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1.
Jack pine and trembling aspen are boreal tree species that are found growing either in naturally regenerated mono-specific stands, or in mixed-wood stands. We conducted a field survey and a manipulative field study to test the productivity-diversity hypothesis, which predicts that mixed-wood stands are more likely to occur on fertile soils, or following fertilization. We surveyed 44 mixed-wood stands and found 43 of these occurring on fertile clay deposits, and only one occurring on a nutrient poor till deposit. By contrast, the area surveyed comprised 45% clay and 55% till deposits. In a second study, we conducted a five year fertilization and brushing trial in a recently burned area dominated by jack pine saplings with patches of regenerating trembling aspen. Fertilization without brushing improved the growth and recruitment of aspen stems, but had no effect on jack pine growth and recruitment. Fertilization + brushing increased the growth of jack pine. Brushing the aspen, with or without fertilization, resulted in higher recruitment of jack pine. We conclude that soil fertility controls the mixing of jack pine with trembling aspen, that fertilization increases the likelihood of encroachment of aspen into areas formerly dominated by jack pine, and that brushing along with fertilization is necessary to promote jack pine growth.  相似文献   

2.
We examined tree species responses under forest harvesting and an increased fire disturbance scenario due to climate warming in northern Wisconsin where northern hardwood and boreal forests are currently predominant. Individual species response at the ecosystem scale was simulated with a gap model, which integrates soil, climate and species data, stratified by ecoregions. Such responses were quantified as species establishment coefficients. These coefficients were used to parameterize a spatially explicit landscape model, LANDIS. Species response to climate warming at the landscape scale was simulated with LANDIS, which integrates ecosystem dynamics with spatial processes including seed dispersal, fire disturbance, and forest harvesting. Under a 5 °C annual temperature increase predicted by global climate models (GCM), our simulation results suggest that significant change in species composition and abundance could occur in the two ecoregions in the study area. In the glacial lake plain (lakeshore) ecoregion under warming conditions, boreal and northern hardwood species such as red oak, sugar maple, white pine, balsam fir, paper birch, yellow birch, and aspen decline gradually during and after climate warming. Southern species such as white ash, hickory, bur oak, black oak, and white oak, which are present in minor amounts before the warming, increase in abundance on the landscape. The transition of the northern hardwood and boreal forest to one dominated by southern species occurs around year 200. In the sand barrens ecoregion under warming conditions, red pine initially benefits from the decline of other northern hardwood species, and its abundance quickly increases. However, red pine and jack pine as well as new southern species are unable to reproduce, and the ecoregion could transform into a region with only grass and shrub species around 250 years under warming climate. Increased fire frequency can accelerate the decline of shade-tolerant species such as balsam fir and sugar maple and accelerate the northward migration of southern species. Forest harvesting accelerated the decline of northern hardwood and boreal tree species. This is especially obvious on the barrens ecoregion, where the intensive cutting regime contributed to the decline of red pine and jack pine already under stressed environments. Forest managers may instead consider a conservative cutting plan or protective management scenarios with limited forest harvesting. This could prolong the transformation of the barrens into prairie from one-half to one tree life cycle.  相似文献   

3.
This study reports 14th-year response of a boreal mixedwood stand to different harvest intensities (uncut, 50% partial cut with and without removal of residuals after 3 years, and clearcut), spot site preparation treatments (none and scalped), and chemical weeding frequencies (none, single, and multiple) in northeastern Ontario. The response variables include the survival and growth of planted white spruce (Picea glauca [Moench] Voss) and jack pine (Pinus banksiana Lamb.), height and density of natural regeneration and shrubs, and cover of shrubs and non-woody vegetation. Harvesting and weeding generally improved survival and growth of planted trees, although white spruce survival did not significantly differ among the three weeding frequencies. Harvesting tended to increase heights of hardwood (mostly trembling aspen (Populus tremuloides Michx.)) and conifer (largely balsam fir (Abies balsamea (L.) Mill.).) natural regeneration, cover and density of shrubs, and cover of herbs, lichens, and ferns. Chemical weeding reduced height, density and cover of shrubs, height and density of hardwood regeneration, and fern cover, but increased moss and lichen cover. Spot scalping did not significantly affect planted seedling, natural regeneration, or the vegetation.Maximum survival and growth of planted white spruce and jack pine were achieved using a combination of clearcutting and multiple weeding. However, partial cutting followed by a single weeding produced acceptable survival and reasonable growth of planted trees, particularly for white spruce. Partial canopy removal alone substantially reduced the amount of hardwood regeneration, relative to clearcutting, but did not adequately suppress understory shrubs. Significant improvement in seedling growth following multiple weedings was evident primarily in the complete canopy removal treatments: 50% partial cut with removal of residuals after 3 years and clearcut. While the effects of harvesting and weeding on planted crop trees found in the 5th-year assessments generally persisted at year 14, survival decreased, likely due to light competition from developing hardwood and shrubs.  相似文献   

4.
Limited scientific information is currently available regarding saproxylic fungal communities in the boreal forest of North America. We aimed to characterize the community development, richness and activity of saproxylic fungi on fresh wood in harvested and unmanaged boreal mixedwood stands of northwestern Québec (Canada). Fresh wood blocks (n = 480) of balsam fir (Abies balsamea (L.) Mill.) and trembling aspen (Populus tremuloides Michx.) were placed on the forest floor in a range of stand conditions (n = 24). Blocks were harvested every 6 months for up to 30 months and characterized for species composition and richness (PCR–DGGE, DNA sequencing), respiration, wood density and lignin and cellulose content. Colonization by a wide range of functional groups proceeded rapidly under different stand conditions. We detected a total of 35 different fungal operational taxonomic units, with the highest species richness at the wood block level being observed within the first 12 months. No differences in community composition were found between wood host species or among stand conditions. However, the variability in fungal communities among blocks (β diversity) was lower on trembling aspen wood compared with balsam fir and decreased over time on trembling aspen wood. Also, fungal activity (respiration and wood decomposition) increased on trembling aspen wood blocks and species richness decreased on balsam fir wood over time in partial-cut sites. The overlap in tree composition among stands, the high volume of logs and the recent management history of these stands may have contributed to the similarity of the saproxylic fungal community among stand types and disturbances.  相似文献   

5.
Large areas of northern coniferous forests once naturally maintained by stand-replacing wildfires have shifted to an anthropogenic disturbance regime of clearcut harvesting followed by natural or artificial regeneration, with unknown consequences for soil biogeochemical processes. We used a comparative approach to investigate the effects of whole-tree harvesting (WTH) vs. stand-replacing wildfire (WF) on soil C and nutrient availability, and nutrition and growth of the succeeding stand, in jack pine (Pinus banksiana) forests of northern Lower Michigan. We compared total carbon (C), total nitrogen (N), potential N mineralization, and extractable phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) among stands regenerated via WTH or WF in two age classes (4–7 years and 12–18 years). We also measured jack pine foliar nutrition and height growth in these same stands, as well as estimating the contribution of legacy dead wood to ecosystem nutrient capital in young stands. We found some evidence in support of our hypothesis that WTH would leave behind greater pools of soil C and N, but lower pools of P and base cations. However, the differences we observed were confined entirely to surface organic horizons, with the two disturbance regimes indistinguishable when viewed cumulatively to our maximum sampling depth of 30 cm. Estimates of nutrient pools in legacy wood inherited by young jack pine stands were also small in comparison to total soil pools (ranging from 1 to 9% depending on the element), suggesting that decomposition and nutrient release from this material is not likely to result in noticeable differences in soil fertility later in stand development. Similar levels of soil nutrients between WTH- and WF-origin stands were reflected in our measures of jack pine foliar nutrition and height growth, which were both unaffected by mode of stand origin. Results from this study suggest that soil nutrient levels following WTH fall within the natural range of variation produced by WF in these jack pine forests; however, comparison with a similar study on boreal jack pine suggests that latitudinal effects on O-horizon nutrient capital may influence the degree to which WTH matches the effects of WF on soil nutrient availability.  相似文献   

6.
In the boreal forest, conifer release treatments can leave a low quality hardwood component, which does not contribute to healthy, productive mixedwood forests. In this study, the growth and quality of trembling aspen (Populus tremuloides Michx.) regeneration were examined 5-7 years after spraying with glyphosate herbicide before and after harvesting. Results were compared to those from a partial cut and clearcut treatment without herbicide treatments. The preharvest spray treatment effectively reduced aspen density and height but did not lower regeneration quality—assessed by stem and crown deformation and stem stain—compared to the postharvest spray and clearcut treatments. Increased stem stain in the postharvest spray treatment was largely associated with the stem section that grew prior to herbicide application—post-herbicide growth was not affected. While the effect of stem stain may be restricted to growth that occurred before herbicide use, stem deformation from stem dieback may have longer term effects. In the partial cut treatments both density and stocking of aspen regeneration were lower, but aspen basal diameter growth, height growth, and quality were similar to those in the clearcut treatment. Thus, preharvest spray should promote conifer growth by reducing the density and growth of aspen regeneration without reducing the quality of aspen; this should be considered a preferred treatment to support for management objectives calling for productive and healthy mixtures of fast-growing aspen and slow-growing conifers.  相似文献   

7.
We examined spatial aspects of harvesting impacts on aspen regeneration at 25 sites in northern Minnesota. These sites had been clearcut or partially harvested 4–11 years ago. At each site, residual overstory, which was composed of trees other than aspen, soil disturbance, and tree regeneration were determined along transects leading away from skid trails into the neighboring stand. We characterized spatial extent of soil disturbance as soil strength using an Eijkelkamp soil cone penetrometer. Soil disturbance dropped off very quickly at the edge of skid trails, suggesting that the impact of harvesting traffic on areas adjacent to skid trails is minor. On skid trails, disturbance levels were higher on sites harvested in summer than on sites harvested in winter. Even after adjustment for differences in soil disturbance, stands harvested in winter had higher regeneration densities and greater aspen height growth than stands harvested in summer, suggesting that aspen regeneration was more sensitive to a given level of soil disturbance on summer-harvested sites versus on winter-harvested sites. Soil disturbance and residual overstory interactively reduced aspen regeneration densities and height growth, indicating that avoidance of soil disturbance is even more critical in partially harvested stands. Predictions based in the spatial patterns of impact found in this study indicated that harvesting conditions may have a great impact in future productivity of a site.  相似文献   

8.
Regeneration characteristics and population dynamics of four major competing plants, trembling aspen (Populus tremuloides Michx.), pin cherry (Prunus pensylvanica L.f.), green alder (Alnus viridis spp. crispa (Aiton) Turril) and beaked hazel (Corylus cornuta Marsh.) were studied from a seven-year-old clearcut in northwestern Ontario, Canada. The site was planted with jack pine two years after clearcutting. Regeneration strategies and population dynamics of these plants were studied by determining their crown diameter, stem density, stem height, stem age, depth of sprouting center, inter-sprout distance, oven-dry weight of shoots, roots plus rhizomes by nondestructive and destructive sampling. Stem density of trembling aspen and pin cherry in 1992 was 4580 and 3600 stems per ha respectively. Much higher stem density was obtained in green alder and beaked hazel during the same time, 27580 and 14600 stems per ha respectively. Substantial reduction in stem density was recorded in trembling aspen (45%) and pin cherry (69%) over two years, 1992–1994. However, reduction in stem density of green alder and beaked hazel for that period was very little (6 and 2%, respectively). Comparison of species' clonal characteristics of above- and below-ground components indicates that trembling aspen and pin cherry possess similar vegetative regeneration strategies that differ from those of green alder and beaked hazel. Ordination of the results of canonical variate analysis of the eight vegetative parameters of the four species arranged the species into two significantly different groups. Based on species regeneration strategies, two potential competition strategies were identified: a vertical competition strategy (VCS) and a horizontal competition strategy (HCS). We argue that the degree and duration of competition can be predicted from the density and ratio of VCS and HCS plants on a site once sufficient empirical data on the species' competitive abilities are gathered. We suggest that future studies should relate the regeneration strategies, population dynamics and competitive abilities of competing plants to competition tolerance of crop trees. This will fine tune our prediction about species interaction based on the present model and better justify the need for vegetation control intervention.  相似文献   

9.
Height–diameter relationships based on stand characteristics (trees/ha, basal area, and dominant stand height) were investigated for balsam fir, balsam poplar, black spruce, jack pine, red pine, trembling aspen, white birch, and white spruce using data from permanent growth study plots in northern Ontario, Canada. Approximately half the data were used to estimate model parameters with the rest used for model evaluation. Multiple Chapman–Richards functions with parameters expressed in terms of various stand characteristics were fit to determine the best models for predicting height.  相似文献   

10.
Specific leaf area (SLA) and leaf area index (LAI) were estimated using site-specific allometric equations for a boreal black spruce (Picea mariana (Mill.) BSP) fire chronosequence in northern Manitoba, Canada. Stands ranged from 3 to 131 years in age and had soils that were categorized as well or poorly drained. The goals of the study were to: (i) measure SLA for the dominant tree and understory species of boreal black spruce-dominated stands, and examine the effect of various biophysical conditions on SLA; and (ii) examine leaf area dynamics of both understory and overstory for well- and poorly drained stands in the chronosequence. Overall, average SLA values for black spruce (n = 215), jack pine (Pinus banksiana Lamb., n = 72) and trembling aspen (Populus tremuloides Michx., n = 27) were 5.82 +/- 1.91, 5.76 +/- 1.91 and 17.42 +/- 2.21 m2 x kg-1, respectively. Foliage age, stand age, vertical position in the canopy and soil drainage had significant effects on SLA. Black spruce dominated overstory LAI in the older stands. Well-drained stands had significantly higher overstory LAI (P < 0.001), but lower understory LAI (P = 0.022), than poorly drained stands. Overstory LAI was negligible in the recent (3-12 years old) burn sites and highest in the 70-year-old burn site (6.8 and 3.0 in the well- and poorly drained stands, respectively), declining significantly (by 30-50%) from this peak in the oldest stands. Understory leaf area represented a significant portion (> 40%) of total leaf area in all stands except the oldest.  相似文献   

11.
We studied late-entry commercial thinning effects on growth, yield, and regeneration in a 48-year-old jack pine(Pinus banksiana Lamb.) stand. Applied thinning intensities were 27, 32, and 47% of merchantable basal area(BA) excluding skidding trails. After 15 years, mean diameter at breast height of surviving trees in the 47% BA removal increased by 4.9 cm(25%) compared to the unthinned control. The 47% BA removal also increased gross merchantable volume(GMV) tree-1by 46% compared to the control. The 27% BA removal had twice as much GMV ha-1compared to the 47% BA removal after15 years. Moreover, cumulative GMV ha-1was much higher in the 27% BA removal than in the unthinned control. The highest thinning intensity produced larger trees on average, while the lowest thinning intensity maximized volume production per hectare. Maintenance of acceptable growing stock throughout the 15-year period in the 27% BA removal could provide other ecosystem functions such as biodiversity enhancement or wildlife habitat by delaying senescence. Regeneration data showed that a shift in species composition occurred in the understory. After 15 years, the understory was dominated by black spruce(Picea mariana(Mill.) B.S.P.), white birch(Betula papyrifera Marsh.), and trembling aspen(Populus tremuloides Michx.). If regenerating jack pine is an objective after final overstory removal, additional efforts will be needed to re-establish this species.  相似文献   

12.
Over the last 20 years, investigations have been carried out to determine the influence of various ecological factors on silver fir natural regeneration in highlands and mountains. However, there has been little research on the structure and development of fir regeneration in lowlands. Results of this study indicate that three main stand characteristics play a very important part in the structure of fir regeneration in the lowland. The results revealed that the quantity, frequency and growth rate of fir regeneration were affected by site conditions. One of the most important ecological factors differentiating quantity and quality of fir regeneration was the proportion of fir in a stand. It was found that, with an increase in the percentage of fir in a stand, the quantity and the sum of heights and the sum of height increments of fir regeneration tends to increase. Results of this study showed that the number and development of fir regeneration were influenced by species composition of a stand; fir regenerated not only in pure fir stands but also in mixed forests. A positive influence of pine and birch canopy on initiation and development of fir regeneration was confirmed. Optimal conditions for the growth and development of fir with respect to species composition were found in mixed fir stands with an admixture of hornbeam. In contrast, results of the study suggest that the worst conditions for fir regeneration were found in the stands composed of species, such as ash, alder, oak, aspen, lime and spruce.  相似文献   

13.
To facilitate ecosystem-specific management of juvenile mixtures of lodgepole pine (Pinus contorta Dougl. Ex Loud. Var. latifolia Engelm.) and trembling aspen (Populus tremuloides Michx.) in south-central British Columbia, we compared the characteristics of pine–aspen competition between a moist sub-boreal spruce and a dry interior Douglas-fir ecosystem. A total of 252 lodgepole pine and their neighbourhoods were examined across four untreated stands, each of which was sampled three times between ages 12 and 24 years. Pine diameter and height decreased with increasing density of trembling aspen at least as tall as the target pine (tall aspen) in both ecosystems. Regression analysis was used to examine the ability of tall aspen density and four competition indices (CIs) to predict pine size. Tall aspen density, which is easily assessed in the field, accounted for 63% and 69% of the variation in pine diameter and height in 20–24 year-old stands, respectively. The most successful competition index, based on the basal diameter ratio (BDR) of trembling aspen to pine accounted for, respectively, 78% and 73% of the variation. In the same stands, R2 values were 1–5% lower when tall aspen density and BDR at age 15–19 years were used to predict size of 20–24-year-old pine.  相似文献   

14.
This paper summarises the results from 35 years-observed thinning experiments on 256 permanent sample plots in 10–60 year-old stands of ash, aspen, birch, oak, pine and spruce in Lithuania. Thinning enhanced crown projection area increment of residual trees. The largest effect was observed in stands of aspen and birch (growth increase by 200%), followed by ash and oak (over 100%), and spruce and pine (about 80%). Thinning also promoted dbh increment, especially in younger stands, and the increase of dbh increment was positively correlated with the thinning intensity. The strongest reaction was exhibited by oak and aspen, while ash, birch and conifers reacted to a lower extent. Low and moderate intensities of thinning stimulated volume production in younger stands while the opposite was observed in older stands with increasing removals. Spruce stands exhibited relatively strongest increase of volume increment and pine, –the weakest, while the effect on deciduous species was intermediate. The results demonstrate that significant increase in volume increment is achievable with thinning of only young forest stands, e.g. 10–20 year-old pine, birch and ash, or 10–30 year-old oak, aspen and spruce.  相似文献   

15.
Cellulose mass loss was measured for four levels of canopy cover,i.e., clearcut, 25%, 75%, and uncut, in northern red oak (Quercus rubra) and red pine (Pinus resinosa) stands in northern Lower Michigan, USA. Cellulose mass loss was more rapid in the clearcut and 25% canopy cover treatments than in the 75% canopy cover and uncut treatments. After 4 month incubation of cellulose filter papers, mass loss rates averaged 75.2% in the clearcut, 56.3% in the 25% canopy cover, 46.9% in the 75% canopy cover, and 45.7% in the uncut stands. For the clearcut and the 25% canopy cover treatments, cellulose mass loss in the mineral soil layer was significantly higher than in the forest floor after 2 and 4 months of incubation, while cellulose mass loss of the uncut treatment was significantly lower in the soil layer than in the forest floor after 4 months of incubation. Cellulose mass loss was not significantly different between the oak and the pine stands (p > 0.05), but cellulose mass loss rates in other canopy cover treatments except for the clearcut were generally higher in red oak stands than in red pine stands. These results suggest that canopy manipulation increases cellulose decomposition and may stimulate nutrient cycling process in canopy removal stands. This study was supported in part by USDA Forest Service and Michigan Technological University.  相似文献   

16.
Whole-tree harvesting (WTH), where logging residues are removed in addition to stems, is widely practised in Fennoscandian boreal forests. WTH increases the export of nutrients from forest ecosystems. The extent of nutrient removals may depend on tree species, harvesting method, and the intensity of harvesting. We developed generalized nutrient equations for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten), and birch (Betula pendula Roth and Betula pubescens Ehrh.) stands to be able to calculate the amounts of nitrogen, phosphorus, potassium, and calcium in stems and above-ground biomass (stem and crown) as a function of stand volume. The equations were based on Fennoscandian literature data from 34 pine, 26 spruce, and 5 birch stands, and they explained, depending on the tree species and nutrient, 61–99% and 56–87% of the variation in the nutrient amounts of stems and above-ground biomass, respectively. The calculations based on the equations showed that nutrient removals caused by stem-only harvesting (SOH) and WTH per harvested stem m3 were smaller in pine than in spruce and birch stands. If the same volume of stem is harvested, nutrient removals are, in general, nearly equal at thinnings and final cuttings in SOH, but larger in thinnings than final cuttings in WTH. If the principal aim is to minimize the nutrient removals per harvested stem m3, the harvesting should be done at mature pine stands. The effect of biomass removal on overall site nutrient status depends on site-specific factors such as atmospheric deposition, weathering of minerals, and the size of the nutrient pools in the soil.  相似文献   

17.
Overstory mortality, understory tree recruitment, and vegetation development were assessed in trembling aspen (Populus tremuloides Michx.) stands following two recent episodes of forest tent caterpillar defoliation (Malacosoma disstria Hbn.) in northeastern Ontario. The results suggest that poplar (aspen and balsam poplar (Populus balsamifera L.)) mortality increased with consecutive years of insect defoliation occurring from the mid-1980s to mid-2000s and the proportion of poplars in the overstory, but decreased with improved pre-defoliation tree vigour (DBH increment). The first outbreak, which lasted from the mid-1980s to early 1990s, was more severe in terms of insect defoliation and contributed more to poplar mortality and decline. The decline began in the late 1990s and peaked in early 2000s. Poplar regeneration and understory shrubs responded rapidly to foliage loss to insect defoliation and mortality of overstory poplars. The regenerated poplars were able to maintain their growth under developing shrubs and residual overstory canopy and numbers were sufficient to compensate for the poplar trees lost to insect infestation. The defoliation-induced overstory decline will accelerate the transition of aspen stands to conifer dominance through enhanced conifer recruitment and growth, and reduced hardwood overstory in aspen-dominated stands, while hardwood dominance will persist in pure aspen stands. From a timber supply perspective, the decline caused by forest tent caterpillar defoliation could delay the availability of aspen stands for harvesting by 40–50 years.  相似文献   

18.
In boreal black-spruce forests of Eastern Canada, a cohort model of ecosystem management has been proposed whereby a combination of both partial and more intensive cutting are used to emulate old-growth stands and the re-establishment of stands following severe wildfire. As with other approaches to coarse filter conservation, partial cutting is hypothesized to maintain and potentially recreate plant and animal assemblages consistent with a range of natural variability. In this study, we used ground-dwelling spiders (Araneae) to evaluate whether partial cutting and a cohort model of ecosystem management are sufficient to preserve biodiversity found in mature and over-mature boreal black spruce stands prone to paludification. We compared the spider fauna (11,628 individuals representing 136 species) in replicated partial cuts, clear cuts and uncut control stands with a chronosequence of mature and over-mature naturally regenerated stands (94-288 years since the last fire) [25 stands in total] in the same region of the northern Clay belt in Québec (Canada). In stands that were old-growth prior to cutting, harvesting had strong repercussions on spider assemblages that were not attenuated by less intensive, partial cutting. The most obvious changes in spider assemblages were related to increased recruitment of species that were nearly absent in uncut stands. Several cosmopolitan species that were widely distributed among stands prior to harvest increased in cut stands. Spider assemblages collected following either cutting methods were not consistent with assemblages found within the chronosequence and thus fell outside the observed range of natural variability. However we did not observe a similar recruitment effect for spider species in younger stands with relatively higher levels of retention. We demonstrate that the interaction between stand age prior to cutting, the degree of paludification as well as remnant basal area are important considerations when evaluating the efficacy of partial cutting to maintain forest spider assemblages and biodiversity at large in black-spruce stands. “We also suggest that retention levels in partial cuts will have to be substantially increased to maintain spider communities within their range of natural variation in managed forested landscapes.” However partial cutting with higher levels of retention, particularly in younger stands, may be useful in coarse filter management particularly for establishing or accelerating spider assemblages towards those found in old-growth stands.  相似文献   

19.
Small seasonally flooded forest ponds have received increased attention due to a growing recognition of their abundance in many landscapes, their importance as habitat for a variety of organisms, and the contributions they make to species and ecosystem diversity. There also is concern over potential negative effects of forest management in adjacent uplands on seasonal pond ecology. Several studies have examined invertebrate and songbird responses to upland harvest around seasonal ponds. Less attention has been given to examining how seasonal pond plant communities respond to adjacent forest harvesting. We studied the response of seasonal pond plant communities to adjacent upland timber harvests, assessing whether buffers around ponds (15.25 m uncut and partially cut) mitigated changes in species abundance and community composition, relative to changes in ponds that were clearcut to the pond margin. We addressed our objective using an operational-scale experiment in northern Minnesota, which included pre-harvest sampling, replicated treatments, and uncut controls. After treatment, changes in tree basal area and canopy openness in the pond basins reflected reductions in upland basal areas. Specifically, control ponds had significantly higher basal area and lower openness than ponds cut to their margins, while ponds with uncut buffers and partially cut buffers were intermediate. Changes in plant communities were evident in the ground layer and shrub/large regeneration layer. After treatment and over time, the control stands did not change significantly in ground layer structure or shrub/large regeneration layer composition. The three upland harvest treatments displayed increasingly greater deviation from their starting conditions and from the control along a gradient of increasing treatment intensity, from the buffer treatment to the partially cut buffer to the clearcut. The response in the ground layer was largely associated with increased sedge and grass cover, while the response in the shrub/large regeneration layer was associated with increases of Salix sp., Alnus incana, and Populus tremuloides. Our results indicate that adjacent upland timber harvest can lead to altered plant communities within seasonal ponds, at least temporarily. Moreover, uncut forest buffers (∼15.25 m) surrounding seasonal ponds can mitigate plant community changes to some degree. If seasonal ponds are an important resource on the management landscape and a high percentage of upland forest is in a recently cut condition at any given time, than use of harvest buffers around seasonal ponds may be an appropriate approach for mitigating short term alteration of pond plant communities.  相似文献   

20.

Mean age, mean and top heights and yield were studied in 20 mixed stands of birch ( Betula pubescens Ehrh. and B. pendula Roth) and Picea abies (L.) Karst. and nine mixed stands of birch and Pinus sylvestris L. in south-eastern Norway. Each mixed stand and the adjacent pure coniferous stand (control) were growing under the same site conditions and had not been commercially thinned. There were no significant differences in mean age at breast height or in top heights between birch and conifers in the mixed stands, while mean height was significantly higher for birch than for spruce. A growth index was calculated based on total volume and age at breast height. For the spruce sites the growth in young mixed stands (birch < 17 m) was superior to that of pure spruce, while the difference was insignificant in older stands. The growth index correlated positively with the ratio between generatively and vegetatively regenerated birch trees, and negatively with the age of the oldest species in the mixture and with site quality. For the pine sites there was no significant difference in the growth index between mixed birch-pine and pure pine stands. A mixture effect of birch on the volume yield of spruce or pine could not be demonstrated.  相似文献   

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