Tree Nutrition Research Articles

Nutrient status of apple leaves not affected by three years of irrigation using partial rootzone drying

AbstractPartial rootzone drying (PRD) is a water‐saving irrigation technology that may affect apple (Malus domestica Borkh cv. Golden Delicious/Malling7)‐tree nutrition if applied for an extended period. The objective of this study was to test the hypothesis that long‐term application of PRD causes seasonal changes in macro‐ and micronutrients of apple leaves. The irrigation treatments were: (1) commercial irrigation as control (CI) and (2) PRD. After 3 years of evaluation, PRD irrigation had saved about 3240 m3 of water per hectare. Leaf xylem water potential was slightly lower in the PRD treatment than in CI. The seasonal concentration of macro‐ and micronutrients was comparable between treatments, although significant differences were found at times. The macronutrient concentrations were within the normal range in PRD apple leaves. All micronutrient concentrations were slightly above the normal range except for Zn, which was slightly below the normal range. No physiological disorders associated with plant nutrition were observed on leaves or fruits. Therefore, data suggest that PRD did not alter apple‐tree nutrition during the 3‐year trial. Thus, PRD may be feasible for apple production in Central Mexico. However, further studies need to be conducted in those regions where groundwater is the main water source for irrigation and rain is negligible, particularly during the growing season.

Chinese Chestnut (Castanea mollissima) as a Niche Crop in the Central Region of the United States

Chinese chestnut (Castanea mollissima Blume) is an exotic species that has potential as a niche crop. As a nut crop, it is relatively precocious in its bearing habit and has resistance to chestnut blight, tolerance to low winter temperatures, and relatively few pests. Current prices for fresh chestnuts are as much as $14/kg. Most U.S. chestnut growers (64%) have small orchards (less than 4 ha) and have been producing this crop for less than 10 years. Commercial chestnut production is low (≈680,000 kg) in the United States, but it is a relatively new industry in the central region. Limitations to growing this crop include a shortage of grafted trees, high tree costs, low yield efficiency, and high labor costs resulting from limited large-scale harvest equipment in the United States. However, results of ongoing research using cultivars on dwarfing rootstocks, thinning of secondary (2°) flowers, and improved tree nutrition will likely enhance profitability of production. In a 2003 Missouri survey, 67% of those interviewed had never consumed Chinese chestnuts but associated chestnut roasting with holidays. Chinese chestnuts provide health benefits. including a source of dietary fiber, a significant amount of vitamin C, no cholesterol, and are gluten-free.

Ectomycorrhizal fungi: the symbiotic route to the root for phosphorus in forest soils

Many forest trees have evolved mutualistic symbioses with ectomycorrhizal (ECM) fungi that contribute to their phosphorus (P) nutrition. Forest productivity is frequently limited by P, a phenomenon that is likely to become more widespread under future conditions of elevated atmospheric CO2 concentration [CO2]. It is thus timely that this review considers current understanding of the key processes (absorption, translocation and transfer to the plant host) in ECM fungus-mediated P nutrition of forest trees. Solubilisation of inorganic P (Pi) and hydrolysis of organic P by ECM fungi in soil occurs largely at the growing mycelial front, where Pi absorption is facilitated by high affinity transporters. While large gaps remain in our understanding of the physiological and molecular mechanisms that underpin movement of P in ECM mycelia in soil and P transfer to the plant, host P demand seems likely to be a key driver of these processes. ECM fungi may make considerable contributions to meeting the likely increased P demand of trees under elevated [CO2] via increased colonization levels, shifts in ECM fungal community structure and changed patterns of EMM production. Further research into the spatial scale of ECM-mediated P movements in soil, along with the interplay between ECM fungi and other soil microflora is advocated.

Bacterial weathering and its contribution to nutrient cycling in temperate forest ecosystems

Unlike farmland, forests growing on acidic soils are among the terrestrial ecosystems that are the least influenced or amended by man. Forests which developed on acidic soils are characterized by an important stock of inorganic nutrients entrapped in poorly weatherable soil minerals. In this context, the mineral-weathering process is of great importance, since such minerals are not easily accessible to tree roots. To date, several bacterial genera have been noted for their ability to weather minerals and, in the case of some of them, to improve tree nutrition. Nevertheless, few studies have focused their analyses on mineral-weathering bacterial communities in relation to geochemical cycles and soil characteristics, their ecological origin, associated tree species and forest management practices. Here we discuss the heterogeneity of the mineral-weathering process in forest soils and present what is known concerning the taxonomic and functional characteristics of mineral-weathering bacteria, as well as the different locations where they have been isolated in forest soils. We also discuss the biotic and abiotic factors that may influence the distribution of these bacteria, such as the effect of tree species or forest management practices.

Application of Multi-Spectral Imaging Technique in the Determination of Leaves Nitrogen Level of Fruit Tree

A new optical instrument for fast determination of pear leaves nitrogen status was designed and fabricated. A multi-spectral imaging system was used as optical detector. In the paper, the principle of multi-spectral imaging for the measurement of leaves nitrogen status was first introduced. Then, the method of using error back propagation artificial neural network (BP-ANN) for calibration modeling was elaborated. Mean reflective light intensities in all images covering blue, green, red and infrared wavelength were taken as the input data to BP-ANN. The structure of BP-ANN with three layers has been optimized to minimize its calibration error. In the test, total 200 leave samples picked from Huang-hua pear trees planted in three orchards with different nitrogen fertilizing schemes. Among them, 150 samples were selected randomly out as for calibration set with the remaining 50 for prediction set. The result shows that correlation coefficient of R2 between predicted and measured values of nitrogen content reaches 0.82 with maximum prediction error less than 4.72(SPAD). The study suggests that the new optical method integrating multi-spectral images with BP-ANN is promising for fast diagnosis of fruit tree nutrition status.

An experimental facility for free air humidity manipulation (FAHM) can alter water flux through deciduous tree canopy

A facility for free air humidity manipulation (FAHM) was established to investigate the effect of increased air humidity on trees’ performance and their canopy functioning with respect to rising air humidity predicted for Northern Europe. The FAHM system enables air relative humidity (RH) to be increased up to 18 units (%) over the ambient level during mist fumigation, depending on the wind speed inside the experimental stand. Water was dispersed inside 14 × 14 m experimental plots in the form of mist with an average particle size of 50 μm from June to August in 2008, and from May to September in 2009. The average increase in RH was 7 units (%) over the whole period of humidification in 2008 ( P < 0.05). The average diurnal stem sap flux density per unit projected leaf area ( F) in silver birch ( Betula pendula Roth.) trees was 24.8% ( P < 0.05) and 27.2% ( P < 0.01) higher in control (C) plots compared to humidification (H) plots during misting in 2008 and 2009, respectively. However, the difference between C and H plots was statistically insignificant ( P > 0.05) in silver birch on the days without misting. In hybrid aspen ( Populus tremula L. × P. tremuloides Michx.) the average difference in F between C and H plots was 61.1% ( P < 0.001) during mist fumigation in the summer of 2009. Nevertheless, the difference was considerable (38.8%; P < 0.001) also on the days without misting, reflecting the impact of plant inner factors on F as a result of long-term acclimation to fumigation. The leaves of silver birch in a humidified plot demonstrated up to 2.4 °C lower ( P < 0.05) leaf temperature ( T L) compared to the control plot in 2009. The decline in T L decreased the humidity gradient between leaf and air by about 1/3, whereas 2/3 of the effect was caused directly by changes in air humidity in the leaf boundary layer. Our preliminary data suggest that the FAHM experimental facility enables water fluxes through a deciduous tree canopy to be reduced and this effect is attributable both to the increased air humidity and decreased leaf temperature. Changes in these two basic factors may create considerable differences in the physiology, anatomy and nutrition of a whole tree, also affecting forest functioning in the light of global climate change.

Long term effects of whole tree harvesting on soil carbon and nutrient sustainability in the UK

The practice of harvesting forest residues is rapidly increasing due to rising demand for renewable energy. However, major concerns have been raised about the sustainability of this practice and its net impact on long term soil ability to support forest productivity, particularly through second and subsequent rotations. In this study, soil chemical properties such as acidity, total N and C, available NO3–N and NH4–N and exchangeable cations were measured in all horizons in peaty gleys soils under one of the oldest experiments in Europe—a 28-year-old second rotation stand of Sitka spruce (Picea sitchensis), in Kielder forest, UK. Treatments included Whole Tree Harvesting (WTH—of all above ground biomass), Conventional stem-only harvesting (CH) of the first rotation crop, and repeated Fertilisation (FE) after the planting of the second rotation forest. This study demonstrates the soil changes underpinning the reduced second rotation tree productivity on these acidic upland sites under WTH, a further 18 years after the investigation by Proe and Dutch (1994). Overall, WTH increased soil acidity significantly (p < 0.05) and reduced soil base saturation whilst FE reduced soil acidity (p < 0.05) and increased soil base saturation as compared to CH. Soil moisture was significantly higher (p < 0.01) under WTH compared to CH and FE plots. There was no evidence that WTH decreased soil organic carbon (SOC) and soil nitrogen (N), but to the contrary there were significantly (p < 0.01) higher concentrations and stocks of total C and N in the WTH soils compared with CH and FE. The depletion of SOC and N in CH and FE plots was attributed to much higher soil mineralisation rates associated with the brash and fertilisation as compared to the WTH plots, where significantly less soil available NO3–N (p < 0.01) was found. In the long term WTH on peaty gley soils appears positive for soil C and N storage. However, WTH had a long term negative impact on soil and tree nutrition of K+ and P, which are currently at deficient levels, but has had a stabilising effect on tree N nutrition as measured in twigs and needles. These results suggest that whilst WTH lead to a reduction in aboveground tree biomass compared to conventional harvest, these practices on selected soil types and certain sites may be beneficial for soil C and N sequestration. The overall findings of this study imply that cost benefit analyses for each site should be carried out before decisions are made on the appropriate type of forest operations (harvesting and replanting), considering both geology and soils in order to serve both environmental benefits, long term sustainability and the available biomass production for timber and biofuel.

Replacement of wildfire by whole-tree harvesting in jack pine forests: Effects on soil fertility and tree nutrition

Large areas of northern coniferous forests once naturally maintained by stand-replacing wildfires have shifted to an anthropogenic disturbance regime of clearcut harvesting followed by natural or artificial regeneration, with unknown consequences for soil biogeochemical processes. We used a comparative approach to investigate the effects of whole-tree harvesting (WTH) vs. stand-replacing wildfire (WF) on soil C and nutrient availability, and nutrition and growth of the succeeding stand, in jack pine ( Pinus banksiana) forests of northern Lower Michigan. We compared total carbon (C), total nitrogen (N), potential N mineralization, and extractable phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) among stands regenerated via WTH or WF in two age classes (4–7 years and 12–18 years). We also measured jack pine foliar nutrition and height growth in these same stands, as well as estimating the contribution of legacy dead wood to ecosystem nutrient capital in young stands. We found some evidence in support of our hypothesis that WTH would leave behind greater pools of soil C and N, but lower pools of P and base cations. However, the differences we observed were confined entirely to surface organic horizons, with the two disturbance regimes indistinguishable when viewed cumulatively to our maximum sampling depth of 30 cm. Estimates of nutrient pools in legacy wood inherited by young jack pine stands were also small in comparison to total soil pools (ranging from 1 to 9% depending on the element), suggesting that decomposition and nutrient release from this material is not likely to result in noticeable differences in soil fertility later in stand development. Similar levels of soil nutrients between WTH- and WF-origin stands were reflected in our measures of jack pine foliar nutrition and height growth, which were both unaffected by mode of stand origin. Results from this study suggest that soil nutrient levels following WTH fall within the natural range of variation produced by WF in these jack pine forests; however, comparison with a similar study on boreal jack pine suggests that latitudinal effects on O-horizon nutrient capital may influence the degree to which WTH matches the effects of WF on soil nutrient availability.

Global climate change and tree nutrition: influence of water availability

The effects of global climate change will regionally be very different, mainly causing considerable changes in temperature and water availability. For Central Europe, for example, increased temperatures are predicted, which will cause increased frequencies and durations of summer drought events. On the other hand, the predicted changes in precipitation patterns will lead to enhanced rainfall during winter and spring, thereby increasing the risk of flooding in Central and Northern Europe. Depending on the sensitivity to reduced water availability on the one hand and oxygen depletion due to waterlogging on the other, physiological performance, growth and competitive ability of trees may be adversely affected. Both drought and excess water availability impair the mineral nutrition of trees by influencing on the one hand the nutrient availability in the soil and on the other hand the physiology of the uptake systems mainly of the mycorrhizal tree roots. Extreme water regimes also change interaction patterns among plants and between plants and microorganisms, and alter the carbon balance of trees and ecosystems. Here we summarize and discuss the present knowledge on tree nutrition under altered water availability as expected to be more common in the future. The focus is on tree mineral nutrient uptake and metabolism as well as on the interaction between carbon allocation and the mineral nutrient balance as affected by reduced and excess water availability.

Global climate change and tree nutrition: effects of elevated CO2 and temperature

Although tree nutrition has not been the primary focus of large climate change experiments on trees, we are beginning to understand its links to elevated atmospheric CO₂ and temperature changes. This review focuses on the major nutrients, namely N and P, and deals with the effects of climate change on the processes that alter their cycling and availability. Current knowledge regarding biotic and abiotic agents of weathering, mobilization and immobilization of these elements will be discussed. To date, controlled environment studies have identified possible effects of climate change on tree nutrition. Only some of these findings, however, were verified in ecosystem scale experiments. Moreover, to be able to predict future effects of climate change on tree nutrition at this scale, we need to progress from studying effects of single factors to analysing interactions between factors such as elevated CO₂, temperature or water availability.

OVERCOMING IRON DEFICIENCY CHLOROSIS IN CITRUS THROUGH INTERCROPPING WITH PERENNIAL GRASS SPECIES

The objective of this experiment was to investigate the influence of intercropping with three different perennial grass species (Festuca ovina L., Festuca rubra subsp. tricophylla L. and Poa nemoralis L.) on the Fe nutritional status of citrumelo 'Swingle' (Citrus paradisi Macf. × Poncirus trifoliata), a highly Fe chlorosis susceptible citrus rootstock. One-year old citrumelo plants were grown in pots on calcareous soil-sand mixture under greenhouse conditions and treated as follows: 1) citrumelo plants grown in a monoculture system (without a companion crop); 2) citrumelo plants fertilized with 18.6 mg Fe per plant in form of FeEDDHA; 3) citrumelo plants separately intercropped with the three perennial grass species. These grasses were sown at a rate of 3 seeds cm -2 , mowed only one time and allowed to re-grow. The experiment lasted five months. Chlorophyll measurements were performed on the youngest fully expanded leaves in terms of SPAD index and at the end of the experiment leaf chlorophyll content (μg cm -2 ), leaf length and width and dry weight of young shoots were determined. Intercropping citrumelo plants with F. rubra was effective almost as FeEDDHA in preventing the development of leaf chlorosis and improving their growth compared to the control plants, while those intercropped with F. ovina overcame Fe deficiency symptoms only after mowing/clipping this grass species. The Poa nemoralis did not demonstrate any potential to prevent leaf chlorosis or improve the growth of citrumelo plants. These results indicate that only Fe-efficient perennial grass species can be utilized as an effective ecological orchard floor management practice to improve the Fe nutrition of fruit trees grown on calcareous soils.

Influence of forest trees on the distribution of mineral weathering-associated bacterial communities of the Scleroderma citrinum mycorrhizosphere.

In acidic forest soils, availability of inorganic nutrients is a tree-growth-limiting factor. A hypothesis to explain sustainable forest development proposes that tree roots select soil microbes involved in central biogeochemical processes, such as mineral weathering, that may contribute to nutrient mobilization and tree nutrition. Here we showed, by combining soil analyses with cultivation-dependent analyses of the culturable bacterial communities associated with the widespread mycorrhizal fungus Scleroderma citrinum, a significant enrichment of bacterial isolates with efficient mineral weathering potentials around the oak and beech mycorrhizal roots compared to bulk soil. Such a difference did not exist in the rhizosphere of Norway spruce. The mineral weathering ability of the bacterial isolates was assessed using a microplaque assay that measures the pH and the amount of iron released from biotite. Using this microplate assay, we demonstrated that the bacterial isolates harboring the most efficient mineral weathering potential belonged to the Burkholderia genus. Notably, previous work revealed that oak and beech harbored very similar pHs in the 5- to 10-cm horizon in both rhizosphere and bulk soil environments. In the spruce rhizosphere, in contrast, the pH was significantly lower than that in bulk soil. Because the production of protons is one of the main mechanisms responsible for mineral weathering, our results suggest that certain tree species have developed indirect strategies for mineral weathering in nutrient-poor soils, which lie in the selection of bacterial communities with efficient mineral weathering potentials.

Relationship among soil parameters, tree nutrition and site index of Pinus radiata D. Don in Asturias, NW Spain

Se estudia en 38 parcelas de 0,1 ha cada una las propiedades del suelo que más influyen en el índice de sitio (IS) de plantaciones de Pinus radiata D. Don de 10 a 54 años de edad y en su estado nutricional en Asturias, considerando diferentes variables de masa y distinto material parental. Los suelos estudiados presentaron un carácter fuertemente ácido, alto contenido de materia orgánica, relación C/N elevada, bajo contenido en bases y P disponible extraído por el método de Mehlich 3 (PM3). Las deficiencias más extendidas fueron en K y P, observándose en algunas parcelas deficiencias en Mg y Ca. Sin embargo, las concentraciones en N fueron siempre superiores al nivel crítico. El P foliar se correlacionó positivamente con la capacidad de intercambio catiónico efectiva y con PM3. El IS osciló entre 9,5 y 28,8 m y estuvo positivamente correlacionado con la concentración de P en acículas y con el K intercambiable en el suelo en todas las parcelas y negativamente con la pendiente y el N foliar en las parcelas desarrolladas sobre cuarcitas y areniscas respectivamente. Los resultados revelan la importancia de la elección del sitio y la necesidad de fertilización en los programas de reforestación.

Hardwood Seedling Growth on Different Mine Spoil Types with and without Topsoil Amendment

The goal of many owners of reclaimed mined land in the Appalachian region is to restore the diverse native hardwood forest for environmental, economic, and cultural reasons. However, native hardwoods often grow poorly on mined sites because they are planted in unsuitable spoils devoid of native topsoil. In a greenhouse experiment, we examined the suitability of four growth media available for use on many mined sites in the central Appalachians-forest topsoil (FT), weathered sandstone (WS), unweathered sandstone (US), and unweathered shale (UH)-as well as the effects of topsoil amendment (none vs. amended) on the growth of three native hardwood species: Fraxinus americana, Quercus rubra, and Liriodendron tulipifera. A 4 x 2 x 3 factorial greenhouse experiment was conducted with planted 1-yr-old seedlings. Tree growth, foliar nutrients, and soil properties were measured and characterized. The WS was the spoil most conducive to growth for F. americana and Q. rubra. Liriodendron tulipifera did not respond to any treatments. Tree growth was highly correlated with mineralizable soil nitrogen and extractable soil phosphorus. Topsoil amendment significantly increased growth on the UH but not on the US or WS. Topsoil amendment increased the number of native herbaceous plants growing in the pots and improved foliar nutrient content in F. americana and L. tulipifera. Many properties of the WS, such as pH, microbial activity, and water availability, more closely approximated the control soil than the US or UH. This study showed that trees are sensitive to spoil type and that certain spoil types that are conducive to good growth of native trees should be used during the reclamation process, particularly if forest topsoil is not applied. Forest topsoil amendment improved tree growth on some spoil materials, improved tree nutrition, and helped restore the native soil organisms and plants that were present before mining.

Foliar Mass and Nutrition of Abies concolor Christmas Trees following Application of Organic and Inorganic Fertilizer

Abstract Fertilization in Christmas tree production is common to increase tree growth and quality, with many recommendations focusing on N as a primary amendment. However, other nutrients may limit growth, or N application may induce deficiency of other nutrients. We applied fertilizer as either ammonium nitrate (AN) or chicken manure compost (CMC) to concolor fir (Abies concolor [Gord. and Glend.] Lindl.) at eight sites across central New York in 2003 and measured foliar mass and macronutrient response (N, P, K, Ca, and Mg) to assess the potential for an inducible nutrient deficiency or nutrient limitation other than N. Foliage mass, N concentration, and N content increased following both fertilizer treatments, indicating that N limits growth at these sites. Macronutrient (P, K, Mg, Ca) concentrations were reduced following AN application because of nutrient dilution following increased growth. Compared with published sufficiency nutrient concentrations, concentrations of P and K were diluted to levels considered limiting to growth. In contrast, there was no reduction in macronutrient concentrations for P, Ca, and Mg in the CMC application, indicating the potential for this amendment to maintain balanced tree nutrition with increased growth. Foliar K content was increased in the CMC treatment, and needle mass (as the primary growth response variable), was correlated with foliar K concentration (r2 = 0.71, P &lt; 0.01). The results indicate a strong possibility of K limitation in concolor fir across a variety of site conditions. With few exceptions, there were no apparent relationships between soil nutrient pools and foliar nutrition, demonstrating the limitation of soil tests as a guide to nutrient amendments.

Exploring and communicating knowledge of trees in the early Royal Society

For nearly 150 years after its foundation, Fellows of the Royal Society collected information on trees, investigated their anatomy and physiology, promoted planting and improved planting practices, and introduced, naturalized and classified foreign species. Their discoveries and advice were widely disseminated and used. Historians have generally neglected this interest, although the Society's first publication was an influential work on trees. They have also overlooked the significance of Stephen Hales's remark in Vegetable Staticks--that he hoped his enquiries into the nature of plants would improve skills in agriculture and gardening-and his linking of sap movement to tree pruning. Fellows' experiments and field trials not only advanced knowledge of the structure, nutrition and growth of trees but also provided empirical evidence supporting instructions for cultivating them.

Nitrogen nutrition of poplar trees

Many forest ecosystems have evolved at sites with growth-limiting nitrogen (N) availability, low N input from external sources and high ecosystem internal cycling of N. By contrast, many poplar species are frequent constituents of floodplain forests where they are exposed to a significant ecosystem external supply of N, mainly nitrate, in the moving water table. Therefore, nitrate is much more important for N nutrition of these poplar species than for many other tree species. We summarise current knowledge of nitrate uptake and its regulation by tree internal signals, as well as acquisition of ammonium and organic N from the soil. Unlike herbaceous plants, N nutrition of trees is sustained by seasonal, tree internal cycling. Recent advances in the understanding of seasonal storage and mobilisation in poplar bark and regulation of these processes by temperature and daylength are addressed. To explore consequences of global climate change on N nutrition of poplar trees, responses of N uptake and metabolism to increased atmospheric CO(2) and O(3) concentrations, increased air and soil temperatures, drought and salt stress are highlighted.

EFFECT OF VARIOUS FOLIAR SPRAYS ON SOME FRUIT QUALITY ATTRIBUTES AND LEAF NUTRITIONAL STATUS OF THE PEACH CULTIVAR ‘ANDROSS’

The effect of various products applied as foliar sprays on some fruit quality attributes and leaf nutritional status of the peach cultivar ‘Andross’ for a three year period is reported. Foliar application of all calcium (Ca) products plus boron (B), did not affect mean fruit weight compared to the control. Application of profical plus calcium phosphite plus power 7-B resulted in an increase of flesh firmness. Low flesh firmness was measured at the potassium nitrate (KNO3) and Chelan-K treatments. Foliar application of all Ca and K products did not alter significantly total soluble solids, total titratable acidity, and length and width of pits in comparison to the control. The highest amount of compact pits (without visual split) for the three year period was measured after foliar application of silene-K. Profical plus calcium phosphite plus power 7-B, and calcium chloride (CaCl2) plus power 7-B gave also good results for the three years. Foliar application of agriphos, chelan-K, silene-K, and KNO3 resulted in an increase of K concentration of leaves compared to the control. Foliar application of CaCl2, bcazin, power-Ca, profical and calcium phosphite plus profical resulted in an increase of Ca concentration of leaves compared to the control for all the years. The efficacy of the foliar sprays varied from year to year indicating the influence of the climatic conditions on tree nutrition.

Intensive biomass removals and site productivity in Canada: A review of relevant issues

A renewed interest in the intensive harvesting of forest biomass as a source of bioenergy in North America raises concerns about the impacts that this practice may have on the maintenance of forest soil productivity. In Canada, such concerns were first voiced in the 1970s, and studies were launched to investigate and predict the impact of intensive forest biomass removal on site productivity. Most of these studies focused on static nutrient budgets. In Canada and around the world, more detailed process models were also developed to study carbon, nitrogen and base cation cycles under different forest harvesting intensities. However, the validity of modelling results is still constrained by our lack of knowledge on the capacity of ecosystems to supply nutrients. A few sets of field trials have been established in Canada to gather empirical data on the impact of biomass removal on soil nutrient reserves as well as on tree nutrition and growth. Although still fairly recent, these field trials, along with the older ones established in other countries with similar site conditions and climates, provide opportunities to refine our understanding of the resilience of ecosystem processes and of the impacts of intensive biomass removal on ecosystem functions. Although numerous knowledge gaps and questions remain, some jurisdictions around the world have nevertheless issued policy directives and developed guidelines for biomass harvesting. As described by the concept of adaptive forest management, ecological monitoring of harvesting operations, scientific field testing and modelling can all interact to produce better knowledge that could then help improve policy directives. Key words: bioenergy, biomass, intensive harvesting, environmental sustainability

Research Knowledge and Needs for Orchard Floor Management in Organic Tree Fruit Systems

While pest management and tree horticulture dominate the research agenda for temperate tree fruits, organic production requires more attention to weed control and nutrient management because of the limited options growers have. Weed control and tree nutrition are interlinked and can have impacts on other parts of the system such as rodent pests, beneficial insect habitat, water use, and soil quality. Trade-offs commonly occur when trying to solve weed control and nutrient management in organic orchards. This article reviews numerous orchard-floor management studies relevant to finding solutions for organic systems and suggests areas for further research. Alternatives to soil tillage are needed, as it can degrade soil and tree performance. Conversely, mulching frequently leads to improved tree performance and increased soil quality but can be a costly practice relative to other options. Currently effective organic analogues to the herbicide strip-grass alley system are lacking. A plant-based solution would be ideal from a sustainability standpoint, but no satisfactory solution has been developed for widespread use.