Why seedlings survive: influence of plant attributes

Seedling survival and successful forest restoration involves many silvicultural practices. One important aspect of a successful forest restoration program is planting quality seedlings with high survival capability. Thus the nursery needs to create seedlings with plant attributes that allow for the best chance of success once a seedling is field planted. Since the mid-twentieth century, research foresters have critically examined plant attributes that confer improved seedling survival to field site conditions. This review describes the value of commonly measured seedling quality material (i.e. shoot height, stem diameter, root mass, shoot to root ratio, drought resistance, mineral nutrient status) and performance (i.e. freezing tolerance and root growth) plant attributes defined as important in answering the question of why seedlings survive after planting. Desirable levels of these plant attributes can increase the speed with which seedlings overcome planting stress, become ‘coupled’ to the forest restoration site, thereby ensuring successful seedling establishment. Although planting seedlings with these desirable plant attributes does not guarantee high survival rates; planting seedlings with desirable plant attributes increases chances for survival after field planting.     

Bareroot versus container stocktypes: a performance comparison

This review examines the published work on bareroot and container stocktypes in forest restoration programs. The objective was to define overall trends between these two stocktypes and describe what they mean in terms of available information on their nursery and field performance. Stock quality assessments show bareroot seedlings have larger shoot systems because they are typically grown at lower densities, and in many instances longer timeframes, than container seedlings. Container systems typically produce seedlings having a lower shoot to root ratio and a greater root growth potential, conferring greater drought avoidance potential. However, assessments of stress resistance and nutrition found no conclusive evidence that either stocktype has a performance advantage, other than the container plug acting as a source of water and nutrient storage available for outplanting performance. Bareroot seedlings are more sensitive to handling practices of lifting, storage, transport and planting and these practices can negatively affect their performance. Container seedlings can have a higher level of field survival which is related, in part, to their greater drought avoidance potential, thereby overcoming planting stress. Bareroot and container seedlings have comparable survival rates on sites with minimal planting stress. Once seedlings are established, bareroot and container seedlings can have comparable field performance. In many instances where plant competition is the main limiting site variable, larger sized bareroot and container stocktypes have the best chance for successful stand establishment. The lack of a natural root form and root distribution for both stocktypes is a debated mechanical stability issue, though risks of windthrow have not been consistently demonstrated for either stocktype.     

The role of nutrients for improving seedling quality in drylands

Forest plantations have been extensively used to combat desertification. In drylands, harsh climate conditions and unfertile soils often preclude seedling establishment. The improvement in seedling quality by manipulating nutrient availability could contribute to increase planting success. However, morpho-functional traits defining optimum seedling quality in drylands, and the fertilization schemes to achieve them, are still under discussion. Several studies suggest that well fertilized seedlings may perform better than nutrient limited seedlings in these environments. However, recent works have shown opposite results. In this review, we discuss the concept of seedling quality in drylands based on an evaluation of the effects of nutrient manipulation on seedling morpho-functional traits and field performance. According to existing data, we hypothesize that nutrient-limited small seedlings may be better adapted to arid environments and unfavorable microsites, where access to water is uncertain and a conservative water use strategy may be advantageous. In contrast, in dry sub-humid areas, areas with deep soils, protected from excess radiation, and areas where irrigation is feasible, well-fertilized big seedlings with high root growth potential may have more chances of success. We discuss this theory in the context of the multiple objectives of dryland restoration and the environmental constrains posed by these areas, and identify knowledge gaps that should be targeted to test our hypothesis.     

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.     

Influence of herbaceous ground cover on forest restoration of eastern US coal surface mines

Competitive effects of dense herbaceous vegetation (ground cover) can inhibit forest restoration on mine sites. Here we review the evidence of ground cover interactions with planted tree seedlings on coal surface mines of the eastern US, discuss recent research into these interactions, and draw conclusions concerning ground cover management when restoring forests on reclaimed coal mines. Reclaimed mine sites have a high potential to support productive forests, however forest establishment is inhibited by reclamation practices that included soil compaction, and the seeding of competitive ground covers. In the first few years after tree planting, a dense ground cover of grass and legume species commonly seeded on mine sites often affect growth and survival negatively. Herbaceous vegetation providing less extensive and competitive ground coverage may either facilitate or inhibit tree establishment, depending on site conditions. The use of quality planting stock promotes the competitive ability of seedlings by improving nutrient status and the ability to capture available resources. Herbaceous species have contrasting functional characteristics, and thus compete differently with trees for available resources. Negative interactions with trees are more frequently reported for non-native cool-season grasses than for native warm-season grasses, while the effects of legumes change over time. Further research is needed to fully understand the mechanisms of tree/ground cover interactions. The development of seeding mixes that can control erosion, facilitate survival and growth of planted trees, and allow establishment by unplanted native species would aid forest restoration on eastern US, coal mines.

     

Ecophysiological variation in two provenances of Pinus flexilis seedlings across an elevation gradient from forest to alpine

Climate change is predicted to cause upward shifts in forest tree distributions, which will require seedling recruitment beyond current forest boundaries. However, predicting the likelihood of successful plant establishment beyond current species' ranges under changing climate is complicated by the interaction of genetic and environmental controls on seedling establishment. To determine how genetics and climate may interact to affect seedling establishment, we transplanted recently germinated seedlings from high- and low-elevation provenances (HI and LO, respectively) of Pinus flexilis in common gardens arrayed along an elevation and canopy gradient from subalpine forest into the alpine zone and examined differences in physiology and morphology between provenances and among sites. Plant dry mass, projected leaf area and shoot:root ratios were 12-40% greater in LO compared with HI seedlings at each elevation. There were no significant changes in these variables among sites except for decreased dry mass of LO seedlings in the alpine site. Photosynthesis, carbon balance (photosynthesis/respiration) and conductance increased >2× with elevation for both provenances, and were 35-77% greater in LO seedlings compared with HI seedlings. There were no differences in dark-adapted chlorophyll fluorescence (Fv/Fm) among sites or between provenances. Our results suggest that for P. flexilis seedlings, provenances selected for above-ground growth may outperform those selected for stress resistance in the absence of harsh climatic conditions, even well above the species' range limits in the alpine zone. This indicates that forest genetics may be important to understanding and managing species' range adjustments due to climate change.     

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.     

Nutrient loading of forest tree seedlings to promote stress resistance and field performance: a Mediterranean perspective

The planting environment of Mediterranean areas is highly challenging as summer drought and winter frost jeopardize survival, and soil infertility limits establishment success. We review the potential for seedling nutrient loading to alleviate these post-planting stresses. A growing body of evidence indicates that nitrogen (N) rich seedlings have improved field performance in Mediterranean environments, due to their ability to grow new roots rapidly and out-compete weeds. In addition, frost resistance during hardening is crucial for relatively cold inland nurseries; recent research shows a positive relationship between N and shoot frost resistance though a knowledge gap exists regarding the influence of nutrition on root frost resistance. Some new evidence also implicates phosphorus as an important driver of seedling response in the Mediterranean due to its influence on root growth and physiology. Nutrient status influences other functional attributes critical to survival in Mediterranean areas, such as drought tolerance, root hydraulic conductivity, and mycorrhization. In light of the apparent benefits of high nutrient reserves for seedling performance in Mediterranean areas, we also review techniques for nursery nutrient loading. Exponential fertilization can be applied when species’ growth patterns match this application regime. However, many Mediterranean species exhibit episodic growth indicating that constant or fall fertilization could be more effective in reaching loading. In particular, late-season fertilization has shown good potential to avert nutrient dilution in the fall and increase frost resistance. Several needs for future research are identified, with special emphasis on the necessity to match fertilization regimes to species ecological traits and planting conditions.     

The influence of hydrogel soil amendment on the survival and growth of newly transplanted Pinus patula seedlings

Hydrogel amendments have been used to improve seedling survival and establishment particularly in dry environments. However, their effect on survival and growth of newly transplanted seedlings under varying water stress conditions is poorly known. In this regard, we examined the effects of Aqua Matrix Forestry~?, a potassium-based water-absorbent polymer, on the survival and early growth of Pinus patula seedlings planted in early-,mid-and late-dry season in the eastern highlands of Zimbabwe. The late-dry season was hotter and received more rainfall than the early-and mid-dry season. Hydrogel increased seedling survival by 34 and 22% in the mid-and late-dry season, respectively. Also, hydrogel-treated seedlings were significantly taller than untreated seedlings(P \ 0.001). The height to root collar diameter ratio of hydrogel-treated seedlings was greater than that of untreated seedlings only in the mid-dry season. In conclusion, increase in survival and early growth of hydrogel-treated seedlings suggests that hydrogels can be used to extend planting beyond the rainy season to include the dry months, a feat previously unattainable due to high seedling mortality. Further, these findings reflect similar findings with other hydrogels, suggesting that improved seedling survival and plant performance may be a general consequence of hydrogel amendments.     

Effect of animal browse protection and fertilizer application on the establishment of planted Nuttall oak seedlings

For establishment to be successful, planted oak must emerge above vegetative competition and browse level. A 3 year study was established in 2000 in a cutover bottomland hardwood forest in west Alabama to examine the influences of seedling browse protection and fertilizer use on growth of Nuttall oak (Quercus nuttallii Palm.) seedlings. The treatments included: control, 1.2 m tall wire tree shelter, and 1.2 m tall plastic tree shelter. Fertilizer (20–10–5) was applied to one-half of all seedlings at planting. Competing vegetation was controlled around all seedlings with mulch mats and herbicide. Fertilization did not affect height growth or successful establishment after 3 years. Four percent of protected seedlings (plastic and wire tree shelters combined) were browsed compared to 95% of control seedlings. After 3 years, plastic tree shelters were the most effective treatment for promoting height growth and successful seedling establishment of Nuttal oak seedlings (193 cm, 92.71% compared to 120 cm, 68.75% and 52 cm, 8.33% for wire tree shelter, and control seedlings, respectively). Animal browse protection is deemed essential for successful seedling establishment in southern bottomland forests where deer density is high (density estimated at 27 km⁻² in vicinity of study area).     

Nursery fertilization enhances survival and physiological status in Canary Island pine (<Emphasis Type="Italic">Pinus canariensis</Emphasis>) seedlings planted in a semiarid environment

We tested the hypothesis that fertilized containerized Pinus canariensis seedlings increases survival when planted in semiarid sites through the improvement of their physiological status during the establishment phase by an increment in root growth. Seedlings were cultured under two different regimes: traditional (in non-fertilized natural soil) and alternative (in fertilized peat). Morphological attributes and nitrogen content were measured before planting. Measurements of survival and growth in the plantation were made periodically for 2 years and physiological plant responses (leaf water potential, gas exchange and chlorophyll fluorescence) during the third summer after planting were tested and finally a set of plants were excavated to measure the same parameters as before planting. Seedlings cultivated using fertilized peat achieved the highest values for all of evaluated parameters. During the third dry season, big seedlings exhibited better physiological status. Therefore, enhanced root growth can result in better water uptake during the dry period thereby increasing survival and growth in the next few years after planting. A feed-back physiological model is proposed to explain P. canariensis establishment in a semiarid environment.     

Assessing the effect of late-season fertilization on Holm oak plant quality: insights from morpho–nutritional characterizations and water relations parameters

Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.     

Importance of root growth in overcoming planting stress

Root growth is critical to the establishment of planted seedlings. Seedlings can undergo stress just after planting if root growth is not sufficient to couple the seedling to available soil water. Stress occurs when a newly planted seedling’s root system can not supply enough water to transpiring needles to maintain a proper water balance and ensure survival. Thus, a newly planted seedling’s ability to overcome planting stress is affected by its root system size and distribution, root–soil contact, and root hydraulic conductivity. This paper describes how factors of root growth and water status of newly planted seedlings are important in overcoming the phenomenon of planting stress which then allows a newly planted seedling to enter the establishment phase of development.     

马尾松不同苗木类型与整地方式造林早期效果的研究

通过对不同苗木类型和整地方式的马尾松幼林的造林成活率、生长状况、生物量和根系特征进行测定，结果表明：容器苗可明显提高造林成活率、当年抽梢高和生物量；整地方式对造林当年的马尾松幼林有一定影响，而在第３年则对幼林树高和抽梢高起着明显促进作用。     

Influence of ground flora on Fraxinus mandshurica seedling growth on abandoned land and beneath forest canopy

A better understanding of root/shoot interactions influencing seedling growth on abandoned land could yield insight into seedling regeneration and restoration of the abandoned lands. Field work had been conducted for 2 years (2008–2009) to investigate the impacts of neighbouring plants on Manchurian Ash (Fraxinus mandshurica) seedling growth under the canopy of an old secondary forest and on the abandoned land exposed to full solar radiation in North-eastern China. Four different interaction treatments were designed for the study: neither shoot nor root interaction, shoot interaction only, root interaction only, and both shoot and root interaction. The presence of either the shoots or roots of neighbours had a competitive effect, reducing the growth of the target seedlings at each site. The total competitive effect of roots and shoots of neighbouring plants was significantly less than the sum of root and shoot competition separately on the abandoned land, but this difference was not significant beneath the forest canopy. Root competition was more restraining than shoot competition on the abandoned land. Target seedlings adjusted their root morphology and growth rates in response to the competitive effects from different parts of the neighbouring plants. Our results indicated that the root:shoot ratios of the target seedlings at the end of the experiment were affected by neither initial tree size nor the competition from either above- or belowground at either site. The results also highlight the importance of reducing root competition in boosting seedling regeneration and forest rehabilitation on the abandoned land.     

单叶省藤组培苗造林初步研究

单叶省藤(CalamussimplicifoliusC F Wei)是我国华南地区的优质商品藤种,其藤茎质量好,为编制家具的优质原料[1～3]。70年代以来的栽培试验表明,它不仅适应性强,而且速生,可广泛栽培于海南、广东、广西、云南和福建等省区,为我国棕榈藤栽培的首选藤种[1]。但野生资源由于长期过度采伐而枯竭,少量试验林未结实或结实甚少,推广栽培因种质资源奇缺而受到严重制约[2]。通过组织培养等生物技术工厂化快繁单叶省藤,是解决扩大栽培种苗问题的最好途径。因而开展了单叶省藤组培和造林技术研究,现将组培苗造林试验结果及其特殊性予以报道。1　…     

三尖杉切根育苗及造林成效的研究

对比试验表明,三尖杉小苗定距移栽切主根1/2～1/3,苗木质量优于无切根,切根是培育三尖杉壮苗的主要技术措施。应用切根苗造林,造林成活率较无切根苗高,幼林生长也更快。     

The influence of hydrogel soil amendment on the survival and growth of newly transplanted <Emphasis Type="Italic">Pinus patula</Emphasis> seedlings

Hydrogel amendments have been used to improve seedling survival and establishment particularly in dry environments. However, their effect on survival and growth of newly transplanted seedlings under varying water stress conditions is poorly known. In this regard, we examined the effects of Aqua Matrix Forestry^®, a potassium-based water-absorbent polymer, on the survival and early growth of Pinus patula seedlings planted in early-, mid- and late-dry season in the eastern highlands of Zimbabwe. The late-dry season was hotter and received more rainfall than the early- and mid-dry season. Hydrogel increased seedling survival by 34 and 22% in the mid- and late-dry season, respectively. Also, hydrogel-treated seedlings were significantly taller than untreated seedlings (P < 0.001). The height to root collar diameter ratio of hydrogel-treated seedlings was greater than that of untreated seedlings only in the mid-dry season. In conclusion, increase in survival and early growth of hydrogel-treated seedlings suggests that hydrogels can be used to extend planting beyond the rainy season to include the dry months, a feat previously unattainable due to high seedling mortality. Further, these findings reflect similar findings with other hydrogels, suggesting that improved seedling survival and plant performance may be a general consequence of hydrogel amendments.     

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.     

Initial seedling morphological characteristics and field performance of two Sudanian savanna species in relation to nursery production period and watering regimes

It has become apparent that some interventions are required to aid the regeneration of woody species in the Sudanian savanna. Direct seeding has been ineffective, thus planting high quality seedlings may be a viable alternative. In this study, we examined the stock quality of two valuable Sudanian savanna species, Acacia macrostachya and Pterocarpus erinaceus. Different nursery production periods were tested as well as the species’ field performance under well-watered and stressed conditions. The results showed that older seedlings (9-month) were morphologically distinct from younger ones (3-month), particularly in the case of P. erinaceus. Eighteen months after planting out, survival and growth of seedlings were not affected by initial seedling size; this was the result of the high root to shoot ratio of seedlings in all age groups at the time of planting. Seedling mortality as high as 30% was observed and attributed to both drought stress and other factors such as herbivory. Regression analyses revealed that initial shoot height was a poor predictor of field performance for both species, but initial root collar diameter accounted for 25% of the variation in diameter of P. erinaceus in the field. We conclude that initial seedling size does not affect survival and growth in the field provided that all sizes of seedling have a high root to shoot ratio at the time of planting. The prediction of field performance could be improved by developing a model that incorporates a wide range of root collar diameter.