Habitat heterogeneity and biotic interactions mediate climate influences on seedling survival in a temperate forest

Seedling stage has long been recognized as the bottleneck of forest regeneration,and the biotic and abiotic processes that dominate at seedling stage largely affect the dynamics of forest.Seedlings might be particularly vulnerable to climate stress,so elucidating the role of interannual climate variation in fostering community dynamics is crucial to understanding the response of forest to climate change.Using seedling survival data of 69 woody species collected for five consecutive years from a 25-ha permanent plot in a temperate deciduous forest,we identified the effects of biotic interactions and habitat factors on seedling survival,and examined how those effects changed over time.We found that interannual climate variations,followed by biotic interactions and habitat conditions,were the most significant predictors of seedling survival.Understory light showed a positive impact on seedling mortality,and seedling survival responded differently to soil and air temperature.Effects of conspecific neighbor density were significantly strengthened with the increase of maximum air temperature and vapor pressure deficits in the growing season,but were weakened by increased maximum soil temperature and precipitation in the non-growing season.Surprisingly,seedling survival was strongly correlated with interannual climate variability at all life stages,and the strength of the correlation increased with seedling age.In addition,the importance of biotic and abiotic factors on seedling survival differed significantly among species-trait groups.Thus,the neighborhood-mediated effects on mortality might be significantly contributing or even inverting the direct effects of varying abiotic conditions on seedling survival,and density-dependent effects could not be the only important factor influencing seedling survival at an early stage.

Seedling survival and growth of Aquilaria malaccensis in different microclimatic conditions of northeast India

We studied seedling survival and growth ofAquilaria malaccensis in three different environmental conditions （homegardens, green house and in different canopy conditions） of northeast India. Results show that mean seasonal survival was highest in green house （95.53%±2.33）, followed by homegardens （89.3%±1.89） and different canopy conditions （77.62%±6.73）; the highest values were found during February to April for both the homegardens （96%±1.68） and green house （98% ± 0.88） and lowest during November to January （78%±2.99） in homegardens and May to July （90%：t：4.53） in green house. In case of transplanted seedlings in different canopy conditions, mean seasonal survival was highest during May to July （98%±1.92） and lowest during August to October （66%±12.81）. However, mean seasonal growth of collar diameter was highest in different canopy conditions （23.99%±1.76） compared to green house （21.52%±2.70） and homegardens （12.44%±1.33） and it was highest during rainy season （May to July） and lowest during dry winter （November to January） in all the three experi- mental sites. These variations may be due to the different microclimatic conditions as well as nutrient status of the soil in all the three experimen- tal sites. Although, seedling quality plays a great role in their survival and growth, based on the result of green house experiment, it can be concluded that maintenance of seedlings in green house conditions during their early growth period may improve both the survival and growth for large scale plantation of the species. Thus, the species can be reintroduced in its natural forest range to compensate the loss of natural population of this precious species in northeast India.

Differential seed removal,germination and seedling growth as determinants of species suitability for forest restoration by direct seeding–A case study from northern Thailand

Background Direct seeding is potentially a more cost-effective alternative to conventional tree planting for restoring tropical forest ecosystems.However,seed loss,due to removal and damage by animals,can substantially reduce seedling establishment.Therefore,this study examined the impact of seed predation on seedling establishment of five tree species,native to upland evergreen forests of northern Thailand:Hovenia dulcis,Alangium kurzii,Prunus cerasoides,Choerospondias axillaris and Horsfieldia amygdalina.We tested the hypothesis that excluding animals would significantly reduce seed removal,and increase both germination and seedling survival.The objective was to calculate a composite index of the relative suitability of the species studied for direct seeding.Methods Seeds were placed on the ground in a deforested site and subjected to five predator-exclusion treatments:wire cage,insecticide,cage+insecticide,open cage and no exclusion(control).Results Seed loss was highest for H.amygdalina(the largest seed tested).Across species,wire cages significantly reduced seed loss by 12.4%compared with controls(P<0.001)suggesting that vertebrates were the major seed predators.Seed germination ranged from 0 to 77%among the species tested.Based on relative species-performance scores(combining measures of survival and seedling growth),P.cerasoides was the most suitable species for direct seeding,followed by A.kurzii and C.axillaris,whilst H.dulcis and H.amygdalina were unsuitable.H.dulcis had small seeds with low seed germination,whereas H.amygdalina was subjected to high seed removal.Conclusion Exclusion of seed predators and the selection of suitable species may substantially increase the success of direct seeding,as a technique for restoring upland evergreen forest ecosystems.Testing more species for their suitability is needed,to provide more diverse options for forest restoration.

Preliminary Study on Optimized Conditions for Dry-cultivated Rice Seedling Planting

The effects of soil moisture content, pot seedling buried depth, and pot seedling height on the survival rate and growth of dry planted seedlings were researched by field experiment. The results showed that the seedling survival rate and growth were enhanced with the increase of soil moisture content after pot seedling transplanting, but there was no significant difference in the survival rate and growth of seedlings with 85% and 100% of soil moisture content. Pot seedling buried depth was one of the important factors affecting the survival rate, and when the pot seedlings were buried 2 cm deep, the seedlings showed high survival rate and excellent growth. Under the same condition of soil moisture content and buried depth, seedlings with pot seedling height of 15 cm had the best survival rate and growth. Therefore, the optimized conditions for dry-cultivated rice seedling planting were soil moisture content of 85%, pot seedling buried depth of 2 cm, and pot seedling height of 15 cm.

Preliminary assessment of growth and survival of green alder(Alnus viridis), a potential biological stabilizer on fly ash disposal sites

This paper presents preliminary assessment of seedling survival and growth of green alder（Alnus viridis（Chaix） DC. in Lam. ＆ DC.） planted on fly ash disposal sites. This kind of post-industrial site is extremely hard to biologically stabilize without top-soiling. The experiment started with surface preparation using NPK start-up mineral fertilizer at 60–36–36 kg ha-1followed by initial stabilization through hydro-seeding with biosolids（sewage sludge 4 Mg ha-1dry mass） and a mixture of grasses（Dactylis glomerata L. and Lolium multiflorum Lam.）（200 kg ha-1）. Subsequently, three-years-old green alder seedlings were planted in plots on two substrate variants：the control（directly on combustion waste） and plots with3 dm3 lignite culm from a nearby mine introduced into the planting pit. Five years of preliminary monitoring show good survival seedling rates and growth parameters（height（h）, average increase in height（Dh）, number of shoots（L o）and leaf nitrogen supply in the fly ash disposal habitat.Treatment of the site with a combination of lignite culm in planting pits and preliminary surface preparation by hydroseeding and mineral fertilization had the most positive effect on green alder seedling parameters. The results indicate that it is possible and beneficial to use green alder for biological stabilization on fly ash disposal sites.

Seed bank and regeneration dynamics of Emmenopterys henryi population on the western side of Wuyi Mountain,South China

Emmenopterys henryi Oliv. (Rubiaceae) is an endangered tree species that is native to China. The wild populations of E. henryi have declined rapidly because of its poor natural regeneration, but the actual regeneration processes are not yet understood. In field tracking surveys and experiments in the Wuyishan Nature Reserve in Southeast China to determine the most important stage that affects the regeneration process, seed bank characteristics, seed germination, and seedling growth dynamics were studied in the typical habitats of E. henryi, Phyllostachys pubescens and broad-leaved forests. Results showed that in both P. pubescens and broad-leaved forests, more than 70% of the E. henryi seeds were distributed in moss and litter layers, and few were found in the soil beneath them. However, seed germination in the soil layer was significantly higher than in the moss and litter layers. Seed density, overall seed quality, and germination rate in the broad-leaved forest were significantly higher than in P. pubescens forest. Seed germination was highest in the microsites around the edge of the crown projection area of E. henryi mother trees. The order of survival rate of the seedlings on different ground surfaces was soil > moss > litter. In both habitats, the average seed density was 24.9 seeds m(-2), and the total germination rate was less than 3.5 parts per thousand. However, seedlings developed from only 1% of the germinated seeds, indicating that the seed germination is the most important stage in the natural regeneration of E. henryi.

Effects of vegetation cover on recruitment of Ulmus pumila L. in Horqin Sandy Land, northeastern China

Understanding the effects of vegetation cover on seedling survival is helpful for promoting vegetation restoration in environmentally fragile zones. This study was conducted in the desertified, moving sand dunes of Horqin Sandy Land, Inner Mongolia, northeastern China. We hyphothesized that （1） seed density （i.e., number/m2） increases as vegetation cover increases, and （2） there will be more surviving seedlings in locations with higher vegetation covers. Total vegetation cover and initial densities of seeds, germinated seeds and surviving seedlings of Ulmus pumilia were evaluated under various vegetation covers in trying to clarify the effects of vegetation cover on the early stages of the plant life history. In agreement with the first hypothesis, initial seed densities were greater （P〈0.05） under higher vegetation covers. The relationship between vegetation cover and initial seed density was represented by a quadratic regression, where a threshold occurred with a vegetation cover of 36% （P〈0.05）. The higher total vegetation covers, however, did not result in increased densities of germinated seeds （P〉0.05）, which on average represented 16.7% of initial seed densities. Even more, three months after the study initiation, total vegetation covers were similar （P〉0.05） at all positions in the dunes, and they determined a similar number （P〉0.05） of surviving seedlings at those positions （i.e. the second hypothesis had to be rejected）. The mean number of seedlings that survived at all positions was only 4.5% of germinated seeds. The number of surviving elm seedlings （0 to 1.7 seedlings/m2） under various vegetations covers （12.2% to 20.8%） at all dune positions by late summer would most likely not contribute to vegetation restoration in the study area.

Experimental approaches to select tree species for forest restoration:effects of light,water availability and interspecific competition in degraded areas

Knowing what native trees can recr uit on degraded areas allows selecting the best species to restore these sites.However,as this information is not often available,experimentation is required before large-scale planting.This study used ex situ experiments to make these decisions on recruitment.Competition with r-strategist plants,excessive solar radiation and water shortage commonly impair tree recruitment in open habitats.The experiments focused on the interactions among these factors and were conducted with three pioneer species from seasonally dry forests of northwest Argentina,Anadenanthera colubrina,Ceiba chodatii and Jacaranda mimosifolia.Seeds of each species were sown at two light levels(sunlight/shade),two rainfall levels(full/reduced)and two levels of interspecific competition(with/without competitor)in a tree nursery.Seedling emergence and survival were monitored over a year and the results indicate that species differentially respond to varying levels of light and water.Seedlings of A.colubrina tolerated water shortages under elevated solar radiation,which are desirable features for forest restoration.Seedlings of C.chodatii tolerated shade and drought,suggesting that they require shading for establishing in open areas.However,J.mimosifolia seedlings neither tolerated full sunlight nor water shortages,suggesting that this species requires shading and regular watering if used in reforestation.Regardless of the effects of light and water,the survival of all species was reduced by interspecific competition.These results highlight the importance of experimentation for selecting the best species for forest restoration and can enhance the cost/benefit ratios of these actions.

Laboratory-and Field-Phenotyping for Drought Stress Tolerance and Diversity Study in Lentil (Lens culinaris Medik.)

Drought susceptibility and low genetic variability are the major constraints of lentil(Lens culinaris Medik.)production worldwide.Development of an efficient pre-field drought phenotyping technique and identification of diversified drought tolerant lentil genotype(s)are therefore vital and necessary.Two separate experiments were conducted using thirty diverse lentil genotypes to isolate drought tolerant genotype(s)as well as to assess their diversity.In both of the experiments,significant(p≤0.01)variation in genotype(G),treatment(T)and G X T was observed for most of the studied traits.In experiment I,genotypes were examined for drought tolerance at the seedlings stage under hydroponic conditions by assessing root and shoot traits.Among the 30 genotypes studied,BM-1247,BM-1227 and BM-502 were selected as highly tolerant to drought stress as they showed maximum seedling survivability and minimum reduction in growth parameters under drought stress.In experiment II,the genotypes were assayed for diversity and drought stress tolerance based on morphological traits grown under field condition.Drought stress caused a substantial reduction in yield attributing traits,however,the genotypes BM-1247,BM-981,BM-1227 and BM-502 were categorized as drought tolerant genotypes with less than 20%yield reduction.The field screening result of drought stress tolerance was coincided well with the results of laboratory screening.Genetic divergence study reflected the presence of considerable diversity among the genotypes.Considering laboratory and field screening results,the genotypes,BM-1247,BM-1227,BM-981 and BM-502 were selected as the best drought tolerant genotypes.This information can be exploited for further breeding in developing drought tolerance in lentil.

Influence of ectomycorrhizal inoculation on Pinus wallichiana and Cedrus deodara seedlings under nursery conditions

A study was undertaken to examine the extent of root colonization by four locally isolated ectomycorrhizal （ECM） fungi （Hebeloma theobrominum, Boletus dryophilus, Scleroderma citrinum and Suillus luteus） and their effects on seedling growth in Pinus wallichiana and Cedrus deodara under nursery conditions. Seedlings of the two conifers were inoculated with mycelium of ECM fungi and were grown in pots containing sterilized forest soil for six months. The percentage of ECM colonization of roots was 38%-52% in Pinus wallichiana and 33%-48~ in Cedrus deodara. ECM colonization increased shoot height, needle number, shoot and root biomass and survival of inoculated seedlings. Among the four ECM fungi Hebeloma theobrominum was more effective with Pinus wallichiana and Scleroderma citrinum with Cedrus deodara in promoting seedling survival and overall growth. All the four ECM fungi used enhanced growth of inoculated seedlings and thus can be used in afforestation and regeneration programmes in degraded forests ecosystems.

Host compatibility interacts with seed dispersal to determine smallscale distribution of a mistletoe in Xishuangbanna,Southwest China

Aims Mistletoe infection between intra- and interspecific hosts can be restricted by seed dispersal, host–mistletoe compatibility and other factors, yet few studies have linked seed dispersal and seedling establishment together for understanding mistletoe plant distribution and demography together in different anthropogenic disturbance forest types at a local scale. The objectives of this study were to examine how three factors—seed disperser behavior, post-dispersal host compatibility and canopy cover—affect the spatial distribution of a generalist mistletoe Dendrophthoe pentandra (Loranthaceae) in plantation and rainforest within Xishuangbanna, Southwest China.MethodsWe observed mistletoe D. pentandra infection patterns at the scale of individual trees and sixteen 400-m2 forest plots in adjacent plantation and rainforest within Xishuangbanna. To elucidate what determines infection patterns at different scales and in different forest types, we observed the behavior of major avian seed dispersers and carried out a seed inoculation experiment to examine how post-dispersal compatibility and light incidence affect the infection of different hosts.Important FindingsDendrophthoe pentandra displayed an aggregated distribution and infected 10 species in our study site, with a significantly higher infection prevalence and intensity in the plantation than in the tropical forest. Different seed dispersers provided contrasting initial mistletoe templates: the specialist frugivore Dicaeum concolor (plain flowerpecker) preferred to fly between mistletoes in infected trees in the plantation and likely intensified existing infections. In contrast, the dietary generalist Pycnonotus jocosus(red-whiskered bulbul) was more likely to visit uninfected trees, thereby establishing new infections. Thus, seed dispersal appears to be an important determinant of the mistletoes distribution, with deposition patterns providing an initial distribution template and determining small-scale patterns. However, post-dispersal and abiotic factors revealed that different host compatibilities and levels of light incidence in different habitats affected the survival of D. pentandra seedlings. Hence, our findings suggest that seed dispersal interacts with host compatibility and canopy cover to determine establishment success, survival and the observed distribution patterns.