Growth Of Tree Seedlings Research Articles

Absence of consistent pattern between seasons or among species in effect of leaf size on insect herbivory

Insect herbivory on plant leaves is a major determinant of plant fitness, especially the growth and survival of tree seedlings in forests. Leaf size is believed to significantly affect the intensity of herbivory. Studies often assume the relationship between leaf size and herbivory to be monotonic; however, this relationship is influenced by many factors—the magnitude and direction of which are different—indicating a complex non-monotonic pattern. In this study, we investigated the herbivory of 5754 leaves of 422 seedlings belonging to 42 subtropical tree species over two seasons in southwest China. The effects of leaf size on herbivory differed among seasons; a hump-shaped pattern was detected in December, while a pattern of monotonic increase was detected in September. A variety of patterns, including complex non-monotonic hump-shaped patterns, as well as patterns indicating monotonic decrease and increase existed among species, although most species displayed no significant correlations. The relationship between leaf size and insect herbivory did not follow a constant rule, but differed across species and seasons, indicating that the effects of leaf size on the foraging preferences of insect herbivores may be contingent on both external (e.g., temperature) and intrinsic (e.g., other leaf traits) factors. Therefore, a one-off survey focusing on few species may not provide complete understanding of the overall pattern of the effect of leaf size on herbivory. Similar variations may also exist in other ecological processes, which should be given due consideration in future studies on biotic interactions.

Age, size and neighbors influence the survival and growth of understory trees in a naturally reproducing population of American chestnut, Castanea dentata

The seedling stage is a critical point in the life history of plants. The survival and growth of tree seedlings can be affected by both the abiotic and biotic environment. Seedlings of both tropical and temperate forests have been shown to experience conspecific negative density dependence (CNDD) and positive density dependence (facilitation). American chestnut was once a common species throughout eastern North America that was decimated by an introduced pathogen in the early 1900 s. Here we present an analysis of chestnut seedling ecology in a unique, sexually reproducing population of American chestnut in central Maine, USA, to understand how both conspecific and heterospecific canopy trees along with size and age influence the survival and growth of understory chestnut trees. Using both a cohort analysis and a static life table approach, we found that seedling survival was lower in the first year of life, and those trees that survive their first and second years had consistently high survival. Our data did not support facilitation as none of the neighborhood indices were positive. We found evidence for CNDD for American chestnuts in the first year of life, but we found no evidence for continued effects beyond the first year. Heterospecifics decreased growth and survival of understory chestnuts beyond the first year of life. Enhanced understanding of American chestnut ecology, particularly at the critical seedling stage, can guide management strategies that support reintroduction efforts.

Beneficial effects of an indigenous arbuscular mycorrhizal consortium on phosphate nutrition and growth of argan tree seedlings

ABSTRACT Morocco decides to launch a program to create additional argan orchards to meet the high national and worldwide demand for argan products, which is a specie so unique in the world threatened by the global climate change effect. The current study aims to evaluate the efficiency of a multi-species consortium of autochthonous mycorrhizal fungi ‘Rhizargan’ isolated from 15 Moroccan argan soils in promoting mineral nutrition intake, phosphatase activities, and plant growth of argan trees. The research was conducted on two contrasting ecotypes of argan (Admine and Lakhsas). For 25 months, the performance of argan seedlings inoculated with Rhizargan consortium was monitored and compared to those inoculated with a pure commercialized strain of Rhizophagus irregularis. The results showed that inoculation with the ‘Rhizargan consortium’ improved plant growth, mineral nutrition, and phosphatases activity more than R. irregularis inoculation. Inoculated Lakhsas and Admine seedlings with Rhizargan consortium increased shoot height by 19% and 26%, and alkaline phosphatase activity by 27% and 14%, as compared to R. irregularis. Our findings can significantly benefit the arganiculture program, as an ecofriendly strategy, by using Rhizargan consortium as biofertilizers adapted to a wider range of argan forest’ pedoclimatic conditions.

Arbuscular mycorrhizal fungi improve nutrient status of Commiphora myrrha seedlings under drought

In dryland ecosystems, tree and shrub seedling establishment, growth and survival are limited by access to water and nutrients. Arbuscular mycorrhizal fungi (AMF) increase seedling establishment and survival by enhancing nutrient and water acquisition. We executed a fully-factorial greenhouse experiment to determine the interactive effect of AMF (with and without), water deficit (four levels), and soil layer (topsoil and subsoil) on the biomass, growth, nutrient concentrations, and mycorrhizal root colonization of seedlings of Commiphora myrrha, a tree species that dominates large areas of dry forest and woodland in the Horn of Africa. Mycorrhizal seedlings had higher root and shoot biomass than non-mycorrhizal seedlings. They also had higher nutrient concentrations in root and shoot. Plant biomass was higher when plants were grown in topsoil at lower soil moisture levels. Mycorrhizal responsiveness was highest at lower soil moisture. The drought response index was higher for mycorrhizal than for non-mycorrhizal plants, indicating enhanced mycorrhizal benefits at lower water supply. Seedlings grew better in topsoil than in subsoil. Mycorrhizal colonization of roots of C. myrrha seedlings was higher with lower moisture and higher in topsoil than in subsoil. The increased performance of mycorrhizal C. myrrha indicates that mycorrhization is a major component of the adaptive strategy of seedlings of this species, similar to other species in these dryland deciduous ecosystems. We conclude that for restoration purposes with this species, nursery seedlings should be mycorrhized because of their enhanced growth performance.

Survival and Growth of Olive Tree (Olea africana) Seedlings Under Open Field Conditions is Enhanced in Hydrogel Amended Soils Media, Teso Subcounty, Kenya

The rapid decline of timber from natural forests against increasing domestic demand for wood products has caused a steady increase in timber prices in Kenya. Recently, research and development institutions have recognized the ecological and economic value of indigenous tree species and therefore have emphasized the importance of their future production on private smallholder farms rather than in large plantations. This situation has been worsened by climate changes such as the frequent high intensity of prolonged droughts and the nature of soils with poor water retention capacity. As a result, unplanted forest regeneration sites have increased hence a need for re-afforestation of these sites to meet the target for the plantation industry. Therefore, there is a need for mass production of Olea africana seedlings for reforestation programs. One such approach is the application of hydrogels or synthetic polymer organic combinations capable of improving the water and nutrient retention of the soil that can support seedling growth. This study sought to investigate the effects of hydrogel application on selected growth characteristics of O. africana. Seeds were germinated and transferred into two sets of tubes of the same size arranged in a complete randomized block design (CRBD) experiment. The sets were subjected to different levels of hydrogel concentration. Under (0gm as control) and 7gm, 14gm, and 21gm) concentration levels of hydrogel mixed with soil in open field conditions. The height and shoot collar diameter of germinated seedlings were measured every two weeks for two months. The survival of O. africana seedlings decreased with time for all treatments irrespective of the addition of hydrogels with the highest (85%) survival of seedlings on soils mixed with 21gm of hydrogel compared to 0gm hydrogel that recorded (15% survival) eight weeks after transplanting. Application of different levels of hydrogel on soils had a significant influence on the survival of transplanted O. africana seedlings (p˂0.05). Generally, the height of O. africana seedlings increased with time for all types of treatments (0, 7, 14 and 21gm of hydrogel); however, the rate of growth of seedlings was highest (0.667cm /week) on soils treated with 21gm of hydrogel and least (0.33cm/week) on 0gm hydrogel. The shoot collar diameter of O. africana seedlings increased with time for all types of treatments (0, 7, 14 and 21gm of hydrogel); however, the average shoot collar diameter of O. africana seedlings was highest (0.088mm/week) on soils inoculated with 21gm hydrogel and least (0.066mm/week) on soils not inoculated with hydrogel. These results imply that a higher dose of hydrogel significantly enhances the survival and growth characteristics (height and shoot collar diameter) of transplanted seedlings by improving the water-holding capacity of soil and making it available for plant uptake during dry conditions. Hydrogels can therefore be used to amend soils for a sustainable mass regeneration of tropical timber species for reforestation programs, increased forest cover and restoration of biodiversity in Kenya

Different responses of growth and physiology to warming and reduced precipitation of two co-existing seedlings in a temperate secondary forest.

Warming and precipitation reduction have been concurrent throughout this century in most temperate regions (e.g., Northeast China) and have increased drought risk to the growth, migration, or mortality of tree seedlings. Coexisting tree species with different functional traits in temperate forests may have inconsistent responses to both warming and decreased precipitation, which could result in a species distribution shift and change in community dynamics. Unfortunately, little is known about the growth and physiological responses of coexisting species to the changes in these two meteorological elements. We selected two coexisting species in a temperate secondary forest of Northeast China: Quercus mongolica Fischer ex Ledebour (drought-tolerant species) and Fraxinus mandschurica Rupr. (drought-intolerant species), and performed an experiment under strictly controlled conditions simulating the predicted warming (+2°C, +4°C) and precipitation reduction (-30%) compared with current conditions and analyzed the growth and physiology of seedlings. The results showed that compared with the control, warming (including +2°C and +4°C) increased the specific area weight and total biomass of F. mandschurica seedlings. These were caused by the increases in foliar N content, the activity of the PSII reaction center, and chlorophyll content. A 2°C increase in temperature and reduced precipitation enhanced root biomass of Q. mongolica, resulting from root length increase. To absorb water in drier soil, seedlings of both species had more negative water potential under the interaction between +4°C and precipitation reduction. Our results demonstrate that drought-tolerant species such as Q. mongolica will adapt to the future drier conditions with the co-occurrence of warming and precipitation reduction, while drought-intolerant species will accommodate warmer environments.

English

The impacts of post-plantation management practices (urea, farm yard manure, and combinations of urea and farmyard manure) on the growth and survival rates of selected indigenous and exotic tree species Cordia africana, Olea europaea, Grevillea robusta, and Cupressus lusitanica at Sutte micro-watershed, Morode kebele in Mirab Abaya district, South Ethiopia were investigated. Soil samples were collected from the experimental site by the zigzag method at 10 m intervals from a 40 m by 80 m plot of land and analysed in Arba Minch University for their physical and chemical properties. Results showed that the mean soil texture was 94.12% sand, 4.66% silt and 1.19% clay, pH (6.95), and total nitrogen and available phosphorous were low, with corresponding results of 0.04% and 2.1 mg/L, respectively. Similarly, soil organic matter, available potassium and cation exchange capacity (CEC) were 2.8%, 1.33 mg/L and 13.2 mg/L, respectively. On the other hand, micronutrients like copper and zinc were 1.18 and 3.2 mg/L, respectively. The concentration of iron was 1.95 mg/L which no longer hampered the growth of planted tree seedlings. The growth of height and root collar diameter (RCD) of planted tree seedlings was measured, and the survival rate was calculated for each tree species for twelve months. Tree seedlings that received the combination of urea and farmyard manure (FYM) showed the longest height, RCD and the highest survival rate in C. lusitanica compared to other three planted seedlings species. The lowest growth in height and survival rate was recorded in O. europaea. The major limiting factors of the study included experimental site due to the presence of sandy soil and the toxicity of copper and zinc. However, these limitations were avoided by testing the soil before planting tree seedlings on selected sites and preparing plantation pits during dry seasons 2 to 3 months before the plantation period. Key words: Farmyard manure, growth, Mirab Abaya, post plantation management, survival rate, tree species, urea.

Which Is the Best Substrate to Regenerate? A Comparative Pot Experiment for Tree Seedling Growth on Decayed Wood and in Soil

Dead wood is an important microsite for seedling regeneration in forest ecosystems. Although recent studies have found important associations between fungal wood decay type (white rot and brown rot) and both density and species composition of regenerating seedlings, its abiotic and biotic mechanisms are unknown. In the present study, pot experiments were conducted with the seedlings of two ectomycorrhizal tree species (Abies veitchii and Betula ermanii) and two arbuscular mycorrhizal tree species (Chamaecyparis obtusa and Cryptomeria japonica) to evaluate their growth using three substrates: brown rot wood, white rot wood, and soil. Results showed that the shoot growth of B. ermanii grown in white rot wood was greater than in other substrates, but this effect disappeared in sterilized substrates, suggesting some biotic positive effects occur in white rot wood. The seedling weights of Cr. japonica and Ch. obtusa were found to be greater in soil than in wood, and this may be partly attributable to the high mycorrhizal rate of their roots in soil. Colonization of arbuscular and ectomycorrhizal fungi was restricted to the seedlings in unsterilized soil. These results demonstrate the importance of the biological mechanisms affecting seedlings’ preferences for a variety of regeneration microsites and illustrate the need for future experiments to include larger sets of seedling species.

Stasis in forest regeneration following deer exclusion and understory gap creation: A 10-year experiment.

Chronically elevated ungulate browse pressure in temperate forests worldwide often generates ecological legacies characterized by low plant diversity and contributes to the formation of dense, nearly monodominant, and highly recalcitrant layers of understory vegetation. Once established, these recalcitrant layers combined with continued browsing may jointly constrain tree establishment and diversity so completely that understory recovery may be unattainable without mitigating browse pressure, the recalcitrant layer, or both. Here, we investigate the independent and synergistic effects of both white-tailed deer (Odocoileus virginianus) browsing and hay-scented fern (Dennstaedtia punctilobula) competition on tree regeneration in a 10-year experiment. Specifically, we examine how tree seedling establishment, growth, and composition are filtered by fern cover versus fern removal (gaps), browser presence versus absence (exclosures), and their combined effects during 10 years at three hardwood forest sites in Pennsylvania, USA. Fern gaps enhanced establishment for multiple tree species, increasing seedling density and diversity, particularly in the first 3 years post-treatment, and enhancing richness (≤1 species) over the course of the experiment. Excluding deer for a decade increased the height growth of other regeneration and altered species composition, but had no effect on diversity, richness, and density. Notably, we observed higher Prunus serotina seedling densities outside exclosures, possibly due to greater secondary dispersal. We argue that browsing legacies in second growth forests established at the turn of the last century created two conditions inimical to diverse forest regeneration: an overstory dominated by two species, P. serotina and Acer rubrum (86% of basal area), and a dense recalcitrant understory layer dominated by a native fern. The first condition limits propagule supply, the second strongly filters seedling establishment, and both create impoverished forest understories composed of few individuals and species. In undisturbed forest understories, the inertia toward impoverishment was sustained across the decade even where browsing was eliminated. Consequently, stand replacing disturbances (whether natural or anthropogenic) that disrupt the understory layer and reinitiate succession may be necessary to propel forests out of their current stasis and down a pathway leading to greater diversity.

Regeneration and growth of tree seedlings and saplings in created gaps of different sizes in a subtropical secondary forest in southern China

Gap-based silvicultural systems are of particular interest in secondary forest management because gaps are associated with regeneration and tree species diversity. However, whether using a range of gap sizes to influence tree regeneration is effective remains unclear. In this study, gaps of different sizes were created to determine their effects on tree regeneration and growth in a secondary Pinus massoniana Lamb. forest in Hunan Province, China. A robustly designed experiment was used with over nine years of repeated measurements. Seedling densities were highest in small gaps, and seedling diversity increased with increasing gap size. Sapling densities and diversity were highest in medium gaps. Within medium and large gaps, saplings were heterogeneously distributed along gradients from opening to closed forest canopy, suggesting gap partitioning of saplings. Emergence rates of three dominant species (Pinus massoniana Lamb, Schima superba Gardn. et Champ., and Cyclobalanopsis glauca (Thunb.) Oerst.) were roughly equal in medium gaps. Regeneration of P. massoniana and C. glauca was spatially diverse as gap sized increased. However, there was little evidence of S. superba divergence within and among gaps, which indicated differential tolerance to shade. A nonlinear mixed-effects model was used to detect effects of microenvironmental variables on diameter–biomass relations. The model suggested that gaps combined with solar radiation, soil moisture, and soil temperature had various effects on sapling biomass accumulation. For saplings with the same basal diameter, estimated average aboveground biomass of S. superba and C. glauca was highest in medium gaps, whereas that of P. massoniana was highest in large gaps. The study suggests that tree regeneration and growth requirements are often not met with a single gap size alone. In practice, a single tree/group selection with medium gaps hybrid approach may be required in subtropical secondary forests to increase regeneration and ecosystem resilience, while also considering other factors such as microenvironmental variables, shade tolerance, and others.

Specific effects of tree species on soil carbon sequestration in a rice-tree association mesocosm experiment: Evidence from natural 13C abundance

Within agroforestry systems, trees greatly contribute to soil carbon (C) sequestration. We still know little about how this contribution varies according to tree species. Here, we quantified the soil C content derived from three main tree species, Eucalyptus robusta, Coffea arabica and Citrus clementina, used in rainfed rice-based agroforestry in the Highlands of Madagascar. A fully factorial controlled mesocosm experiment was performed, with seedlings of the tree species planted with or without rice in a Ferralsol. The natural 13C abundance in the soil was measured to assess tree- and rice-derived C. One year after planting, Eucalyptus robusta was the species exhibiting the highest tree-derived C values, with 148 g C m−2 on average. In contrast, Citrus clementina transferred only 12 g C m−2 to the soil. No significant contribution of Coffea arabica to the soil C stock was found. The presence of rice affected neither the growth of tree seedlings nor their abilities to provide C to the soil. The difference in soil C sequestration among tree species was significantly correlated with differential root biomass. Tree root biomass was significantly correlated with soil δ13C. This experimental assay highlighted the contrasting contributions of tree species to ecological processes such as soil C sequestration at the early stage of agroforestry establishment. Further studies considering tree density and spatial arrangement should be conducted under field conditions to gain further insights into tree contributions to soil C sequestration in agroforestry systems.

The impact of tree removal on standing grass biomass, seedling establishment and growth of woody species

The removal of trees in rangelands can create gaps and lead to increased grass production that could suppress subsequent tree seedling establishment and growth. However, gaps can also enhance the growth of remaining trees. We conducted a field experiment at two savanna sites with different soil texture and woody species. We used 24 plots at each site to determine the effect of tree-removal intensities (0%, 10%, 20%, 50%, 75% and 100%) on grass production, tree-seedling establishment and growth, and growth of the remaining large trees. Site 1 was on previously cultivated severely-eroded clay-dominated soils, encroached by a monospecific stand of Vachellia tortilis. Site 2 had never been cultivated, and was on sandy soils with several woody species. At Site 1, 75 and 100% tree removal significantly reduced standing grass biomass towards the end of the first growing season, with no differences towards the end of the second season. At Site 2, tree removal significantly increased standing grass biomass. There was no significant effect of tree removal on tree seedling establishment at Site 1, but at Site 2 tree removal had a significantly negative effect on overall tree seedling establishment. At both sites, there were no significant differences in tree seedling growth. Moderate (50%) to high (75%) removal of trees had a positive effect on the growth of remaining large trees at both study sites. We found that tree seedling establishment could be affected by the level of grass biomass following tree removal, but other factors including soil erosion are also important considerations. Reduced tree competition facilitates growth of remaining large trees. An implication of these findings is that, regardless of the substantial costs of woody plant control, the recovery of key ecosystem services such as an increased forage production may not be realised. However, we recognise that this may be system-specific.

PEMATAHAN DORMANSI BENIH DAN PERTUMBUHAN SEMAI KAYU ULES (Helicteres isora Linn.)

Screw tree is a shrub from family Malvaceae that has many benefits in pharmacy. Screw tree seed has very hard seed coat, so the seed must be treated before germination. The aim of this research was to assess the characteristic of fruit and seeds, effect of seed breaking dormancy, and effect of NPK fertilizer dosage on the growth of screw tree (Helicteres isora) seedlings. The results indicated that screw tree fruits belong to dry fruits with capsule form and has 5 follicles that has different direction. Screw tree seed is orthodox type that has 9 ̶ 36 seeds in one follicle with triangle and square shape. Germination technique in laboratory with soaking the seeds in hot water 100oC until the water cool for 48 hours treatment produced the best germination amounting to 65.0%. Germination technique in green house with soaking the seeds in hot water 100oC until the water cool for 24 hours treatment was the best germination amounting to 77.0%. Seedlings fertilized with 1 g NPK doses increased screw tree growth in diameter parameter of 6.35 mm and shoot-root ratio parameter of 3.9 compared to control.

PEMATAHAN DORMANSI BENIH DAN PERTUMBUHAN SEMAI KAYU ULES (Helicteres isora Linn.)

Screw tree is a shrub from family Malvaceae that has many benefits in pharmacy. Screw tree seed has very hard seed coat, so the seed must be treated before germination. The aim of this research was to assess the characteristic of fruit and seeds, effect of seed breaking dormancy, and effect of NPK fertilizer dosage on the growth of screw tree (Helicteres isora) seedlings. The results indicated that screw tree fruits belong to dry fruits with capsule form and has 5 follicles that has different direction. Screw tree seed is orthodox type that has 9 ̶ 36 seeds in one follicle with triangle and square shape. Germination technique in laboratory with soaking the seeds in hot water 100oC until the water cool for 48 hours treatment produced the best germination amounting to 65.0%. Germination technique in green house with soaking the seeds in hot water 100oC until the water cool for 24 hours treatment was the best germination amounting to 77.0%. Seedlings fertilized with 1 g NPK doses increased screw tree growth in diameter parameter of 6.35 mm and shoot-root ratio parameter of 3.9 compared to control.

Variation in the chemical quality of woody supplements for nursery growing media affects growth of tree seedlings

Tree seedlings are produced in tree nurseries. However, nursery-grown seedlings often exhibit poor performance after outplanting due to the lack of adaptation to harsh natural conditions. These nursery-grown seedlings do not necessarily possess well-developed ectomycorrhizal symbionts, which help to obtain nutrients and increase resilience in exchange for seedling photoassimilated carbon. To improve the quality of the seedlings in natural conditions, we sowed spruce seeds on growing media with the addition of wood chips, i.e. stemwood chips or polyphenol- and resin acid-rich knotwood chips. Wood chips were chosen because they are common forest side-streams, and their compounds have shown a potential to improve mycorrhization and seedling fitness. Wood chips initially decreased the growth of seedlings. However, this effect levelled off with time and depended on the quality of the wood. Wood chips had no effect on mycorrhization. Further testing of the wood material showed that wood chips seemed to decrease seedling growth via nitrogen (N) immobilisation rather than a direct toxic effect. The phenomenon of N immobilisation on wood chips could be explored further to develop a slow-release N source, aptly reflecting N availability in natural conditions. Slow-release N source based on wood chips could be beneficial both to increase survival in natural conditions and for environment protection.

Effect of arbuscular mycorrhizal fungi and planting media on seedlings growth of Helicteres isora L. in the nursery

A screw tree (Helicteres isora L.) is a small/large shrub species that grows and spreads in many Asian countries, including Indonesia (NTT and Maluku). It is a medicinal plant commonly used to treat many diseases, such as bleeding and constipation. This study aimed to determine the effect of Arbuscular Mycorrhizal (AM) fungi and planting media on the growth of screw tree seedlings in a nursery. This research was conducted at Bogor Forest Research and Development Center’s nursery, Indonesia. This study consisted of two factors: AM fungi with three levels, namely control, Glomus aggregatum and Glomus clarum and growth media with two levels, namely mixed media of soil: rice husk charcoal (2:1) and mixed soil of media: rice husk charcoal: cocopeat (2:1:1). The results showed that treatment of G. aggregatum and soil mixed of media: rice husk charcoal: cocopeat (2:1:1) was significantly different from other treatments except for G. clarum and soil mixture of media: rice husk charcoal: cocopeat (2:1:1) that significantly increased height, diameter and dry weight of seedlings and the values were 97, 56, 126 and 46, 37, 127% compared to the control. Mycorrhizal dependency of screw tree was very high (126 and 127%). Generally, interaction treatment of G. clarum and mixed media of soil: rice husk charcoal: cocopeat (2:1:1) increased the growth of 11-month-old screw tree in the nursery.

Environmental Influences on Density and Height Growth of Natural Ponderosa Pine Regeneration following Wildfires

Over the past century the size and severity of wildfires, as well as post-fire recovery processes (e.g., seedling establishment), have been altered from historical levels due to management policies and changing climate. Tree seedling establishment and growth drive future overstory tree dynamics after wildfire. Post-fire tree regeneration can be highly variable depending on burn severity, pre-fire forest condition, tree regeneration strategies, and climate; however, few studies have examined how different abiotic and biotic factors impact seedling density and growth and the interactions among those factors. We measured seedling density and height growth in the period 2015–2016 on three wildfires that burned in ponderosa pine (Pinus ponderosa) forests in the period 2000–2007 across broad environmental and burn severity gradients. Using a non-parametric multiplicative regression model, we found that downed woody fuel load, duff depth, and fall precipitation best explained variation in seedling density, while the distance to nearest seed tree, a soil productivity index, duff depth, and spring precipitation as snow best explained seedling height growth. Overall, results highlight the importance of burn severity and post-fire climate in tree regeneration, although the primary factors influencing seedling density and height growth vary. Drier conditions and changes to precipitation seasonality have the potential to influence tree establishment, survival, and growth in post-fire environments, which could lead to significant impacts for long-term forest recovery.

Silicon as mitigator of salt stress in mango tree seedlings

The use of saline water dramatically reduces the growth and development of plants. Thus, salt stress mitigation can be important to allow the use of this water in the agriculture. This study aimed to evaluate the effect of silicon as attenuators of effects caused by salt stress on seedlings of “Espada” mango tree variety. An experiment was conducted under completely randomized experimental design in a factorial scheme (5 x 2). The factors studied consisted of silicon concentrations (0, 50, 100, 150 and 200 mg L-1) and irrigation with low water (0.8 dS m-1) and high (6 dS m-1) electrical conductivity and the growth of mango tree seedlings was assessed 70 days after sowing (DAS) by the height, number of leaves, stem diameter, dry matter of root, aerial part and total, dry matter content, Dickson Quality Index and Index of tolerance to salinity. The application of silicon via leaf mitigates the deleterious effects of salt stress in mango seedlings. Silicon 200 mg L-1 promotes higher growth, dry matter accumulation and 100 mg L-1 concentration provides higher salt tolerance in mango seedlings. Electrical conductivity in the irrigation water at 6 dS m-1 reduce the growth and quality the of mango tree seedlings

Effects of Above- and Below-Ground Interactions of Plants on Growth of Tree Seedlings in Low-Elevation Tropical Rainforests on Hainan Island, China

Understanding the effects of above- and below-ground interactions on seedling growth is pivotal for identifying the key drivers of secondary forest succession. However, it is still unclear whether the effects of above- and below-ground interactions of plants are consistent for seedling growth of deciduous and evergreen species. There are two types of broadleaved forests (i.e., tropical lowland rainforest and tropical deciduous monsoon rainforest) in the low-elevation (<800 m) areas of Hainan Island in China. Here, 32 seedling transplanting plots (1 × 1 m2) were established in the tropical lowland rainforest and the tropical deciduous monsoon rainforest, respectively. Four treatments (each with 16 replicates) were carried out to reduce above- and below-ground interactions of plants in the low-elevation forests: removal of vegetation (R), root trenching (T), removal of vegetation and root trenching (R + T), and no vegetation removal or trenching (as the control) (C). Seedlings of four deciduous species and four evergreen species were planted to observe their performance in the experiments. The relative growth rates (RGR) of the seedlings were measured to distinguish the relative effects of above- and below-ground interactions. The photosynthetically active radiation (PAR) was measured as a proxy for above-ground interaction and the root biomass was used as a proxy for below-ground interaction. The relationships between seedling RGR and PAR/root biomass were examined. Results showed that: (1) R and R+T treatments significantly increased the seedlings RGR, but T treatment had no effect on the RGR; (2) the growth rates of deciduous species were greater than those of the evergreen species; and (3) seedling growth rates were increased with more PAR. Our study suggests that above-ground vegetation removal had a stronger effect than trenching on the growth and assembly of tree seedlings in the low-elevation tropical rainforests.

Do early‐successional weeds facilitate or compete with seedlings in forest restoration? Disentangling abiotic versus biotic factors

Abstract Semi‐arid forests need cost‐effective restoration strategies to address their severe degradation. Tree shelters are often used to minimize abiotic and biotic stress during seedling establishment. We asked if early‐successional weeds act as a natural shelter by facilitating native seedlings, contingent on abiotic and biotic stressors and seedling ecological strategy. We conducted a manipulative weed exclusion experiment at a semi‐arid site in South Texas targeted for large‐scale forest restoration to discern the net effect of weeds on the growth and survival of target thornscrub tree and shrub seedlings. We assessed the roles of contrasting seedling ecological strategies (fast vs. slow growth habit), temporal variation in abiotic stress, microclimate and mammalian herbivory in modulating weed–seedling interactions. Ungulate herbivory on seedlings was common, of similar frequency across most species, but not diminished by the presence of weed neighbours. On average, seedlings growing adjacent to weed neighbours experienced modest but non‐significant increases in both height and mortality after 6 months, relative to weed‐excluded areas. However, seedlings without significant herbivory and adjacent to weed neighbours grew more vigorously (increased height and branching) during hot and dry periods, particularly those species with a fast growth habit. Although seedling light‐saturated photosynthetic capacity (Asat) and air temperature were unaffected by weed presence during hot and dry periods, afternoon light levels were reduced by approximately 50%, possibly indicative of lower leaf temperatures and improved seedling water status. Our results show that realizing the facilitative potential of weeds in semi‐arid forest restoration requires minimizing mammalian herbivory and temporally separating competition for resources. Managing for intermediate but not excessive levels of forb canopy cover is likely required to reduce high radiation loads and reduce transpiration without adverse competitive effects. Longer‐term experiments manipulating cover crop identity, cover and mammalian herbivory will inform whether forbs can be effectively exploited to enhance restoration success at large scales.