Plant quality assessment: an industrial perspective

The regions of the world using operational seedling testing to any significant extent are Canada, Britain, Sweden, and the Pacific Northwest region of the United States. Testing has been used operationally for batch culling (to ensure quality), as well as for research into improved nursery cultural practices. Savings from testing for seedling survival are substantial. However, growth gains from operational testing are more tenuous. Reduced rotation lengths and lower weeding costs are more likely to be associated with planting larger stock, rather than planting stock with higher physiological quality.Large opportunities for savings exist for regions and organizations that produce poor quality stock, have high planting costs, or both. New tests have been developed and some are becoming operational. New tests might be more effective than existing tests. However, in the regions most involved in seedling testing, plantation survival has increased over the last ten years. Subsequently, additional investments in operational testing will likely achieve diminishing returns.     

The operational planting stock quality testing program at Weyerhaeuser

The value of the Seedling Testing System (STS) is five-fold. First, it minimizes the utilization of poor quality stock that might result in regeneration failure. Second, it assists nursery managers in estimating cold hardiness of seedlings in support of the nursery frost control program. Third, it helps prevent crop losses due to pathological problems in the greenhouse and nursery. Fourth, it helps the nursery staff develop good working relationships with outside customers who benefit from the testing service. Fifth, it is a valuable tool for the nursery and tree improvement research program.     

Recent trends in nursery practice in New Zealand

The plantation resource in New Zealand is now 1.73 million hectares, of which 90% is Pinus radiataD. Don (radiata pine). The resource has been expanding at over 50,000 ha per year since 1992, although new planting is currently declining. In 1998, new planting and restocking of previously clear-felled areas was 81,100 ha. Initial stocking rates vary, but are typically in the range of 800–1000 plants per hectare, requiring around 80 million nursery plants to be raised per year.Sufficient open-pollinated seed is produced for New Zealand requirements. An increasing proportion of more expensive control-pollinated seed is being used to increase genetic gain. This has led to increased use of vegetative propagation by cuttings and tissue culture, providing more than 25% of current planting stock. These propagules, especially cuttings, often have better early performance compared with seedlings, perhaps because of their larger size. Clonal forestry options are also now being evaluated.Seedling quality specifications have been well defined for bare-root radiata pine, but not well quantified for more recent plant types such as vegetative propagules or container-grown plants. Both root system quality and physiological age can be important for vegetative propagules. These propagules, especially cuttings with a physiological age of less than 4 years, have performed as well as seedlings for growth, and have been better than seedlings for stem form and early stability. Container-growing of planting stock is being introduced with this more valuable genetic material, and issues of plant quality are being raised, as it is expensive to grow large stock in containers. More research should be done to determine what plant quality standards are required to ensure successful establishment with these stock types.     

Relationships between site and stock quality in Pinus halepensis Mill. reforestation on semiarid landscapes in eastern Spain

The influence of site and stock quality factors in Aleppo pine (Pinus halepensis Mill.) plantation establishment has been studied. Five stocklots with a contrasting seedling quality were planted on six different sites showing different ecologic conditions in a same regional context. This reciprocal study indicated that site factors (climate, meteorology and soil) explained most of the variability found over stock quality factors (material and performance attributes) in the overall performance results (F values for final survival were 64.2 and 14.1 for site and stocklot, respectively). There were significant interactions between both factors in survival (F = 2.03 for final survival) and first growth, indicating that the seedling quality attributes associated with a better performance depended on site conditions, with physiological attributes being more dependent on the site than morphological attributes. The lower the site quality (poor performance), the higher the importance of stock quality, especially that related with seedling size and macronutrient content, which showed positive correlations (p < 0.05) with survival, yielding differences of over 30% between stocklots. In general, a milder climate and a shallow site meant a higher mortality. The meteorology during the two years after planting confirmed this trend as survival was preferably correlated with temperature variables instead of with precipitation. In the first year, climate factors affected seedling performance more than the soil texture, whereas, in the second, growth was correlated (p < 0.01) with clay and silt percentages, confirming a predominant effect of site over time. Soil depth is discussed as a basic variable possessing a determinant influence on the overall results.     

Operational Effectiveness of Centralized Nursery for Small-Scale Forestry in San Carlos City, Negros Occidental, the Philippines: Lessons Learned in Seedling Production for Commercial Energy Crop Plantations

One way to maximize potential income of smallholder tree farmers is to ensure high quality of planting material. In San Carlos City, Negros Occidental, the Philippines, great importance is placed on seedling quality because Energy Crop Plantations (ECPs) managed under a Short-Rotation Coppice (SRC) system will involve a single planting for several three-year coppices. High seedling quality requires superior seed provenances and seedling propagation methods. Throughout the establishment of the nursery facility, and the propagation of planting stock, data collection, reporting and database systems have been designed to capture relevant costs and technical information. Training has been provided to nursery personnel and labourers to enable them to operate the nursery and produce high quality seedlings. This paper reports a practical operational evaluation of all materials and procedures followed in nursery establishment and seedling production. Economies of scale in nursery operation are achieved at a production level of at least 90,000 seedlings per planting season of three months in the year. The production cost is estimated at PhP 3.57/seedling, excluding the cost of the nursery infrastructure and overheads. Cost comparison with decentralized or contracted nurseries shows little variation at a total cost of PhP 4.12/seedling. However, with these alternative nursery arrangements there is high risk of producing low quality seedlings by possible reduction of inputs and skipping quality enhancement procedures to reduce production cost.     

The status and future of stock quality testing

Stock quality testing (SQT) is a vital component of forest regeneration programs world-wide. SQT consists of stock quality control (SQC) during production at the nursery and planting stock quality assessment (PSQA) prior to planting. Current tests being used for SQC and PSQA are reviewed, indicating whether they are used on an operational or research scale. Prediction of growth by PSQA is still not far advanced, and the operational application of physiological methods in particular in SQT is still limited, although progress varies according to country or region. Challenges in implementation of operational SQT are reviewed, and a 'total quality management' approach to addressing the challenges is proposed.     

山地色木槭大苗培育技术

本文介绍了色木槭生物学特征、山地育苗地选择以及栽培技术中苗木选择、起苗、苗木处理、栽植、修剪方法、病虫害防治技术。     

Comparing large containerized and bareroot conifer stock on sites of contrasting vegetation composition in a non-herbicide scenario

Planting stock selection is an integral part of plantation management, as forest nursery practices influence the physiological status of the seedlings and their capacity to cope with resource availability on different planting sites. We thus compared the 11th-year dimensions and survival of large white spruce (Picea glauca) and black spruce (P. mariana) seedlings produced as 2 + 2 bareroot or 2 + 0 container stock (cell volume of 350 cm³), used to reduce the need for competition control. Using complete split-block designs, we evaluated the seedling competitive potential and response to mechanical release on two sites of contrasting ecological fertility and vegetation dominance in Quebec, Canada. We found that large spruce seedlings can be successfully established on high-competition sites in a context where chemical herbicides cannot be used. These stock types had a limited impact on survival and growth, and both stock responded similarly to mechanical vegetation control. In this context, the choice of stock type should prioritize the highest quality large seedling based on operational considerations such as availability and ease of transportation. Mechanical site preparation was not necessary to promote seedling growth and survival on these sub-boreal sites.     

Quantifying root system quality of nursery seedlings and relationship to outplanting performance

With over 1.5 billion forest tree seedlings produced annually in the USA, seedling quality assessment is critical to ensure reforestation success. While height and root-collar diameter are the most common traits evaluated during seedling quality assessment, above-ground morphology is not always an accurate predictor of performance after outplanting. Root system morphology and physiological status may provide a more accurate indication of seedling potential. However, relatively few studies have attempted to quantitatively assess root system quality in relation to outplanting success. Large root volume, high root fibrosity, and an increased number of first-order lateral roots have shown some correlation to improved field performance. Physiological seedling quality assessment is commonly practiced through evaluation of root growth potential. Other tests, such as root electrolyte leakage, have also shown some potential as measures of seedling physiological quality. This review identifies current methods of assessing seedling root system quality and discusses potential shortcomings of these methods. An increased understanding of the suitability of current tests, coupled with the development of new tests and multiple parameter relationships, may foster the development of species and site-specific targets for seedling root system quality assessment. The production of seedlings with root systems that meet high morphological and physiological standards better enables seedlings to rapidly establish and thrive upon outplanting.     

Looking for the “silver bullet” -- can one test do it all?

Seedling quality tests should ideally fulfill several conceptual and practical requirements which are explored in this paper. Difficulties in making predictions of seedlings' field performance arise from several constraints that are discussed. Some proposed criteria are evaluated for quality testing methods, and some new reasons are considered. The reasons for seedling quality tests have to be clearly stated as tests have different purposes during nursery culture, at lifting, and pre-planting. Rooted cuttings (stecklings) and seedlings produced using embryogenesis (emblings) have additional quality requirements. Eleven rating criteria for seedling quality tests are proposed and the feasibility of using anyone of the 11 tests as a silver bullet are assessed using these criteria. New purposes for seedling testing will result from the forest management goals of genetic diversity, diversification in use of silvicultural systems, and climate change. Future tests may apply results of molecular genetics research on gene expression and genome mapping. Expert systems will become available which will integrate and build on existing data. Seedling morphology will remain the basis for stock type selection and an important characteristic of stock quality. Nursery production should aim for uniform planting stocks wherein the need for culling is minimized, but batch culling is possible. A silver bullet does not exist as no single test can be applied throughout the nursery culture, lifting and pre-planting stages for all species and conditions. However, continuing emphasis on quality has resulted in detailed characterization of the whole nursery growing environment, suggestions of major areas for improvement, and increased field performance. Future research efforts should focus on a better understanding of acclimatization of seedlings on the planting site.     

Seedling quality and field performance of commercial stocklots of containerized holm oak (Quercus ilex) in Mediterranean Spain: an approach for establishing a quality standard

Holm oak is the hardwood most used for reforestation in Mediterranean Spain, which makes the development of stock quality standards in order to improve establishment success, a priority. However, its nursery culture is characterized by a wide range of practices resulting in stock heterogeneity and a potentially varied outplanting performance. Previous research has focused on specific seedling quality attributes, obviating the integral effect of nursery culture on overall quality. We studied growing regime, seedling quality, and field performance in nine holm oak stocklots produced in commercial nurseries during two consecutive growing years. Results proved variations in field performance were related to stocklot quality and, hence, to the growing regime practised. This dependence on stock quality may vary with planting site weather: in the drier year, survival was related to attributes like height, water status and K concentration, while, in the second, milder year, only growth performance was related to nutrient concentrations, plant size and water status. Results indicated the following quality standards for height: 12–17 cm, diameter: 3.5–4.8 mm, shoot and root weights: 1.3–1.6 and 2.8–4.7 g, respectively, N–P–K foliar concentrations: over 10–0.9–3.7 mg g⁻¹, respectively and in water status parameters: E_MX < 5 MPa and SWD_TL > 15%. These attributes can be adjusted using nursery cultural practices in order to meet seedling quality standards for holm oak for planting across similar sites.     

Quality Assessment of Temperate Zone Deciduous Hardwood Seedlings

Research regarding seedling quality issues has been performed for decades and focused primarily on conifer species, which comprise the greatest proportion of nursery production worldwide. Demand for hardwood seedlings, particularly for conservation purposes, has increased steadily in recent years, emphasizing the need for seedling quality assessment protocols specific to these species. Important differences between conifer (gymnosperm) and hardwood (angiosperm) species require the creation of seedling evaluative programs specific to each group. Variation in phenology and ecological adaptability of hardwood species limits the validity of inferences made between and within genera. Annual cycles of leaf emergence followed by abscission in temperate hardwoods necessitate examination of seasonal variation in indicators of physiological condition that do not require leaf tissue (e.g., mineral nutrition, electrolyte leakage). Also, it is crucial to identify appropriate sampling periods and plant tissues for testing such that test results may be accurately compared. Though certain parameters (e.g., morphological) may be readily used in both conifer and hardwood seedling quality testing programs with little modification, additional refinement is needed to improve predictive capacity for hardwoods across a variety of environments. We review the current state of knowledge regarding seedling quality testing of temperate deciduous hardwood species, discuss limitations in incorporating traditional components of quality testing programs, and set priorities for future study.     

Assessing the Quality of Seedlings in Small-scale Nurseries in the Highlands of Cameroon: The Use of Growth Characteristics and Quality Thresholds as Indicators

In developing countries seedlings are often produced in small-scale nurseries as a means to raise tree planting materials and, provided they are of high quality, these can form the basis for successful forest plantation initiatives. This study uses morphological characteristics to assess the quality of seedlings of three tree species (Persea americana, Cola acuminata and Dacryodes edulis) in the Western Highlands of Cameroon. The growth characteristics and quality indicators of seedlings produced in two nursery categories were compared—three nurseries collaborating with the tree domestication program implemented by the World Agroforestry Centre (Category 1) and three nurseries collaborating with government and non-governmental projects (Category 2). Seedlings produced in nurseries in the first nursery category were found to be uniform in terms of growth characteristics and quality indicators. In the second category, there were relatively higher seedling proportions having measured parameters out of threshold standards for root to shoot ratio and for sturdiness quotient. Significant differences between nursery categories (at α = 0.05) were detected in root collar diameter of C. acuminata and D. edulis and in shoot dry weight of D. edulis. These differences could be attributed to better nursery management as a results of training and technical backstopping received by nursery operators in Category 1. The level of experience of nursery operators in both categories was found to be insufficient and greater exposure to skills and knowledge could enhance the production of high quality seedlings.     

Ectomycorrhizal inoculation with Pisolithus tinctorius increases the performance of Quercus suber L. (cork oak) nursery and field seedlings

Mediterranean ecosystems are characterized by large arid areas where the patchy distribution of trees offers little protection against harsh climate conditions for seedling establishment. Climate change is predicted to result in an increase in these arid regions, with pronounced effects on vegetation. Production of seedlings with developed ectomycorrhizas is a promising strategy for minimizing the initial transplant shock, thereby increasing plant survival and growth during the first, most critical years of a plantation. One important species in the Mediterranean basin is Quercus suber (cork oak), which occurs, together with other evergreen oak species, in an agro-silvo-pastoral system that represents an example of sustainable land use in Europe. In this study, a Pisolithus tinctorius isolate was used for ectomycorrhizal colonization of cork oak nursery seedlings, and the effects on aboveground plant growth and leaf structural and physiological parameters were investigated. Ectomycorrhizal development resulted in a significant increase in leaf area, dry weight, nitrogen content, and photosynthetic pigments, and mycorrhizal plants showed a higher photosynthetic capacity and water use efficiency. Nursery-inoculated plants established in the field showed increased survival and growth during the first year after transplant. These results indicate a potential for further enhancing the use of mycorrhizal inoculation as a cultivation practice in forest nurseries. Considering the difficulty of soil restoration under limiting environmental conditions, nursery inoculation with ectomycorrhizal fungi can be an important advantage for improving the quality of seedling stock and its performance after out-planting in the field, benefiting the regeneration of arid regions and the reintroduction of inocula of ectomycorrhizal fungi into these areas.     

金沙江干热河谷3个造林树种裸根1年生苗的育苗密度研究

对川楝、新银合欢、苏门答腊金合欢3个金沙江干热河谷上段区主要造林树种不同育苗密度所培育裸根1年生苗的光生理效应、苗木的形态质量及其经济效益进行了研究。在其他育苗措施相同的情况下,苗木密度是决定其苗木质量的主要因素。随着苗木密度的增大,3树种裸根1年生苗木的总体质量随之下降,以低密度时为佳。3个树种裸根1年生苗的一级苗产量分别在其苗木密度为75株/m2、100株/m2为高,而以75株/m2时最高,虽然此时苗木的净收入不是最大值,但投入/产出比值最大。而二、三级苗木产量随其密度的增加而增加,当苗木密度为150株/m2时三级苗所占百分率接近国家标准15%的许可界限。据此3个树种的裸根1年生苗培育的苗木密度以75株/m2、100株/m2为宜,而以75株/m2为最优。     

Regulating the Quality of Seedlings for Forest Restoration: Lessons from the National Greening Program in the Philippines

The use of low quality planting material is one of the major reasons for the limited success of past reforestation programs in the Philippines and elsewhere in the tropics. In the Philippines, a national policy has been in place since 2010, which regulates the quality of seedlings. As part of the policy, government reforestation programs are required to use only high quality seedlings from accredited seedling suppliers. A survey of nurseries producing seedlings for the National Greening Program in Eastern Visayas and Northern Mindanao regions was carried out to determine the effectiveness and challenges in implementing the forest nursery accreditation policy. The survey identified factors that limit the effectiveness of seedling quality regulation including lack of auditing of seedling quality in accredited nurseries, insufficient monitoring of the seedling supply chain among the network of nurseries supplying seedlings for reforestation programs, inadequate seedling production schedules, and inappropriate criteria for seedling quality assessment. The limited sources of high quality germplasm, nursery operators’ limited information on the attributes of high quality planting materials and lack of knowledge about high quality seedling production technologies contributed to the widespread production of low quality seedlings. The lack of seedling quality checks makes the government’s bidding scheme of seedling purchases prone to favouring the proliferation of low quality seedlings that are usually sold at lower prices. Nursery accreditation represents a major initiative in promoting the success of Philippine reforestation but our study found that considerable improvement of the policy and of its implementation is necessary. From our study, key lessons can be learned for the implementation of forest landscape restoration initiatives in other tropical developing countries.     

元宝枫嫁接技术研究

元宝枫的嫁接活率依砧木类型、砧木龄级、嫁接时间及嫁接方法的不同而有明显的差异。条件适宜，方法得当时，嫁接苗成活率可达８０％以上。嫁接苗在接后第三者有４３％植株开花结果，结果年限比实生苗早２年以上，试验证明，采用嫁接技术繁殖质优、早果元宝枫苗木，方法可行，值得推广。     

Promoting seedling stress resistance through nursery techniques in China

Plantation forestry is one of the most important approaches to restoring forest cover in China. Of the remaining sites suitable for afforestation in China, 52?% are considered harsh and only 13?% considered good, which indicates that successfully establishing a plantation in the future will become more and more difficult. Seedling quality in terms of morphology, physiology, and viability is a critical aspect for successful plantation establishment. Due to a large area in need of afforestation, and because of its diverse harsh sites, many studies have focused on nursery techniques of promoting seedling stress resistance, including inoculating ectomycorrhizal fungi, applying plant growth regulators, use of fall fertilization, induced water stresses, or a combined use of these methods. Most of relevant results of this research have been published in Chinese, and are unknown to researchers from other countries. Moreover, no comprehensive review of stress resistance research in forest tree seedlings in China has been completed. Therefore, this review intends to provide a concise synthesis of literature related to plant manipulation techniques that offer seedling stress resistance in Chinese nurseries, discuss potential shortcomings of these studies, and define priorities for future seedling stress resistance research. With this paper we hope to enhance communication about nursery and plantation seedling culture among researchers from China and other countries.     

Stock quality assessment through an integrated approach

Forest regeneration can be improved by matching seedling stock with reforestation site environmental conditions. To achieve this improvement, one must characterize seedling performance potential with anticipated field site conditions. A theoretical performance potential index (PPI) has been developed to forecast seedling field performance during the first growing season on a reforestation site. PPI includes material and performance attribute tests that characterize seedling performance potential under optimum and limiting environmental conditions. Test results are standardized and then integrated resulting in a comprehensive assessment procedure. The PPI concept is demonstrated using containerized western hemlock (Tsuga heterophylla (Raf.) Sarg.) seedlings subjected to a series of dormancy induction treatments and the results are compared with actual seedling performance during the first growing season on a reforestation site. Results indicated that PPI values for western hemlock seedlings treated with various dormancy induction treatments corresponded to field performance. Possible use of PPI in stock selection is discussed.     

Absolute and relative growth of Douglas-fir seedlings of different sizes

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings of a single seed source were grown in a bare-root nursery for two years to produce five different stock types by varying spacing and transplanting treatments. They were then planted in the forest together with one-year-old container seedlings of the same seed source, which constituted a sixth treatment. Stem volume mean relative growth rate (R(v)) was low immediately after planting for all stock types except the container seedlings, and increased over the following 7.6 years. An 8-week greenhouse test of the six stock types showed that dry weight mean relative growth rate (R(w)) generally decreased with seedling dry weight, but this effect was less obvious after planting, because only the three smaller stock types showed a decrease in R(w) with size. In another experiment, bare-root Douglas-fir seedlings were grown at five different spacings in a nursery for two years, and seedlings from each spacing treatment were sorted into large or small by height. The resulting 10 treatments were planted in the forest and stem volumes determined over 6.7 years. The linear effect of nursery spacing on stem volume was no longer evident 3.6 years after planting, but large seedlings had greater stem volume than the small seedlings throughout the 6.7 years of the study. There was no indication that R(v) declined with time, but small seedlings had higher R(v) than large seedlings. Relative growth rates of two-year-old Douglas-fir were depressed for a year or two after planting, but then remained relatively constant, or increased during the ensuing 5 years. Relative growth rates of smaller seedlings were greater than those of larger seedlings so that relative biomass differences decreased with time, and the time advantage (the time necessary for small seedlings to reach the present biomass of large stock) of larger stock decreased. Absolute size differences increased with time.