Seedling Density Research Articles

Optimum Basic Seedling Density and Yield and Quality Characteristics of Unmanned Aerial Seeding Rice

Unmanned aerial seeding (UAS) is an efficient unmanned rice planting method with broad application prospects. But its optimum basic seedling number and yield and quality characteristics remain unclear. Field experiments were conducted to compare UAS, unmanned dry direct seeding (UDDS), and unmanned carpet transplanting (UCT) methods using inbred japonica rice variety Nanjing 5718. The UAS method was subdivided into four planting density treatments (UAS105, UAS150, UAS195, and UAS240 = 105, 150, 195, and 240 seedlings/m2, respectively). The results showed that increasing the basic seedling density first increased the yield but then it decreased, and UAS195 produced a significantly higher yield. On the other hand, the grain processing, appearance, and taste quality deteriorated with improved nutritional quality. Among the three planting methods, UAS (UAS195) yielded less than UCT due to there being fewer spikelets per panicle, a lower grain-filling rate, and less photosynthetic activity after heading. However, UAS (UAS195) produced more yields than UDDS by having more panicles, more spikelets per panicle, and more biomass accumulation. Both UAS195 and UDDS had poorer grain processing, appearance, and nutritional quality than UCT, but increased amylose content and taste values. Therefore, UAS195 could be an alternative planting method for inbred japonica rice with coordinated yield, quality, and production efficiency.

Impacts of Earthquake and Earthquake-induced Disasters on Community Forests in Nepal

Managing the commons is a challenging issue during crisis such as earthquakes. We considered four community forests, two from Gorkha and one from each of Dolakha and Sindupalchowk districts that were major earthquake affected areas. The study made use of ecological and socioeconomic survey techniques to assess the impacts of earthquake on community forests and management status of those forests. We calculated density of seedling, sapling and tree species and diameter size distribution of trees. We also analysed the forest status changes before and after the earthquake events and distribution of timber and fire wood in the community forest user groups. Seedling, sapling and adult trees number wise regeneration status of trees was good in all the studied forest whereas DBH size class diagram were bell shaped indicating unsustainable regeneration. Most of the respondents reported poor forest management after the earthquake and wood distribution has drastically increased after the earthquake 2015. From this study it is recommended that community forest management practices should be resilient to disasters and prepare alternative solutions to lower the pressure on forest products so as to maintain sustainable regeneration of forest trees and regular supplies of resources in future.

Assessment of changes in the normalized difference vegetation index (NDVI) of farmlands of Stavropol Territory, Russia, during the period of active vegetation in 2020 based on medium spatial resolution images

Aim. Assess changes in the NDVI of agricultural land in Stavropol Territory under the influence of weather and climate conditions.Methods. Based on earth remote sensing data, the spectral/vegetation index NDVI was calculated. We used data from the Meteor‐M satellite with a spatial resolution of 60 m for the active vegetation period of 2020 (May to September), which made it possible to calculate the NDVI value at different times of the active vegetation period of the main types of agricultural land in the Stavropol Territory. To explain the spatial and temporal variability of NDVI, an analysis of the conditions of heat and moisture supply was carried out using Walter's climatograms at weather stations located in the steppe and semi‐desert landscapes of Stavropol Territory.Results. In 2020, the period of active vegetation in the steppe and semidesert landscapes of Stavropol Territory began in the first ten days of April, when the air temperature rose above +10°С, and ended in mid‐October. In accordance with the change in heat and moisture supply, the NDVI value changed: in general, maximum values were observed in spring and early summer and, as aridity increased, the areas corresponding to low NDVI values increased everywhere. In the steppe zone, where the main crops of winter wheat are located, the NDVI value decreased from 0.45–0.3 at the beginning of the active vegetation period to 0.15 at the end. NDVI values of 0.15–0.30, corresponding to different types of herbaceous vegetation, prevailed at the end of the active vegetation period.Conclusion. The spatial and temporal distribution of the NDVI value over the territory of the Stavropol Territory reflects, first of all, changes in the conditions of heat and moisture supply. The timing of the course of the phenological phases of natural and cultivated vegetation depends on the latter. 2020 was characterized by sufficient moisture at the beginning of active vegetation, as reflected in the high density of seedlings, and, accordingly, a large area of NDVI, corresponding not only to herbaceous, but also to shrubby vegetation within the steppe landscapes. The increase in moisture deficit and harvesting in the second half and end of summer leveled the differences between the steppe and semi‐desert landscapes, since the maximum areas were occupied by territories with NDVI values of 0.15–0.3.

Effects of tree density and herbaceous plants on tree seedling survival across the growing and non-growing season in a temperate forest

Tree seedling survival is critical for estimating forest recruitment, but it remain elusive about how neighboring tree’s density and herbaceous plants affect it. To assess the relative importance of tree density and herbaceous plants on tree seedling survival during the growing season and non-growing season, we established a two-year experiment with seedling census and removal of herbaceous plants in both secondary and old-growth temperate forest sites in the temperate forests of northeastern China. A total of 3,443 seedlings in 17 tree species were surveyed in this study. We found that both tree density and herbaceous plants significantly affected tree seedling survival, but the specific effects depended on shade tolerance, seedling growth stage and growing season. Conspecific adult neighbors had significant negative effects on the survival of shade-tolerant seedlings during the growing season, while conspecific seedling densities positively correlated with shade-intolerant seedlings. Herb removal significantly improved the survival of newly germinated and shade-intolerant seedlings during the growing season. Furthermore, we found that the survivals of both newly germinated and established seedlings differed seasonally in response to adult, seedling neighbors and herb removal. Herb removal enhances seedling survival during the non-growing season by offsetting the negative effects of conspecific adult neighbors during the growing season. Our findings provide new evidence for seedlings’ shade tolerance, growth stage and seasonal dependence of density dependence in temperate forests, and highlight the significance of herbaceous plants for seedling survival, an important factor that has been neglected in many previous studies.

Effect of forest fire on soil properties and natural regeneration in Chirpine (Pinus roxburghii) forests of Himachal Pradesh, India

Abstract. Sharma Y, Gupta T, Gupta RK, Sharma PP. 2023. Effect of forest fire on soil properties and natural regeneration in Chirpine (Pinus roxburghii) forests of Himachal Pradesh, India. Asian J For 7: 125-132. Forest fires have a significant impact on the physical environment, such as land cover, land use, forest ecosystems, and biodiversity. The present study was carried out to quantify the effect of forest fire on soil properties and natural regeneration of Chirpine (Pinus roxburghii Sargent) forests in Himachal Pradesh, India. Data collection was conducted at six different sites in three forest divisions, namely Solan Forest Division, Hamirpur Forest Division and Dehra Forest Division during the year 2020. Burnt and unburnt forests were selected at each site and were compared with each other to study the effect of fire. The results reported that electrical conductivity, pH, available nitrogen, available phosphorus, available potassium were higher in burnt forests when compared to unburnt forests of the studied sites whereas organic carbon (%) was lower in burnt forests as compared to unburnt forests. Seedling density of trees was found higher in burnt forests whereas sapling density was found higher in unburnt forests. This indicates that fire is good for regeneration but frequent fires can be detrimental for the survival of seedlings. Frequent forest fires need to be prevented and that can be done mainly by social awareness and developing strategies for use of pine needles in farming practices and commercial use in paper, pulp and wood industries.

Production of Nephelium lappaceum Seedlings using Different Volumes of Tubes and Cultivation Densities

Rambutan (Nephelium lappaceum) fruit is a potential non-timber forest in tropical countries such as Indonesia due to its high economic potential. However, it is necessary to know the silvicultural aspects of the species in order to produce high-quality seedlings. The volume of the tube used and the spacing between seedlings can influence the quality of the seedlings. Thus, this work aimed to evaluate the production of seedlings of N. lappaceum through different densities of seedlings per tray and volumes of tubes. The experiment was installed in the nursery of the Technology Foundation of the state of Acre in Rio Branco. A completely randomized design with two factors (2 × 3) was adopted, considering two volumes of tubes, 110 cm³ and 180 cm³, and three seedling densities per tray, 1/3, 2/3, and 3/3. After 120 days, it was observed that the seedlings produced in tubes with a volume of 180 cm3 had greater aerial length and stem diameter in relation to the density of seedlings per tray, seedlings produced in less dense trays (1/3) had a higher Dickson quality index. Therefore, it is inferred that seedlings of N. lappaceum are favored when tubes with a volume of 180 cm³ and a density per tray of 1/3 are used. Keywords: Dickson quality index, fruitful species, initial growth, non-timber forest product, seedling production

Does shading and ground cover of moss and litter improve germination and establishment of Betula pendula Roth, Salix caprea L. and Populus tremula L. seedlings during drought stress in climate change? – A greenhouse study

The climate change is leading to a significant increase in temperatures and dry periods in spring, for example in parts of middle and north Europe. Thus, the important factor for tree growth, the water availability, decreases on forest sites. It is to be expected that the successful establishment of pioneer tree species as pre-forests on large damaged areas will considerable be limited in the future. The phases of germination and establishment are the most dangerous phase in the life of trees. In this greenhouse study, we tested how different microsite conditions (open soil, moss and litter cover as well as different shading) under reduced water availability influence establishment success and growth of Betula pendula, Populus tremula and Salix caprea.The initial high germination success were reduced to 14%, 7% and 12% for Populus tremula, Salix caprea and Betula pendula, respectively, and the growth were significantly slower when the relevant soil water resource was just above the permanent wilting point. Therefore, in the first year the germination and establishment is linked to persistent moist conditions. If the soil dries out during germination, e.g. if there is no watering for more than 3 weeks, all seedlings died. Equivalent germination microsites (shading or ground cover) with comparable possible seedling densities to the moist open soil does not exist under water stress. Although moss and litter cover retain longer soil moisture under extremely dry conditions and guarantee significantly better seedling development than on open soil, initially significantly fewer seeds germinate on these substrate types.Radiation shows no influence on germination and seedling survival. The seedlings are able to survive radiation conditions of 3% and 27% of open area radiation. This makes establishment possible under (remaining) light canopy, at the edge of damaged areas or in small islands of remaining shelter trees on damaged areas. However, radiation had a significant effect on growth. With increasing radiation, shoot lengths and above ground biomasses are higher and the root collar diameter larger.Overall, Betula pendula is the most drought stress resistant of the tested tree species. While Populus tremula and Salix caprea already had problems establishing themselves on dry sites, the problem will become more serious under climate change. The lack of moist, vegetation-free open soils will result in a significant reduction of establishment success for tested pioneer tree species in climate change.

Vegetation Analysis as Indicator of Mangrove Degradation Level in Keboromo Village, Tayu

Mangrove degradation is one of the most common issues in the coastal areas of Java, which can cause ecological impacts and even disadvantage for local community. The mangrove forest degradation can be identified based on the vegetation analysis results, which could potentially contribute to the mangrove ecosystem management and rehabilitation programs in the coastal areas. Mangroves in Keboromo Village was the rehabilitation and cultivation area, but often get damaged by ocean waves. This study aims to determine the ecological and vegetation conditions of mangrove ecosystems consist of species composition, density, canopy cover, tree height, and environmental parameters were held in February 2023. The method used was direct observation using transect quadrants of 10x10 m2. The average mangrove density of all observation stations was 3.425 individuals/ha for the tree category, 575 individuals/ha for the sapling category, and 250 individuals/ha for the seedling category. The average percentage of canopy cover was 78.41%. The average height of mangrove trees at all stations is 4.15 m. The environmental parameters were still compatible with the water quality standard for biota and mangrove life. The mangrove forest degradation level based on standard criteria and guidelines for determining mangrove degradation is categorized as low, indicated by mangrove density >1500 individuals/ha and canopy cover >75%. Poor conditions were measured for sapling and seedling densities, which may be caused by environmental factors unsupportive for mangrove regeneration. Based on the results of mangrove vegetation analysis in Keboromo Village, it can state the mangrove ecosystem condition is good. However, management programs are needed to keep the mangroves sustainable.

Floristic Assessment of Natural Regeneration in an Enhanced Post-Remediated Hydrocarbon Impacted Land: A Window for Selection of Remediation Potential Native Macrophyte

Aim: The study was aimed at revealing the composition and demographic status of forest regeneration in a post remediatied hydrocarbon impacted site by enhanced natural attenuation.
 Study Design: A stratified systematic transect method was used to assess the regeneration status.
 Place and Duration of Study: Field sampling: in parts of Edovna vegetation landscape in Emohua Local Council area of Rivers State, Niger Delta, Nigeria and site remediation activity carried out for 10 weeks.
 Methodology: Site remediation treatment technique, Vegetation assessment, Regeneration Assessment and data analysis were carried out.
 Results: The hydrocarbon activities around the SPDC marginal oil field manifold in Emuoha study area negatively impacted the Edovna forest vegetation landscape at Umuobizu resulting to a retrogressively mosaic trend condition. However, following the p-RENA process a progressively secondary succession has resulted to such classified flora: as lowland secondary vegetation mosaic nature, with heterogeneous continuum in spatial and closed horizontal assemblage of structural arrangement. Several species of diverse life forms were found existing through diverse mode of regeneration. New species were found regenerating and were absent as adult. Greater mode of single level of regeneration than multiplier level of regeneration was exhibited among the recruits through coppicing, stolon, seedling, sapling, rhizome and tuber. The HG exhibited greater multiplier mode while HH had greater single mode of regeneration. The herbaceous recruits among the life forms revealed a secondary physiognomic unit, heterogeneous in nature as a result of the regeneration process with few regenerating shrubby recruits. A total of 115,549 seedlings and 7,825 saplings ha-1 of 96 recruits of 70 genera under 23 families were found in 800 m2 sampled site. The dominant family was Poaceae richest in species diversity (24 species). The phytosociological composition of recruits has recorded highest frequency (1675), abundance (621), density ha-1 (49,600), IVI (104.81), diversity richness (11.75) and evenness (5.96) with Herbaceous herb (HH) in highest number of regenerating recruits in the order (HH>HG>Sh>HCl>HS>ShCl>T) of habit forms. The Chamaephytes and Hemi-cryptophytes across diverse herbaceous life forms, Mesophanerophytes, Microphaneropytes, Nanophanerophytes and Hemi-cryptophytes across shrubby life forms and a megaphanerophyte tree life form were recorded among recruits. The percentage mode of regeneration had 40 recruits of herbaceous form that exhibited 12 multiplier and 4 single mode of regeneration respectively. Four shrubby recruits exhibited 2 multiplier and 13 recruits exhibited 2 single mode of regeneration.
 Conclusion: The demographic status of regeneration revealed a greater seedling density than sapling density thus implying a successful and new regeneration which through protection of natural regeneration can return back to it complete forest cover again. It can be deduced in this present study that the success of natural regeneration depends on both the demographic status and rate of establishment of natural recruits which was maximal at the p-RENA landscape of the study site across the herbaceous, tree and shrubby recruits in the present study.

Reproductive characteristics in an understory bamboo and gradual environmental changes after its dieback provide an extended opportunity for overstory tree regeneration in a mixed cool-temperate forest in central Japan.

The reproductive characteristics of understory bamboo and the effects of dieback on overstory tree seedlings through temporal changes in the environment at the forest floor have only been examined in a few bamboo species, due to the unpredictable occurrence of flowering events and long intervals between them but provide valuable information on tree regeneration and succession in a forest with dense dwarf bamboo cover. We investigated environmental conditions and assessed seedlings (< 30-cm tall) of the dwarf bamboo Sasa borealis and overstory tree species at 44-50 measurement points during 2016-2021, which included a S. borealis mass flowering event in 2017. We also conducted seed germination tests to determine germination rates and patterns in S. borealis. Environmental factors affecting seedling recruitment of S. borealis and of overstory trees were analysed using spatiotemporal generalized linear mixed models in the Bayesian framework. We observed gradual temporal changes in the environment, including increasing canopy openness and decreasing maximum height of dead S. borealis culms. The seeds germinated slowly and the emergence of current-year S. borealis seedlings peaked in spring-summer in 2019. The tree seedling density after 2019 increased significantly compared to that before the dieback. The model results suggest that tree seedling establishment was enhanced by increased light availability. Continuous field observation beginning before S. borealis dieback revealed gradually enhanced tree recruitment in response to slow decay of the remaining dead culms and slow recovery of S. borealis. The seedling regeneration pattern of understory bamboo partly contributes to a prolonged opportunity for overstory tree regeneration.

Contribution of assisted natural regeneration (ANR) to climate change mitigation and diversification of ecosystem services in Dan saga village (Maradi-Niger)

As an agro-ecological intensification technique, assisted natural regeneration (ANR) protects agrosystems and guarantees cereal production in a Sahelian context of high demographic pressure and climate variability. This study aims to assess the local perception of assisted natural regeneration in mitigating the effects of drought and climate change and its impacts on soil fertility and crop production. Surveys, based on a participatory approach of individual and collective consultations, were conducted with stakeholders. The water profile and bulk density of areas under ANR and outside ANR were determined from soil samples taken in the rainy and dry seasons at different depths (0 - 200 cm). Vegetative growth and yield components were monitored on 100 plots of 100 m2 (10x10m) with 50 plots in ANR and 50 in non-ANR areas. The results showed that both zones had the same species composition for the dominant woody species, but their average densities were higher in the areas under assisted natural regeneration than in the areas without. Density is lower in the aureoles close to the village than those far from it in any zone. Soil moisture content is higher in the ANR and non-ANR areas than in the non-ANR area in the shallow horizons. However, in the deep horizons down to 200 cm, the volume moisture is higher in the Non-NAR and Uncovered NAR zones respectively than in the Under-Cover NAR zone. Apart from the seedling density, all agronomic performance parameters are significantly higher in the RNA zone than in the non-RAN zone. In terms of farmers' perception, the practice of ANR attenuates the impacts on natural resources (water, land, vegetation) and on production systems. More than 92.2% of the respondents reported that increased dust winds, increased night time temperature, decreased rainfall events as well as their amounts in height are the impacts experienced before the practice of ANR. The practice of ANR contributes to the mitigation of climate variability, improvement of soil structure and carbon sequestration.

Rape seedling density estimation in‐field conditions based on improved multi‐column convolutional neural network

AbstractEarly‐stage rape seedling density is closely related to yield estimation, growth diagnosis, cultivated area statistics, and field management. Currently, manual sampling and counting, which are inefficient and inaccurate, are heavily relied upon to estimate rape seedling density. Computer vision techniques have emerged as a promising solution to the automation of this task, as digital images have become more commonplace. Farmland field environments, however, face many challenges, including scale variation, denseness, and background occlusion. An improved multi‐column convolutional neural network, called seedling rape density prediction network (SRDPNet), has been proposed in this study to resolve the issues related to accurate density estimation and counting of rape seedlings in complex farmland scenarios. Based on the multi‐column convolutional attention encoder, filters of different sizes are used to capture the basic feature of rape seedlings at various scales. The channel attention and position attention modules are introduced into branches to alleviate the impact of low counting accuracy caused by background error and growth state differences. The SRDPNet was validated using the seedling rapeseed plant counting (SRPC) dataset created in this study. The experimental results showed that the SRDPNet demonstrated high accurate counting performance for the SRPC dataset with a high coefficient of determination (R2 = 0.97396) and mean absolute error (MAE = 3.26, mean square error = 4.56), which are superior to that of the comparison method. SRDPNet can effectively solve the visual challenges of rape seedlings in complex farmland scenes and improve the robustness for complex visual variations.

Effect of Abiotic Stresses from Drought, Temperature, and Density on Germination and Seedling Growth of Barley (Hordeum vulgare L.).

Seed germination and seedling growth are highly sensitive to deficit moisture and temperature stress. This study was designed to investigate barley (Hordeum vulgare L.) seeds' germination and seedling growth under conditions of abiotic stresses. Constant temperature levels of 5, 10, 15, 20, 25, 30, and 35 °C were used for the germination test. Drought and waterlogging stresses using 30 different water levels were examined using two methods: either based at 1 milliliter intervals or, on the other hand, as percentages of thousand kernel weight (TKW). Seedling density in a petri dish and antifungal application techniques were also investigated. Temperature significantly impacted germination time and seedling development with an ideal range of 15-20 °C, with a more comprehensive range to 10 °C. Higher temperatures reversely affected germination percentage, and the lower ones affected the germination and seedling growth rate. Germination commenced at 130% water of the TKW, and the ideal water range for seedling development was greater and more extensive than the range for germination, which means there is a difference between the starting point for germination and the seedling development. Seed size define germination water requirements and provides an objective and more precise basis suggesting an optimal range supply of 720% and 1080% of TKW for barley seedling development. A total of 10 seeds per 9 cm petri dish may be preferable over greater densities. The techniques of priming seeds with an antifungal solution (Bordóilé or Hypo) or antifungal application at even 5 ppm in the media significantly prevented fungal growth. This study is novel regarding the levels and types of abiotic stresses, the crop, the experimental and measurement techniques, and in comparison to the previous studies.

Mud cracks promote colonization by pioneer saltmarsh plants

Saltmarshes are valued as key buffering ecosystems against global climate change and sea level rise. However, the knowledge deficit regarding links between colonization of saltmarsh fringes by plants and mud cracking in the lateral dimension considerably limits our understanding of marsh resilience. Here, the role of mud cracks in colonization by saltmarsh plants was investigated. A combination of field experiments, remote sensing, and experimental results revealed that: (1) potential mud cracking zones were formed at the seaward edge of saltmarshes under the influence of tide-induced wetting–drying cycles, where mud cracks were extensively distributed and colonized by new seedlings. (2) The seedling density in the mud cracks was higher than that in the patches, and seedlings in the mud cracks sprouted earlier than those in the patches. The results implied that mud cracking enhanced colonization by saltmarsh plants, rather than being a water stressor. (3) The two main ecological functions of mud cracks in saltmarsh colonization were acting as “seed traps” and “seedling growth promoters.” (4) Mud cracking could be a key factor influencing saltmarsh resilience, especially by promoting the colonization and dispersal of saltmarsh plants. Rapid colonization of potential zones with mud cracks could occur as soon as seeds are available. Our results could facilitate the development of appropriate saltmarsh rehabilitation strategies.

Forest thinning and climate interactions driving early-stage regeneration dynamics of maritime pine in Mediterranean areas

There is growing concern that changing climate and disturbance regimes are and will result in widespread forest regeneration failure, and thus, there is an increasing need for developing management and adaptation strategies to promote regeneration under climate change. Maritime pine (Pinus pinaster), an ecologically and economically relevant tree species inside and outside its natural range, will likely face such difficulties as drought is the main cause of seedling mortality in this species. Understanding the interactions between silviculture and climate conditions is therefore crucial to inform sound adaptive forest management. However, the evidence on how forest thinning may contribute to enhanced regeneration remains divided and not fully understood, especially in the context of climate change. Hence, the general goal of this study was to evaluate the effect of thinning as a forest management strategy to promote the natural regeneration of P. pinaster stands in Mediterranean areas, and to understand how climatic, edaphic and topographic factors influence the effectiveness of this silvicultural practice. This was done by comparing 13 pairs of thinned and control plots along a thinning intensity gradient (23–69 % in stand basal area) in northeastern Iberian Peninsula and by measuring early-stage regeneration dynamics, namely the density, survival and growth of seedlings for 5 consecutive years. Thinning had a strong positive effect on the establishment and survival of P. pinaster seedlings as well as a weak positive effect on early primary and secondary growth. Not only was the number of seedlings and survival in thinned plots considerably higher than in control plots (15.0 ± 2.5 vs 1.5 ± 0.5 seedlings per plot; 23 ± 4 % vs 0.7 ± 0.3 % survival) but both seedling density and survival increased with increasing thinning intensity (3-fold and 5-fold, respectively), which matches the light-demanding nature of this species. Such a positive effect of thinning was further modulated by climatic and soil conditions. Overall, the advantage conferred by thinning to seedling establishment and survival was stronger under drier and warmer conditions, which suggests that thinning is particularly beneficial in alleviating competition in water-limited forest ecosystems. Considering that the Mediterranean region is predicted to become warmer and drier under global warming, our findings indicate that thinning will likely become an increasingly important management strategy to ensure the natural regeneration, adaptation and resilience of pine forests in the face of climate change.

Natural regeneration potential and dynamics in boreal lichen woodlands of eastern Canada following soil scarification

Boreal lichen woodlands (LWs) are stable low tree-density zones of the Canadian boreal forest whose afforestation has been proposed as a way to create new C sinks and thus mitigate climate change. Planting operations in these remote areas are however costly and time-consuming, and may not be necessary when soil scarification is followed by dense natural regeneration. In the present study, we assessed the natural regeneration potential and dynamics in six boreal LWs of Québec, Canada, 11 years after soil scarification. The number, size (height and stem diameter) and age of seedlings were measured in 2-4 sampling plots per site (18 plots in total). Our data show that scarification operations produced on average 1,400 m2 ha–1 of exposed mineral soil (scarification intensity of 14%) with, however, a large within-site variability. The natural regeneration was mainly composed of black spruce seedlings (&amp;gt; 95%), averaged ∼12,000 seedlings ha–1 across the six sites and significantly varied among sites, mostly due to the variation in scarification intensity. Seedling density averaged ∼9 seedlings m–2 of exposed mineral soil and increased with seed tree mean diameter at breast height (DBH) (R2 = 0.51; P &amp;lt; 0.05) but not with the density of seed trees, revealing the importance of old and large seed trees in natural regeneration success. Together, scarification intensity and the DBH of remaining seed trees explained ∼60% of the variation in natural regeneration density across the 18 sampled plots. The rate of establishment of seedlings was generally high – with on average 60% of the carrying capacity of the substrate being reached within three years following scarification – and increased with seed tree mean DBH (R2 = 0.77; P &amp;lt; 0.05). However, the growth rate of seedlings was very low. Eleven years after scarification, 60% of the seedlings were &amp;lt; 15 cm and the height of 10-yr-old seedlings averaged 27.5 cm. Thus, even though seedling establishment was successful, the biomass accumulated by the natural regeneration was negligible in the span of a decade. Therefore, the implementation of afforestation following scarification appears to be necessary to create significant C sinks in the midterm.

Less fuel for the next fire? Short-interval fire delays forest recovery and interacting drivers amplify effects.

As 21st-century climate and disturbance dynamics depart from historic baselines, ecosystem resilience is uncertain. Multiple drivers are changing simultaneously, and interactions among drivers could amplify ecosystem vulnerability to change. Subalpine forests in Greater Yellowstone (Northern Rocky Mountains, USA) were historically resilient to infrequent (100-300 year), severe fire. We sampled paired short-interval (<30-year) and long-interval (>125-year) post-fire plots most recently burned between 1988 and 2018 to address two questions: (1) How do short-interval fire, climate, topography, and distance to unburned live forest edge interact to affect post-fire forest regeneration? (2) How do forest biomass and fuels vary following short-interval versus long-interval severe fires? Mean post-fire live tree stem density was an order of magnitude lower following short-interval versus long-interval fires (3240 vs. 28,741 stems ha-1 , respectively). Differences between paired plots were amplified at longer distances to live forest edge. Surprisingly, warmer-drier climate was associated with higher seedling densities even after short-interval fire, likely relating to regional variation in serotiny of lodgepole pine (Pinus contorta var. latifolia). Unlike conifers, density of aspen (Populus tremuloides), a deciduous resprouter, increased with short-interval versus long-interval fires (mean 384 vs. 62 stems ha-1 , respectively). Live biomass and canopy fuels remained low nearly 30 years after short-interval fire, in contrast with rapid recovery after long-interval fire, suggesting that future burn severity may be reduced for several decades following reburns. Short-interval plots also had half as much dead woody biomass compared with long-interval plots (60 vs. 121 Mg ha-1 ), primarily due to the absence of large snags. Our results suggest differences in tree regeneration following short-interval versus long-interval fires will be especially pronounced where serotiny was high historically. Propagule limitation will also interact with short-interval fires to diminish tree regeneration but lessen subsequent burn severity. Amplifying driver interactions are likely to threaten forest resilience under expected trajectories of a future fire.

Birch establishes anywhere! So, what is there to know about natural regeneration and direct seeding of birch?

We tested three soil scarification approaches of varying intensity (intensive preparation exposing bare mineral soil, medium intensity with a mixture of organic material and mineral soil, and control without site preparation) on six clear-felled sites in two localities in northern and central Sweden between 2018 and 2021. The effect of soil scarification intensity and soil moisture on the occurrence of naturally regenerated birch seedlings was tested one, two and three years after soil scarification, and the density of direct-seeded birch seedlings one year after seeding. In addition, we tested the effect of the annual seed rain, and differences between the two birch species, on the density of direct-seeded seedlings. Soil scarification and its interaction with soil moisture had a significant positive effect on both the occurrence of naturally regenerated birch seedlings and the density of direct-seeded birch seedlings. There was no significant effect of neither annual natural seed rain nor species choice on direct-seeded seedling density. Time since soil scarification had a significant effect on the occurrence of naturally regenerated birch seedlings. In moist soils with high volumetric water content (≥ 28%), birch seeds germinate at high rates and seedlings survive without soil scarification. In mesic soils, birch seeds germinate with higher rates after soil scarification. In dry soils, birch seeds rarely germinate regardless of any disturbance of the humus layer.

Distance and density dependence in two native Bornean dipterocarp species.

The Janzen-Connell hypothesis proposes that density and distance-dependent mortality generated by specialist natural enemies prevent competitive dominance. Much literature on Janzen-Connell mechanisms comes from the neotropics, and evidence of the role of distance and density-dependence is still relatively sparse. We tested the predictions of the Janzen-Connell hypothesis in a South-East Asian system dominated by mast fruiting species. We hypothesized that seedling survival would decrease with distance and density, seedling growth would increase, and herbivory would decrease, according to the predictions of the Janzen-Connell hypothesis. Experiments were conducted to determine the strength of the Janzen-Connell mechanism by manipulating the density and identity of tree species as a function of the distance from parent trees. Survival of conspecific seedlings was reduced near adult trees of one species, but not another. High densities of seedlings decreased the growth of conspecific seedlings of both species. In both species, herbivory rates decreased with distance in low-density areas. This study indicates that dipterocarp species experienced weak Janzen-Connell effects of distance and density dependence at the growth stage studied. Future studies in this system might focus on earlier life-history stages such as seeds and small seedlings, as well as studying mortality during mast-seeding events.

Assessment of multiple herbicide protection seed treatments for seed-based restoration of native perennial bunchgrasses and sagebrush across multiple sites and years.

The invasion of exotic, annual plant species is a leading contributor to ecological degradation in drylands globally, and the use of pre-emergent herbicide to control these species is common. Pre-emergent herbicides pose challenges for seed-based restoration due to toxicity to the seeds of desired species. Herbicide protection (HP) technologies pose a potential solution by using activated carbon seed treatments to protect desirable seeds from herbicide exposure. In the sagebrush steppe ecosystem of North America, we used an adaptive small plot design over three planting years to test for effects on seeding outcomes (seedling density and size) of large and small multi-seed HP pellets, several single-seed HP coatings, and carbon banding treatments at geographically dispersed sites for several perennial bunchgrasses and the keystone perennial shrub, Wyoming big sagebrush. We also compared different methods of seed delivery and litter pre-seeding management. Seeding success was low overall, especially for sagebrush, and it was clear that other, often less predictable barriers to establishment than herbicide exposure, such as inadequate spring moisture, were strong drivers of seeding outcomes. Despite this, HP treatments were associated with higher seedling density than bare seed in multiple instances, most notably for grasses. The large HP pellet occasionally outperformed the small HP pellet, and several HP coatings performed similarly to the small pellet. Surprisingly, we did not see consistent negative effects of pre-emergent herbicide on unprotected bare seed. We conclude that HP seed treatments show some promise to improve seeding success in the presence of herbicide, but that consistent success will require further improvements to HP treatments as well as integration with other innovations and approaches.