Polylepis australis’ regeneration niche in relation to seed dispersal,site characteristics and livestock density

Establishment of Polylepis forests endemic to the mountains of South America may be affected by seed dispersal, site characteristics and livestock density. Polylepis australis (“tabaquillo”) grows in the high mountains of central Argentina, where we set up 76 square study plots of 900 m². To determine dispersal distance, we distributed 6 seed traps per plot in and around 20 plots. To determine the best site characteristics and livestock stoking rates, at two river basins differing in historic stocking rates, we analyzed the presence of seedlings in 56 plots and recorded topography, vegetation types and indicators of livestock activity. We also measured microsite characteristics in a sample of 32 comparable pairs of 1 m² quadrats, with and without seedlings. Maximum recorded dispersal distance of P. australis seeds was 6 m, and seedlings were found no more than 10 m from seed trees. The numbers of seedlings and seed trees were 3.5 and 4 times higher, respectively, in the basin with less livestock. At the 900 m² plot scale, a Poisson regression indicated a positive relationship between seedling number and P. australis canopy cover. At the quadrat scale (1 m²), seedlings were found in quadrats with significantly lower evidence of soil erosion than comparison quadrats without seedlings. We conclude that the main limitations to recruitment are short seed dispersal distances, lack of seed trees and extreme soil erosion. Management should therefore aim at preserving seed trees and reducing livestock density to prevent erosion.     

Petroleum flotation technique upgrades the germinability of <Emphasis Type="Italic">Casuarina equisetifolia</Emphasis> seed lots

The germination of Casuarina equisetifolia Forst seed lots is low (40–50%) even when freshly collected. This study aimed at upgrading the germination performance by removing non-germinable seeds using petroleum flotation technique. Seeds collected from 19 individual trees in seedling seed orchards in India were assessed using X-ray to determine the proportion of different seed lot fractions. The feasibility of petroleum ether as a separation medium was tested. Morphological characters of floating and sunken seeds were further studied using image analysis technique to examine their effects on the separation efficiency. The X-ray analysis revealed a large quantity of shrivelled, empty and insect-damaged seeds, altogether accounting 50%, which were the causes of low percentage germination of un-graded seed lots (48%). Petroleum flotation resulted in 90% germination in the sunken fraction and 4% in the floating fraction. The separation was distinct for most seed lots, except few seed lots that had relatively low germination in the sunken fractions and more than 10% germination in the floating fractions. As a whole, petroleum flotation appears to be a feasible technique to upgrade the germination of C. equisetifolia seed lots, and its efficacy is influenced by wing surface area, seed density and wing quotient of filled and empty seeds.     

Organic substance metabolism during seed germination ofPinus bungeana

The metabolism of fats, proteins and carbohydrates and change of enzyme of seeds ofpinus bungeana during the germination were conducted by the methods of gas-liquid chromatography, flow injection, colorimetric analysis of spectrophotometer, to provide theoretical basis for seeds dormancy, germination and storage of seeds of forest tree. The results indicate that (1) carbohydrates were first utilized during germination of seed ofpinus bungeana; (2) stored substances in seeds began to decompose quickly after radicale broke through seed coats; (3) the activity of enzymes in the seeds does not always coincides with the increase or decrease in quantity of its responsible substance during germination of the seed. Changes in stored substance relate to metabalism of other metabolism of other materials and the use of hydrolysates.     

Culling phenotypically inferior trees in seed production area enhances seed and seedling quality of <Emphasis Type="Italic">Acacia auriculiformis</Emphasis>

Improvement in seed and seedling quality of Acacia auriculiformis after culling phenotypically inferior trees was studied in a 6-year old seed production area (SPA). A 5-ha plantation was identified, of which 2.3 ha was converted into SPA. The initial stocking, 1 612 trees·ha⁻¹, was thinned down to 982 trees·ha⁻¹ based on growth characteristics. The following fruiting season, seeds were collected from 10 randomly selected trees in culled and non-culled stands, and seed physical characters, germination and seedling traits were assessed. Seed weight, seed thickness and percentage germination increased by 32.1%, 4.43% and 22.37%, respectively in the culled stand compared to the non-culled stand. Culling also increased the speed of germination, seedling dry weight and seedling vigor index. Heritability values were high for seed weight (0.974) and seed thickness (0.948) while medium values were observed for percentage germination (0.577) and total dry weight (0.534). Predicted genetic gain was 11.13% and 11.22% for seed weight and percentage germination, respectively. The actual gain was 32.1, 51.9 and 22.9% for seed weight, percentage germination and total dry matter, respectively. In conclusion, SPAs established by culling inferior trees could serve as sources of good quality seeds for reforestation programs until genetically improved seeds are made available.     

Seed production in Polylepis australis (Rosaceae) as influenced by tree size, livestock and interannual climate variations in the mountains of central Argentina

The expansion of tree species within a grassland-woodland matrix relies heavily on an abundant seed crop, which may be affected by many factors; among these, browsing by livestock has gone largely ignored. Here we explore how seed production is affected by tree size, grazing by large domestic herbivores and interannual climate fluctuations in a small-sized tree (Polylepis australis, Rosaceae), which dominates the remnant forests in the high mountains of central Argentina. Seed number and seed mass per tree were quantified in 100 different-sized trees located in areas with and without livestock. Using seed traps we also determined seed rain variation in 15 plots between 2005 and 2008. The estimated number of seeds per tree ranged from 0 to 224,000 and increased with tree height (power relation); for trees smaller than 354 cm in height, seed production was lower in areas with livestock and higher in areas without livestock. Mass per seed increased with tree height, with no significant livestock effect. The largest seed rain was recorded in 2008, probably due to growth of seed trees and not in response to climate. To promote seed production and forest expansion, livestock should be excluded from areas with small trees, such as forest edges.     

Optimal germination condition by sulfuric acid pretreatment to improve seed germination of Sabina vulgaris Ant.

Understanding the germination traits of plants is important not only for understanding natural regeneration processes but also for developing seedling production techniques for planting. Sabina vulgaris Ant. is a common species used for reforestation in semi-arid areas of the Mu-Us Desert, in Inner Mongolia, China, but its extremely low germination rate, both in situ and in vivo, is a bottleneck for seedling production. Sulfuric acid pretreatment was applied to improve germination, and the germination rate was compared for different soaking time (10, 30, 60, 90, and 120 min), different temperatures (10, 15, 20, 30, and 35°C) and under different lighting conditions (dark and light). Sulfuric acid treatment gave a high germination rate, reaching 60% at 30 days after sowing. However, the non-treated seeds produced no germination. The optimal treatment time in sulfuric acid was 120 min. Germination after sulfuric acid treatment increased at incubation temperatures from 10 to 30°C, but decreased at 35°C. Incubation at 25–30°C gave maximum germination of more than 50%. Light treatment had little effect on germination. Pretreatment with sulfuric acid improved water absorption by the embryo by creating cracks and cavities in the seed coat tissue. These results indicated that S. vulgaris seeds have physical dormancy caused by their hard seed coats, which prevents absorption of water into the embryo. A combination of pretreatment with sulfuric acid and incubation at 25–30°C was most effective in improving the germination of S. vulgaris seeds.     

Effects of tallowtree seed coat on seed germination

We measured physiological parameters including water uptake, in-vitro embryo germination ratio, and seed coat structure observed by scanning electron microscopy (SEM) to explore the influence of seed coat on the germination of seeds of tallow tree (Sapium sebiferum (Linn) Roxb.). Tallow tree seeds had good water permeability. We found that germination of cabbage seeds was inhibited when cabbage seeds were soaked in extracted solutions from tallow tree seed coat. Seed coat structure at the side of the radicle appeared to be a barrier to seed germination. We tested methods to break tallow tree seed dormancy. Dormancy of tallow tree seeds was overcome by soaking the seeds in 500 mg·L-1 or 1000 mg·L-1 GA3, followed by 100 days of cold stratification.     

The soil seed bank of the threatened plant <Emphasis Type="Italic">Magnolia stellata</Emphasis> is subordinate to the emergence of current-year seedlings

We studied seed bank formation of the threatened star magnolia, Magnolia stellata, to examine the early stage of regeneration. Forty-five seedling plots (2 × 2 m), each including a soil-sampling quadrat (40 × 40 cm), were established randomly under or around the crowns of mature M. stellata trees. Seeds of M. stellata were collected from each quadrat to a depth of 5 cm. Only four seeds of M. stellata were found (0.56 seeds/m²) and all were located under mature crowns. Current-year seedlings were abundant in water channels, on moss, or under mature crowns, suggesting that the seeds may require wet soil conditions for germination. Magnolia stellata seeds show considerable germination below the crowns of mature trees in the year following masting, while some seeds remain dormant in the soil. Considering the soil seed bank and the current-year seedling bank of M. stellata, a frequent supply of seed is essential for the regeneration of this species. Thus, it is important to maintain mature trees in addition to promoting seed production.     

Variations in seed germination of Hippophae salicifolia with different presoaking treatments

Mature seeds of H. salicifolia, collected from five provenances (i.e. Hanuman Chatti, Helang, Lata, Rambara and Janggal Chatti) in west Himalaya, India, were treated with stratification (at 4°C for 15, 30 and 60 days) and in different concentrations of GA₃ (5, 10, 20 mM), KNO₃ (50, 100, 200 mM) and Thiourea (50, 100, 200 mM) solution to determine the variations in seed germination. Results reveal that the germination rates of seeds from different provenances under different pre-sowing treatments are significantly increased compared to those in control (24%–30%). The seeds treated with Thiourea (100 mM) have highest germination rate (76%–83% for different seed sources), followed by those (63%–71% for different seed sources) pretreated with stratification (4°C, 30 days). GA3 treatment significantly shortens the mean germination time (MGT) and improves seed germination percentage. Considering the practical applicability and cost effectiveness, thiourea (100 mM) and stratification (at 4°C) treatments for seed germination are recommended for mass multiplication through seeds of H. salicifolia in village/forest nurseries of the west Himalaya, India.     

Effect of water-spray cooling treatment in a Douglas-fir seed orchard on seed germination

Overhead-cooling treatment used to delay flowering produced non-significant effects on germination capacity, germination rate, germination value, and abnormal germination of seeds from a 13-year-old Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedling seed orchard. The percentage of variation accounted for by cooling treatment ranged from 0.0 to 1.0%. In contrast, variation among trees within treatments ranged from 28 to 46%. These effects were significant, indicating that each tree has an individual germination pattern. The temporal delay of reproductive phenology caused by temperature manipulation as a result of the cooling treatment was judged to be within the species' biological limits.     

Predispersal seed predation in Acacia macrostachya,its impact on seed viability,and germination responses to scarification and dry heat treatments

Predispersal seed predation among individual Acacia macrostachya trees over two sites in Burkina Faso was assessed. In addition, the effects of seed predation on seed viability; germination responses to scarification (mechanical, hot water at 60, 70 and 80°C, and sulphuric acid for 10, 20 and 30 min) and dry heat (at 60, 70 and 80°C for 15, 30 and 60 min each) treatments were investigated under laboratory conditions. The results indicated a large difference in predation intensity among individual trees, as well as between sites. Predispersal predation significantly decreased seed germination, particularly when the number of insect larvae per seed increased. Scarified and unscarified seeds germinated equally well, except for hot water treatments of high temperature. This indicates lack of physical dormancy and dispersed seeds can readily germinate provided that conditions for germination are conducive. Seeds exposed to dry heat treatments also germinated close to 97% under low intensity and short exposure times. This suggests that fire, under natural condition, plays a key role in triggering germination of A. macrostachya seeds.     

Variability in the pod and seed parameters and nuclear DNA content of Tunisian populations of <Emphasis Type="Italic">Ceratonia siliqua</Emphasis> L.

The carob tree (Ceratonia siliqua L.) is widely used in arid and semi-arid areas of Mediterranean countries for industrial, agricultural and ornamental purposes. We wished to determine the variability of its morphological parameters in relation to its exploitation for commercial purposes. Thirteen cultivated and 15 spontaneous populations of C. siliqua from various edapho-climatic zones of Tunisia were compared to determine the variation in pod and seed parameters, for trees growing in situ, and in 2C nuclear DNA content (determined by flow cytometry), for seedlings grown from seeds collected in situ. Analysis of variance showed significant differences (P < 0.0001) between sites for fresh weight, length, width, internal and external thickness of pods, the pod length/width ratio, percentage of viable seeds and seed fresh weight. The mean pod fresh weights (range 8.63–36.03 g) of cultivated C. siliqua were significantly greater than those of spontaneous trees (7.70–19.39). Similarly, for other morphological characters (pod length, width and thickness and seed weight), the cultivated trees showed the highest mean values: 19.46 cm, 2.22 cm, 0.91 cm and 0.20 g, respectively. How this variability could be exploited for agronomic and commercial purposes is discussed. The variation of the examined morphological characters was not correlated with the quantity of DNA, since there were no significant differences in nuclear DNA content among the cultivated or spontaneous individuals. The mean 2C nuclear DNA content was 1.20–1.30 pg, indicating the trees to be diploid (2n = 24).     

Variable dormancy in seed of Pinus contorta

Seeds of lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) collected southwest of Grande Praire, Alberta at three different times and altitudes between August 20, 1984 and August 15, 1985 showed variable responses to stratification. The responses were related to seed ripeness, as judged through evaluations of cone moisture contents, and with the length of time that the cones had remained on the trees. Unripe seeds started to lose germination in the third year after pollination when on the tree. Mature seeds which lost germination by late fall 1984 regained it by the next fall, while most unripe seeds did not. Immature seeds increased their need for stratification over time while mature seeds did not. Seeds should be left on the tree until the end of the third year to insure maximum viability because they do not reach maturity until then.     

Effect of seed coverings and seed pretreatments on the germination response of <Emphasis Type="Italic">Alnus glutinosa</Emphasis> and <Emphasis Type="Italic">Betula pubescens</Emphasis> seeds

The germination of common alder (Alnus glutinosa (L.) Gaertn.) and downey birch (Betula pubescens Ehrh.) seeds is often poor in bare-root nurseries. The effect of a variety of seed coverings and a few seed pretreatments on seedling emergence was examined in this study in an attempt to address this problem. Seeds of each species were sown in trays containing nursery soil, covered with grit, gravel, sand, combinations of these coverings, a hydromulch or a sealed plastic cloche and then incubated for 6 weeks at 17–20°C. The grit combined with sand or gravel, the hydromulch and the cloche increased seedling emergence when compared with the standard grit. In another experiment, seeds of each species were fully imbibed (FI) (>50% moisture content, MC), as per standard practice, or adjusted to target MC (TMC) (30–35% MC) levels, and then chilled to release dormancy. Some seeds of each MC treatment were primed at 20°C for 2 days following chilling, after which all seeds were evaluated in laboratory tests and a nursery trial. Germination potential of the FI seeds declined in the lab tests by the second test date, which was reflected in low seedling emergence in the nursery in birch. The primed FI seeds of alder germinated most rapidly in the nursery, but other effects were not significant. Seedling emergence was better in the nursery in response to the TMC than the FI pretreatment in birch.

Seedling growth and establishment in natural stands of yellow-cedar (Chamaecyparis nootkatensis) seedlings derived from the use of modified seed dormancy-breaking treatments

Following dispersal from the parent tree, seeds of yellow-cedar (Chamaecyparis nootkatensis[D. Don] Spach) exhibit low germination, primarily as a result of coat-imposed dormancy. Dormancy of the mature (intact) seed is effectively terminated by traditional warm/cold treatments. A chemical treatment using the anaesthetic 1-propanol combined with a three day warm water soak (30 °C), a two day GA₃ treatment and 60 d of moist chilling not only promotes high germinability of yellow-cedar seeds, but also elicits vigorous post-germinative growth following seedling emergence under nursery greenhouse conditions. Here we compare the effectiveness of the more traditional warm/cold treatments with the chemical treatment in terms of their capacity to elicit vigorous growth and establishment in natural stands following transplant of seedlings from a nursery greenhouse environment. Two seed lots (42313 and 43697) and open-pollinated seed from parent trees 13-6 and 19-8 showed equivalent seedling growth in natural stands following the chemical treatment and two traditional warm/cold treatments typically used for dormancy breakage by the forest industry and by the Ministry of Forests in British Columbia. The chemical protocol offers the advantage of reducing the time required to break seed dormancy. We have now demonstrated that it yields seedlings that exhibit vigorous growth and are capable of withstanding the vagaries of the environment.     

Density-dependent selfing and its effects on seed performance in a tropical canopy tree species, Shorea acuminata (Dipterocarpaceae)

In the conservation and management practices of natural forests, sound reproduction and regeneration form the basis of the maintenance and viability of the tree populations. To obtain and serve biological information for sustainable forest management, we investigated reproductive biology and inbreeding depression in seeds of an important dipterocarp tree species, Shorea acuminata (Dipterocarpaceae), by both field and laboratory experiments. Results of parental analysis of immature and mature seeds showed that selfing rates varied greatly, from 7.6 to 88.4% among eight mother trees, and the mean overall selfing rate was 38.3%. Observed outcrossing events within a 40-ha study plot were predominantly (76.5%) short-distance events with a mating distance (md) ≤ 100 m. Since the selfing rate sharply decreased with increase in the number of flowering conspecifics (i.e., individuals of the same species) within a 100-m radius from the mother trees, the local density of flowering conspecifics appears to be the key factor determining the outcrossing rate in S. acuminata. However, the extremely high selfing rate (88.4%) observed for one tree could not be simply explained by the low local density of flowering conspecifics. Instead, differences in its flowering phenology (its flowering peaked ca. a week earlier than most of the other examined individuals) may have severely limited its receipt of pollen from other conspecifics, and thus promoted selfing. Since there were no significant differences in the proportion of selfed progeny between immature and mature seed stages, there was no evidence of selective abortion of selfed seeds during seed development. However, the seed mass of outcrossed progeny was heavier than that of selfed progeny, and heavier seeds showed higher success rates at germination and seedling establishment. These results suggest that inbreeding depression resulted in reductions in seed mass and may reduce the fitness of selfed seeds in S. acuminata. In addition, the outcrossing rate of S. acuminata was more sensitive to low local conspecific flowering-tree densities than that of a sympatric bee-pollinated dipterocarp species with greater pollination distances. These results suggest that the management of local adult-tree densities is important for avoiding selfing and inbreeding depression in future generations, especially in a species like S. acuminata with predominantly short-distance pollination.     

Natural Variation in Seed Characteristics of Eastern White Pine (Pinus strobus L.)

Natural variation in seed characteristics of eastern white pine (Pinus strobus L.) trees and its relationship with the size, form, and crown class of parent trees was examined in second-growth, white pine mixedwood stands in Ontario. Cones were collected prior to and following partial harvesting of two stands during 2 years of above-average seed production. Fully enlarged seed extracted from mature cones was X-rayed to determine seed yield per cone, the percentage of sound, partially filled, and empty seed, and the sound seed mass for each tree. Variation in seed yield per cone, the proportion of sound, partially filled, and empty seed, and seed mass was much greater among individuals than between stands or seed years. The strength and significance of the relationship of seed mass with sound seed yield differed with stand and seed year. In uncut stands, seed mass was higher for trees with dominant crown class, larger live crown ratios, and smaller height to diameter ratios, suggesting tree vigour and microsite quality influence seed mass. Proportion of partially filled seeds was significantly reduced in both stands in the second year likely due to increased growing degree days during female gametophyte development. The implications of these results to natural and artificial regeneration of white pine are discussed.     

Pollen dispersal in a hinoki (Chamaecyparis obtusa) seed orchard detected using a chloroplast DNA marker

Pollen dispersal was estimated in two test plots in a hinoki (Chamaecyparis obtusa) seed orchard using a chloroplast DNA marker, the spacer region between thetrnD andtrnY genes, and SSCP (single strand conformation polymorphism). In Plot 1, 2,020 seeds from 40 trees within 30 m of the marker tree were analyzed using the PCR-SSCP method. In Plot 2, 1,850 seeds from 37 trees were analyzed in the same manner. The results revealed that the maximum pollen dispersal distance in the two plots exceeded 25 m. Pollen dispersal appeared to be inversely proportional to the distance from the marker tree. The effective pollen dispersal was suggested to be less than about 20 m in a mature hinoki seed orchard. Adjacent trees had an excessive influence when the pollen density was increased by artificial flower stimulation. Therefore, it was suggested that seed production better resembles ideal random mating when carried out as naturally as possible. In conclusion, the SSCP chloroplast DNA marker was a useful tool for amassing basic information on pollen management in seed orchards of coniferous species.     

Growth response, phosphorus content and root colonization of Polylepis australis Bitt. seedlings inoculated with different soil types

Polylepis forests are one of the most endangered high mountain ecosystems of South America and reforestation with native Polylepis species has been highly recommended. Greenhouse bioassays were set up to determine the influence of three different soils on growth and phosphorous nutrition of Polylepis australis seedlings. Soils were collected from a grassland, a rare mature forest and a forest degraded due to repeated fires. We identified the arbuscular mycorrhizal fungi (AMF) present in the three soils and after 12 months we harvested the seedlings to evaluate root and shoot biomass, plant P content and root colonization by native AMF and dark septate endophytes (DSE). The soil inocula contained 26 AMF morphospecies. Grassland inoculum showed the highest AMF richness, and mature forest showed a different AMF community assembly from grassland and degraded forest inocula. Root biomass and root colonization were highest in seedlings inoculated with mature forest soil, meanwhile shoot biomass and plant P content were similar between all treatments. AMF colonization correlated negatively with DSE and root biomass was negatively correlated with DSE colonization, thus these fungal symbionts could be competing for resources. Our results indicate that AMF inoculum from the mature forest stand has the potential to improve P. australis performance, probably due to the dominance of Glomeraceae and Acaulosporaceae families. However, other soil microorganisms could be together with AMF in the natural inocula, affecting the growth response of P. australis seedlings. Future studies evaluating the effect of these inocula under field conditions should be carried out.     

Quantitative variation among Kenyan populations of Acacia senegal (L.) Willd. for gum production, seed and growth traits

Acacia senegal (L.) Willd. is an African leguminous multipurpose tree species belonging to subfamily Mimosoideae and subgenus Aculeiferum, highly valued for gum arabic production. This study estimated the genetic diversity within and among Kenyan populations of the species in the Bulla Sambul, Kutulo, Wamba and Meisori populations based on 12 quantitative traits, which included; tree height, diameter at breast height (DBH), number of branches, bark thickness, gum weight and various pod and seed traits on 20 randomly selected trees in every population. Duncan’s multiple range test (DMRT) and the dendrogram distinctively divided the populations into two groups; Wamba and Meisori in one group while Bulla Sambul and Kutulo in the other, indicating geographical structuring of the genetic variability. The trees were larger, taller with greater pod and seed traits in the Wamba and Meisori than the Bulla Sambul and Kutulo populations. Contrarily, trees had lighter seeds, more branches with higher gum weight in the Kutulo and Bulla Sambul than the Wamba and Meisori populations. The Shannon–Weaver diversity index (H), depicted 1,000-seed weight as the most varied trait across the populations. These findings provide essential information on the genetic diversity of the species, necessary for delineation of particular zones for seed sources for germplasm conservation, selection for domestication and improved gum arabic production.