The role of cold storage and seed source in the germination of three Mediterranean shrub species with contrasting dormancy types

Context

The use of native species in ecological restoration is highly recommended but, in practice, it is often impaired by knowledge gaps in the germination ecology of suitable species.

Aims

This study aimed to assess the role of storage conditions and seed source on the germination of three Mediterranean shrub species with contrasting types of dormancy.

Methods

Ripe fruits were harvested at two or three distant locations in mainland Portugal. Seeds were subjected to three treatments consisting in different storage conditions: cold storage at low and high moisture conditions, plus a control. Five replicates of up to 30 seeds were placed under constant temperature conditions and germination was monitored weekly during 14 weeks.

Results

The effect of cold storage at high moisture on germination differed between the three species and seed source played a significant role in the germination of all three species. In the case of the species with dormancy, the observed differences in germination could reflect changes in the species’ dormancy degree or sensitivity to dormancy breaking factors across their geographical range. In the case of Pistacia lentiscus (no dormancy), the results suggested a possible adaptation of the northern seed source to high moisture conditions.

Conclusions

The observed differences between species agreed well with their dormancy types, and the seed source-related differences could be adaptive features, as they seemed related with local climate conditions.     

Assessing genetic variation to improve stem straightness in Eucalyptus globulus

Context

Stem straightness is an important trait for growers and processors of Eucalyptus globulus logs for solid-wood products.

Aims

The aims of the study were to determine the extent of genetic variation in stem deviation from straightness in E. globulus and assess the utility of a six-point subjective scoring method as a selection criterion for stem straightness.

Methods

Two E. globulus progeny trials, grown under solid-wood product regimes, were studied. At age 9 years (post-thinning), stem straightness was measured using both image analysis and a six-point subjective scale. Diameter at breast height (DBH; 1.3 m) was measured at both age 5 (pre-thinning) and age 9 years.

Results

Significant additive genetic variation was observed. Strong, positive and significant additive genetic correlations were observed between the stem straightness assessment methods and between DBH at ages 5 and 9 years. Significant positive genetic correlations were shown between subjectively scored stem straightness and DBH at both ages 5 and 9 years.

Conclusion

The six-point subjective scoring method is a cost-effective selection criterion for stem straightness in E. globulus. The image measurement technique may be applied where objective estimates of stem straightness are required, for training purposes and to verify subjective scores.     

Understanding biological characteristics of <Emphasis Type="Italic">Acacia melanoxylon</Emphasis> in relation to fire to implement control measurements

Key message

Acacia melanoxylon produces abundant seeds leading to large seed banks in the soil. These seeds display a large viability and their germination is stimulated by heat. To control the populations, it is necessary to remove adults and young individuals, and to prevent seedling establishment after fire occupying the space with rapid growth and high competitive native species.

Context

Acacia melanoxylon displays a widespread distribution in South West Europe, and an improved knowledge of its reproductive characteristics is required in order to control its expansion.

Aims

This experiment was designed to provide useful indicators for an efficient management of A. melanoxylon populations based on its biological cycle in relation to fire.

Methods

We explored the reproductive biology of A. melanoxylon, from seed dissemination—–quantifying seed rain over a year, their germination with and without fire—the seedling and sapling banks and the structure of the adult population. We analysed the effects of fire, seed maturation and scarification on the viability of seeds and the stimulation of seed germination in the aerial seed bank and in the different strata of the soil seed bank.

Results

Our results indicate that A. melanoxylon produced millions of seeds per ha and per year, half of which germinated and the other half went to the soil seed bank, maintaining the viability many years. The germination was the most critical step in the population dynamics of this species, and fire stimulates germination up to 90%.

Conclusion

A. melanoxylon adults and seedlings removal, followed by colonization of rapid growth and high competitive native species that cover the ground very quickly would be a good control action.

     

Improving the estimation of landscape scale seed dispersal by integrating seedling recruitment

? Context

Dispersal and recruitment play a critical role in determining the abundance and the spatial structure of regeneration.

? Aim

In this study, we estimated landscape scale seed dispersal using the inverse modeling method by fitting seedling counts to seed tree location and fertility in the European silver fir Abies alba Miller.

? Methods

Seed trees and seedlings from three age cohorts were counted in 30 plots on Mont Ventoux (southeastern France) at elevations from 995 to 1,605?m, where the following ecological variables were measured: elevation, slope, aspect, light availability, and tree density. We developed and fitted a dispersal model, including a new parameter, recruitment rate, which depended both on the ecological characteristics of the plots and on seed production.

? Results

Elevation was the factor that affected seedling recruitment the most, with an optimum value at around 1,200?m. Estimated A. alba seed dispersal distances were short (median values for the three cohorts, respectively, 16.4?C13.2?C19.6?m).

? Discussion

We demonstrated that including the ecological characteristics of plots and post-dispersal recruitment processes realistically reduced estimates of seed dispersal distances which are otherwise grossly over-estimated using inverse modeling procedures.     

A new approach for tracking seed dispersal of large plants: soaking seeds with 15N-urea

Context

Although various tracking methods have been used in many ecosystems to investigate seed dispersal and seedling recruitment, it is still difficult to measure seed dispersal patterns due to methodological challenges in tracking seed movement away from parent trees and in finding the locations of seedlings.

Aim

Here, we aimed to develop a new approach to track seed dispersal by animals in the field.

Methods

Our approach involves soaking seeds directly into ¹⁵N-urea solutions with different dosages to enrich them isotopically. This new method is expected to create a reliable differentiation between the enriched seeds and natural ones and consequently between the corresponding seedlings.

Results

We showed that acorns of Quercus variabilis and Cyclobalanopsis glauca and seeds of Pinus koraiensis soaked in ¹⁵N-urea solutions were successfully enriched. We did not find that δ ¹⁵N value of seeds was a linear function of ¹⁵N-urea soaking duration. However, with high urea dosage and extending soaking duration, the δ ¹⁵N values in seedlings of Q. variabilis and P. koraiensis were higher than those of normal plants. As expected, ¹⁵N isotope was significantly diluted in the growing seedlings germinated from ¹⁵N-enriched seeds. Using the ¹⁵N-urea soaking method, we successfully located five seedlings of Q. variabilis germinated from the enriched acorns in the field.

Discussion

The ¹⁵N-urea soaking technique is powerful in tracking seed dispersal and seedling recruitment. This new method solves some of the problems inherent in traditional methods for tracking secondary seed dispersal and could further improve the study of seed dispersal ecology.     

Genetic structures of Calophyllum inophyllum L., a tree employing sea-drift seed dispersal in the northern extreme of its distribution

? Context

Little is known about the potential of gene flow and resulting genetic structures of trees employing sea-drifting seed dispersal in island populations.

? Aims

Current genetic structure and the magnitude of historical gene flow were estimated in island populations of Calophyllum inophyllum L., a typical plant employing sea-drifting seed dispersal.

? Methods

Samples were collected from the northern extreme of the species’ distribution (Taiwan and the Sakishima, Daito, and Ogasawara Islands, Japan) and genotyped using 15 EST-SSR markers. Genetic differentiation (F _ST and AMOVA), genetic structure (STRUCTRE analysis), and historical gene flow (assignment testing) were determined.

? Results

Frequent gene flow within and rare gene flow among island groups was determined using assignment testing. Clear genetic structures were also detected using the STRUCTURE analysis, which demonstrated differentiation between dominant clusters among geographically constructed island groups.

? Conclusions

The potential for gene flow via sea-drifting seed dispersal was high, and this was possible even among small islands. However, the extent and frequency of gene flow were not great enough to prevent genetic differentiation in a range of over a few hundred kilometers.     

Mast seeding in deciduous forests of the northern Apennines (Italy) and its influence on wild boar population dynamics

Context

Pulsed food resources may strongly affect the population dynamics of several consumer species, with consequences on the ecosystem. One of the most common pulsed resources is forest mast seeding.

Aims

We analysed mast seeding in deciduous forests in a mountainous area of northern Apennines and its effect on population dynamics of wild boar (Sus scrofa L.).

Methods

We performed a quantitative, 20-year analysis on annual seed production in Turkey oak (Quercus cerris L.), beech (Fagus sylvatica L.) and chestnut (Castanea sativa Mill.) forest stands using litter traps. The wild boar population density was estimated by means of drive censuses and hunting bag records. The role of other biotic (density of predators) and abiotic (climate) factors potentially affecting wild boar mortality was also investigated.

Results

Turkey oak and chestnut showed high levels of seed production, whereas lower levels were found in beech. The pulsed resources of chestnut and Turkey oak positively affected piglet density. Analyses also highlighted the influence of snow cover and wolves on wild boar population dynamics.

Conclusion

Wild boar can be considered a pulse rate species, the management of which can be improved by annual monitoring of seed production.     

Is there a risk-dilution effect of naturally fallen fruits on post-dispersal seed predation by wood mice?

Aims

The aim of this study was to test the hypothesis that heavy predation of fallen fruits reduces the predation of neighboring post-dispersed seeds.

Methods

We performed a seed/fruit removal cafeteria experiment to assess the effects of seed species, of fruit species, and of density of fallen fruits on seed predation by wood mice (Apodemus sp.). In total, 6,930 seeds and 9,660 fruits from seven species were used. A generalized linear mixed model procedure was used to test these effects.

Results

Seed predation was significantly affected by the species of both seeds and neighboring fruits, but not by their density. Multiple comparison tests showed that most of treatments tested had no significant effects of species and density of neighboring fruits on seed removal. However, seed removal was significantly lower in some treatments with fruits than in the treatments without fruits for one of the seven seed species tested. Seed removal of two species tested was significantly differed among some treatments with different fruit species.

Conclusion

Most of the results in this study do not support our overall hypothesis. However, a part of results supported our hypothesis, suggesting that seed removal is affected by complex interactions between the preference of wood mice for fruits and fruiting environment.     

Optimal seed water content and storage temperature for preservation of Populus nigra L. germplasm

Context

Black poplar (Populus nigra L.) is an alluvial forest tree species whose genetic pool is decreasing in Europe. Poplar trees produce short-lived seeds that do not store well.

Aim

The feasibility of seed storage in conventional and cryogenic conditions after their desiccation from water content (WC) of 0.15 to 0.07 g H₂O g^?1 dry mass (g g^?1) was investigated.

Methods

Seed germinability was evaluated (seeds with a radicle and green cotyledons were counted) after storage of seeds for a period of 3 to 24 months at different temperatures: 20°, 10°, 3°, ?3°, ?10°, ?20° or ?196°C.

Results

Seeds desiccated to a 0.07 g g^?1 WC can be stored successfully at ?10 °C and ?20 °C for at least 2 years. A significant decrease in germination was observed only after 12 months of seed storage (WC 0.15 g g^?1) at temperatures above 0 °C. We demonstrated that both fresh (0.15 g g^?1 WC) and desiccated (0.07 g g^?1 WC) seeds can be preserved at ?196 °C for at least 2 years.

Conclusions

Seed storage temperature and time of storage were statistically significant factors affecting seed storability. The presented data provide a foundation for the successful gene banking of P. nigra seeds.     

Patterns of longitudinal and tangential maturation stresses in Eucalyptus nitens plantation trees

Context

Tree orientation is controlled by asymmetric mechanical stresses set during wood maturation. The magnitude of maturation stress differs between longitudinal and tangential directions, and between normal and tension woods.

Aims

We aimed at evaluating patterns of maturation stress on eucalypt plantation trees and their relation with growth, with a focus on tangential stress evaluation.

Methods

Released maturation strains along longitudinal and tangential directions were measured around the circumference of 29 Eucalyptus nitens trees, including both straight and leaning trees.

Results

Most trees produced asymmetric patterns of longitudinal maturation strain, but more than half of the maturation strain variability occurred between trees. Many trees produced high longitudinal tensile stress all around their circumference. High longitudinal tensile stress was not systematically associated with the presence of gelatinous layer. The average magnitude of released longitudinal maturation strain was found negatively correlated to the growth rate. A methodology is proposed to ensure reliable evaluation of released maturation strain in both longitudinal and tangential directions. Tangential strain evaluated with this method was lower than previously reported.

Conclusion

The stress was always tensile along the longitudinal direction and compressive along the tangential direction, and their respective magnitude was positively correlated. This correlation does not result from a Poisson effect but may be related to the mechanism of maturation stress generation.     

Independent lines of evidence of a genetic relationship between acoustic wave velocity and kraft pulp yield in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis>

Key message

Multiple lines of evidence suggest acoustic wave velocity (AWV) would provide a rapid and efficient method to indirectly select for superior pulp yield in Eucalyptus globulus breeding programs.

Context

Eucalyptus globulus is one of the most widely planted hardwood species in temperate regions of the world and is primarily grown for pulpwood.

Aims

To determine if acoustic wave velocity (AWV) can be used to indirectly select for kraft pulp yield in E. globulus.

Methods

Genetic group effects, additive and non-additive variance components, and genetic correlations were estimated for AWV and pulpwood traits, including Kraft pulp yield. In a separate trial, the relative position of quantitative trait loci (QTL) for these traits was compared.

Results

Estimated narrow-sense heritabilities for AWV and pulp yield were both 0.26, and these traits were strongly genetically correlated (0.84). Furthermore, co-located QTL for these traits were identified. Further evidence that AWV could be used to indirectly select for pulp yield was provided by the ranking of genetic groups—Otways and King Island had the highest AWV and pulp yield and Strzelecki and Tasmania the lowest. There was no evidence of dominance variation in wood property traits.

Conclusion

Together, these findings suggest that AWV could be used as a selection criterion for kraft pulp yield in E. globulus breeding programs.

     

Fire severity as a key factor in post-fire regeneration of Pinus pinaster (Ait.) in Central Portugal

Context

Mediterranean pine woodlands are strongly affected by wildfires; however, there are knowledge gaps in the role of fire severity on Pinus pinaster Ait. regeneration.

Objectives

The principal questions were: (a) does post-fire regeneration of Maritime Pine differ where canopies were consumed to a low vs. high degree and (b) which factors, besides fire severity, could explain these differences.

Methods

Pine recruitment was monitored from 2 to 36?months after a summer wildfire in 18 25?m² plots, equally divided over two fire severity classes based on crown consumption. Besides the degree of crown consumption, three quantitative fire severity indices as well as post-fire site conditions, seed input and understory vegetation recovery were measured.

Results

Pine seedling densities were consistently higher in the plots with low than high crown consumption but due to marked spatial variability, they were only significantly different at two out of the eight sampling occasions. This variability could be explained by a quantitative index based on the diameter of twigs, as well as by seed input and post-fire site conditions (ash and litter cover).

Conclusion

Fire severity was found to strongly affect the pine recruitment following wildfire, using both a qualitative visual severity index and a quantitative, more labour-intensive one.     

Plasticity of reproductive allocation of a woody species (Ulex europaeus) in response to variation in resource availability

Context

While many woody perennials grow and reproduce in varying environments, their ability to modify their reproductive allocation under varying resource availability is unclear.

Aims

This study aimed to demonstrate the occurrence of plasticity of reproductive allocation in a pioneer woody species (Ulex europaeus).

Methods

We studied seed production in 144 plants under different irradiance and population densities. We measured their basal area, their whole shoot biomass and photosynthetic biomass, and their reproductive output (number of fruits per individual and number of seeds per fruit).

Results

We found that newly produced photosynthetic biomass was influenced by environmental variation, which in turn determined its reproductive output. In addition, in low light conditions investment in reproduction was more reduced than investment in growth indicating plasticity of reproductive allocation.

Conclusion

These results provide the first evidence for plasticity of reproductive allocation of a woody plant. It may lead to the ability of this pioneer species to survive and to continue to reproduce even at low rates in non-optimal shady habitats and to maintain a non-empty seed bank in forest systems with long unfavourable periods between two disturbances.     

Genetic parameters and comparison between native and local landraces of Eucalyptus globulus Labill. ssp. globulus growing in the central highlands of Colombia

Aims

The objective of this study was to compare the merit of the Colombian landrace relative to the various Australian native races of Eucalyptus globulus Labill. ssp. globulus and study the genetic control of key traits such as growth, wood density, and leaf phase change in the unique conditions of the Colombian highlands.

Methods

The genetic study was based on open-pollinated families from native Australian and Colombian landrace origin, tested across four trials spanning two generations of breeding. A multisite mixed linear model with genetic groups was fitted to the data to estimate race merit and the variance and covariances between traits, ages, and sites.

Results

Race effects for growth were small and only significant at the older site. In contrast, races differ significantly for height to phase change and density. The Colombian landrace and South and NE Tasmania races changed leaf type at a higher tree height. King Island and Recherche Bay had low density values, whereas the Colombian landrace had the highest. Heritability was moderate for growth traits (between 0.09 and 0.40), high for height to phase change (between 0.42 and 0.69), and moderate for wood density (0.28). The genetic correlation between growth and height to phase change was in general positive, but variable across sites. There was no correlation between growth and density. Despite large differences in growth between trials, pairwise genetic correlations suggest that genotype-by-site interaction is negligible. However, there was a poor correspondence between first-generation (ex-native stands) and second-generation families (ex-multi-provenance progeny trial). This suggests that breeding value estimates based on native open-pollinated material are unreliable.

Conclusion

Results confirm negligible race differences for growth, but not for wood density. Future breeding efforts should include the various genetic backgrounds including the Colombian landrace which constitutes a very important source, especially because of its high density. Despite a low Genotype by Environment interaction, the poor genetic correspondence between the first- and second-generation trials indicates that selections for growth should be based on information coming mainly from the advanced-generation trials.     

Relationship between tree morphology and growth stress in mature European beech stands

Aims

In European Beech (Fagus sylvatica L.) large growth stresses lead to severe log end splitting that devaluate beech timber. Our study aimed at detecting relationships between growth stress and some morphology parameters in trees.

Methods

Growth stress indicators were recorded for 440 mature trees in nine stands from five European countries, together with morphology parameters.

Results

Most trees displayed an uneven distribution of growth stress around the trunk. Moreover, growth stress intensity varied largely between individual trees. Geometry of the trunk was a poor predictor of growth stress intensity. Crown asymmetry resulted in a larger stress dissymmetry within trees. Trunk inclination was not correlated to max tension stress, contrary to what is usually found in younger trees. In the case of small inclination, growth stress was close to expected from biomechanics of restoring verticality. Trees exhibiting a larger inclination probably evolved a different mechanical solution: a rather large crown, lower tree slenderness and a sufficient asymmetry in growth stress as to prevent a higher inclination due to growth.

Conclusion

A large slenderness is the best accurate predictor of a large growth stress, although variations in the ratio height/diameter at breast height explained only 10 % of the variability of growth stress. A large crown surface was the best predictor of a low level of growth stress. A large spacing between trees seems a good solution to lower the risk of growth stress in mature beech.     

Growth response to climate and drought change along an aridity gradient in the southernmost Pinus nigra relict forests

Context

Tree populations at the rear edge of species distribution are sensitive to climate stress and drought. However, growth responses of these tree populations to those stressors may vary along climatic gradients.

Aims

To analyze growth responses to climate and drought using dendrochronology in rear-edge Pinus nigra populations located along an aridity gradient.

Methods

Tree-ring width chronologies were built for the twentieth century and related to monthly climatic variables, a drought index (Standardized Precipitation–Evapotranspiration Index), and two atmospheric circulation patterns (North Atlantic and Western Mediterranean Oscillations).

Results

Growth was enhanced by wet and cold previous autumns and warm late winters before tree-ring formation. The influence of the previous year conditions on growth increased during the past century. Growth was significantly related to North Atlantic and Western Mediterranean Oscillations in two out of five sites. The strongest responses of growth to the drought index were observed in the most xeric sites.

Conclusion

Dry conditions before tree-ring formation constrain growth in rear-edge P. nigra populations. The comparisons of climate-growth responses along aridity gradients allow characterizing the sensitivity of relict stands to climate warming.     

Cause–effect relationship among morphological adaptations,growth, and gas exchange response of pedunculate oak seedlings to waterlogging

Context

In response to waterlogging, pedunculate oak is known to develop adventitious roots and hypertrophied lenticels. However, to date, a link between these adaptations and the ability to maintain net CO₂ assimilation rates and growth has not been demonstrated.

Aims

The aim of this study was to explore the cause–effect relationship between the ability to form morphological adaptations (hypertrophied lenticels and adventitious roots) and the capacity to maintain high assimilation rate and growth.

Methods

The occurrence of morphological adaptations and the parameters of photosynthesis were monitored over 20 days of waterlogging in 5-week-old pedunculate oak seedlings presenting similar morphological development.

Results

Based on the development or not of morphological adaptations, the following three categories of responses were identified: development of hypertrophied lenticels and adventitious roots, development of hypertrophied lenticels alone, and the lack of development of adaptive structures. These categories, ranked in the order given, corresponded to decreasing levels of initial net CO₂ assimilation rate growth and photosynthesis parameters observed during waterlogging.

Conclusion

We observed a two-way cause–effect relationship between the capacity to form adaptive structures and the assimilation rate. Indeed, the initial assimilation rate determined the occurrence of hypertrophied lenticels and growth during stress, and then the development of morphological adaptations enhanced the ability to maintain assimilation levels during the stress.     

Adventitious sprouting of Pinus leiophylla in response to salt stress

Context

Although adventitious shoots are produced in many tree species in response to injury, little is known about the effects of salinity on sprouting.

Aims

The main objective was to examine the sprouting capacity of Pinus leiophylla seedlings in relation to injury and physiological changes induced by NaCl.

Methods

Seedlings were grown in controlled-environment growth rooms and treated with 0, 100, 150, and 200 mM NaCl. Numbers of adventitious shoots were recorded and growth and physiological parameters measured after 64 days of treatments and following a 30-day recovery period.

Results

NaCl treatments triggered sprouting of adventitious shoots, mainly in the lower parts of the stems. However, fewer sprouts were induced by 200 mM NaCl compared with the lower concentration treatments. These changes were accompanied by needle necrosis, decreased chlorophyll concentrations, seedling dry mass, and stem diameter. Stomatal conductance, net photosynthesis, and root hydraulic conductance decreased with increasing NaCl concentrations and did not return to the control levels after 30 days of stress relief.

Conclusions

Pinus leiophylla has the regeneration potential when exposed to salinity. However, very high salt concentrations induce severe physiological impairments and, consequently, a decrease of this regeneration potential.     

Decline of genetic diversity of sessile oak at the retracting (xeric) limits

Context

Genetic diversity of sessile oak (Quercus petraea) populations in Hungary was assessed close to the retracting, low-elevation, low-latitude (xeric) distribution limits.

Objective

We aimed at tracing an assumed effect of climatic factors on genetic diversity, particularly at the southern, low elevation limits of distribution.

Methods

Genetic diversity at isozyme-coding loci was analysed in populations, and related to the climate of the sites where the populations grow. A locus-wise analysis proved to be essential to follow responses.

Results

A climate-related cline was found at seven isoenzyme-coding gene loci. Declining allelic numbers and heterozygosity indicated lower diversity at warmer and drier sites. The majority of loci were responsive to precipitation factors, others to temperature. Genetic clustering was neither related to geographic distance nor to random or historic effects.

Conclusions

The results suggest that climatic stress may elicit a genetic diversity loss in populations, which may reduce their plasticity and adaptive potential. The selective pressure may override historic effects and gene flow. With respect to expected climate change, the correlation of diversity with some climatic factors gains specific importance. If supported by further investigations, the results might be utilised for reconsidering conservation strategies and rules for use of forest reproductive material.     

Multi-coefficient goal programming in thinning schedules to increase carbon sequestration and improve forest structure

Context

Current decision analysis techniques are ineffective for planning thinning operation to improve the forest structure.

Aims

The purpose of this study is to use multi-coefficient goal programming (GP) to plan a thinning schedule that allows more carbon sequestration and diverse forest structure.

Methods

A multi-coefficient GP is applied to plan a thinning schedule for a 2,633-ha plantation forest.

Results

This technique efficiently fine-tunes the thinning schedule to obtain 420,500 tons of carbon sequestration which was a little higher than the result by a multi-segment goal programming (MSGP). Moreover, a fixed-ratio multi-coefficient GP is applied to efficiently generate mosaic of thinned areas with various thinning intensities. Although the captured carbon by a fixed-ratio multi-coefficient GP is lower, the thinned areas can provide various habitats for forest life with multiform contrasting edges.

Conclusion

The use of a multi-coefficient GP allows practicable planning of better thinning alternatives to increase carbon sequestration and forest structure.