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1.
Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to assess available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL<20–35%; BA>30 m2/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL=35–70%; BA=15–35 m2/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL>80–90%; BA<15–20 m2/ha) with the spruce having a tendency to outgrow the others. However, in terms of establishment, such conditions favor spruce and inhibit fir and beech.  相似文献   

2.
The objective of this study was to determine the rate of nitrogen (N) mineralization in response to various levels of canopy cover in red pine (Pinus resinosa Ait.) stands. Experimental plots consisted of various levels of canopy cover,i.e., clearcut, 25% (50% during first sampling year), 75%, and uncut in red pine plantations in northern Lower Michigan, USA. Net N mineralization and nitrification in the top 15 cm of mineral soil were examined during the first two growing seasons (1991–1992) following the canopy cover manipulations, using anin situ buried bag technique. Mean net N mineralization over the course of both growing seasons (May–October) ranged from 26.9 kg ha−1 per growing season in the clearcut treatment to 13.4 kg ha−1 per growing season in the uncut stand. Net N mineralization and nitrification increased significantly in the clearcut treatment compared to the uncut treatment during the second growing season only. However, net N mineralization and nitrification did not differ significantly between the partial canopy cover treatments and the uncut stand. Increased N mineralization and nitrification in the clearcut during the second growing season may be associated with increased soil temperature and changes of organic matter quality with time since canopy removal. This study was supported in part by the USDA Forest Service and Michigan Technological University.  相似文献   

3.
In the intermediate cutting intensity experiment of a Cunninghamia lanceolata plantation for 20 years, the changing pattern of natural thinning in these stands, with different intermediate cutting intensities, was studied. The relationship between the number of trees removed by natural thinning and stand density and site conditions was explained. The mathematical equation M = K 1·K 2 of natural thinning lines of C. lanceolata stand density management maps was tested and the relationship of diameter, height and canopy structure of stands with different intermediate cutting intensities are proposed. Our study of natural thinning in these stands indicates that the starting and peak periods of natural thinning in the check and slightly thinned plots were both early. The amount of thinned wood was large and the course of thinning proceeded continuously. The three levels of thinning: the slight thinning period, the intensive thinning period and the continued thinning period could be divided on the basis of the amount of thinned wood. Natural thinning would be a very long process without artificial interference. The starting and peak periods of thinning in the middle and strong intermediate felling are both late and present intermittence. Their thinning stages were not clearly evident. Through our studies, we also discovered that stand density and site conditions had important effects on the number of dead and dying trees, but that density was more important than site conditions. By way of tests, the relative error of the mathematical equation of natural thinning lines of C. lanceolata stand density management maps was 3.91% and the precision was relatively high. The practical test results of the stands, given different intermediate cutting intensities and different site indices, show that the relative error of the check plots was 5.23%, while the relative errors of the other tested items were all < 5%, well within the allowable experimental error. The mathematical equation was comparatively practical. The study demonstrated the distribution laws of diameter and height classes of the stand at different intermediate cutting intensities. From this study we also obtained the growth differences and changing dynamics of the height to the first branch, canopy length and relative canopy height of the stand at different intermediate cutting intensities and various related patterns with an increase of stand age and proposed a mathematical model relating stand age and the single-tree periodic volume increment. __________ Translated from Scientia Silvae Sinicae, 2006, 42(1): 55–62 [[译自: 林业科学]  相似文献   

4.
Chrimes  Dillon; Nilson  Kristina 《Forestry》2005,78(4):433-442
The study aimed specifically at investigating if canopy opennesswas a better predictor of the height growth of Norway spruce(Picea abies (L.) Karst.) advance regeneration than overstoreybasal area or overstorey standing volume. In 1990, a field experimentwith 3 x 2 factorial design and two replications (blocks) wasestablished in an uneven-aged Norway spruce forest. Plots hada net plot area of 30 x 30 m, each with a 10-m-wide treatedbuffer zone. Three overstorey density levels retained approximately15, 40 and 70 per cent of the pre-harvest overstorey standingvolume and were allotted to the plots. Two types of thinningthat harvested smaller trees or harvested larger trees wererandomly allocated to each pair of overstorey density plots.In mid-June 2000, canopy openness was estimated from hemisphericalphotographs taken at five marked points in the centre of eachof the plots at 0.9 m from ground to the top of the ‘fish-eye’camera lens. Regression results showed that canopy opennesswas a better predictor of height increments of spruce seedlings(0.1< height < 0.5 m), saplings (0.5 height < 2.0m), and small trees (height 2.0 m, diameter at 1.3 m height< 5 cm) than with overstorey basal area (m2 ha–1) oroverstorey standing volume (m3 ha–1). The height incrementof the spruce advance regeneration was not significantly correlatedto stand basal area or to standing volume. Overstorey basalarea in the net plots was significantly negative (P 0.05) withmean canopy openness estimates, and the r2 value was 0.40. Resultsindicated that basal area was not linearly related to canopyopenness as it increased, which might explain the lack of predictivepower of retained basal area on spruce regeneration height indense stands in boreal Sweden.  相似文献   

5.
The purpose of the present study is to model the regeneration success using quantifiable growth factors. The hypothesis is that the regeneration success can be predicted from a model that incorporates canopy and ground flora leaf area indexes (LAI), soil water content and soil carbon content. In April 1992, 10 plots (1 m2) were established in each of 22 Danish beech stands with natural regeneration originating from the 1989 seed fall. The regeneration success was investigated until autumn 1994. In each of the 220 plots the light conditions, soil water supply and soil carbon content were quantified. The survival was high during the study period. From spring 1992 to autumn 1993 the mean number of saplings decreased from 58 m−2 to 54 m−2. The sapling number was reduced by increased canopy density but it was neither influenced by water supply nor by soil carbon content. The height growth variation was evident. After the fifth growing season (autumn 1994) the height of the tallest sam3pling per plot ranged from 7 to 120 cm. Generally, an increased canopy opening increased the potential for and variance of height growth. Increased soil water content caused a significant increase in the growth of the saplings; whereas, a significant reduction in growth occurred with increased soil carbon content. The shading from the competing ground flora had no significant effect. However, the contribution to the total sum of squares from the quantitative variables of the relevant statistical models was only 3%–13%. Therefore, the models were unable to predict regeneration success satisfactorily and it was not possible to establish the causal effects underlying silvicultural treatments and site. It is concluded that the beech saplings probably were so well established at the beginning of the study that they had become tolerant to poor growing conditions, such as the drought in 1992. This indicates that the growing conditions during the early phases of seedling establishment may be crucial for the regeneration success. For silviculturists, these conclusions stress the importance of creating favourable growth conditions prior to the first growing season. Future research should examine the early phases of seedling establishment by quantifying growth factors in more detail than was done in the present study.  相似文献   

6.
A bark beetle (Ips typographus) infestation caused the death of almost all Norway spruce (Picea abies) trees in a mountain forest in the Swiss Alps. We developed a tree regeneration model, ‘RegSnag’ (=REGeneration in a SNAG stand), to project the future amount and height of tree regeneration in these snag stands. The model combines a height-class structured tree module with a microsite-based module of snag decay and ground-vegetation succession. Microsite-specific rates of germination, mortality and height growth were modelled for four tree species (Picea abies, Sorbus aucuparia, Acer pseudoplatanus and Betula pendula) in eight height classes (from seedlings to saplings 5 m tall) and on 26 microsite types (e.g. moss, grass). Model tests with independent field data from 8 years after the Picea die-back demonstrated that microsites had a considerable effect on the development of tree regeneration on both the montane and the subalpine level. With microsite-specific parameters, the height and frequency of Picea in each microsite could be simulated more accurately than without considering microsite effects (e.g. bias of 8 vs. 119 saplings ha−1 on the montane level). Results of simulations 40 years into the future suggest that about 330–930 Picea saplings per ha out of those that germinated in 1994 and 1996 will reach a height of 5 m within 30–35 years after Picea die-back. This is due to differences in seed inflow and browsing intensities. Picea and not Betula or Sorbus trees will replace the current herbaceous vegetation in these snag stands.  相似文献   

7.
We present results of individual-based root system measurement and analysis applied for Larix gmelinii trees growing on the continuous permafrost region of central Siberia. The data of root excavation taken from the three stands were used for the analyses; young (26 years old), mature (105 years old), and uneven-aged over-mature stand (220 years old). In this article, we highlight two topics: (1) factors affecting spatio-temporal pattern of root system development, and (2) interactions between aboveground (i.e., crown) and belowground (i.e., root) competition. For the first topic, the detailed observation of lateral roots was applied to one sample tree of the overmature stand. The tree constructed a superficial (<30 cm in depth) and rather asymmetric root system, and each lateral root expanded mainly into elevated mounds rather than depressed troughs. This indicated that spatial development of an individual root system was largely affected by microtopography (i.e., earth hummocks). For these lateral roots, elongation growth curves were reconstructed using annual-ring data, and annual growth rates and patterns were compared among them. The comparison suggested that temporal root system development is associated with differences in carbon allocation among the lateral roots. For the second topic, we examined relationships between individual crown projection area (CA) and horizontal rooting area (RA) for the sample trees of each stand. RA was almost equal to CA in the young stand, while RA was much larger (three or four times) than CA in the mature and overmature stands. Two measures of stand-level space occupation, crown area index (aboveground: CAI; sum of CAs per unit land area) and rooting area index (belowground: RAI; sum of RAs), were estimated in each stand. The estimates of RAI (1.3–1.8 m2 m−2) exceeded unity in all stands. In contrast, CAI exceeded unity (1.3 m2 m−2) only in the young stand, and was much smaller (<0.3 m2 m−2) in the two older stands. These between-stand differences in RAI–CAI relationships suggest that intertree competition for both aboveground and belowground spaces occurred in the young stand, but only belowground competition still occurred in the two older stands. Based on this finding, we hypothesized that competition below the ground may become predominant as a stand ages in L. gmelinii forests. Methodological limitations of our analysis are also discussed, especially for the analysis using the two indices of space occupation (CAI, RAI).  相似文献   

8.
The increasing commercial interest and advancing exploitation of new remote territories of the boreal forest require deeper knowledge of the productivity of these ecosystems. Canadian boreal forests are commonly assumed to be evenly aged, but recent studies show that frequent small-scale disturbances can lead to uneven-aged class distributions. However, how age distribution affects tree growth and stand productivity at high latitudes remains an unanswered question. Dynamics of tree growth in even- and uneven-aged stands at the limit of the closed black spruce (Picea mariana) forest in Quebec (Canada) were assessed on 18 plots with ages ranging from 77 to 340 years. Height, diameter and age of all trees were measured. Stem analysis was performed on the 10 dominant trees of each plot by measuring tree-ring widths on discs collected each meter from the stem, and the growth dynamics in height, diameter and volume were estimated according to tree age. Although growth followed a sigmoid pattern with similar shapes and asymptotes in even- and uneven-aged stands, trees in the latter showed curves more flattened and with increases delayed in time. Growth rates in even-aged plots were at least twice those of uneven-aged plots. The vigorous growth rates occurred earlier in trees of even-aged plots with a culmination of the mean annual increment in height, diameter and volume estimated at 40–80 years, 90–110 years earlier than in uneven-aged plots. Stand volume ranged between 30 and 238 m3 ha−1 with 75% of stands showing values lower than 120 m3 ha−1 and higher volumes occurring at greater dominant heights and stand densities. Results demonstrated the different growth dynamics of black spruce in single- and multi-cohort stands and suggested the need for information on the stand structure when estimating the effective or potential growth performance for forest management of this species.  相似文献   

9.
The objective of our study was to examine whether distribution of regeneration in uneven-aged fir (Abies alba Mill.) forests is related to the spatial pattern of trees. In 12 sample plots of size 0.45–1.00 ha (in total 8.65 ha, with stand basal areas ranging from 27.6 m2 ha–1 to 39.5 m2 ha–1), all live and dead trees above 5 cm in d1.3 were mapped and their diameters measured. In eight plots, all live and dead fir saplings were mapped. In three plots, the number of live fir saplings and seedlings was registered on small systematically distributed circular plots. The values of an analytically developed index of stand influence were compared in patches occupied and unoccupied by live or dead fir regeneration. Contrary to preliminary assumptions, only in a few cases did saplings and trees 5–15 cm in d1.3 appear more often in gaps and looser stand patches. Rather, in many plots, the opposite tendency was observed. The seedling density showed a weak but positive correlation with the index of influence. If the spatial pattern of regeneration reflects the spatially varying mortality of juvenile trees, then no evidence was found that stand competition was the most important factor inducing this mortality. On the contrary, on the basis of the results obtained, we can presume that the survival rate of juvenile firs was higher in patches with a relatively higher local basal area. Thus, it was hypothesised that, first, dispersion of regeneration in uneven-aged fir forests is controlled by easy-to-change edaphic factors such as humus form and acidity of the upper soil horizons, and second, that these soil features are linked with the spatial pattern of trees.  相似文献   

10.
The biomass and the spatial distribution of fine and small roots were studied in two Japanese black pine (Pinus thunbergii Parl.) stands growing on a sandy soil. More biomass of fine and small roots was found in the 17-year-old than in the 40-year-old stand. There were 62 g m−2 of fine roots and 56 g m−2 of small roots in the older stand, which represented mean values of 608 g for fine and 552 g for small roots per tree, respectively. In the younger stand, a total of 85 g m−2 of fine roots and 66 g m−2 of small roots were determined, representing a mean of 238 g for fine and 186 g for small roots per tree, respectively. Fine and small root biomasses decreased linearly with a soil depth of 0–50 cm in the older stand. In the younger stand, the fine and small roots developed only up to a depth of 30 cm. Horizontal distributions (with regard to distance from a tree) of both root groups were homogeneous. A positive correlation in the amount of biomass of fine and small roots per m2 relative to tree size was found. Fine and small root biomasses increased consistently from April to July in both stands. The results also indicated earlier growth activity of the fine roots than small roots at the beginning of the growing season. The seasonal increases in fine and small root biomasses were slightly higher in the younger stand than the older stand.  相似文献   

11.
The structure of natural subalpine spruce forest in the Zadná Pol’ana massif of the Western Carpathians was analysed. We focused on the variability of different aspects of stand structure, tree decay and regeneration processes in altitudinal gradient. We used systematic sampling, covering an area of 2 km2, to detect even subtle changes in stand structure within one forest type over a range of less than 200 m in elevation. Mean stand density was 290 trees (>7 cm DBH) per hectare, average basal area was 41 m2 ha−1, and the volume accumulation in living trees amounted to 500 m3/ha−1. Stand volume decreased by more than 50% between 1,260 and 1,434 m a.s.l. This means for an increase of altitude of 100 m that stand volume decreased by nearly 200 m3. Neither stand density nor basal area was related to elevation. Maximum tree height was strongly correlated to elevation, and it decreased on average by 6 m for each 100 m increment of altitude. No significant changes in the maximum spruce diameter were recorded in relation to the elevation gradient. Spatial distribution of trees was biased toward regularity at lower altitudes. Tree clustering increased with increasing altitude. The stock of coarse woody debris (CWD) decreased slightly along the altitudinal gradient, but changes were not significant. Density of spruce saplings and their number growing on CWD significantly increased across the elevation gradient. Despite the fact that the analysed forest tract was relatively large, highly variable in respect to environmental factors, and that stand volume, spatial structure, and tree height displayed strong variability along the elevation gradient, the diameter structure of stands and regeneration measures were uniform. Our results suggest that the recruitment of new trees in the Zadná Pol’ana subalpine spruce forest is not temporally continuous even at a scale of several square kilometres.  相似文献   

12.
A growth model for a plantation of Paraserianthes falcataria was provisionally derived from measurements of 32 permanent plots taken over a period of 2 years in Pare, Indonesia. This model first predicts height growth with the polymorphic site index equation. Then density-related growth and mortality, that is, diameter and stand density, are calculated to satisfy the mathematical relationship for the reciprocal and self-thinning equations, both of which were based on the maximum size–density line with the slope of −1.759 identified in this study. Cumulative predictions on diameter and stand density, starting with each of three age classes, 3, 4, and 5 years after planting, and continuing for the next 2 years, agreed well with the observations of age-class mean. An exception was for stands that were 7 years old, which were marginal, but closest to the rotation age of 8 years. Contrasting height/diameter relationships among the three age classes were described reasonably well with this model, and the predicted basal growth area was found to agree fairly well with observations. These results suggest that the growth model presented here has good potential for applying size–density control for plantations of P. falcataria. However, measurements for an additional few years might be necessary to derive a model that will more accurately predict diameter size at the rotation age.  相似文献   

13.
This study aims to estimate stand density and stand volume in Cryptomeria japonica and Chamaecyparis obtusa stands from high-resolution satellite data and verify the reliability and uncertainty of the data. Sixty circular sample plots of 0.04 ha each were established. Their stand densities were estimated from the number of tree crowns derived from high-resolution satellite data using the watershed method. Stand densities derived from field surveys in the sample plots were compared with those obtained from high-resolution satellite data by stand age class. As a result, there was a positive correlation between them for sample plots of 41 years of age and over (R = 0.82); however, there was no correlation between them for sample plots of 40 years and under. Individual diameters at breast height (DBH) were estimated from crown areas obtained from high-resolution satellite data for the two species. Using the estimated DBH, individual tree heights were predicted from the height–diameter curves. Stand volumes were estimated from the sum of individual volumes, which were derived from volume formulas having two variables, i.e., DBH and height. Stand volumes derived from the field survey were compared with those obtained from high-resolution satellite data. The correlation coefficient between them for stands of 41 years of age and over was 0.78.  相似文献   

14.
In order to understand the effects of thinning on microsite conditions and natural regeneration in the larch plantation, thinning experiment was conducted in a 40-year-old Larix olgensis plantation in Qingyuan County in eastern Liaoning Province, China in 2003-2004 Five thinning treatments （0%, 10.2%, 19.8%, 29.7% and 40.3% thinned） were designed on the same site. After thinning, canopy openness and the microsite conditions such as photosynthetic photon flux density （PPFD）, soil moisture content, and soil temperature were measured in one growing season. Meanwhile, the investigation of natural regeneration was conducted at the end of the growing season. The results showed that the canopy openness increased with the increase of thinning intensities. PPFD and soil temperature and soil moisture content in different soil layers were positively relative with canopy openness after thinning. The richness of regenerating tree species did not significantly increase （p=0.30） after one growing season since thinning, but the regeneration density and frequency of tree species increased significantly （p〈0.05）. In addition, the number of regenerating tree species increased, and the increment was correlated with the characteristics of iudividual tree species. The increasing percentage of regenerating seedlings of the shade-intolerant tree species was more than that of shade-tolerant tree species. Among the investigated regeneration species, the biggest response of seedling emergency to the canopy openness was Phellodendron amurense. This paper confirmed the following conclusions： after thinning, the variety of regenerating tree species was correlative with the characteristics of regenerating tree species, and the distribution of unthinned trees and the site conditions in the investigated larch plantation were the additional factors influencing, the regeneration.  相似文献   

15.
In autumn 2001, 15 canopy gaps were selected for study in RumerhedgeWood, a semi-natural, mesotrophic beechwood in southern England.The gaps were located in mature, beech-dominated stands, andhad originated from openings created during a thinning in theearly 1980s and wind damage in 1987/1990 and/or the consequentsalvage operations. The extent of each gap and surrounding treeswere mapped. Tree/shrub regeneration, ground vegetation, bareearth, leaf litter and canopy openness (using a canopy-scope)were measured within and around the gaps using a 5 x 5-m gridand placing a 1 x 1-m quadrat at each grid intersection (totalnumber of quadrats = 400). Most of the gaps were <75 m2 inarea. The largest was 241 m2. They were generally irregularin shape and there was little or no understorey present. Mostsurrounding trees were beech Fagus sylvatica L. Bramble Rubusfruticosus L. formed a moderate to dense ground vegetation belowmost gaps and declined around the edges only once the gap openingwas substantially obscured. Apart from a few larger saplings,most regeneration was small and of beech. Most of the latterappeared to be in their fifth or sixth growing season, were10–35 cm tall, had an erect base and flat top, had increasedby <5 cm in height during 2001 and were not browsed by deer.Their height and growth form was related to (1) their positionwithin gaps, (2) the degree of canopy openness and (3) the coverof ground vegetation. This was translated into the followingzonation—(1) around the centre of larger gaps: canopyopenness increased to >15 per cent; bramble cover was nearcomplete; litter depth was low; many places had no beech seedlings,but some of the few present were among the tallest, most uprightand fastest growing; (2) towards the edges of the large gapsor directly below smaller gaps: canopy openness was about 4–10per cent; bramble cover was slightly less; beech seedlings weremoderately abundant but patchy, generally shorter, more flattopped and slow growing than in the gap centre, albeit somewere still among the tallest, most upright and fastest growing;(3) beyond the edge of the large/medium gaps (with the gap onlypartially visible) or directly below very small gaps: canopyopenness was only about 2–3 per cent; bramble was muchreduced; beech seedlings were at their most abundant but stillpatchy in distribution and even shorter, more flat topped andslower growing than in the above zone; (4) in an outer zonebeyond or almost beyond the sight of the gaps: canopy opennesswas <2 per cent; bramble was weak and sparse; beech seedlingswere mostly at low densities and predominately short, slow growingand flat topped. This ring pattern of beech regeneration appearedto relate mainly to (1) differences in light availability affectingthe survival, growth rate and form of seedlings; (2) competitionfrom bramble and possibly (3) limited dispersal of beech seedinto gaps. Recommendations are given for managers who wish touse natural regeneration to restock beech woodland.  相似文献   

16.
Conversion of monoculture plantations to mixed stands with greater diversity is an important aim of sustainable forest management, and in Britain, this is concentrated on the restoration of native broadleaved woodland on ancient woodland sites that were planted with conifers. Current British guidelines for this restoration have rarely been examined, and this study is the first to test their value for natural regeneration. The survival and growth of naturally regenerating ash (Fraxinus excelsior L.) seedlings was observed in thinned, selectively felled and clearfelled plots within a c. 40-year-old stand of Corsican pine (Pinus nigra Arnold ssp. laricio Maire). After felling in 2001, the ground flora in all treatments became dominated by bramble (Rubus fruticosus L. agg.) and its cover 5 years after felling was 75–95?% at a height of 0.9–1.2?m. During the study, seedling numbers declined 80–90?%. Although bramble had some adverse effects, seedling survival was unaffected by felling treatment. Seedling growth varied between treatments with those in the clearfell being tallest. Mean height of seedlings was always less than that of bramble, but by 2006 65?% of quadrats in the clearfelled plots had well-established individuals taller than the bramble compared with 35?% in the thinned plots. Models that described the relationships between seedling growth, basal area and bramble were complex, but results clearly indicate that maintaining canopy cover during restoration is probably an ineffective method of suppressing bramble on sites where it grows well. Results do not support the current British advice on conversion, but this may reflect the characteristics of pine canopies and the maintenance of canopy cover during conversion may be appropriate in stands of species, which cast more shade.  相似文献   

17.
This study examines the structural characteristics of the tree layer, dead wood, canopy openings, and regeneration patterns of a spruce old-growth forest in the Bohemian Forest, Czech Republic. An old-growth stand with minor human influence and a stand that was presumably logged about 200 years ago were analyzed and compared, as some forest managers considered the presumable human impact as a reason for salvage logging. Even though the stands differed in tree density, height and DBH structure, it was not possible to conclude whether it was due to management history or the environmental differences. The volume of dead wood also differed between the stands. There was about 142 and 83 m3 ha−1 of dead wood in the old-growth stand and presumably logged stand, respectively. The amount of dead wood found in the old-growth stand was comparable with values reported from spruce old-growth stands across Central Europe. In both stands, many canopy trees were arranged in linear patterns, which was a result of spruce regeneration on nurse logs. This suggests that the origin and development of the stands were characterized by natural processes and during the past 200 years typical old-growth structural characteristics have already evolved.  相似文献   

18.
Natural regeneration in Mongolian pine, Pinus sylvesttis var. mongolica, forest at Honghuaerji of China （the original of the natural Mongolian pine, forest on sandy land） was studied in 2004. The total mean values of regeneration indexes were higher in mature stands （more than 80% individual stems were older than 50 years）, the maximum of regeneration index reached 29 seedlings, m^ 2, with lowest values in the younger stand, e.g., in 32-year old and 43-year old stands. The stand age was an important factor determining the natural regeneration, which was the best in the older stands in this investigation （e.g. about 80-year old）. The regeneration index seemed not to be closely in relation to canopy openness although Mongolian pine is a photophilic tree species. In each type of gaps, natural regeneration was very well. Regeneration indexes were satisfactory at the south and east edges in the circle gaps; and at the east edge of the narrow-square gaps. Results indicated that Mongolian pine, seedlings could endure shading understory, but it would not enter the canopy layer without gap or large disturbance, e.g., fire, wind/snow damage or clear cutting etc. These results may provide potentially references to the management and afforestation of Mongolian pine, plantations on sandy land in arid and semi-arid areas. Researches such as the comprehensive comparisons on regeneration, structure and ecological conditions and so on between natural Mongolian pine, forests and plantations should be conducted in the future.  相似文献   

19.
Robinia pseudoacacia stands act as a typical ecological protection forest in hilly semi-arid area of China. Two fields of surface runoff were separately set up inR. pseudoacacia stand and its clearcut area in the western Liaoning Province (18°50’–122°25’ E, 40°24’–42°34’ N) for measuring the characteristics of runoff and sediment as well as soil moisture dynamics. Contractive analysis of the two land types showed that there existed a significant difference in volumes of runoff and sediment between the sites ofR. pseudoacacia stand and its clearcut area. The runoff volume and sediment volume in clearcut are were much bigger than those inR. pseudoacacia stand, with an increase amount of 40%–177% for runoff and 180%–400% for sediment. Hydrograph of surface runoff of typical rainfall showed that the peak value of runoff inR. pseudoacacia stand was decreased by 1.0–2.5×10−3m3·s−1 compared with that in its clearcut area, and the occurring time of peak value of runoff inR. pseudoacacia stand was 10–20 min later than that in its clearcut area. Harmonic analysis of soil moisture dynamics indicated that the soil moisture inR. pseudoacacia stand was 2.3% higher than that in clearcut area, and the soil moisture both inR. pseudoacia stand and its clearcut area could be divided into dry season and humid season and varied periodically with annual raifall precipitation. It was concluded thatR. pseudoacacia stand plays a very important role in storing water, increasing soil moisture, and reducing surface runoff and soil erosion. Foundation item: This paper was supported by Chinese “863” Plan Water-Saving Agriculture (2002AA2Z4321), the Key Knowledge Innovation Project (SCXZY0103), and The “Tenth-five” Plan of Liaoning Province (2001212001). Biography: GAO Peng (1967-), male, Dr. candidate, associate professor of Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan  相似文献   

20.
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   

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