Interactive effects of nitrogen and water availabilities on gas exchange and whole-plant carbon allocation in poplar

Cuttings of balsam spire hybrid poplar (Populus trichocarpa var. Hastata Henry x Populus balsamifera var. Michauxii (Dode) Farwell) were grown in sand culture and irrigated every 2 (W) or 10 (w) days with a solution containing either 3.0 (N) or 0.5 (n) mol nitrogen m(-3) for 90 days. Trees in the WN (control) and wn treatments had stable leaf nitrogen concentrations averaging 19.4 and 8.4 mg g(-1), respectively, over the course of the experiment. Trees in the Wn and wN treatments had a similar leaf nitrogen concentration, which increased from 12.0 to 15.8 mg g(-1) during the experiment. By the final harvest, mean stomatal conductances of trees in the wN and wn treatments were less than those of trees in the Wn and WN treatments (1.8 versus 4.6 mm s(-1)). Compared to the WN treatment, biomass at the final harvest was reduced by 61, 72 and 75% in the Wn, wN and wn treatments, respectively. At the final harvest, WN trees had a mean total leaf area of 4750 +/- 380 cm(2) tree(-1) and carried 164 +/- 8 leaves tree(-1) with a specific leaf area of 181 +/- 16 cm(2) g(-1), whereas Wn trees had a smaller mean total leaf area (1310 +/- 30 cm(2) tree(-1)), because of the production of fewer leaves (41 +/- 6) with a smaller specific leaf area (154 +/- 2 cm(2) g(-1)). A greater proportion of biomass was allocated to roots in Wn trees than in WN trees, but component nitrogen concentrations adjusted such that there was no Wn treatment effect on nitrogen allocation. Compared with WN trees, rates of photosynthesis and respiration per unit weight of tissue of Wn trees decreased by 28 and 31%, respectively, but the rate of photosynthesis per unit leaf nitrogen remained unaltered. The wN and Wn trees had similar leaf nitrogen concentrations; however, compared with the Wn treatment, the wN treatment decreased mean total leaf area (750 +/- 50 cm(2) tree(-1)), number of leaves per tree (29 +/- 2) and specific leaf area (140 +/- 6 cm(2) g(-1)), but increased the allocation of biomass and nitrogen to roots. Net photosynthetic rate per unit leaf nitrogen was 45% lower in the wN treatment than in the other treatments. Rates of net photosynthesis and respiration per unit weight of tissue were 48 and 33% less, respectively, in wN trees than in Wn trees.     

Somaclonal variation in growth, leaf phenotype and gas exchange characteristics of poplar: utilization of leaf morphotype analysis as a basis for selection

Populus hybrid TT32 lines produced from 15 treatment tissue culture regimes exhibited somaclonal variation in morphological and gas exchange parameters. Within four years of regeneration, discrete lines showing statistically validated superior, or inferior, growth performance relative to the parental reference clone were identified. Significant differences in the ratio of leaf length/width between treatment lines provided the earliest reliable indicator of the divergence in overall growth performance. Despite discernible variation in leaf phenotype among primary regenerants and secondary propagules within individual lines, the leaf length/width ratio was identified as a potential parameter for predicting growth performance. Its subsequent use led to the recognition of four distinct leaf morphotypes; cordate, ovate, reniform and oval. Two or more of these morphotypes were distributed within each of the original 15 treatment lines. Regrouping the data on the basis of leaf morphotype resulted in a clear segregation of the morphological traits, and revealed differences that were not readily apparent by statistical analysis based on treatment groups. The demonstration of similar relative performances by individual morphotypes with respect to a range of growth and gas exchange parameters confirmed that variation in leaf morphology was indicative of differential photosynthetic performance. Somaclonal variants with a leaf morphology was indicative of differential photosynthetic performance. Somaclonal variants with a leaf morphotype closest to that of the parental line showed the highest overall potential for selection, suggesting that the greatest benefits accrue from a minimal disturbance of the parental leaf phenotype.     

Genetic variation in productivity, leaf traits and carbon isotope discrimination in hybrid poplars cultivated on contrasting sites

? We examined the relationships between productivity, leaf traits and carbon isotope discrimination in bulk leaf matter (Δ₁) and in phloem sap (Δ_s) from more than 5-year-old trees belonging to Populus deltoides × P. nigra and Populus trichocarpa × P. deltoides; trees were grown in alluvial and non alluvial sites in a commercial poplar plantation.

? On both sites, a large genetic variability was evidenced for all variables. The genotypic ranking remained stable between years for all variables, while it differed between sites. Δ₁ scaled positively with Δ_s and neither Δ₁ nor Δ_s were correlated with productivity. A significant genotype by site interaction was evident for all variables. The non alluvial site resulted in lower productivity, and in thicker/denser leaves with lower nitrogen and carbon contents. Noteworthy, the genotypic ranking for Δ₁ measured at the alluvial site was similar to that previously established in a glasshouse.

? As observed in previous studies from younger trees, there is a potential to select genotypes, combining high productivity and high water-use efficiency, for growth in moderately drought-prone areas.

     

Effects of two iron sources on iron and cadmium allocation in poplar (Populus alba) plants exposed to cadmium

Effects of 10 microM cadmium (supplied as Cd nitrate) on the utilization and allocation of iron (Fe) were investigated in poplar (Populus alba L.) plants grown in nutrient solution with Fe(III)-EDTA or Fe(III)-citrate as the Fe source. The effects of Cd were also compared with those of Fe deprivation. The accumulation of Fe in roots was 10-fold higher in plants grown with Fe-citrate than with Fe-EDTA. Cadmium decreased leaf chlorophyll concentrations and photosynthetic rates, and these decreases were more marked in plants grown with Fe-citrate than with Fe-EDTA. In both Fe treatments, addition of Cd caused large increases in root and shoot apoplasmic and non-apoplasmic Cd contents and increases in root Fe content; however, Cd decreased shoot Fe content, especially in plants grown with Fe-citrate. New leaves of plants grown with Fe-citrate had small cellular (non-apoplasmic) Fe pools, whereas these pools were large in new leaves of plants grown with Fe-EDTA. Non-apoplasmic Cd pools in new leaves were smaller in plants grown with Fe-citrate than with Fe-EDTA, indicating that inactivation of non-apoplasmic Cd pools is facilitated more by Fe-EDTA than by Fe-citrate. In the presence of Cd, Fe-EDTA was also superior to Fe-citrate in maintaining an adequate Fe supply to poplar shoots. Differences in plant responses to Fe-EDTA and Fe-citrate may reflect differences in long-distance transport of Fe rather than in acquisition of Fe by roots.     

Induction and stability of somaclonal variation in growth, leaf phenotype and gas exchange characteristics of poplar regenerated from callus culture

Populus trichocarpa Torr. and Grey x P. balsamifera L. TT32 lines were regenerated from calli that had been maintained under differing in vitro conditions for sixteen months. In the final months, calli were maintained with one of six concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D, 0.1, 0.2, 0.3, 0.4, 0.5 or 0.6 mg l(-1))and regenerated with 0.25, 0.50 or 1.0 mg l(-1) benzylaminopurine (BA). Regenerant lines were obtained from 15 of these 18 treatments. The spectrum of variation in several morphological, physiological and leaf gas exchange traits was evaluated in the primary regenerants in 1986, and in their secondary vegetative propagules in the two subsequent years, in relation to differences in the original culture conditions. The results indicate that somoclonal variation was induced largely as a result of prolonged culture in the presence of 2,4-D, but that the terminal maintenance and regeneration phases also induced changes in the regenerants. Qualitative differences among the regenerant lines were detected by the end of 1986. For most traits, these differences were statistically confirmed within the 3-year period. The treatment lines ultimately diverged sufficiently to produce lines showing general performance that was either above or below that of the original TT32 clone. An early visible indicator of this divergence was variation in leaf shape (leaf length/width ratio), which could be related to 2,4-D-BA interactions in the final stages of culture. Graphic illustration of the independent effects of either 2,4-D or BA on stem height and gas exchange parameters suggested an inverse relationship with BA concentration and a complex interaction with 2,4-D. Significant correlations were detected between gas exchange parameters and morphological characteristics representing leaf form and stem development. Overall, the results indicate the presence of somaclonal lines that offer potential for the selective improvement of growth using morphological and gas exchange parameters as screening tools.     

Ovipositional preference and larval performance of poplar defoliator, Clostera restitura on different poplar clones in north-western India

We evaluated ten poplar clones (G-3, G-48, L-50/88, L-154/84, L-156/89, S7C8, S7C15,WSL-22, WSL-29 and Uday) for ovipositional preference and larval performance of Clostera restitura. Female moths did not show any preference with respect to clones for oviposition. Significant differences were observed for number of eggs laidon different plant parts. C. restitura laid eggs in clusters, preferably onupper surface of leaf and size of the egg cluster varied from 15 to 167eggs. Clones varied for their relative resistance and susceptibility to C.restitura. L-50/88; L-156/89 were identified as most resistant clone basedon minimum leaf consumption, whereas S7C15 was found to be most susceptible clone to C. restitura. In multiple choice experiments, no feeding preference by C. restitura larvae was detected amongst different poplar clones. After initial settlement of larvae on a particular clone, thelarvae remained confined to that clone and negligible inter-clonal movement was noticed subsequently. The fresh pupal weight was correlated negatively (r = 0.37) with percentage surface leaf area eaten and positively (r = 0.47) with length of larval period, measured on different clones. Relationship between percentage leaf area eaten and length of larval period was negative (r = 0.23). Owing to relative resistance of L-50/88 and L-156/89 against C. restitura, these clones can be recommended for plantation in defoliator prone areas in north-western India.     

Tree establishment and management on farms in the drylands: evaluation of different systems adopted by small-scale farmers in Mutomo District,Kenya

Agroforestry systems in Sub-Saharan African drylands are complex and heterogeneous in nature even under similar biophysical conditions. This can be attributed to household needs and socioeconomic status which influence the species and utility of the adopted trees. This has an impact on the trees establishment and management system through planting or Farmer Managed Natural Regeneration (FMNR). This study evaluates how trees for different utilities are managed and which socioeconomic factors influence these decisions. The study used primary data collected in Mutomo District, Kenya through a household survey based on a structured questionnaire. A paired sample t-test was done to assess the preferred mode of adopting trees for different utilities while factor analysis was used to characterize the households as either planting trees or practicing FMNR. Multiple linear regression using household regression factor scores as independent variables and socioeconomic indicators as dependent variables was done to ascertain which socioeconomic factors affect tree adoption. The results show that trees planted were mostly exotic species valued for their nutrition and commercial value, while FMNR was used for subsistence products and environmental services. Household size, livestock levels and mobility had a positive correlation with tree planting, while income, access to markets and roads had an inverse correlation. Access to natural woodland, distance to the nearest motorable road and land size had a positive correlation with tree protection. It is hoped that this knowledge will act as a reference point when designing agroforestry projects in similar areas to ensure they are more aligned to specific site and household conditions.     

Predicting the productivity of a young hybrid poplar clone under intensive plantation management in northern Alberta,Canada using soil and site characteristics

Site productivity of the hybrid poplar clone Brooks6 was predicted using soil and site information from 6, 4-year-old plantations in north-east Alberta. Predictions were made at both the local and microsite scales. Percent sand (R ² = 0.352, P = 0.001) was the best single predictor of hybrid poplar productivity, showing a curved relationship. Soil pH also showed a curved but weaker relationship with hybrid poplar productivity (R ² = 0.133, P = 0.100). Maximum tree productivity occurred at sand contents between 55 and 70% and pH values near 6. Other variables, including foliar nutrient concentrations, foliar δ¹³C, electrical conductivity, depth of the A horizon and total chemistry of the soil, were also related to hybrid poplar productivity at the local and microsite scales. However, all of these variables were correlated to either soil texture (percent sand) or pH. At the microsite scale within plantations, percent sand was the most important predictor of tree productivity and explained more than 50% of the variability within plantations, although the relationship varied by plantation. In plantations with fine textures, sandier microsites were associated with increased growth while in sandy plantations, finer textured microsites were more productive. As a whole, the growth of the hybrid poplar clone Brooks6 appears to be mostly influenced by a combination of soil water and nutrient availability, the former being impacted by soil texture and the latter being governed by soil pH.     

Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants grown in different N regimes and sprayed with urea in autumn

Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants fertigated with different nitrogen (N) treatments and sprayed with urea in autumn were studied. Stock plants propagated from poplar cuttings were trained to a single shoot and fertigated with 0, 5, 10, 15 or 20 mmol l(-1) N during the first growing season. In October, a subset of stock plants from each N fertigation treatment was sprayed twice with either 3% urea or water, and overwintered outside. In March, total tree biomass and total N concentration and content of stems were estimated for stock plants in each treatment, and cuttings were taken from the middle of each stock plant and stored in plastic bags at 2 degrees C. In mid-April, cuttings were planted in 7.5-l pots containing N-free medium and grown outdoors with a weekly fertigation with nutrient solution containing 0 or 10 mmol l(-1) 15NH4 15NO3. In mid-July, cuttings were harvested, and new shoot (new stems and leaves), shank (old cutting stem) and roots were analyzed for new biomass growth and total N and 15N content. Growth of stock plants was positively related to N supply in the previous growing season. Foliar urea application in autumn had no effect on subsequent stock plant growth even though urea sprays increased both N concentration and content in stem tissues. Biomass growth of cuttings obtained from stock plants was closely related to their N content when the cuttings were grown in an N-free medium regardless of previous treatments applied to the stock plants. When N was supplied in the growth medium, the strength of the relationship between regrowth and N content of cuttings was significantly reduced. Cuttings from stock plants treated with foliar urea and grown in a N-free medium remobilized between 75 and 82% of their total N for new growth, whereas cuttings from plants receiving no urea spray remobilized only between 60 and 69% of their total N for new growth. Current N fertilization of the cuttings reduced the percentage of N remobilized. We conclude that new growth of poplar cuttings in spring was more dependent on currently applied N than on reserve N, and urea N applied as a spray in autumn was more easily remobilized than N taken up by roots during the previous season.     

Site preparation,fertilization, and 10-year yields of hybrid poplar on a clearcut forest site in eastern Maine,USA

Cuttings of two similar hybrid poplar clones were planted on a drum-chopped, chip-harvested clearcut in eastern Maine. The site had never been previously cleared for agriculture. The coarse loamy glacial till soils were acid (pH < 5.0) and moist—moderately well—to somewhat poorly drained. Control, lime (L), L nitrogen (N), L phosphorus (P), LNP, and LNP potassium (K) treatments were established. Competing woody vegetation was mowed once per year for the first three years on half the area. Each mowed treatment produced significantly greater hybrid poplar biomass than the corresponding unmowed treatment. After 10 years, the mowed+LNPK treatment attained the greatest total biomass, 45 Mgha^-1, while the unmowed control attained the least, 2 Mgha^-1. On mowed plots, L produced 4 times the biomass of control: 32 vs 8 Mgha^-1. Unmowed plots with L and N produced about as much hybrid poplar biomass as the mowed control (8 Mgha^-1). Mowing and L each improved survival as well as growth.Deceased     

Studies on the abundance, biology and harmfulness of leaf beetles (Coleoptera: Chrysomelidae) in natural bush vegetation in Isparta, Turkey

Leaf beetle occurrence and abundance on certain shrubs and bushes were surveyed during 2002–2003 in several natural habitats of Isparta. The 34 leaf-beetle species collected are listed and classified according to their relative percentage of the total caught and to their associated host plants. In all habitats sampled, leaf beetles showed a preference for plants from the genera Quercus and Crataegus. Some abundant species causing serious damage to their food plants are discussed.     

Short-term impacts of nutrient manipulations on leaf gas exchange and biomass partitioning in contrasting 2-year-old Pinus taeda clones during seedling establishment

We conducted a 1-year greenhouse experiment to assess the impact of nutrient manipulations on seedling growth, biomass partitioning, and leaf gas exchange between two fast growing Pinus taeda clones that differed in growth efficiency. After 1 year we observed significant treatment and treatment by clone effects on growth, biomass partitioning, and gas exchange parameters. Fertilization increased total seedling biomass 18% primarily through an increase in foliage and coarse-roots. Clones did not differ in total seedling biomass, however, clone 85 produced more stem than clone 93 leading to 37% greater stem:leaf, while clone 93 maintained more branch biomass. The logging residue treatment increased stem:leaf by 30%, but had no effect on total biomass or partitioning. Differences in leaf morphology resulted in significantly greater canopy leaf area in clone 93 than clone 85. Increased foliar N concentration from fertilization had only minor effects on specific photosynthesis under saturating light (A_Sat), but lowered stomatal conductance (g_s), transpiration (E), and internal to external CO₂ concentration ratio (C_i/C_a) as well as improved water use efficiency (WUE) independently of genotype. When gas exchange data was scaled to the canopy level both genotypes achieved similar canopy level CO₂ assimilation rates, but our data suggests they did this by different means. Although we did see a small effect of nutrient limitations in total canopy photosynthesis under saturating light (A_Canopy), A_Sat, and total leaf area (TLA), our foliar N concentration ([N]) indicated that our level of logging residue incorporation did not cause [N] to decrease below sufficiency limits. From a practical standpoint, a better understanding of strategies for capturing and partition C may lead to better selection of clonal material, thereby, optimizing productivity.     

The economics of carbon sequestration through pest management: application to forested landbases in New Brunswick and Saskatchewan,Canada

This analysis employs a spruce budworm (Choristoneura fumiferana Clem.) decision support system to examine costs and benefits of sequestering (protecting) carbon in forests through pest management. We analyzed 24 alternative spruce budworm protection scenarios for outbreaks on Prince Albert Forest Management Area (PAFMA) in Saskatchewan and Crown License 1 in New Brunswick. Scenarios included two outbreak severities (moderate and severe), three protection frequencies (very aggressive—protecting every year of the outbreak; aggressive—protecting the peak 3 years of outbreak; and semi-aggressive—protecting every second year of outbreak), and four protection program sizes (10,000 ha, 25,000 ha, 100,000 ha, or 150,000 ha). Under a severe outbreak, the largest (150,000 ha), very aggressive protection scenario provided the highest net CO₂ protected at 24.95 million metric tons (Mt) in PAFMA and 29.19 Mt in License 1. This protection scenario also provided the highest net present value at $64.23 M and $91.36 M in PAFMA and License 1, respectively. On the other hand, benefit/cost ratios were maximized under the smallest (10,000 ha) protection size at 11.90 and 15.37 using the aggressive and semi-aggressive protection frequencies in PAFMA and License 1, respectively. Finally, the discounted cost per ton of CO₂ protected was minimized at $0.48 and $0.37 using the smallest aggressive and semi-aggressive protection frequencies in PAFMA and License 1, respectively. The comparable costs and benefits from the moderate outbreak scenarios were similar, but generally less than, the severe outbreak scenarios. These results provide forest managers with important information needed to justify such carbon sequestration programs on economic grounds.     

Retention of native woody vegetation on farms in Australia: management considerations,planning guidelines and information gaps

Australia's forests and woodlands have been extensively cleared since European settlement. Cropping regions have the least retained native vegetation, with the greatest depletion of forests and woodlands being observed in Western Australia and South Australia. Salinisation, erosion and landslides have resulted from excessive clearing and inappropriate tree removal from particular units within the landscape. Major problems in cropping regions are the dramatic reduction in total woody cover and the fragmentation of retained vegetation into isolated remnant patches which tend to be very small (<10–15 ha). Those states with little remnant vegetation have legislation which restricts further clearing and the main emphasis is on managing remnant patches for conservation. For those states with a large proportion of woody vegetation uncleared, the main priority is to ensure that past mistakes are not repeated and that any vegetation clearance is based upon sound ecological principles.Throughout Australia, the condition of the remaining vegetation is of great concern and management guidelines for both conservation and production are being sought. Clearing may lead directly to soil erosion, but often the cause of erosion is inappropriate post-clearing management. Overgrazing is a major cause of vegetation and soil degradation, particularly in semi-arid regions.An understanding of the complex inter-relationship between woody vegetation, grazing and fire is necessary if 1) flora and fauna are to be conserved; 2) hydrological balance is to be maintained; and 3) rural industries are to remain viable. Planning at the catchment level is necessary to implement strategies to meet conservation and hydrological goals. Within that framework, individual property planning must include consideration of the area of native woody vegetation to be retained and its configuration. In many cases, the purpose of retention will influence the decisions of where and how native vegetation should be retained.     

Dynamic oak-scrub to forest succession: Effects of management on understorey vegetation,humus forms and soils

Active management for preservation of conserved ecosystems is receiving increased attention, as management probably is the most important factor for the temporal and spatial distribution of understorey vegetation, and probably humus forms and soil nutrient cycling as well. The present study investigates this issue on well-drained sandy soils in the ancient woodlands of Hald Ege, Denmark, which was preserved in 1915. Four types of management have continued since then: (i) managed, pure oak, (ii) non-managed, beech-oak, (iii) grazed oak and (iv) coppiced oak stands. Data consisted of two independent present-day data sets from all types of management, and one comparison between data from 1916 and now. Relations between forest type and possible explanatory variables, such as land-use history and characteristics of forest, humus layer, soil and understorey, were studied using principal component (PCA) and correspondence (DCA) analyses. Results showed that grazing mammals have kept the oak forest in a state resembling the pre-preservation stage with respect to both vegetation and humus forms. Here, light penetration to the forest floor during the entire growing season supported a diverse flora and a moder or mull-type of decomposition. The non-managed plots were in contrast succeeded into a dark beech-oak forest with thick humus layers and a drastic decrease in understorey species number. The present analysis hence supports the theory that management is necessary to conserve oak-scrubs and open woodlands from successional changes of herbaceous forest vegetation, humus forms and understorey vegetation.     

Effects of shade on growth, biomass allocation and leaf morphology in European yew (Taxus baccata L.)

The impact of shade on the growth of European yew (Taxus baccata L.) saplings was investigated over a three-year period using artificial shading to simulate four different light regimes (3, 7, 27 and 100 % relative photosynthetic photon flux density, RPPFD). There was no mortality attributable to shading even under the 3 % RPPFD treatment. Increasing shade was positively associated with specific leaf area, leaf length, leaf width and total chlorophyll content, but negatively associated with plant height, stem diameter, total dry weight and root to leaf and shoot ratio. Discoloration of the foliage occurred in plants grown in 100 % RPPFD conditions (resulting in reduced growth rates) and those transferred to 100 % RPPFD conditions after being shade-acclimated for 2 years. Evidence suggests that T. baccata has the ability to regenerate beneath a lighter canopy but beneath denser canopies gap dynamics will play an important role in facilitating successful regeneration and this needs to be reflected in management of natural populations of this declining species.     

Influence of vegetation restoration on matrix structure and erosion resistance of iron tailings sites in eastern Hebei,China

The effects of vegetation restoration on matrix structure and erosion resistance of iron tailings were studied at dump sites in Malanzhuang, Qian'an, Hebei province, China. The restoration process involved soil spray sowing restoration model with Rhus typhina, soil and iron tailings admixture spray sowing restoration model with Amorpha fruticosa Linn. and six-hole brick restoration model with Pinus tabulaeformis Carriere.–Amorpha fruticosa Linn. mixed-forest, and direct restoration model with Hippophae rhamnoides and Sabina vulgaris. Results show that the composition and distribution of particles and aggregates were closely related to erosion resistance(P < 0.05), indicating that matrix structure of iron tailings play an important role in erosion resistance. The improvement in matrix structure of iron tailings by the different restoration models was in the order of R. typhina soil spray sowing > A. fruticosa soil and iron tailings admixture spray sowing > mixed-forest six-hole brick >H. rhamnoides direct restoration > S. vulgaris direct restoration. The R. typhina soil spray sowing restorationmodel resulted in the greatest improvement in matrix structure of iron tailings, increasing the clay(10.6%) and large particle aggregates(18.7%) contents significantly(P < 0.01). Simultaneously, particle population, grading conditions(Cu= 28.86, Cs= 1.65), and aggregate stability(6.02) were significantly improved. The A. fruticosa soil and iron tailings admixture spray sowing restoration model,which effectively improved particle distribution(Cu-= 8.51, Cs= 1.07), increased the number of large aggregates considerably(9.6%), thereby increasing aggregate stability(6.2). The six-hole brick model significantly increased the number of large aggregates(4.0%) and improved the stability of aggregates(6.2). H. rhamnoides direct restoration improved the stability of aggregates(5.1)but showed no other significant improvements. The effect of S. vulgaris direct restoration on matrix structure of iron tailings was not significant. Due to its dependence on matrix structure of iron tailings, the erosion resistance of R.typhina soil spray sowing restoration model was the greatest, while that of S. vulgaris direct restoration was the weakest. There was no significant difference in the erosion resistance of the other models. Overall, vegetation restoration supplemented by soil spray sowing restoration and engineering measures is superior to in situ direct vegetation restoration in the short-term. In-situ direct restoration has long-term ecological significance because of its advanced concept of near-natural restoration and the advantages of low cost, easy operation, and low secondary damage.     

Economic returns from enhancing loblolly pine establishment on two upland sites: Effects of seedling grade,fertilization, hexazinone,and intensive soil cultivation

On two well drained Coastal Plain sites, early (4-year) and mid-rotation (12-year) performance of loblolly pine (Pinus taeda L.) was examined in relation to mechanical site preparation, herbaceous weed control, and fertilization with diammonium phosphate (DAP). In addition, seedling grade as determined by groundline diameter (GLD) was a fourth factor evaluated. Of the four factors examined, seedling grade was the only factor to consistently improve fourth-year survival. In Alabama, seedlings with a 2.5 mm GLD averaged 62% survival while 5.1 mm seedlings averaged 83% survival. In Virginia, 1.3 mm seedlings had 73% survival and 5.1 mm seedlings had 79% survival. Calculated volume gains from increasing seedling grade suggest that a 1 mm increase in GLD could amount to an additional 7 to 12 m³/ha at age 12. Seedling size and mechanical site preparation were partly exchangeable in influencing survival and growth. Use of hexazinone on late planted seedlings increased mortality at both sites. Applications of hexazinone increased volume/ha when combined with DAP fertilization. Fertilization with DAP increased 12-year volume/ha only when weeds were controlled with hexazinone or disking.Alabama Agricultural Experiment Station Journal Series No. 9-933657.     

Growth dynamics and biomass accumulation of 8-year-old hybrid poplar clones in a short-rotation plantation on a clayey-sandy mining substrate with respect to plant nutrition and water budget

In 1995 a short-rotation plantation (2.5 ha) was established in the mining region Welzow-Süd in Brandenburg, Germany, on a clayey-sandy, lignite- and pyrite-free substrate in order to study the biomass potentials of fast-growing tree species (hybrid poplar clones). In this study, special emphasis was placed on yield aspects as well as on the interaction between soil and plants, especially with regard to the plant nutrition and soil–water relationships. So far, the results indicate that the cultivation of hybrid poplar clones in a short-rotation plantation is an adequate tool for establishing alternative land-use systems in the post-mining landscape as a potential source of biomass energy. Aboveground biomass production ranged from 24–49 t dry matter (DM) per hectare at age 8. In particular during this period of investigation, nitrogen nutrition of the clones decreased to below a threshold of 20 mg g^–1 DM in the year 2002. Investigations of the water budget of low- and high-yielding clones indicated that differences in the biomass accumulation seemed to be accompanied by different water-use efficiencies.