A report of Siwalik forest around Letang Raja-Rani wetland, Morang, eastern Nepal

Species composition, phytosociological status and soil characteristics of Siwalik forest occurring around Raja-Rani wetland, Letang municipality, eastern Nepal was studied. A total of 47 tree species belonging to 40 genera and 26 families were reported. Dominant and co-dominant trees were Shorea robusta (IVI=133.4) and Schima wallichii (IVI=70.6), respectively. In the forest total tree density, basal cover area, seedling density, fallen dead density and dead standing density were 378.4 trees ha-1, 163.7 m2 ha-1, 105250 individual ha-1, 4 trees ha-1 and 1.6 trees ha-1, respectively. Irregular girth class distribution and high stump density (136.8 tree ha-1) denote disturbance. Soil physicochemical characteristics were: acidic soil (pH 4.8), moisture (12.5%), water holding capacity (50.05%), bulk density (1.17 g cm-3), porosity (0.55%), humus (8.6%), organic carbon (0.52%), nitrogen (0.1%), phosphorus (33 kg ha-1), and potassium (300 kg ha-1). Regulating human encroachment to ensure natural regeneration of species to maintain the viability of the Letang Raja-Rani wetland site and integrity of the local ecosystem is strongly recommended.

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

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

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.

Short-term study on the yak dung seed bank on the Qinghai-Tibetan Plateau: effects of grazing season, seed characteristics and forage preferences

Aims Viable seeds in herbivore dung constitute the dung seed bank, and the contribution of livestock dung to this seed bank in grazing pastures is often overlooked. Grazing season (warm and cold), seed characteristics (size and shape), and forage preference are the main factors that affect the size and composition of the dung seed bank and ultimately affect grassland ecology. However, how these three factors interact is unclear. Methods We collected yak dung as well as seeds of the common plant species from warm- and cold-season alpine meadows in northeastern Qinghai-Tibetan Plateau, and explored how grazing season (warm and cold), seed characteristics (size and shape) and foraging preferences (temporary cages method) affects yak dung seedling density, richness and diversity in an alpine pasture. Results Forty-three plant species (mainly perennials) germinated from yak dung. Dung seedling density, richness, and diversity did not differ significantly between the two grazing seasons. Small to medium-sized spherical seeds (seed size < 10 mg, shape index < 0.5) had the greatest germination potential. Conclusions Yaks vary their forage preference depending on the season (phenological period), and endozoochory occurs throughout both grazing seasons. Seed shape and size directly regulate the dung seedling density, richness, and diversity. Dung seedlings increase the heterogeneity of the aboveground vegetation near the microsites of the dung pieces and therefore promote grassland patching. Our study demonstrates that grazing season, seed characteristics, and yak forage preferences affect the dung seed bank in grazing ecosystems.

Response of the Leek (Allium porrum)-Mycorrhizal Fungus Symbiosis to Cutting Levels, Light Exposure and Seedling Density

This work aims to assess the leek-arbuscular fungus symbiosis response to the effect of cutting and light exposure on the one hand, and the impact of seedling density on this symbiosis on the other hand. Allium Porrum was grown in a container in two different trials. Four species of arbuscular mycorrhizal fungi, Glomus hoi, Scutellospora gregaria, Rhizophagus intraradices and Gigaspora margarita were used to constitute the mycorrhizal inoculum. After 150 days of growth and inoculation, a series of cuts were made on the aerial part (0% = zero cut, 50% = half cut, 100% = whole cut). Plants that had undergone these treatments were placed in shade and sun for 30 days. The leek density per bag was varied by the order of 1, 2, 3 and 4 plant (s) by the pocket density test. Results showed that for 0% of cut in the shade, the vesicle occurrence decreases from 83.33% to 52.22%, and from 90% to 25.5% for 50% of cut in the shade. On the other hand, there is a significant increase in intra-root spores for a complete cut compared to other levels of cuts. For extra-root sporulation, under light, cuts have a negative and weak effect (from -11 to -3%) while in the absence of light, cuts have significant positive effects (from +16 to +61%). Regarding seedling density, the best root colonization (90%) and biomass production (14 g) are obtained with three plants per pot, but it is rather with a density of two plants per pot that extra-root sporulation is higher (153 spores/g). Variation in light, cut level and density significantly affects the development of mycorrhizal fungi.

Moisture and vegetation cover limit ponderosa pine regeneration in high-severity burn patches in the southwestern US

Background Fire regimes are shifting in ponderosa pine (Pinus ponderosa Lawson & C. Lawson)-dominated forests, raising concern regarding future vegetation patterns and forest resilience, particularly within high-severity burn patches. The southwestern US has recently experienced a marked increase in large fires that produce large, high-severity patch interiors, with few surviving trees. These areas could be more susceptible for forest loss and conversions to alternative vegetation types than areas closer to the forest edge with more available seed sources. To better understand forest recovery, we surveyed ponderosa pine regeneration within edge and core areas (>200 m from edge) of high-severity patches in ten fires that burned between 1996 to 2008 across Arizona and New Mexico, USA. Specifically, we compared regeneration density, height, and canopy cover in patch edge and core areas and used generalized linear models to investigate the abiotic and biotic factors that contribute to ponderosa pine seedling establishment and density. Results High-severity burn-patch edge and core plots were not significantly different in seedling density, height, or canopy cover across fires. Seedling establishment was more likely at higher-elevation mesic sites and less likely when Gambel oak (Quercus gambelii Nutt.) was more abundant. Seedling density was negatively impacted by shrub, grass, and Gambel oak cover. Conclusions Regeneration density varied among fires but analysis of regeneration in aggregated edge and core plots showed that abundance of seed availability was not the sole factor that limited ponderosa pine regeneration, probably because of surviving tree refugia within high-severity burn patches. Furthermore, our findings emphasize that ponderosa pine regeneration in our study area was significantly impacted by xeric topographic environments and vegetation competition. Continued warm and dry conditions and increased wildfire activity may delay the natural recovery of ponderosa pine forests, underscoring the importance of restoration efforts in large, high-severity burn patches.

Seedling diversity and spatial distribution of some conifers and associated tree species in highly disturbed Western Himalayan regions in Pakistan

This article encompasses the impacts of disturbance, regeneration potential of conifers and the dynamics of tree species seedlings along the spatial scale in Murree forest. The seedling status preferably of conifers along with associated broadleaved dominant tree species is determined by a quantitative evaluation of diversity functions. An empirical approach is applied to predicting the future of seedlings under stress as well as the current hypothetical appearance of seedlings in the forest. The need of analysing diversity of this forest is due to highly disturbed conditions there, and this paper is designed to know the recent trends of species diversity in the area. Species diversity and species abundance at a seedling level are estimated by using standard formulas of diversity measurements. Thirty stands are used for the evaluation of seedling abundance in highly disturbed conditions with the examination of diversity in the area. Seedling density is too low in the forest whereas diversity is also in poor condition. Seedlings from four conifers with three broadleaved species in different stands indicated the low density of future trees. The mean density·ha^–1 of pine seedlings is consecutively low in Pinus wallichiana (16 ± 2), Pinus roxburghii (11 ± 3), Cedrus deodara (9 ± 3), Abies pindrow (8 ± 3). The correlation coefficient is as low as 0.76, 0.66 and 0.61 in Pinus roxburghii, Cedrus deodara and Abies pindrow, respectively, while Pinus wallichiana showed a significant correlation, i.e. P &gt; 0.5. Hence, this study claims that the survival of the forest is threatened as seedling density and diversity are too low. This forest needs serious attention towards preventing and conserving pines and other associated species seedlings for the existence of this forest in future.

Plant-plant interactions change during succession on nurse logs in a northern temperate rainforest

Plant-plant interactions can vary depending on the severity of the environment. Positive interactions, such as facilitation, are important in early life stages while negative interactions, such as competition, predominate in later stages. Through succession, plant-plant interactions often change from facilitative to competitive. In northern temperate rainforests, gap dynamics result in tree falls that facilitate tree regeneration (nurse logs) as well as bryophyte succession. While the importance of nurse logs for tree seedlings is known, how the interactions of bryophyte communities and tree seedlings vary through succession of the log remains unclear. We examined the relationships of tree seedlings, bryophyte community composition, bryophyte depth, and percent canopy cover in 166 plots on nurse logs and the forest floor in the Hoh rainforest in Washington, USA. Tree seedling density was highest on young logs with early-colonizing bryophyte species (e.g., Rhizomnium glabrescens), and lowest on decayed logs with Hylocomium splendens, a long-lived moss that reaches depths >20 cm. As a result, bryophyte depth increased with nurse log decay and was negatively associated with tree seedling density. Tree seedling density was 4.6x higher on nurse logs than on the forest floor, which was likely due to competitive exclusion by H. splendens. Nurse logs had 17 species of bryophytes while the forest floor had six, indicating that nurse logs contribute to maintaining bryophyte diversity. Nurse logs are essential for forest dynamics as they enable both tree seedlings and smaller bryophyte species to avoid competition with the dominant forest floor bryophyte, H. splendens. Given that H. splendens has a global distribution and is often dominant in forested systems across the northern hemisphere, it is likely a widespread driver of plant community structure. Our findings indicate that plant-plant interactions shift with succession on nurse logs from facilitative to competitive and, thus, influence forest community structure and dynamics.