Survival Of Tree Seedlings Research Articles

An enemy's enemy is an ally: Competitive indirect interactions mediate coexistence of trees, grasses, and subshrubs in neotropical savanna

AbstractSavannas are complex ecosystems where multiple growth forms, including grasses, trees, and subshrubs, coexist through intricate ecological interactions. Understanding the mechanisms that promote this coexistence is key to conserving savanna biodiversity. This study investigated the effects of grass competition on the survival and growth of trees and subshrubs, as well as the interactions between these two growth forms. Using three species of trees and three species of subshrubs, we conducted a greenhouse experiment to assess how competition between trees and subshrubs is influenced by the presence of grass. We found that grass competition significantly reduced the survival of tree seedlings, while subshrubs were unaffected. When trees and subshrubs competed directly, subshrub biomass was reduced, but only in the absence of grass. Tree seedling biomass was not affected by subshrubs, but was negatively impacted by grass in the absence of subshrubs. Both root and stem biomass of trees and subshrubs were reduced by grass competition; however, this effect was mitigated when grasses, subshrubs, and trees competed simultaneously. These results indicate that when grasses, subshrubs, and trees compete together, the intensity of competition is reduced, promoting coexistence and contributing to the balance of growth forms in savanna ecosystems. While fire is an important factor in savanna dynamics, our study emphasizes the critical role of competition in maintaining this balance. Future studies should explore how fire and competition interact to further our understanding of biodiversity and ecosystem function in Neotropical savannas.Abstract in Portuguese is available with online material.

Liana versus tree seedling responses to spatial and temporal variation in dry season severity

AbstractLianas are key components of tropical forests, particularly at sites with more severe dry seasons. In contrast, trees are more abundant and speciose in wetter areas. The seasonal growth advantage (SGA) hypothesis postulates that such contrasting distributions are produced by higher liana growth relative to trees during seasonal droughts. The SGA has been investigated for larger size classes (e.g., ≥5 cm diameter at 1.3 m, dbh), but rarely for seedlings. Using eight annual censuses of >12,000 seedlings of 483 tree and liana species conducted at eight 1‐ha plots spanning a strong rainfall gradient in central Panama, we evaluated whether liana seedlings had higher growth and/or survival rates than tree seedlings at sites with stronger droughts. We also tested whether an extreme El Niño drought during the study period had a more negative effect on tree compared to liana seedlings. The absolute density of liana seedlings was similar across the rainfall gradient, ranging from 0.32 individuals/m2 (0.20–0.49, 95% credible interval [CI]) at the driest end of the gradient and 0.27 individuals/m2 (0.13–0.51 95% CI) at the wettest end of the gradient. The relative density of liana seedlings compared to tree seedlings was higher at sites with stronger dry seasons (0.27, 0.21–0.33, 95% CI), compared to wetter sites (0.12, 0.04–0.20 95% CI), due to lower tree seedling densities at drier sites. However, liana seedlings did not grow or survive better than tree seedlings in drier sites compared to wetter sites. Tree seedlings were more negatively impacted in terms of mortality by the extreme El Niño drought than liana seedlings, with an increase in annual mortality rate of 0.013 (0.003–0.025 95% CI) compared to lianas of −0.009 (−0.028 to 0.008 95% CI), but not growth. Our results indicate that lianas do not have a SGA over trees at the seedling stage. Instead, higher survival of liana versus tree seedlings during severe droughts or differences in liana versus tree fecundity or germination across the rainfall gradient likely explain why liana seedlings have higher relative densities at drier sites.

NATIVE MYCORRHIZAE FROM ETHIOPIA IMPROVE TREE GROWTH AND SEEDLINGS SURVIVAL CONTRIBUTING TO THE GREEN LEGACY PROGRAM

<p><strong>Background</strong>: A rapid production of tree seedlings in nurseries with a high survival rate after transplanting is important to respond to the current demand for programs of restoration of arid environments by forestation. The low level of seedlings’ survival and establishment, caused by low moisture and nutrient content of soils, has been a bottleneck to reaching the target of the forest national restoration in Ethiopia of last years. It is suggested that, inoculation with root-associated plant growth promoting microorganisms could help to ameliorate this scenario and also respond to the Ethiopia's Green Legacy Program. <strong>Objective</strong>: To assess the potential of inoculation with arbuscular mycorrhizal fungi (AMF) native to Ethiopia to improve the survival and growth of trees that could be used in afforestation programs in Ethiopia. <strong>Methodology</strong>: The study was carried out in three stages: (1) soil samples associated with roots of selected acacia species (T<sub>1</sub>-AMF of<em> A. abyssinica</em>, T<sub>2</sub>-AMF of<em> A. seyal</em>, T<sub>3</sub>-AMF<em> </em>of <em>A. tortilis </em>and<em> </em>T<sub>4</sub>-Control) were collected of highland and lowland areas from Ethiopia, (2) Sorghum (<a href="https://www.researchgate.net/publication/342429051_Evaluation_of_sorghum_Sorghum_bicolor_L_Moench_variety_performance_in_the_lowlands_area_of_wag_lasta_north_eastern_Ethiopia"><em>Sorghum bicolor</em> (L.), provided by the Melkasa Agricultural Research Center-(MARC) served as a trap plant for </a>the AMF consortium multiplication and (3) plant growth promotion by AMF was assessed throughout inoculations of seedlings of<em> </em><em>Delonix regia</em> (Hook.) Raf.,<em> Sesbania grandiflora </em>(L.)<em>, Cassia fistula </em>L<em>., </em>and<em> Azadirachta indica </em>A. Juss., trees<em>. </em><strong>Results</strong>: All inoculated seedlings showed significantly greater responses in all growth and mycorrhizal parameters over the non-inoculated trees. Consortium T<sub>2</sub>-AMF associated to roots of<em> A. seyal </em>from lowlands of Batu, showed significantly greater responses in all plant growth and mycorrhizal parameters over the AMF inoculums associated to other tree species evaluated. Significant and positive correlations were found between mycorrhizae and plant-growth parameters<em>. </em><strong>Implications:</strong> Our results suggest that inoculation with native arbuscular mycorrhizal fungi indigenous from Ethiopia has the potential to significantly enhance survival and growth rates of tree seedlings. This could thereby advance national reforestation goals and addressing challenges in seedling establishment in arid environments. <strong>Conclusion</strong>: The potential for growth promotion and establishment of tree seedlings evidenced, implies that further efforts should be directed towards the in-mass production of AMF-based inoculants, particularly associated with <em>A. seyal</em> roots.</p>

Organic Mulching Alters the Soil Microclimate, Increases Survival and Growth of Tree Seedlings in Restoration Planting

Organic Mulching Alters the Soil Microclimate, Increases Survival and Growth of Tree Seedlings in Restoration Planting

Cattle and nurse trees shape subtropical forest–grassland ecotones

Abstract South American subtropical landscapes are dominated by open grasslands and mosaics of forest–grassland formations. Forests are often restricted to riverine margins with sharp forest–grassland ecotones. Understanding the mechanisms maintaining forest–grassland ecotones is important to anticipate the effects of changing climate and disturbance regimes on the extent of these biomes and the ecosystem services they provide. We used a combination of field surveys and long‐term field experiments to explore the mechanisms that explain tree cover expansion at the ecotone of riverine forests and grasslands in central Uruguay, within the South American Campos. We assessed the role of tree seed dispersal and seedling establishment limitations, and experimentally tested for the effects of cattle, nurse tree cover and grasses on the recruitment of forest and grassland tree species at the forest–grassland ecotone. We found that forest expansion depends on the interplay between cattle and nurse trees. Vachellia caven trees colonize the grassland successfully and facilitate the formation of forest patches by enhancing seed accumulation and seedling establishment of forest tree species. Surprisingly, grass cover had mostly positive effects on early seedling survival of forest tree seedlings. However, cattle limits tree seedling growth and survival, especially of forest tree species. This results in a nucleated vegetation pattern of tree patches that ultimately limits forest expansion. Synthesis and applications. Tree cover can potentially expand on the subtropical South American grasslands. Reductions in cattle densities and increases in rainfall levels associated with climate change could facilitate forest expansion in this region.

Open geospatial data can predict the early field performance of Scots pine, Norway spruce and silver birch seedlings in Nordic boreal forests

ABSTRACT Accurate knowledge of site conditions and their effects on regeneration establishment is important for selecting the most appropriate tree species and regeneration methods for a given regeneration site. This study examined the response of the first-year field performance of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth.) seedlings in boreal forests to variables available in open forest and natural resources datasets. Survival, height increment and damage of planted tree seedlings and the success of direct seeding of pine were analysed on a total of 284 plots (1000 m2) in 18 regeneration experiments established in 2020–2022 in southern and central Finland. The height increment of silver birch was higher than that of conifers, while the lowest mortality rate was found for spruce. In the generalised linear mixed models, topographic wetness index, soil texture, site type and growing stock at clearcut explained the species-specific survival and height increment of planted seedlings and the success of pine seeding. Low-cost, open geospatial data effectively provide useful details on the site conditions suitable for diversifying tree species composition in boreal forests instead of monocultures.

Facilitation drives tree seedling survival at alpine treelines

Abstract Alpine treelines are considered ecological monitors recording the impacts of climate change on trees and forests. To date, most treeline research has focused on how climate change drives treeline dynamics. However, little is known about how biotic interactions mediate treeline shifts, particularly in the case of tree recruitment, a bottleneck of treeline dynamics. We hypothesized that inter- and intraspecific facilitation determined the establishment and survival of tree seedlings at alpine treelines. To test this hypothesis, 630 Abies georgei var. smithii seedlings with different ages (4–6, 7–9 and 10–15 years old) were transplanted into three growth habitats (canopy-in, canopy-out and meadow) across the alpine treeline ecotone (4300–4500 m) in the Sygera Mountains, on the southeastern Qinghai-Tibetan Plateau. Microclimate, height growth, mortality rates and leaf functional traits of transplanted seedlings were measured over 3 years. We found that the variations in leaf functional traits were driven by microclimate. After the transplantation, the leaf concentrations of soluble sugars and starch and C:P ratio increased, whereas leaf size decreased. The resource use of seedlings gradually shifted to a more conservative strategy as indicated by changes in non-structural carbohydrates and nutrient concentrations. Radiation, temperature and moisture conditions, mediated by plant interactions, influenced seedling mortality and annual growth by affecting leaf morphological traits. Our findings illustrate how facilitation plays a crucial role in altering solar radiation and leaf trait functioning, determining seedling survival and growth at alpine treelines. We provide new insights into the underlying mechanisms for tree establishment and alpine treeline shifts in response to climate change.

Tree and grass competition in savannas: Interactive effects of soil moisture, grass defoliation and grass species identity on the growth and survival of tree seedlings

AbstractWe experimentally examined the influence of grass competition, grass species identity (taxa) and water availability on the seedling growth and survival of two dominant tree species (Vachellia (formerly Acacia) robusta and V. tortilis) of the Serengeti National Park in Tanzania. Despite being widely distributed, the species have an opposing overstorey dominance across a rainfall and productivity gradient, with V. robusta dominating the more productive mesic sites and V. tortilis in the lower productivity, drier sites. We investigated the role of different grass species, which vary in distribution and abundance across the rainfall gradient, in influencing the growth and survival of Vachellia seedlings. We found a significant effect of grass competition but no effect of grass species identity on the growth or survival of seedlings. Seedling survival was highest in the absence of grass competition, intermediate when grasses were defoliated to simulate grazing and lowest when grown with ungrazed grasses. Grass competition had a more negative effect on the stem diameter of V. tortilis than V. robusta. All V. tortilis seedlings grown under a combination of drought conditions and unclipped grasses died by the end of the experiment. However, reduced grass competition by simulated grazing improved V. tortilis seedling survival to comparable levels achieved by V. robusta species. Our study advances our understanding of tree and grass competition across environmental gradients and suggests that the presence of grass and soil moisture have species‐specific effects on tree seedling growth and survival in African savannas.

Survival, growth, and functional traits of tropical wet forest tree seedlings across an experimental soil moisture gradient in Puerto Rico.

Droughts are predicted to become more frequent and intense in many tropical regions, which may cause shifts in plant community composition. Especially in diverse tropical communities, understanding how traits mediate demographic responses to drought can help provide insight into the effects of climate change on these ecosystems. To understand tropical tree responses to reduced soil moisture, we grew seedlings of eight species across an experimental soil moisture gradient at the Luquillo Experimental Forest, Puerto Rico. We quantified survival and growth over an 8-month period and characterized demographic responses in terms of tolerance to low soil moisture-defined as survival and growth rates under low soil moisture conditions-and sensitivity to variation in soil moisture-defined as more pronounced changes in demographic rates across the observed range of soil moisture. We then compared demographic responses with interspecific variation in a suite of 11 (root, stem, and leaf) functional traits, measured on individuals that survived the experiment. Lower soil moisture was associated with reduced survival and growth but traits mediated species-specific responses. Species with relatively conservative traits (e.g., high leaf mass per area), had higher survival at low soil moisture whereas species with more extensive root systems were more sensitive to soil moisture, in that they exhibited more pronounced changes in growth across the experimental soil moisture gradient. Our results suggest that increasing drought will favor species with more conservative traits that confer greater survival in low soil moisture conditions.

Seedling survival and plantation success in the drylands of Northern Ethiopia

We studied tree seedling survival rates and plantation success of the Growth and Transformation Plan I—GTP I (2011–2015) in the drylands of Northern Ethiopia. The study was carried out in six randomly selected districts of Tigrai region that represent three agro-ecological zones: the highland, midland and lowland. A biophysical survey was conducted to assess the survival rates of tree seedlings and the success rate of the plantation interventions. The study employed both primary and secondary data sources. Results revealed that there were variations (P < 0.05) in the survival of planted tree seedlings among plantation sites of the same village, between the villages of the same district and among the districts. The regional mean survival rate of planted tree seedlings was 53%. The planting interventions were not encouraging due to lack of pre- and post-planting management, moisture stress, poor soil and site conditions, planting an unmanageable number of seedlings, weak law enforcement and lack of proper monitoring and evaluation mechanisms. In the study areas, four types of ownership were identified: private, communal, state and youth groups. Among the ownership types, private ownership had the highest rate of success, whereas community ownership had the lowest rate. For sustaining successful plantation development, watering, pre- and post-planting management of planted tree seedlings and permanent employment of guards are important.

Investigation of Moisture Collection Structures and Introduction of Resistant Tree Species in the Semi-Arid Slopes of Tigray, Ethiopia

Vegetation cover degradation is a serious problem in low-rainfall areas of Ethiopia. A field experiment was carried out for three years on two degraded hillsides in Kilte Awlaelo district, Tigray, Ethiopia. The objective was to evaluate the effect of moisture harvesting structures on the survival and growth of tree seedlings. The treatments were micro basin, micro trench, eyebrow basin, and conventional pit as moisture harvesting structures combined with three multi-purpose tree seedlings, namely, Schinus molle, Grevillea robusta, and Olea europaea. The set-up was a split-plot design with three replications. Seedling survival, plant height, and collar diameter data were collected. The collected data were analyzed using GenStat 16 edition software by general liner model. Statistically significant differences between and among treatment means were assessed using the least significant difference (LSD) at the 5% level of significance. The results in the main effect showed eyebrow basin &gt; micro basin &gt; micro trench &gt; conventional pit in the upper site, and micro basin &gt; eyebrow basin &gt; micro trench &gt; conventional pit in the lower site in their order of level of significance in enhancing the seedlings survival and growth performance. The interaction effects also showed Schinus molle backed with an eyebrow and micro-basin in the above structure pit position had the highest survival rate and growth performance. Hence, the eyebrow basin and micro basin as moisture harvesting structures planted with Schinus molle tree species at the above pit position should be demonstrated and scaled up in moisture-stressed areas of Kilte Awlaelo district.

Modification of Density Dependence and Habitat Filtering on Seedling Survival of Different Mycorrhizal-Type Tree Species in Temperate Forests

Conspecific negative density dependence (CNDD) and habitat filtering are critical to seedling survival. However, the relative importance of the two processes in affecting survival of seedlings with different types of mycorrhizae remains unclear. In this study, the effects of CNDD and habitat filtering on the survival of tree seedlings with different mycorrhizal types were investigated at different successional stages of a temperate forest in the Changbai Mountain Natural Reserve, Northeast China. Conspecific negative density dependence and habitat filtering significantly affected seedling survival. In the early successional stage, the interactions between conspecific neighbor tree density and light availability and soil properties significantly negatively affected survival of all species and arbuscular mycorrhizal (AM) seedlings in the community, but not that of ectomycorrhizal (EcM) seedlings, and the CNDD effect was stronger on AM seedlings than on EcM seedlings. In the mid-successional stage, CNDD effects were stronger on EcM seedlings. Therefore, different types of mycorrhizal seedlings responded differently to CNDD and habitat filtering mechanisms during community succession, and thus, tree mycorrhizal association could determine the effects of CNDD and habitat filtering on seedling survival in temperate forests.

The role of secondary forest in the survival and growth of native species: Tree planting field experiment in the delta of the Paraná River (Argentina)

Secondary forests constitute 74% of the world's natural forests and, while the conservation value of primary forests is irreplaceable, secondary forests can provide important biological conservation services and secure the future of many species. In the frontal zone of the Paraná River delta (Argentina), post-abandonment secondary forests are developed, composed of exotic species, but in which regeneration of native plant species is observed. The objective of this study was to evaluate the role of secondary forest in the conservation of native trees. For this, the survival and growth of 60 seedlings, belonging to four native tree species and planted inside and outside a secondary forest, were analyzed for one year. Results indicates that the average survival within the secondary forest (89%) is significantly higher than outside it (66%) and that, in the range studied (6 to 41 cm), the survival odds increase by 10% with each centimeter that the seedling's initial height increases. Height growth of seedlings is, on average, 144% higher in the absence of forest cover and differs according to species, with Allophylus edulis and Myrsine parvula being the species with the highest growth and Lonchocarpus nitidus the lowest. After one year monitoring, it is noted that the secondary forest is an environment conducive to the survival of native tree seedlings, although it imposes growth limitations typical of environments with forest physiognomy. Also, that the planting of native trees can constitute an adequate ecological restoration technique for the recovery of native riparian forest in the frontal zone of the Paraná River delta.

UAVs for monitoring responses of regenerating forests under increasing climate change-driven droughts - a review

The impact of climate change-driven droughts on regenerating forests is poorly understood due to the complexities involved in regeneration processes and the difficulties in measuring the relevant parameters with sufficient spatial and temporal resolution in a timely manner. Drought increases tree mortality in both undisturbed and disturbed forests and may influence forest regeneration dynamics from seed germination to the recruitment, growth, and survival of tree seedlings. Seedlings and small saplings may be more susceptible to changes in water availability than larger individuals due to their shallower roots that may be unable to reach the deeper, moist soil layers, and due to uneven competition with adult trees for soil moisture. The potential range shifts and local extinction of drought-sensitive species can also result in changes in forest species community composition and diversity loss at different scales. There is a need for precise and low-cost monitoring systems that facilitate better capturing of the complexities of such processes for restoration measures. The objective of this paper is to study the use of UAVs (Unmanned Aerial Vehicles) for monitoring responses of regenerating forests under increasing climate change-driven droughts. UAVs have several advantages over traditional field-based monitoring techniques and flexibility in selecting the required spatiotemporal resolution over other remote sensing methods, making them a promising tool for monitoring forest recovery. Although further research is required to ensure the accuracy and effectiveness of UAV-facilitated measures for monitoring forest regeneration, UAVs possess great potential in forest management in the event of increasing occurrences of climate-change driven droughts.

Review on Factors Affecting Early Survival of Tree /Shrub Seedlings and it’s Remedy in Restoration Sites of Ethiopia

Abstract Restoration activities in degraded and/or deforested forest landscapes are common and old occurrences around the world. Tree planting is common in most forest landscape restoration initiatives. In Ethiopia, eight seedling-based landscape restoration options are identified to alleviate land degradation and its consequences. The primary purpose of this work was to review factors affecting the early survival of tree and shrub seedlings and their remedies in the restoration sites of Ethiopia. Drought and moisture stress, low soil fertility, poor seedling quality, weak species site matching, termites, livestock grazing, and seasonal frost are the basic factors that hinder the survival and growth of seedlings in the field. In situ rainwater harvesting structures, fertilizer application, the use of quality seedlings, the right species site matching, and the exclusion of livestock and grazing animals from planted seedlings are the remedies that must be employed to increase the success of tree-based restoration practices. Thus, further investigation of the factors affecting the survival of seedlings in the out-planting sites and remediation accordingly is necessary to ensure the productivity and sustainability of restoration practices in Ethiopia.

Effects of native and invasive grasses on the survival and growth of tree seedlings in a neotropical savanna

Effects of native and invasive grasses on the survival and growth of tree seedlings in a neotropical savanna

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.

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