Influence of fire regimes on lodgepole pine stand age and density across the Yellowstone National Park (USA) landscape

A probabilistic spatial model was created based on empirical data to examine the influence of different fire regimes on stand structure of lodgepole pine (Pinus contorta var. latifolia) forests across a >500,000-ha landscape in Yellowstone National Park, Wyoming, USA. We asked how variation in the frequency of large fire events affects (1) the mean and annual variability of age and tree density (defined by postfire sapling density and subsequent stand density) of lodgepole pine stands and (2) the spatial pattern of stand age and density across the landscape. The model incorporates spatial and temporal variation in fire and serotiny in predicting postfire sapling densities of lodgepole pine. Empirical self-thinning and in-filling curves alter initital postfire sapling densities over decades to centuries. In response to a six-fold increase in the probability of large fires (0.003 to 0.018 year⁻¹), mean stand age declined from 291 to 121 years. Mean stand density did not increase appreciably at high elevations (1,029 to 1,249 stems ha⁻¹) where serotiny was low and postfire sapling density was relatively low (1,252 to 2,203 stems ha⁻¹). At low elevations, where prefire serotiny and postfire lodgepole pine density are high, mean stand densities increased from 2,807 to 7,664 stems ha⁻¹. Spatially, the patterns of stand age became more simplified across the landscape, yet patterns of stand density became more complex. In response to more frequent stand replacing fires, very high annual variability in postfire sapling density is expected, with higher means and greater variation in stand density across lodgepole pine landscapes, especially in the few decades following large fires.     

Fire severity and seed source influence lodgepole pine (<Emphasis Type="Italic">Pinus contorta</Emphasis> var. <Emphasis Type="Italic">murrayana</Emphasis>) regeneration in the southern cascades,Lassen volcanic National Park,California

Rocky Mountain lodgepole pine, (Pinus contorta var. latifolia) regenerates quickly after high severity fire because seeds from serotinous cones are released immediately post-fire. Sierra lodgepole pine (P. contorta var. murrayana) forests burn with variable intensity resulting in different levels of severity and because this variety of lodgepole pine does not have serotinous cones, little is known about what factors influence post-fire regeneration. This study quantifies tree regeneration in a low, moderate, and high severity burn patch in a Sierra lodgepole forest 24 years after fire. Regeneration was measured in ten plots in each severity type. In each plot, we quantified pre- and post-fire forest structure (basal area, density), counted and aged tree seedlings and saplings of all species, and measured distance to the nearest seed bearing tree. There was no difference in the density of seedlings and saplings among severity classes. Distance and direction to the nearest seed bearing lodgepole pine were the best predictors of lodgepole seedling and sapling density in high severity plots. In contrast to Rocky Mountain lodgepole pine, regeneration of Sierra lodgepole pine appears to rely on in-seeding from surviving trees in low or moderate severity burn patches or live trees next to high severity burn patches. Our data demonstrate that Sierra lodgepole pine follows stand development pathways hypothesized for non-serotinous stands of Rocky Mountain lodgepole pine.     

Spatial patterns of sand pine invasion into longleaf pine forests in the Florida Panhandle

Land use practices since European settlement have had profound effects on the composition and structure of certain forested ecosystems in the southeastern U.S. Coastal Plain. One significant change since the turn of the century has been the invasion of upland pine forests by sand pine in the state of Florida panhandle and peninsula. This study quantified sand pine extent and expansion and examined links between sand pine distribution and environmental factors in the Florida panhandle. Geographic information system analysis using aerial photographs (1949 and 1994) showed sand pine expansion and also increased canopy cover of sand pine over time. There was a high rate of conversion of longleaf pine to sand pine from 1949 to 1994 (44%), and conversion of sparse sand pine stands to dense sand pine stands (69%). Therefore, widespread changes in the Florida landscape were evident during a relatively short time period. Adjacency analyses showed a strong negative association between longleaf pine and dense sand pine and a positive association between riparian vegetation and dense sand pine. Distribution of sand pine across elevation demonstrated that sand pine expanded inland and upland into longleaf-pine forests. In 1949, sand pine was selectively located on sites below 30 m in elevations; by 1994, sparse and moderately dense sand-pine stands were found at all elevations. Thus, any area that may receive an input of sand pine seeds, most notably from riparian areas, is vulnerable to establishment.     

Post-fire aspen seedling recruitment across the Yellowstone (USA) Landscape

Landscape patterns of quaking aspen (Populus tremuloides) seedling occurrence and abundance were studied after a rare recruitment event following the 1988 fires in Yellowstone National Park, Wyoming, USA. Belt transects (1 to 17 km in length, 4 m width) along 18 foot trails were surveyed for aspen seedlings on the subalpine plateau of the Park, along gradients of elevation and geologic substrate, during the summer of 1996. Aspen seedling presence and density were characterized as a function of elevation, geologic substrate, slope, aspect, vegetation/cover type, presence of burned forest, and distance to nearest adult aspen stand. Presence of aspen seedlings was best predicted by the incidence of burned forest and proximity to adult aspen; aspen seedlings were only found in burned forest and were more likely to occur closer to adult aspen clones. When tested against independent data collected in 1997, the logistic regression model for aspen seedling presence performed well (overall accuracy = 73%, Tau_p = 0.41). When present, variation in aspen seedling density at local scales (≤ 200 m) was largely explained by elevation, with higher densities observed at lower elevations. At broad scales (> 1 km), seedling density was a function of cover type, elevation, aspect, slope, and burn severity, with greater seedling density in more severely burned forested habitats on southerly, shallow slopes at lower elevations. Aspen seedling densities ranged from 0 to 46,000 seedlings/ha with a median density of 2,000/ha on sites where they occurred. Aspen seedlings were most abundant in the south central and southwest central regions of the park, approximately an order of magnitude less abundant in the southeast region, and nearly absent in the north central area. Establishment of new aspen stands on Yellowstone's subalpine plateau would represent a substantial change in the landscape. However, the long-term fate of these postfire aspen seedlings is not known. This revised version was published online in August 2006 with corrections to the Cover Date.     

Predictors of bark beetle activity and scale-dependent spatial heterogeneity change during the course of an outbreak in a subalpine forest

Climate conditions and forest structure interact to determine the extent and severity of bark beetle outbreaks, yet the relative importance of each may vary though the course of an outbreak. In 2008, we conducted field surveys and reconstructed forest conditions at multiple stages within a recent mountain pine beetle (MPB) outbreak in Rocky Mountain National Park, Colorado. At each stage in the outbreak, we examined changes in (1) lodgepole pine mortality and surviving stand structure, (2) the influence of topographic versus stand structure variables on mortality rates, and (3) stand complexity and landscape heterogeneity. Lodgepole pine mortality reduced basal area by 71 %, but only 47 % of stems were killed. Relative to pre-outbreak stands, surviving stands had lower mean dbh (11.0 vs. 17.4 cm), lower basal area (8.5 vs. 29.3 m² ha^?1), lower density (915 vs. 1,393 stems ha^?1), and higher proportions of non-host species (23.1 vs. 10.6 % m² ha^?1). Factors predicting mortality rates changed through the course of the outbreak. Tree mortality during the early stage of the outbreak was associated with warm, dry sites and abundant large trees. During the middle and late stages, mortality was associated with stand structure alone. Stand complexity increased, as defined by stand-scale variability in density, basal area, and the proportion of susceptible trees. Landscape heterogeneity decreased according to semi-variograms of tree diameter and basal area. Increased stand complexity may inhibit future MPB population development, but decreased landscape heterogeneity may facilitate outbreak spread across the landscape if a future outbreak were to irrupt.     

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.     

Reconstructing Landscape-scale Tree Invasion Using Survey Notes in the Medicine Bow Mountains, Wyoming, USA

We assessed landscape-scale invasions of openings in mountain forests by native tree species since EuroAmerican settlement (ca. 1870–1899). We reconstructed historical openings across a 250,240 ha area in the Medicine Bow Mountains, Wyoming, using notes from the original General Land Office (GLO) surveys, and compared historical openings to modern openings interpreted from digital aerial photography. We constructed logistic regression models to describe and predict tree invasion, based on a set of environmental and land use predictors. Openings have decreased by about 7.3% in the last ca. 110 years. Invasion was more likely to occur on moister sites, indicated by high values for steady-state wetness, low values for evaporative demand, proximity to streams, and topographic settings in basins or channels. More invasion also occurred on unprotected public land, in openings surrounded by lodgepole pine and aspen, and on mesic soils. The relatively slow rates of invasion in the study area may be driven by climate and land use.     

Complex interactions shaping aspen dynamics in the Greater Yellowstone Ecosystem

Loss of aspen (Populus tremuloides) has generated concern for aspen persistence across much of the western United States. However, most studies of aspen change have been at local scales and our understanding of aspen dynamics at broader scales is limited. At local scales, aspen loss has been attributed to fire exclusion, ungulate herbivory, and climate change. Understanding the links between biophysical setting and aspen presence, growth, and dynamics is necessary to develop a large-scale perspective on aspen dynamics. Specific objectives of this research were to (1) map aspen distribution and abundance across the Greater Yellowstone Ecosystem (GYE), (2) measure aspen change in the GYE over the past 50 years (3) determine if aspen loss occurs in particular biophysical settings and (4) investigate the links between biophysical setting and aspen presence, growth, and change in canopy cover. We found that aspen is rare in the GYE, occupying 1.4% of the region. We found an average of 10% aspen loss overall, much lower than that suggested by smaller-scale studies. Aspen loss corresponded with biophysical settings with the lowest aspen growth rates, where aspen was most abundant. The highest aspen growth rates were at the margins of its current distribution, so most aspen occur in biophysical settings less favorable to their growth.     

Spatial prediction of caterpillar (<Emphasis Type="Italic">Ormiscodes</Emphasis>) defoliation in Patagonian <Emphasis Type="Italic">Nothofagus</Emphasis> forests

In the temperate forests of the southern Andes, southern beech species (Nothofagus), the dominant tree species of the region, experience severe defoliation caused by caterpillars of the Ormiscodes genus (Lepidoptera: Saturniidae). Despite the recent increase in defoliation frequency in some areas, there is no quantitative information on the spatial extent and dynamics of these outbreaks. This study examines the spatial patterns of O. amphimone outbreaks in relation to landscape heterogeneity. We mapped defoliation events caused by O. amphimone in northern (ca. 40–41°S) and southern Patagonian (ca. 49°S) Nothofagus forests from Landsat imagery and analyzed their spatial associations with vegetation cover type, topography (elevation, slope angle, aspect) and mean annual precipitation using overlay analyses. We used these data and relationships to develop a logistic regression model in order to generate maps of predicted susceptibility to defoliation by O. amphimone for each study area. Forests of N. pumilio are typically more susceptible to O. amphimone outbreaks than lower elevation forests of other Nothofagus species (N. dombeyi and N. antarctica). Stands located at intermediate elevations and on gentle slopes (<15°) are also more susceptible to defoliation than higher and lower elevation stands located on high angle slopes. Stands in areas with intermediate to high precipitation, relative to the distribution of Nothofagus along the precipitation gradient, are more susceptible to O. amphimone attack than are drier areas. Our study represents the first mapping and spatial analysis of insect defoliator outbreaks in Nothofagus forests in South America.     

Early forest dynamics in stand-replacing fire patches in the northern Sierra Nevada, California, USA

There is considerable concern over the occurrence of stand-replacing fire in forest types historically associated with low- to moderate-severity fire. The concern is largely over whether contemporary levels of stand-replacing fire are outside the historical range of variability, and what natural forest recovery is in these forest types following stand-replacing fire. In this study we quantified shrub characteristics and tree regeneration patterns in stand-replacing patches for five fires in the northern Sierra Nevada. These fires occurred between 1999 and 2008, and our field measurements were conducted in 2010. We analyzed tree regeneration patterns at two scales: patch level, in which field observations and spatial data were aggregated for a given stand-replacing patch, and plot level. Although tree regeneration densities varied considerably across sampled fires, over 50 % of the patches and approximately 80 % all plots had no tree regeneration. The percentage of patches, and to a greater extent plots, without pine regeneration was even higher, 72 and 87 %, respectively. Hardwood regeneration was present on a higher proportion of plots than either the pine or non-pine conifer groups. Shrub cover was generally high, with approximately 60 % of both patches and individual plots exceeding 60 % cover. Patch characteristics (size, perimeter-to-area ratio, distance-to-edge) appeared to have little effect on observed tree regeneration patterns. Conifer regeneration was higher in areas with post-fire management activities (salvage harvesting, planting). Our results indicate that the natural return of pine/mixed-conifer forests is uncertain in many areas affected by stand-replacing fire.     

Spatial patterns of large natural fires in Sierra Nevada wilderness areas

The effects of fire on vegetation vary based on the properties and amount of existing biomass (or fuel) in a forest stand, weather conditions, and topography. Identifying controls over the spatial patterning of fire-induced vegetation change, or fire severity, is critical in understanding fire as a landscape scale process. We use gridded estimates of fire severity, derived from Landsat ETM+ imagery, to identify the biotic and abiotic factors contributing to the observed spatial patterns of fire severity in two large natural fires. Regression tree analysis indicates the importance of weather, topography, and vegetation variables in explaining fire severity patterns between the two fires. Relative humidity explained the highest proportion of total sum of squares throughout the Hoover fire (Yosemite National Park, 2001). The lowest fire severity corresponded with increased relative humidity. For the Williams fire (Sequoia/Kings Canyon National Parks, 2003) dominant vegetation type explains the highest proportion of sum of squares. Dominant vegetation was also important in determining fire severity throughout the Hoover fire. In both fires, forest stands that were dominated by lodgepole pine (Pinus contorta) burned at highest severity, while red fir (Abies magnifica) stands corresponded with the lowest fire severities. There was evidence in both fires that lower wind speed corresponded with higher fire severity, although the highest fire severity in the Williams fire occurred during increased wind speed. Additionally, in the vegetation types that were associated with lower severity, burn severity was lowest when the time since last fire was fewer than 11 and 17 years for the Williams and Hoover fires, respectively. Based on the factors and patterns identified, managers can anticipate the effects of management ignited and naturally ignited fires at the forest stand and the landscape levels.     

Modeling fire and landform influences on the distribution of old-growth pinyon-juniper woodland

Expansion of Pinus and Juniperus species into shrub steppe in semi-arid regions of the western United States has been widely documented and attributed in part to fire exclusion. If decreased fire frequency has been an important cause of woodland expansion, one would expect to find age structures dominated by younger trees on more fire-prone sites, with old-growth pinyon-juniper woodland limited to sites with lower fire risk. We compared current old-growth distribution with spatial models for fire risk in a 19-km² watershed in central Nevada, USA. Multiple GIS models were developed to represent fire susceptibility, according to abiotic factors representing fuels and topographic barriers to fire spread. We also developed cellular automata models to generate fire susceptibility surfaces that additionally account for neighborhood effects. Rule-based GIS models failed to predict old-growth distribution better than random models. Cellular automata models incorporating spatial heterogeneity of site productivity predicted old-growth distribution better than random models but with low accuracy, ranging from 58% agreement at the single-pixel (0.09-ha) scale to 80% agreement for 20-pixel neighborhoods. The best statistical model for predicting old-growth occurrence included the negative effect of topographic convergence index (local wetness), and the positive effects of solar insolation and proximity to rock outcrops. Results support the hypothesis that old-growth woodlands in the Great Basin are more likely to occur on sites with low fire risk. However, weak relationships suggest that old-growth woodlands have not been confined to fire-safe sites. Conservation efforts should consider the landscape context of old-growth woodlands across a broad landscape, with an emphasis on conserving landscape variability in tree age structure.     

Estimating regional forest productivity and water yield using an ecosystem model linked to a GIS

We used the PnET-II model of forest carbon and water balances to estimate regional forest productivity and runoff for the northeastern United States. The model was run at 30 arc sec resolution (approximately 1 km) in conjunction with a Geographic Information System that contained monthly climate data and a satellite-derived land cover map. Predicted net primary production (NPP) ranged from 700 to 1450 g m² yr¹ with a regional mean of 1084 g m² yr¹. Validation at a number of locations within the region showed close agreement between predicted and observed values. Disagreement at two sites was proportional to differences between measured foliar N concentrations and values used in the model. Predicted runoff ranged from 24 to 150 cm yr¹with a regional mean of 63 cm yr¹. Predictions agreed well with observed values from U.S. Geologic Survey watersheds across the region although there was a slight bias towards overprediction at high elevations and underprediction at lower elevations.Spatial patterns in NPP followed patterns of precipitation and growing degree days, depending on the degree of predicted water versus energy limitation within each forest type. Randomized sensitivity analyses indicated that NPP within hardwood and pine forests was limited by variables controlling water availability (precipitation and soil water holding capacity) to a greater extent than foliar nitrogen, suggesting greater limitations by water than nitrogen for these forest types. In contrast, spruce-fir NPP was not sensitive to water availability and was highly sensitivity to foliar N, indicating greater limitation by available nitrogen. Although more work is needed to fully understand the relative importance of water versus nitrogen limitation in northeastern forests, these results suggests that spatial patterns of NPP for hardwoods and pines can be largely captured using currently available data sets, while substantial uncertainties exist for spruce-fir.     

Plant-pest interactions in time and space: A Douglas-fir bark beetle outbreak as a case study

A conceptual model of Douglas-fir bark beetle (Dendroctonus pseudotsugae) dynamics and associated host tree mortality across multiple spatial and temporal scales was developed, then used to guide a study of the association between the occurrence of beetle- killed trees and factors that might render trees more susceptible to attack. Long-term records of beetle kill showed that beetle epidemics were associated with windstorms and drought at statewide and local spatial scales. At the landscape scale, beetle kill was associated with (i) portions of the landscape that were potentially drier (southern aspects, lower elevations) and (ii) portions of the landscape that had more mature and old-growth conifer vegetation. The patches of beetle-killed trees were aggregated with respect to other patches at scales of approximately 1 and 4 km. At the scale of the individual tree, there was not a strong relationship between beetle kill and resistance to attack measured by tree growth rate prior to attack. Our results show that landscape-scale phenomena and temporal patterns were more strongly correlated with beetle-kill events than was recent growth history at the scale of individual trees. We suggest that the multi-scale approach we employed is useful for elucidating the relative roles of fine- versus coarse-scale constraints on ecological processes.     

Multi-scale landscape and seascape patterns associated with marbled murrelet nesting areas on the U.S. west coast

Habitat for wide-ranging species should be addressed at multiple scales to fully understand factors that limit populations. The marbled murrelet (Brachyramphus marmoratus), a threatened seabird, forages on the ocean and nests inland in large trees. We developed statistical relationships between murrelet use (occupancy and abundance) and habitat variables quantified across many spatial scales (statewide to local) and two time periods in California and southern Oregon, USA. We also addressed (1) if old-growth forest fragmentation was negatively associated with murrelet use, and (2) if some nesting areas are more important than others due to their proximity to high quality marine habitat. Most landscapes used for nesting were restricted to low elevation areas with frequent fog. Birds were most abundant in unfragmented old-growth forests located within a matrix of mature second-growth forest. Murrelets were less likely to occupy old-growth habitat if it was isolated (> 5 km) from other nesting murrelets. We found a time lag in response to fragmentation, where at least a few years were required before birds abandoned fragmented forests. Compared to landscapes with little tono murrelet use, landscapes with many murrelets were closer to the ocean's bays, river mouths, sandy shores, submarine canyons, and marine waters with consistently high primary productivity. Within local landscapes (≤ 800ha), inland factors limited bird abundance, but at the broadest landscape scale studied (3200 ha), proximity to marine habitat was most limiting. Management should focus on protecting or creating large, contiguous old-growth forest stands, especially in low-elevation areas near productive marine habitat. This revised version was published online in July 2006 with corrections to the Cover Date.     

Accessibility as a determinant of landscape transformation in western Honduras: linking pattern and process

This study evaluates the relationship between landscape accessibility and land cover change in Western Honduras, and demonstrates how these relationships are influenced by social and economic processes of land use change in the region. The study area presents a complex mosaic of land cover change processes that involve approximately equal amounts of reforestation and deforestation. Landsat Thematic Mapper (TM) satellite imagery of 1987, 1991 and 1996 was used to create three single date classifications and a land cover change image depicting the sequence of changes in land cover between 1987–1991–1996. An accessibility analysis examined land cover change and landscape fragmentation relative to elevation and distance from roads. Between 1987 and 1991, results follow ‘expected’ trends, with more accessible areas experiencing greater deforestation and fragmentation. Between 1991 and 1996 this trend reverses. Increased deforestation is found in areas distant from roads, and at higher elevations; a result of government policies promoting expansion of mountain coffee production for export. A ban on logging, and abandonment of marginally productive agricultural fields due to agricultural intensification in other parts of the landscape, has led to increased regrowth in accessible regions of the landscape. Roads and elevation also present different obstacles in terms of their accessibility, with the smallest patches of cyclical clearing and regrowth, relating mostly to the agricultural fallow cycle, found at the highest elevations but located close to roads. This research highlights the need to locate analyses of land cover change within the context of local socio-economic policies and land use processes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Forest roads and landscape structure in the southern Rocky Mountains

Roadless areas on public lands may serve as environmental baselines against which human-caused impacts on landscape structure can be measured. We examined landscape structure across a gradient of road densities, from no roads to heavily roaded, and across several spatial scales. Our study area was comprised of 46,000 ha on the Roosevelt National Forest in north-central Colorado. When forest stands were delineated on the basis of seral stage and covertype, no relationship was evident between average stand size and road density. Topography appeared to exert a greater influence on average stand size than did road density. There was a significant positive correlation between the fractal dimension of forest stands and road density across all scales. Early-seral stands existed in greater proportions adjacent to roads, suggesting that the effects of roads on landscape structure are somewhat localized. We also looked at changes in landscape structure when stand boundaries were delineated by roads in addition to covertype and seral stage. Overall, there was a large increase in small stands with simple shapes, concurrent with a decline in the number of stands > 100 ha. We conclude that attempts to quantify the departure from naturalness in roaded areas requires an understanding of the factors controlling the structure of unroaded landscapes, particularly where the influence of topography is great. Because roads in forested landscapes influence a variety of biotic and abiotic processes, we suggest that roads should be considered as an inherent component of landscape structure. Furthermore, plans involving both the routing of new roads and the closure of existing ones should be designed so as to optimize the structure of landscape mosaics, given a set of conservation goals.     

Microhabitat conditions and landscape pattern explain nocturnal rodent activity,but not seed removal,in burned and unburned lodgepole pine forests

Context

Disturbances create spatial variation in environments that may influence animal foraging. Granivory by rodents can influence seed supply and thus plant establishment. However, effects of disturbance patterns on rodent seed removal in western North American conifer forests are generally unknown.

Objectives

We conducted a study in lodgepole pine (Pinus contorta var. latifolia) forests of Greater Yellowstone (Wyoming, USA) to answer: (1) How do seed removal and rodent activity vary between recently burned and adjacent unburned forests and with distance from fire perimeter? (2) Which microhabitat conditions explain variability in seed removal and rodent activity?

Methods

One or two years after wildfires, we established transects (n = 23) with four stations each: at 10 and 40 m from the fire perimeter in both burned and unburned forest. At stations, we deployed trays with lodgepole pine seeds and cameras pointed at trays for 28 days and quantified habitat structure and seed abundance.

Results

Seed removal, which averaged 85%, and diurnal rodent activity did not differ between burned and unburned forests or with distance from the fire perimeter; however, nocturnal rodent activity was lower in burned forests. Seed removal and diurnal rodent activity were not associated with any microhabitat conditions we measured. However, nocturnal rodent activity was associated with microhabitat in both burned and unburned forests.

Conclusions

High seed removal rates suggested that rodent foraging was not reduced by high-severity wildfire. If observed seed removal represents natural conditions, post-dispersal seed predation could influence post-fire recruitment of a widespread foundation tree species.

     

Long-term,landscape patterns of past fire events in a montane ponderosa pine forest of central Colorado

Parameters of fire regimes, including fire frequency, spatial extent of burned areas, fire severity, and season of fire occurrence, influence vegetation patterns over multiple scales. In this study, centuries-long patterns of fire events in a montane ponderosa pine – Douglas-fir forest landscape surrounding Cheesman Lake in central Colorado were reconstructed from fire-scarred trees and inferences from forest stand ages. We crossdated 153 fire-scarred trees from an approximately 4000 ha study area that recorded 77 total fire years from 1197 to the present. Spatial extent of burned areas during fire years varied from the scale of single trees or small clusters of trees to fires that burned across the entire landscape. Intervals between fire years varied from 1 to 29 years across the entire landscape to 3 to 58 years in one stand, to over 100 years in other stands. Large portions of the landscape did not record any fire for a 128 year-long period from 1723 to 1851. Fire severity varied from low-intensity surface fires to large-scale, stand-destroying fires, especially during the 1851 fire year but also possibly during other years. Fires occurred throughout tree growing seasons and both before and after growing seasons. These results suggest that the fire regime has varied considerably across the study area during the past several centuries. Since fires influence plant establishment and mortality on the landscape, these results further suggest that vegetation patterns changed at multiple scales during this period. The fire history from Cheesman Lake documents a greater range in fire behavior in ponderosa pine forests than generally has been found in previous studies.     

A comparison of local and general models of leaf area and biomass of urban trees in USA

Ecosystem service estimation is a very popular topic. Many urban studies use the i-Tree Eco model developed by US Forest Service to estimate ecosystem services. Several ecosystem service estimation studies have been conducted acting upon the assumption that relationships developed elsewhere are applicable to sites that vary in species, site, climate, and environmental conditions. This study tested the accuracy of highly used existing leaf area and biomass models when used outside the region in which it was developed. To do this, we measured 74 urban trees from five species in Stevens Point, Wisconsin collecting data such as diameter at breast height (Dbh), tree height, height to the base of live crown, crown width, crown volume, leaf area, and leaf dry weight biomass. Using the data, we developed two models each to predict leaf area and biomass. Using ten independent samples, we compared our predictions with predictions from the existing models which are also used in i-Tree. Our results indicated that the local models developed in the current study predicted leaf area and biomass better than existing models which had higher prediction error. The difference in prediction will ultimately affect ecosystem services estimation when. using i-Tree, and future studies should acknowledge the difference.