Establishment Of New Seedlings Research Articles

Reproductive traits in four spontaneous Pappophorum vaginatum populations in arid Argentina

Arid zones, where native rangelands are common, are essentials for millions of people livelihood. These areas support 50% of the world's livestock and are where 44% of the world's food is grown. In rangelands of Central Argentina, Pappophorum vaginatum is basically the unique, warm-season perennial grass species palatable to grazing livestock. Our major objective was to determine variability in reproductive characteristics among four spontaneous, overgrazed populations (i.e., P1, P2, P3, P4) of that species to identify promissory materials for domestication. Studies were conducted during three consecutive growing seasons within the southwestern part of the Phytogeographical Province of the Monte, in southwestern Buenos Aires, Argentina. Measured reproductive characteristics were related to flowering initiation, seed production and natural reseeding potential. Significant differences were found for flowering initiation and natural reseeding potential, but not for viable anthecia per plant among the four populations of P. vaginatum. This species fructified from the beginning to the end of the studied growing seasons with a great anthecia production per plant. The light weight of these anthecia and their awns would favor a great wind dispersal and most likely the establishment of new seedlings of P. vaginatum. This suggests that sexual reproduction might have a relatively greater importance than asexual reproduction (i.e., tillering) in the persistence of the overgrazed P. vaginatum in the plant communities of the studied region. Selection of plant materials with a late flowering initiation will allow to extend the forage production of a better quality. The variability among and within populations found on this study supports the idea that would be promissory to start selection programs to obtain improved germplasm to reincorporate to grasslands of the south of the Phytogeographical Region of the Monte (Argentina) not only to increase livestock production but also to recover and maintain biodiversity.

Andropogon gayanus Kunth invasion in the Cerrado: from seed production to seedling establishment along roadsides

Andropogon gayanus Kunth is a highly invasive grass, but the importance of the seed reproduction for its spread has not been evaluated in Cerrado. This study measured the seed reproduction of A. gayanus by assessing parameters from seed production to seed establishment. The study used replicates in three natural reserves located near Brasilia. In each area, sites adjacent to roads were selected. For seed production, panicles were covered with a fine-mesh cloth to collect the seeds. Seeds were counted and analyzed for viability. After seed dispersal, seeds on the soil surface and 3-cm-deep soil samples were collected. Seeds were counted and germinated, and the soil samples were kept in a greenhouse, to estimate the density of the germinable soil seed bank. For emergence depth, seeds were sown at the surface, 1, 2 or 3 cm depth. For seed longevity, bags of seeds were buried in the field and analyzed for viability monthly. Each inflorescence produced an average of 604 seeds (22% viability). Surface seed density was highest at the road edge (> 5000 seeds/m2), with average germination of 29%. Mean soil seed bank reached 232 seedlings/m2 at the roadside. Seeds were able to emerge from all burying depths. The viability of buried seeds decreased to 2% after 1 year. Only seedlings by the border were able to establish. Data show a massive investment in seeds, with low recruitment. We recommend that A. gayanus be controlled by impairing its dispersal, to prevent the establishment of new seedlings.

Interaction between Seed Detectability and Seed Preference Affects Harvest Rates of Granivorous Rodents

Granivorous rodents commonly exhibit preferences for seeds of particular plant species. However, among buried seeds that are available, rodents may find that alternate, less desirable seeds are more easily located by olfaction than preferred seeds. Seeds of Indian ricegrass (Achnatherum hymenoides) are a highly preferred food resource for seed-caching desert heteromyid rodents. We tested relative abilities of heteromyids to locate buried caches of Indian ricegrass seeds versus seeds of another plant species (cheatgrass, Bromus tectorum) that are common in heteromyid diets at a western Nevada field site. Rodents located more cheatgrass than Indian ricegrass seed caches in the field when seeds were unaltered. When ground, however, detectability of preferred Indian ricegrass seeds increased, presumably due to release of volatile compounds inside seeds, and more ground Indian ricegrass seed caches were found and removed compared with ground cheatgrass caches. Grinding cheatgrass seeds did not affect harvest rates of cheatgrass caches. Results of a laboratory cache removal experiment using 2 heteromyid species, Merriam's kangaroo rats (Dipodomys merriami) and long-tailed pocket mice (Chaetodipus formosus), mirrored field cache removal results. Dispersal of Indian ricegrass seeds and establishment of new seedlings occurs largely through emergence of seedlings from heteromyid scatterhoard caches. Our results suggest that Indian ricegrass seeds may have been selected for reduced olfactory detectability to minimize the probability that they are recovered by rodents for later consumption once they have been cached.

The Effect of Logging and Strip Cutting on Forest Floor Light Condition and Following Change

We monitored changes in light conditions at a primary forest and two managed forest sites (one with line planting) after reduced-impact logging in Central Kalimantan, Indonesia. We also assessed the effect of the light conditions on seedlings in the planting lines. Hemispherical photographs were taken over a period of 31 months in three 50 × 50-m quadrats at each site and in three 100-m transects along the planting lines. The location of each photo was categorized according to the corresponding type of disturbance, including skid trails, logging gaps, and planting lines. Following logging, the level of canopy openness (CO) increased at both managed forest sites and did not differ significantly between the two. However, CO was greater in skid trails and logging gaps than in planting lines. After 31 months, the mean level of CO at each managed site had decreased significantly due to the establishment of new seedlings. Correlations between changes in CO and the growth of planted seedlings suggested that growth was inhibited by the invasion of the new species. However, the level of CO along the planting lines was greater than that at other disturbed locations. A high level of CO promoted invasion by new species that colonized the space. Line planting may influence forest dynamics and maintain a high level of CO.

Life and death of Picea abies after bark-beetle outbreak: ecological processes driving seedling recruitment.

The severity and spatial extent of bark-beetle outbreaks substantially increased in recent decades worldwide. The ongoing controversy about natural forest recovery after these outbreaks highlights the need for individual-based long-term studies, which disentangle processes driving forest regeneration. However, such studies have been lacking. To fill this gap, we followed the fates of 2,552 individual seedlings for 12years after a large-scale bark-beetle outbreak that caused complete canopy dieback in mountain Norway spruce (Picea abies) forests in southeast Germany. We explore the contribution of advance, disturbance-related, and post-disturbance regeneration to forest recovery. Most seedlings originated directly within the three-year dieback of canopy trees induced by bark-beetle outbreak. After complete canopy dieback, the establishment of new seedlings was minimal. Surprisingly, advance regeneration formed only a minor part of all regeneration. However, because it had the highest survival rate, its importance increased over time. The most important factor influencing the survival of seedlings after disturbance was their height. Survival was further modified by microsite: seedlings established on dead wood survived best, whereas almost all seedlings surrounded by graminoids died. For 5cm tall seedlings, annual mortality ranged from 20 to 50% according to the rooting microsite. However, for seedlings taller than 50cm, annual mortality was below 5% at all microsites. While microsite modified seedling mortality, it did not affect seedling height growth. A model of regeneration dynamics based on short-term observations accurately predicts regeneration height growth, but substantially underestimates mortality rate, thus predicting more surviving seedlings than were observed. We found that P.abies forests were able to regenerate naturally even after severe bark-beetle outbreaks owing to advance and particularly disturbance-related regeneration. This, together with microsite-specific mortality, yields structurally and spatially diverse forests. Our study thus highlights the so far unrecognized importance of disturbance-related regeneration for stand recovery after bark-beetle outbreaks.

Regeneration dynamics and resilience of unmanaged mountain forests in the Northern Limestone Alps following bark beetle-induced spruce dieback

Mountain forests provide many important ecosystem services including protection against avalanche and rock fall. These services often depend on a continuity of forest cover and therefore on ecological stability—resistance and resilience to disturbance. Natural regeneration following large-scale disturbance is an important component of forest resilience but in the mountain forests of the Alps is not well understood. This restricts management decision making, particularly in the face of an increased threat to the currently dominant Norway spruce from the bark beetle (Ips typographus). In light of this, we analyzed bark beetle infestation patterns, forest structure, selected tree regeneration characteristics and species composition on 96 study plots on a chronosequence of bark beetle-induced natural forest succession in unmanaged mountain forest ecosystems in southeastern Germany. The most advanced plots were twenty years on from the bark beetle-induced dieback of mature Norway spruce, and the majority were already quite densely stocked. The regeneration was clustered and was dominated by sycamore maple and Norway spruce. Most notably, the proportion of advance regeneration was negligible with the vast majority of the seedlings having germinated after the disturbance event. The findings suggest that these forests are naturally resilient in terms of regeneration if high browsing intensities do not prohibit the establishment of new seedlings. The bark beetle outbreaks appear to have generated an acceleration of development away from human influenced pure Norway spruce forests toward a more natural species composition. Nevertheless, Norway spruce will remain the dominant species for at least the next generation. These findings are important for managers intending to uphold protective forest functions. The integration of naturally evolving gaps as elements which diversify environmental conditions on the forest stand level as well as on the landscape scale is recommended for close-to-nature forest management.

Seedling survival and establishment in small canopy openings in drained spruce mires in Northern Finland

A large proportion of drained spruce mire stands is currently approaching regeneration maturity in Finland. Traditional regeneration methods with effective site preparation and planting generally result in satisfactory seedling stands also in spruce mires. However, natural regeneration methods may be more appropriate in protecting watercourses and minimizing regeneration costs. We studied the survival of advance growth and establishment of new seedlings in small canopy openings that were cut at three different diameters in two experimental drained spruce mire stands in Northern Finland (Tervola and Oulu) in 2004. The number of seedlings was repeatedly surveyed from five small circular plots (one 10 m and four 5 m plots in size) located within the opening. Advance growth which survived the cutting and new seedlings were separated in the surveys. The density of advance growth was on average 9000 ha after cutting, and it decreased by 30% during the five-year monitoring period (2006–2010) due to natural mortality. The number of new seedlings increased rapidly within the three years after cutting the openings. In 2010, 11 000–26 000 new seedlings ha in Tervola and 12 000–16 000 ha in Oulu on average were observed. The size of the opening had no clear effect on the regeneration result. The proportion of birch of the new seedlings increased with time and opening size in Tervola. The results show that Norway spruce regenerates naturally in small canopy openings cut in mature drained spruce mire stands.22–1–1–1

Linking frugivore activity to early recruitment of a bird dispersed tree, Eugenia umbelliflora (Myrtaceae) in the Atlantic rainforest

AbstractSeed dispersal by animals is a complex process involving several distinct stages: fruit removal by frugivores, seed delivery in different microhabitats, seed germination, seedling establishment, and adult recruitment. Nevertheless, studies conducted until now have provided scarce information concerning the sequence of stages in a plant's life cycle in its entirety. The main objective of this study was to evaluate the immediate consequences of frugivore activity for Eugenia umbelliflora (Myrtaceae) early recruitment by measuring the relative importance of each fruit‐eating bird species on the establishment of new seedlings in scrub and low restinga vegetation in the Atlantic rainforest, Brazil. We conducted focal tree observations on E. umbelliflora trees recording birds' feeding behaviour and post‐feeding movements. We also recorded the fate of dispersed seeds in scrub and low restinga vegetation. We recorded 17 bird species interacting with fruits in 55 h of observation. Only 30% of the handled fruits were successfully removed. From 108 post flight movements of exit from the fruiting trees, 30.6% were to scrub and 69.4% to low restinga forest. Proportion of seed germination was higher in low restinga than in the scrub vegetation. Incorporating the probabilities of seeds' removal, deposition, and germination in both sites, we found that the relative importance of each frugivorous bird as seed dispersers varies largely among species. Turdus amaurochalinus and Turdus rufiventris were the best dispersers, together representing almost 12% probability of seed germination following removal. Our results show the importance of assessing the overall consequence of seed dispersal within the framework of disperser effectiveness, providing a more comprehensive and realistic evaluation of the relative importance of different seed dispersers on plant population dynamics.

Effects of salinity and sand burial on germination and establishment of Blutaparon portulacoides (St.Hil.) Mears (Amaranthaceae) on backshore of southern Brazil

The effect of different salinities on the germination was tested during 40 days in laboratory, using six concentrations of NaCl (0, 45, 80, 130, 170 and 215 mM NaCl) and three concentrations of seawater (25, 30 and 35‰). In addition, the survival and growth of seedlings were tested in five constant salinity regimes (0, 45, 80, 130 and 170 mM NaCl) as well as in five regimes of simulating seawater overwash. The effect of sand burial on the germination was tested during 40 days in the laboratory, using five different depth (0, 1, 2, 4 and 6 cm). Additionally, 100 seedlings (2-weeks old) were planted along the backshore and their survival and sand deposition observed at 5-day intervals, during 30 days. The results showed that total germination declines with increased salinity concentration, the same was observed for lag time. The effects of salinity on seedling growth showed that height and distance between nodes were a more sensitive indicator of salinity stress, showing a gradual reduction in growth with increase of NaCl. Seedlings showed a gradual decrease in survival and dry biomass in relation to the frequency of flooding with seawater. The germination of B. portulacoides seeds decresed significantly at depths greater than 2 cm, and was inhibited at 6 cm. Seedlings showed high mortality at even low sand burial. The results obtained in laboratory on germination and growth of B. portulacoides in salinities above those normal in its natural habitat could explain why it is a dominant species at the backshore. However, sand deposition is a major environmental factor that determines the establishment of new seedlings. Key words: salt tolerance, seedling growth, dune species, Atlantic coast.

Creeping Bentgrass Seedling Tolerance to Herbicides and Paclobutrazol

The tolerance of creeping bentgrass (Agrostis stolonifera L.) seedlings to many herbicides has not been evaluated. Three field studies were conducted between fall and spring from 1998 to 2002 to assess creeping bentgrass seedling tolerance to five herbicides and paclobutrazol. The primary objectives of this investigation were to assess bentgrass tolerance to these chemicals when applied at various timings following seedling emergence, and establishment of new seedlings as influenced by potential soil residues in the spring following a fall application of the chemicals. Treatments were applied 2, 4, or 7 weeks after either `Crenshaw' or `L-93' creeping bentgrass seedlings had emerged. Siduron (6.7 and 9.0 kg·ha-1) and bensulide (8.4 kg·ha-1) were noninjurious when applied two weeks after seedling emergence (2 WASE). Bensulide (14 kg·ha-1), ethofumesate (0.84 kg·ha-1), prodiamine (0.36 kg·ha-1) and paclobutrazol (0.14 kg·ha-1) were too injurious to apply 2 WASE, but they were generally safe to apply at 4 WASE. Chlorsulfuron (0.14 kg·ha-1) was extremely phytotoxic to seedlings when applied 2 WASE. Plots were treated with glyphosate and overseeded the following spring. The overwintering soil residuals of prodiamine and bensulide (14.0 kg·ha-1) unacceptably reduced spring establishment. All other herbicides and paclobutrazol had little or no adverse residual effects on spring establishment. Chemical names used: N-(phosphonomethyl)gycline (glyphosate); (±)-(R*,R*)-beta-[(4-chlorophenyl)methyl]-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol); 2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate (ethofumesate); S-(0,0-diisopropyl phosphorodithioate) ester of N-(2-mercaptoethyl) benzenesulfonamide (bensulide); [1-(2-methylcyclohexyl)-3-phenylurea] (siduron); N3,N3-di-n-propyl-2,4-dinitro-6-(trifluoromethyl)-m-phenylenediamine (prodiamine); 2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl] benzenesulfonamide (chlorsulfuron).

An approach to tree thinning to structure southern African savannas for long-term restoration from bush encroachment

Due to bush encroachment the grazing capacity of large areas of the southern African savanna has declined, often to such an extent that many previously economic livestock properties are now no longer economically viable. Attempts at restoring encroached areas by the removal of some or all of the woody plants will normally result in an increase of grass production and thus also the grazing capacity. However, the results of woody plant removal may differ between vegetation types, with the outcome determined by both negative and positive responses to tree removal. The rapid establishment of tree seedlings after the removal of some or all of the mature woody plants may reduce the effective time span of restoration measures. In many cases the resultant re-establishment of new woody seedlings may in time develop into a state that is worse than the original state. This paper is an attempt to summarize existing knowledge on the importance of woody plants in savanna and explore measures, based on ecosystem dynamics, which can be utilized to restore encroached areas more successfully. It is hypothesized that a more stable environment can be created by maintaining or restoring savanna structure (large trees). In a structured savanna, large trees are able to suppress the establishment of new seedlings, while maintaining the other benefits of woody plants like soil enrichment and the provision of food to browsing herbivore species. Effective restoration of encroached areas should not be considered a once-off event, but rather a long-term commitment.

Case Study: 36 Years of Dwarf Mistletoe in a Regenerating Black Spruce Stand in Northern Minnesota

Abstract Current practice in dwarf mistletoe infested black spruce stands calls for eradication of all trees taller than 5 ft. In a stand harvested 36 years ago, fewer than 1 tree per acre taller than 3 ft remained. Since that time, Arceuthobium pusillum has survived and spread to new areas of the stand. From 16 infected trees per acre, the population has increased to 173 infected trees per acre in 1998. As establishment of new seedlings declines, the proportion of infected trees will increase greatly. The projected spread of dwarf mistletoe, and the resulting mortality of black spruce during the remainder of the rotation will cause unacceptable yield losses. Eradication of all black spruce after harvesting is necessary to prevent serious losses from dwarf mistletoe infestation in the new stand. North. J. Appl. For. 21(3):150–153.

Species composition and dynamics in two hardwood stands in Vermont: a disturbance history

Stand composition and structure utilizing stem analysis was studied in two hardwood stands in Vermont. In a mixed hardwood stand with some white pine and hemlock, a major entry of new trees in the main canopy seems associated with harvesting coincident with land exchange. More recent partial cuttings have promoted establishment of new seedlings or development of suppressed advanced-growth shade-tolerant beech, ( Fagus grandifolia, Ehrh.), hophornbeam ( Ostrya virginiana, (Mill) K. Koch), and striped maple ( Acer pensylvanicum, L.). Very few sugar maple and red oak seedlings and saplings are present. In a northern hardwood stand some red spruce ( Picea rubens, Sarg.), that were 240 to 306 years old, became established before any known harvest, and exhibited release following harvests of the mid-1800s. This major harvest, coupled with the differential growth between spruce and hardwoods, and seed/seedling availability, resulted in a major change in stand composition. Trees now in the main canopy of sampled stands appear to have either been released or newly established following various harvests. Harvests have been of such frequency that natural disturbances seem insignificant. Many of the competitive understory species have become abundant following harvests of the 1960s and 1980s and may have been present as advanced growth and responded to the release. Following the harvest of 1981–1982, abundant yellow birch became established on skid trails. Elsewhere in the stand, yellow birch seedlings and saplings are only in great abundance in areas that were possibly sizable gaps following earlier harvesting. The dynamics of tree entry and growth in gaps of small or large size probably occur in a similar way in many other stands of the region. Though the sampling of this study is limited, there is no suggestion of continuous tree establishment at any particular location, the new age classes seem associated with either a gap or stand replacing disturbance attributed to harvesting.

Soil properties and seedling establishment in soils from monodominant and high‐diversity stands of the tropical deciduous forests of México

Abstract. The hypothesis that soils from mature monodominant forests are unfavourable for establishment of tree species other than the dominant was tested for a lowland tropical deciduous forest with stands dominated by Celaenodendron mexicanum Standl. (CS). This species of Euphorbiaceae occurs almost exclusively in monodominant stands in which recruitment of other species appears to be poor. Soil properties were examined and experiments were conducted on germination and establishment of Celaenodendron mexicanum and three other species common in adjacent high‐diversity mixed stands (MS): Recchia mexicana Moc. & Sessé, Caesalpinia eriostachys Benth., and Cordia alliodora (Ruiz & Pav.) Oken. Soil moisture regimes are affected by topographic position in the study area, but Celaenodendron mexicanum was found occupying hillsides as well as flatlands, and slope gradients of its stands were typical of the region. The microsites occupied in relation to soil moisture and light availability also appear to be undistinctive. There were no significant differences between stand types in any soil property (pH, O.C., total N, total P, avail. P, K, Ca, Mg, Na, Mn, Fe, Cu, Zn concentrations). A stand of intermediate dominance of Celaenodendron (ICS) did not differ from its adjacent mixed stand (MS) in soil texture or most of the nutrients tested; however, seasonally restricted differences in the contents of Fe and Mn (ICS<MS) were detected. In fact, the contents of most nutrients in all the stands changed significantly between seasons: mostly, they were lower in the wet season.Germination percentages and seedling survival to 4 months did not differ between CS and MS soils in greenhouse tests, and in field tests Caesalpinia eriostachys established in both stand types.The results suggest that the distinction between monodominance and high diversity is not maintained by some simple physiological restriction on the establishment of new seedlings.

Évolution de la régénération après la coupe de peuplements récoltés selon différents procédés d'exploitation

Between 1982 and 1984, 289 sample plots were established on cutovers distributed across the mixed and the boreal forest zones of Québec. Regeneration surveys before and after clearcutting were used to determine the proportion of regeneration destroyed by four different harvesting systems. Moreover, information on the evolution of the regeneration over the medium term was gathered from surveys realized five and ten years following logging. For all stands combined, harvesting resulted in a reduction of 25 to 40% of the stocking of the regeneration. The lowest decrease in stocking was produced by a feller-forwarder that was more efficient to protect regeneration shorter than 50 cm as compared to harvesting systems using cable skidders. Differences between harvesting systems were no longer apparent after the first five-year-period following logging because establishment of new seedlings was observed in most of the sampled cutovers. The ability of balsam fir to establish under a canopy generally caused an increase of its proportion in the new stands as compared to the original stands. The proportion of hardwood species also tended to increase in comparison to the original stand in such a way that some conifer stands would evolve toward mixed stands if no change in stand composition occurred after the first ten-year period following logging. Natural regeneration of jack pine stands after harvesting seems difficult to obtain since these stands have scarce advance regeneration that is partially destroyed during logging operations. Plantation, fill plantation or seeding could be applied in these stands but harvesting methods providing protection for regeneration should be used in the other stands in order to protect advance regeneration and particularly tall individuals. Key words: clearcutting, advance regeneration, harvesting system, cable skidders, feller-forwarder

POLLINATION BIOLOGY, SEED PRODUCTION, AND POPULATION STRUCTURE IN QUEEN‐OF‐THE‐PRAIRIE, FILIPENDULA RUBRA (ROSACEAE) AT BOTKIN FEN, MISSOURI

Queen‐of‐the‐prairie, Filipendula rubra (Rosaceae), is a perennial, rhizomatous herb restricted to calcareous fens, spring seeps, and wet prairies, and is distributed in the northcentral United States from Iowa to New York. Because of the scarcity of adequate habitat, F. rubra is a rare and endangered species in several states. At Botkin Fen and other fens in Missouri, F. rubra possesses limited sexual reproduction. A study was conducted to determine causal mechanisms of its limited seed production that may be barriers to establishing this rare and endangered species in other fens in Missouri. A genetic‐ecological hypothesis was supported. F. rubra was found to be self‐incompatible. At Botkin Fen, most inflorescences produced very few seeds because most (85.4%) belonged to a single clone. Pollinators (Lassioglossum sp.) had a high probability of transporting pollen with the same self‐incompatibility alleles. A few genetically different clones did produce significant quantities of seed. However, this seed, with its significant pool of genetic variability, was not recruited into the population. Apparently, competition from the dense sedges and grasses prevented the establishment of new seedlings.