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1.
G. Singh 《New Forests》2012,43(3):349-364
Natural resource conservation and rehabilitation are the best options to control land degradation and enhance biomass for fodder and fuelwood. Rainwater harvesting structures viz. Contour trench (CT), gradonie (G), box trench (BT) and V-ditch (VD) with a control were prepared in <10%, 10–20% and >20% slopes and Acacia catechu L. seedlings were planted in August 2005 to enhance soil water, nutrient and biomass and to rehabilitate degraded hill. Soil pH, SOC and NH4-N decreased while EC, NO3-N and PO4-P increased in June 2009. Soil water, nutrients, plant growth and biomass were highest (P < 0.05) in <10% and lowest in 10–20% slopes. Soil waters were 13 and 52% greater in >20 and <10% than in soil at 10–20% slope. The soil waters were 18, 16, 24 and 14% greater in CT, G, BT and VD treatments, respectively over control, which enhanced plant height and collar diameter in December 2009 over 2005. The highest growth and biomass were in CT and VD plots, respectively. Herbage biomass was highest (P < 0.05) in <10% slope in 2005, 10–20% slope in 2006/2008 and >20% slope in 2007/2009. Harvesting of rainwater increased herbage biomass by 24–71%, and was highest in VD plots. Conclusively, rainwater harvesting enhanced soil water, nutrients, vegetation covers and plant growth and biomass during restoration of degraded hills. Gradonie and CT/BT facilitated herbage and plant growth, respectively, whereas V-ditch was effective for both.  相似文献   

2.
Over-exploitation and rural growth have severely damaged native vegetations of Aravalli hills in Rajasthan, India. This study was conducted to evaluate the effects of different restoration practices (i.e., rainwater harvesting (RWH) and planting of tree seedlings) on improve- ment in soil water and nutrients and growth and biomass of herbaceous vegetation. Contour trench (CT), Gradonie (G), Box trench (BT), V-ditch (VD) and a control were imposed on 75 plots (each of 700 m 2 ) in natural slope gradient defined as <10%, 10% 20% and >20% slopes in 2005. Each plot had three micro-sites of 1-m 2 at up (USP), middle (MSP) and lower (LSP) part of the plot for observation in 2008. The existed gradient (due to soil texture and topographic features) of soil pH, EC, SOC, NH 4 - N, NO 3 -N and PO 4 -P in June 2005 between >20% to <10% slopes were decreased in 2008 after applying RWH techniques. Such improvement in soil status promoted vegetation growth and biomass in higher slope gra- dients. Soil water, species diversity and herbage biomass increased from USP to LSP, and RWH techniques had positive role in improving SOC, nutrients, vegetation population, evenness and growth at MSP. Despite of lowest SWC, regular rain and greater soil water usage enhanced green and dry herbage biomasses in 10% 20% and >20% slopes, compared with <10% slope. The highest diversity in CT treatment was related to herbage biomass, which was enhanced further by highest concentrations of SOC and PO 4 -P. Further, CT treatment was found to be the best treat- ment in minimizing biomass variance in different slopes. Conclusively, soil texture and topographic features controlled soil water and nutrients availability. Rainwater harvesting techniques increased soil water storage and nutrient retention and also enhanced vegetation status and biomass by minimizing the effects of hillslopes. Thus depending upon the site conditions, suitable RWH technique could be adopted to increase herb- age biomass while rehabilitating the degraded hills.  相似文献   

3.
Throughout eastern North America, stands of northern red oak (Quercus rubra L.) are undergoing successional replacement by shade-tolerant competitors. In the Great Lakes-St. Lawrence (GLSL) forest region, Q. rubra approaches the northern limit of its distribution, and ecosystem-specific silvicultural directives are needed to promote regeneration. We used an inductive, ordination-based approach to explore patterns in understorey plant community composition and microenvironment under different partial harvest treatments applied in a GLSL hardwood stand, and related these to characteristics of natural seedlings of Q. rubra and its competitors Acer rubrum and Acer saccharum.Two years after harvest, we established 2 m × 2 m plots in a stratified random design under 70% (n = 20) and 50% (n = 19) crown closure uniform shelterwood, group selection (n = 15), and uncut upper slope (n = 10) and lower slope (n = 10) areas. Percent cover of understorey vascular plant species, and a suite of microclimatic and edaphic variables were measured in each plot. Density, mean diameter and mean height of seedlings in the understorey (height <1 m) were determined in each plot for Q. rubra, A. rubrum and A. saccharum.Correspondence analysis (CA) ordination extracted two major axes explaining 21.6% of the total inertia in the species cover by plot matrix. Axis one separated uncut plots from the 50% shelterwood along a gradient of canopy cover associated with partial harvest treatments. Plot scores on axis one (13.2%) reflected a shift in dominance of the understorey from shade-tolerant Acer spp. to shade-intolerant colonizers, Rubus idaeus and Carex spp. Plot scores on axis one were directly (p < 0.05) associated with total understorey plant cover, litter depth, soil temperature and pH, but not with measures of plant diversity. Axis two (8.4%) separated plots from upper slope and lower slope areas, and plot scores were inversely associated (p < 0.05) with soil pH, phosphorus and nitrogen levels. Along axis two there was a shift in dominance from competitive (e.g. A. saccharum) to stress-tolerant (e.g. A. rubrum) species as soil fertility declined. Stepwise linear regression indicated seedling diameter in Q. rubra, A. rubrum and A. saccharum was inversely related to canopy cover. This suggests all three species benefited from partial harvest, although the relationship was strongest in Q. rubra. Patterns in understorey composition, microenvironment and seedling characteristics provide the basis to identify the main competitors of Q. rubra seedlings and adjust regeneration efforts along gradients of canopy closure and soil fertility under partial harvest systems within the GLSL forest region.  相似文献   

4.
The effect of tree harvesting on soil mineral nitrogen and microbiological activity were investigated in an agrisilvicultural system consisting of wheat cultivated along the sides of a poplar plantation in Sweden from 1993 to 1995. Sampling for mineral nitrogen was carried out in three layers down to 90 cm at two distances, near (0.5–1.5 m) and far (4.0–5.0 m) from rows of standing, ST, and harvested trees, HT. Sampling for basic respiration and substrate-induced respiration was carried out in the 0–10 cm layer in 1993 and in the 0–10 cm and 10–20 cm layers in 1994 at the same distances from trees.There was a higher concentration of ammonium and lower concentration of nitrate closer to trees, indicating an efficient uptake of nitrate by trees and enhanced N mineralization close to trees. Shortly after tree harvesting, there were higher concentrations of nitrate and ammonium in the 0–30 cm soil layer near the harvested trees than near standing trees, suggesting a derease in nitrogen uptake by tree roots. The soil microbiological activity was lower in the harvested than the standing plots of trees, which is considered as an indication of the important role of root exudates in maintaining a larger microbial biomass close to trees.  相似文献   

5.
The influence of different in situ rainwater harvesting and moisture conservation methods on soil moisture storage and growth of Tamarix ramosissima was studied in the semiarid loess region of China from 2002 to 2004. The treatments included control (T1), trench (T2), saucer covered by plastic film (T3), bare ridge and bare furrow (T4), plastic-covered ridge and bare furrow (T5), and plastic-covered ridge and gravel-covered furrow (T6). The results indicated that soil water storage for the T5 and T6 was significantly higher than the control. The T6 treatments produced the highest amount of soil water storage, 18–137 mm more than the controls at soil depth of 0–100 cm and 40–75 mm at soil depth of 100–200 cm. No significant differences in soil water storage were found between the T2, T3, T4 and the control treatments at soil depth of 0–100 cm, but soil water storage at soil depth of 100–200 cm was significantly higher for the T2, T3, T4 treatment than the control.Rainwater harvesting and moisture conservation treatments increased growth of T. ramosissima, tree height was significantly higher for the rainwater harvesting and moisture conservation treatments than the controls. Tree height, crown diameter and collar girth for the T6 treatments increased by 70, 57 and 79% as compared to the controls. No significant differences in crown diameter and collar girth were observed between T1, T2 and T3 or T4 and T5 treatments in some years. The effectiveness of the different treatments for the tree height, crown diameter and collar girth was in the order of T6, T5, T4, T3, T2 and T1.  相似文献   

6.
One of the main threats to the sustainability of community forestry in the Selva Maya is insufficient regeneration of commercial tree species. We evaluated the regeneration status of 22 commercial tree species in a managed semideciduous tropical rain forest in Southern Mexico. The study was carried out in six harvesting areas along a 16-year chronosequence. In each area, 10 transects (1000 m2) were established and all trees >50 cm height and <10 cm diameter were recorded. We evaluated the relationships between seedling and sapling abundance, and canopy cover and disturbance condition (closed forest, canopy gap, log landing, skid road, primary road and secondary road). The area occupied by closed forest canopy increased with age of harvesting area (65–91% of sampled area), while the area occupied by canopy gaps decreased (22–9%). Log landings occupied less than 1% of the sampled area. The predominant canopy cover was 75–80% in all harvesting areas, even in the most recently harvested areas. The highest densities of seedlings and saplings, of both shade tolerant and intolerant species, were found in log landing and skid trails, followed by secondary roads. Even Simarouba glauca, a shade tolerant species, displayed higher densities in sites with ≤65% of canopy cover. Our results support previous findings and indicate that the levels of disturbance caused by existing harvesting procedures may be inadequate to promote sufficient regeneration of not only light demanding desirable species but also for some of the evaluated shade tolerant species of commercial interest. Seedling and sapling densities exhibited by Swietenia macrophylla, for example, are insufficient to support current harvesting rates. The application of a spatial mixed system with patch-cuts of different sizes, a consequence of group felling, could be applied to provide the necessary conditions for the regeneration of the main commercial species.  相似文献   

7.
Forest restoration treatments involving selection harvest and prescribed fire have been applied throughout the Rocky Mountain West with only a limited understanding of how these treatments influence plant community composition and soil processes. Forest restoration treatments, especially those involving fire, have the potential to reduce N capital on site. Unfortunately there has been only limited effort to investigate the effects of forest restoration treatments on forest ecosystem N inputs, especially free living N-fixation in soil and woody residues. Recent studies have highlighted the potential for decaying woody roots to serve as hot spots for N-fixation. The fire and fire surrogates (FFS) study site at Lubrecht Experimental Forest in Western Montana provided a unique opportunity to investigate the effect of restoration treatments on N-fixation. We set out to examine how prescribed fire, selection harvest, and a combination of both influence free living N-fixing bacteria that colonize decomposing woody roots, mineral soil, and soil crusts. Soil, root, and soil crust samples were collected from replicated treatment plots in August 2005 and soil samples were recollected in May 2006 just following snowmelt. Acetylene reduction assays were run on all samples, and extractable inorganic N and potentially mineralizable N (PMN) were measured in mineral soil. While restoration treatments caused an increase in dead roots associated with stumps and fire killed trees, N-fixation rates were nearly non-existent in these root systems. Nitrogen-fixation rates were not significantly influenced by treatments in decomposing woody roots or in mineral soil, but were slightly greater (P < 0.10) in soil crusts when the control stand was compared to treated plots. Nitrogen-fixation rates were also greater in mineral soil than in roots. Soil collected in August exhibited greater rates of N-fixation than soil collected in May which we attributed to higher moisture and an increase in available N following spring thaw. Average rates of free living N-fixation across the treatment plots at Lubrecht were low (0.26 kg N ha−1 year−1), but over time we estimate that these sources, along with the sparse population of symbiotic N-fixing plants and wet N deposition, would replenish soil N lost through fire or harvesting in approximately 40–100 years.  相似文献   

8.
Oleskog  Gunilla  Sahlén  Kenneth 《New Forests》2000,20(2):119-133
The objective of this investigation was to comparemoisture conditions and Scots pine (Pinussylvestris L.) seed germination percentages in fourtypes of seedbed substrates, (i.e., feather mosses,mineral soil, humus, and ground organic material). Twoexperiments were conducted, with and withoutirrigation, in the summer of 1996 in a stand innorthern Sweden. The moisture conditions weredetermined by periodically weighing seedsamples. When plots were not irrigated, no seedsgerminated, probably because conditions were too dryin the seedbeds, as indicated by the low seed moisturecontent (under 15%). However, during rainy days, seedmoisture contents were relatively high (20–45%). Onthe irrigated plots the seeds germinated on allseedbed substrates, with the best germinationoccurring in humus (about 40%). Seed moisturecontents were high and relatively consistent in allirrigated seedbed substrates (35–55%). Inirrigated plots temperature rather than moisture, wasa limiting factor, and germination was highest in thewarmest seedbed types which are generally regarded aspoor germination substrates. We suggest that seedbedsin areas scheduled for harvesting be prepared in thestand before clear-cutting, and that the preparationshould enhance not only the substrates's water-holdingcapacity, but its thermal conductivity as well.  相似文献   

9.
Leaf nitrogen nutrition of hinoki cypress (Chamaecyparis obtusa Endlicher) was investigated at three positions along a slope over a period of 3 years. At each slope position, nitrogen properties were compared in patch-cut plots (0.06–0.09 ha) and uncut control plots (0.04 ha). Nitrogen cycling at the lower slope was characterized by a higher rate of soil nitrogen mineralization, and higher nitrogen concentration in fresh leaves and leaf-litter. The soil nitrogen mineralization rate and fresh-leaf nitrogen concentration in the patch-cut plots were higher than those in the control plots. However, leaf-litter nitrogen concentration did not differ between the patch-cut and control plots. The results suggest that slope position strongly affects leaf nitrogen nutrition of hinoki cypress and soil nitrogen availability. By contrast, patch cutting does not affect leaf-litter nitrogen concentration. These findings indicated that hinoki cypress would not enhance forest nitrogen cycling through changes in leaf-litter nitrogen concentration after patch cutting.  相似文献   

10.
A six-year soil conservation trial was conducted on a steep slope, 44%, with a subhumid climate, based on very closely spaced (90 cm) hedgerows, using three intraspecific hybrids ofLeucaena leucocephala. Soil loss averaged 2.0 t/ha per year on theLeucaena plots compared with an initial 80 t/ha per year on the unprotected control plot, falling to 27 t/ha per year after the top soil had been eroded. After 6 years, micro terraces of 35 cm high and 81 cm wide had developed on the intercropped plots, with substantially improved soil properties. Maize yield (unfertilized) were maintained at 1.5–2.0 t/ha on the protected plots, compared with a progressive fall from 0.8 to 0.5 t/ha on the sole maize control.  相似文献   

11.
Burton  P.  Bedford  L.  Goldstein  M.  Osberg  M. 《New Forests》2000,20(1):23-44
A disk-trenching experiment in thesub-boreal spruce zone of central British Columbia,Canada, established three plots (0.12 to 0.26 ha each)with trenches running east–west, and another threeplots with north–south trenches. Approximately 200Pinus contorta Dougl. seedlings were planted ineach of 13 microsites: berm, hinge, and trenchpositions in each of north, south, east, and westaspects, and in untreated locations between furrows.Soil temperature and soil moisture of representativemicrosites were monitored for 3 years; seedlingdiameter, height, and vigour were monitored annuallyfor ten growing seasons. Based on tenth-year stemvolumes, performance on south-, east-, and west-facingmicrosites was significantly greater than onnorth-facing or untreated microsites. Superior growthwas noted on all berm and hinge positions other thanthose facing north. Microsites identified as best inyear 5 were also best in year 10. On east-, south- orwest-facing berm positions, stem volume averaged 47%to 54% greater than that of control seedlings in year5, but had suffered greater mortality. Seedlings oneast-, south- or west-facing hinges were 46% to 61%(year 5), or 36% to 47% (year 10) larger thancontrol seedlings. Both east–west and north–southdisk-trenching treatments are useful for increasingseedling growth, with planting spot selection beingmore important overall than trench orientation. Thestand-level effectiveness of north–south disktrenching was greatest, because the creation of coolnorth-facing microsites was avoided.  相似文献   

12.
Mountain forests are traditionally used for cattle grazing during the dry season in southern Bolivia. To evaluate browsing intensity and damage to young trees and shrubs, a forest grazing area was monitored for about 3 months in both 2006 and 2007. Three similar paddocks of about 3 ha each, consisting of grassland and forest in a ratio of about 1:3 were stocked with 0.9, 1.6 and 2.6 tropical livestock units per ha (equivalents of 250 kg of body weight), reflecting low, medium and high stocking densities. Six 5 m × 5 m plots were mapped out within each paddock in 2006. Three additional plots per paddock were added in 2007. Within plots, the individuals of 18 woody species were coded and evaluated weekly for intensity of browsing. Intensity was quantified using five-scale categories reflecting the proportions of plant tissue removed (0 = no browsing, 1 = 1–25%, 2 = 26–50%, 3 = 51–75% and 4 = 76–100%). Across all plant species, the average category of browsing intensity, as determined in the post-grazing evaluation, was affected (P < 0.001) by stocking density. Browsing intensity increased in an approximately linear manner from 1.58 to 2.18 and 2.77 with low, medium and high stocking density, respectively. There was no significant difference between years. Most woody species followed the same general response pattern to stocking density, although some species were only noticeably browsed at high stocking density while a few others were intensively browsed at all stocking densities. The onset of browsing on woody species was observed only after some weeks had passed, indicating that herbaceous plants were preferred as a forage resource. The proportion of fatally damaged individuals, as assessed about 8 months after grazing in 2006, were 10.6%, 8.6% and 11.4% for low, medium and high stocking density, respectively. The percentage of completely browsed individuals increased with stocking density, but 80% of those plant individuals recovered following a resting period of 8 months. However, although most woody species recovered from browsing and fatal damage was infrequent, long-term changes in woody plant species composition and structure caused by grazing cannot be excluded. High stocking density in particular may reduce the vigour of heavily browsed species.  相似文献   

13.
Climate change is expected to increase the frequency and severity of drought events over the next few decades in Western Europe. Consequently, there is a crucial need for an efficient tool for field water budget diagnosis to enable forest managers to estimate tree survival and productivity. Robust estimates of water budget using soil and topography were compared for their ability to predict site yield of Quercus petraea (Matt.) Liebl. Site yield was estimated using site index at 100 years. Ninety-nine even-aged high-forest stands located in northern France were investigated. Water budget was estimated by topographic position and soil water capacity (SWC) calculated for different soil depths down to a maximum 2.0 m. (1) Site index predictions improved when calculating SWC for increasing depths until 1.0 m. (2) Site index predictions did not improve when calculating SWC at depths below 1.0 m, thus confirming that the water contained in deep soil layers is not used for tree growth but probably contributes to tree fitness or survival by maintaining a not too negative in-tree water potential. (3) Topographic position was also a predictor of site index in addition to SWC. Practical recommendations for estimating extractable soil water content are given.  相似文献   

14.
The objective of this study was to compare the vegetation structure and soil properties among old-growth tropical dry forests representing three categories of grazing intensity by cattle (light, moderate and heavy grazing) and a category of 20–30-yr-old secondary forest experiencing occasional grazing in a locality in northwestern Mexico. Within each forest type, three 0.1 ha plots located in different grazing ranges (“potreros”) were used as replicates. All woody plants (stem ≥ 2.0 cm diameter at 1.30 m height, DBH) were identified and measured in each plot. Mean basal area and above-ground biomass (AGB) were significantly higher in the moderately grazed old-growth forest. Species density was significantly lower in the secondary forest, where a leguminous tree species was dominant. Accumulation of AGB after 20–30 yr of secondary forest recovery accounted for 43% of the old-growth forest AGB. Soil properties varied among forest categories but did not follow a consistent pattern: mean total N and organic matter content were highest in the old-growth forest with moderate grazing; cation exchange capacity (CEC) was similar among the three old-growth forests categories, but it was significantly lower in the secondary forest compared to the old-growth forest with low grazing. Canonical Correspondence Analysis showed that CEC was highly correlated with the actual species distribution in the study area, especially with Acacia cochliacantha the dominant species of the secondary forest category. Resprouting capacity of the persisting species in the old-growth forests experiencing chronic disturbance could have contributed to the maintenance of some of the structural characteristics of a mature forest. Tropical secondary forests seem to accumulate AGB relatively fast, reflecting their potential for carbon storage and provision for other ecosystem services; therefore, they deserve urgent protection measures.  相似文献   

15.
Soil physical properties were measured on field runoff plots established on a tropical Alfisol in Western Nigeria. Evolution of soil physical properties was assessed over a period of 6 years beginning in 1982 (when soil was cleared off its secondary regrowth) till 1987. Changes in soil physical properties were measured for six systems including plow-till, no-till, contour hedgerows of Leucaena leucocephala established 2- and 4-m apart, and contour hedgerows of Gliricidia sepium established 2- and 4-m apart. Soil physical properties were measured once every year during the dry season following the harvest of second season crops.Over the 6-year period, there were no significant differences in relative contents of textural separates of sand, silt and clay for the surface 0–5 and 5–10 cm layers. The gravel concentration of the surface 0–5 and 5–10 cm layers, however, increased significantly due to plowing and mixing of the surface and subsoil layers. Soil bulk density of 0–5 and 5–10 cm layers, respectively, increased in all treatments from initial values of 1.02 and 1.16 g cm–3 in 1982 to 1.43 and 1.65 g cm–3 at the end of cropping cycle in 1986. The maximum increase in soil bulk density was observed for the no-till treatment. Accordingly, there was an increase in penetration resistance of the surface 0–5 cm layer from an average value of 25.3 kPa in 1982 to 210.7 kPa in 1986. The highest penetration resistance (353 kPa) of 5–10 cm layer was recorded for the no-till treatment. In accord with total porosity, the gravimetric soil moisture retention at zero suction was the lowest for the no-till and the highest for a Gliricidia-based system. There were significant improvements in available water capacity (AWC) of the soil by both Leucaena and Gliricidia-based systems. In comparison with the no-till system, increase in AWC by Leucaena- and Gliricidia-based systems, respectively, was 42 and 56 percent by weight for 0–5 cm depth and 12 and 58 percent by weight for 5–10 cm depth. Alterations in pF curves by agroforestry-based systems were attributed to improvements in soil structure and structural porosity.  相似文献   

16.
Conversion of native forest ecosystem to cropland has considerably degraded the soil nutrient levels in the Bale Mountains, south-eastern highlands of Ethiopia. This study investigated the effects of land use change through conversion of native forest to cropland and/or grazing land on soil pH (H2O), base cations (Ca2+, Mg2+, K+, Na+), CEC and percentage base saturation (PBS) in three adjacent land-use types: cropland, grazing land and native forest. A total of 108 soil samples (3 replications × 3 land-use types × 4 profiles × 3 soil depth layers, 0–0.2, 0.2–0.4 and 0.4–1.0 m) were collected for laboratory analyses. Results showed that soil pH, Na+ and K+, CEC, and PBS varied significantly with respect to land use and soil depth while Ca2+and Mg2+ varied with soil depth (ρ < 0.05). Conversion of native forest ecosystem to cropland during a 15-year period significantly increased soil pH and PBS while reducing Na+ and K+. The CEC in the cropland was reduced by 37.7% (2.6% per annum) compared to the native forest, which could be attributed to the decline in organic matter concentrations. If such rapid declines in soil nutrient concentrations continue unabated, the soils will reach at the point of no return within a few decades. Although the effect of grazing on most of the properties was found to be minimal, adapting the number of stock to the carrying capacity of the land and thereby enhancing the natural regeneration, combined with proper cropland management practices could help restoring soil nutrients for sustainable agricultural production and ecosystem functions.  相似文献   

17.
Silvopastoral systems in New Zealand that incorporate trees planted to control soil erosion on hills largely rely on the productivity of the pastoral system for financial returns. The effect on pasture productivity of increasing the tree canopy height by pruning Italian gray alder (Alnus cordata) was investigated by measuring the response of light, soil moisture, soil temperature, pasture production of major pasture species, and grazing behaviour of sheep. A split-plot design with four replicates was used. The main plot treatments were three levels of shade (81, 23, and 12% of available photosynthetic photon flux (PPF)), created by pruning 11 year old alder grown at the same density. The sub-plot treatments were four pasture mixes: perennial ryegrass (Lolium perenne), Yorkshire fog (Holcus lanatus), and cocksfoot (Dactylis glomerata), each sown with white clover (Trifolium repens), and cocksfoot sown with lotus (Lotus pedunculatus). Soil temperature was highest under light shade. Total herbage yield at 50 mm stubble height from October to May under heavy and medium shade was 60 and 80%, respectively, of the total herbage harvested under light shade. Cocksfoot had the greatest herbage yield, either with lotus or white clover. The tillering of perennial ryegrass was suppressed by shade more than for the other grass species making ryegrass unsuitable for use in this silvopastoral system. More sheep grazed in the light shade than in the heavy shade, but there was no difference in sheep preference for cocksfoot or Yorkshire fog. Lotus was grazed more frequently than white clover. Pruning of alder to increase canopy height has the potential to improve the productivity of the understorey pasture and its acceptability to sheep.  相似文献   

18.
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   

19.
The rates of fine sediment deposition were compared among three logged and three reference stream reaches 2–3 years before and 3–4 years after logging to assess the environmental impacts of partial harvesting as a novel riparian management strategy for boreal forest streams. The partial-harvest logging resulted in 10, 21 and 28% average basal area removal from riparian buffers at the three logged sites, adjacent to upland clearcut areas. No significant differences from pre-logging or reference-site sedimentation patterns were detected for two of the three logged sites. At the site with the most intense riparian logging (WR2), significant increases of 3–5 times higher than pre-logging or reference levels were detected in fine inorganic sediment (250–1000 μm) load and accumulation in the first year after logging, but no significant change was detected in fine organic sediments or very fine sediments (0.5–250 μm). The increased inorganic sediment deposition at WR2 was temporary with no significant differences from reference or pre-logging levels detectable by summer of the second post-logging year. Logging impacts on fine sedimentation in streams appeared to have been mitigated by careful logging practices including winter harvesting in riparian areas to reduce ground disturbance, and a tendency to avoid immediate (within 3–5 m) stream-side areas. Where it is feasible and advisable to conduct partial harvesting in riparian buffers of boreal forest streams, the logging can be conducted without posing significant risk of increased sediment inputs to streams when careful logging practices are followed.  相似文献   

20.
This study addresses concerns that harvesting marketable pine straw from forests may decrease timber productivity by allowing water to evaporate more quickly from the soil surface. Three harvesting schedules and a control treatment (no straw harvest) were replicated six times on 24 plots (0.18 ha each), and compared to determine harvesting effects on water content of the soil vadose zone in an established (16 yr) loblolly (Pinus taeda L.) plantation (3.0?×?1.5 m2 tree spacing). Pine straw harvesting tended to decrease volumetric soil water content (%) at depths below 20 cm, but the effect was significant (p < .05) only at the 50-cm depth in Weeks 3 and 4 (late June) of the study, when water content at this depth averaged 20.9% for soils where straw was harvested annually, and 30.2% for soils where the straw was never harvested (control). In soils where pine straw had been allowed to accumulate for at least a year after the previous harvest, average water content was not significantly different than in the control plots. Therefore, pine straw harvesting can potentially lengthen drought-stress periods for loblolly pine on some soils during the 1st yr after pine straw has been removed.  相似文献   

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