover in burned areas was restored rapidly by native species, making post-fire rehabilitation generally unnecessary and possibly even counterproductive. While 20th-century fire suppression has affected systems like Yellowstone far less than other ecosystems, managing forests, people, and property in wildfire areas is an ongoing challenge. Insights gained and lessons learned from the Yellowstone fires may be applied elsewhere and can help inform fire policy.

Carbon Storage on Landscapes with Stand-replacing Fires

Abstract Many conifer forests experience stand-replacing wildfires, and these fires and subsequent recovery can change the amount of carbon released to the atmosphere because conifer forests contain large carbon stores. Stand-replacing fires switch ecosystems to being a net source of carbon as decomposition exceeds photosynthesis—a short-term effect (years to decades) that may be important over the next century if fire frequency increases. Over the long term (many centuries), net carbon storage through a fire cycle is zero if stands replace themselves. Therefore, equilibrium response of landscape carbon storage to changes in fire frequency will depend on how stand age distribution changes, on the carbon storage of different stand ages, and on postfire regeneration. In a case study of Yellowstone National Park, equilibrium values of landscape carbon storage were resistant to large changes in fire frequency because these forests regenerate quickly, the current fire interval is very long, the most rapid changes in carbon storage occur in the first century, and carbon storage is similar for stands of different ages. The conversion of forest to meadow or to sparser forest can have a large impact on landscape carbon storage, and this process is likely to be important for many conifer forests.

Coarse Woody Debris following Fire and Logging in Wyoming Lodgepole Pine Forests

The accumulation and decomposition of coarse woody debris (CWD) are processes that affect habitat, soil structure and organic matter inputs, and energy and nutrient flows in forest ecosystems. Natural disturbances such as fires typically produce large quantities of CWD as trees fall and break, whereas human disturbances such as timber harvesting remove much of the CWD. Our objective was to compare the amount of CWD removed and left behind after clear-cutting to the amount consumed and left behind after natural fires in Rocky Mountain lodgepole pine. The masses of fallen logs, dead-standing trees, stumps, and root crowns more than 7.5 cm in diameter were estimated in clear-cut and intact lodgepole pine forests in Wyoming and compared to estimates made in burned and unburned stands in Yellowstone National Park (YNP), where no timber harvesting has occurred. Estimates of downed CWD consumed or converted to charcoal during an intense crown fire were also made in YNP. No significant differences in biomass of downed CWD more than 7.5 cm in diameter were detected between burned stands and those following a single clear-cut. However, the total mass of downed CWD plus the mass of snags that will become CWD was nearly twice as high in burned stands than in clear-cuts. In YNP, approximately 8% of the downed CWD was consumed by fire and an additional 8% was converted to charcoal, for an estimated loss of about 16%. In contrast, approximately four times more wood (70%) was removed by clear-cutting. Considering all CWD more than 7.5 cm in diameter that was either still present in the stand or removed by harvesting, slash treatment, or burning, clear-cut stands lost an average of 80 Mg ha−1 whereas stands that burned gained an average of 95 Mg ha−1. Some CWD remains as slash and stumps left behind after harvesting, but stands subjected to repeated harvesting will have forest floor and surface soil characteristics that are beyond the historic range of variability of naturally developing stands.

Watershed analysis of forest fragmentation by clearcuts and roads in a Wyoming forest

Remotely sensed data and a Geographic Information System were used to compare the effects of clearcutting and road-building on the landscape pattern of the Bighorn National Forest, in north-central Wyoming. Landscape patterns were quantified for each of 12 watersheds on a series of four maps that differed only in the degree of clearcutting and road density. We analyzed several landscape pattern metrics for the landscape as a whole and for the lodgepole pine and spruce/fir cover classes across these maps, and determined the relative effects of clearcutting and road building on the pattern of each watershed. At both the landscape- and cover class-scales, clearcutting and road building resulted in increased fragmentation as represented by a distinct suite of landscape structural changes. Patch core area and mean patch size decreased, and edge density and patch density increased as a result of clearcuts and roads. Clearcuts and roads simplified patch shapes at the landscape scale, but increased the complexity of lodgepole pine patches. Roads appeared to be a more significant agent of change than clearcuts, and roads which were more evenly distributed across a watershed had a greater effect on landscape pattern than did those which were densely clustered. Examining individual watersheds allows for the comparison of fragmentation among watersheds, as well as across the landscape as a whole. Similar studies of landscape structure in other National Forests and on other public lands may help to identify and prevent further fragmentation of these areas.

Inorganic nitrogen availability after severe stand-replacing fire in the Greater Yellowstone ecosystem

Understanding ecosystem processes as they relate to wildfire and vegetation dynamics is of growing importance as fire frequency and extent increase throughout the western United States. However, the effects of severe, stand-replacing wildfires are poorly understood. We studied inorganic nitrogen pools and mineralization rates after stand-replacing wildfires in the Greater Yellowstone Ecosystem, Wyoming. After fires that burned in summer 2000, soil ammonium concentration peaked in 2001 (33 mg NH4-N· kgsoil−1); soil nitrate increased subsequently (2.7 mg NO3-N·kgsoil−1 in 2003) but was still low. However, annual net ammonification rates were largely negative from 2001 to 2004, indicating ammonium depletion. Thus, although net nitrification rates were positive, annual net nitrogen mineralization (net ammonification plus net nitrification) remained low. Aboveground net primary production (ANPP) increased from 0.25 to 1.6 Mg·ha−1·yr−1 from 2001 to 2004, but variation in ANPP among stands was not related to net nitrogen mineralization rates. Across a broader temporal gradient (stand age zero to >250 yr), negative rates of net annual ammonification were especially pronounced in the first postfire year. Laboratory incubations using 15N isotope pool dilution revealed that gross production of ammonium was reduced and ammonium consumption greatly exceeded gross production during the initial postfire years. Our results suggest a microbial nitrogen sink for several years after severe, stand-replacing fire, confirming earlier hypotheses about postdisturbance succession and nutrient cycling in cold, fire-dominated coniferous forests. Postfire forests in Yellowstone seem to be highly conservative for nitrogen, and microbial immobilization of ammonium plays a key role during early succession.

Postfire changes in forest carbon storage over a 300-year chronosequence of Pinus contorta-dominated forests

A warming climate may increase the frequency and severity of stand-replacing wildfires, reducing carbon (C) storage in forest ecosystems. Understanding the variability of postfire C cycling on heterogeneous landscapes is critical for predicting changes in C storage with more frequent disturbance. We measured C pools and fluxes for 77 lodgepole pine (Pinus contorta Dougl. ex Loud var. latifolia Engelm.) stands in and around Yellowstone National Park (YNP) along a 300-year chronosequence to examine how quickly forest C pools recover after a stand-replacing fire, their variability through time across a complex landscape, and the role of stand structure in this variability. Carbon accumulation after fire was rapid relative to the historical mean fire interval of 150–300 years, recovering nearly 80% of prefire C in 50 years and 90% within 100 years. Net ecosystem carbon balance (NECB) declined monotonically, from 160 g C·m−2·yr−1 at age 12 to 5 g C·m−2·yr−1 at age 250, but was never negative after disturbance....

Temporal and spatial dynamics of coarse woody debris in harvested and unharvested lodgepole pine forests

Abstract Coarse woody debris (CWD) biomass was measured and mapped in burned, clearcut, and intact lodgepole pine forests in two areas of the Rocky Mountains of Wyoming: the Medicine Bow National Forest (MBNF) and Yellowstone National Park (YNP). In addition, the amount of CWD consumed or converted to charcoal by fire was estimated in a recently burned stand in YNP. A spatially explicit simulation model (DEADWOOD) was then created to simulate the effects of various clearcutting and fire regimes on CWD over a 1000-yr period. Approximately 8% of downed CWD were consumed during a single fire and an additional 8% was converted to charcoal. After 1000 yr of simulation, 100-yr fire-return intervals produced CWD that occupied more of the forest floor than did 200- or 300-yr intervals. The time required for 100% occupancy of the forest floor by CWD was 1125, 1350, and 1300 yr for 100-, 200-, and 300-yr fire-return intervals, respectively. Simulations suggest that current harvest and post-harvest slash treatment regimes will require at least four centuries longer for 100% of the forest floor to be occupied by CWD (1800–3600 yr) than under fire regimes. This may have important effects on soil characteristics. Only when post-harvest CWD slash was doubled over the current amounts did clearcutting leave sufficient CWD to maintain forest floor CWD within the historic range of variability for naturally developing post-fire stands.

Interactions of White Pine Blister Rust and Mountain Pine Beetle in Whitebark Pine Ecosystems in the Southern Greater Yellowstone Area

ABSTRACT: Whitebark pine (Pinus albicaulis) is a fundamental component of alpine and subalpine habitats in the Greater Yellowstone Ecosystem. The magnitude of current white pine blister rust (WPBR) infection caused by the pathogen Cronartium ribicola and mountain pine beetle (MPB; Dendroctonus ponderosae) impacts, combined with the effect of climate change on beetle population dynamics, are placing this foundation species in a precarious state. We collected stand- and tree-level data in three whitebark pine systems in the southern Greater Yellowstone Ecosystem to evaluate current conditions and to determine how characteristics of individual whitebark pine trees, including the presence and severity of white pine blister rust, influence host selection by the MPB. Data revealed that 45% of all whitebark pine trees sampled were dead. In addition, 67% of all trees sampled were attacked by MPB, 83% were infected with WPBR, and 62% were affected by both. Whitebark pine trees that were selected as hosts by MPB exhibited significantly greater blister rust severity than trees that were not selected. Multiple logistic regression analyses identified a complex set of tree characteristics related to host selection by MPB; in addition to rust severity, stand type (mixed species or pure whitebark pine) and tree diameter were also significant predictors of selection. The interaction among MPB selection patterns, blister rust severity, tree diameter, and stand type quantified in this study will likely continue to influence the disturbance pattern and severity in whitebark pine ecosystems in the Greater Yellowstone Area. Understanding these patterns is critical to successful management of whitebark pine forests in this region.

Twenty‐four years after the Yellowstone Fires: Are postfire lodgepole pine stands converging in structure and function?

Disturbance and succession have long been of interest in ecology, but how landscape patterns of ecosystem structure and function evolve following large disturbances is poorly understood. After nearly 25 years, lodgepole pine (Pinus contorta var. latifolia) forests that regenerated after the 1988 Yellowstone Fires (Wyoming, USA) offer a prime opportunity to track the fate of disturbance-created heterogeneity in stand structure and function in a wilderness setting. In 2012, we resampled 72 permanent plots to ask (1) How have postfire stand structure and function changed between 11 and 24 yr postfire, and what variables explain these patterns and changes? (2) How has landscape-level (among-stand) variability in postfire stand structure and function changed between 11 and 24 yr postfire? We expected to see evidence of convergence beginning to emerge, but also that initial postfire stem density would still determine trajectories of biomass accumulation. After 24 yr, postfire lodgepole pine density remained very high (mean = 21,738 stems/ha, range = 0-344,067 stems/ha). Stem density increased in most plots between 11 and 24 yr postfire, but declined sharply where 11-yr-postfire stem density was > 72,000 stems/ha. Stems were small in high-density stands, but stand-level lodgepole pine leaf area, foliage biomass, and live aboveground biomass increased over time and with increasing stem density. After 24 yr, mean annual lodgepole pine aboveground net primary production (ANPP) was high (mean = 5 Mg · ha⁻¹ · yr⁻¹, range = 0-16.5 Mg · ha⁻¹ · yr⁻¹). Among stands, lodgepole pine ANPP increased with stem density, which explained 69% of the variation; another 8% of the variation was explained by environmental covariates. Early patterns of postfire lodgepole pine regeneration, which were contingent on prefire serotiny and fire severity, remained the dominant driver of stand structure and function. We observed mechanisms that would lead to convergence in stem density (structure) over time, but it was landscape variation in functional variables that declined substantially. Stand structure and function have not converged across the burned landscape, but our evidence suggests function will converge sooner than structure.

Variation in foliar nitrogen and aboveground net primary production in young postfire lodgepole pine

Understanding nutrient dynamics of young postfire forests may yield important insights about how stands de- velop following stand-replacing wildfires. We studied 15-year-old lodgepole pine stands that regenerated naturally follow- ing the 1988 Yellowstone fires to address two questions: (1) How do foliar nitrogen (N) concentration and total foliar N vary with lodgepole pine density and aboveground net primary production? (2) Is foliar N related to litter production and to rates of gross production, consumption, and net production of soil NH4 + and NO3 - ? Foliar N concentration of new lodge- pole pine needles averaged 1.38%; only stands at very high density (>80 000 treesha -1 ) approached moderate N limitation. Foliar N concentration in composite (all-age) needles averaged 1.08%, varied among stands (0.87%-1.39%), and declined with increasing tree density. The foliar N pool averaged 48.3 kg Nha -1 , varied among stands (3.6-218.4 kg Nha -1 ), and in- creased with aboveground net primary production. Total foliar N was not related to laboratory estimates of net production of NH4 + or NO3 - in soils. Lodgepole pine foliage is a strong N sink, and N does not appear to be limiting at this early suc-