Fire history and fire–climate relationships along a fire regime gradient in the Santa Fe Municipal Watershed, NM, USA

The Santa Fe municipal watershed provides up to 40% of the city's water and is at high risk of a stand-replacing fire that could threaten the water resource and cause severe ecological damage. Restoration and crown fire hazard reduction in the ponderosa pine (PP) forest is in progress, but the historic role of crown fire in the mixed-conifer/aspen (MC) and spruce-dominated forests is unknown but necessary to guide management here and in similar forests throughout the southwestern United States. The objective of our study was to use dendroecological techniques to reconstruct fire history and fire–climate relationships along an elevation, forest type, and fire regime gradient in the Santa Fe River watershed and provide historical ecological data to guide management. We combined systematic (gridded) sampling of forest age structure with targeted sampling of fire scars, tree-ring growth changes/injuries, and death dates to reconstruct fire occurrence and severity in the 7016 ha study area (elevation 2330–3650 m). Fire scars from 141 trees (at 41 plots) and age structure of 438 trees (from 26 transects) were used to reconstruct 110 unique fire years (1296–2008). The majority (79.0%) of fires burned during the late spring/early summer. Widespread fires that scarred more than 25% of the recording trees were more frequent in PP (mean fire interval (MFI)_25% = 20.8 years) compared to the MC forest (31.6 years). Only 24% of the fires in PP were recorded in the MC forest, but these accounted for a large percent of all MC fires (69%). Fire occurrence was associated with anomalously wet (and usually El Niño) years preceding anomalously dry (and usually La Niña) years both in PP and in the MC forest. Fire in the MC occurred during more severe drought (mean summer Palmer Drought Severity Index; PDSI = −2.59), compared to the adjacent PP forest (PDSI = −1.03). The last fire in the spruce forest (1685) was largely stand-replacing (1200 ha, 93% of sampled area), recorded as fire scars at 68% of plots throughout the MC and PP forests, and burned during a severe, regional drought (PDSI = −6.92). The drought–fire relationship reconstructed in all forest types suggests that if droughts become more frequent and severe, as predicted, the probability of large, severe fire occurrence will increase.     

Fire history and fire management implications in the Yukon Flats National Wildlife Refuge, interior Alaska

We conducted this investigation in response to criticisms that the current Alaska Interagency Fire Management Plans are allowing too much of the landscape in interior Alaska to burn annually. To address this issue, we analyzed fire history patterns within the Yukon Flats National Wildlife Refuge, interior Alaska. We dated 40 fires on 27 landscape points within the refuge boundaries using standard dendrochorological methods. Fire return intervals based on tree ring data ranged from 37 to 166 years (mean = 90 ± 32 years; N = 38) over the 250 year time frame covered by this study. We found no significant differences in the frequency of fire occurence over time. There was no evidence to suggest that changes in fire management policy have significantly altered the fire regime in the Yukon Flats area. However, the lack of significant differences over time may be due in part to the relatively short time period that fires were actively suppressed in Alaska. The full suppression era (1939–1984) may have been too short to significantly alter the fire regime in all areas of interior Alaska.     

Variation in moth occurrence and implications for foraging habitat of Ozark big-eared bats

We investigated patterns of moth occurrence among habitats in two different landscapes surrounding roosts of the endangered Ozark big-eared bat (Corynorhinus townsendii ingens) from May to August 2005, and compared these data with published results on the diet of this subspecies. Landscapes were situated in the Ozark Mountains, USA, and consisted of a fragmented, agricultural landscape and a contiguous national forest. We captured 8720 moths constituting ≥314 species and 22 families. Pastures demonstrated a lower abundance and richness of moths than other habitats in the fragmented landscape (p < 0.05). Neither abundance nor richness of moths varied by habitat in the forested landscape, but we did observe variation among roost locations (p < 0.05). Abundant families of moths (n ≥ 100 specimens captured) did vary in abundance among habitats in both landscapes (p < 0.05), with poletimber stands, riparian forest and upland forest selected, and pasture, forest edge, sawtimber and sapling stands avoided by at least one family of moths. Density and richness of woody plant species were correlated with the occurrence of moths at sampling sites. We recommend maintaining habitat heterogeneity around roosts of the Ozark big-eared bat to encourage an abundance and richness of moth prey, and suggest that forested riparian corridors are important habitat elements for Ozark big-eared bats foraging in fragmented landscapes.     

Forest structure and woody plant species composition along a fire chronosequence in mixed pine–oak forest in the Sierra Madre Oriental, Northeast Mexico

Although wildfires are occurring frequently in the pine–oak forests in the Sierra Madre Oriental (northeastern Mexico), data on post-fire succession and forest structure are still rare. Our objectives were to (1) assess the changes in woody plant species composition after fire and to (2) to relate successional patterns to environmental variability. Based on their fire history 23 plots were selected in the Parque Ecológico Chipinque (PECH). Changes in forest structure across the chronosequence of burned stands were deduced from density, height and diameter measurements of trees and shrubs (>5 cm in diameter) in all plots of 1000 m². Differences in woody plant species composition among the plots were evaluated using Shannon evenness measure and the Whittaker's measure and by Hierarchical cluster analysis and Detrended Correspondence Analysis. Hierarchical cluster analysis showed a high similarity among all recently burned plots, independed of the aspect. Multivariate analysis showed that local environmental factors, including time since fire, continue to structure species composition. Oak species (mainly Quercus rysophylla) resprouted successfully after fire and dominated young post-fire stands. Pine species (Pinus pseudotrobus and Pinus teocote) only appeared 18 years after fire and were the dominating species in mature stands (62 years after fire). In contrast, woody plant species composition in older stands tended also to be influenced by factors such as aspect and by the potential solar radiation (PSR) during the growing season. The results demonstrate that in the PECH, natural regeneration is sufficient and woody plant species composition will be similar to pre-fire conditions after 60 years of succession. We conclude that the park managers should consider incorporating natural disturbance regimes into their management practices.     

Post-fire tree stress and growth following smoldering duff fires

Understanding the proximate causes of post-fire conifer mortality due to smoldering duff fires is essential to the restoration and management of coniferous forests throughout North America. To better understand duff fire-caused mortality, we investigated tree stress and radial growth following experimental fires in a long-unburned forest on deep sands in northern Florida, USA. We burned basal fuels surrounding 80 mature Pinus palustris Mill. in a randomized experiment comparing the effects of basal burning treatments on stem vascular meristems; surficial roots; root and stem combinations; and a non-smoldering control. We examined the effects of duration of lethal temperatures (>60 °C) on subsequent pine radial growth and root non-structural carbohydrates (starch and sugar). Duff and mineral soil temperatures in the experimental fires consistently exceeded 60 °C for over an hour following ignition, with lethal temperatures of shorter duration recorded 20 cm below the mineral soil surface. Duff heating was best explained by day-of-burn Oe horizon moisture (P = 0.01), although little variation was explained (R² = 0.24). Post-fire changes in latewood radial increment in the year following fires was related to duration of temperatures >60 °C 10 cm deep in the mineral soil (P = 0.07), but explained little variability in post-fire growth (R² = 0.17). In contrast, changes in non-structural carbohydrate content in coarse roots (2–5 mm diameter) 120 days following burning were more strongly correlated with the duration of lethal heating 5 cm below the mineral soil surface (P = 0.02; R² = 0.53). Results from this study implicate the role of mineral soil heating in the post-fire decline of mature longleaf pine following restoration fires in sandy soils.     

Ponderosa pine snag densities following multiple fires in the Gila Wilderness,New Mexico

Fires create and consume snags (standing dead trees), an important structural and ecological component of ponderosa pine forests. The effects of repeated fires on snag densities in ponderosa pine forests of the southwestern USA have not been studied. Line intercept sampling was used to estimate snag densities in areas of the Gila Wilderness that had burned one to three times under Wildland Fire Use for Resource Benefit (WFU), a fire management policy implemented since 1974 aimed at restoring natural fire regimes. Twenty randomly located transects were measured in areas burned since 1946; six in once-burned areas, six in twice-burned areas and eight in thrice-burned areas. The mean density ± standard errors of large (>47.5 cm dbh) snags for areas that burned once, twice and thrice was 7.0 ± 2.7, 4.4 ± 1.1 and 4.1 ± 1.3 snags/ha, respectively. Differences in snag densities between once- and multiple-burned areas were significant (F-test; p < 0.05). There was no significant difference in density of large snags between twice- and thrice-burned areas. Proportions of type 1 snags (recently created) were higher in once- and twice-burned areas than in areas that burned three times, likely reflecting high tree mortality and snag recruitment resulting from an initial entry fire. Type 3 snags (charred by previous fire) were more abundant in areas that burned multiple times. The lack of differences in snag densities between areas that burned two and three times suggests that repeated fires leave many snags standing. The increasing proportion of type 3 snags with repeated fires supports this conclusion.     

Fuels and fire behavior in chipped and unchipped plots: Implications for land management near the wildland/urban interface

Fire behavior was measured and modeled from eight 1 ha experimental plots located in the Francis Marion National Forest, South Carolina, during prescribed burns on February 12 and February 20, 2003. Four of the plots had been subjected to mechanical chipping during 2002 to remove woody understory growth and to reduce large downed woody debris from the aftermath of Hurricane Hugo in 1989. The remaining four (control) plots were left untreated. The burns were low intensity (mean flame length = 36.2 cm) and slow moving (mean spread rate = 1.18 m min⁻¹). Neither flame length nor rate of spread differed significantly between treatments (ANOVA F's < 0.5, P > 0.7, d.f. = 1,4). Post-burn observations provided somewhat more convincing evidence of treatment effects on fire behavior. According to transect data, only slightly more than half the area in the chip plots burned as compared to upwards of 80% in the burn-only plots. BehavePlus and Hough–Albini (HA) fire models correctly predicted the low intensity, slow moving fires given the observed wind and fuel moisture conditions. Accuracy of BehavePlus predictions depended on the value for fuel height entered in the model. Use of mean fuel height for the fuel depth parameter, as is typically recommended, somewhat overestimated fire hazard in the burn-only plots. However, limiting fuel height to the observed litter depth resulted in roughly accurate predictions. HA predictions for untreated fuels were close to correct even without adjusting fuel depth. When provided with two “high-risk” fuel and fire weather scenarios both models predicted more extreme fire behavior in the untreated fuels. In contrast, chipping appeared to protect against dangerous wildfires as long as fuel heights remained low. Smoke monitoring data from a companion study carried out in the same plots indicated a 60% reduction in smoke particulate production from chipped areas, roughly consistent with predictions of the fire effects model FOFEM. Mechanical chipping is apparently a useful method for limiting fire-hazard and smoke production in long-unburned fuels. However, questions remain concerning the long-term fate of heavy chip fuels and resultant effects on fire and smoke during severe drought.     

黑龙江省1980—2005年森林火灾时空特征

森林火灾是林火失去人为控制,在森林内自然蔓延和扩展,对生态系统和人类带来一定危害和损失的森林起火。森林火灾属世界性、跨国性的重大自然灾害,进入20世纪80—90年代以来,全球气候变暖导致森林火灾有上升的趋势,虽然各国的森林防火费用不断增加,但森林火灾发生的面积并未相     

Densification, stand-replacement wildfire, and extirpation of mixed conifer forest in Cuyamaca Rancho State Park, southern California

A century of fire suppression culminated in wildfire on 28 October 2003 that stand-replaced nearly an entire 4000 ha “sky island” of mixed conifer forest (MCF) on Cuyamaca Mountain in the Peninsular Range of southern California. We studied the fire affected Cuyamaca Rancho State Park (CRSP), which represents a microcosm of the MCF covering approximately 5.5 × 10⁶ ha (14%) of California, to evaluate how fire suppression unintentionally destabilizes this ecosystem. We document significant changes in forest composition, tree density, and stem diameter class distribution over a 75-year period at CRSP by replicating ground-based measurements sampled in 1932 for the Weislander Vegetation Type Map (VTM) survey. Average conifer density more than doubled, from 271 ± 82 trees ha⁻¹ (standard error) to 716 ± 79 ha⁻¹. Repeat aerial photographs for 1928 and 1995 also show significant increase in canopy cover from 47 ± 2% to 89 ± 1%. Changes comprise mostly ingrowth of shade-tolerant Calocedrus decurrens [Torr.] Floren. in the smallest stem diameter class (10–29.9 cm dbh). The 1932 density of overstory conifer trees (>60 cm dbh) and 1928 canopy cover at CRSP were similar to modern MCF in the Sierra San Pedro Mártir (SSPM), 200 km S in Baja California, Mexico, where fire suppression had not been practiced, verifying that the historical data from the early twentieth century represent a valid “baseline” for evaluating changes in forest structure. Forest successions after modern crown fires in southern California demonstrate that MCF is replaced by oak woodlands and shrubs. Post-fire regeneration in severely burned stands at CRSP includes abundant basal sprouting of Quercus chrysolepis Liebm. and Quercus kelloggii Newb., but only few seedlings of Abies concolor [Gord. and Glend.] Lindl (average 16 ± 14 ha⁻¹), while whole stands of C. decurrens, Pinus lambertiana Dougl., and Pinus ponderosa Laws. were extirpated. Prescribed burning failed to mitigate the crown fire hazard in MCF at CRSP because the low-intensity surface fires were small relative to the overall forest area, and did not thin the dense understory of sapling and pole-size trees. We propose that larger, more intense prescribed understory burns are needed to conserve California's MCF.     

Prescribed fire,snag population dynamics,and avian nest site selection

Snags are an important resource for a wide variety of organisms, including cavity-nesting birds. We documented snag attributes in a mixed-conifer forest dominated by ponderosa pine in the Sierra Nevada, California where fire is being applied during spring. A total of 328 snags were monitored before and after fire on plots burned once, burned twice, or left unburned to assess the effects of prescribed fire on snag populations. The greatest loss of snags (7.1 snags ha⁻¹ or 43%) followed the first introduction of fire after a long fire-free period. On plots burned a second time 21% of snags (3.6 snags ha⁻¹) were lost, whereas 8% (1.4 snags ha⁻¹) were lost on unburned control plots in the same time period. New snags replaced many of those lost reducing the net snag losses to 12% (2.0 ha⁻¹) for plots burned once, and 3% (0.5 ha⁻¹) for plots burned twice and unburned plots. We also examined snags used by cavity-nesting birds. Snags preferred for nesting were generally ponderosa pine (Pinus ponderosa), larger diameter, and moderately decayed as compared to available snags. For monitored snags that met the preferred criteria, there was a net loss (1.7 snag ha⁻¹ or 34%) after the first burn, while the loss of useable snags was less than 1 snag ha⁻¹ following the second burn (15%) or on unburned controls (8%). We recommend protection of preferred snags, in particular large ponderosa pines, especially during primary fire applications on fire-suppressed landscapes.     

The effects of fire on the regeneration of a Quercus douglasii stand in Quail Ridge Reserve, Berryessa Valley (California)

Wildfire is an important element in the dynamics of the blue oak (Quercus douglasii) stand. We evaluated the effect of fire in the regeneration of a stand in Quail Ridge. This protected area is located on a peninsula formed by the flooding of Berryessa Valley (California) which has helped it maintain many elements of the native flora. Major vegetation types are blue oak woodland and forest (Q. douglasii, Fagaceae), chamise chaparral (Adenostoma fasciculatum, Rosaceae), and grasslands. In the blue oak stand, 14 plots were randomly located: seven in the burned area and seven outside of the burned areas (control). The effect of fire on sexual regeneration, asexual regeneration, mortality and species composition was analyzed. The fire caused changes in canopy cover, soil cover and litter cover. Asexual regeneration was significantly favored by the fire, but the effect on sexual regeneration was not significant. Fire caused a significant reduction in the basal area of Q. wislizeni and Arctostaphylos manzanita and a reduction in the density of Heteromeles arbutifolia. We concluded that fire does not have a significant effect on the sexual regeneration of Q. douglasii or Q. wislizeni. Fire does stimulate asexual regeneration in both species of oaks, but grazing reduces the regenerative effect of fire. Fire increases regeneration of Arctostaphylos manzanita and Heteromeles arbutifolia by stimulating asexual and sexual regeneration. The occupancies of these chaparral species are further enhanced by their lower palatability compared to both species of oaks.     

Influence of coarse wood and pine saplings on nitrogen mineralization and microbial communities in young post-fire Pinus contorta

Nitrogen (N) limits productivity in many coniferous forests of the western US, but the influence of post-fire structure on N cycling rates in early successional stands is not well understood. We asked if the heterogeneity created by downed wood and regenerating pine saplings affected N mineralization and microbial community composition in 15-yr old lodgepole pine (Pinus contorta var. latifolia) stands established after the 1988 fires in Yellowstone National Park (Wyoming, USA). In three 0.25-ha plots, we measured annual in situ net N mineralization in mineral soil using resin cores (n = 100 per plot) under pine saplings, downed wood (legacy logs that survived the fire, and fire-killed trees that had fallen and were contacting or elevated above the ground), and in bare mineral soil. Annual in situ net N mineralization and net nitrification rates were both greater in bare mineral soil (8.4 ± 0.6 and 3.6 ± 0.3 mg N kg_soil⁻¹ yr⁻¹, respectively) than under pine saplings, contact logs, or elevated logs (ca. 3.9 ± 0.5 and 0.8 ± 0.1 mg N kg_soil⁻¹ yr⁻¹, respectively). Net nitrification was positively related to net N mineralization under all treatments except for elevated logs. In laboratory incubations using ¹⁵N pool dilution, NH₄⁺ consumption exceeded gross production by a factor of two in all treatments, but consumption and gross production were similar among treatments. Contrary to our initial hypothesis, microbial community composition also did not vary among treatments. Thus, two- to three-fold differences in in situ net N mineralization rates occurred despite the similarity in microbial communities and laboratory measures of gross production and consumption of NH₄⁺ among treatments. These results suggest the importance of microclimate on in situ annual soil N transformations, and differences among sites suggest that broader scale landscape conditions may also be important.     

Immediate effects of fire-severity on soil invertebrates in cut and uncut pine forests

We studied how variations in fire severity and the degree of cutting before burning affected soil invertebrates in a Pinus sylvestris forest in central Sweden. A varied depth of burn in the mor layer was obtained by exclusion of rain and addition of fuel in small plots (1 m×2 m) in clear-cut, selectively cut and uncut part of the forest before large-scale prescribed burning took place. Soil samples were taken from the plots immediately before, the day after, and two months after the fire. The overall mortality of invertebrates depended on the proportion of organic soil consumed by the fire, and for individual taxa it ranged between 59 and 100%. Invertebrates that lived deeper in soil suffered lesser mortality than those in the vegetation and litter layers did. Greater mobility in soil (Staphylinidae) or a thick cuticle (Oribatediae, Elateridae) may have contributed to the higher survival observed in these taxa. The beetles Atomaria pulchra (Cryptophagidae), Corticaria rubripes (Lathridiidae), and other fire-favoured insects colonised the burned forest the very day the fire burned. These species preferred the hard-burned plots and the uncut stand for colonisation. Sixty days after the fire, the abundance of invertebrates was lower in the burned cut stands compared to the burned uncut stand. The species composition of beetles in the burned stands was then characterised by a few very abundant fire-favoured species.     

Valuing acorn dispersal and resprouting capacity ecological functions to ensure Mediterranean forest resilience after fire

Ecological processes within forests provide vital ecosystem services to society, most of which depend on the persistence of tree cover that can be altered after the impact of a disturbance. The aim of the present study was to examine the role of seed dispersal and resprouting that mediate resilience to large fires and evaluate the economic costs that these ecological functions provide. We used field data from 412 plots of the Spanish National Forest Inventory providing information on pre- and post-fire conditions of Mediterranean Pinus spp. and Quercus spp.-dominated forests. Then, we determined the need for restoration (N _Rest) and estimated the minimum pre-fire densities needed to ensure adequate post-fire cover. Economic valuations were assessed through three different scenarios (Sc) of possible human-management actions aimed at ensuring proper post-fire tree cover: Sc. 1) a pre-fire management scenario evaluating the costs of planting Quercus spp. seedlings in the understory, mimicking the whole dispersal function; Sc. 2) a pre-fire scenario in which enrichment plantations increased the densities of natural oaks; and Sc. 3) a post-fire scenario where the restoration is done through planting pines within the burned area. Approximately 90% of the burned area (371 out of 412 plots) was able to recover after fire supporting the view that Mediterranean forests are resilient to fire. This resilience was primarily mediated by biotic seed dispersal and posterior resprouting of tree species. These ecological functions saved between 626 and 1,326 €/ha compared to the human-management actions. Ensuring key ecological processes within forests increases forest resilience and recovery after fire leading to a generally significant saving of economic resources. In a perspective of increased future impact of disturbances and decrease availability of economic resources for forest management, the implications of the present study can be far reaching and extended to other forest planning exercises.     

Characterization of forest fires in Catalonia (north-east Spain)

The present study analyses the temporal variation in the distribution of the number of fires, area burned and fire sizes in Catalonia using fire data from 1942 to 2002. The study shows variations in the distribution of fire size over recent decades, with a significant increase in the number of very large fires. The study also analyses relationships between characteristics of the forest (altitude, slope, aspect, living fuels and species composition) and the probability of the fire occurrence. The analysis is based on the overlay of forest cover data and perimeters of forest fires during the period (1986–2002). Of the analysed variables, altitude affects most the probability of fire occurrence, with higher proportions of burned forest area at lower altitudes. Stand’s vertical structure is also relevant, with lower proportions of burned area in stands with mature tree cover without understory. The study helps to analyse the strengths and weaknesses of forest and fire management policies, especially those related to forest and fuel management at the landscape level.     

Historic and current fire regimes in the Great Xing’an Mountains,northeastern China: Implications for long-term forest management

Understanding both historic and current fire regimes is indispensable to sustainable forest landscape management. In this paper, we use a spatially explicit landscape simulation model, LANDIS, to simulate historic and current fire regimes in the Great Xing’an Mountains, in northeastern China. We analyzed fire frequency, fire size, fire intensity, and spatial pattern of burnt patches. Our simulated results show that fire frequency under the current fire scenario is lower than under the historic fire scenario; total area burnt is larger with lower fire intensity under the historic fire scenario, and smaller with higher fire intensity under the current fire scenario. We also found most areas were burned by high intensity fires under the current fire scenario, but by low to moderate fires under the historic fire scenario. Burnt patches exhibit a different pattern between the two simulation scenarios. Large patches burnt by high intensity class fires dominate the landscape under the current fire scenario, and under historic fire scenario, patches burnt by low to moderate fire intensity fires have relatively larger size than those burnt by high intensity fires. Based on these simulated results, we suggest that prescribed burning or coarse woody debris reduction should be incorporated into forest management plans in this region, especially on north-facing slopes. Tree planting may be a better management option on these severely burned areas whereas prescribed burning after small area selective cutting, retaining dispersed seed trees, may be a sound forest management alternative in areas except for the severely burned patches.     

Recoupling fire and aspen recruitment after wolf reintroduction in Yellowstone National Park,USA

We report on the recent growth of upland aspen (Populus tremuloides Michx.) thickets in northwestern Yellowstone National Park, USA following wolf (Canis lupus L.) reintroduction in 1995. We compared aspen growth patterns in an area burned by the 1988 fires to aspen growth patterns in an adjacent unburned area. Elk (Cervus elaphus L.) are the principal ungulates that use this area to meet foraging needs. Within a 2 m × 6 m belt transect established in each aspen thicket, we measured aspen densities and recorded annual browsing and height information on the three tallest post-1988 aspen stems. We found greater densities (p < 0.01) in the burned area relative to the unburned area. A decline in the percentage of stems browsed in the burned area began in 1997, with no measured browsing occurring since 2001. In contrast, the percentage of stems browsed in the unburned area began declining in 2002, with 41% of stems still being browsed in 2004. We hypothesize that the combined effect of fire and a subsequent decrease in herbivory following wolf reintroduction facilitated aspen growth. We further propose that, in addition to any changes in elk density in recent years, a recoupling of fire with increased predation risk from wolves may create a positive feedback loop that improves aspen recruitment.     

Understorey plant community characteristics and natural hardwood regeneration under three partial harvest treatments applied in a northern red oak (Quercus rubra L.) stand in the Great Lakes-St. Lawrence forest region of Canada

Throughout eastern North America, stands of northern red oak (Quercus rubra L.) are undergoing successional replacement by shade-tolerant competitors. In the Great Lakes-St. Lawrence (GLSL) forest region, Q. rubra approaches the northern limit of its distribution, and ecosystem-specific silvicultural directives are needed to promote regeneration. We used an inductive, ordination-based approach to explore patterns in understorey plant community composition and microenvironment under different partial harvest treatments applied in a GLSL hardwood stand, and related these to characteristics of natural seedlings of Q. rubra and its competitors Acer rubrum and Acer saccharum.Two years after harvest, we established 2 m × 2 m plots in a stratified random design under 70% (n = 20) and 50% (n = 19) crown closure uniform shelterwood, group selection (n = 15), and uncut upper slope (n = 10) and lower slope (n = 10) areas. Percent cover of understorey vascular plant species, and a suite of microclimatic and edaphic variables were measured in each plot. Density, mean diameter and mean height of seedlings in the understorey (height <1 m) were determined in each plot for Q. rubra, A. rubrum and A. saccharum.Correspondence analysis (CA) ordination extracted two major axes explaining 21.6% of the total inertia in the species cover by plot matrix. Axis one separated uncut plots from the 50% shelterwood along a gradient of canopy cover associated with partial harvest treatments. Plot scores on axis one (13.2%) reflected a shift in dominance of the understorey from shade-tolerant Acer spp. to shade-intolerant colonizers, Rubus idaeus and Carex spp. Plot scores on axis one were directly (p < 0.05) associated with total understorey plant cover, litter depth, soil temperature and pH, but not with measures of plant diversity. Axis two (8.4%) separated plots from upper slope and lower slope areas, and plot scores were inversely associated (p < 0.05) with soil pH, phosphorus and nitrogen levels. Along axis two there was a shift in dominance from competitive (e.g. A. saccharum) to stress-tolerant (e.g. A. rubrum) species as soil fertility declined. Stepwise linear regression indicated seedling diameter in Q. rubra, A. rubrum and A. saccharum was inversely related to canopy cover. This suggests all three species benefited from partial harvest, although the relationship was strongest in Q. rubra. Patterns in understorey composition, microenvironment and seedling characteristics provide the basis to identify the main competitors of Q. rubra seedlings and adjust regeneration efforts along gradients of canopy closure and soil fertility under partial harvest systems within the GLSL forest region.     

Dendrochronology-based fire history of mixed-conifer forests in the San Jacinto Mountains,California

The growing public awareness of the increasing number of large wildfires across forested landscapes, coupled with needs of resource base management has accelerated research into forest reference conditions and the historical role of fire in coniferous ecosystems. This work investigates historical fire regimes of mixed-conifer forests in the San Jacinto Mountains of southern California using fire-scar dendrochronology. As such this is the first reconstruction of fire history in the mixed-conifer forests of southern California using landscape-scale systematic-based fire-scar dendrochronology. The pre-historical fire size, seasonality, and frequency within these forests are reconstructed and demonstrated graphically, employing systematic sampling and Geographical Information System (GIS) reconstruction. A 250 m grid system was overlaid upon a 270 ha sample location, and fire-scar samples were collected from each of the grid intersection points. Fire-scar dendrochronology resulted in a 653 years long chronology, indicating a point mean fire return interval of 5.2 years, and an area wide grand mean fire interval of 32.2 years. The majority of fires occurred within latewood or at the ring boundary. Graphic modelling of fire events indicate three-quarters of all fires sampled were less than 6.25 ha in size, but burned over 50% of the area sampled during the period; only a small portion of fires were larger than 18 ha within the sample area. Use of systematic sampling is an important step in modeling long-term frequency and effects of fire on a landscape level, and is invaluable to the long-term management planning.