Tree Seedling Establishment Research Articles

Changes in plant diversity and composition across forest edges bordered by Austroeupatorium inulifolium invaded grasslands in the Knuckles Conservation Area, Sri Lanka

Austroeupatorium inulifolium has become a ferocious invader over the years in many ecosystems in the wet zone of Sri Lanka, including the grasslands of the Knuckles Conservation Area (KCA). Two field studies were conducted to assess the impacts of Austroeupatorium invasion on the diversity and composition of the plant communities. In the first study, three habitat categories were identified: less-invaded grassland (LIG), highly-invaded grassland (HIG) and the forest-grassland edge (FGE) adjacent to HIG. In the second study, two transects were selected that run across the FGE bordered by less or highly invaded grasslands (FGE-LIG and FGE-HIG). At each community, 5 linear quadrats (12 m x 3 m) were laid parallel to the FGE at different distances away from the edge to the forest interior and the open grassland. Each quadrate was further sub-divided into 3 quadrats. Three such transects were studied for each community. In both studies, the vegetation less than 2 m in height was enumerated. The stem density and abundance of Austroeupatorium were significantly higher in HIG and FGE compared to LIG. However, the plant community at FGE was less diverse than that of HIG and LIG. Tree saplings were observed only in the HIG, suggesting its favourable conditions for their establishment. The abundance of Austroeupatorium was markedly reduced towards the forest interior, suggesting that the FGE acts as a barrier against invasion towards the forest. The tree sapling abundance decreased from the forest interior towards the open grassland but the abundance was higher in transects bordered by HIG than by LIG. This suggests a facilitative effect on the forest tree regeneration potential under the Austroeupatorium canopy. The invasion may have led to improved micro-climatic and edaphic conditions and may also have facilitated the tree seedling establishment and survival in the forest interior as far as 10 m away from the FGE. Current findings depict positive impacts of Austroeupatorium-invaded grasslands on the forest regeneration process. Therefore, it is time to explore the positive effects of exotic species, especially when they colonize highly degraded landscapes, rather than generalizing that all invasive species cause detrimental impacts on every landscape.DOI: http://dx.doi.org/10.4038/cjsbs.v42i2.6607 Ceylon Journal of Science (Bio. Sci.) 42(2): 29-43, 2013

Can Austroeupatorium inulifolium Invasion Favour Tree Species Establishment on Highly-Degraded Man-made Grasslands

It is well known that invasive species alter vegetation structure and composition, but most ofthe evidence to support this claim come from natural ecosystems. In many instances, thesestudies reported negative consequences on these natural habitats. Within last few years, thehighly degraded grasslands at the Knuckles Conservation Area (KCA) have rapidly invadedby Austroeupatorium inulifolium, a notorious invasive species. The present study was aimedat investigating the impacts of Austroeupatorium on grassland communities, and also to seeany positive role in forest expansion process towards these invasive grasslands by borderingforest remnants.A complete vegetation sampling was carried out in 3 grassland communities having differentlevels of invasion; grasslands densely-invaded with Austroeupatorium (HIG), and lessdenselyinvaded (LIG) and the forest-grassland edge (FGE). For each grassland community,nine randomly placed 4 m2 quadrates were used to enumerate the vegetation. Anothersampling was carried out using two forest-grassland edge (FGE) communities; forest remnantbordered by LIG (FGE- LIG) and forest remnant bordered by HIG (FGE- HIG). At each site,5 linear quadrates (3 m x 12 m) were placed parallel to the FGE at different distances; 0(edge), 5 and 10 m away from the edge towards the grassland and towards the forest interior.Six such transects were sampled for each FGE category.A total of 30 species have been identified belonging to 20 families in HIG while 21 species(belonged to 14 families) and 14 species (belonged to 9 families) were identified from LIGand FGE respectively. Tree saplings (4 species) were recorded only in HIG. The two edgehabitats showed somewhat different vegetation composition. Of the 182 and 430 individualsof tree saplings encountered at FGE-LIG and FGE-HIG respectively, majority of them werefound in quadrates laid inside the forest (76 and 88% respectively). Abundance and richnessof tree saplings were significantly higher at 10 m towards the forest interior bordered by HIGthan that of LIG.Present results suggested that Austroeupatorium invasion has a facilitative effect on treeseedling establishment probably through enhanced shading effect and improved edaphicconditions. The results also suggest that Austroeupatorium invasion has the potential tochange the community structure in forest-grassland edges which eventually influence thevegetation community in the forest interior, at least up to 10 m. The facilitative effect ofAustroeupatorium invasion on the forest tree establishment needs further studies to verify itslong-term effect on these grasslands.

Comparison of the penetration of primary and lateral roots of pea and different tree seedlings growing in hard soils

Establishment and survival of tree seedlings in hard soils depends on production of deep root systems. This study evaluated the primary and lateral roots of an annual crop and several tree species growing in soils of varying strength. We grew peas and acacias by direct seeding, plus three eucalypts by direct seeding and transplanting, and measured various root characteristics. At all levels of soil compaction, the primary roots of acacia were thicker and they elongated faster than did those of the eucalypts. However, lateral roots of transplanted eucalypts elongated faster than their primary roots, and the rate of root elongation was negatively correlated with soil penetration resistance, especially for Eucalyptus camaldulensis. The primary root diameter of all plants increased with increasing penetration resistance, but acacia roots continued to elongate faster than pea roots. Pea plants produced most of their roots in the top 5 cm, whereas tree roots were more uniformly distributed with depth. Although not statistically significant at P = 0.05, the relative rate of root elongation in very hard soil correlated modestly (P = 0.11) with the maximum root growth pressure of four tree species. These variations in root growth behaviour can be related to the intrinsic variability of root characteristics for each plant species and the natural abundance of each species in different environments.

Cross-scale modeling of surface temperature and tree seedling establishment in mountain landscapes

IntroductionEstimating surface temperature from above-ground field measurements is important for understanding the complex landscape patterns of plant seedling survival and establishment, processes which occur at heights of only several centimeters. Currently, future climate models predict temperature at 2 m above ground, leaving ground-surface microclimate not well characterized.MethodsUsing a network of field temperature sensors and climate models, a ground-surface temperature method was used to estimate microclimate variability of minimum and maximum temperature. Temperature lapse rates were derived from field temperature sensors and distributed across the landscape capturing differences in solar radiation and cold air drainages modeled at a 30-m spatial resolution.ResultsThe surface temperature estimation method used for this analysis successfully estimated minimum surface temperatures on north-facing, south-facing, valley, and ridgeline topographic settings, and when compared to measured temperatures yielded an R2 of 0.88, 0.80, 0.88, and 0.80, respectively. Maximum surface temperatures generally had slightly more spatial variability than minimum surface temperatures, resulting in R2 values of 0.86, 0.77, 0.72, and 0.79 for north-facing, south-facing, valley, and ridgeline topographic settings. Quasi-Poisson regressions predicting recruitment of Quercus kelloggii (black oak) seedlings from temperature variables were significantly improved using these estimates of surface temperature compared to air temperature modeled at 2 m.ConclusionPredicting minimum and maximum ground-surface temperatures using a downscaled climate model coupled with temperature lapse rates estimated from field measurements provides a method for modeling temperature effects on plant recruitment. Such methods could be applied to improve projections of species’ range shifts under climate change. Areas of complex topography can provide intricate microclimates that may allow species to redistribute locally as climate changes.

Do plant traits explain tree seedling survival in bogs?

Summary Moss‐dominated peat bogs store approximately 30% of global soil carbon. A climate induced‐shift from current moss‐dominated conditions to tree‐dominated states is expected to strongly affect their functioning and carbon sequestration capacity. Consequently, unravelling the mechanisms that may explain successful tree seedling establishment in these ecosystems is highly relevant. To assess the role of drought on early tree seedling establishment and the relative importance of plant traits in tree seedling survival, we conducted a factorial glasshouse experiment with seven conifer species. Our results show that drought inhibits moss growth, thereby increasing survival of tree seedlings. Survival success was higher in Pinus than in Picea species, ranking Pinus banksiana > Pinus sylvestris > Pinus nigra > Picea mariana > Picea glauca, Picea sitchensis > Picea rubens. We found that those species most successful under dry and wet conditions combined a fast shoot growth with high seed mass. We conclude that plant traits contribute to explaining successful early tree seedling establishment in bogs.

Linking restoration outcomes with mechanism: the role of site preparation, fertilisation and revegetation timing relative to soil density and water content

Global land use and ongoing climate change highlight the importance of ecological restoration as an emerging discipline and underscore the need for successful revegetation techniques. To link mechanistic drivers of seedling establishment with techniques to increase revegetation success, we undertook field-based experiments in degraded peri-urban woodlands in Mediterranean southwestern Australia using two iconic tree species. Over the course of an entire growing season, our objectives were to: (1) characterise soil moisture profiles in relation to site preparation techniques (ripping and created ashbeds) and (2) determine whether early seedling establishment can be increased through site preparation techniques (ripping and ashbeds), plant treatments (various fertilisers and biochar) and early planting during the wet season. Ripping significantly reduced soil compaction and was associated with a significant soil moisture stratification; moisture penetrated to greater depths in soils that were ripped or treated with ashbeds. Particular site preparation techniques (ripping) and early planting significantly increased early establishment, health and growth of tree seedlings. Fertilisation effects varied by species with generally neutral effects on seedlings. Finally, seedlings planted in ripped soils had significantly longer, deeper root systems accessing portions of the soil profile with higher summer moisture. Techniques such as ripping, even in deep sandy soils, reduce soil compaction and alter moisture availability within the soil profile, promoting deeper root growth and thus increasing revegetation success in these degraded Mediterranean ecosystems. Linkage of revegetation outcomes with plant response and physical soil properties associated with particular treatments provides critical knowledge for both restoration scientists and land managers.

Which are the factors controlling tree seedling establishment in North Italian floodplain forests invaded by non-native tree species?

In hardwood floodplain forests of the North Italian Po Plain the non-native and light-demanding tree species Prunus serotina Ehrh. and Robinia pseudoacacia L. coexist with the native tree species Carpinus betulus L., Quercus robur L., and Ulmus minor Mill. In order to identify the factors controlling the establishment of seedlings of these species, we focused on the scale of micro-plots, which provide safe sites for tree species regeneration. We used seedling and sapling counts as the response variable. For modelling the seedling regeneration in relation to a multivariate set of 15 measured soil and stand characteristics, a hurdle negative binomial model was applied and then compared with a non-metric multidimensional scaling ordination, visualising the relationships between the regenerating species and the environmental parameters. In general, it could be shown that there are species-specific differences in the requirements for seedling regeneration between the five target species, and that the most important parameters affecting seedling establishment were the availability of potential seed sources, soil humidity, and light availability. Q.robur and C. betulus showed a wide ecological range regarding soil humidity, whereas U. minor was restricted to moister soils, and the two non-native species only occurred on dry soils. In addition, R. pseudoacacia and Q. robur regenerated very scarcely under the closed canopy inside the stands and were highly dependent on large scale disturbance events. After a disturbance, the presence of R. pseudoacacia in the canopy promoted the seedling regeneration of Q. robur. P.serotina was found to regenerate frequently in the closed forest and to persist for a long time under shade, but also needs forest gaps to establish in the canopy. We believe that P. serotina was wrongly classified as a shade-intolerant species in the past. We suggest that it is a competitive invader in a broad range of resource availability. In conclusion, with regard to the further forest development, it could be assumed that the absence of disturbance events resulting in large openings leads to a reduction in the number of P. serotina, R. pseudoacacia, and Q. robur individuals during succession. Nevertheless, disturbances on wetter soils, e.g. related to the natural river dynamics, will clearly favour the seedling regeneration of Q. robur compared to the non-native species, which are generally limited to the drier sites of the floodplain forests.

Shrub Cover Influence on Seedling Growth and Survival Following Logging of a Tropical Forest

AbstractLogging in tropical forests may create large canopy openings. These gaps provide suitable conditions for some opportunistic shrubs and herbs to take advantage of the surge in resources and rapidly colonize disturbed sites. This dense plant cover may limit forest regeneration by interfering with tree seedling establishment, growth, and survival by altering the light and nutrients available to seedlings, modifying herbivore behavior, or a number of other factors. In Kibale National Park (Uganda), old logging sites are mainly covered by dense stands of Acanthus pubescens Engl., which appear to inhibit tree regeneration. We wanted to identify the ecological processes underlying this regeneration collapse. To do so, we designed a factorial experiment to evaluate the influences of herbivory and vegetation cover on the growth and survival of tree seedlings. We compared the survival and growth of transplanted tree seedlings in A. pubescens stands and logged forests, in the presence or absence of the understory vegetation layer (logged forest) or vegetation cover (A. pubescens), and with or without herbivory. We found no evidence to support the hypothesis that herbivory is significantly higher under dense A. pubescens cover. Seedling survival was not influenced by the environment. Seedling growth, however, was positively influenced by the removal of A. pubescens, suggesting that changes in resource availability associated with the presence of A. pubescens, may be important for regeneration. Our results suggest that sustained cutting of A. pubescens cover could foster the growth of established seedlings and could lead to tree regeneration and habitat restoration.

Survivors, not invaders, control forest development following simulated hurricane

Wind disturbance profoundly shapes temperate forests but few studies have evaluated patterns and mechanisms of long-term forest dynamics following major windthrows. In 1990, we initiated a large hurricane simulation experiment in a 0.8-ha manipulation (pulldown) and 0.6-ha control area of a maturing Quercus rubra--Acer rubrum forest in New England. We toppled 276 trees in the pulldown, using a winch and cable, in the northwesterly direction of natural treefall from major hurricanes. Eighty percent of canopy trees and two-thirds of all trees > or = 5 cm dbh (diameter at breast height) suffered direct and indirect damage. We used 20 years of measurements to evaluate the trajectory and mechanisms of forest response after intense disturbance. Based on the patch size and disturbance magnitude, we expected pioneer tree and understory species to drive succession. The first decade of analyses emphasized tree seedling establishment and sprouting by damaged trees as the dominant mechanisms of forest recovery in this extensive damaged area. However, despite 80% canopy damage and 8000-m2 patch size, surviving overstory and advance regeneration controlled longer-term forest development. Residual oaks make up 42% of stand basal area after 20 years. The new cohort of trees, dominated by black birch advance regeneration, contributes 30% of stand basal area. There were shifts in understory vegetation composition and cover, but few species were gained or lost after 20 years. Stand productivity rebounded quickly (litterfall recovered to pre-disturbance levels in six years), but we predict that basal area in the pulldown will lag behind the control (which gained 6 m2/ha over 20 years) for decades to come. This controlled experiment showed that although the scale and intensity of damage were great, abundant advance regeneration, understory vegetation, and damaged trees remained, allowing the forest to resist changes in ecosystem processes and invasion by new species.

Phytometric assessment of alder seedling establishment in fen and bog: implications for forest expansion mechanisms in mire ecosystems

Aims Rapid forest expansion as a result of anthropogenic activities has been observed in many mires. However, it is unclear which environmental factors are driving this expansion because there have been no systematic investigations into mire-specific tree seedling establishment. This study investigated factors affecting the establishment of common alder (Alnus japonica) in a mire.

Hydrological Minimal Model for Savanna Fire Frequency Assessment

Savanna is the environmental state in between grassland and forest where trees and grasses coexist without one displacing the other. It is commonly accepted that limited resources, herbivores and fire are responsible for the maintenance of savanna, although, the origin and the dynamics of this ecosystem are poorly understood.A minimal model for soil moisture and biomass balance, based on the interdependence between moisture availability, biomass growth and fire regime has been formulated. Fire is modeled as a grass predator in a context where grasses are better adapted to drought and trees are superior competitor for light. The fire regime is not defined a-priori, but rather it is affected by species composition and fuel availability. The ecosystem itself self-regulates the tree-grass ratios dictating the frequency and intensity of fire and grazing, by reducing fuel availability, further affects the fire regime. In pastoral area, under water scarcity conditions fire frequency increases with grazing; under more wet condition, when tree seedling establishment is not limited by resources availability, grazing leads the system to a no- fire regime.

Restoring a seasonal wetland using woven black plastic weed mat to overcome a weed threshold

SummaryLittle information is available on the use of woven black polypropylene weed control mat in ecological restoration. At a 6.5‐ha area of fertile Vertosol soil ex‐farmland near Perth, Western Australia, concerted efforts to control weed using conventional methods such as herbicides, fire and cultivation proved ineffective. After 5 years, weeds still dominated the site, and native plant establishment was poor. Small‐scale preliminary trials of various weed suppression coverings were then undertaken, with plastic weed mat the most cost‐effective in overcoming the weed threshold, permitting native tree seedling establishment. In a larger‐scale trial of weed mat over the whole site, weeds were controlled and high levels of native plant establishment achieved, with a diverse range of understorey, midstorey and overstorey species providing 56% projected foliage cover. This ensured that completion criteria were finally satisfied. These results suggest that weed mat may be effective for weed control in large‐scale restoration where conventional methods have failed, as long as ultimate removal or decomposition and other issues are addressed.

Control of Reed Canarygrass Promotes Wetland Herb and Tree Seedling Establishment in an Upper Mississippi River Floodplain Forest

Phalaris arundinacea (reed canarygrass) is recognized as a problematic invader of North American marshes, decreasing biodiversity and persisting in the face of control efforts. Less is known about its ecology or management in forested wetlands, providing an opportunity to apply information about factors critical to an invader’s control in one wetland type to another. In a potted plant experiment and in the field, we documented strong competitive effects of reed canarygrass on the establishment and early growth of tree seedlings. In the field, we demonstrated the effectiveness of a novel restoration strategy, combining site scarification with late fall applications of pre-emergent herbicides. Treatments delayed reed canarygrass emergence the following spring, creating a window of opportunity for the early growth of native plants in the absence of competition from the grass. They also allowed for follow-up herbicide treatments during the growing season. We documented greater establishment of wetland herbs and tree seedlings in treated areas. Data from small exclosures suggest, however, that deer browsing can limit tree seedling height growth in floodplain restorations. Slower tree growth will delay canopy closure, potentially allowing reed canarygrass re-invasion. Thus, it may be necessary to protect tree seedlings from herbivory to assure forest regeneration.

Effects of wood decomposer fungi on tree seedling establishment on coarse woody debris

Although decomposer fungi have been recognized to play important roles in forest carbon and nutrient cycling as well as soil humus formation, their effects on forest dynamics, such as tree regeneration, are far less well understood than the effects of symbiotic and pathogenic fungi. In this study, I focused on tree regeneration on fallen woody debris, “nurse logs”. I examined the effects of wood decomposer fungi on species composition and population densities of tree seedlings (height <50 cm) established on these logs. In an abandoned tract of coppice forest in Honshu, Japan, a thick litter layer had accumulated on the forest floor and seedlings of the small-seeded pioneer tree species Clethra barbinervis (Ericales) were found to be preferentially established on rotting fallen logs of the Japanese red pine Pinus densiflora. C. barbinervis seedling establishment was considerably reduced on soil probably because there were impediments to colonization on the ground, such as the thick litter layer, which was less well developed on logs. In contrast, larger-seeded species such as Aphananthe aspera, Carpinus spp., Quercus serrata, and Rhus trichocarpa preferentially established on soil. Characteristics of wood decomposition by fungi varied among logs, and this variability significantly influenced C. barbinervis seedling density. Seedling density was significantly higher on brown-rotted logs than that on logs belonging to other decay types. Wood pH was lower in brown-rotted logs than that in logs belonging to other decay types and was negatively correlated with seedling density. Thus, pine coarse woody debris and the functional diversity of wood inhabiting fungi influence the establishment of diverse tree seedlings in this abandoned Japanese coppice forest.

Can overstorey retention be used to control bramble (Rubus fruticosus L. agg.) during regeneration of forests?

Summary Silvicultural systems which retain canopy cover during the regeneration phase have become an increasingly important form of management, but their effectiveness in controlling weed species has not been extensively studied. The development of bramble, which is a widespread competitive weed species, was observed within a c. 35-year-old Corsican pine stand thinned to remove 10, 20, 40 and 80 per cent of basal area. Cover, height and numbers of inflorescences and berries were recorded in each of the 3 years following thinning and were generally ranked according to intensity of thinning, but there were no significant differences between treatments. Shoot length, estimated using a grid-intersection method, was significantly lower in the 10 per cent compared with the 40 and 80 per cent thinning treatments. The initial length of bramble shoot present, and basal area and number of trees remaining could be used in various combinations to predict cover, height and shoot length. Although the bramble thicket was generally less well developed in the less-intense thinning treatments, these did not appear to enhance the establishment of trees. Seedlings grew best in the 80 per cent treatment and overall their mean heights were generally lower than that of bramble. Retention of overstorey cover in order to suppress bramble growth and promote tree seedling establishment during forest regeneration may not succeed.

Effects of deer abundance on broad-leaf tree seedling establishment in the understory of Abies sachalinensis plantations

Browsing by sika deer (Cervus nippon) has significant negative effects on regeneration in many forests in Japan; however, the effects of browsing on regeneration processes have not been determined quantitatively. Our study was conducted in Abies sachalinensis plantations in seven tracts with differences in deer abundance on Hokkaido, northern Japan, to identify indicators for the effects of deer on the regeneration of broad-leaf species from observing seedlings. Five 5 × 20-m plots were located within each tract, and the densities of seedlings 30–200 cm tall and percentages of browsed seedlings were determined. We used sightings per unit effort (SPUE) by hunters and spotlight survey counts (SLCs) as indices of deer abundance for each tract. Seedling density was negatively correlated with deer abundance and coverage of dwarf bamboo, and basal areas of overstory trees also affected number of seedlings. Percentage of browsed seedlings was positively correlated with deer abundance, and it was affected by deer preferences among seedling species. However, the percentage of browsed seedlings was more clearly related to deer abundance than seedling density. There were few seedlings of tree species ≥100 cm tall in tracts with the highest deer abundance. Based on these results, deer abundances of SPUE >6 sightings per hunter-day or SLC >15 animals per 10 km are likely to prevent regeneration of broad-leaf species. The percentage of browsed seedlings and density and browsing damage on tree seedlings ≥100 cm tall are useful indicators of the effects of deer.

Salvage Logging Versus the Use of Burnt Wood as a Nurse Object to Promote Post‐Fire Tree Seedling Establishment

Intense debate surrounds the effects of post‐fire salvage logging (SL) versus nonintervention policies on forest regeneration, but scant support is available from experimental studies. We analyze the effect of three post‐fire management treatments on the recruitment of a serotinous pine (Pinus pinaster) at a Mediterranean mountain. Treatments were applied 7 months after the fire and differ in the degree of intervention, ranging from “no intervention” (NI, all trees left standing) to “partial cut plus lopping” (PCL, felling most of the trees, cutting the main branches, and leaving all the biomass in situ without mastication), and “SL” (felling and piling the logs, and masticating the woody debris). Seedling survival after 3 years was the highest in PCL (47.3% versus 38.7% in SL). This was associated with the amelioration of microclimatic conditions under the scattered branches, which reduced radiation and soil temperature while increasing soil moisture. Seedling density after 2 years was approximately 5.5 times higher in PCL than in SL, as in SL a large fraction of seedlings was lost as a consequence of mechanized mastication. The NI treatment showed the lowest seedling survival (17.3%). Nevertheless, seedling density was similar to SL. Seedling growth scarcely differed among treatments. Our results show that branches left onsite acted as nurse objects that improved key microclimatic conditions for seedling recruitment. This creates a facilitative interaction ideal for seedling establishment in moisture‐deficient ecosystems, as it provides the benefit of a shading overstory but without underground competition.

Woody plant seedling distribution under invasive Lantana camara thickets in a dry-forest plot in Mudumalai, southern India

Abstract:Lantana camara, a shrub of Central and South American origin, has become invasive across dry forests worldwide. The effect of the thicket-forming habit of L. camara as a dispersal and recruitment barrier in a community of native woody seedlings was examined in a 50-ha permanent plot located in the seasonally dry forest of Mudumalai, southern India. Sixty 100-m2 plots were enumerated for native woody seedlings between 10–100 cm in height. Of these, 30 plots had no L. camara thickets, while the other 30 had dense thickets. The frequency of occurrence and abundance of seedlings were modelled as a function of dispersal mode (mammal, bird or mechanical) and affinities to forest habitats (dry forest, moist forest or ubiquitous) as well as presence or absence of dense L. camara thickets. Furthermore, frequency of occurrence and abundance of individual species were also compared between thickets and no L. camara. At the community level, L. camara density, dispersal mode and forest habitat affinities of species determined both frequency of occurrence and abundance of seedlings, with the abundance of dry-forest mammal-dispersed species and ubiquitous mechanically dispersed species being significantly lower under L. camara thickets. Phyllanthus emblica and Kydia calycina were found to be significantly less abundant under L. camara, whereas most other species were not affected by the presence of thickets. It was inferred that, by affecting the establishment of native tree seedlings, L. camara thickets could eventually alter the community composition of such forests.

アズマネザサ、リター、動物による食害が耕作放棄地における自生木本の定着に与える影響

アズマネザサ、リター、動物による食害が耕作放棄地における自生木本の定着に与える影響

Influence of ammonium and nitrate supply on growth, nitrate reductase activity and N-use efficiency in a natural hybrid pine and its parents

Aims Selection of tree species with a high capacity to assimilate N and efficiently utilize N resources would facilitate the success of initial tree seedling establishment in infertile soils. The preference for N forms was tested using three pine species (Pinus densata, Pinus tabuliformis and Pinus yunnanensis). Pinus densata is a natural diploid hybrid between P. tabuliformis and P. yunnanensis. Methods Seedlings of three pine species were supplied with nitrate-N, ammonium-N (at two different pH regimes) or combined ammonium and nitrate as a nitrogen source in perlite culture in a controlled environment. Important Findings Seedlings of P. densata had higher total biomass and net photosynthesis when supplied with nitrate-N and ammonium nitrate than with ammonium-N. In parental species, total biomass and net photosynthesis for P. yunnanensis seedlings was higher in ammonium-N than in nitrate-N, whereas the other parental species P. tabuliformis had the highest total biomass among species for all treatments except ammonium with CaCO3. Most morphological traits in P. densata seedlings were intermediate between its two parental species. However, N-use efficiency and photosynthetic N-use efficiency of P. densata significantly exceeded both parents when supplied with nitrate-N and ammonium nitrate. The results suggested that the diploid hybrid tree species P. densata has a preference for nitrate and is not well adapted to ammonium-N as a sole nitrogen source regardless of the growth medium pH. Based on changes in environmental conditions, such as predicted future temperature increases in high altitude areas associated with climate change, P. densata is likely to be increasingly competitive and have wide adaptation in high altitude regions.