Growth and thinning effects during a rotation period of hybrid aspen in southern Sweden

Hybrid aspen is an interesting tree species for wood production in northern Europe. In this study we examined growth dynamics over the whole rotation period. Height and diameter development, as well as annual growth of stem volume and stem biomass, were repeatedly recorded in 14 planted and 2 root sucker stands, aged up to 26 years, in southern Sweden. A main aim was to study the productivity level for hybrid aspen forestry with an expected rotation period of about 25 years. The study verified earlier prognoses, showing a mean annual increment (MAI) of 19.5 m³ of stem wood ha^?1 yr^?1 after 25 years. This corresponds to a dry weight of stem biomass of 7.2 tons dry matter (DM) ha^?1 yr^?1. Maximum MAI was still not reached after 25 years, although the growth curve was flattening out. If branch biomass is included, MAI is estimated to about 9 tons DM ha^?1 yr^?1 and further improvements in growth is expected by using the best genotypically selected clones available. Results from three different thinning regimens showed that thinning intensity provided significantly larger diameter growth, while no significant yield effects were seen among the thinning regimens.     

Water Use Efficiency, Carbon Isotope Discrimination and Biomass Production of Two Sugar Beet Varieties Under Well-Watered and Dry Conditions

Two sugar beet (Beta vulgaris sp.) varieties, which were supposed to differ in drought tolerance, were exposed to drought stress in a growth chamber and a container experiment in field. The aim was to test for (i) differences between the varieties in water use efficiency (WUE), biomass production and distribution and (ii) the relationship between WUE and carbon isotope discrimination (Δ), and between biomass production and Δ. Significant differences in WUE were detected between plants of well‐watered and drought treatments in both experiments, but not between the varieties. Production losses due to drought were large for both varieties in both experiments. Losses in the growth chamber were up to 50 % of plant dry weight and the corresponding value in the field was 24 %, when plants were given 60 and 30 %, respectively, of the full‐watered treatments. Significant negative correlations between WUE and Δ were found, but not between biomass production and Δ, when both varieties were included. Negative correlations between WUE and Δ were also found for each variety separately. The results suggest that Δ estimates from leaf tissue of sugar beet may provide a useful tool for genetic selection of drought‐tolerant sugar beet varieties.     

Leaf nutrient analysis in Salix viminalis (L.) energy forest stands growing on agricultural land

The seasonal pattern of morphological leaf characteristics, leaf nutrient and carbohydrate contents in two energy forest stands growing on fertile clay soil and consisting of Salix viminalis (L.) was investigated. One of the stands was irrigated and liquid fertilized (IL) daily from May to August while the other stand was untreated (C). The study was carried out on shoots growing for their second year on five-year-old roots. A pronounced seasonal variation in length, weight, and area of leaves of the same developmental stage was observed, while differences between the stands were small. The leaf content of carbohydrates and starch was low. Nitrogen was the only nutrient that was significantly higher in the IL stand compared with the C stand throughout the growing season. The small differences between stands were most probably an effect of the initially high soil fertility. Different bases for expressing plant nutrient status during the growing season, i.e. nutrient amount per leaf dry weight with and without carbohydrates, nutrient amounts per leaf or leaf area, nutrient proportions in leaves, and nutrient amounts in the total canopy, were compared and discussed. It was concluded that the common expression, nutrient weight per dry weight of leaves, without correction for non-structural carbohydrates, was adequate to describe the nutrient situation in well-growing basket willow plantations. The most appropriate time for leaf sampling was proposed to be the phase of most intensive growth.     

Detection and diversity of viruses infecting African yam (Dioscorea rotundata) in a collection and F1 progenies in Côte d'Ivoire shed light to plant-to-plant viral transmission

Yam (Dioscorea spp.) is a major staple food whose production is hampered by viral diseases. However, the prevalence, diversity, transmission, and impact of yam-infecting viruses remain poorly documented. This study reports on the symptomatology, prevalence, and molecular diversity of eight viruses in 38 D. rotundata accessions from a germplasm collection and 206 F₁ hybrid progenies maintained in Côte d'Ivoire. Mean severity scores as assessed from leaf symptoms ranged from 2 to 4 in the germplasm collection and from 1 to 3 in F₁ hybrids, respectively. Dioscorea mosaic-associated virus (DMaV), potexviruses, and yam mosaic virus (YMV) were detected by PCR-based diagnosis tools in single and mixed infections in both the D. rotundata collection and F₁ progenies, whereas badnaviruses were detected only in the germplasm collection. In contrast, cucumber mosaic virus (CMV), yam macluraviruses, yam asymptomatic virus 1 (YaV1), and yam mild mosaic virus (YMMV) could not be detected. No correlation could be established between severity scores and indexing results. Phylogenetic analysis performed on partial viral sequences amplified from infected samples unveiled the presence of two putative novel viral species belonging to genera Badnavirus and Potexvirus and provided evidence for plant-to-plant transmission of YMV, DMaV, and yam potexviruses.     

Establishment strategies for poplars,including mulch and plant types,on agricultural land in Sweden

Biomass from forestry is one of the largest components of Sweden’s renewable resources. Poplars are currently the highest producing tree species available and are therefore natural choices for biomass-oriented production. Growing poplars has been of most interest on agricultural land, but the knowledge and experience about their cultivation is still limited. Factors that have a large impact on the regeneration results are plant material, competing vegetation, browsing and damage caused by voles or climatic factors. Due to large establishment costs, there is a need to find methods to secure the establishment both biologically and economically. In this study the effect of plastic mulch in combination with three different plant types (short cuttings, long cuttings and rooted plants) were tested at three different sites. Five years after planting, the overall effect of mulch was an improved plant survival and growth. In most cases, long cuttings outperformed short cuttings and rooted plants. Clonal differences were present, indicating the importance of using plant material adapted to site conditions. All sites were heavily affected by browsing and during the experimental period 100% of the plants were damaged at some point. Planting poplars without fencing is therefore doubtful. Results from this study conclude that poplars can be established with success on agricultural land if proper measures are used depending on the site to be planted.     

Effects of soil preparation methods and plant types on the establishment of poplars on forest land

Key message

The success of poplar plantations on forest land was affected by soil preparation, plant type, site, and clone. Mounding in combination with large plant types (rooted plants or long cuttings) of site-adapted clones achieved the highest survival and growth.

Context

Poplars (Populus species and hybrids) are fast-growing trees used to make various products. In north European countries, they are mainly grown on agricultural land, but interest in planting poplars on forest land has increased.

Aims

Plant damage and mortality problems occur on forest land, probably due to soil conditions and competing vegetation. It is therefore of interest to investigate whether combinations of soil preparation methods and plant materials can improve establishment.

Methods

At three sites in southern Sweden, the effects of four soil preparation treatments (no soil preparation, patch scarification, mounding, soil inversion) in combination with three plant types (short cuttings, long cuttings, rooted plants) were studied.

Results

Survival and growth were significantly influenced by site, soil preparation method, plant type, and their interactions. Mounding resulted in the best overall performance on all sites. Interactions between site and plant type revealed differences in growth dependent on site conditions, but rooted plants and long cuttings were in general most successful. Patch scarification and short cuttings were associated with lower survival and growth.

Conclusion

Soil preparation is needed to support survival and early growth, but the combination of method and plant type must be adapted to site conditions. The choice of clones should also be considered.

     

Productivity and thinning effects in hybrid aspen (Populus tremula L. x P. tremuloides Michx.) stands in southern Sweden

The productivity of hybrid aspen stands in southern Sweden,originating from clone selections performed during the 1980s,was investigated. Thirteen former research and demonstrationsites were included. Repeated measurements of tree diametersand heights were taken, from which yields were estimated. Theresults indicate that the mean annual increment, obtained withoutany artificial addition of fertilizers or irrigation, will exceed20 m³ of stem wood ha^–1 a^–1 during a 20–25-yearrotation period. This corresponds to a total average woody biomassproduction, including branches, of over 8 tonnes dry matterha^–1 a^–1. These production levels show that hybridaspen is a competitive alternative for short rotation forestryin Sweden, and that the clone selection programme has greatlyenhanced productivity, compared with published growth ratesof the material previously used. For comparison, two standsthat regenerated via root suckers from material used in thebreeding programme up to the 1960s were included. They showedhigher growth than the 13 planted stands, mainly due to higherstem density and faster height development. This indicates thateven further increases in hybrid aspen yield are possible instands derived from suckers of the most recently selected clones.Thinning studies, including three different weights of thinning,were carried out on five of the sites. Five years after thestart of the treatments, stands given no thinning showed significantlyhigher current annual increment, but significantly smaller meanstem diameter than stands in which thinning was applied. However,the faster diameter development (and thus higher volumes ofvaluable wood assortments) associated with heavier thinningsmay compensate economically under current market conditionsfor the loss in total volume production.     

Biomass production and allocation, including fine-root turnover, and annual N uptake in lysimeter-grown basket willows

Annual net primary production (NPP) and N uptake were estimated for lysimeter-grown basket willows (Salix viminalis L.) during 3 years after planting. The willows were grown in a stand structure and continuously supplied with water and liquid fertilizer through drip tubes. The lysimeters contained either clay from the site or washed quartz sand. Shoot growth and leaf litter were measured and fine-root dynamics observed in minirhizotrons. Destructive samples were taken annually in late autumn and entire root systems were washed out. Dry mass and N content of all plant parts were determined. Fine-root production was estimated by two methods, based on destructive samplings and observations in minirhizotrons.

The proportion of biomass allocated below ground increased considerably when estimates based on accumulated NPP were compared with those based on standing dry mass. In the first year, 49 and 58% of annual NPP in willows grown in clay and sand, respectively, was belowground. In subsequent years the proportions were 36–38% and 33–40%. Most belowground production was fine roots. Relatively more N was used belowground in the first year than subsequently, but no substrate-induced differences were observed in the allocation pattern. Both annual NPP and N uptake was always higher in plants in clay than in those in sand: in the final 2 years, 21–22 tonnes DM ha⁻¹ year⁻¹ and 190 kg N ha⁻¹ year⁻¹ in clay, and 9–10 tonnes DM ha⁻¹ year⁻¹ and 100 kg N ha⁻¹ year⁻¹ in sand.     

Root preparation technique and storage affect results of seedling quality evaluation in Norway spruce

Evaluation of tree seedling quality is necessary for improving technology for forest nursery production and seedling handling. Nutrient status can be measured to determine seedling quality, but it can be affected by seedling handling techniques. In this study effects of root preparation technique and storage regime on content of macro nutrients (N, P, K, S, Ca, Mg) in fine roots of Norway spruce (Picea abies (L.) Karst.) plants were investigated. The root preparation techniques were: (a) rinse in tap or (b) deionised water, and (c) dry preparation. These techniques were tested on seedlings subjected to four storage regimes: (1) no storage, (2) deep freezing below −20°C, and long-term (3) cold (+1 to +3°C) and (4) frozen (−3 to −4°C) storage. From the results it was concluded that the nutrient status in needles is not sufficient to describe the whole plant nutrient status in stored dormant plants, fine roots should also be included. The results also showed that deep freezing of fine roots before nutrient analyses should be avoided. Losses of K, P, S, and Mg were substantial with this method. Deionised water or dry preparation is preferred since tap water contains substantial amounts of ions that may affect the analyses.