High Seedling Densities Research Articles

Ex-situ restoration of the Mediterranean forest-forming macroalga Ericaria amentacea: optimizing growth in culture may not be the key to growth in the field

Evidence of local and regional declines in the canopy-forming alga Ericaria amentacea, a foundation species of diverse marine forest communities on exposed Mediterranean coasts, have spurred restoration efforts focused on sustainable ex-situ techniques. The need to balance the costs of culture maintenance and the susceptibility of early life stages to stressors in the native habitat, including rapid, often extreme shifts in temperature, hydrodynamics and nutrient availability, have driven current efforts to create a culture environment that primes seedlings for outplant, increasing their resilience rather than maximizing growth. We tested the effects of 1) higher culture temperature (25°C) combined with wave simulation and 2) reduced nutrient loads (10% of standard protocol) with wave simulation on post-culture and outplant outcomes relative to optimal growth conditions in established protocols (20°C, no waves, high-nutrient culture medium). While increased temperature and water motion negatively affected seedling growth in culture, and higher nutrients caused oxidative stress likely associated with enhanced epiphyte overgrowth, these effects were not clearly translated into patterns of long-term growth in the field. Instead, survival in the initial days post-outplant appeared to be the bottleneck for restoration potential, where substrates with persisting seedlings at one month were generally found with flourishing juveniles at four months. Larger clumps of seedlings, in turn, were strongly associated with both initial survival and future growth. These results underscore the importance of the zygote settlement phase to establish high seedling densities, which may be optimized by phenological monitoring of the donor population. They also suggest that less-controlled, more environmentally-realistic culture conditions involving the introduction of mild stress may enhance the survival of early life stages of E. amentacea during the transition to the native environment, simultaneously providing a means to reduce human resource costs in culture and move toward scaling up.

Differential effects of leaf litter and rhizosphere soil microbes on competition between invasive and native plants

Invasive plants commonly compete with native plants in the introduced range; however, how leaf litter and rhizosphere soil microbes influence the competition between invasive and native plants with varying microbial sources and seedling densities remains to be characterized. In this study, the invasive plant Ageratina adenophora (Asteraceae) and two cooccurring native plant species, Senecio scandens (Asteraceae) and Achyranthes bidentata (Amaranthaceae), were used as experimental plants to test their impacts in a greenhouse. We observed that leaf litter and rhizosphere soil microbes negatively or neutrally impacted invasive or native plant growth when competing. However, microbes enhanced the competitive dominance of A. adenophora over S. scandens but weakened its competitiveness over A. bidentata. Leaf litter microbes were more beneficial for A. adenophora growth and thus made it more competitive than rhizosphere soil microbes when competing with S. scandens. Regardless of the presence or absence of microbes, conspecific inoculation was better for A. adenophora growth and thus enhanced competition dominance more than heterospecific inoculation when competing with A. bidentata. A high seedling density was more beneficial for A. adenophora competition dominance than a low density was when A. adenophora was competing with S. scandens. Nonetheless, the relative competitiveness of A. adenophora was greater than that of the two native species; in particular, A. adenophora had stronger competitive dominance over A. bidentata than over S. scandens. Our data confirmed that the important role of leaf litter microbes in the competition between invasive and native plants cannot be ignored.

Bornean tropical forests recovering from logging at risk of regeneration failure.

Active restoration through silvicultural treatments (enrichment planting, cutting climbers and liberation thinning) is considered an important intervention in logged forests. However, its ability to enhance regeneration is key for long-term recovery of logged forests, which remains poorly understood, particularly for the production and survival of seedlings in subsequent generations. To understand the long-term impacts of logging and restoration we tracked the diversity, survival and traits of seedlings that germinated immediately after a mast fruiting in North Borneo in unlogged and logged forests 30-35 years after logging. We monitored 5119 seedlings from germination for ~1.5 years across a mixed landscape of unlogged forests (ULs), naturally regenerating logged forests (NR) and actively restored logged forests via rehabilitative silvicultural treatments (AR), 15-27 years after restoration. We measured 14 leaf, root and biomass allocation traits on 399 seedlings from 15 species. Soon after fruiting, UL and AR forests had higher seedling densities than NR forest, but survival was the lowest in AR forests in the first 6 months. Community composition differed among forest types; AR and NR forests had lower species richness and lower evenness than UL forests by 5-6 months post-mast but did not differ between them. Differences in community composition altered community-weighted mean trait values across forest types, with higher root biomass allocation in NR relative to UL forest. Traits influenced mortality ~3 months post-mast, with more acquisitive traits and relative aboveground investment favoured in AR forests relative to UL forests. Our findings of reduced seedling survival and diversity suggest long time lags in post-logging recruitment, particularly for some taxa. Active restoration of logged forests recovers initial seedling production, but elevated mortality in AR forests lowers the efficacy of active restoration to enhance recruitment or diversity of seedling communities. This suggests current active restoration practices may fail to overcome barriers to regeneration in logged forests, which may drive long-term changes in future forest plant communities.

Silvicultural treatments improve pest and disease conditions of white pine (Pinus strobus) residual trees and regeneration

Managing multiple forest insect pests and diseases is challenging. For example, in eastern white pine (Pinus strobus) stands whereas partial shading and high seedling density is encouraged to reduce damage by white pine blister rust (Cronartium ribicola) and white pine weevil (Pissodes strobi), dense conditions in the understory may increase damage by foliar diseases such as brown spot needle blight (Lecanosticta acicola) and Caliciopsis canker (Caliciopsis pinea). We evaluated the effect of silvicultural treatments, shelterwoods (residual basal area < 18 m2 ha−1), low density thinnings (residual basal area ≤ 14 m2 ha−1), patch cuts (1.2 ha openings), and untreated controls on damage by these insect pest and diseases in residual overstory trees and regeneration. Shelterwoods and low density thinnings provided a good balance of some shading and reduced stem density, which resulted in less weevil damage and foliar disease severity. Crown condition and quality of regeneration was better in all treatments compared to unmanaged controls. Shelterwoods, low density thinnings and patch cuts have the added benefit on increasing seral habitat, resulting in greater songbird diversity.

Forest resilience and regeneration dynamics following wildfire disturbance

AbstractSpecies that are adapted to specific disturbance regimes may be sensitive to changes such as severity, frequency, and extent of ecosystem perturbation. Along range margins, these sensitivities may be exacerbated by concurrent changes in climate resulting in loss of resilience and shifts to alternative ecosystem states. Pinus banksiana (jack pine) is a serotinous species dependent on fire disturbance to open cones, release seed, reduce understory competition, and expose mineral soil. The Altona Flat Rock in northern New York is a globally rare sandstone pine barrens, at the southern edge of jack pine's range. In the summer of 2018, a wildfire burned approximately 200 ha of the Flat Rock barrens, providing the opportunity to study post‐disturbance jack pine and understory resilience. We aimed to establish if jack pine regeneration would occur, and if so, would it be influenced by fire severity, pre‐fire stand characteristics, and competition. We predicted that higher seedling densities would be associated with higher burn severity, higher pre‐fire jack pine stand density, and lesser understory competition. We collected seedling density and understory composition data annually from 2019 to 2022 across 45 plots spanning the disturbed and adjacent undisturbed barrens. In 2021 and 2022, seedling heights were also collected. Seedling densities following the disturbance ranged from 275,385 to 390,513 ha−1; = 357,821 ha−1. Jack pine seedling density was positively associated with fire severity and moss abundance for all years. Pre‐fire stand density along with ericaceous shrub, grass, and duff abundance were also positively associated with seedling density in some years. Seedling height was positively associated with fire severity along with grass and blueberry abundance. These factors, for both establishment/survival and growth, point to the importance of seed supply, microsite conditions, and facilitation in jack pine regeneration success. At this point, it does not appear that the interaction of disturbance with changing climate has shifted enough to prevent the recovery of this ecosystem to its pre‐disturbance jack pine‐dominated state. However, ongoing climate change may still have an impact on seedlings/saplings as this forest continues to mature.

Seedling performance in a dioecious tree species is similar near female and male conspecific adults despite differences in colonization by arbuscular mycorrhizal fungi

Plant–soil feedbacks (PSFs) are a key driver of species diversity and composition in plant communities worldwide; however, the factors that may cause feedbacks to vary within species are rarely examined. In dioecious species, the strength of feedbacks may differ near female plants that produce seed versus near male plants (which do not) because repeated inputs of seeds and high seedling densities near females may cause accumulation of host‐specific soil microbes that influence seedling performance. To test whether conspecific seedling performance is reduced near seed‐producing female trees relative to male or heterospecific trees, we conducted shadehouse and field experiments with a dioecious tropical tree species, Virola surinamensis (Myristicaceae), on Barro Colorado Island, Panama. The shadehouse experiment isolated the effect of soil microbial communities on seedling growth and allowed us to quantify colonization by mutualistic arbuscular mycorrhizal (AM) fungi, while the field experiment allowed us to assess seedling survival and growth in the presence of nearby conspecific adults and seedlings. In both experiments, seedling performance was similar between seedlings grown in the soil microbial communities and field environments underneath female conspecific, male conspecific, and heterospecific trees. However, contrary to expectation, seedling colonization by AM fungi was higher in male conspecific soil microbial communities than in female or heterospecific soil microbial communities at the end of the shadehouse experiment. Together, our experiments show that while differences among female and male plants in dioecious species may influence the association of conspecific seedlings with AM fungi in their soils, this variation does not necessarily translate directly to differences in seedling performance, at least over the time frame of our experiments. Studies of additional dioecious species are needed to help determine differences in soil microbial communities beneath male and female plants and to assess the role of seed input versus adult root systems in driving PSFs.

Enhanced Natural Regeneration Potential of Sessile Oak in Northern Hungary: Role of Artificially Increased Density of Insectivorous Birds

Both artificial and natural regeneration of oaks strongly depend on the quantity and quality of the acorn crop, which show high year-to-year variation. The volume of the acorn crop is influenced by many factors including biotic and abiotic effects. The quality (i.e., germination ability, nutrient reserves) of acorns can be decreased by carpophagous insect and fungal pathogen damage or by inadequate weather conditions. Defoliating insects (caterpillars, sawfly larva, etc.) can significantly decrease the acorn crop as well. The most important predators of the defoliators are insectivorous birds during their nesting period. However, in the oak forests of the northern Hungarian mountains, there is a shortage of natural nesting holes. The main aim of our study was to artificially increase the number of the available nesting holes by nest boxes and to maximize the number of breeding insectivorous birds and register the direct (Lepidoptera densities) and indirect (acorn crop quantity and quality) effects of their presence. We found only slight effects on Lepidoptera densities, so we failed to demonstrate a direct effect in the relatively low time frame of our study. But, we could show the indirect positive effect of increased predation on the health state of the acorn crop, resulting in higher seedling densities, which may improve the natural regeneration potential of sessile oak. This result supports the outstanding importance of natural nesting holes in broadleaved forests.

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.

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.

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.

Community Structure, Regeneration Status and Tree Biomass of Shorea robusta Gaertn. in Charpala Community Forest, Rupandehi District, Central Nepal

Sal is a multipurpose tropical tree that grows as the dominant plant species in Nepal’s lowlands. A comparative study of the Sal population structure was carried out in two blocks of Charpala Community Forest, Rupandehi. A total of 161 species of vascular plants, belonging to 135 genera and 69 families, were recorded, where Fabaceae (26 species) was the dominant family. Densities of Sal trees, saplings, and seedlings per hectare were 4000, 1945, and 742 respectively. A reverse J-shaped curve in the population structure of Block 1 indicated active natural regeneration. However, in Block 2, the lower densities of seedlings and saplings, and the higher densities of intermediate diameter classes indicated insufficient spontaneous regeneration. Average tree biomass and carbon stocks were 522.49 Mg/ha-1 and 245.57 Mg/ha-1, respectively. While Block 2 outperformed Block 1 in terms of tree density, carbon stock, and biomass, Block 1 had the higher density of seedlings and saplings, which improved the regeneration status of that site. Increased demand for lumber for construction has put existing Sal strands in Nepal under pressure. Therefore, a detailed study of its population makeup and natural renewal is crucial.

The effects of light, conspecific density and soil fungi on seedling growth of temperate tree species

Tree regeneration is an important ecological process which impacts community dynamics and determines future forest structure and functioning. Seedling growth, as a key driver of tree regeneration, is strikingly affected by multiple abiotic and biotic factors, such as light environment, conspecific density and soil fungi. However, the interactive effects of these factors remain largely unclear. In this study, we addressed this knowledge gap for seedlings of two dominant canopy tree species, i.e., ash (Fraxinus mandshurica) and linden (Tilia amurensis) in northeast China using a split-plot experiment for light availability (30 and 80% of full light) and conspecific density (2 and 8 seedlings) with soil collected from underneath conspecific adult trees. We examined the effects of light and conspecific density on seedling growth, and explored the effects of the two treatment combinations on soil fungi, and the effects of soil fungi on seedling growth. Higher light availability slightly increased ash seedling growth, but significantly decreased linden seedling growth. Conversely, higher conspecific density depressed ash seedling growth, but improved linden seedling growth. Light and conspecific density had no significant interactive effects on ash seedlings, but lower light availability and higher conspecific density tended to increase linden seedling growth. In addition, soil fungi, which were slightly impacted by light and ash seedling density, had no significant effects on ash seedling growth. However, linden seedling growth was positively affected by ectomycorrhizal fungi, which was greatly increased under lower light availability or higher seedling density. Overall, ash seedling growth may be mainly affected by available resources, controlled by light and conspecific density, while responses of linden seedlings to light and conspecific density can be regulated by soil fungi. These response differences of species to environments may be an important mechanism driving forest community dynamics in temperate forests.

Natural Regeneration of Parkia biglobosa (Néré): Status and variation along the South-North climatic gradient in Mali

Parkia biglobosa offers food, medicine and income to rural populations. A study, was undertaken in three agro-climatic zones in southern Mali, to characterise P. biglobosa populations. Plots of 0.25 ha each were established in fields and fallows and adult trees in the plots were monitored. Natural regeneration was monitored in five subplots of 12.5 m x 12.5 m = 156.25 m2 each within each plot and data were collected from 2019 to 2021. Natural regeneration of P. biglobosa was found to be very weak in all sites. The mean density of seedlings varied from 11 to 24 seedlings ha-1 with a decreasing trend from 2019 to 2021. In Zanzoni, where the weakest regeneration was observed, the density varied from 0 to 8 seedlings ha-1. The highest density of seedlings was observed in Somasso in 2019 (42 seedlings ha-1) and 2020 (30 seedlings ha-1). In 2021, the highest density was observed in Diou (25 seedlings ha-1). The weakness of natural regeneration is very alarming for this tree species facing several other threats (ageing and decreasing adult tree populations, sanitary constraints, several pressures, etc.). It is therefore very important and imperative to investigate ways for regenerating the species for its sustainability and for maintaining the parklands biodiversity. Artificial regeneration (planting), could be the one and ultimate way to ensure the sustainability of P. biglobosa.

Vegetation Structure and Regeneration Status of the Western Escarpment of the Rift Valley of the Gamo Zone, Southern Ethiopia

Understanding the structure and regeneration of forest resources contributes to identifying the elements of diversity, endemism, threatened and endangered species. This study was conducted in the western escarpment of the Rift valley of the Gamo Zone, Southern Ethiopia. The main objective was to investigate structure and regeneration status of the study area. A systematic sampling method was used to collect vegetation data from a total 102 quadrats, each 20 × 20 m (400 m2) and five 1 × 1 m (1 m2) sub-quadrats were established at the four corners and at the centre for sapling and seedling estimation. Tree and shrub species were listed; Height (H ≥ 1.5 m) and DBH ≥ 2 cm were measured and recorded. R-statically software and Microsoft Excel were used to record and analyse the data. A total of 126 plant species belonging to 43 families and 90 genera were identified. The most dominant families were Fabaceae, followed by Anacardiaceae and Euphorbiaceae. Most frequent species were Euclea divinorum (84.3%), followed by Rhus natalensis (83.3%), Terminalia brownii (74.5%). DBH class ≤ 5cm had highest density (63.6%) and DBH ≥ 25.1 cm had the lowest density (0.87%). Three population patterns have been observed; inverted J, J-shaped and irregular shaped. 93% of species had IVI values b/n 1 - 4, 65% of species IVI values Pappea capensis, Combretum molle, Terminalia brownii, Euclea divinorum had highest IVI values. In the vertical stratification, lower story was 91.3% of the individuals. Only a few species contributed to the high density of saplings (440.2/ha) and seedlings (825.49/ha) while most had very little or no saplings and seedlings at all. Thus, in order to revert the current forest structure and regeneration to the previous natural state, it is considered important to minimize the influence of the human interference, grazing and raising awareness to surrounding community.

A test of the Janzen‐Connell hypothesis in a species‐rich Mediterranean woodland

AbstractThe Janzen‐Connell (JC) hypothesis predicts that conspecific negative density dependence contributes to the maintenance of plant diversity by lowering the recruitment of locally abundant plant species. The JC hypothesis is a widely evoked explanation for the high species diversity in tropical forests, but remains poorly tested in other species‐rich systems such as Mediterranean woodlands. As such, we tested if the JC operates and the role of soil‐borne oomycetes in a species‐rich Mediterranean woodland of Western Australia, where post‐fire recruitment can lead to high seedling densities, using the common Banksia attenuata as a case study. We attempted to decipher the effects of oomycete pathogens and distance from conspecific trees on intraspecific seedling survival and growth. Contrary to the JC hypothesis, we found little evidence of negative density dependence, but our results suggest positive density dependence survival under conspecific trees. Oomycete‐driven mortality in seedlings was also found regardless of the type of tree. Our results suggest that short‐term seedling recruitment patterns in this species‐rich, fire‐prone ecosystem do not follow the JC hypothesis. Future studies should explore whether negative conspecific density and distance dependence could play a greater role in later stages of the post‐fire recovery process.

The response of the invasive princess tree (Paulownia tomentosa) to wildland fire and other disturbances in an Appalachian hardwood forest

This study examined the response of princess tree (Paulownia tomentosa) to different disturbances and its potential to spread throughout its current range in the U.S. The study was established in Shawnee State Forest in southern Ohio, USA, which has historically experienced disturbances from mining, logging, ice storms and wildfire. Plots were established for vegetation sampling where fire had occurred with and without princess tree present, and where no fire had occurred with and without princess tree present. To determine the influence of disturbance types on the density of princess tree, redundancy analysis (RDA) was used. High stem density of princess tree seedlings occurred in areas that experienced high fire intensities and herbicide treatment. Seedlings on southwest slopes increased in abundance as the time from the last logging activity increases. Princess tree saplings were present in greater densities in areas that experienced medium fire intensities and the highest ice storm damage. Sapling density is greatest as ground cover and vegetation height increases and slope decreases. Princess trees reach maximum stem density on northeast slopes in areas not impacted by the 2009 fire. All disturbances considered, including wildfire, have created conditions conducive to princess tree growth and expansion into forest areas.

Population structure and regeneration pattern of Himalayan birch (Betula utilis D.Don) in the timberline zone of Nanda Devi Biosphere Reserve, Western Himalaya, India

ABSTRACT The present study aimed to analyse the population structure, forest composition and regeneration dynamics of Betula utilis D.Don in two core zone of Nanda Devi Biosphere Reserve. A total of 346 plants species belonging to 198 genera and 82 families were recorded dominated by Asteraceae (24) followed by Rosaceae (21 species) and Ranunculaceae (19 species), respectively. The total tree stand density was ranged between 1133 ind.ha−1 and 2137 ind.ha−1 in the south and north aspect of the each sites. Among tree species B. utilis was showed the dominant tree species with highest density ranged between 663 ind.ha−1 and 1525 ind.ha−1 at north and south aspects of both sites. Highest seedling density (1033 saplings ha−1 and 1783 seedlings ha−1) and sapling density (1033 saplings ha−1 and 1470 saplings ha−1) was recorded for B. utilis in north and south aspects. The density-diameter curve of B. utilis forest resembled a reverse J-shape which exhibits good regeneration with higher number of individuals in seedling and sapling stages, followed by a sharp decline in tree classes. This study suggests urgent need of long term ecological monitoring of timberline zone to assess the significant change in timberline vegetation and development of sustainable management plans.

Effects of stand features and soil enzyme activity on spontaneous pedunculate oak regeneration in Scots pine dominated stands \u2013 implication for forest management

BackgroundA challenge in current forestry is adaptation of managed forests to climate change, which is likely to alter the main processes of forest dynamics, i.e. natural regeneration. Scots pine will probably lose some parts of its distribution area in Europe. However, two native oaks, pedunculate and sessile may maintain or expand the area of their occurrence in central Europe. The utilization of spontaneous (not initialized by foresters) oak regeneration in Scots pine stands for the creation of next generation stands is one of the adaptation methods to climate change. Many factors influencing pedunculate oak regeneration are well known, but there is a lack of knowledge on the relation between soil enzyme activity and the establishment and development of the species. The aim of the study was to identify the relationships among stand characteristics, herb species composition, soil enzyme activity and the establishment or recruitment of oak regeneration in Scots pine-dominated stands.ResultsThe one of the most influential factors shaping the oak seedling count was dehydrogenase activity in the humus horizon. We found that plots without litter and fern cover had higher seedling density. The raspberry ground cover and birch crown projection area had a positive influence on oak seedling number. The factor indicating good conditions for high density of oak saplings was phosphatase activity in the organic horizon. The same enzyme activity but in humus horizon described conditions in which more numerous recruits were observed.ConclusionsThe activity of soil enzymes can be used as the predictor of the establishment and advancement of oak regeneration but also could be seen as a new dimension of oak regeneration. The general density of spontaneous oak regeneration was not sufficient for the creation of new generation forest stands dominated by oak, but it is possible to use them as admixtures in new generation stands.

Seed encrusting with salicylic acid: A novel approach to improve establishment of grass species in ecological restoration.

To achieve global ambitions in large scale ecological restoration, there is a need for approaches that improve the efficiency of seed-based interventions, particularly in overcoming the bottleneck in the transition from germination to seedling establishment. In this study, we tested a novel seed-based application of the plant stress modulator compound salicylic acid as a means to reduce seedling losses in the seed-to-seedling phase. Seed coating technology (encrusting) was developed as a precursor for optimising field sowing for three grass species commonly used in restoration programs, Austrostipa scabra, Microlaena stipoides, and Rytidosperma geniculatum. Salicylic acid (SA, 0.1mM) was delivered to seeds via imbibition and seed encrusting. The effects of SA on seed germination were examined under controlled water-limited conditions (drought resilience) in laboratory setting and on seed germination, seedling emergence, seedling growth and plant survival in field conditions. Salicylic acid did not impact germination under water stress in controlled laboratory conditions and did not affect seedling emergence in the field. However, seedling survival and growth were improved in plants grown from SA treated seeds (imbibed and encrusted) under field conditions. When SA delivery methods of imbibing and coating were compared, there was no significant difference in survival and growth, showing that seed coating has potential to deliver SA. Effect of intraspecific competition as a result of seedling density was also considered. Seedling survival over the dry summer season was more than double at low seedling density (40 plants/m2) compared to high seedling density (380 plants/m2). Overall, adjustment of seeding rate according to expected emergence combined with the use of salicylic acid via coating could improve seed use efficiency in seed-based restoration.

Sustainable Large-Scale Aquaculture of the Northern Hemisphere Sea Lettuce, Ulva fenestrata, in an Off-Shore Seafarm

The growing world population demands an increase in sustainable resources for biorefining. The opening of new farm grounds and the cultivation of extractive species, such as marine seaweeds, increases worldwide, aiming to provide renewable biomass for food and non-food applications. The potential for European large-scale open ocean farming of the commercial green seaweed crop Ulva is not yet fully realized. Here we conducted manipulative cultivation experiments in order to investigate the effects of hatchery temperature (10 and 15 °C), nutrient addition (PES and 3xPES) and swarmer density (500 and 10,000 swarmers ml−1) on the biomass yield and biochemical composition (fatty acid, protein, carbohydrate, pigment and phenolic content) of off-shore cultivated Ulva fenestrata in a Swedish seafarm. High seedling densities were optimal for the growth of this northern hemisphere crop strain and significantly increased the mean biomass yield by ~84% compared to low seedling densities. Variations of nutrients or changes in temperature levels during the hatchery phase were not necessary to increase the subsequent growth in an open-water seafarm, however effects of the factors on the thallus habitus (thallus length/width) were observed. We found no significant effect of the environmental factors applied in the hatchery on the total fatty acid or crude protein content in the off-shore cultivated Ulva. However, low seedling density and low temperature increased the total carbohydrate content and furthermore, high temperature in combination with high nutrient levels decreased the pigment content (chlorophyll a, b, carotenoids). Low temperature in combination with high nutrient levels increased the phenolic content. Our study confirms the successful and sustainable potential for large-scale off-shore cultivation of the Scandinavian crop U. fenestrata. We conclude that high seedling density in the hatchery is most important for increasing the total biomass yield of sea-farmed U. fenestrata, and that changing temperature or addition of nutrients overall does not have a large effect on the biochemical composition. To summarize, our study contributes novel insights into the large-scale off-shore cultivation potential of northern hemisphere U. fenestrata and underpins suitable pre-treatments during the hatchery phase of seedlings to facilitate a successful and cost-efficient large-scale rope cultivation.