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1.
Shrub encroachment has become a problem in many rangeland systems across the United States due to a reduction in the disturbances, primarily fire, which historically maintained them. The shrub saw palmetto (Serenoa repens) has become abundant in many habitats of the southeastern Coastal Plain, including Florida. When fire regimes are altered or fires are suppressed, this species can proliferate leading to significant changes in the ecosystem, particularly the herbaceous vegetation. Prescribed burning and roller chopping are management activities often used to control saw palmetto. However, little is known about the effects these treatments have on this shrub, particularly when applied in different seasons. We compared the seasonal effects of prescribed burning, roller chopping, and combinations of the two on saw palmetto. The effects of treatments on saw palmetto were assessed using a paired-sample approach, where saw palmetto height, cover, and density were compared between sampling locations randomly located within treated (e.g., burned) and untreated areas. Dormant season burning had no effect on saw palmetto density and height and only temporarily reduced cover, with rapid regrowth occurring the first year post-treatment. Growing season burning also had no effect on saw palmetto density. However, saw palmetto cover was lower on growing season burn compared to control sites the first year post-treatment and height the first and second year post-treatment. The combination of burning and roller chopping, despite having no effect on saw palmetto density, did result in lower saw palmetto height compared to controls the first and second year post-treatment. The effect of roller chopping/burning on saw palmetto cover depended on season and year. Saw palmetto cover and height were lower on dormant and growing season roller chop than control sites the first and second year post-treatment, but only growing season roller chopping had an effect on saw palmetto density. The single application of a dormant or growing season burn is not recommended for control of high-density saw palmetto, however, it may be suitable to maintain areas where saw palmetto levels are low and proliferation of the species is not a threat. Dormant and growing season roller chopping showed the greatest potential for rapid saw palmetto control. Growing season roller chopping is recommended if significant reductions in saw palmetto density are desired.  相似文献   

2.
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3.
After an absence of approximately 70 years, gray wolves (Canis lupus) were re-introduced into Yellowstone National Park in the mid-1990s. We studied the potential influence of wolf/ungulate interactions upon willow (Salix spp.) growth in the valleys of the Gallatin and Lamar Rivers, as well as Slough and Soda Butte Creeks, in the northern Yellowstone ecosystem. When we compared willow heights from photographs taken prior to 1998 (willows <2 m tall) with those taken in 2004, we found an increase in willow height for 22 of 42 sites within the study area. Based on comparisons of the chronosequence photos, since wolf introduction none of the 16 upland riparian sites showed an increase in willow height, while 22 of 26 of the valley-bottom riparian sites had willow height increases. In 2004, willow height exhibited a strong inverse relationship with the percentage of browsed stems (r = −0.81, p < 0.01, n = 42). Results of regressions for valley-bottom sites indicated that view distance, impediment distance, and the number of bison (Bison bison) flops were inversely related to willow height (p ≤ 0.02). Increased willow heights were not significantly (p = 0.18) related to patterns of moisture availability. Willow height increases documented in this study appear to have been at least partially due to behaviorally mediated trophic cascades involving wolves and ungulates, via a mechanism of predation risk. While willow release (i.e., increased height growth) within the study area is in a very early stage, results suggest potentially important indirect effects of a top carnivore in a terrestrial food chain that may aid in the restoration of riparian species and the preservation of biodiversity.  相似文献   

4.
Pre-commercial thinning (PCT) is a silvicultural practice that can provide diverse understory and overstory vegetation conditions. We tested the hypothesis that relative habitat use by snowshoe hare (Lepus americanus), mule deer (Odocoileus hemionus), and moose (Alces alces) would increase in response to enhanced abundance of herbs and shrubs, and species diversity and structural diversity of conifers, in heavily thinned (≤1000 stems/ha) stands, at 12–15 years post-thinning. Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three young pine stands thinned to densities of 500 stems/ha (low), 1000 stems/ha (medium), and 2000 stems/ha (high), with an unthinned young pine and old-growth pine stand for comparison.

Relative habitat use, based on counts of fecal pellets and pellet-groups, was similar among the five treatment stands for hares (P = 0.24), deer (P = 0.23), and moose (P = 0.16). However, low-density stands (500 stems/ha) had ca. 3–20 times as many deer pellet-groups, and ca. 2–4 times as many moose pellet-groups, than other stands. Low-density stands had significantly greater canopy openness, volume of shrubs <2 m, and horizontal hiding cover <1.6 m than other treatments. Relative habitat use by deer and moose was positively related to understory characteristics such as enhanced abundance of forage and security cover. These results support our hypothesis that deer and moose responded positively to enhanced volume of herbs and shrubs as well as to species diversity and structural diversity of conifers and overall vegetation in heavily thinned (≤1000 stems/ha) stands at 12–15 years post-thinning. Our results suggest that ungulate management would be enhanced if greater emphasis was placed on forage enhancement throughout the year, which differs from current management recommendations which tend to focus on winter range and snow-interception cover.  相似文献   


5.
The occurrence of Scots pine (Pinus sylvestris L.) seedlings and saplings (<2.0 m in height and suppressed by grazing) and ground characteristics were recorded in a 300 ha block of natural pine forest in 1993. The density of red deer (Cervus elaphus L.) was then reduced by exclosure to approximately 3–4 deer km−2, which is below the threshold at which pine regeneration should occur. Numbers and performance of pine seedlings and saplings were further monitored 2 and 4 years after exclosure. Numbers of young pine increased over time. In the three years with observations 97–99% of pine seedlings and saplings were recorded within 20 m of a seed source. Stepwise multiple regression was used to explore the relationships of pine establishment with plot characteristics for (a) all observation plots (n = 178) and (b) plots within 20 m of a seed source (n = 154). The factors most closely related to the number of pine seedlings and saplings in 1997 were, for (a), seed–source distance, vegetation height, blaeberry cover, slope and deer pellet-group density in 1993, all but the last having negative effects. For (b), vegetation height, blaeberry cover and slope were again selected predictors, and again had negative effects. Possible mechanisms by which the selected main effects may influence pine regeneration are discussed, the positive relationship to deer density being considered to reflect the creation of gaps in the sward suitable for germination. However, the amounts of variation explained in the models were low, being 16% for (a) and 13% for (b), reflecting the patchy nature and diverse age of the regeneration.  相似文献   

6.
We evaluated ground-layer plant diversity and community composition in northern hardwood forests among uncut controls and stands managed with even-age or uneven-age silvicultural systems. Even-age treatments included diameter-limit cuttings (20-cm diameter at 30-cm stem height) in 1952 and shelterwood removals in 1964. Uneven-age treatments included three intensities of selection harvest (light, 20.6 m2/ha residual basal area after harvest; medium, 17.2 m2/ha residual basal area; and heavy, 13.8 m2/ha residual basal area) that were applied in 1952, 1962, 1972, and 1982. All treatments were winter logged over snow pack. In 1991, plant diversity and community composition were examined. Species richness for spring ephemerals ranged from 1 to 6 species/150-m2, spring ephemeral diversity (Shannon's Index of Diversity) averaged 0.57 ± 0.04 and evenness averaged 0.45 ± 0.03. Summer flowering species richness ranged from 1 to 18 species/1-m2, with an average diversity of 0.71 ± 0.07 and evenness of 0.42 ± 0.03. We found no significant differences among treatments for any of these variables, although power to detect a difference (at p = 0.05) was low in all cases (0.15–0.55) due to high variance and low replication. Community composition was not significantly different among the treatments, for either spring (p = 0.09) or summer (p = 0.79) flora. Few exotic species were found in any treatment. Lack of exotic invasions and minimal differences in plant diversity or composition among treatments may be due, in part, to the negligible amount of soil disturbance that resulted from winter logging. While other (unmeasured) ecosystem components may differ among these silvicultural treatments, our results suggest that ground-layer plant communities in northern hardwood ecosystems are either resistant to change or have recovered within the 40 years since disturbance in the even-age treatments and within 10 years since disturbance in the uneven-age treatments.  相似文献   

7.
In 1989, the first recorded outbreak of hemlock looper (Lambdina fiscellaria fiscellaria (Guen.)) occurred in New Brunswick, Canada. Data were collected from ten plots established in an area infested from 1992–1994, to assess impacts of hemlock looper. Ocular and branch sample assessments of current defoliation and ocular assessments of total defoliation (all age classes of foliage) were conducted for balsam fir (Abies balsamea [L.] Mill.), white spruce (Picea glauca [Moench] Voss), and black spruce (Picea mariana (Mill.) B.S.P.). Stand response was assessed and related to cumulative defoliation. Ocular assessments were found to accurately estimate defoliation, which was significantly related to tree mortality. Ninety-two percent of balsam fir trees that had cumulative defoliation >90% died. Mortality of balsam fir was significantly (p < 0.05) related to tree size, in both lightly and severely defoliated plots; trees with DBH <11 cm sustained 22–48% higher mortality than larger trees. Mortality of balsam fir, in terms of both percent stems/ha and m3/ha merchantable volume, increased exponentially in relation to three estimates of cumulative (summed) plot mean defoliation. The strongest relationships (r2 = 0.75–0.79) were between mortality and the ocular defoliation assessment for 1990–1993 foliage. Tree mortality caused by the looper outbreak ranged from 4–14% stems/ha in lightly defoliated and from 32–100% in severely defoliated plots; merchantable volume killed was 3–14 m3/ha and 51–119 m3/ha, respectively. Relationships between mortality and defoliation were similar when defoliation was assessed for 1987–1993 and 1990–1993 foliage age classes.  相似文献   

8.
Fire is an important component of the historic disturbance regime of oak and pine forests that occupy sandy soils of the coastal outwash plain of the northeastern US. Today prescribed fire is used for fuel reduction and for restoration and maintenance of habitat for rare plant and animal, animal species. We evaluated the effects of the frequency and seasonality of prescribed burning on the soils of a Cape Cod, Massachusetts's coastal oak-pine forest. We compared soil bulk density, pH and acidity, total extractable cations and total soil carbon (C) and nitrogen (N) in unburned plots and in plots burned over a 12-year period, along a gradient of frequency (every 1–4 years), in either spring (March/April) or summer (July/August). Summer burning decreased soil organic horizon thickness more than spring burning, but only summer burning every 1–2 years reduced organic horizons compared with controls. Burning increased soil bulk density of the organic horizon only in the annual summer burns and did not affect bulk density of mineral soil. Burn frequency had no effect on pH in organic soil, but burning every year in summer increased pH of organic soil from 4.01 to 4.95 and of mineral soil from 4.20 to 4.79. Burning had no significant effect on organic or mineral soil percent C, percent N, C:N, soil exchangeable Ca2+, Mg2+, K+ or total soil C or N. Overall effects of burning on soil chemistry were minor. Our results suggest that annual summer burns may be required to reduce soil organic matter thickness to produce conditions that would regularly allow seed germination for oak and for grassland species that are conservation targets. Managers may have to look to other measures, such as combinations of fire with mechanical treatments (e.g., soil scarification) to further promote grasses and forbs in forests where establishment of these plants is a high priority.  相似文献   

9.
Three treatments designed to initiate the process of restoring the surface fire regime and open forest structure of a southwestern ponderosa pine forest were compared on the Kaibab National Forest along the Grand Canyon’s South Rim. The treatments were: (1) full restoration (FULL)—thinning trees to emulate stand structure prior to fire regime disruption ca. 1887, forest floor fuel treatment, and prescribed burning, (2) minimal thinning (MIN)—removing young trees only around living old-growth (pre-1887) trees, fuel treatment, and prescribed burning, (3) burn-only (BURN)—representing the current management policy in Grand Canyon National Park (GCNP), and (4) CONTROL. Each treatment was applied to a 12 ha unit. Compared to reconstructed 1887 conditions, all study sites were much more dense prior to treatment (94–176 trees/ha in 1887, compared to 783–3693 trees/ha in 1997). However, basal area increases were less striking (12.6–20.3 in 1887, 17.5–27.0 m2/ha in 1997), reflecting past harvest and dwarf mistletoe reduction treatments that removed many large pines. In 2000, 1 year after treatment, tree densities were reduced to 11, 23, and 37 of pre-treatment levels in the FULL, MIN, and BURN treatments, respectively. Understory plant communities showed significant declines in richness and plant frequency across years, probably due to a severe drought in 2000 (60% of average precipitation). No differences in plant communities were observed across treatments, despite the mechanized disturbance associated with tree removal in the FULL treatment. Prescribed fire behavior (flame length, flaming zone depth) and effects (bole char, crown scorch) were similar across all three burned treatments. Simulated fire behavior under dry, windy conditions was reduced in all three treatments compared to the control. The FULL treatment was much less susceptible to crownfire due to reduced crown bulk density and crown fuel load and increased crown base height. Crownfire susceptibility of the BURN treatment was only slightly reduced, while the MIN treatment was intermediate. Compared to the reference conditions of forest structure, the FULL treatment represented the most rapid and comprehensive restoration treatment, although the residual stand was at the low end of historical density. The BURN treatment thinned many small trees but had minor effects on crownfire susceptibility. Effects of the MIN treatment fell between FULL and BURN. The experimental treatments may be useful for the creation of defensible firebreaks near developments, roads, and boundaries with the FULL treatment, supplemented by MIN and BURN treatments over larger areas.  相似文献   

10.
Biomass burning in tropical forests – the normal practice to prepare land for agriculture and ranching – has been a major source of CO2 emitted to the atmosphere. Mass transformations by burning are still little studied in the tropics. The present study estimated parameters, such as the stock of carbon contained in the biomass, burning efficiency and the formation of charcoal and ashes in a tropical moist forest. Two sets of plots arranged in the form of ‘stars' (720 m2 total) were installed in a 3.5 ha area of forest that had been felled for planting pasture at Fazenda Nova Vida, Ariquemes, Rondônia. Each ‘star' had six rays measuring 2 m × 30 m; alternating rays were designated for pre-burn and post-burn measurements. All above-ground biomass present in the plots was weighed directly before the burn in the pre-burn rays and after the burn in the post-burn rays. Pieces of wood with diameter ≥10 cm also had their biomasses estimated from volume estimates, using line-intersect sampling (LIS) in order to increase the area of sampling and to allow volume loss to be estimated as an increment based on individual pieces measured before, and after, the burn at the same point (as opposed to inferring change as a difference between independent estimates of stocks). The initial above-ground biomass (dry weight) before the burn was estimated at 306.5 ± 48.6 (mean ± SE) Mg ha−1, with an additional 4.5 Mg ha−1 for trees left standing. Carbon stock in the initial biomass (including trees left standing) was 141.3 (Mg C) ha−1. After burning, carbon stock was reduced by 36.8% (burning efficiency). The stocks of charcoal and ash formed in the burn were, respectively, 6.4 ± 2.7 and 5.7 ± 1.0 Mg ha−1. The destructive and nondestructive (LIS) methods did not differ significantly (t-test, p > 0.05) in estimating post-burn stocks of wood and charcoal. The results of this study contribute to improving the estimates of parameters needed for global carbon calculations and point to ways in which estimates of these parameters could be further improved.  相似文献   

11.
Nitrogen fertilization in the nursery, along with altering the configuration of forest gaps, may improve the reforestation success of longleaf pine seedlings. During the very droughty 1998 growing season in Florida and Georgia, survival was higher under the forest canopy than in small (0.10 ha, 36 m diameter) and large (1.6 ha, 144 m diameter) canopy gaps. In the large gaps, survival of containerized seedlings was higher along the edges, particularly the SW edge. Shade from adult trees and the nurse effect of shrubs increased survival, while grass competition reduced survival. During dry years part of the “exclusionary zone” along the edge of canopy gaps (SW sector) may serve as a “survival zone”, at least in the short term. A model using oval-shaped gaps oriented from NW to SE, with an area of 0.25 ha is proposed to maximize the survival and growth of artificially regenerated longleaf pine seedlings.  相似文献   

12.
Alcoa World Alumina Australia has been rehabilitating bauxite mines in the jarrah (Eucalyptus marginata) forest of Western Australia for more than 35 years. It is a requirement of Alcoa’s completion criteria that rehabilitated areas can be incorporated into the prescribed burning program implemented in the surrounding forest. Rehabilitated areas may be more susceptible to nutrient losses following burning because of their relatively young age and reliance on N fixation from a legume understorey. The objective of this study was to assess the impact that prescribed burning has on the nutrient pools within rehabilitated ecosystems 5 and 8 years after fire, and compare these responses to unburnt rehabilitated areas and the unmined forest. The nutrient status of sites established in previous studies were assessed five (burnt and unburnt forest, 1989 and 1992 rehabilitation) and 8 (spring, autumn and unburnt 1981/1982 rehabilitation) years after burning. Soil, litter and understorey samples were collected and analysed for nutrient content. Burning 1981/1982 rehabilitation in either season 8 years earlier had no long-term negative effect on the nutrient status of the rehabilitation compared to the unburnt controls. Spring burning increased the nitrogen status of the rehabilitated areas by 52 kg ha−1 compared with the unburnt control. Sites rehabilitated in 1989 and burnt 5 years ago showed similar post-fire recovery of nitrogen status to that of the burnt native forest sites (77–85%), while 1992 rehabilitation sites had only recovered 52% of the of the nitrogen of the unburnt sites. Therefore, the impact of burning on nitrogen status was greatest in the 5-year-old rehabilitation and least in the 12–13-year-old sites. Phosphorus was less affected by burning than nitrogen largely because the majority of P is bound in the soil in the jarrah forest. It is recommended that rehabilitated sites are burnt under low intensity in spring when they are 12–15-year-old to ensure rapid post-fire recovery of nutrients.  相似文献   

13.
Dense Rhododendron ponticum (L.) understories of eastern beech (Fagus orientalis Lipsky) stands in the Black Sea Region (BSR) of Turkey create challenging forest vegetation management problems relative to beech regeneration. Rhododendron traditionally is controlled in Turkish forests with grubbing and bulldozing. The effects of these practices on nutrient removal and natural beech regeneration have not been quantitatively studied. Two woody vegetation control treatments (bulldozing and hand-grubbing) were installed during late summer, 2002 in three mature beech stands with dense rhododendron understories in the Düzce Forest Management Directorate, in the Turkish western BSR. Aboveground biomass of each vegetation component, total aboveground vegetation biomass, nutrient concentrations, organic matter (OM) removal, and total amount of OM nutrients were determined for each woody vegetation control treatment. Soil bulk density and nutrient content, and beech seedling biomass, nutrient content, and natural regeneration also were studied. One year after treatment, the machine site preparation by bulldozing (MSP) that removed understory vegetation and attached roots, reduced mean forest floor OM content by about 84%, when compared to hand-grubbing. Mean soil C, N, K and Mg concentrations on the bulldozed sites were 36, 27, 50 and 55% less, respectively, than those on the grubbed sites. Total C and Mg amounts at the 5–10 cm soil depth were 24 and 47% lower, respectively, for mechanical site preparation (MSP) sites, when compared to grubbed sites. Overall, soil bulk density did not differ significantly between the grubbing and MSP treatments. Frequent passes on designated transects on MSP sites resulted in a significant (P < 0.01) one-third increase in bulk density of the first 20 cm soil depth, when compared to grubbed sites. No natural beech regeneration occurred on untreated control sites. Mineral soil exposure on the MSP sites increased beech seedling germination substantially. One year after treatment, the mean number of naturally regenerated seedlings for MSP sites was 2.5 times greater than for grubbed sites. Woody control treatments had significant effects upon beech seedling chemistry, with N, P, K, Ca and Mg concentrations averaging 35, 47, 12, 33 and 25% lower, respectively, for MSP sites, when compared to grubbed sites. However, mean seedling biomass and nutrient content were significantly greater (P < 0.05) on MSP sites. Long-term effects from windrowing on MSP site residues, associated topsoil and nutrients need to be evaluated.  相似文献   

14.
Forest drains and streams on blanket peatland in western Ireland were sampled weekly, 1996–2000, using continuous, depth-proportional passive sampling, and analysed for molybdate-reactive phosphorus (MRP) by the acid–antimony-molybdate method. The study area was largely clearfelled and partly reforested with wind-rowing, drainage, planting, and aerially applied rock phosphate equivalent to 70 kg P/ha. Further felled areas were not wind-rowed, drained or fertilised for reforestation. Catchment areas were of the following orders: 1 ha (two forest drains); 10–20 ha (two semi-permanent drains, one permanent stream); 1–3 km2 (three permanent streams). Streamwater from three undisturbed closed-canopy-forest catchments had pre-felling median concentrations of MRP (all values are μg MRP l−1) of 9 (catchment approximately 1 km2), 13 (1 ha) and 93 (1 ha). Clearfelling was associated with large increases (maxima 305, 4164 and 3530 μg MRP l−1) in MRP concentrations in each case. Following protracted mechanical operations in four other catchments of ca. 1 km2, 20, 10 and 10 ha, with apparently existing elevated MRP concentrations (medians 41, 328, 102, 214 μg MRP l−1) fertilising gave major rises (maxima 218, 2723, 806, 2323 μg MRP l−1). The three smaller catchments showed subsequent exponential-type declines, while the 1 km2 catchment had sustained high values (median 74 μg MRP l−1) over the remaining study period. The higher values in this one larger stream were seasonally cyclical, with a late summer maximum. Annual median MRP values above 70 μg l−1 represent a seriously polluted state for these streams, which qualify as waterways under relevant statutes, but it is not clear what implications these results have for downstream river-water quality in larger channels.  相似文献   

15.
Little information is available comparing historic and modern sand savannas, and how remnants respond to restored fire. We compared short- and long-term effects of restored fire on the Tefft Savanna, a 197 ha eastern sand savanna in northwest Indiana that had undergone three decades of fire protection. U.S. Public Land Survey data from Tefft in 1833 indicate black and white oak barrens, and pin oak savanna, with trees averaging 50 stems/ha and 4 m2/ha basal area. We used ordination and a digital elevation model to assess topographic distribution of tree species in 1986. In 1986, we also compared initial effects of high- and low-intensity dormant season fire on woody vegetation among nine blocks containing black oak, white oak, and pin oak stands. Twenty years later, we compared the same blocks, all of which had been burned three times per decade with low-intensity fires. In 1986, black oak, white oak and pin oak occurred across a gradient of decreasing elevation and slope. At that time, unburned black oak and white oak stands averaged >400 stems/ha and about 10 m2/ha basal area, and their smaller size classes contained non-oak woody vegetation that apparently had invaded with fire exclusion. After initial burns, black oak and white oak stands receiving high-intensity fire averaged <200 stems/ha and had significantly lower oak canopy cover and basal area than unburned stands. Stands receiving low-intensity fire had intermediate oak canopy cover, with basal area similar to unburned stands. Pin oak stands were more fire-resistant, apparently because spring flooding often reduced fire effects. Density, cover and basal area of non-oak tree species were much lower than oaks, and were not reduced by initial burning. Repeated low-intensity burning over 20 years tended to maintain structure caused by initial fires. However, it reduced lower size class stem densities, promoted post-fire sprouting into the shrub layer, and allowed oak basal area to increase in larger size classes. Time since fire regulated shrub layer structure on a 4-year cycle. Density and cover of trees and shrubs returned to pre-burn conditions by the second and fourth growing seasons after fire, respectively, with non-oak tree species exceeding pre-burn cover and density by the fourth season. These results suggest that high-intensity fire is more important than repeated low-intensity burning in structuring and restoring eastern sand savanna, and that non-oak tree species, once established, may be resistant to low-intensity fire.  相似文献   

16.
Forestry practices such as fuel-reduction burning and maintenance of road networks can negatively impact avian assemblages, both directly by changing habitat structure and indirectly by creating conditions favorable for predators or competitors. The Brigalow Belt forests include some of the largest contiguous areas of native forest in the temperate and sub-humid zones of eastern Australia. Over 1 million ha of these forests are proposed to be converted from forestry to conservation tenure, yet the impacts on the avifauna of current and potential future forest management practices are not known. We investigated the influence of road edges and habitat type and structure on the avifauna of a 356 000 ha forest. Survey sites were either <50 m or >300 m from a road, and in either cypress pine Callitris glaucophylla forest, spotted gum Corymbia citriodora forest with a regenerating cypress pine/buloke Allocasuarina luehmannii understorey or spotted gum forest with an open understorey due to fuel-reduction burning. The avifauna differed significantly among vegetation types but not with proximity to a road, with the greatest differences between cypress pine and both types of spotted gum forest. The noisy miner Manorina melanocephala, an aggressive avian competitor, appears to be the factor mediating these assemblage-level differences. Noisy miners were rare in cypress pine forest but were three times more numerous than any other species in spotted gum forest. Spotted gum forest with a regenerating understorey had fewer noisy miners. Although total bird abundance was highest in open spotted gum forest, the species richness and abundance of passerines smaller than noisy miners was significantly lower in this forest type. Abundance of small passerines was eight times higher in sites where <3 noisy miners were recorded. Only one species, the eastern yellow robin, was influenced by proximity to a road edge. Cypress pine forest is potentially an important refuge for smaller birds. The results suggest that burning regimes that reduce regeneration of the cypress pine and buloke subcanopy in spotted gum forest potentially are exacerbating the problem of noisy miner domination of the avifauna.  相似文献   

17.
Long-term effects of salvage logging on coarse woody debris were evaluated on four stand-replacing wildfires ages 1, 11, 17, and 35 years on the Okanogan-Wenatchee National Forest in the eastern Cascades of Washington. Total biomass averaged roughly 60 Mg ha−1 across all sites, although the proportion of logs to snags increased over the chronosequence. Units that had been salvage logged had lower log biomass than unsalvaged units, except for the most recently burned site, where salvaged stands had higher log biomass. Mesic aspects had higher log biomass than dry aspects. Post-fire regeneration increased in density over time. In a complementary experiment, soils heating and surrogate-root mortality caused by burning of logs were measured to assess the potential site damage if fire was reintroduced in these forests. Experimentally burned logs produced lethal surface temperatures (60 °C) extending up to 10 cm laterally beyond the logs. Logs burned in late season produced higher surface temperatures than those burned in early season. Thermocouples buried at depth showed mean maximum temperatures exponentially declined with soil depth. Large logs, decayed logs, and those burned in late season caused higher soil temperatures than small logs, sound logs, and those burned in early season. Small diameter (1.25 cm), live Douglas-fir branch dowels, buried in soil and used as surrogates for small roots, indicated that cambial tissue was damaged to 10 cm depth and to 10 cm distance adjacent to burned logs. When lethal soil temperature zones were projected out to 10 cm from each log, lethal cover ranged up to 24.7% on unsalvaged portions of the oldest fire, almost twice the lethal cover on salvaged portions. Where prescribed fire is introduced to post-wildfire stands aged 20–30 years, effects of root heating from smoldering coarse woody debris will be minimized by burning in spring, at least on mesic sites. There may be some long-term advantages for managers if excessive coarse woody debris loads are reduced early in the post-wildfire period.  相似文献   

18.
The profitability of growing a naturally emerged birch (Betula pendula Roth or Betula pubescens Ehrh.) overstory in a young Norway spruce (Picea abies (L.) Karst.) plantation was examined with empirical stand structure, growth and yield, logging cost, and logging damage models. In the projected alternatives, an overstory of either birch species was thinned to 200–1000 stems per ha at the age of 15 years and retained for another 15 years. Development of the remaining spruce stand was simulated up to rotation age (70–85 years). Alternative treatments included removing the overstory completely at 15 years, and managing a pure spruce stand that was kept free of birch throughout.

Growing a birch overstory of 200–1000 stems per ha up to age 30 years resulted in a 61–93 m3 ha−1 or 9.1–16.8% yield loss for the spruce stand due to growth retardation, and a mortality of 382–498 out of 1900 stems per ha through logging damage. This was compensated for or exceeded by the additional yield of the birch (54–173 m3 ha−1) except for the lowest stocking (200–400 stems per ha) alternatives with B. pubescens. Treatment regimes with a birch overstory were clearly the most profitable alternatives, yielding up to 151% (B. pendula) and 113% (B. pubescens) of the net present value of the pure spruce alternative, at 4% interest rate. Removing the birch overstory already at 15 years was the least profitable alternative with 79 and 83% net present values, respectively. The most profitable treatment with current technology, price, and cost structure appears to be to grow 500–800 birch per ha up to about age 40 years for B. pendula and 45–50 years for B. pubescens.  相似文献   


19.
Between 1987 and 2000, a spruce beetle (Dendroctonus rufipennis) outbreak infested 1.19 million ha of spruce (Picea spp.) forests in Alaska, killing most of the large diameter trees. We evaluated whether these forests would recover to their pre-outbreak density, and determined the site conditions on which spruce germinated and survived following the spruce beetle outbreak in forests of the Anchor River watershed, Kenai Peninsula, Alaska. White spruce (Picea glauca) and Lutz's spruce (Picea × lutzii), a hybrid between white and Sitka spruce (Picea sitchensis), dominate the study area. We measured the pre- and post-outbreak density of spruce in 108 3 m × 80 m plots across the study area by recording all live trees and all dead trees >1.5 m tall in each plot. To determine the fine scale site conditions on which spruce germinated and survived, we measured ground surface and substrate characteristics within 20 cm circular plots around a subset of post-outbreak spruce seedlings. The density of post-outbreak spruce (855/ha) was adequate to restock the stands to their pre-outbreak densities (643/ha) for trees >1.5 m tall. We could not accurately estimate recovery for pre-outbreak spruce seedlings because dead seedlings may have decayed in the 5–18 years since the beetle outbreak occurred. At the fine scale, spruce that germinated post-outbreak grew on a wide variety of substrates including downed log, stump, mesic organic mat, peat, hummocks and mineral soil. They exhibited a strong preference for downed logs (53%) and stumps (4%), and most (91%) of the downed logs and stumps that spruce rooted on were heavily decayed. This preference for heavily decayed logs and stumps was especially evident given that their combined mean cover was only 2% in the 3 m × 80 m plots. Within the 3 m × 80 m plots, spruce seedling survival was negatively correlated with bluejoint (Calamagrostis canadensis) litter cover.  相似文献   

20.
We compared patterns of acorn dispersal and predation by wood mice among four tree species (Quercus serrata, Quercus crispula, Castanea crenata, and Juglans mandshurica var. sieboldiana) that are abundant in cool temperate woodlands. We devised an acorn dispersal experiment using 400 magnet-inserted acorns and a magnetic locator in a 1.8-ha study plot, which spanned a cut-over area and an adjacent deciduous forest. Ten wire mesh baskets, each containing 40 acorns (10 acorns per species), were placed on the border between these two habitat types. About 13.0% (n = 52) of the total acorns remained in the baskets, while 77.3% (n = 309) were dispersed throughout the study plot and subsequently retrieved using the magnetic locator. Microhabitat, distance, and burial depth of transported acorns were significantly different among species. In the cut-over area, J. mandshurica var. sieboldiana acorns were dispersed under fallen trees or branches and near stumps, and were buried deeply in the soil. Dispersal distances of J. mandshurica var. sieboldiana acorns were significantly greater than those of Q. serrata acorns. The number and microhabitat of transported acorns significantly differed between habitat types. J. mandshurica var. sieboldiana acorns were dispersed in the cut-over area rather than in the forest. For all four species, the numbers of acorns delivered to fallen trees or branches, stumps, and crumbled soil with overhang under any vegetation type were greater in the cut-over area than in the forest.  相似文献   

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