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.     

Increase in size and nitrogen concentration enhances seedling survival in Mediterranean plantations. Insights from an ecophysiological conceptual model of plant survival

Reduction in size and tissue nutrient concentration is widely considered to increase seedling drought resistance in dry and oligotrophic plantation sites. However, much evidence indicates that increase in size and tissue nutrient concentration improves seedling survival in Mediterranean forest plantations. This suggests that the ecophysiological processes and functional attributes relevant for early seedling survival in Mediterranean climate must be reconsidered. We propose a ecophysiological conceptual model for seedling survival in Mediterranean-climate plantations to provide a physiological explanation of the frequent positive relationship between outplanting performance and seedling size and nutrient concentration. The model considers the physiological processes outlined in the plantation establishment model of Burdett (Can J For Res 20:415–427, 1990), but incorporates other physiological processes that drive seedling survival, such as N remobilization, carbohydrate storage and plant hydraulics. The model considers that seedling survival in Mediterranean climates is linked to high growth capacity during the wet season. The model is for container plants and is based on three main principles, (1) Mediterranean climates are not dry the entire year but usually have two seasons of contrasting water availability; (2) summer drought is the main cause of seedling mortality; in this context, deep and large roots is a key trait for avoiding lethal water stress; (3) attainment of large root systems in the dry season is promoted when seedlings have high growth during the wet season. High growth is achieved when seedlings can divert large amount of resources to support new root and shoot growth. Functional traits that confer high photosynthesis, nutrient remobilization capacity, and non-structural carbohydrate storage promote high growth. Increases in seedling size and nutrient concentration strongly affect these physiological processes. Traits that confer high drought resistance are of low value during the wet season because hinder growth capacity. We provide specific evidence to support the model and finally we discuss its implications and the factors that may alter the frequent increase in performance with increase in seedling size and tissue nutrient concentration.     

阔叶树容器苗应用技术研究

通过对容器苗与裸根苗相比,容器苗具有成活率高,移栽季节长,移栽后苗期生长快、林分相对均匀、个体差异小等优点,是提高造林质量的重要手段之一.试验表明,一般情况下容器苗移栽可不受季节限制,但应尽可能避开在高温且长期干旱季节进行移栽.最佳移栽季节为常规格造林季节、雨季和9月;造林容器苗不宜过大,要保持根球、枝叶完整,避免受损.     

Consequences of dry-season seed dispersal on seedling establishment of dry forest trees: Should we store seeds until the rains?

We examined the following hypotheses: (i) seeds of dry forest trees have high pre- and post-germination mortality by desiccation due to the time between seed dispersal and germination and to irregular rains at the onset of the rainy season; (ii) seedlings from seeds dispersed in the dry season which survive the dry spells are larger at the end of the first rainy season than those dispersed in the rainy season because the former have more time to grow. We evaluated the possible trade-off between few large seedlings (resulting from natural dispersal) × many small seedlings (resulting from delayed dispersal) on seedling survival during the dry season. We sowed eight tree species in a greenhouse in September, simulating the natural dispersal timing (before the rains), and in November, when rains are more constant. Because shading can counteract the effects of desiccation, we applied three levels of shade (10%, 40% and 72% of PPFD). From September 2005 to December 2006, we provided the daily precipitation of a median year from a major patch of dry forest in Central Brazil. At the end of the rainy season, a subset of seedlings was collected for growth measurements (dry mass) and the remainder was left to follow the dry season survivorship. The lower germination expected for seeds dispersed in the dry season and in full sun was not confirmed for species that had some dormancy. The delayed dispersal was advantageous for the initial establishment of fast germinating species, but it was irrelevant or even disadvantageous for others. Also, the greenhouse weather was certainly milder than the natural environment, reducing the potential for mortality by desiccation. The growth of the four species of higher dormancy were not affected by timing of seed dispersal, while three out of four fast germinating species had higher root biomass when dispersed in the dry season. The growth during the rainy season did not affect seedling survival during the dry season. Keeping seeds to sow when rain is constant might be a good strategy to increase the establishment of fast-germinating tree species.     

Shrubs facilitating seedling performance in ungulate-dominated systems: biotic versus abiotic mechanisms of plant facilitation

Shrubs are important microsites that facilitate seedling performance in abiotically stressed environments. However, shrub facilitation might work differently in ecosystems with high biotic stress (e.g., ungulate-dominated environments). We wonder whether ungulates through their preferences for different shrubs affect the facilitation process of seedlings, and whether this process remains consistent across different levels of abiotic stress. We study seedling performance (survival and growth) of a Mediterranean oak (Quercus pyrenaica) in three microsites (open, preferred and non-preferred shrubs by ungulates) for two contrasting climatic environments and throughout a complete growing season (increasing abiotic stress). Overall, there was a positive effect of shrubs in seedling survival. We found a microsite effect on seedling growth but this effect differed depending on the abiotic environment, with seedlings growing better in open microsites in the less stressful site. The larger abiotic context (climate) played an important role in determining which microsite is the most favorable for seedling growth but not necessarily for the eventual survival of seedlings. Wild ungulates started to damage seedlings early in the growing season, whereas abiotic stress (desiccation) affected mostly those plants that were not previously attacked by animals, showing the hierarchical effect (earlier and longer effect) of the biotic over the abiotic mortality agents. Non-preferred shrubs worked better as nurse shrubs only under high ungulate pressure. From the abiotic perspective, preferred and non-preferred shrubs did not apparently differ in the facilitation effect. Importantly, we found a greater facilitative effect of shrubs on the survival than on the growth of seedlings.     

Tree seedling survival and growth in logged and undisturbed seasonal deciduous forest fragments in central Brazil

We evaluated the survival and growth of Amburana cearensis, Cedrela fissilis, and Sterculia striata seedlings in three seasonally tropical dry forest fragments that were subjected to different logging levels (intact, intermediately and heavily logged). In each fragment, we planted 40 seedlings of each species and monitored these over a period of 1 year. The highest seedling survival rate (64%) occurred in the heavily logged fragment, which, however, also had the highest mortality risk for all species during the dry season. Only S. striata seedlings had different survival rates among the fragments. Height and diameter growth were higher at sites with higher canopy openness in the wet season. The survival and growth rates of seedlings planted in logged fragments indicate that this technique can be applied to restore and enrich logged forests of the Paran? River Basin.     

Comparison of container-grown Pinus taeda L. seedlings raised outdoors and in a growth chamber in sunlight

Two annual crops of container-grown loblolly pine (Pinus taeda L.) seedlings raised outdoors differed from those grown inside a covered chamber with a clear top. After a 90-day growth period, outside-grown container seedlings had shorter heights, smaller root collar diameters, and lower root, stem, foliage, shoot, and total dry weights than chamber-grown seedlings. Fall-planted, outside-grown seedlings raised the first year had up to 10% higher field survival than those from the chamber. However, chamber-grown container seedlings that survived retained their initial height and diameter advantages following one complete growing season. Fall-planted seedlings raised the second year showed no differences due to growth treatments when favorable weather for seedling growth occurred after field-planting. Container-grown seedlings raised outdoors during the summer months are well suited for fall-outplanting.     

红椆播种苗移栽容器育苗技术研究

为提高红椆苗木质量和造林成活率,对红椆2年生直播苗和2年生撒播苗移栽容器苗苗木质量进行对比试验,同时采用不同规格容器和遮荫处理对1年生撒播苗移栽到容器后苗木的成活率和生长量进行比较试验。结果表明:容器育苗可显著提高红椆苗苗高、地径、主根长、地上部分干重、地下部分干重;容器规格对移栽后苗木成活率影响不显著,但对苗木生长有显著影响;采用80%遮阳网遮荫,容器苗成活率较高,苗木高生长也显著增加,但苗木地径生长与60%遮阳网遮荫处理的苗木差异不显著。     

苗木类型对油茶造林效果的影响

针对油茶造林成活率不高的问题,调查了不同油茶苗木类型对造林效果的影响。结果表明:容器苗的造林成活率及造林后幼林长势明显优于裸根苗,以无纺布轻基质苗最好,造林成活率达90.6%。苗龄对容器苗造林成活率有较大影响,其中以3年生容器杯大苗的造林成活率最高,造林成活率达98.3%。容器杯实生苗的造林成活率及造林后幼林前期生长要优于容器杯嫁接苗,但花芽出现的时间较容器杯嫁接苗要晚。     

Germination and early growth of sown Quercus robur L. in relation to soil preparation, sowing depths and prevention against predation

A field experiment was established in the autumn of 1992 in order to study predation of acorns, germination and early growth of oak seedlings. The experiment was established on a clearcut and an adjacent oak shelterwood in southern Sweden. In the experiment, a total of 6 840 acorns were sown. The sowing was carried out with different vegetation control and soil preparation treatments and with different planting depths.The germination percentage was highest for acorns sown at five cm depth and lowest for acorns sown on top of the soil, and lower for acorns sown in areas where the humus layer had been removed than in areas where the humus layer was retained. There was no difference in the percentage germination after two growing seasons between acorns sown inside the shelterwood and acorns sown on the clearcut. The height of the seedlings was lowest when the humus was removed while the number of leaves per seedling was lowest for seedlings in untreated areas after two growing seasons. Furthermore, seedlings in untreated areas showed the lowest relative height growth rate during the second growing season. In spite of higher biomass of ground vegetation in undisturbed areas compared to treated areas, no effect of the soil and vegetation control treatments could be found on soil water potentials. The soil temperature and photosynthetic active radiation at seedling level were higher in areas where soil preparation and vegetation control had been performed. However, it was concluded that neither low soil water availability nor low light levels could be the only cause of lower relative height growth rate during the second growing season for seedlings in undisturbed areas.     

Effect of Gap Size on Seedling Establishment of Tsuga longibracteata

Effects of three gaps which are large （118 m^2）, medium （86 m^2） and small （20 m^2）, respectively, and under canopy of Tsuga longibracteata forest on the seedling establishment of T. longibracteata were studied through seed burial experiments from December 2003 to January 2005 in Tianbaoyan National Nature Reserve of Fujian, China. The results showed that the area of gap had an evident effect on the seedling establishment of T. longibracteata. The seedling emergence rates of T. longibracteata in plots of large gap, medium gap, small gap and under canopy were 10%, 10%, 4% and 6%, representing an increasing trend along with the gap size increasing without a significant difference. Rain eroding and insects feeding were two main factors leading to seedling death. The larger the gap size was, the more seedlings were killed by rain erosion and the fewer seedlings were killed by insects feeding. The emergence time of seedlings was almost same in all plots while their death time was different respectively. The gap size had a significant impact on seedling survival rate. The seedling survival rate was highest in the medium gap plot （27.0%） and next to the highest in large gap plot （7.3%）, and seedling in small gap plot and under canopy plot died out after one growing season. Increased light supply in gaps was favorable for the seedlings growth and survival. Increased light supply in the large gap could enhance the growth of seedling leaf and root of T. longibracteata, and the seedling in turn allocated more dry mass to root and leaf, but it has little impact on the growth of stem. This research indicates that T. longibracteata is a pioneer species and its seedling establishment need a medium or large gap （〉50 m^2）.     

Why do large,nitrogen rich seedlings better resist stressful transplanting conditions? A physiological analysis in two functionally contrasting Mediterranean forest species

We analysed the physiological bases that explain why large and high nitrogen (N) concentration seedlings frequently have improved survival and growth relative to small seedlings in Mediterranean woodland plantations. Large seedlings of Aleppo pine (Pinus halepensis Mill.) and holm oak (Quercus ilex L.) with high N concentration (L+), and small seedlings with either high (S+) or low (S−) N concentration, were planted on two sites of different weed competition intensity that created contrasting stress conditions. Seedling survival, growth, gas exchange, N remobilization (N_R) and uptake (N_U), and water potential were assessed through the first growing season. Weeds reduced survival and growth, but seedling response to weed competition varied among phenotypes and between species. At the end of the first growing season, L+ Aleppo pine seedlings had higher survival than both small seedling types in presence of weeds but no differences were observed in absence of weeds. Mortality differences among phenotypes occurred in spring but not in summer. L+ Aleppo pines grew more than small Aleppo pines independently of weed competition. No holm oak seedling type survived in presence of weeds and no mortality differences among phenotypes where observed in absence of weeds, although L+ holm oak seedlings grew more than small seedlings. Mortality and growth differences in Aleppo pine were linked to marked physiological differences among phenotypes while physiological differences were small among holm oak phenotypes. L+ Aleppo pines had greater root growth, gas exchange, N_R, and N_U than small seedlings, irrespective of their N concentration. Seedling size in Aleppo pine had a greater role in the performance of transplanted seedlings than N concentration. The functional differences among oak phenotypes were small whereas they were large in pine seedlings, which led to smaller differences in transplanting performance in holm oak than in pine. This suggests that the nursery seedling quality improvement for planting in dry sites could depend on the species-specific phenotypic plasticity and functional strategy. Improved transplanting performance in large Aleppo pine seedlings relative to small seedlings was linked to greater gas exchange, root growth and N cycling.     

大兴安岭干旱阳坡火烧迹地更新技术研究

在大兴安岭林区的干旱阳坡火烧迹地进行了整地方式、苗木T/R比、造林季节和保苗剂应用对造林成活率影响的研究。结果表明:鱼鳞坑整地能够降低土壤温度,增加土壤含水率,进而提高樟子松苗木造林成活率;随着苗木T/R比的降低,樟子松苗木造林成活率增加;樟子松和落叶松苗木春季造林成活率均高于秋季;使用HRC保苗剂后樟子松和落叶松苗木造林成活率平均增加13.7个百分点。     

Is light the key factor for success of tube shelters in forest restoration plantings under Mediterranean climates?

Tube shelters were designed to protect against browsing, but they improve seedling survival in Mediterranean dry climates. Mechanisms for this response, however, are not fully understood and this knowledge can be useful to help design optimal tube shelters for Mediterranean species and climates. Our objective in this study was to determine if the positive effect of tube shelters is due to enhanced growth during the wet season or to reduced light stress during the dry season. We performed two independent experiments. In the first, we assessed root growth during the wet season in two Mediterranean species with contrasting light tolerance (Quercus ilex L. and Pinus halepensis Mill.) growing in tubes with varying light transmissivity. In the second experiment, we studied the response of a Quercus ilex plantation to different shelter treatments. Root growth during the wet season was reduced with decreasing light transmissivity in the shade intolerant P. halepensis, but not in the shade tolerant Quercus ilex. Survival of Q. ilex shaded by a mesh shelter only during summer was higher than in unsheltered seedlings and similar to the survival in tube and mesh shelters during the whole season. This suggests that shade during the dry period was the main factor explaining survival in this species. This effect could be related to the lower leaf temperature recorded in sheltered seedlings. We conclude that Q. ilex (and perhaps other late successional, shade tolerant Mediterranean species) should be planted in tubes with the currently used light transmissivity because these shelters reduce light stress in summer without impairing root growth in the wet season. However, current tubes impair root growth in P. halepensis (and likely other pioneer, shade intolerant Mediterranean species), so higher transmissivity tubes may be necessary. Optimal transmissivity for tube shelter in Mediterranean climates is species-specific and identifiable as the point that minimizes light stress during summer without impairing root growth in the wet season.     

Growth and Nutritional Responses of Juvenile Jeffrey Pine to Post-Planting Fertilization

Abstract

Broadcast fertilization of a three-year-old Jeffrey pine (Pinus jeffreyi Grev. & Balf.) plantation growing on an eroded Sierra Nevada site was examined for its capacity to enhance seedling growth. The amendments chosen for the study included controlled release and conventional soluble formulations that contained a variety of N forms, but all featured high N content along with other nutrients. Four application rates were used, and all amendments were distributed around the base of the seedlings as top dressing. Four seasons after treatment application, fertilized seedlings were 129% larger in height, 93% larger in diameter, and 865% greater in shoot volume than unfertilized seedlings overall. Seedling sizes generally increased with application rate, and by a small margin, the controlled release fertilizer outperformed the other formulations. Relative growth analysis suggested that stimulation by the amendments would continue beyond four seasons. Foliar analysis conducted early and again late during the study revealed that N and P concentrations were consistently raised by fertilization, which likely accounts for much of the accompanying growth gains, while Ca, Fe, Mn, B, and Al concentrations were consistently reduced. Either early or late, foliar K was also raised while Mg, S, Zn, and Cu were reduced. Collectively, these results indicate that fertilization with a variety of high N formulations can increase the availability and uptake of critical nutrients sufficiently to impart in Jeffrey pine on low quality sites a substantial growth advantage.     

Shade shelters increase survival and photosynthetic performance of oak transplants at abandoned fields in semi-arid climates

Forest restorations conducted in semiarid, seasonally dry climates must deal with the intense drought stress that affects tree seedlings during the dry season. Although this water deficit is the most commonly invoked source of mortality for seedlings, several other environmental factors may also preclude survival of transplants. For instance, it has been widely reported that excessive light reduces the efficiency of the photosynthetic apparatus, hence decreasing plant survival, but most seedling transplants in deforested areas are conducted under these light conditions. This study is focused in determining whether excessive light affects the photosynthetic performance and survival of Quercus coccolobifolia, a Mexican oak species, when their seedlings are transplanted in semiarid deforested areas. Further, this study tests the possibility of using artificial shade shelters to improve the ecophysiological performance and survival of seedlings. Oak seedlings were transplanted under full sunlight conditions and beneath artificial shade shelters of two different colors: white and black. To reduce water stress, and hence isolate the effects of light treatments, a drip irrigation system was implemented at each experimental plot. Seedling survival was monitored weekly for 128 days and photosynthetic performance was assessed by measuring chlorophyll fluorescence at three opportunities during the experiment. Sun-exposed seedlings showed lower photosynthetic performance and survival rates than those beneath shelters of both colors. These results suggest that sunlight damage can reduce seedling survival when they are transplanted in exposed sites, and that shade shelters can improve the success of forest restoration programs in semiarid climates.     

黧蒴栲芽苗截根移栽育苗及造林成效研究

为了提高黧蒴栲苗木质量和造林成活率,利用随机区组设计开展了黧蒴栲芽苗截根移栽、截根苗造林对比试验.结果表明：黧蒴栲芽苗截根处理对苗高、主根长、一级侧根数、叶干重、茎枝干重、根器官干重有极显著影响,对苗木地径、一级侧根长度有显著影响.芽苗截根处理后苗木高度增加17.51％、地径增加13.72％.不同剪叶处理方式对黧蒴栲苗木造林成活率有极显著影响,芽苗截根苗造林以剪叶75％效果最好,造林成活率达95.86％,而未剪叶苗造林成活率为57.69％;应用芽苗截根苗造林可提高造林成活率17.0％～24.0％,增加当年树高、地径生长量分别为18.22％、15.44％.     

银杏早播密播培育壮苗技术

采取提前健芽、高密度播种培育银杏实生苗，能使幼苗在高温干旱到来之前就已半水质化，此时苗木叶片已封行，减少水分蒸发，降低床面温度，改善了小气候，有效地促进苗木根系生长，加大地上部分生长量，提高了苗木级别；通过黑网遮荫能防止或减轻苗木颈癌病、叶桔病的发生，提高了成苗率；同时亦提高了土地利用率，节约劳力与农药肥料的用量，从而降低苗木成本。     

切根、截顶对湿地松裸根苗生长调控效果的研究

在江西景德镇和安徽泾县布置了１年生湿地松裸根苗生长后期切和截顶试验，研究其对苗木形态和造林表现的效应及其例题应用制度。两年的结果表明，切根苗的高、径及主根形态指标均低于未切根苗，而侧须根系增加，早切根多次切根处理效应最显著。     

米老排组培苗移植及其影响因素

为提高主要栽培珍贵树种米老排(Mytilaria laosensis)组培苗的移植成活率,以选育的优良无性系组培生根苗为材料,研究炼苗方式、基质、苗木规格、植后施肥及移植季节等对移植成活率和苗木生长发育的影响.结果表明:松盖炼苗3 d,出瓶苗高度大于2 cm,植后3 d喷施1 MS大量元素营养液是较好的处理,在大棚条件下移植,不带黄心土的轻基质和河沙都是适合基质,移植成活率90%以上,在大田条件下移植,以黄心土:泥炭土=1:1或黄心土:蛭石=1:1为基质移植成活率较高.移植季节以4月成活率最高,9月、10月其次,考虑到我国南方地区最佳造林季节为3—5月,为减少苗圃管理成本,米老排组培苗生产安排在9—10月出瓶移植是比较合理的选择.