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1.
In this study, the pathogen and parasite spectra of Turkish populations of the great spruce bark beetle Dendroctonus micans (Kugelann) (Coleoptera: Curculionidae, Scolytinae) are analysed. In addition to the previously studied infective green alga
Helicosporidium, three more pathogens and parasites, i.e. the yeast Metschnikowia sp., the neogregarine Mattesia sp. and a nematode, were recorded here for the first time. The pathogens and parasites occur in different quantities and
combinations in outbreaks of the beetle at five Turkish localities. 相似文献
2.
Data from Forestry Commission fertilizer experiments were analysedto determine the influence of site factors on the growth responseof Sitka spruce (Picea sitchensis (Bong.) Carr.) following applicationsof phosphate and potassium at time of planting. Multiple regressionanalysis revealed that growth response was influenced by soiltype and was related to the foliar nutrient levels of untreatedcontrols. Growth response to application of phosphate was alsoinfluenced by lithology. No relationships were found betweengrowth response and elevation or annual rainfall. Received 29 January 1990. 相似文献
3.
《Forest Ecology and Management》2004,201(1):89-104
Samples of Norway spruce (Picea abies [L.] Karst) were dendrochronologically investigated in order to detect infestations by Dendroctonus micans (Kug.), the great spruce bark beetle (Col. Scolytidae), a relatively recent introduction to France. Uninfested natural forests located in the north-eastern French Alps and heavily infested plantations in the Ardèche region (Massif Central) were compared. The penetration holes bored in trunks by the bark beetle induced visible marks on wood, such as extreme ring width reductions, locally missing rings and crescent-shaped resin patches between consecutive rings that make possible a post-infestation dating.The outbreak began in 1979, 5 years prior to first insect visual detection by foresters. In the infested forest, tree basal area growth was not as sustained as in uninfested natural stands, but showed an inflection point at an unusually young tree age (from 30 to 40 years). Ring widths showing extreme synchronous radial growth reductions were caused either by excessively cold periods (e.g. in 1948, 1980, 1984, 1992) or by summer drought (as in 1986). Most of these weak growth years were shared with uninfested sites. In healthy forests, the consequences of extremely cold years were usually recorded only in high elevation stands, especially near the timberline, whereas summer drought effects were mostly visible in low altitude forests. By contrast, both phenomena were recorded in the infected Ardèche plantation. An analysis of tree-rings and monthly climate confirmed that Norway spruce growth in Ardèche plantations was reduced by excessively low minimum temperature during most parts of the year prior to ring formation, by higher than average maximum temperature during current spring and summer, and by drought in winter, spring and summer. Thus, the regional Ardèche climate with both cold winters and dry summers (especially in July) seems to weaken spruce trees planted there. Moreover, tree sensitivity to climate was found to be greatly enhanced by insect infestation. Such interactions between climatic stress and insect outbreak led to forest dieback in a 15–20-year period, when trees were still young (less than 70 years), and without any tree recovery. Therefore, in that region spruce plantations should be replaced by non-host species of Dendroctonus micans, especially where soil conditions may exacerbate drought effects. 相似文献
4.
《Forest Ecology and Management》2006,227(3):219-232
When spruce beetles (Dendroctonus rufipennis) thin a forest canopy, surviving trees grow more rapidly for decades until the canopy closes and growth is suppressed through competition. We used measurements of tree rings to detect such growth releases and reconstruct the history of spruce beetle outbreaks at 23 mature spruce (Picea spp.) forests on and near the Kenai Peninsula, Alaska and four mature white spruce (Picea glauca) forests in Kluane National Park and Reserve, Yukon Territory. On the Kenai Peninsula, all stands showed evidence of 1–5 thinning events with thinning occurring across several stands during the 1810s, 1850s, 1870–1880s, 1910s, and 1970–1980s, which we interpreted as regional spruce beetle outbreaks. However, in the Kluane region we only found evidence of substantial thinning in one stand from 1934 to 1942 and thinning was only detected across stands during this same time period. Over the last 250 years, spruce beetle outbreaks therefore occurred commonly among spruce forests on the Kenai Peninsula, at a mean return interval of 52 years, and rarely among spruce forests in the Kluane region where cold winter temperatures and fire appear to more strongly regulate spruce beetle population size. The massive 1990s outbreaks witnessed in both regions appeared to be related to extremely high summer temperatures. Recent outbreaks on the Kenai Peninsula (1971–1996) were positively associated with the 5-year backwards running average of summer temperature. We suggest that warm temperature influences spruce beetle population size through a combination of increased overwinter survival, a doubling of the maturation rate from 2 years to 1 year, and regional drought-induced stress of mature host trees. However, this relationship decoupled after 1996, presumably because spruce beetles had killed most of the susceptible mature spruce in the region. Thus sufficient numbers of mature spruce are needed in order for warm summer temperatures to trigger outbreaks on a regional scale. Following the sequential and large outbreaks of the 1850s, 1870–1880s, and 1910s, spruce beetle outbreaks did not occur widely again until the 1970s. This suggests that it may take decades before spruce forests on the Kenai Peninsula mature following the 1990s outbreak and again become susceptible to another large spruce beetle outbreak. However, if the recent warming trend continues, endemic levels of spruce beetles will likely be high enough to perennially thin the forests as soon as the trees reach susceptible size. 相似文献
5.
The growth of semi-checked Sitka spruce (Picea sitcbensis Carr.)on heathland has been stimulated to different degrees by theannual application of litter of Scots pine (Pinus sylvestrisL.), Corsican pine (P. nigra var. calabrica Schneid), Lodgepolepine (P. contorta Dougl.), Japanese larch (Larix leptolepisGord.), and Sitka spruce, at rates corresponding to normal plantationconditions, following an initial heavier rate. Foliar analysissuggests that the response is at least partially attributableto the influence of the litters on the nitrogen nutrition ofthe spruce and differences between litters appear to be largelydetermined by their total nitrogen contents. In this respect,Japanese larch, with an annual needle fall generally greaterthan that of the pines and a higher nitrogen content, offersthe best promise as a nurse species for spruce. 相似文献
6.
《Forest Ecology and Management》2006,227(3):275-283
The presence of over 429,000 ha of forest with spruce (Picea spp.) recently killed by spruce beetles (Dendroctonus rufipennis) on the Kenai Peninsula has raised the specter of catastrophic wildfire. Dendrochronological evidence indicated that spruce beetle outbreaks occurred on average every 50 years in these forests. We used 121 radiocarbon-dated soil charcoal samples collected from throw mounds of recently blown over trees to reconstruct the regional fire history for the last ca. 2500 years and found no relation between fire activity and past spruce beetle outbreaks. Soil charcoal data suggest that upland forests of white (Picea glauca) and Lutz (Picea x lutzii) spruce have not on average burned for 600 years (time-since-fire range 90 to ∼1500 years, at 22 sites) and that the mean fire interval was 400–600 years. It would thus appear that 10 or more spruce beetle outbreaks can occur for every cycle of fire in these forests. We caution, however, that a trend of warmer summers coupled with an increasing human population and associated sources of ignitions may create a greater fire risk in all fuel types than was present during the time period covered by our study. We suggest that forest management focus on creating fuel breaks between valued human infrastructure and all types of forest fuels, both green and dead. 相似文献
7.
《Forest Ecology and Management》2006,227(3):207-218
A recent outbreak of spruce beetles (Dendroctonus rufipennis) in forests on the Kenai Peninsula, Alaska was met with substantial variation in response among people and communities situated within this changing landscape. Interviews and mail surveys administered to residents in six Kenai Peninsula communities revealed differences in perception of biophysical, social, and economic impacts that resulted from changing forest conditions related to the spruce beetle outbreak. Together, the qualitative and quantitative data provided evidence of collective experience and community risk perception across Kenai Peninsula communities. Fire, falling trees, declining quality of watersheds and wildlife habitat, economic fluctuations, landscape change, and emotional loss were some of the issues faced. In some communities, increased timber harvesting brought short-term, positive economic change in the wake of the spruce beetle outbreak. In other communities, the loss of a living spruce (Picea spp.) forest profoundly affected quality of life, and led to community conflict, increased risk perception of future impacts, and economic challenges. Biophysical changes were keenly felt by many residents. Communities at different stages in the spruce beetle outbreak revealed temporal and spatial variations in perceived impacts. The diverse array of perceived impacts and risks from the spruce beetle outbreak in Kenai Peninsula communities presents both opportunities and obstacles for forest management in the context of changing forest conditions. 相似文献
8.
Sitka spruce and Douglas fir transplants were kept under threecold storage regimes: (1) bare-root in a humidified cold store(H); (2) sealed in polythene bags in a humidified cold store(HP); (3) sealed in polythene bags in a direct cold store (D).Regimes H and D are routinely used in current practice. Plants of both species had significantly (P < 0.001) lowerroot moisture content (RMC) in treatment H within 4 weeks ofstorage; this difference was maintained throughout the periodof storage and potentially damaging levels of RMC were reachedwithin 8 weeks. Sitka spruce had significantly (P < 0.001)higher root growth potential (RGP) than Douglas fir throughoutthe storage period. Differences in RGP between storage treatmentswere not significant until 12 weeks after storage when treatmentH was poorer (P < 0.05) than treatments HP and D. The survival of plants from treatment H after 1 year in thefield was significantly poorer (P < 0.001) than the othertreatments in both species. Height increment was also less intreatment H than the other treatments (P < 0.001) after 1year. However, this difference disappeared in the second season.After 1 year there were no differences in root collar diameter(RCD) increment between storage treatments but Douglas fir showedgreater increment (P < 0.001) than Sitka spruce. Rapid assessment of RMC in slightly over 48 h makes this a potentiallyuseful test of planting stock quality during and after coldstorage. 相似文献
9.
The paper discusses the results obtained to date from a uniqueseries of Norway spruce spacing plots established in 1910 inBavaria. There is a series often plots covering initial spacingsranging between 3 ft. 7 in. and 6 ft. 7 in. and an eleventhplot, spaced at just over 13 ft., and interplanted 6 years laterat 3 ft x 3 ft. The plots have only been twice thinned and havesuffered no windfall in spite of their rapid growth. The results of the latest assessment by Prof. Vanselow, in 1949,have been summarized in a recent German forestry journal, andin the present paper extracts from Vanselow's data have beenconverted into English units. Although spacing has had no apparent effect on height growth,other factors such as B.H. girth, form of stem, branching, andaverage volume per tree show the expected response to increasedspacing. There is some indication of a reduction in total yieldto date with increasing spacing in the main series of plots.The plot spaced at 13 feet has many features of special interest,inter alia the death by suppression of 97 per cent, of the plantsused to fill up. Vanselow concludes that the optimum initial spacing for spruceon similar sites lies within the narrow range of 4 ft. 6 in.and 5 ft. 3 in. This accords closely with current Forestry Commissionpractice. Received 1 April 1951. 相似文献
10.
Species mixtures, although promising for improving the growthof spruce on nitrogendeficient sites, carry a risk of competitionfrom the admixed nurse species. The mixture of Scots pine (Pinussylvestris) and Norway spruce (Picea abies) planted at GisburnForest in 1955, in which nutritional benefits have been observed,provided a unique opportunity to study competition between thesespecies. Pure plots of both species as well as the mixture werereplicated in three blocks, allowing the effects of interplantingon the survival and mean diameter of each species to be testedstatistically. Further, the grouped arrangement of the speciesin mixed plots presented a variety of competitive configurationsbetween the two species. Instead of demonstrating the nursing benefit of pine to spruce,comparisons of mean diameters in pure and mixed stands indicatedthat spruce suffered and pine benefited from their interplantingat this site. Frequency distributions of tree diameters confirmedthat spruce tended to be suppressed in mixture and pine dominant.Neighbour analysis revealed that spruce were significantly smallerwhen adjacent to pine and that this effect was mainly due tothe larger size of pines. The increased height of spruce atthis site, previously attributed to a nutritional benefit conferredby pine, was probably due to competition for light from an overtoppingnurse. Nurse varieties must be carefully selected if they areto promote rather than suppress the growth of crop trees. 相似文献
11.
R. Jakuš 《Journal of pest science》1998,71(3):41-49
583 spruce stands in an area affected by air pollution and bark beetle outbreak in Eastern Slovakia were studied in 1996.
According to bark beetle infestation of dominant and codominant trees, stands were classified into following types of spruce
stand decline:Ips typographus-A,Ips typographus-B,Polygraphus poligraphus, I. typographus/P. poligraphus—A,I. typographus/P. poligraphus—B. The presence of attacked trees in forest edges, bark beetle spots and forest interior was the key important factor for
the classification.
Data from forest inventory and forest management evidence together with data on types of spruce stands decline were used in
further analyses. Results shows that the distribution of forest stands classified into different types or uninfested stands
is related mainly to host size and site quality. The percentage of spruce, exposition of stands and stand density showed significant
effects. The mechanisms of spreading of studied bark beetle outbreak could be explained by direct effects of stress of trees
caused by an abrupt increase of level of solar irradiation and by weakening of trees by the honey fungus. 相似文献
12.
The chemical composition of needle and leaf litter from Scots pine, Norway spruce and white birch in Scandinavian forests 总被引：8，自引：0，他引：8
Needle litter from 14 stands of Scots pine (Pinus silvestris,L.), 13 stands of Norway spruce (Picea abies (L.) Karst.) andleaf litter from three stands of white birch (Betula pubescensEhrh.) were analysed for chemical composition. The concentrationsof the elements N, P, K, Ca, Mg and Mn as well as solid organiccomponents (lignin, cellulose and hemicelluloses) and solubleswere determined. When the average chemical compositions werecompared the Scots pine needle litter was clearly the most nutrient-poorlitter type. Of the solid organic-chemical components the ligninfraction dominated in the spruce and birch litter whereas thecellulose dominated in the pine needle litter. When Norway spruce and Scots pine were growing in adjacent standson soils with the same bedrock origin the spruce litter hadsignificantly higher concentrations of nutrients (N, P, K, Ca,Mg, Mn) than the pine needle litter. At sites where Norway spruceand white birch were growing in adjacent stands, the birch leaflitter had generally higher concentrations of nutrients. However, significant or nearly significant differences were onlyobtained for Mg (P = 0.002), K (P = 0.056) and N (P = 0.087),probably due to the few replicates of stands compared. Concerningorganic chemical components, the spruce needle litter had significantlyhigher concentrations of lignin and mannan than all the otherlitters and lower levels of ethanol-soluble substances, celluloseand galactan than the pine needle litter. Further, it had lowerconcentrations of water solubles, rhamnan and xylan than thebirch litter. No relationships were established between the nutrient statusof the conifer litters and the site index H100 (the dominantheight of the trees at a reference age of 100 years) of thestands. Concentrations of solid carbohydrates in the litterswere, however, positively correlated with site index (P <0.001). Further, the concentration of nitrogen in the pine needlelitter was negatively correlated with the latitude of the sites(P < 0.01). The influence of litter chemistry on the decompositionof litter and nutrient cycling of forests is discussed. 相似文献
13.
The frequency and intensity of ecosystem disturbance, including outbreaks of forest insects and forest fires, is expected to increase in the future as a result of higher temperatures and prolonged drought. While many studies have concentrated on the future climatic impacts on fire, little is known about the impact of future climate on insect infestation. Paleoecological techniques are important in this regard in identifying the potential relationships between climate and insect outbreaks in the past, as a predictive tool for the future. We examine a high-resolution 20th century record of spruce beetle (Dendroctonus rufipennis) infestation from a small, subalpine lake, comparing the paleoecological record to the historical and tree-ring record of the event. An extensive spruce beetle outbreak occurred in northwestern Colorado during the 1940s and 1950s, causing widespread mortality of mature Picea engelmannii. Pollen analysis of this period documents the decline of Picea and its replacement locally by Abies lasiocarpa, paralleling age and composition studies of modern forest stands in the region. This study is a proof of concept that, when applied to longer sedimentary records, could produce a detailed record of infestation for the Late Holocene or older time periods. This information will be useful to forest managers in efforts to plan for the effects of D. rufipennis infestations, and subsequent succession within high elevation conifer forests. 相似文献
14.
Marginal upland soils may be used for forestry or sheep grazing.In the State Forests of South Wales a study of selective plantingshows the greatest volume yield is generally obtained from Sitkaspruce (Picea sitchensis) planted in ridge-crest soils. Yieldsfrom Sitka spruce on ridge-flank soils are reduced by the presenceof Ericaceae on upper slopes and the dryness of the soils onlower slopes. Contrary to this trend, the nutritional valueof the pasture for sheep is lowest on ridge crests and increasesdownslope, being greatest on the Agrostis pastures of lowerslopes. Further, reclamation is most economically accomplishedon ridge flanks where they are not too steep. Although profitcomparisons are very difficult to make, ridge slopes might bemore usefully allocated to sheep grazing and ridge crests toSitka spruce forests. To be economically viable, a forest mustbe large, but within any new forestry acquisitions the largerareas occupied by slope soils might be reclaimed or utilizedas sheep pastures. 相似文献
15.
Macedonian pine is little known in Britain as a forest tree.Information comes mainly from its native range in the Balkanmountains, and from specimen trees and young forest plots inBritain. Following a visit in 1982 to Yugoslavia and Bulgaria,the author describes the site conditions and ecological relationsof this species to Scots pine, Norway spruce and Silver fir.Early growth is characteristically slow, even on favourablesites, though it improves after 6–10 years and basal areaincrement may later exceed that of other pines. Growth and behaviourin British stands (mainly 20 years old, but a few older ones)is recorded. Stands of P. peuce are typically healthy and haveexcellent form. Insect and fungal damage is minimal. Early timbertests show specific gravity and strength are low, but the woodis very stable in drying and could have a use in joinery. Seedfrom selected stands will now be used for provenance testing. 相似文献
16.
Robinia pseudoacacia ‘Idaho’ is one of several multi-purpose trees used in ornamental, soil and water conservation, fodder and nectar sources. Plant abiotic stress tolerance transformed by genes could meet the requirements for reclamation of arid or alkalid lands and vegetation restoration. For this paper, we studied the effects of auxin and cytokine on Idaho locust in vitro regeneration and the establishment of gene transformation systems for plants mediated by Agrobacterium tumefaciens. Results showed that the ratios of cytokinin and auxin were the major factors affecting adventitious bud differentiation on a MS medium; the concentration of 0.5 mg•L–1 6-BA benefitted callus proliferation and 0.25 mg•L–1 IBA promoted shoot rooting; however, a higher IBA concentration will inhibit rooting. The most effective antitoxin for screening transgenic Idaho locust shoots was G418 and the most sensitive concentra-tion of it was 8 mg•L–1. 相似文献
17.
CANNELL M. G. R.; TABBUSH P. M.; DEANS J. D.; HOLLINGSWORTH M. K.; SHEPPARD L. J.; PHILIPSON J. J.; MURRAY M. B. 《Forestry》1990,63(1):9-27
Seedlings (transplants) of 2+1 Sitka spruce (Picea sitchensis(Bong.) Carr.) and 1 + 1 Douglas fir (Pseudotsuga menziesii(Mirb.) Franco) were grown in a nursery at the Bush Estate,Scotland. Batches were lifted and cold stored at 0.5°C inNovember, December and January. Changes in growth, shoot apicalmitotic index, root growth potential (RGP), carbohydrate content,bud dormancy and shoot frost hardiness were monitored throughoutthe winter by taking samples at intervals from the nursery andfrom cold storage. Frost hardening occurred during the later stages of bud development(as mitotic indices decreased); autumn hardening was arrestedwhen seedlings were put in cold store, and some dehardeningoccurred in cold storage, especially in spring. Bud dormancystarted, and was greatest, just after bud growth (mitotic activity)virtually ceased; chilling in cold store was almost as effectivein releasing dormancy as natural chilling. The concentrationof total nonstructural carbohydrates stayed more or less constantat 100–150mg g–1 from September to April in thenursery; in cold storage carbohydrates were depleted at 0.4–0.6mgg–1 d–1 (corresponding to respiration at 0.03–0.05mgCO2 g–1 h–1) until there was only 40–50mgg–1. Root growth potentials in the nursery increased in December,once the buds ceased growth, became dormant and had receivedsome chilling. Sitka spruce was ‘storable’ in November,before RGPs increased, but they then failed to achieve maximalfrost hardiness or ROP. Winter RGPs were high in Sitka spruceand were increased or maintained in cold storage, whereas RGPswere low in Douglas fir and decreased immediately after storage(except when stored in January). By the end of April, the RGPof cold stored Sitka spruce was much higher than that of directlifted plants. ROP changes in the nursery and in cold storagewere not consistently related to changes in seedling carbohydratecontents, shoot frost hardiness or bud dormancy. In practical terms, it was concluded that (1) the optimum dateto start lifting bare- rooted conifer transplants in the autumnis when their shoot apical mitotic indices have decreased tonear zero, and their RGPs have risen sharply; (2) high RGPsmay depend as much on the morphology of the roots (e.g. numberof undamaged root apices) as on the physiology of the shoots(e.g. carbohydrate status, dormancy and frost hardiness); and(3) in spring, transplants kept in cold storage since November,December or January are more frost hardy, slightly more dormant,and (in May) have higher RGPs than transplants lifted from thenursery. 相似文献
18.
A total of 210 Norway spruce trees with stem wounds resulting from bark peeling by moose (Alces alces) were examined in three 45–50-year-old stands that contained 20-30% of damaged trees. Injured stems were between 8 and 40 cm diameter at breast height (d.b.h.) and showed 1 to 23-year-old wounds. Wounds varied in size from 2 to 4815 cm2. The size of injury correlated negatively with the age of the injury (r=-0.24; p=0.004), and positive correlation was established between the age of the injury and d.b.h. of the wounded tree (r=0.50; p=0.0001). Each wound was sampled once using an increment borer and fungi were isolated. Among basidiomycetes, Stereum sanguinolentum was the most common (isolated from 26.7% of the damaged stems). Other common species were Cylindrobasidium evolvens (23.8%), Amylostereum areolatum (5.2%), A. chailletii (0.5%), Heterobasidion annosum (5.2%), Peni-ophorapithya (1.4%), Sistotrema brinkmannii (1.0%). The ascomycete Nectria fuckeliana was the most common among all fungi (present in 35.7% of bark peeling wounds). The frequency of S. sanguinolentum infection correlated positively with the age of the injury (r=0.27; p=0.001) and the opposite relationship was revealed for C. evolvens (r=?0.30; p=0.0001). Furthermore, C. evolvens infection correlated positively with the wound size (r=0.30; p=0.0001) and negatively with the tree d.b.h. (r=?0.20; p=0.004). A positive correlation was found between tree d. b. h. and the occurrence in stems of H. annosum (r=0.23; p=0.001 and N. fuckeliana (r=0.23; p=0.0006). The spruce bark beetle Dendroctonus micans attacked 14.8% of wounded trees. Presence in stems of N. fuckeliana was associated significantly with the D. micans attack (r=0.190; p =0.006; χ2 test: p=0.01). Except for a negative correlation between infections of S. sanguinolentum and H. annosum (r=-0.140; p=0.04), no significant relationship between fungal species was found. 相似文献
19.
《Forest Ecology and Management》2006,227(3):233-246
Forests of the Kenai Peninsula, Alaska experienced widespread spruce (Picea spp.) mortality during a massive spruce beetle (Dendroctonus rufipennis) infestation over a 15-year period. In 1987, and again in 2000, the U.S. Forest Service, Pacific Northwest Research Station, Forest Inventory and Analysis Program conducted initial and remeasurement inventories of forest vegetation to assess the broad-scale impacts of this infestation. Analysis of vegetation composition was conducted with indirect gradient analysis using nonmetric multidimensional scaling to determine the overall pattern of vegetation change resulting from the infestation and to evaluate the effect of vegetation change on forest regeneration. For the latter we specifically assessed the impact of the grass bluejoint (Calamagrostis canadensis) on white spruce (Picea glauca) and paper birch (Betula papyrifera) regeneration. Changes in vegetation composition varied both in magnitude and direction among geographic regions of the Kenai Peninsula. Forests of the southern Kenai Lowland showed the most marked change in composition indicated by relatively large distances between 1987 and 2000 measurements in ordination space. Specific changes included high white spruce mortality (87% reduction in basal area of white spruce >12.7 cm diameter-at-breast height (dbh)) and increased cover of early successional species such as bluejoint and fireweed (Chamerion angustifolium). Forests of the Kenai Mountains showed a different directional change in composition characterized by moderate white spruce mortality (46% reduction) and increased cover of late-successional mountain hemlock (Tsuga mertensiana). Forests of the Gulf Coast and northern Kenai Lowland had lower levels of spruce mortality (22% reduction of Sitka spruce (Picea sitchensis) and 28% reduction of white spruce, respectively) and did not show consistent directional changes in vegetation composition. Bluejoint increased by ≥10% in cover on 12 of 33 vegetation plots on the southern Kenai Lowland but did not increase by these amounts on the 82 plots sampled elsewhere on the Kenai Peninsula. Across the Kenai Lowland, however, regeneration of white spruce and paper birch did not change in response to the outbreak or related increases in bluejoint cover from 1987 to 2000. Although some infested areas will be slow to reforest owing to few trees and no seedlings, we found no evidence of widespread reductions in regeneration following the massive spruce beetle infestation. 相似文献
20.
An account of the silviculture of Norway and Sitka spruce (Piceaabies and P. sitchensis) practiced in the West (Scotland) Conservancyof the Forestry Commission in the past 50 years. Present methodsare summarized and future developments forecast. A more intensiveform of silviculture is advocated for Sitka spruce. 相似文献