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1.
In this paper, we present a two-stage approach for characterizing the structure of Pinus sylvestris L. stands in forests of central Spain. The first stage was to delimit forest stands using eCognition and a digital canopy height model (DCHM) derived from lidar data. The polygons were then clustered (k-means algorithm) into forest structure types based on the DCHM data within forest stands. Hypsographs of each polygon and field data validated the separability of structure types. In the study area, 112 polygons of Pinus sylvestris were segmented and classified into five forest structure types, ranging from high dense forest canopy (850 trees ha−1 and Loreýs height of 17.4 m) to scarce tree coverage (60 tree ha−1 and Loreýs height of 9.7 m). Our results indicate that the best variables for the definition and characterization of forest structure in these forests are the median and standard deviation (S.D.), both derived from lidar data. In these forest types, lidar median height and standard deviation (S.D.) varied from 15.8 m (S.D. of 5.6 m) to 2.6 m (S.D. of 4.5 m). The present approach could have an operational application in the inventory procedure and forest management plans.  相似文献   

2.
The suitability of Trichogramma brassicae Bezd. (Hymenoptera: Trichogrammatidae) to control the silver Y moth, Autographa gamma (L.) (Lepidoptera: Noctuidae) in spinach was investigated under greenhouse and field conditions. Two strains of T. brassicae were selected to study host searching efficiency and dispersal ability of the wasps on spinach. The experiments were conducted with defined release densities. The results show that T. brassicae strain I failed to locate host eggs in all experiments. In contrast, T. brassicae strain II females were able to locate 37% of the exposed egg clusters in the greenhouse within 48 h. Individuals colonised rapidly at least an area of 0.25 m2. At distances up to 26 cm to the release point of the T. brassicae females, parasitization rate was 100%. Moreover, under field conditions silver Y moth eggs were exposed two times for 48 h on 12 experimental plots of 100 m2 in two spinach fields. During the first exposure interval, i.e. 4 days after mass release of T. brassicae strain II, overall parasitization rates reached 20% on both fields. Furthermore parasitization rates still reached 16 and 19% during the second exposure interval, i.e. 9 days after natural enemy release, indicating a constant Trichogramma activity over time. Parasitization rates were highest in the close vicinity of the release point, i.e. 86%, whereas 6.5 m away the mean parasitization rate decreased to 3%. In conclusion results indicate a high potential of T. brassicae strain II as antagonist of A. gamma. Nevertheless the dispersal ability of T. brassicae strain II was limited, but adjustment of release densities and techniques might compensate this disadvantage.  相似文献   

3.
A study was carried out in the Lama forest reserve of Benin to characterize the habitat of Afzelia africana Sm., an endangered multipurpose tree species (found in African humid, dry forests and woodlands), in order to define a sustainable management strategy for its conservation. An estimation of species density was done on 100 square plots of 1 ha each, while tree height and dbh of all the species were measured on subplots of 50 m × 30 m within the 1 ha plots. The regenerations of A. africana (dbh < 10 cm) were counted in the diagonal quadrats of the principal plots. Presence–absence data of the species was subjected to multidimensional scaling and results showed four vegetation communities including: young fallow, old fallow, typical dense forest and degraded dense forest. Significant differences were noted between the four communities with respect to dendrometric parameters of the species. High values of these parameters were noted for the species in typical dense forest (5.2 stems/ha, 66.7 cm, 17.9 m, 7.9 m2/ha and 38.8% for the tree-density, the mean diameter, the mean height, basal area and basal area contribution of the species, respectively) whereas the lowest values were obtained for the old preforest fallow as far as the mean diameter (59.7 cm), the mean height (15.7 m) and the basal area contribution (27.7%) of the species were concerned. In general, the basal area of A. africana in the over vegetation types was less than 3 m2/ha. No A. africana tree was found in the young preforest fallow while more than 80% of A. africana trees were found in the typical dense forest community. Stem diameter and height structures of the species in all the four communities showed a left dissymmetric Gaussian shape and were well adjusted to Weibull distribution.  相似文献   

4.
Twelve commercial nominal 4 × 8 ft.2 (1,200 × 2,400 mm2) wood-based panels, Medium Density Fiberboard, Particleboard, Oriented Strand Board and Plywood, were scanned for horizontal density distribution using a high resolution and accuracy digital X-ray system. Density distribution at a size of grid cell varying from 0.5 × 0.5 to 12 × 12 in.2 (12.7 × 12.7 to 304.8 × 304.8 mm2) was analyzed based on the X-ray scanned images of the panels. Detailed density distribution characteristics of the four types of wood-based panels are presented in this research. Comparisons of density variation are carried out between different panel types and between different spatial resolutions (i.e. sizes of grid cells). Results of analysis and comparison in density distribution are presented in different forms with industrial as well as academic implications.  相似文献   

5.
利用目前流行的高分辨率可见光无人机遥感影像生成树木冠层高度模型,采用分水岭分割算法提取单木树高的研究具有重要理论和实践意义。以位于云南省富民县的天然云南松纯林为研究对象,通过大疆Phantom 4 Pro无人机获取低空可见光遥感影像,利用Pix4D Mapper对无人机影像进行预处理及三维重建,生成三维点云,利用LiDAR360处理三维点云,构建DSM,DEM并生成CHM;采用分水岭分割算法对不同郁闭度条件下获得的CHM进行单木分割及树高提取,对提取结果进行精度评价。结果表明:分水岭分割算法能够准确分割CHM,利用无人机可见光遥感影像进行单木树高提取是可行的;将基于无人机可见光影像提取的树高值与野外实地调查得到的树高值进行对比,R2为0.893,RMSE为1.23m,估测精度为87.58%;同时,林分郁闭度会对单木树高估测产生影响,根据不同郁闭度条件下提取的3组样木树高与实地测量树高的决定系数(R2)分别是0.857,0.939和0.921,RMSE分别为1.450,1.097,0.896m,在低郁闭度林分内树高估测的精度显著高于高郁闭度林分。  相似文献   

6.
Estimation of shrub biomass by airborne LiDAR data in small forest stands   总被引：2，自引：0，他引：2  
The presence of shrub vegetation is very significant in Mediterranean ecosystems. However, the difficulty involved in shrub management and the lack of information about behavior of this vegetation means that these areas are often left out of spatial planning projects. Airborne LiDAR (Light Detection And Ranging) has been used successfully in forestry to estimate dendrometric and dasometric variables that allow to characterize forest structure. In contrast, little research has focused on shrub vegetation. The objective of this study was to estimate dry biomass of shrub vegetation in 83 stands of radius 0.5 m using variables derived from LiDAR data. Dominant species was Quercus coccifera, one of the most characteristic species of the Mediterranean forests. Density of LiDAR data in the analyzed stands varied from 2 points/m2 to 16 points/m2, being the average 8 points/m2 and the standard deviation 4.5 points/m2. Under these conditions, predictions of biomass were performed calculating the mean height, the maximum height and the percentile values 80th, 90th, and 95th derived from LiDAR in concentric areas whose radius varied from 0.50 m to 3.5 m from the center of the stand. The maximum R2 and the minimum RMSE for dry biomass estimations were obtained when the percentile 95th of LiDAR data was calculated in an area of radius 1.5 m, being 0.48 and 1.45 kg, respectively. For this radius, it was found that for the stands (n = 39) where the DTM is calculated with high accuracy (RMSE lower than 0.20 m) and with a high density of LiDAR data (more than 8 points/m2) the R2 value was 0.73. These results show the possibility of estimating shrub biomass in small areas when the density of LiDAR data is high and errors associated to the DTM are low. These results would allow us to improve the knowledge about shrub behavior avoiding the cost of field measurements and clear cutting actions.  相似文献   

7.
The population changes of early successional forest species, Wendlandia paniculata, Schima wallichii, Camellia tsaii, and Lithocarpus ducampii, were described and analyzed in a chronosequence of 1–30 year-old secondary forests representing regrowth after shifting cultivation in northwestern Vietnam, utilizing 51 temporary plots for stem census. Another five temporary plots were used for stem census in surrounding old-growth forest for comparison. In the first year after land abandonment, seedling stem density (H < 2 m) was 65,800/ha, increasing to 161,200/ha by third year, then sharply decreasing to 2,500/ha in 21–30 year-old forests. The sapling stratum (H ≥ 2 m and DBH < 5 cm) started to be recruited in the fifth year, increasing to reach a peak density of 4,530 stems/ha at year ten, then decreased to 580 stems/ha at year 21–30. The tree stratum (DBH ≥ 5 cm) achieved the maximum density of 600 stems/ha at year ten. Meanwhile, the density of all strata in the old-growth forest was 2,980 stems/ha. Sprouts played an important role, accounting for 34% at the first year then increased gradually to 73% at year 21–30. Total basal area attained a peak at 5.43 m2/ha at year ten; it was 4.9 m2/ha in the old-growth forest. These four species played an important role in providing ecological services for recruitment of other species during the first 10 years of fallow stand development, which increased to 35 species in 21–30 year-old secondary forest.  相似文献   

8.
Logging is an integral component of most conceptual models that relate human land-use and climate change to tropical deforestation via positive-feedbacks involving fire. Given that grass invasions can substantially alter fire regimes, we studied grass distributions in a tropical dry forest 1–5 yr after selective logging, and experimentally tested the effect of forest fire on populations of invasive grasses. In unlogged forests and in microhabitats created by selective logging we found a total of four alien and 16 native grass species. Grasses covered 2% of unlogged and 4% of logged forest, with grass cover in logged forest concentrated in areas directly disturbed by logging; log landings and roads had relatively greater grass cover (37% and 17%, respectively) than did skid trails (10%) and felling gaps (8%). Total grass cover and grass species richness increased with canopy openness and were greatest in sites most severely disturbed by logging. The grass flora of these disturbed areas was composed mostly of native ruderal species (e.g., Digitaria insularis, Leptochloa virgata), a native bamboo (Guadua paniculata), and Urochloa (Panicum) maxima, a caespitose C4 pasture grass introduced from Africa. Urochloa maxima formed monodominant stands (up to 91% cover and 2–3 m tall) and grew on 69% of log landings and 38% of roads. To better understand the potentially synergistic effects of logging and fire on the early stages of grass invasion, we tested the effect of a 12-ha experimental fire on U. maxima populations in a selectively logged forest. Three years after the fire, the area covered by alien grass in burned forest increased fourfold from 400 m2 (pre-fire) to 1660 m2; over the same period in a logged but unburned (control) area, U. maxima cover decreased from 398 m2 to 276 m2. Increased canopy openness due to fire-induced tree mortality corresponded with the greater magnitude of grass invasion following fire. Selective logging of this dry forest on the southern edge of the Amazon Basin promotes alien grass invasion; when coupled with fire, the rate of invasion substantially increased. Recognition of the grass-promoting potential of selective logging is important for understanding the possible fates of tropical forests in fire-prone regions.  相似文献   

9.
The net photosythetical rate, respiration rate, light compensation point and light saturation point ofLarix olgensis andFraxinus manshurica were measured by Model-865 Co2 Infrared Analyzer under controlled conditions (in coviron phytotron). For net photosythetical rate ofLarix ogensis andFraxinus manshurica, the optimum air temperature was 25, 28 °C respectively, the optimum soil water potantial was −20, −10 kPa repectively, the optimum soil water content was 20.31 %, 23.42% respectively, and the optimum air humidity was 90%. The optimum soil water potantial of respiration rate was −30 kPa. The light compensation point for the two species was 3.36, 4.8 μ mol / m2s respectively and light saturation was 804, 880 μ mol / m2s. The project supported by National Natural Science Foundation of China  相似文献   

10.
Cable yarding systems are widely used in mountainous forests of Austria. The goal of this paper is to determine optimal road spacing (ORS) of yarding operations by tower yarder in Styria to help logging planners minimize logging costs. A total of 591 working cycles were used to develop the multiple regression model using stepwise method to predict yarding time per cycle. The production and cost in whole tree uphill yarding were 6.70 m3/PSH and 27.60 Euro/m3, respectively. The roading, yarding and installation cost per cubic meter were computed for different yarding distances and graphed as a function of road spacing. The minimum total cost and ORS were 42.88 Euro/m3 and 261 m, respectively for one-way yarding. For two-way yarding, the minimum estimated total cost, ORS and optimal road density would be 38.48 Euro/m3, 373 m and 26.8 m/ha, respectively. The results showed increasing harvested volume decreases ORS and that increased roading cost increases ORS. The load volume has a significant effect on ORS.  相似文献   

11.
In 2004 and 2005, the yield, leaf area, dry weight and dry weight partitions of soybeans were determined at the Agroforestry Research Site (ARS) (est. 1987, Ontario, Canada). Soybean was intercropped with poplar (Populus deltoides x nigra DN-177 L., 556 m3crown tree−1), silver maple (Acer saccharinum L., 308 m3), black walnut (Juglans nigra L., 148 m3) and pecan (Carya illinoensis Wangenh., 114 m3), or grown alone (monoculture). Yield of soybean was not different in either year between the monoculture and the black walnut or pecan intercrops. In the poplar and silver maple treatments, yield was 66 and 85% (2004 and 2005) lower than in the monoculture. Despite the fact that different tree species were used, there was a significant negative linear regression between yield and tree crown volume (R 2 = 0.76, P = 0.0049 and R 2 = 0.93, P < 0.0001 in 2004 and 2005, respectively). With increasing tree crown volume, soybean tended to partition more dry matter to the photosynthetic and reproductive parts and less to structural tissue and petiole. This demonstrates the phenotypic flexibility of the crop component in agroforestry systems. Contrary to theoretical predictions, soybean leaves were thicker as shade increased (increase by 6.2 × 10−4–1.2 × 10−3 mg cm−2, per unit of crown volume), pointing to competitive interactions specific to tree-based intercrops.  相似文献   

12.
The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha−1, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha−1 during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha−1 and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m2 m−2 and specific leaf area (SLA) 15.0 ± 0.1 m2 kg−1. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m2 kg−1, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass unit of short roots were 145.3 ± 8.6 m g−1, 58.6 ± 3.0 kg m−3 and 103.7 ± 5.5 tips mg−1, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha−1, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha−1 yr−1 (55 and 27%), respectively, of which 29.1 kg ha−1 N and 2.8 kg ha−1 P were accumulated in the above-ground part of the stand.  相似文献   

13.
The potential contribution of agroforestry systems to the management and genetic resources conservation in iroko (Milicia excelsa), an important and valuable timber tree species in sub-Saharan Africa, is addressed in this paper. The structure and dynamics of traditional agroforestry systems and the ecological structure of Milicia excelsa populations in farmlands were studied through a survey carried out in 100 farmlands covering the natural range of iroko in Benin. Forty-five species belonging to 24 plant families were recorded in traditional agroforestry systems. Average tree density varied from 1 to 7 stems ha−1 with diversity index ranging from 2.6 to 2.9. Milicia excelsa occurred sparsely in agroforestry systems in all regions, with density ranging from 1 to 4 stems ha−1; stand basal area varying from 33.10−4 to 129.10−4 m2 ha−1, and negligible seedling regeneration. However, male and female trees were apparently evenly distributed on farmlands in all regions (F/M > 0). Iroko trees produced viable seeds with moderate germination rate and early growth (germination rate 22% and height 7.29 cm after 3 months). Suggestions are made regarding optimal densities for iroko conservation in farmlands, according to farmers’ socioeconomic conditions in different regions, in order to improve traditional agroforestry systems and their use as biological corridors in conservation of Milicia excelsa genetic resources.  相似文献   

14.
We selected a warm/dry mixed conifer forest (ponderosa pine, white fir, Douglas-fir, and aspen) in southwestern Colorado to reconstruct historical conditions of fire regime and forest structure in preparation for an experiment in ecological restoration. Although mixed conifer forests are of high ecological and social value in the Southwest, they have been less studied than ponderosa pine forests. Fire-scar analysis on a 150-ha area showed recurring fires at mean intervals of 24 years (all fires with minimum of 2 sample trees scarred) to 32 years (fire scarring 25% or more of sample trees) from the 16th century until the abrupt cessation of fire after 1868, concurrent with European settlement. There was no evidence in age or species-specific data of severe burning at the scale of the study blocks (approximately 200 ha). The forest remained unharvested throughout most of the 20th century, until a cut in the early 1990s removed approximately equal basal areas of ponderosa pine and white fir. Forest structure had already changed substantially, however. Total basal area increased from an average of 11 m2 ha−1 in 1870 to 27 m2 ha−1 in 2003, despite harvesting of at least 8.4 m2 ha−1. Ponderosa pine declined from representing nearly two-thirds of basal area in 1870 to one-third in 2003. The other species increased dramatically, especially white fir, which went from 12% to 35% of basal area and dominated stand density with an average of 392 trees ha−1. Total tree density increased from 142 trees ha−1 in 1870 to 677 trees ha−1 in 2003. The ecological changes that occurred here since the 19th century have been in exactly the opposite direction considering the warm, fire-favoring climate expected in the 21st century. If warm/dry mixed conifer forests of southern Colorado are to have a reasonable chance for persistence under the future climate regime, restoring conditions more similar to the frequently burned, open forests of the past is likely to be a useful starting point.  相似文献   

15.
Cork oak (Quercus suber L.) has a dense wood that allows high-quality uses. In the present work, we study the influence of vessel characteristics, measured through image analysis and optical microscopy, on wood density, measured using X-ray microdensitometry, on 40-year-old trees. Vessel area increases with cambial age (5403–33064 μm2), while wood density decreases (1.229–0.836 g/cm3). The number of vessels is relatively constant at 6 vessels/mm2, while vessel proportion in cross-section increases from 3.3% near the pith to 20.5% near the bark. In growth rings closest to the pith, with high wood density and low vessel area, the relationship between the two variables is linear (R 2 = −32.1%, P < 0.01) but with increasing tree age and vessel size, the wood density remains rather constant, suggesting that decreases in density might compromise mechanical support of the tree at a stage when the increase in cross-sectional area alone might not provide mechanical stability. Other anatomical characteristics not considered in this study, like large xylem rays that increase with cambial age, may be responsible for the constant density.  相似文献   

16.
Restoring longleaf pine (Pinus palustris Mill.) over much of its original range requires artificial regeneration. In central Louisiana, USA, two fertilization levels—No (NF) or Yes (F-36 kg/ha N and 40 kg/ha P) in combination with three vegetation treatments—Check, four prescribed fires (PF), or multi-year vegetation control by herbicidal and mechanical means (IVM) were applied to container-grown longleaf pine plantings in a grass savanna. After 10 years, P concentration in longleaf pine foliage was less on NF plots than F plots, but fertilization did not significantly affect tree stature. Survival was greater on NF plots than F plots, and so, NF plots were more productive (NF—63 m3/ha and F—45 m3/ha). Pine trees on IVM plots (37 dm3/tree) were significantly larger than on Check and PF plots, which averaged 17 dm3/tree. Survival was better on IVM plots (88%) than PF plots (78%), which was better than Checks (58%). Consequently, IVM plots were most productive (99 m3/ha), followed by PF plots (44 m3/ha), and lastly Checks (28 m3/ha). PF plots had greater grass cover (38%) than Check and IVM plots, which averaged 5%, whereas PF and IVM plots had less understory arborescent cover (an average of 25%) than Checks (91%). A wildfire in March 2007 reduced pine survival by 22, 14, and 1 percentage points on IVM, Check, and PF plots, respectively. Seven months later, longleaf pine production had decreased to 92 m3/ha on IVM plots while increasing to 55 m3/ha on PF plots and 30 m3/ha on Checks. Overall, the wildfire rejuvenated the herbaceous plant community. Grass cover on Check and IVM plots averaged 20% while grass cover on PF plots was 36%. Forb cover increased on all treatments from 2% before the wildfire to 13% seven months after the wildfire. Understory arborescent cover decreased on Checks to 62% but increased slightly on PF and IVM plots and averaged 30%.  相似文献   

17.
Accurate prediction of whole-tree wood basic density (BD) from indirect density measures is important for estimating Eucalytpus globulus breeding values and genetic gain. We measured 100 E. globulus trees at 6.5 years of age on each of a high productivity site (Albany) and a low productivity site (Esperance), sampling 16 full-sib families and seven open-pollinated ‘check’ seedlots. On each tree we assessed pilodyn penetration at 1.3 m and BD of: (a) the outer 10 mm which was penetrated by the pilodyn pin of a bark-bark core, (b) a whole bark-bark core at 1.3 m, (c) a cross-sectional disk at 1.3 m and (d) the whole tree, represented by cross-sectional disks at five heights. Site effects and genetic values for families and checks were determined by mixed model analysis. A trend of increasing BD from pith to bark was more pronounced at Albany, where wood formed before age 3.5 years was 12 kg/m3 less dense than at Esperance (P = 0.01) and wood formed from 3.5 to 6.5 years was 27 kg/m3 denser than at Esperance (P < 0.001). Mean whole-tree BD was 19 kg/m3 greater at Albany (P < 0.001). Pilodyn penetration was well-correlated with BD of the 10 mm sample of penetrated wood and this relationship was not greatly affected by site variation. Genetic values for pilodyn penetration formed precise relationships with BD of breast-height discs and whole-tree BD although they were site-specific. Pilodyn penetration was a better predictor for genetic values of whole-tree BD than were bark-bark cores.  相似文献   

18.
The aim of the present study was to quantify the effects of roe deer browsing relative to the effects of soil preparation, shelterwood density (light) and seed fall. Ultimately, the goal was better silvicultural guidelines to support the use of natural beech regeneration in the close-to-nature forestry context. In spring 1995, an experiment on natural regeneration with three experimental stands (0.28–0.6 ha) was installed in a beech (Fagus sylvatica) dominated broadleaved forest inhabited by a dense roe deer (Capreolus capreolus) population (24 deer km−2). The autumn of 1995 offered a large beech mast (stand average 307–1168 beechnuts m−2).Treatments installed included fencing to exclude deer, soil preparation, shelterwood thinning, and the relevant control treatments. Roe deer and soil preparation had dramatic effects on regeneration from the moment the seedlings sprouted in the spring 1996. The regeneration sprouted only sparsely in the unprepared seedbed producing only 5 seedlings m−2 (average across fence treatments) after 2 months, which was reduced to 1 sapling m−2 8 years later. Deer had no significant effect on the regeneration density of the unprepared seedbed. In contrast, the cultivated seedbeds produced initially (after 2 months) up to 191 seedlings m−2 protected by fence, whereas the densities in the unfenced treatments peaked by 22 seedlings m−2. By the end of the study, these densities were reduced to 22 saplings m−2 in the permanently fenced mineral soil seedbed and to 2 saplings m−2 in the unfenced mineral soil seedbed. Regeneration height outside the permanent fence was generally only half the height of the regeneration inside. Additionally, we found significantly positive effects of increasing light and seed fall on regeneration density and of light on regeneration growth.We conclude that the roe deer only reduced the regeneration density of the dense regenerations established in the cultivated seedbeds. However, the regeneration density of the unprepared seedbed was not sufficient to support a future high quality stand. We found no treatment that within the timeframe of this study could support successful regeneration establishment outside the permanent fences. Whether this will change in the future with more time given for the regeneration to establish is yet to be revealed.  相似文献   

19.
Photosynthetic photon flux density (PPFD) during the growing season and regeneration growth (height and base stem diameter) were investigated in two natural stands in the Patagonian region of Chile, one without silvicultural management and another with a regenerative felling under a shelterwood system. PPFD was measured by means of fifteen sensors (quantum Li-190SA) installed in each stand and distributed within three canopy openness grades. Four regeneration plots (1 m2) were established around each sensor. In each of the plots, the height and base diameter of ten labelled plants within the upper regeneration layer were measured in the growing seasons 2001–2002 and 2002–2003. In the stand with regeneration felling total PPFD in the growing season was 2.5–2.9 times higher than in the stand without intervention. In both stands, total PPFD in the growing season increased by about 420 mmol/m2 when the relative canopy, which was in the range between 30 and 70%, was reduced by 10%. An identical behaviour was observed for the height and base stem diameter increases reflecting a clear effect of intervention and canopy coverage on the magnitude of PPFD received by the regeneration and its development.  相似文献   

20.
In 1987–89 the CATIE-GTZ Agroforestry Project set up experiments with five timber tree species planted in single lines on twelve farm boundaries in cooperation with local farmers. When the trees were five years old, their height, diameter and total stem volume were: Acacia mangium 17 m, 19 cm and 67 m3 km–1, Cordia alliodora 14 m, 20 cm and 46 m3 km–1, Eucalyptus deglupta 22 m, 24 cm and 85 m3 km–1, Tectona grandis 17 m, 20 m and 64 m3 km–1, Terminalia ivorensis 18 m, 23 cm and 104 m3 km–1. Considering these excellent growth rates, planting of Cordia alliodora, Eucalyptus deglupta and Tectona grandis in lines on farm boundaries should be promoted. T. ivorensis and A. mangium are not recommendable for sites with impeded drainage because of mortality caused by root rot, mostly due to Rosellinia sp.  相似文献   

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