High Seedling Mortality Research Articles

BUMDes Strategies for Successful Banana Planting Programs

General Background: Village-Owned Enterprises (BUMDes) are essential for enhancing local economies through agricultural initiatives. Specific Background: In Krembung Village, Sidoarjo Regency, a banana planting program has been implemented to improve productivity and income. Knowledge Gap: However, challenges like high seedling mortality and inadequate practices hinder success. Aims: This study analyzes BUMDes strategies in executing the banana program, focusing on community involvement and resource management. Results: While strength and progress indicators are optimal, the value aspect is suboptimal due to significant seedling losses. Community support for banana cultivation has been strong. Novelty: The research highlights practical challenges and strategic approaches in managing BUMDes agricultural programs. Implications: Findings emphasize the need for better resource allocation and community engagement to enhance agricultural initiatives, providing insights for improving BUMDes operations and promoting sustainable rural development. Highlights: Community Involvement: Strong local support is crucial for the success of the banana planting program. Resource Management: Effective allocation and management of resources are necessary to mitigate seedling mortality. Strategic Approaches: Implementing targeted strategies can enhance agricultural productivity and economic benefits for the village. Keywords: BUMDes, Banana Planting, Community Engagement, Agricultural Productivity, Village Potential

Distinct effects of phyllosphere and rhizosphere microbes on invader Ageratina adenophora during its early life stages.

Microbes strongly affect invasive plant growth. However, how phyllosphere and rhizosphere soil microbes distinctively affect seedling mortality and growth of invaders across ontogeny under varying soil nutrient levels remains unclear. In this study, we used the invader Ageratina adenophora to evaluate these effects. We found that higher proportions of potential pathogens were detected in core microbial taxa in leaf litter than rhizosphere soil and thus leaf inoculation had more adverse effects on seed germination and seedling survival than soil inoculation. Microbial inoculation at different growth stages altered the microbial community and functions of seedlings, and earlier inoculation had a more adverse effect on seedling survival and growth. The soil nutrient level did not affect microbe-mediated seedling growth and the relative abundance of the microbial community and functions involved in seedling growth. The effects of some microbial genera on seedling survival are distinct from those on growth. Moreover, the A. adenophora seedling-killing effects of fungal strains isolated from dead seedlings by non-sterile leaf inoculation exhibited significant phylogenetic signals, by which strains of Allophoma and Alternaria generally caused high seedling mortality. Our study stresses the essential role of A. adenophora litter microbes in population establishment by regulating seedling density and growth.

Distinct effects of phyllosphere and rhizosphere microbes on invader Ageratina adenophora during its early life stages

Microbes strongly affect invasive plant growth. However, how phyllosphere and rhizosphere soil microbes distinctively affect seedling mortality and growth of invaders across ontogeny under varying soil nutrient levels remains unclear. In this study, we used the invader Ageratina adenophora to evaluate these effects. We found that higher proportions of potential pathogens were detected in core microbial taxa in leaf litter than rhizosphere soil and thus leaf inoculation had more adverse effects on seed germination and seedling survival than soil inoculation. Microbial inoculation at different growth stages altered the microbial community and functions of seedlings, and earlier inoculation had a more adverse effect on seedling survival and growth. The soil nutrient level did not affect microbe-mediated seedling growth and the relative abundance of the microbial community and functions involved in seedling growth. The effects of some microbial genera on seedling survival are distinct from those on growth. Moreover, the A. adenophora seedling-killing effects of fungal strains isolated from dead seedlings by non-sterile leaf inoculation exhibited significant phylogenetic signals, by which strains of Allophoma and Alternaria generally caused high seedling mortality. Our study stresses the essential role of A. adenophora litter microbes in population establishment by regulating seedling density and growth.

Comprehensive review of the skin use of bakuchiol: physicochemical properties, sources, bioactivities, nanotechnology delivery systems, regulatory and toxicological concerns

AbstractBakuchiol is a meroterpene that has recently aroused great interest in the cosmetic and pharmaceutical industries. Its main source is the seeds of Psoralea corylifolia, a medicinal plant native to Asia, despite having a wide geographical distribution. However, this medicinal herb faces endangerment due to low seed germination rates and high seedling mortality. In this context, this review article highlights studies that have focused on describing plant regeneration from root fragments. Subsequently, given its morphological similarity to other species, a technique that can be used to verify the authenticity of the plant and prevent counterfeiting is also mentioned and explored. Additionally, a “green” extraction method for obtaining bakuchiol is presented, and the possibility of obtaining bakuchiol through chemical synthesis routes is also explored. Furthermore, we provide an exhaustive description of bakuchiol's wide range of biological activities, with particular relevance to the skin. The main skin bioactivities of bakuchiol include antifungal, antibacterial, antioxidant, anti-inflammatory, antiaging, depigmenting, and anticancer. However, the particular physicochemical properties of bakuchiol require and benefit from the development of innovative skin delivery systems that allow its encapsulation. These include micro- and nano-sized systems for therapeutic and cosmetic applications, which are also carefully described in this review article. Finally, regulatory issues, metabolic considerations, and toxicological concerns related to the use of bakuchiol in cosmetic and dermopharmaceutical formulations will be addressed, relating not only to the user but also to the environment. Graphical abstract

Population dynamics of Trichoderma harzianum in bio- fortified compost against soil-borne potato diseases

Soil-borne diseases pose significant challenges to global potato cultivation, resulting in yield losses and economic implications. Utilizing biological control agents offers a sustainable and environmentally and friendly approach to manage these diseases. Before implementing the experiment in the field, a series of in-vitro tests were conducted to select a virulent isolate of the tested pathogens and an effective antagonistic isolate of Trichoderma harzianum. In the pathogenicity test, isolate RS-1 of Rhizoctonia solani and isolate SR-8 of Sclerotium rolfsii exhibited the highest virulence against two pathogens in potato variety ‘Cardinal’ in regard to seedling mortality (44.44-88.88%). During in vitro screening, T. harzianum isolate Tri 7 displayed the greatest ability to inhibit the mycelium growth of all tested pathogens. In the field trial, the highest seedling mortality (69.06%) was observed in T2 (Fresh seeds+ Soil inoculated with R. solani and S. rolfsii). However, the highest seedling mortality (86.94%) was reduced by treatment T7 (Fresh seeds+ Soil inoculated with R. solani and S. rolfsii +500g wheat grain colonized with Trichoderma fortified poultry compost). Treatment T7 also recorded the lowest incidences of stem canker (7.83%) and stem rot (8.64%), whereas the highest disease incidences occurred in the T2 treatment plot. Notably, treatment T7 gave the highest yield of 30.94 tons/ha, while the control plot T2 yielded the lowest at 12.17 tons/ha. Initially, Trichoderma population was minimal prior to the application of Trichoderma- fortified compost. However, populations gradually increased over time, peaking at 3 months across all treatments except the control, where no Trichoderma was applied. However, a decline in T. harzianum population was noted one month after potato harvesting. This approach offers a potential solution for managing potato soil-borne diseases in a sustainable and environmentally friendly manner. Ann. Bangladesh Agric. (2023) 27 (1): 81-92

Effects of soil mulches and conditioners on seedling emergence and survival of Astragalus nigricans Barneby in an arid steppe rangeland

Soil mulches and conditioners have been shown to improve soil moisture conservation, infiltration, and seed germination and survival, but their interactive effects with sporadic rainfall and the existing vegetation have rarely been considered. In an experimental field study, we assessed the effects of soil additives (sawdust and hydrogel) and mulches (river sand and plant debris) on seedling emergence and survival of Astragalus nigricans Barneby, in the rangelands of Mashhad, northeast Iran. We also assessed any effects on soil moisture and temperature several days after rain in July 2017 and May 2018 and weed composition, density, and diversity. The most successful treatment was hydrogel, associated with earlier seedling emergence for A. nigricans, greater seedling survival, and biomass production. Sawdust and sand treatments were useful for root proliferation and seedling emergence in the spring of the first season, but they led to high seedling mortality under drought. Debris of Artemisia khorasanica shoots was the most efficient and consistent treatment for soil moisture conservation and temperature stability in both years, but its possible allelopathic effects led to high seedling mortality and a long delay (41 days) on seedling emergence. Plant debris also negatively affected the density, richness, and diversity of nontarget plant species. Despite differences among different rainfall events, mulch treatments have an important role in regenerating degraded rangelands.

Experimental drier climates affect hydraulics and induce high mortality of seedlings of three northern conifer species

The future climate of northern temperate forests is projected to be drier and warmer by the end of this century. As a result, more drought-induced forest dieback events are anticipated in northeastern North America, and assessing the vulnerability of dominant tree species to drought is critical for understanding the future composition of these forests. In a greenhouse experiment, we exposed two-year-old seedlings of Picea glauca (Moench) Voss, Picea mariana (Mill.) B.S.P. and Pinus strobus L. to three future climate treatments for southern Quebec, Canada, and evaluated their mortality, growth, and foliage water status responses to soil water availability and atmospheric drought. Using a unique approach, climate treatments emulated droughts of different frequencies, durations, and intensities. Treatments closely simulated one growing season, with changes in air temperature and relative humidity every six hours and daily adjustment in the amount of water delivered to the seedlings. The three species experienced high mortality (75%) in all water-limited treatments compared to a control treatment that provided non-limiting soil moisture (0% mortality). The biomass of the seedlings that survived was 40% lower than that of control seedlings. Our results confirmed that the hydraulic safety margins, defined as the difference between seasonal minimum water potential and xylem water potential leading to 12, 50 and 88% of hydraulic conductivity loss, were good predictors of probability of tree mortality. Therefore, hydraulic safety margins are useful functional traits that can be used to compare the vulnerability of various species to drought and then provide crucial information to practitioners and policymakers to adjust forest management to climate change. We showed that three dominant conifer species of northern temperate forests were highly vulnerable to drought in future climates. Because drought is projected to be a significant threat to forests, understanding potentially adaptive physiological responses to drought, such as hydraulic safety margins of tree seedlings, is important for predicting the response of forest regeneration and composition in warmer and drier climates.

Quantitative and qualitative assessment of pine seedlings under controlled undergrowth disturbance: Fire and soil scarification

Scots pine (Pinus sylvestris L.) is the most widespread forest tree species in Central Europe. The range of Scots pine depends on the influence of forest management on stand species composition, as the potential for the natural regeneration of Scots pine monocultures is smaller than the current range of the species. To achieve regeneration, pine requires specific ecological conditions, including adequate soil preparation. The literature notes that the effective natural regeneration of pine requires fire or mixing the organic soil layer with the mineral layer. This hypothesis was critically evaluated carrying out work with the main objective of comparing the germination and growth dynamic of pine seedlings in two variants, simulating fire or soil scarification against natural conditions. The research focused on analyzing the growth of pine seedlings from germination to the final number of seedlings, which remained unchanged until the end of the experiment. The evaluation was carried out in soil monoliths from Kampinos National Park (KNP), in which seeds from a homogeneous mother stand were planted. The quantitative and qualitative characteristics of the seedlings were statistically evaluated, including analyses of their root system characteristics. The results confirmed the positive effect of mixing an organic and mineral layer at the germination stage and during the subsequent growth of the pine. The seedlings had a high survival rate (65.3%). However, the positive effect of fire on the regenerative capacity of pine could not be confirmed; the number of obtained seedlings (29.5%) was significantly lower than in the control variant. In addition, the “fire variant” was characterized by high seedling mortality immediately after germination. Root systems were important for the survival of the seedlings, the development of which was affected by the tested variant. The analyses performed may have implications for the development of research on the possible natural regeneration of Pines after natural disturbances. Additional topic that needs further research is the response of seedling root systems to changes in soil conditions.

Reducing Exotic Annual Grass Competition did not Improve Shrub Restoration Success During a Drought

Restoration of native shrub species is challenging but direly needed in arid and semiarid rangelands globally as native shrubs provide critical habitat for wildlife and livestock forage. Restoration of antelope bitterbrush (Purshia tridentata Pursh DC), a wildlife-important shrub, is often a priority on western US rangelands. One challenge to bitterbrush restoration is competitive exotic annual grasses. Exotic annual grasses can be successfully controlled with pre-emergent herbicides, but the effects of controlling exotic annual grasses with pre-emergent herbicides on bitterbrush survival and growth are unknown. We evaluated the effects of applying a pre-emergent herbicide, imazapic, to control exotic annual grasses on planted bitterbrush seedlings and existing vegetation for 2 yr post treatment at five sites in southeastern Oregon. Imazapic application reduced exotic annual grass cover and density but did not improve bitterbrush establishment. Exotic annual grass control did lead to an increase in native perennial bunchgrass cover. We suspect the lack of treatment effect was caused by high mortality of bitterbrush seedlings from drought in the first year. By the second year, bitterbrush was largely lost across the study sites with only four individuals surviving. The high bitterbrush seedling mortality observed in this study highlights that multiple barriers to restoration success likely exist in arid and semiarid rangelands. For successful restoration, land managers and restoration practitioners need to have a plan and resources for overcoming multiple barriers, which may require several restoration attempts should initial attempts be unsuccessful.

Root Morphology, Anatomy, and Mycorrhiza of Peristylus goodyeroides (D.Don) Lindl. (Orchidaceae) in Different Life Stages: Ecological Significance and Implication for Conservation

Orchid roots have vital functions for water absorption, nutrient uptake, a place of symbiosis with mycorrhizal fungi, adaptation, and survival. The aim of the present study was to investigate root traits in terms of root morphological, anatomical, and mycorrhizal features of a terrestrial orchid, Peristylus goodyeroides in relation to an ecological significance of root traits in survival of seedlings, juveniles, and adults of the orchid. Results showed that some morphological characters (root length and depth), anatomical features (cortical cell size, xylem number and diameter), and mycorrhizal features (peloton size and number) were significantly different between seedlings, juveniles, and adults. In relation to root functional traits, lowest root length, depth, xylem number and diameter, peloton size and number in seedlings can be associated with low capacity in water and nutrient acquisition that might explain low survival of seedlings relative to juveniles and adults. Present study has implication for orchid conservation suggesting high attention in low survival rate of seedlings related to specificity in some of their morphological, anatomical, and mycorrhizal features which can be associated with low capacity in water and nutrient acquisition. It is vital to ensure water availability for seedlings, particularly, during dry seasons to decrease high mortality of seedlings as such high mortality can have adverse impacts on long-term survival of the orchid population.

Provenance Variation in Early Survival, Growth, and Carbon Isotope Discrimination of Southwestern Ponderosa Pine Growing in Three Common Gardens across an Elevational Gradient

We investigated early survival, growth, and carbon isotope discrimination of ponderosa pine (Pinus ponderosa Lawson & C. Lawson var. scopulorum Engelm.) seedlings from different provenances using common gardens across an elevational gradient in order to examine the potential for adaptation to extreme environments and constraints to artificial regeneration. Twenty-one provenances from a range of elevations across Arizona and New Mexico were planted in three common gardens: a high-elevation meadow in aspen-mixed conifer forest, a mid-elevation ponderosa pine forest, and a low-elevation pinyon juniper woodland. Two years after planting in 2018, survival was highest at the mid-elevation site (54%), low at the high-elevation site (1.5%), and 0% at the low-elevation site. At the hot and dry low-elevation site, provenances from low-elevations survived longer than provenances from mid- and high-elevations, which suggests greater drought tolerance of low-elevation provenances. Mortality agents changed from abiotic (drought) to biotic (herbivory) with an increase in elevation across sites. High mortality of seedlings planted at high-elevation sites from biotic agents, such as rodents, may challenge efforts to establish ponderosa pine in assisted migration projects. Seedlings had significantly higher growth rate and carbon isotope discrimination (∆13C) at the mid-elevation site than the high-elevation site. Provenances differed significantly in diameter, and ∆13C, but not in height growth rate for the first year after planting. Provenance variation in ∆13C suggests genetic variation in water use efficiency that may be useful for future evaluation of southwestern ponderosa pine seed sources for reforestation.

High Seedling Mortality of Scots Pine Caused by Heterobasidion annosum s.s.

This study provides new information on the infection biology and pathogenicity of an important root-rot fungus, Heterobasidion annosum sensu stricto (Fr.) Bref., through a detailed examination of the vegetative spread of clonal individuals and their capacity to produce fruiting bodies on young pine seedlings. The seedlings were planted in a clear-cutting area (c. 1.2 ha in size) after a pine generation that showed slight external symptoms of Heterobasidion root rot. The first dead seedlings were found five years after planting and during a nine-year monitoring period; nearly 600 seedlings were killed by H. annosum s.s. in 48 individual disease centers. Based on pairing tests of 482 isolates, 117 different H. annosum s.s. genotypes were identified. On average, 2.9 genotypes occurred in a single disease center. The extensive secondary spread of genotypes within root systems (up to 48 pine seedlings infected by the same genotype) resulted in annually expanding disease centers. In addition, more than half of the seedlings killed by H. annosum s.s. produced perennial fruiting bodies thus providing air-borne inoculum. The risk of spore infection should be taken into account in any type of cutting operation in young pine stands. Moreover, new control measures directed towards the secondary spread of H. annosum s.s. in pine regeneration are urgently needed in order to maintain the productivity of the pine forest on infested sites.

Characterization of a Disjunct Population of Eastern Hemlock (Tsuga canadensis) and Surrounding Plant Communities in the North Carolina Piedmont after 65 Years of Forest Change

Hemlock Bluffs Nature Preserve is a 57-ha preserve in the piedmont of North Carolina. A small disjunct Tsuga canadensis (Eastern Hemlock) population exists in the preserve, primarily within a microclimate on a north-facing bluff. A study published in 1956 included a 1952–1953 inventory of the hemlock population as well as records of the local flora and climate. We re-inventoried the Eastern Hemlock population, conducted a new floristic survey, and recorded new climate data in the preserve in 2018–2019. Our new data reveal a notable change in both the Eastern Hemlock population and preserve-wide stand structure. Only 2% average light transmittance through the canopy was recorded in the preserve in the 2019 growing season, compared to 11% in the 1953 growing season (P = 0.02). At least 7 plant taxa underwent notable shifts in distribution, mostly moving down-slope on the bluff face. Average ambient air temperatures on the bluff were 1.62 °C higher in 2018–2019 than in 1952–1953. Canopy closure, inbreeding depression, increased temperatures, erosion, and browsing by Odocoileus virginianus (White-tailed Deer) all likely contribute to low Eastern Hemlock seed germination and high seedling mortality within the preserve. These factors may also partially account for observed shifts in floristic distribution. In addition to mortality caused by Adelges tsugae (Hemlock Woolly Adelgid), these environmental changes endanger the future viability of this Eastern Hemlock population.

Soil erosion facilitates shrub encroachment in Patagonian herbaceous steppes

AbstractPrevious studies in northeastern Patagonia suggested that, mainly as a consequence of overgrazing by sheep, the herbaceous steppes are being replaced by shrub steppes dominated by Chuquiraga avellanedae as a consequence of shrub encroachment. The herbaceous steppe presents a thick sandy loam to loamy sand A‐horizon lying on a clay‐horizon while the shrub steppe presents the clay‐horizon at or near the soil surface. The thickness reduction of the remaining A‐horizon and the formation of desert pavements are evidence of soil erosion. As previous studies suggested that shrub encroachment co‐occurs with the erosion of the sandy A‐horizon, we hypothesized that shrub encroachment is favored by the presence of an clay‐horizon near the soil surface. We expected that C. avellanedae emergence and establishment would be higher as the clay horizon is closer to the soil surface and the A‐horizon is reduced. We performed field and greenhouse experiments to evaluate seedling emergence and establishment along a gradient of A‐horizon thickness. We found that the presence of a relatively thin sandy layer on the surface had a negative influence on both shrub emergence and establishment. The summer drought was not a critical period for the seedlings. Conversely, the highest seedling mortality took place during late winter in sandy soils, suggesting that these soils are more susceptible to frost heaving than clay soils. In conclusion, soil erosion in the northeastern Patagonian steppes would indirectly facilitate shrub encroachment due to differences in frost heaving susceptibility between sandy and clay soils.

Effects of Organic and Inorganic Fertilizers on Growth and Nutrient Uptake by Young Cacao (Theobroma cacao L.)

Sustainable cacao cultivation in Ghana has been seriously hampered by high seedling mortality due to the low soil fertility of lands used for the establishment of new cacao farms. Alleviating the low soil fertility to enhance sustainable cacao cultivation requires the use of fertilizers. A study was therefore conducted at the Cocoa Research Institute of Ghana to determine the effect of integrated application of poultry manure (PM) and sulphate of ammonia (SOA) fertilizers on survival, growth, and nutrient uptake by cacao seedlings under marginal field conditions. A randomized complete block design with four replications was used to evaluate the effects of six treatments. Traits assessed were percentage survival, height, trunk cross-sectional area (TCSA), and nutrient uptake. Results from the study showed no significant differences in soil N and K among the treatments. PM-amended plots had significantly higher soil P than nonamended control and SOA alone. Seedling survival rate ranged from 73.3 to 89.3% with a higher proportion of surviving plants in PM amended soils. The application of PM alone and its combination with SOA improved growth. Cacao trees of T4 (75% recommended dosage of SOA + PM) had the largest TCSA increment, which was significantly different from the other soil treatments. Leaf nutrient concentrations in cacao of T4 were higher than the other soil treatments. It was therefore concluded that T4 could be used during cacao establishment in marginal areas for improved plant survival and growth.

Asking the Wrong Question in Explaining Tropical Diversity

Enhancement of plant diversity via the Janzen-Connell mechanism is often measured relative to neutral models that ignore species' competitive differences. Recent modelling indicates this mechanism is ineffective when included in models incorporating species' demographic variations. This suggests we have been asking the wrong questions when measuring the effectiveness of diversity-enhancing mechanisms.

Thermal niche for germination and early seedling establishment at the leading edge of two pine species, under a changing climate

Pines are the most popular species for reforestation in Mexico, however reforestation programs have little success due to a high mortality of pine seedlings. Shifts in the distribution range due to climate change has been predicted for many species specially at their distribution borders. Understanding the thermal limits of germination and early seedling growth at the leading edge population in current and future climates could enable the development of suitable propagation practices and conservation strategies. Seeds of Pinus douglasiana and Pinus maximinoi, from their northern distribution range in a temperate sub humid region, were germinated and seedlings were grown across a range of temperatures from 10 to 35 °C. A cardinal temperature model was then employed to obtain the thermal coefficients for seed germination, seedling growth and survival. Projected temperature increase by 2090 according to IPCC scenarios RCP 2.6 and RCP 8.5 were used to predict the germination and early establishment behaviour of both species. Thermal requirements were similar between species and in different developmental stages showing base temperatures of 9.4−10 °C for germination, 9.8 °C for root growth, 9.6 °C for shoot appearance and 8.4 °C for shoot growth; and thermal time requirements of 65−69 °C d for germination, 107 °C d for root growth, 103−107 °C d for shoot appearance and 140−141 °Cd for shoot growth. However, seedling survival was higher at 20 and 25 °C. Different sensitivities to low temperatures for germination and seedling establishment could be factors that drive ecological divergence between these species and explain their altitudinal tolerances. As timing of germination and seedling growth are expected to be accelerated under climate change scenarios, seedling establishment and survival in both species could be altered .

Use of Neem leaves as soil amendment for the control of collar rot disease of chickpea

Chickpea (Cicer arietinum L.) is an important grain legume that is attacked by the fungal pathogen, Sclerotium rolfsii, responsible for collar rot disease. In the present study, the pathogen was isolated from diseased chickpea seedlings and identified on molecular basis using internal transcribed spacer (ITS) and β-tubulin markers. To control this pathogen, an in vivo study was carried out, using Neem (Azadirachta indica A. Juss.) leaf dry biomass (1, 2, and 3%) as soil amendment. A broad-spectrum fungicide mancozeb was selected as a reference and the data regarding plant growth and mortality rates were calculated. In positive control, the highest seedling mortality (56%) was recorded in comparison to negative control (0%) after 30 days of sowing. In 1, 2, and 3% concentrations of A. indica dry leaf biomass, the seedling mortalities were 49, 38, and 38%, respectively. On the other hand, the mancozeb-treated seedlings showed the lowest plant mortality rate (28%). Soil treatments with mancozeb as well as with 1 and 2% leaf biomass concentrations showed marked differences in root and shoot dry biomasses over positive control. In a laboratory bioassay, methanolic leaf extract of Neem of 0.5 to 3.5% concentrations reduced biomass of S. rolfsii by 86–90% over control. The present study concluded that 2% A. indica leaf amendment was the most useful concentration for management of collar rot disease of chickpea.

Abies religiosa Seedling Limitations for Passive Restoration Practices at the Monarch Butterfly Biosphere Reserve in Mexico

To recover the structure and functionality of a deforested ecosystem, two strategies of ecological restoration are considered: active restoration, which eliminates the disturbance agents and implements strategies to accelerate site recovery, and passive restoration, which eliminates disturbance agents, allowing natural regeneration to occur. Prior to choosing passive restoration, a field evaluation of the potential for natural regeneration is important. In this context, seedling and sapling density as well as patterns of recruitment and survival are appropriate indicators of restoration potential. In the present study, we deduced the potential of sacred fir (Abies religiosa) forest of the Monarch Butterfly Biosphere Reserve to recover by natural regeneration through seedling and sapling density and mortality, since A. religiosa is the dominant tree species in wintering sites of monarch butterfly. In 2015, we evaluated seedling density in 53 sites along an elevational gradient (3050-3550 m above sea level; m a.s.l.). There was a higher density of seedlings and saplings established in canopy gaps, compared to sites under dense forest canopy. Seedling recruitment was higher in sites at intermediate elevations (3050 to 3300 m a.s.l.) than in those at higher elevations. In a second survey, we studied A. religiosa seedling mortality over the dry season of 2016 to identify the environmental variables that cause the high seedling mortality and very low recruitment. Recently emerged seedling mortality was 49.2% at the end of the dry season (June 2016). The highest monthly mortality (14.3%) was recorded in April, a dry and warm month with the lowest values of moss thickness and soil moisture. We found no negative effects of moss layer on seedling mortality; indeed, moss appears to slow soil moisture reduction at the critical end of the warm and dry season. Soil and moss moisture values in April seem to be a critical factor for A. religiosa seedling recruitment, and we expect this condition will deteriorate under projected climatic change scenarios. Thus, the potential of MBBR A. religiosa forest to recover by passive restoration is highly constrained and will require management actions to achieve successful restoration outcomes.

Drought Hardening Contributes to the Maintenance of Proportions of Non-Embolized Xylem and Cambium Status during Consecutive Dry Treatment in Container-Grown Seedling of Japanese Cedar (Cryptomeria japonica)

Climate models in Japan predict that the annual mean air temperature and number of consecutive dry days will increase in the future, leading to high seedling mortality rates. Maintaining high survival rates of Cryptomeria japonica seedlings, a commercially important tree species, is therefore, important in terms of appropriate forest management under climate change. Although drought hardening, in which seedlings are acclimated to dry conditions in the nursery prior to planting, contributes to increased survival under drought conditions, little is known about the effective irrigation frequency of drought hardening in C. japonica seedlings. In this study, we therefore, examine the effectiveness of different drought-hardening treatments in C. japonica. We first clarify the effects on physiological and morphological traits by comparing three drought-hardening treatments [control (C): Irrigation once daily; mild (M): irrigation once every three days; and severe (S): irrigation once every five days] for one month. Next, to confirm the effects during consecutive dry treatment, we stopped irrigation for 13 days and once again compared the physiological traits between the three drought-hardening treatments. Drought hardening reduced whole-plant transpiration (Ewhole), resulting in conserved water use, and this tendency was particularly evident under the S treatment. Moreover, during consecutive dry treatment, the Ewhole, proportions of non-embolized xylem, and cambium status of basal stem regions were maintained for the longest duration under the S treatment, followed by the M treatment. Our findings suggest that the efficiency of drought hardening increased with drought severity. Furthermore, one month of drought hardening contributed to both water conservation and the maintenance of cell differentiation under consecutive dry treatment, likely increasing the tolerance and survival of C. japonica seedlings under prolonged drought.