Short Rotation Forestry Research Articles

Soil mycobiomes in native European aspen forests and hybrid aspen plantations have a similar fungal richness but different compositions, mainly driven by edaphic and floristic factors.

The cultivation of short-rotation tree species on non-forest land is increasing due to the growing demand for woody biomass for the future bioeconomy and to mitigate climate change impacts. However, forest plantations are often seen as a trade-off between climate benefits and low biodiversity. The diversity and composition of soil fungal biota in plantations of hybrid aspen, one of the most planted tree species for short-rotation forestry in Northern Europe, are poorly studied. The goal of this study was to obtain baseline knowledge about the soil fungal biota and the edaphic, floristic and management factors that drive fungal richness and communities in 18-year-old hybrid aspen plantations on former agricultural soils and compare the fungal biota with those of European aspen stands on native forest land in a 130-year chronosequence. Sites were categorized as hybrid aspen (17-18-year-old plantations) and native aspen stands of three age classes (8-29, 30-55, and 65-131-year-old stands). High-throughput sequencing was applied to soil samples to investigate fungal diversity and assemblages. Native aspen forests showed a higher ectomycorrhizal (EcM) fungal OTU richness than plantations, regardless of forest age. Short-distance type EcM genera dominated in both plantations and forests. The richness of saprotrophic fungi was similar between native forest and plantation sites and was highest in the middle-aged class (30-55-year-old stands) in the native aspen stands. The fungal communities of native forests and plantations were significantly different. Community composition varied more, and the natural forest sites were more diverse than the relatively homogeneous plantations. Soil pH was the best explanatory variable to describe soil fungal communities in hybrid aspen stands. Soil fungal community composition did not show any clear patterns between the age classes of native aspen stands. We conclude that edaphic factors are more important in describing fungal communities in both native aspen forest sites and hybrid aspen plantation sites than forest thinning, age, or former land use for plantations. Although first-generation hybrid aspen plantations and native forests are similar in overall fungal diversity, their taxonomic and functional composition is strikingly different. Therefore, hybrid aspen plantations can be used to reduce felling pressure on native forests; however, our knowledge is still insufficient to conclude that plantations could replace native aspen forests from the soil biodiversity perspective.

Long-Term Effect of Wood Ash and Wastewater Sludge Fertilization on Tree Growth in Short-Rotation Forest Plantations on Abandoned Agricultural Land: A Case Study

Short-rotation forest plantations on former agricultural land capture CO2, provide bioeconomic materials, and mitigate climate change. This study aimed to enhance our understanding of the long-term effects of wood ash and wastewater sludge fertilization on various tree species (birch, hybrid aspen, grey alder, black alder, and hybrid alder) in short-rotation forestry plantations on abandoned agricultural land where tree growth measurements were taken over an 11-year period. After 11 years, the highest aboveground biomass (AGB) was observed for hybrid aspen clone No. 4 under wastewater sludge treatment (109.0 t ha−1), birch under wood ash treatment (34.3 t ha−1), black alder under wastewater sludge treatment (33.6 t ha−1), grey alder under wastewater sludge treatment (40.9 t ha−1), hybrid alder under control conditions (36.2 t ha−1), and hybrid aspen clone No. 28 under wood ash treatment (37.2 t ha−1). The average survival rate was 73% in control plots, 81% under wastewater sludge treatment, and 78% under wood ash treatment. Short-term positive impacts on tree growth were observed, effects that were not consistent over the long term. The impact of these treatments on tree growth varied between species, and the effects tended to diminish over time, which must be considered before fertilization.

C stocks in abandoned short rotation forestry (SRF) plantations in Central Italy

C stocks in abandoned short rotation forestry (SRF) plantations in Central Italy

Soil fungal diversity of birch plantations on former agricultural land resembles naturally regenerated birch stands on agricultural and forest land

Short-rotation forestry on former agricultural soils is a novel silvicultural system for producing woody biomass and mitigating climate change through CO2 uptake. However, tree plantations are often criticized for their low biodiversity and are sometimes referred to as “green deserts”. We hypothesize that regarding biodiversity, the spontaneous natural regeneration of birch on former agricultural lands may be preferable to plantations. In this study, we compared soil fungal diversity and composition of fast-growing silver birch (Betula pendula Roth) plantations on former agricultural lands (n = 11) with naturally regenerated birch stands on former agricultural lands (n = 11) and native forest birch stands (n = 11) at the age of 21–28 years in hemiboreal Estonia. PacBio third-generation sequencing was carried out to analyse fungal species richness and composition in the soil samples. Sequencing of the fungal ITS region from 33 birch stand soil samples yielded 2830 fungal OTUs. We found that the total fungal species richness, per sample species richness, Shannon diversity index, and Pielou's evenness index did not differ significantly between the studied stand types. However, fungal community composition of both plantations and naturally regenerated stands on former agricultural lands differed significantly from the native forest stands, indicating that previous land use (agriculture vs. forest) had a stronger effect on fungal assemblages than the used regeneration method (planting vs. natural regeneration). The relative abundance of ectomycorrhizal and arbuscular mycorrhizal fungi was higher, and the relative abundance of saprotrophic fungi was lower in plantations than in native birch dominated forest stands. Soil chemical properties were found to be weak explanatory variables for describing soil fungal richness and composition. We identified historical surrounding forest cover, stand age, stand distance from a native forest, and soil Mg content as the factors significantly affecting soil fungal communities. These results indicate that fast-growing birch plantations established on former agricultural soils or naturally regenerated stands on such soils in the Northern Europe region harbour soil fungal diversity levels similar to those of same-aged native birch forests.

Suitability of Fast-Growing Tree Species (Salix spp., Populus spp., Alnus spp.) for the Establishment of Economic Agroforestry Zones for Biomass Energy in the Baltic Sea Region

The main goal of this review was to provide an assessment of the potential of fast-growing tree species for the suitable transformation of agroforestry areas for biomass production in the Baltic Sea region. Our interest was to highlight the research on the management process of agroforestry zones by establishing short rotation plantations with the tree species Salix spp., Populus spp. and Alnus spp. to explore the prospects of planning these zones as biomass producers. Short rotation forestry (SRF) with trees whose rotation period is 15 to 30 years, depending on the species, is the most suitable approach for management of these agroforestry zones. Willows (Salix spp.) and poplars (Populus spp.) are suitable for short rotation coppice (SRC), as these tree species can be harvested at much shorter intervals, respectively, 1–5 and 4–10 years, facilitating their use in agricultural systems. The rotation period of Alnus spp. in short rotation plantations for energy wood production is generally assessed to be 15–30 years. The black alder plantations in agroforestry zones are used for sawnwood and firewood production, with a rotation period of 20–40 years. The calculated repayment period of the economic agroforestry zone is about 10–15 years, if 2021 costs and prices are used.

The Value of Hybrid Aspen Coppice Investment under Different Discount Rate, Price and Management Scenarios: A Case Study of Estonia

Hybrid aspen is one of the most promising tree species for short-rotation forestry in Northern Europe. After the clearcutting of hybrid aspen plantation, the next generation arises from root and stump sprouts. The economic feasibility of different management strategies of hybrid aspen coppice stands has not yet been comprehensively evaluated in Northern Europe. We compared the land expectation values (LEVs) of hybrid aspen coppice stands managed according to four scenarios: three early thinning methods (corridor, cross-corridor and single-tree) followed by conventional management and intensive bioenergy production (repeated harvests in 5-year rotations) over a 25-year period in hemiboreal Estonia. We considered the historic price volatility of aspen wood assortments under various discount rates (1–20%). We found that the 25-year rotation with different early thinning methods was more profitable than short bioenergy cycles in the case of low discount rates (<5%). The LEV of short coppice cycles for only bioenergy production became more profitable in comparison with those by thinning methods, when higher discount rates (>10%) were applied. Hybrid aspen coppice stands can be managed profitably, but more risks are taken when the management strategy focuses only on bioenergy production.

The Impact of Different Environmental Conditions during Vegetative Propagation on Growth, Survival, and Biochemical Characteristics in Populus Hybrids in Clonal Field Trial

To have a cleaner environment, good well-being, and improve the health of citizens it is necessary to expand green urban and suburban areas using productive and adapted material of tree species. The quality of urban greenery, resistance to negative climate change factors and pollution, as well as efficiency of short-rotation forestry in suburban areas, depends primarily on the selection of hybrids and clones, suitable for the local environmental conditions. We postulate that ecogenetic response, phenotypic plasticity, and genotypic variation of hybrid poplars (Populus L.) grown in plantations are affected not only by the peculiarities of hybrids and clones, but also by environmental conditions of their vegetative propagation. The aim of the present study was to estimate growth and biochemical responses, the phenotypic plasticity, genotypic variation of adaptive traits, and genetically regulated adaptability of Populus hybrids in field trials which may be predisposed by the simulated contrasting temperature conditions at their vegetative propagation phase. The research was performed with the 20 cultivars and experimental clones of one intraspecific cross and four different interspecific hybrids of poplars propagated under six contrasting temperature regimes in phytotron. The results suggest that certain environmental conditions during vegetative propagation not only have a short-term effect on tree viability and growth, but also can help to adapt to climate change conditions and grow successfully in the long-term. It was found that tree growth and biochemical traits (the chlorophyll A and B, pigments content and the chlorophyll A/B ratio) of hybrid poplar clones grown in field trials, as well as their traits’ genetic parameters, were affected by the rooting-growing conditions during vegetative propagation phase. Hybrids P. balsamifera × P. trichocarpa, and P. trichocarpa × P. trichocarpa have shown the most substantial changes of biochemical traits across vegetative propagation treatments in field trial. Rooting-growing conditions during vegetative propagation had also an impact on coefficients of genotypic variation and heritability in hybrid poplar clones when grown in field trials.

Wastewater Treatment and Wood Production of Willow System in Cold Climate

This article studied how wastewater treatment performance of a short rotation forestry system was influenced by the seasonal operational changes under the extreme Mongolian winter conditions. For this reason, two beds planted with Willow (Salix spec.) and Poplar (Populus spec.) trees were operated over a period of two years under two different seasonal conditions: (A) “external winter storage” and (B) “internal winter storage” of pretreated wastewater. For operational condition A, the tree-bed was loaded with wastewater for only 4 summer months. For this operational condition it was considered that the treatment bed was fed with primary treated wastewater, which was stored in a sealed pond during the remaining 8 months. The other Bed B was irrigated throughout the year (12 months) with the same daily loading rate. In winter, the wastewater accumulated as ice in the tree-bed. Bed A, with external winter storage, showed mass removal percentage up to 95%, while the bed with internal winter storage showed mass removal rates up to 86% for pollutants such as COD, BOD5, TN, and TP. A high yield of biomass was recorded for both beds with slight differences. Based on the results, a design recommendation was developed for full-scale systems of short rotation coppice irrigated with wastewater under various operational conditions, which show these systems to be a viable method for treating wastewater and producing biomass for energy production in Mongolia.

Isoprene and monoterpene emissions from alder, aspen and spruce short-rotation forest plantations in the United Kingdom

Abstract. An expansion of bioenergy has been proposed to help reduce fossil-fuel greenhouse gas emissions, and short-rotation forestry (SRF) can contribute to this expansion. However, SRF plantations could also be sources of biogenic volatile organic compound (BVOC) emissions, which can impact atmospheric air quality. In this study, emissions of isoprene and 11 monoterpenes from the branches and forest floor of hybrid aspen, Italian alder and Sitka spruce stands in an SRF field trial in central Scotland were measured during two years (2018–2019) and used to derive emission potentials for different seasons. Sitka spruce was included as a comparison as it is the most extensive plantation species in the UK. Winter and spring emissions of isoprene and monoterpenes were small compared to those in summer. Sitka spruce had a standardised mean emission rate of 15 µgCg-1h-1 for isoprene in the dry and warm summer of 2018 – more than double the emissions in 2019. However, standardised mean isoprene emissions from hybrid aspen were similar across both years, approximately 23 µgCg-1h-1, and standardised mean isoprene emissions from Italian alder were very low. Mean standardised total monoterpene emissions for these species followed a similar pattern of higher standardised emissions in the warmer year: Sitka spruce emitting 4.5 and 2.3 µgCg-1h-1 for 2018 and 2019, aspen emitting 0.3 and 0.09 µgCg-1h-1, and Italian alder emitting 1.5 and 0.2 µgCg-1h-1, respectively. In contrast to these foliage emissions, the forest floor was only a small source of monoterpenes, typically 1 or 2 orders of magnitude lower than foliage emissions on a unit of ground area basis. Estimates of total annual emissions from each plantation type per hectare were derived using the MEGAN 2.1 model. The modelled total BVOC (isoprene and monoterpenes) emissions of SRF hybrid aspen plantations were approximately half those of Sitka spruce for plantations of the same age. Italian alder SRF emissions were 20 times smaller than from Sitka spruce. The expansion of bioenergy plantations to 0.7 Mha has been suggested for the UK to help achieve net-zero greenhouse gas emissions by 2050. The model estimates show that, with such an expansion, total UK BVOC emissions would increase between <1 % and 35 %, depending on the tree species planted. Whereas increases might be small on a national scale, regional increases might have a larger impact on local air quality.

Development of a Modality-Invariant Multi-Layer Perceptron to Predict Operational Events in Motor-Manual Willow Felling Operations

Motor-manual operations are commonly implemented in the traditional and short rotation forestry. Deep knowledge of their performance is needed for various strategic, tactical and operational decisions that rely on large amounts of data. To overcome the limitations of traditional analytical methods, Artificial Intelligence (AI) has been lately used to deal with various types of signals and problems to be solved. However, the reliability of AI models depends largely on the quality of the signals and on the sensing modalities used. Multimodal sensing was found to be suitable in developing AI models able to learn time and location-related data dependencies. For many reasons, such as the uncertainty of preserving the sensing location and the inter- and intra-variability of operational conditions and work behavior, the approach is particularly useful for monitoring motor-manual operations. The main aim of this study was to check if the use of acceleration data sensed at two locations on a brush cutter could provide a robust AI model characterized by invariance to data sensing location. As such, a Multi-Layer Perceptron (MLP) with backpropagation was developed and used to learn and classify operational events from bimodally-collected acceleration data. The data needed for training and testing was collected in the central part of Romania. Data collection modalities were treated by fusion in the training dataset, then four single-modality testing datasets were used to check the performance of the model on a binary classification problem. Fine tuning of the regularization parameters (α term) has led to acceptable testing and generalization errors of the model measured as the binary cross-entropy (log loss). Irrespective of the hyperparameters’ tunning strategy, the classification accuracy (CA) was found to be very high, in many cases approaching 100%. However, the best models were those characterized by α set at 0.0001 and 0.1, for which the CA in the test datasets ranged from 99.1% to 99.9% and from 99.5% to 99.9%, respectively. Hence, data fusion in the training set was found to be a good strategy to build a robust model, able to deal with data collected by single modalities. As such, the developed MLP model not only removes the problem of sensor placement in such applications, but also automatically classifies the events in the time domain, enabling the integration of data collection, handling and analysis in a simple less resource-demanding workflow, and making it a feasible alternative to the traditional approach to the problem.

Efeito da adubação mineral e densidade de plantio nas características dendrométricas de plantações de eucalipto de rápido crescimento

Para alcançar um maior equilíbrio nutricional nas plantações de eucalipto conduzidas no sistema florestal de curta rotação (SFCR), este estudo teve como objetivo avaliar o efeito de diferentes espaçamentos de plantio (1429 árvores ha-1 a 7142 árvores ha-1) e três regimes de adubação (D1 – 25% da dose comercial, D2 – 50% da dose comercial e D3 – dose comercial) nas características dendrométricas e no índice de competição entre as árvores nas plantações de clones híbridos de Eucalyptus urophylla × Eucalyptus grandis aos dois anos de idade. Por meio do ajuste da função Weibull dois parâmetros, observou-se uma maior frequência de árvores nas classes diamétricas superiores com o aumento da área útil por árvore e da dose de adubação, o que indicou uma menor competição entre os indivíduos, sendo esse comportamento corroborado pelo maior índice de espaçamento relativo encontrado. O tratamento com 3571 árvores ha-1 (2,8 m × 1,0 m) e com aplicação de metade da dose comercial praticada tradicionalmente nas plantações de eucalipto seria aquele com maior sustentabilidade nutricional.

Comparison of the Initial Growth of Different Poplar Clones on Four Sites in Western Slovakia\u2014Preliminary Results

This study was conducted to evaluate four hybrid poplar comparison tests along a groundwater availability gradient in Western Slovakia. The weather fluctuation during the 3-year study period was described with indices, such as the Forestry Aridity Index (FAI) or the hydrothermal coefficient (HTC). The soil chemical and physical parameters were determined from soil samples from the two upper horizons. The nutrient status and supply of the trees were categorized based on leaf elemental analysis. Altogether, 21 different clones from 6 genomic groups were compared. The survival (SRV), diameter at breast height (DBH), and height of the trees (H) had been measured annually since the plantations were established, and from these measurements, mean annual height increment (MAHI) values were derived. These weather, edaphic, and clonal factors were evaluated and compared. Significant effects of the site (edaphic factors) were found as the primary source of variance and clonal differences as secondary sources of variance among the growth of trees. The interaction of site × clone effects was not significant. The results showed that for short rotation forestry (SRF), the site parameters—especially groundwater availability—are key factors.

Nutrient (N, P, K) use efficiency and nitrogen balance in a bioenergy plantation of Populus deltoides clone Lux in San Piero A Grado (Pisa), Italy

Energy crops have proved to be a viable alternative to fossil fuels. However, high biomass production always means that large quantities of nutrients from the soil are removed at harvest. The goal of this work was to estimate nutrient (nitrogen, phosphorous, potassium) use efficiency (NUE) and nitrogen balance in an eight-year-old Populus deltoides clone Lux, short rotation forestry under two cutting cycles, every two (biennial) and three (triennial) years, carried out under Mediterranean climate conditions. Results indicate that NUE, for all the analyzed elements, contained variations with slightly higher values for nitrogen and phosphorous in the triennial cycle. Although poplar cultivation has a positive nutrient efficiency, in terms of nitrogen, there is significant loss of this element in the crop cycle.

Accumulation of chemically degraded organic carbon in the soil profile of Chinese fir plantations

Short-rotation forestry relies on frequent harvests of fast-growing trees, which could deplete soil fertility and soil organic carbon (SOC) reserves. Our objective was to measure the accumulation of SOC fractions, namely the dissolved organic carbon, microbial biomass carbon, particulate organic carbon, permanganate-oxidizable carbon, and non-oxidizable organic carbon, in the soil profile of a Chinese fir plantation. Chronosequences of Chinese fir aged 7, 12, and 33 yr were sampled at depths of 0–20 cm, 20–40 cm, and 40–60 cm. The SOC stock (0–60 cm) was unchanged in the first 12 yr, but after 33 yr, there was a 41%–56% increase in the SOC stock, which reached 81.2 Mg ha−1 (P < 0.05). Permanganate-oxidizable carbon increased with time in the 0–20 cm layer but not in deeper soil depths, whereas non-oxidizable organic carbon accumulated preferentially in the 40–60 cm layer of the soil profile. Inputs of chemically complex plant litter in the soil profile may be important to maintain the oxidizable and non-oxidizable organic carbon in Chinese fir plantations.

Evaluation of Bioenergy Potential and Relative Impact of Microclimate Conditions for Sustainable Fuel Pellets Production and Carbon Sequestration of Short-Rotation Forestry (Populus × Canadensis Moench.) in Reclaimed Land, South Korea: Three-Year Monitoring

It is important to manage sustainable short-rotation coppices (SRCs), having an important role in carbon sink and bioenergy output, because most of SRCs in South Korea were established on reclaimed land. However, during the last three years, the growth pattern of the SRCs was remarkably changed with soil condition. This study aimed to identify the sustainability of SRCs used for carbon storage, biomass and fuel pellet production, monitoring the neighboring vegetation of SRCs by land-use exchange, examine physiological changes of poplar in a seasonal trend, and to evaluate whether poplar is suitable for making wood pellets over time. The calculated biomass yield per area of poplar grown was 103.07 Mg per total area (55.6 ha), and volumes of carbon dioxide absorption were estimated to be 329.72 Mg CO2. Wood pellet quality based on the criteria scored third grade, indicating that poplar is appropriate to be manufactured as fuel pellets. Moreover, monitoring of the flora distribution in SRCs revealed changes in species composition. As halophyte was increased during drought, soil organic matter, net growth and total chlorophyll of poplar were significantly decreased. These findings indicate that physiological changes and growth pattern of SRCs may be negatively affected by microclimate and provide better understanding for the effective management of SRCs amid environmental changes.

Ecogenetic plasticity and genetic variation in Populus hybrids under the impact of simulated climate change related stressors


 To meet the needs of carbon sequestration and production of raw materials from renewable natural resources for the timber market of the European Union, it is necessary to expand forest plantation areas. The efficiency of short rotation forestry depends primarily on the selection of hybrids and clones, suitable for the local environmental conditions. We postulate that ecogenetic response, ecogenetic plasticity and genotypic variation of different hybrids of poplars (Populus L.) depend both on the type of stressors (spring frosts, summer drought, increased UV-B radiation, warm winters) and peculiarities of the cross-bred species as well as on their genetic preadaptations to native environmental conditions of their origin. The aim of the study was to estimate the ecogenetic plasticity, genotypic variation of adaptive traits and adaptability of Populus hybrids under simulated conditions of the expected climate change.
 The research was performed with the cultivars and experimental clones of three different intraspecific hybrids of poplars (P. nigra L., P. deltoides Bartr. ex Marsh, and P. trichocarpa Torr. & Gray.) and four interspecific hybrids of poplars (P. deltoides L. × P. nigra, P. deltoides × P. trichocarpa, P. maximowiczii A. Henry × P. trichocarpa, and P. balsamifera L. × P. trichocarpa).
 Simulated spring frosts and summer drought treatments had a substantial impact on growth of trees, but the hybrid and clone effects were also significant and showed that many hybrids and clones in general retain their features/differences under stressful environmental conditions. A strongly expressed hybrid and clone interactions with simulated frost and drought effects (genotype-environment interaction, G × E) showed different ecogenetic response, plasticity and specific ecological preferences of the clones and hybrids. The sensitivity of hybrids to UV-B radiation varied and depended on the origin of their parental trees and this sensitivity partially reflected their susceptibility also to other stressors. Warm winters adversely effected the growth of some hybrids while others - P. nigra × P. nigra and P. trichocarpa × P. trichocarpa, which parents originated from the southern part of their natural distribution range have increased their growth. This treatment also resulted in reduction of the heritability and genotypic variation of growth traits.
 
 Keywords: poplars, clones, genotype-environment interaction, genetic variation, heritability

Intensive Mechanical Site Preparation to Establish Short Rotation Hybrid Poplar Plantations—A Case-Study in Québec, Canada

Because they generate more wood per area and time, short rotation plantations are likely to play an increasing role in meeting the global increase in the demand for wood fiber. To be successful, high-yield plantations require costly intensive silviculture regimes to ensure the survival and maximize yields. While hybrid poplar (Populus spp.) is frequently used in intensive, short rotation forestry, it is particularly sensitive to competition and resource levels. Mechanical site preparation is thus of great importance to create microsites that provide sufficient light levels and adequate soil water and nutrient availability. We conducted an experiment in Québec (Canada) to compare two intensive site preparation treatments commonly used to establish hybrid poplar. We compared the effects of double-blade site preparation (V-blade), mounding and a control on hybrid poplar growth and nutritional status four growing seasons after planting on recently harvested forested sites. We also evaluated the effects of site preparation and planted poplar on inorganic soil N. Our results confirmed general positive effects of site preparation on the early growth of hybrid poplar clones. After four growing seasons, survival was higher in the mounding treatment (99%) than in the V-blade (91%) and the control (48%). Saplings planted in the V-blade and in the mounding treatments had mean diameters that were respectively 91% and 155% larger than saplings planted in the control plots. Saplings were 68% taller in the mounding treatment than the control plots, but differences between the V-blade and controls were not significant. We did not detect significant effects of site preparation or the presence of planted hybrid poplar on soil inorganic N. Sapling foliar nutrient concentrations were not influenced by the site preparation treatments. Based on these results, mounding appears to be a good management approach to establish hybrid poplar plantations under the ecological conditions we have studied, as it is less likely to cause erosion because of the localized nature of the treatment. However, these environmental benefits need to be balanced against economic and social considerations.

Biomass and Volume Modeling along with Carbon Concentration Variations of Short-Rotation Poplar Plantations

Short-rotation forestry is of interest to provide biomass for bioenergy and act as a carbon sink to mitigate global warming. The Poplar tree (Populus × xiaohei) is a fast-growing and high-yielding tree species in Northeast China. In this study, a total of 128 Populus × xiaohei trees from the Songnen Plain, Heilongjiang Province, Northeastern China, were harvested. Several available independent variables, such as tree diameter at breast height (D), tree’s total height (H), crown width (CW), and crown length (CL), were differently combined to develop three additive biomass model systems and eight stem volume models for Populus × xiaohei tree. Variance explained within the three additive biomass model systems ranged from 83% to 98%, which was lowest for the foliage models, and highest for the stem biomass models. Similar findings were found in the stem volume models, in which the models explained more than 94% of the variance. The additional predictors, such as H, CL, or CW, evidently enhanced the model fitting and performance for the total and components biomass along with the stem volume models. Furthermore, the biomass conversion and expansion factors (BCEFs) of the root (118.2 kg/m3), stem (380.2 kg/m3), branch (90.7 kg/m3), and foliage (31.2 kg/m3) were also calculated. The carbon concentrations of Populus × xiaohei in root, stem, branch, and foliage components were 45.98%, 47.74%, 48.32%, and 48.46%, respectively. Overall, the newly established models in this study provided complete and comprehensive tools for quantifying the biomass and stem volume of Populus × xiaohei, which might be essential to be specifically utilized in the Chinese National Forest Inventory.

Herbivore Gender Effects on Volatile Induction in Aspen and on Olfactory Responses in Leaf Beetles

Hybrid aspen (Populus tremula × tremuloides Michx.) is a fast-growing tree species used for short-rotation forestry in northern latitudes. Aspen species have a rich herbivore fauna, including defoliating leaf beetles that induce emissions of volatile organic compounds (VOCs) when feeding on aspen leaves. We investigated the differential induction of VOCs by male and female Phratora laticollis leaf beetles feeding on hybrid aspen and the differences in the orientation of beetles in response to gender-specific induced VOCs. The hypotheses for the study were (1) the VOCs in the headspace of plants infested with beetles of the two genders individually and in mixed aggregates would vary subtly, and (2) foraging adult beetles would be able to detect differences in VOC blends and use them to fine-tune their orientation choices. In Y-tube bioassays, both females and males preferred VOCs from leaves damaged by one gender (females or males) over undamaged leaves. However, if leaves were damaged by a two-gender population, neither females nor males indicated a preference over volatiles of undamaged leaves. Leaves damaged by both beetle genders simultaneously had significantly increased green leaf volatile (GLV), benzenoid and homoterpene emissions compared to undamaged leaves. Emissions of these compounds possibly indicate higher herbivore pressure and a higher risk of attack by parasitoids and predators and could thus be the cause of the lack of beetle preference. Our findings provide new basic information on gender-based host plant selection by herbivores and may be helpful in the development of sustainable biogenic VOC-based herbivore-control methods for intensive short-rotation hybrid aspen production.

Development of Willow Tree Yield-Mapping Technology.

With today’s environmental challenges, developing sustainable energy sources is crucial. From this perspective, woody biomass has been, and continues to be, a significant research interest. The goal of this research was to develop new technology for mapping willow tree yield grown in a short-rotation forestry (SRF) system. The system gathered the physical characteristics of willow trees on-the-go, while the trees were being harvested. Features assessed include the number of trees harvested and their diameter. To complete this task, a machine-vision system featuring an RGB-D stereovision camera was built. The system tagged these data with the corresponding geographical coordinates using a Global Navigation Satellite System (GNSS) receiver. The proposed yield-mapping system showed promising detection results considering the complex background and variable light conditions encountered in the outdoors. Of the 40 randomly selected and manually observed trees in a row, 36 were successfully detected, yielding a 90% detection rate. The correctly detected tree rate of all trees within the scenes was actually 71.8% since the system tended to be sensitive to branches, thus, falsely detecting them as trees. Manual validation of the diameter estimation function showed a poor coefficient of determination and a root mean square error (RMSE) of 10.7 mm.