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1.
Norway spruce is one of the most important conifer tree species in Europe, paramount for timber provision, habitat, recreation, and protection of mountain roads and settlements from natural hazards. Although natural Norway spruce forests exhibit diverse structures, even-aged stands can arise after disturbance or as the result of common silvicultural practice, including off-site afforestation. Many even-aged Norway spruce forests face issues such as senescence, insufficient regeneration, mechanical stability, sensitivity to biotic disturbances, and restoration. We propose the use of Density Management Diagrams (DMD), stand-scale graphical models designed to project growth and yield of even-aged forests, as a heuristic tool for assessing the structure and development of even-aged Norway spruce stands. DMDs are predicated on basic tree allometry and the assumption that self-thinning occurs predictably in forest stands. We designed a DMD for Norway spruce in temperate Europe based on wide-ranging forest inventory data. Quantitative relationships between tree- and stand-level variables that describe resistance to selected natural disturbances were superimposed on the DMD. These susceptibility zones were used to demonstrate assessment and possible management actions related to, for example, windfirmness and effectiveness of the protective function against rockfall or avalanches. The Norway spruce DMD provides forest managers and silviculturists a simple, easy-to-use, tool for evaluating stand dynamics and scheduling needed density management actions.  相似文献   

2.

Understanding how species-specific disturbances affect the dynamics of mixed forests is becoming increasingly important due to rapidly changing disturbance regimes. This study estimated the effect of Norway spruce (Picea abies (L.) Karst.) mortality on the disturbance processes in two mixed beech stands of the Western Carpathians that were affected by a bark beetle outbreak. We evaluated the size distribution, fraction of canopy and expanded gaps, the characteristics of gapmakers and the contribution of different species to gap size. The measured canopy gap fraction was <5%, and most canopy gaps were small (<100 m2). Spruce was the most abundant gapmaker, and its share among gapmakers was 3–6 times higher than its share in the canopy. We found that the increase in spruce mortality due to the outbreak resulted in a fine-scale mortality pattern. However, spruce gapmakers did not contribute much to gap area size, as shown by a weak correlation between the number of spruce gapmakers and the area of expanded gaps. Diameter distribution of living versus recently dead trees showed that beech mortality occurred disproportionately in large size classes. However, dead spruce trees were equally frequent in all diameter classes, which means beetles did not exclusively attack larger trees in these stands during the outbreak. We conclude that spruce mortality may have influenced successional processes by giving a competitive advantage to two other species that were not affected by the outbreak, provided that a high deer browsing intensity does not hinder the regeneration of new seedlings.

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3.
To test the direct regeneration hypothesis and support natural disturbance-based forest management we characterized the structure and composition of boreal mixedwood forests regenerating after large wildfires and examined the influence of pre-fire stand composition and post-fire competing vegetation. In stands which had been deciduous (Populus sp.)-dominated, conifer (white spruce)-dominated, or mixed pre-fire we measured regeneration stocking (presence in 10 m2 plots), density and height 10–20 years post-burn in five wildfires in Alberta, Canada. Most plots regenerated to the deciduous or mixed stocking types; plots in the older fire and in stands that were pure conifer pre-fire had higher amounts of conifer regeneration. Surprisingly, regeneration in pre-fire ‘pure’ white spruce stands was most often to pine, although these had not been recorded in the pre-fire inventory. Pre-fire deciduous stands were the most resilient in that poplar species dominated their post-fire regeneration in terms of stocking, density and height. These stands also had the highest diversity of regenerating tree species and the most unstocked plots. High grass cover negatively affected regeneration density of both deciduous and conifer trees. Our results demonstrate the natural occurrence of regeneration gaps, pre- to post-fire changes in forest composition, and high variation in post-fire regeneration composition. These should be taken into consideration when developing goals for post-harvest regeneration mimicking natural disturbance.  相似文献   

4.
Montane Norway spruce forests of Central Europe have a very long tradition of use for timber production; however, recently there has been increasing concern for their role in maintaining biological diversity. This concern, coupled with recent severe windstorms that led to wide-spread bark beetle outbreaks, has brought the management of montane spruce forests to the forefront of public policy discussions in Central Europe. In order to shed light on the natural development and current structure of mature montane spruce forests, we established four 0.25 ha research plots in a semi-natural montane spruce forest in the Šumava Mountains (The Bohemian Forest), Czech Republic. We mapped all trees, extracted increment cores for age and growth-pattern analyses, and inventoried all current tree regeneration, including the substrates on which it was found. Stands were characterized by uni-modal tree diameter distributions and high basal areas (56.6 m2 ha−1 on average), indicating a natural transition from the stem exclusion phase towards the understory reinitiation phase. The stands showed largely single-cohort recruitment age structures, however, with recruitment spanning seven decades. Our analyses suggest that this cohort existed as advance regeneration prior to major disturbances in the late 1800s, which included post-bark beetle salvage logging. Spatial pattern analyses of living and dead stems combined, showed an increase in uniformity of living trees, pointing to the role of natural density-dependent mortality. However, past growth patterns and historical documentation suggest that low intensity canopy disturbances (wind and snow) also caused mortality and diversified canopy structure. Because the stands developed naturally over the past 120+ years and thus escaped thinning operations, high volumes of coarse woody debris (94 m3 ha−1) and snag densities (546 stems ha−1) have accrued. Advance spruce regeneration was quite abundant and existed primarily on deadwood substrates, even though these occupied only a small percent of stand area. Because of salvage logging in the late 1880s, these stands do not qualify, according to the traditional paradigm, as natural spruce forests. As a result, they are recently subject to active management practices including salvage logging that remove dead and dying trees. Given the importance of deadwood for forest regeneration and recovery from disturbance, as demonstrated in this study, we argue that dead wood removal may limit future natural regeneration in these stands. Thus, the purported benefits of removing dead and dying trees from semi-natural forests must be carefully weighed against the potential detrimental impacts on natural spruce forest regeneration and biodiversity.  相似文献   

5.
An outbreak of the mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB), currently affecting over 10.1 million hectares of lodgepole pine forests (Pinus contorta Dougl.) in British Columbia, Canada, is the largest in recorded history. We examined the dynamics of even-aged lodgepole pine forests in southern British Columbia, which were undergoing this MPB outbreak. Using dendroecology and forest measurements we reconstructed the stand processes of stand initiation, stand disturbances, tree mortality, and regeneration, and explained the current stand structure and the potential MPB impacts in selected stands. Our results indicate that stand-replacing fires initiated even-aged seral lodgepole pine stands in this region. In the absence of fire in the 20th century, multiple MPB disturbances, which each resulted in partial canopy removal, modified the simple one-layer structure of the fire-origin stands by the initiation of post-MPB disturbance regeneration layers, transforming the stands into complex, multi-aged stands. Despite high overstory mortality due to the current MPB outbreak, regeneration layers, which are likely to survive the current outbreak, will provide important ecological legacies and will contribute to mid-term timber supply.  相似文献   

6.
The impact of natural disturbances on the canopy (trees ≥14 m high) and sapling stratum (>0.3 and ≤14 m high) composition was studied in nemoral old-growth forests located within the southern boreal zone in Central Russia (Central Forest Reserve, 32°29′–33°01′E, 56°26′–56°31′N). I hypothesized that the current disturbance regime does not allow the maintenance of current spruce abundance in the canopy, and, as a result, there is a continuous shift in the canopy composition towards a greater abundance of deciduous species. Three 300×20 m2 transects were established to estimate the proportions of stand under non-closed unexpanded canopy gaps. Data on sapling composition of 49 canopy gaps were used to analyze pattern of gap refuting in these forests. Additionally, data from three forest inventories showed changes in canopy composition over a period from 1972 to 1990.

The current status of nemoral forests is characterized by the high proportion of stand area under treefall gaps (71%). The loss of spruce from the canopy caused by treefalls (53% of the total basal area of gap-makers) was slightly greater than its canopy abundance (45%). Canopy gaps of all sizes encouraged spruce regeneration which might be due to a decrease in sapling mortality and/or more active recruitment of spruce seedlings. After a gap was formed, the presence of spruce in sapling strata increased. However, within both small (<200 m2 in size) and large (>200 m2) gaps, tall (>6 m) spruce saplings did not reach the level of its abundance in the tree canopy. In gaps, tall (>6 m) saplings of lime (Tilia cordata) and elm (Ulmus glabra) grew more quickly than those of spruce and maple. These data suggested a decrease in canopy spruce and an increase in deciduous species in the near future which supported the original hypothesis. Analysis of forest inventory records revealed similar changes in the canopy structure over the past two decades. However, the observed high proportion of stand area under gaps implies that for the next few decades large areas of nemoral communities will be occupied by relatively young stands. This may, in turn, decrease the frequency of large-scale treefalls revegetated mainly by deciduous saplings.  相似文献   


7.
Disturbance patterns are strongly coupled with forest composition and structure, and patterns change through time in response to shifts in climate, anthropogenic impacts and other factors. Knowledge of the natural disturbance patterns for establishing baseline conditions for a forest type or ecosystem facilitates change detection for other elements of the biophysical system important to management and conservation. Dendrochronological reconstructions from old-growth forest remnants throughout northeastern North America document average decadal rates of disturbance of 5%–<10% over the last 150–300 years. Relatively frequent, low severity disturbance characterized by small gaps representing canopy openings made by 1–3 trees prevail in these forests dominated by varying mixtures of late-successional tree species. Few studies, though, have explicitly characterized differences related to composition or topographic setting in old-growth landscapes. We addressed this by comparing the temporal and spatial disturbance patterns reconstructed from tree rings at two spatial resolutions (0.5 ha and 200 m2). Sites were selected to assess the influence of topography (slope) and cover type in stands where red spruce (Picea rubens Sarg) and balsam fir (Abies balsamea L. Mill) were key components. Low rates of disturbance (average <10% per decade) and small gap sizes (≤30 m2) prevailed in all stands during the decades from 1850–1980. Episodic pulses of disturbance, of nearly moderate intensity in some stands, opened ca. 20–30% of the canopy area and were associated with wind events and/or insect outbreaks that differentially affected stands. We found no significant difference in the average temporal rates of disturbance related to cover type or topography in 0.5-ha plots. However, the influence of these factors was evident in comparisons of gap areas estimated for 200-m2 plot sections. At this resolution, the largest canopy openings (≥100 m2) occurred most frequently in slope sites, enabling pulses of canopy accession for Betula alleghaniensis (Britton). Whereas the smallest canopy openings (≤30 m2) dominated softwood stands, favoring red spruce, balsam fir and other shade-tolerant species throughout the forest. The variable effects of common disturbance agents, regardless of topographic position and/or cover types, points to the important role of biological legacies determining stand structure and composition on subsequent disturbance events and long-term patterns.  相似文献   

8.
Subtropical forests in the Ryukyu Islands have been degraded by silvicultural practices, and thus their structural attributes are being shifted to other states dominated by a few tree species. This study clarified the mechanisms of the change, and examined the effect of clear logging on the resilience of a subtropical forest. Sprouting regeneration and typhoon disturbance were introduced into an individual-based model, SEIB-DGVM, for describing stand development and succession. The regeneration dynamics from young secondary to old-growth stands were reproduced fairly well with the model. Sprouting recruitment produced high stem density at the beginning of stand development, which caused a self-thinning trajectory following the −3/2 power law. In the late development stage after 70 years, tree species diversity fluctuated because of the regenerative response of sprouting species and the facilitatory effect of typhoon disturbance on the coexistence of subordinate species. The death of canopy trees because of typhoon disturbances reduced the dominance of Castanopsis sieboldii, and depressed its dominance in the understory. Consequently, the understory species could establish by virtue of fallen canopy trees, and tree species diversity increased at the stand level. Clear logging experiments in the model revealed that species diversity deteriorated, especially in the stand dominated by sprouting species. Resilience of subtropical forests was determined by initial species composition before clear logging. Our simulation results suggest that repeated logging drives subtropical forests with high species diversity to a stand monopolized by C. sieboldii.  相似文献   

9.
Wind throw is a common disturbance in forest ecosystems. Because many forests are intensively used our knowledge on forest dynamics after such disturbances is limited. In the Bavarian Forest National Park/Germany after the wind throw event in summer 1983, we started our long-term observation in nearly natural Norway spruce forests within 5-year intervals up to 2010. A part of the affected stands was cleared, while another part was left untouched for natural development. Here, we focused on the tree species regeneration, using an individual-based approach. We expected that tree species regeneration in both management types would follow different succession pathways. Indeed, we found different regeneration characteristics, depending on whether the area had been cleared or left unmanaged. For example, for the target species Norway spruce, a chronic regeneration during the first two decades with low numbers, but a high survival rate of individuals, and for the pioneer species birch, pulse regeneration with high numbers of individuals only at the beginning and high individual loss during the following years occurred. Unmanaged and cleared wind throw areas, respectively, offer different quantities of micro-sites: the pit and mound structure as mineral soil disturbance was limited to less than 1/4 in the untouched area, whereas there was mineral soil disturbance more or less everywhere on the cleared parts. Type and intensity of disturbance allow a wide range of succession pathways after wind throw, based on the fundamental processes of germination and competition. Therefore, for protection area management as well as for forest management, the human activity immediately after the event is crucial. Because each management impact will change the succession pathway fundamentally any impact has to be omitted in protection areas with the main goal of natural vegetation succession. Also in managed forests abdication of any impact on small areas may improve the natural structures and biodiversity of forests.  相似文献   

10.
The emergence of Norway spruce seedlings on different types of germination sites in uneven-aged Norway spruce dominated stands four years after selection harvesting was studied. The data were collected from 20 stands in southern Finland. In each stand, ground cover was measured from a set of 64 one square metre subplots on a permanent experimental plot of 1600?m2. Correlation analysis, direct comparison of subplots with and without seedlings and mixed-effects models were used to estimate the influence of ground and tree cover on seedling occurrence. Grass cover, dwarf shrub cover, cover of certain moss species and close vicinity of trees decreased the occurrence probability and number of seedlings, while greater stand and local basal area around the subplots increased the seedling number. The cover of vegetation free surfaces, usually considered as good germination sites, was rather low. Variation in seedling emergence between plots was high. We concluded that spruce regeneration was slightly more abundant in stands with greater overall stand density and local density within a stand in postharvest conditions.  相似文献   

11.
We focused our attention on quantifying the factor complex of forest regeneration in 423 mature and old stands with contrasting environmental conditions. We recorded the microhabitat selection of tree recruits, the frequency of tree seedlings, and evaluated the drivers of sapling abundance and diversity. The majority of forest regeneration was established on undisturbed forest floor. Dead wood was a frequent substrate in spruce-(co)dominated forests. Seedling frequency within a stand was related to the site-type specific productivity gradient of stands—pine seedlings were common in low-productivity and spruce in high-productivity boreal forests. Seedlings of temperate broad-leaved trees dominated in productive boreonemoral forests, except for oak, which showed a uniform distribution of abundance in all forest site-types. Sapling abundance was dictated by forest site-type, and facilitated by stand diversity, variability in stand closure, lying dead wood, abundant moss, and a thick organic layer. Only in boreal forests was sapling abundance suppressed by the abundant spruce and younger trees. Upon considering the relationship between sapling abundance and species richness, sapling diversity was dependent on forest site-type, suppressed by stand density and dead wood (old gap) abundance, and facilitated by stand diversity. In addition, boreonemoral stands, competition from herbs, and facilitation by mosses occurred. The observed pattern of tree recruitment points to the importance of top-down effects of the overstory, competing or facilitating interactions with forest floor vegetation, and availability of regeneration microhabitats, which in complex make their ecology comparable with forest herbs. Natural forest regeneration can be enhanced if silvicultural methods support mixed stands and enhance field layer diversity. Oak can provide the universal tree species to improve stand structure over a wide range of habitats.  相似文献   

12.
Black spruce forests growing on clay soils in northwestern Quebec change structure from dense even-aged stands to open uneven-aged stands such that almost all forests older than 200 years have an open canopy. These forests become unproductive over time because they are prone to paludification. The main goal of our study was to document the transition between dense and open stands in terms of gap dynamics, with a focus on tree regeneration. Our objective was to determine whether forests remain open due to a lack of regeneration, a lack of growth or both. Nine stands along a 50–250-year-old time since fire gradient were sampled with the line intersect sampling method. Gap fraction increased with stand age and reached a maximum of 77% in the oldest site. In old-growth stands, gaps were interconnected due to the low density of these forests. Most of the gap makers were found with broken stems. Regeneration was dominated by black spruce layers and was relatively abundant (1.71 stems/m2). However, the majority of gap fillers were smaller than 1 m in height in stands of all ages. Instead of a lack of regeneration, the opening of the forests is due to a lack of growth associated with cold and wet organic deposits. Partial harvesting could be implemented on the most productive sites, while management techniques including soil disturbances will be required on low productivity sites to recreate good growth conditions.  相似文献   

13.
Following disturbances, early-seral stages of forests provide a variety of structures. Whether this variety is a short-term phenomenon or influences forest succession for several decades or even longer is not known. We tested the hypotheses that after spruce dieback caused by bark beetles, a high spatial heterogeneity of stand structures will persist within stands and among stands even in advanced early-seral stages and that species taxonomical and functional diversity measures will reflect this heterogeneity. We used a chronosequence of unmanaged forests in the Berchtesgaden National Park (Germany) consisting of mature undisturbed spruce stands (control), stands belonging to an initial early-seral stage (~3 years after disturbance) and stands in an advanced early-seral stage (~20 years after disturbance). We analysed diversity and heterogeneity of these forest stands including stand structure, species density, species composition and functional–phylogenetic diversity of vascular plants, wood-inhabiting fungi and saproxylic beetles within plots, among plots of the same successional stage and among stages. Stands of the advanced early-seral stage were characterized by a high spatial heterogeneity of structural attributes, such as crown cover, regeneration density and spatial distribution of trees. Among-plot taxonomic beta diversity was highest in the advanced early-seral stage for beetles, but lowest for fungi, while beta diversity of plants among plots remained unchanged during succession. The mosaic of successional stages initiated by bark beetles increased the gamma diversity of the study area, especially for fungi and beetles. Our findings support the hypothesis that structural heterogeneity continues for at least two decades at stand and landscape scales and that species turnover among successional stages is a major mechanism for gamma diversity in forests after bark beetle disturbance.  相似文献   

14.
The aim of this study is to investigate the effects of forest conversion on forest floor vegetation. ‘Ecological’ forest conversion, as defined by an interdisciplinary southern Black Forest project group, describes the transformation of even-aged spruce (Picea abies L. H. Karst.) stands to structured continuous cover forests consisting of spruce (Picea abies), silver fir (Abies alba Mill.) and beech (Fagus sylvatica L.). In order to analyse the conversion process, four conversion stages were defined in a conceptual forest development model. Four forest districts deemed to be representative of the southern Black Forest region were selected for the study. The ground vegetation was initially classified independently from the stand structures. Subsequently, the relationship between stand structures, as determined by development stage, and ground vegetation was analysed. It was revealed that forest conversion modified the ground vegetation. The main factors influencing ground vegetation were the influence of broadleaves, predominately beech (F. sylvatica), on the canopy composition and litter coverage on the one hand; and the canopy coverage of spruce, the proportion of needle litter and the associated light penetration on the other. The prevalence of moss and vascular plant species preferring acidic sites found in spruce forests decreased during the transition process, whereas, species requiring a moderate base supply increased in abundance. The continuous cover forest representing the final stage of conversion increasingly contained a mixture of ground vegetation species normally associated exclusively with either conifer or deciduous forest. Due to the fact that there is an associated ground vegetation specific to the different stages of forest conversion in stands dominated by Norway spruce or European beech and a mixture in the latest conversion stages, large-scale forest conversion should be avoided in favour of management promoting a diversity of silvicultural goals and treatments in neighbouring stands. Only a variety of treatments ensures the maintenance of floristic diversity in the long-term.  相似文献   

15.
A process-based ecosystem model was used to assess the impacts of changing climate on net photosynthesis and total stem wood growth in relation to water availability in two unmanaged Norway spruce (Picea abies) dominant stands with a mixture of Scots pine (Pinus sylvestris) and birch (Betula sp.). The mixed stands were grown over a 100-year rotation (2000-99) in southern and northern Finland with initial species shares of 50, 25 and 25% for Norway spruce, Scots pine and birch, respectively. In addition, pure Norway spruce, Scots pine and birch stands were used as a comparison to identify whether species' response is different in mixed and pure stands. Soil type and moisture conditions (moderate drought) were expected to be the same at the beginning of the simulations irrespective of site location. Regardless of tree species, both annual net canopy photosynthesis (P(nc)) and total stem wood growth (V(s)) were, on average, lower on the southern site under the changing climate compared with the current climate (difference increasing toward the end of the rotation); the opposite was the case for the northern site. Regarding the stand water budget, evapotranspiration (E(T)) was higher under the changing climate regardless of site location. Transpiration and evaporation from the canopy affected water depletion the most. Norway spruce and birch accounted for most of the water depletion in mixed stands on both sites regardless of climatic condition. The annual soil water deficit (W(d)) was higher on the southern site under the changing climate. On the northern site, the situation was the opposite. According to our results, the growth of pure Norway spruce stands in southern Finland could be even lower than the growth of Norway spruce in mixed stands under the changing climate. The opposite was found for pure Scots pine and birch stands due to lower water depletion. This indicates that in the future the management should be properly adapted to climate change in order to sustain the productivity of mixed stands dominated by Norway spruce.  相似文献   

16.
The single-tree selection system is an important option for management of Norway spruce (Picea abies (L.) Karst.) and silver fir (Abies alba Mill.) forests because it provides continuous cover, requires low investments for tending, and promotes natural regeneration as well as high stand resistance and elasticity. It is often regarded as a very conservative system that usually results in only minor spatiotemporal changes in forest structure and composition. We studied management history, structural changes, regeneration dynamics, and light climate of a traditional single-tree farmer selection silver fir-Norway spruce forest (site typology Bazzanio-Abietetum). Stand structure was analyzed on five 0.25 ha permanent plots in 1994, 2001, and 2008. Regeneration density and height growth, forest floor vegetation, and light climate were also assessed on 1.5 × 1.5 m regeneration subplots in 2001 and 2008. Tree cores extracted from dominant trees from both species in two plots were used for reconstructing stand history and age structure of the canopy layer. We documented the forest response to three types of selection management regimes: excessive, normal, and conservative. Excessive management with harvest intensity significantly above the increment was documented until the late 1950s, including two peaks of heavy fellings (diameter limit cut) in the 1880s and 1930s, which favoured establishment of Norway spruce and released regeneration. The period that followed was characterized by normal selection management, but was nevertheless marked by a decline of silver fir as a result of air pollution and several droughts. This led to sanitary fellings that were carried out from the late 1970s to the early 1990s. In the last two decades conservative management followed, which led to suppression and decline of regeneration, especially of Norway spruce, and loss of selection structure. Although we recorded lower regeneration potential of silver fir compared with Norway spruce within the seedling category, silver fir outcompeted Norway spruce within the small-sized tree category (1 cm < dbh ? 10 cm) because of its superior height growth in low light levels (diffuse light <6%) and occupied a greater share of the canopy. Nevertheless, we anticipate that over the long-term the low light regime will also cause regeneration decline of silver fir and broadleaves. Our research revealed significant structural changes in a single-tree farmer selection forest during the last 150 years. These were a result of variable management regime and environment. A farmer single-tree selection system could better mimic the natural disturbance regime if spatiotemporal combinations of diverse felling regimes would be used.  相似文献   

17.
Gap-associated spruce (Picea abies (L.) Karst.) regeneration in Sphagnum-Myrtillus stands of south taiga forests (Central Forest Biosphere reserve, Tver region, Russia) was studied to evaluate the role of different disturbances in spruce dynamics. Sampled gaps (n=70) ranged from 40 m2 to 1.7 ha in size, and from 1 to 70 years since disturbance moment. Formation of gaps lead to increase in the number of stems per ha in all gap size classes (small: 40–200 m2, medium: 200–3000 m2, and large: >3000 m2 gaps). Spruce was the most important species in gap refilling, although its role was not the same in different gap classes. The highest values of relative abundance (compared to other species) were recorded in small gaps, and much lower values – in middle and large gaps. However, as refilling of gaps proceeded, spruce showed rather active regeneration in middle and large gaps and partly regained its abundance in middle-age disturbances. In general, all types of gaps studied supported spruce regeneration into the forest canopy. Almost perfect correlation between predicted outcome of spruce dynamics in gaps and its current role in the canopy of Sphagnum-Myrtillus stands suggests a good adaptation of this species to the current disturbance regime and a steady state of the these forests.  相似文献   

18.
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   

19.
In the boreal forest of Alberta, fire and wind often open gaps in the canopy where late-successional species can establish and over time cause a shift in the species distribution from deciduous (e.g., trembling aspen) dominated to mixedwood, to shade-tolerant conifer (e.g., white spruce) dominated stands. This study attempted to understand the change of density-dependent competition in a boreal chronosequence and the role of tree competition in affecting stand structure and mortality. Four 1-ha stem-mapped plots were established to represent a chronosequence comprised of aspen dominated, mixedwood, and spruce dominated stands in Alberta. Second order spatial point-pattern analysis using Ripley's K(t) function showed that intraspecific competition is a prevailing force causing conspecific tree mortality and thus shaping the stand structure. The results of bivariate K(t) function analysis did not reveal sufficient evidence of interspecific competition. This suggested that competitive interaction among heterospecific trees was not strong enough to cause significant tree mortality, but the analysis of marked correlation function revealed that interspecific competition could have a negative impact on tree growth. This study highlights the importance of density-dependent competition in understanding stand dynamics of boreal forests over succession.  相似文献   

20.
Macroscopic charcoal and pollen analysis were used to study the disturbance history and development of a boreal Norway spruce (Picea abies (L.) Karst.) forest landscape in southeastern Norway. The sites studied were natural forests and the charcoal records showed no evidence of fire disturbance that could have broken the continuity in the spruce forests that were established ca. 1700 years ago. Consequently, true spruce forest ecosystem continuity was documented on a landscape level. However, fire disturbed the mixed pine-deciduous forest ecosystems that preceded the present spruce forests, suggesting a shift from fire-prone, to fire-free forest ecosystems.It is argued that the studied forest landscape has the potential to be an important natural reference for future forestry, that would be required to mimic natural forest dynamics to be biologically sustainable. A stereotypic promiscuous use of fire in the regeneration phase may cause serious damages in forest ecosystems that have developed without the impact of fire disturbance.  相似文献   

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