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51.
Loice Mildred Akinyi OMORO Raija LAIHO Michael STARR Petri K.E.PELLIKKA 《中国林学(英文版)》2011,13(3):198-210
The relationship between soil properties and spatial distribution of native woody species was studied in three Taita Hills forest fragments which, although degraded, are ranked among 34 biodiversity hotspots of the world due to their high biodiversity of both plant and animal species. This relationship was assessed by using Spearman correlation and principal component analyses (PCA). The results of these analyses should be useful in instituting forest restoration programs that are crucial for the forests. Both the soil and vegetation studied were sampled from 17 subplots in the natural forest fragments of Ngangao (120 ha), Chawia (86 ha) and Mbololo (185 ha). The soil variables measured were: pH, texture, soil nutrients of C, N, Ca, P, K, Mg and Na. In total 36 native tree species from 13 families were identified from the three forest fragments. Ordination results show that axis 1 accounted for 35% and axis 2 for 25% of the total variation in species composition, indicating that the structure of vegetation is related to two major environmental gradients. The correlation analyses of species and soil properties showed that Na and clay particles were the most important determinants of species distribution; pH and soil variables such as C, N, Ca and P also played minor roles. Unexpectedly, some species (e.g. Psychotria petitii) showed positive relationships with Na attributed to possible substitution for K. Relationships with P were both positive (e.g. Craibia zimmermannii) and negative (e.g. Albizia gummifera) with some species, attributable to pH levels. An ANOVA for soil variables showed that there were differences in the Ca content in Mbololo (due to the parent material) and P in Ngangao where a special relationship was observed between some of the species. The presence of gaps accounted for the distribution of seedlings but not for the saplings, whose distribution responded more to factors similar to those to which mature trees respond. Soil-species relationships that were established may be utilized along with soil analyses when choosing native species for restoration. 相似文献
52.
Ion Catalin Petri?an Burghard von Lüpke Any Mary Petri?an 《European Journal of Forest Research》2011,130(5):813-828
In Central Europe, the conversion of pure Norway spruce stands (Picea abies [L.] Karst.) into mixed stands with beech (Fagus silvatica L.) and other species like e.g. Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) is accomplished mainly by underplanting of seedlings beneath the canopy of overstorey spruce trees after
partial cutting treatments what means exposure to shade and below-ground root competition by the overstorey to the seedlings.
Particularly about the second factor, our knowledge is limited. Therefore, we carried out a below-ground competition exclusion
experiment by root trenching and investigated the effects on soil resources, growth, and biomass partitioning of underplanted
beech and Douglas fir saplings under target diameter and strip cutting treatments. The exclusion of overstorey root competition
by trenching increased the soil water potential in the second year that had a fairly dry growing season and led to significantly
higher foliar concentrations of most nutrients, particularly in Douglas fir, indicating an amended nutrient supply. Both improvements
were accompanied by an increase in length and diameter increment of the underplanted saplings, appearing in both species only
after having surpassed a species-specific threshold light value (Douglas fir 16% of above canopy radiation, beech 22%). We
also found significant interactions between trenching and light for specific fine root length and further biomass and morphological
parameters. Judged by the much steeper increase in height and diameter growth with increasing light after release from below-ground
competition, Douglas fir saplings appeared to be more sensitive to root competition than beech saplings what conforms to older
findings for beech. According to our results, a strip cutting seems to be more appropriate than a target diameter cutting
treatment to replace a pure spruce stand by a mixed stand with beech and Douglas fir. 相似文献
53.
Adventitious shoot regeneration from hypocotyl slices of mature apricot seeds has been achieved with regeneration percentages of 31.7%, 44.4%, and 46.9% for the cultivars ‘Canino’, ‘Dorada’, and ‘Moniqui’, respectively. Regeneration was significantly affected by the parental origin of the explants (P < 0.05) but not by thidiazuron or 3-indolebutyric acid for any of the three cultivars, at the levels tested. None of the other factors studied (basal medium, 2,4 dichlorophenoxy-acetic acid pulses, dark incubation period, or addition of silver thiosulfate) affected significantly shoot regeneration percentage from ‘Canino’ hypocotyl sections. The effect of paromomycin on regeneration was genotype-dependent and different dose–response curves were obtained for each cultivar. While 40 μM paromomycin completely inhibited regeneration from ‘Canino’ sections, some buds were obtained from ‘Dorada’ and ‘Moniqui’ explants. The two aminoglycoside antibiotics tested, kanamycin and paromomycin, showed differing toxicity on ‘Canino’. A lower concentration of kanamycin (20 μM) than of paromomycin inhibited totally adventitious regeneration from ‘Canino’ explants. Agrobacterium-mediated transformation experiments, with the non-oncogenic strain AGL1 harboring the binary plasmid p35SGUSINT, were performed and GUS assays were carried out after four weeks to determinate stable transformation events. The utilization of paromomycin (10 μM) as the selective agent increased significantly both the number of explants that presented at least one transformation event (P < 0.05) and the number of large area or calli expressing the gus gene (P < 0.001), compared with the addition of kanamycin (10 μM). Moreover, when 10 μM paromomycin was added to the medium some massively transformed explants were observed and a chimerical bud was regenerated. 相似文献
54.
Vision begins with photoisomerization of visual pigments. Thermal energy can complement photon energy to drive photoisomerization, but it also triggers spontaneous pigment activation as noise that interferes with light detection. For half a century, the mechanism underlying this dark noise has remained controversial. We report here a quantitative relation between a pigment's photoactivation energy and its peak-absorption wavelength, λ(max). Using this relation and assuming that pigment activations by light and heat go through the same ground-state isomerization energy barrier, we can predict the relative noise of diverse pigments with multi-vibrational-mode thermal statistics. The agreement between predictions and our measurements strongly suggests that pigment noise arises from canonical isomerization. The predicted high noise for pigments with λ(max) in the infrared presumably explains why they apparently do not exist in nature. 相似文献
55.
Estimating collateral mortality from towed fishing gear 总被引:6,自引:0,他引:6
More than 50% of the world's total marine catch (approximately 81 million tonnes) is harvested using towed fishing gears (i.e. Danish seines, dredges and otter and beam trawls). As for all methods, the total fishing mortality of these gears comprises the reported (landed) and unreported catch and other unaccounted, collateral deaths due to (i) avoiding, (ii) escaping, (iii) dropping out of the gear during fishing, (iv) discarding from the vessel, (v) ghost fishing of lost gear, (vi) habitat destruction or subsequent (vii) predation and (viii) infection from any of the above. The inherent poor selectivity of many towed gears, combined with their broad spatial deployment, means that there is considerable potential for cumulative effects of (i)–(viii) listed above on total fishing mortality, and subsequent wide‐scale negative impacts on stocks of important species. In this paper, we develop a strategy for minimizing this unwanted exploitation by reviewing all the primary literature studies that have estimated collateral, unaccounted fishing mortalities and identifying the key causal factors. We located more than 80 relevant published studies (between 1890 and early 2006) that quantified the mortalities of more than 120 species of escaping (26 papers) or discarded (62 papers) bivalves, cephalopods, crustaceans, echinoderms, elasmobranches, reptiles, teleosts and miscellaneous organisms. Seven of these studies also included the estimates of mortalities caused by dropping out of gears, predation and infection [(iii), (vii) and (viii) listed above]. Owing to several key biological (physiology, size and catch volume and composition), environmental (temperature, hypoxia, sea state and availability of light) and technical (gear design, tow duration and speed) factors, catch‐and‐escape or catch‐and‐discarding mechanisms were identified to evoke cumulative negative effects on the health of most organisms. We propose that because the mortalities of discards typically are much greater than escapees, the primary focus of efforts to mitigate unaccounted fishing mortalities should concentrate on the rapid, passive, size and species selection of non‐target organisms from the anterior sections of towed gears during fishing. Once maximum selection has been achieved and demonstrated to cause few mortalities, efforts should be made to modify other operational and/or post‐capture handling procedures that address the key causal factors listed above. 相似文献
56.
Potential activities of enzymes involved in N,C, P and S cycling in boreal forest soil under different tree species 总被引:1,自引:0,他引:1
The aim of this study was to compare the potential activity of enzymes involved in N, C, P and S cycling in the humus layer under three tree species: silver birch, Norway spruce and Scots pine. For arylsulphatase and protease the highest activities were found under birch, whereas beta-glucosidase activity was highest under pine. Beta-glucosaminidase and acid phosphatase showed similar activities regardless of tree species. Our studies show that soils under these species may differ enzymatically from each other. Enzyme activity studies under different tree species need more attention as the activity of different enzymes influences on soil nutrient availability in boreal forest soil. 相似文献
57.
58.
The inverse of the relative increment rate of size is proposed as a measure of the maturity of a forest tree. The heartwood content within bole cross sections is modeled semiempirically using asymptotic fitting. It is shown that the present proposal for a definition of maturity statistically explains heartwood content far better than age or size. The heartwood content appears to be independent on growth rate and tree size. 相似文献
59.
Norway spruce dust was impregnated with aqueous solutions of chromated copper wood preservatives. Immediately after treatment,
observation of CO2 evolution and O2 consumption were performed. Significant quantities of CO2 were released during reaction of chromium (K2Cr2O7) containing solutions with wood or brown rotted wood. Nevertheless, during reaction of cellulose with these preservatives
we did not observe evolution of CO2. The presence of copper did not influence on concentration of CO2. Opposite to CO2 evolution, treatment of wood and brown rotted wood resulted in O2 consumption. The oxygen concentration decrease in the measuring chamber was approximately 5 times greater than increase of
concentration of carbon dioxide. Electron paramagnetic resonance (EPR) observations of chromium fixation showed that chromium
is reduced from Cr(VI) to Cr(III) with Cr(V) as an intermediate on wood, brown rotted wood and cellulose. However, the reduction
on wood and brown rotted wood was faster than the reduction on cellulose, as determined from changes of Cr signals in EPR
spectra. So, evolution of CO2 and consumption of O2 as well as EPR signals of Cr species thus indicate that brown rotted wood, consisting of lignin and hemicelluloses in contact
with Cr(VI) reacts more intensively than cellulose, and possibly, oxidation mechanisms of lignin and cellulose with Cr(VI)
are different.
Received: 20 July 2000 相似文献
60.
Methodology comparison for slope correction in canopy leaf area index estimation using hemispherical photography 总被引:1,自引:0,他引:1
The slope effect and correction methods for estimation of canopy gap fraction, leaf area index (LAI), mean leaf angle and clumping index using hemispherical photography, were investigated. The evaluation was carried out in tropical cloud forest and plantations in South-East Kenya in order to consider a range of canopy architecture and slopes up to 65%. The aim was to compare two acquisition techniques and various correction procedures. All estimates assume uniform slope, canopy parallel to ground and homogeneous canopy structure at the photo site level.
- (1) Photographs oriented to local zenith (levelled acquisition). Calculation and removal of sky parts of the hemisphere obstructed by topography. Azimuthal inversion of gap fraction without prior averaging, deriving local LAI estimates (quasi-random model). (i) Fixed path lengths over azimuths. Zenith reference axis. LAI referred to horizontal and corrected for topographic shading. (ii) Variable path lengths over azimuths. Normal to slope reference axis. LAI adjusted to horizontal by dividing by the slope cosine.
- (2) Photographs oriented parallel to slope (tilted acquisition). Fixed path lengths over azimuths. Normal to slope reference axis. LAI adjusted to horizontal by dividing by the slope cosine. Azimuthal inversion of gap fraction without prior averaging, deriving local LAI estimates (quasi-random model).