Genetic variation in susceptibility to pine wilt disease of maritime pine (<Emphasis Type="Italic">Pinus pinaster</Emphasis> Aiton) half-sib families

Key message

This paper presents a greenhouse study for assessing the genetic variation in maritime pine (Pinus pinaster Aiton) in response to pinewood nematode (Bursaphelenchus xylophilus (Steiner et Buhren) Nickle), which is a causal agent of pine wilt disease. Fifteen out of 96 half-sib families were selected as less susceptible. This experiment is an important first step for creating a resistance breeding program.

Context

Pine wilt disease is caused by the pinewood nematode (Bursaphelenchus xylophilus (Steiner et Buhren) Nickle), a quarantine pest, and is a concern to maritime pine (Pinus pinaster) in Portugal due to its economic, environmental, and social impacts. This disease is regarded as a major threat to European forests.

Aims

This paper aimed to evaluate the genetic variation in maritime pine families that were inoculated with pinewood nematode, identify the most resistant families, and establish the guidelines for a resistance improvement program.

Methods

Two-year-old half-sib progenies obtained from 96 plus trees were inoculated. The plants were monitored for survival on four different dates. The statistical analysis followed the mixed model theory.

Results

Genetic variability of the susceptibility to pine wilt disease was observed. At 157 days after inoculation, the 15 highest genetic ranking families out of 96 were selected, having a predicted survival mean of 15.6% instead of 11.0% on average for the all 96 families.

Conclusion

This study allows for the implementation of an improvement program to help control pine wilt disease.

     

Effectiveness of spatial analysis in <Emphasis Type="Italic">Cryptomeria japonica</Emphasis> D. Don (sugi) forward selection revealed by validation using progeny and clonal tests

Key message

Accurate evaluation of genetic performances of trees is crucial in order to improve the efficiency of forest tree breeding. We revealed that spatial analysis is effective for predicting individual tree breeding values at the forward selection stage of Cryptomeria japonica D. Don (sugi) breeding program by using a novel validation approach.

Context

In the process of selecting genetically superior trees for breeding, appropriate handling of environmental effects is important in order to precisely evaluate candidate trees. Spatial analysis has been an effective statistical approach for genetic evaluation at sites with heterogeneous microenvironments. However, the efficiency of spatial analysis on forward selection has not been validated on a practical scale to date.

Aims

This study aimed to reveal the effectiveness of spatial analysis, which incorporates spatially autocorrelated residuals into mixed models, for the prediction of breeding values at the forward selection stage by validation using progeny or clonal tests of forward-selected individuals.

Methods

Tree height was analyzed by ordinary randomized complete block design models and spatial models incorporating spatially autocorrelated residuals in a linear mixed model framework, and model selection was conducted at thirty Cryptomeria japonica D. Don breeding population sites having various topographical ruggedness. For validation, three clonal tests and one progeny test of individuals selected from three and four breeding populations, respectively, were used. The effectiveness of forward selection using the two models was evaluated based on the correlation between individual breeding values at the stage of forward selection and genotypic and breeding values that were estimated by clonal and progeny tests.

Results

Spatial models were more predictive than ordinary models in all cases. Spatial correlation parameters tend to increase with the topographical ruggedness index of each site. The correlation coefficients between breeding values at the time of forward selection and genotypic or breeding values evaluated in succeeding clonal and progeny tests were significantly higher in spatial models than in ordinary models in six out of nine cases.

Conclusion

Validation using progeny and clonal tests of forward-selected individual trees revealed that spatial analysis is more effective for the evaluation of genetic performance of individuals at the stage of forward selection in Cryptomeria japonica.

     

Rapid assessment of wood traits for large-scale breeding selection in <Emphasis Type="Italic">Picea mariana</Emphasis> [Mill.] B.S.P.

Key message

Pilodyn and acoustic velocity measurements on standing trees, used for predicting density and stiffness, can be good genetic selection tools for black spruce. Genetic parameters and selection efficiency were conserved in two breeding zones with contrasted bioclimatic conditions.

Context

Given the recent progress made in the black spruce genetic improvement program, the integration of juvenile wood mechanical properties as selection criteria is increasingly relevant.

Aims

This study aims to estimate the genetic parameters of in situ wood density and modulus of elasticity (MoE) measurements and to verify the efficiency of various measuring methods used for large-scale selection of black spruce based on wood quality.

Methods

Height, diameter, wood density, and some indirect measures of density (penetration and drilling resistance) and MoE (acoustical velocity and Pilodyn) were estimated on 2400 24-year-old trees of 120 open-pollinated families in progeny trials located in the continuous boreal or mixed forest subzones.

Results

Heritability of growth, density, and indirect density measurements varied from low to moderate and was moderate for acoustical velocity in both vegetation subzones. Expected genetic gains for wood properties based on in situ methods were higher for MoE proxy estimation combining Pilodyn and acoustic velocity.

Conclusion

Acoustic velocity is a good predictor of MoE. It is virtually unaffected by the environment and can be used on a large scale in the same manner as the Pilodyn for density. Using a proxy estimation that combines both methods helps optimize genetic gain for MoE.

     

Plastic response of four maritime pine (<Emphasis Type="Italic">Pinus pinaster</Emphasis> Aiton) families to controlled soil water deficit

Key message

Separating the internal (ontogenetic) and external (environmental) components of maritime pine development during controlled soil water deficit helps to highlight the plastic response. The adjusted measurements reveal significant differences between families for their plastic response for several physiology and growth traits.

Context

Soil water deficit is and will be a growing problem in some regions. Pinus pinaster Ait. is a species of commercial interest and is recognized as a drought-avoiding species. It is thus of interest to evaluate the adaptation potential of P. pinaster to soil water deficit.

Aims

This paper aims to estimate the plastic response to the variation of water availability at the family level (half-sibs).

Methods

Two-year-old P. pinaster cuttings from four families were submitted during 6 weeks to two contrasting watering regimes. The experiment started in April 2011 shortly after sprouting. The photosynthesis and stomatal conductance to water vapor were measured on 1-year-old needles. Intrinsic water-use efficiency was calculated as the ratio of photosynthesis to stomatal conductance. Radial growth, length of terminal shoot, and total height were also measured. The ontogenetic component of tree development was estimated on the well-watered trees for all the traits. Then, this development effect was eliminated from the data collected on the trees submitted to the soil water deficit in order to keep only the effect of this soil water deficit.

Results

After 6 weeks of reduced watering, the value of all adjusted traits decreased. An average plastic response to the variation of water availability was found to be significant and variable at the family level for the six adjusted variables.

Conclusion

These results suggest that there is genetic variation of phenotypic plasticity to drought in P. pinaster for several traits, including stomatal conductance, which appears to be a promising variable for future selection for resistance to drought.

     

Comparing morphology and physiology of southeastern US <Emphasis Type="Italic">Pinus</Emphasis> seedlings: implications for adaptation to surface fire regimes

Key message

The suite of traits expressed as seedlings by coastal and mountain longleaf pine and south Florida slash pine suggest they can survive fire in the seedling stage. In contrast, loblolly pine and typical slash pine tolerate fire when mature but do not exhibit traits that allow them to survive fire when young, representing a different strategy for survival in frequently burned communities.

Context

Fire is an important driver in the distribution and abundance of southern US pine species, and seedling fire tolerance often determines individual survival under frequent fire regimes.

Aims

We investigated seedling growth, biomass allocation, needle distribution, bark thickness, and total non-structural carbohydrate (TNC) storage in taproots and related them to the expression of fire-tolerance for five species or types, including loblolly pine (Pinus taeda L.), two longleaf pine (P. palustris Mill.) types representing two distinct ecological communities (coastal and mountain) and two slash pine (P. elliottii Englem.) varieties.

Methods

We analyzed the relationship of seedling growth, biomass characteristics, and total non-structural carbohydrate storage between species by using analysis of variance.

Results

Both coastal and mountain longleaf pines had thick bark, long, densely arranged needles, and a grass-stage. South Florida slash pine shared the same suite of traits but, contrary to previous reports, displayed reduced height growth rather than a grass-stage. In contrast, loblolly pine and typical slash pine had faster height growth, more branching, lower needle density, and thinner bark. Both longleaf pines and south Florida slash pine also had higher TNC storage in taproots than either loblolly or typical slash pines.

Conclusion

The relative strength of expression of these fire-adaptation traits among the five species types generally matches the fire-return intervals associated with each species’ habitat, suggesting the importance of fire regimes in determining the distribution and abundance of the studied species.

     

Mixing oak and pine trees does not improve the functional response to severe drought in central French forests

Key message

Mixing sessile oak and Scots pine in central France to reduce intraspecific competition for water resources did not improve the ability of these two species to withstand severe drought during the summer.

Context

In order to reduce the impact of increasingly extreme droughts on forests, managers must adapt their practices to future climate conditions. Maintaining a greater diversity of tree species in temperate forest ecosystems is one of the recommended options.

Aims

We addressed how interactions between sessile oak and Scots pine in mixed forests in central France affect their functional response to drought.

Methods

We characterized the carbon isotope composition (δ¹³C) in the tree growth rings formed during wet (2001, 2007) or dry (2003, 2004) summers for each of the two species growing both in pure and in mixed stands in order to compare the effect of stand composition on variations in carbon isotope discrimination (Δ¹³C) among contrasted years.

Results

The severe drought in 2003 induced a strong decrease in Δ¹³C for all trees and in all stands as compared to 2001. This decrease was greater in pine than in oak. There was no significant difference between pure and mixed stands in the response of either species to drought.

Conclusion

Mixing sessile oak and Scots pine in stands in central France does not improve the ability of either species to withstand severe drought during the summer.

     

Tannin-caprolactam and Tannin-PEG formulations as outdoor wood preservatives: biological properties

Key Message

This article presents the enhancement in boron fixation as well as the improved biological resistance against fungi and termites for wood samples treated with tannin-caprolactam and tannin-PEG formulations.

Context

Although the recently developed tannin-boron wood preservatives have shown high biological protection, they presented also average resistance against weathering. The tannin-caprolactam formulations have shown improved weathering resistances and dimensional stability.

Aims

For this reason, more detailed biological tests were performed to evaluate the influence of the caprolactam and PEG on the biological resistance.

Methods

In this paper, the boron leaching of the tannin-caprolactam and tannin-PEG impregnated Scots pine specimens was observed and the biocidal effect against fungi (Antrodia spp. and Coniophora puteana) and insects (Reticulitermes flavipes and Hylotrupes bajulus) were determined according to the guidelines of EN 113, EN 117, and EN 47.

Results

The advanced formulations containing PEG have shown interesting resistance against fungal decay, but very low penetration and weak resistance against larvae while the tannin-caprolactam preservatives have shown overall improved biological performances and higher boron fixations.

Conclusion

The biocidal activity of the caprolactam-added formulations was overall enhanced and therefore these formulations are confirmed to be an interesting alternative for the wood preservation in outdoor environment.

     

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.

     

Growth phenology in <Emphasis Type="Italic">Pinus halepensis</Emphasis> Mill.: apical shoot bud content and shoot elongation

Key message

The chronology of periods of organogenesis and elongation is highlighted in Pinus halepensis.The two first growth units of an annual shoot are preformed inside the bud during the previous year. The following growth units are formed during the spring or summer of the current year.

Context

Analysis of annual shoot length growth phenology is crucial to assess the impact of climate change on tree production. Little is known about the basic growth characteristics and the phenology of pines.

Aims

The present study disentangles the roles of shoot organogenesis vs elongation in the annual growth cycle of the polycyclic Aleppo pine.

Methods

Growth of young Pinus halepensis trees was monitored monthly for 1 year. At each monitoring date, the bud content and meristem dimensions of the main stem shoots apices were analyzed.

Results

The two first growth units of an annual shoot are preformed inside the bud during the previous year. The following growth units are formed during the spring or summer of the current year. The gap between a shoot organogenesis and its elongation may vary from 1 month, for the last growth unit, to half a year, for the first growth units.

Conclusion

Our results underline the importance of taking seasonal environmental conditions from both the previous and the current year into account, in order to study the plasticity of annual shoot growth and its response to climate change and variability.

     

Below-ground hydraulic constraints during drought-induced decline in Scots pine

Key message

Below-crown hydraulic resistance, a proxy for below-ground hydraulic resistance, increased during drought in Scots pine, but larger increases were not associated to drought-induced defoliation. Accounting for variable below-ground hydraulic conductance in response to drought may be needed for accurate predictions of forest water fluxes and drought responses in xeric forests.

Context

Hydraulic deterioration is an important trigger of drought-induced tree mortality. However, the role of below-ground hydraulic constraints remains largely unknown.

Aims

We investigated the association between drought-induced defoliation and seasonal dynamics of below-crown hydraulic resistance (a proxy for below-ground hydraulic resistance), associated to variations in water supply and demand in a field population of Scots pine (Pinus sylvestris L.)

Methods

Below-crown hydraulic resistance (r_bc) of defoliated and non-defoliated pines was obtained from the relationship between maximum leaf-specific sap flow rates and maximum stem pressure difference estimated from xylem radius variations. The percent contribution of r_bc to whole-tree hydraulic resistance (%r_bc) was calculated by comparing stem water potential variations with the water potential difference between the leaves and the soil.

Results

r_bc and %r_bc increased with drought in both defoliated and non-defoliated pines. However, non-defoliated trees showed larger increases in r_bc between spring and summer. The difference between defoliation classes is unexplained by differences in root embolism, and it is possibly related to seasonal changes in other properties of the roots and the soil-root interface.

Conclusion

Our results highlight the importance of increasing below-ground hydraulic constraints during summer drought but do not clearly link drought-induced defoliation with severe below-ground hydraulic impairment in Scots pine.

     

Adaptive management rules for <Emphasis Type="Italic">Pinus nigra</Emphasis> Arnold ssp<Emphasis Type="Italic">. salzmannii</Emphasis> stands under risk of fire

Key message

We generate flexible management rules for black pine stands, adaptable to alternative stand management situations and entailing thinnings, final-felling, and salvage cuts, based on the results on 270 stand level optimizations.

Context

Forest management instructions often rely on the anticipated prediction of the stand development, which poses a challenge on variable economic and environmental conditions. Instead, an alternative approach to better adapt forest management decisions to changing conditions is defining flexible rules based on thresholds that trigger management operations.

Aims

This article develops rules for the adaptive management of P. nigra stands in Catalonia (Spain) addressing the risk of fire and post-fire forest management.

Methods

The stochastic version of the simulation-optimization system RODAL was used to optimize the management of forest stands in three sites under different fire probability levels. A total of 270 optimizations were done varying site fertility, fire probability, and economic factors. The results of the optimizations were used as the basis of flexible forest management rules for adaptive stand management.

Results

The developed management rules defined the basal area limit for thinning, the thinning intensity, the mean tree diameter at which regeneration cuttings should start, and the basal area below which a salvage cutting should be done. Fire risk was not a significant predictor of the models for thinning and final cutting rules.

Conclusion

The presented rules provide a flexible tool for forest management during the stand development and under changing conditions when the management objective is to maximize economic profitability of timber production.

     

Comparing nearest neighbor configurations in the prediction of species-specific diameter distributions

Key message

We examine how the configurations in nearest neighbor imputation affect the performance of predicted species-specific diameter distributions. The simultaneous nearest neighbor imputation for all tree species and separate imputation by tree species are evaluated with total volume calibration as a prediction method for diameter distributions.

Context

This study considers the predictions of species-specific diameter distributions in Finnish boreal forests by means of airborne laser scanning (ALS) data and aerial images.

Aims

The aim was to investigate different configurations in non-parametric nearest neighbor (NN) imputation and to determine how changes in configurations affect prediction error rates for timber assortment volumes and the error indices of the diameter distributions.

Methods

Non-parametric NN imputation was used as a modeling method and was applied in two different ways: (1) diameter distributions were predicted at the same time for all tree species by simultaneous NN imputation, and (2) diameter distributions were predicted for one tree species at a time by separate NN imputation. Calibration to a regression-based total volume prediction was applied in both cases.

Results

The results indicated that significant changes in the volume prediction error rates for timber assortment and for error indices can be achieved by the selection of responses, calibration to total volume, and separate NN imputation by tree species.

Conclusion

Overall, the selection of response variables in NN imputation and calibration to total volume improved the predicted diameter distribution error rates. The most successful prediction performance of diameter distribution was achieved by separate NN imputation by tree species.

     

Dynamics of diameter and height increment of Norway spruce and Scots pine in southern Finland

Key message

Onset and cessation of radial and height increment of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in southern Finland were independent phenomena. They both contributed to the increment period duration, which was a more crucial factor defining the magnitude of annual radial and height increment.

Context

Phenology of diameter and height increment is a critical component of growth, also contributing to damage and survival of trees.

Aims

We quantified annual variation in intra-annual tracheid production and height increment of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.).

Methods

The number of tracheids and the day of the year for the onset and cessation of tracheid production were monitored from microcores collected repeatedly during growing seasons 2001–2012 in southern Finland. Weekly height increment was also measured in an adjacent sapling stand in 2008–2012.

Results

The first tracheids in pine were found around mid-May and in spruce a week later. The cessation of the tracheid production occurred during the last week of August for both tree species. Increment onset and cessation were independent phenomena, both contributing to the magnitude of tracheid production via increment period duration, which appeared to be a more crucial factor defining the number of tracheids. Duration of the height increment period was also related to shoot length but the connection was less tight than the link between the duration of tracheid production and the number of tracheids. A thermal threshold around 100 d.d. (degree days) was found for the onset of radial increment. No single environmental factor triggered the cessation of tracheid production, but in some years, soil water availability appeared to play a role.

Conclusion

The results indicate that extending growing seasons due to the climatic warming may increase growth in the Finnish forests.

     

Genetic parameters for growth and wood chemical properties in <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> × <Emphasis Type="Italic">E. tereticornis</Emphasis> hybrids

Key message

Growth and wood chemical properties are important pulpwood traits. Their narrow-sense heritability ranged from 0.03 to 0.49 in Eucalyptus urophylla × E. tereticornis hybrids, indicating low to moderate levels of genetic control. Genetic correlations were mostly favorable for simultaneous improvement on growth and wood traits. Additive and non-additive genetic effects should be considered in making a hybrid breeding strategy.

Context

Eucalypt hybrids are widely planted for pulpwood production purposes. Genetic variations and correlations for growth and wood chemical traits remain to be explored in Eucalyptus interspecific hybrids.

Aims

Our objectives were to clarify the heritability of growth and wood chemical traits and determine the genetic correlations between traits and between trials in E. urophylla × E. tereticornis hybrids.

Methods

Two trials of 59 E. urophylla × E. tereticornis hybrids derived from an incomplete factorial mating design were investigated at age 10 for growth (height and diameter) and wood chemical properties (basic density, cellulose content, hemi-cellulose content, lignin content, and syringyl-to-guaiacyl ratio). Mixed linear models were used to estimate genetic parameters.

Results

Narrow-sense heritability estimates were 0.13?0.22 in growth and 0.03?0.49 in wood traits, indicating low to moderate levels of additive genetic control. Genetic correlations were mostly positively significant for growth with basic density and cellulose content but negatively significant with hemi-cellulose and lignin contents, being favourablefavorable for pulpwood breeding purpose. Type-B correlations between sites were significant for all the traits except diameter and lignin content.

Conclusion

Hybrid superiority warrants the breeding efforts. An appropriate breeding strategy should be able to capture both additive and non-additive genetic effects.

     

Variation in pinewood nematode susceptibility among <Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait. provenances from the Iberian Peninsula and France

Key message

Pinus pinaster Ait. susceptibility to pinewood nematode significantly differed among provenances, and the two Atlantic provenances of the Iberian Peninsula being the most affected. However, significant provenance × environment interaction was found. Provenance susceptibility was related to basal diameter, number of branches and oleoresin flow, and some climatic parameters.

Context

The pinewood nematode Bursaphelenchus xylophilus, native to North America, is an important pest affecting pine forests throughout Eurasia. In Europe, it has been detected in Portugal and Spain and is primarily associated with Pinus pinaster, an important Mediterranean tree species.

Aims

We have investigated the differences in susceptibility among several P. pinaster provenances in the Iberian Peninsula and France, as well as their relationship to certain growth traits and physiological parameters.

Methods

Three independent inoculation tests were performed on 3 to 4-year-old trees, followed by assessment of growth traits and physiological variables, along with time course destructive sampling for nematode quantification.

Results

The results showed significant differences among provenances for almost all growth traits, wilting, and mortality, though a significant provenance × environment interaction was also detected. Two Atlantic provenances, Noroeste-Litoral and Leiria, displayed the largest susceptibility to pinewood nematode. Changes in susceptibility to B. xylophilus between experiments were influenced by temperature and seasonality. Autumn precipitation and mean maximum temperature during summer at the original provenance sites could be related to provenance susceptibility.

Conclusion

Noroeste-Litoral and Leiria were the most disease-affected provenances. This study emphasizes the need for further research on how tree growth stage influences susceptibility and on the possibility of cross-breeding among provenances.

     

<Emphasis Type="Italic">Quercus suber</Emphasis> forest and <Emphasis Type="Italic">Pinus</Emphasis> plantations show different post-fire resilience in Mediterranean north-western Africa

Key message

In the African rim of the Western Mediterranean Basin, cork oak forests and pine plantations coexist. Under similar fire regimes, cork oak forest is more resilient in terms of habitat structure (canopy, understory, and complexity of vegetation strata) than pine plantation. By contrast, both woodland types show similar resilience in plant species composition. Resilience in habitat structure varies between the two woodland types because of the resprouting and seeding strategies of cork oak and pine species, respectively. These differences can be relevant for the conservation of biodiversity of forested ecosystems in a future scenario of increased fire frequency and scale in the Mediterranean basin.

Context

Wildfires have major impacts on ecosystems globally. In fire-prone regions, plant species have developed adaptive traits (resprouting and seeding) to survive and persist due to long evolutionary coexistence with fire. In the African rim of the Western Mediterranean Basin, cork oak forest and pine plantation are the most frequently burnt woodlands. Both species have different strategies to respond fire: cork oak is a resprouter while pines are mostly seeders.

Aims

We have examined the hypothesis that pine plantations are less resilient in habitat structure (canopy, understory, diversity of vegetation strata) and plant composition than cork oak woodlands.

Methods

The habitat structure and plant species composition were measured in 30 burnt and 30 unburnt 700-m transects at 12 burnt sites from north-western Africa, where the two forest types can coexist. Habitat structure and plant species composition were compared between burnt and unburnt transects from cork oak and pine plantation woodlands with generalized linear mixed models and general linear models.

Results

The results showed significant interaction effect of fire and forest type, since cork oak forest was more resilient to fire than was pine plantation in habitat structure. By contrast, both forest types were resilient to fire in the composition of the plant communities, i.e., plant composition prior to fire did not change afterwards.

Conclusion

The higher structural resilience of cork oak forest compared to pine plantation is related to the resprouting and seeding strategies, respectively, of the dominant tree species. Differences in the responses to fire need to be considered in conservation planning for the maintenance of the Mediterranean biodiversity in a future scenario of changes in fire regime.

     

The relative importance of soil properties and regional climate as drivers of productivity in southern Patagonia’s <Emphasis Type="Italic">Nothofagus antarctica</Emphasis> forests

Key message

Soil texture and temperature-related variables were the variables that most contributed to Nothofagus antarctica forest height in southern Patagonia. This information may be useful for improving forest management, for instance related to the establishment of silvopastoral systems or selection of suitable sites for forest reforestation in southern Patagonia.

Context

Changes in forest productivity result from a combination of climate, topography, and soil properties.

Aims

The relative importance of edaphic and climatic variables as drivers of productivity in Nothofagus antarctica forests of southern Patagonia, Argentina, was evaluated.

Methods

A total of 48 mature stands of N. antarctica were selected. For each study site, we measured the height of three mature dominant trees, as an indicator of productivity. Seven soil, five spatial, and 19 climatic features were determined and related to forest productivity. Through partial least squares regression analyses, we obtained a model that was an effective predictor of height of mature dominant trees in the regional data set presented here.

Results

The four variables that most contributed to the predictive power of the model were altitude, temperature annual range, soil texture, and temperature seasonality.

Conclusion

The information gathered in this study suggested that the incidence of the soil and temperature-related variables on the height of dominant trees, at the regionally evaluated scale, was higher than the effect of water-related variables.

     

Beneath the mistletoe: parasitized trees host a more diverse herbaceous vegetation and are more visited by rabbits

? Key message

Parasitism by mistletoe increases the cover and diversity of herbaceous vegetation under the host tree and attracts the activity of rabbits in comparison to control trees. Thus, the effects on forest community go beyond the parasitized tree.

? Context

Mistletoes are a diverse group of aerial hemiparasitic plants and are considered keystone species in forest ecosystems around the world. They produce nutrient-enriched litter, which exerts a substantial effect on soil-nutrient concentration, and the enriched nutrient patch alters the vegetation at the site as well as the associated fauna.

? Aims

Our goal is to ascertain whether mistletoe (Viscum album) parasitism of pine forest of a Mediterranean mountain favors herbaceous vegetation and attracts mammalian herbivores.

? Methods

We recorded in Sierra de Baza (SE Spain) the composition of the herbaceous vegetation under pines with and without mistletoe parasitism, and estimated the rabbit activity at the same sites by collecting their excrements.

? Results

An effect on herbaceous vegetation, especially in grasses belonging to the family Poaceae, was reflected in a notable increase in soil cover, species richness, and species diversity beneath parasitized pines with respect to unparasitized ones. As a consequence, parasitized pines attract the activity of rabbits, as shown by a fivefold quantity of excrement with respect to control ones.

? Conclusion

Parasitism by mistletoe, by creating patches of greater nutrient availability under the host canopy, extends its effects beyond the host tree to other members of the forest community, such as herbaceous plants and associated herbivorous animals, which in turn contribute to environmental heterogeneity with their activity.

     

Natural conifer regeneration patterns in temperate forests across the Inland Northwest,USA

Key message

Natural regeneration patterns of conifer species were studied. Seedling regeneration follows patterns responding to stand structure and site condition factors along shade and drought tolerance gradients. Our findings can assist in adaptive forest management for maintaining sustainable regeneration and plant biodiversity.

Context

Seedling regeneration can vary with stand factors of overstory trees and understory non-tree vegetation and site conditions.

Aims

Natural seedling regeneration patterns of coniferous species were investigated using Forest Inventory and Analysis (FIA) data of 10 common species across the Inland Northwest, USA.

Methods

Zero-inflated negative binomial models were developed to understand the responses of natural regeneration to stand factors and site conditions.

Results

Seedling occurrence varies along shade and drought tolerance gradients responding to stand structure and site conditions. Two moderate shade-tolerant species of different drought tolerance contributed as a transition. Strong response patterns were revealed for seedling density, in which seedling density was improved with the presence of conspecific trees while limited by competition, especially from the understory vegetation layer.

Conclusion

Overstory structure and understory vegetation could improve or hinder natural regeneration of coniferous tree species given different shade tolerance and site conditions. Our findings can be effectively implemented in adaptive forest management for maintaining sustainable regeneration of specific conifers in broad temperate mixed forests.

     

Local-scale diversity and adaptation along elevational gradients assessed by reciprocal transplant experiments: lack of local adaptation in silver fir populations

Key message

Silver fir transplantations along elevational gradients revealed a high diversity but no local adaptation. Populations displayed similar abilities to adapt to new environments including those due to climate change.

Context

The sustainability of forest stands depends on the ability of species and communities to adapt by combining plasticity and genetic evolution. Although well-documented at the scale of species distributions, the variability and adaptation of forest tree genetic resources are less understood at the short-distance scale.

Aims

We analysed the effects of genetic and environmental factors on the local-scale phenotypic diversity of traits related to adaptation in Abies alba. We also sought to highlight local adaptation, revealing past selection.

Methods

Six adaptive traits related to growth, phenology and survival were measured on seedlings from 57 half-sib families collected from 15 provenances and planted in a nine-site reciprocal transplant experiment distributed along three elevational gradients.

Results

Most part of the phenotypic variability was attributed to the environmental factors. Provenances and families had also significant effects on seedling performances, but the genetic variability was mostly attributed to the families. No pattern of local adaptation was observed, except in the presence of lateral branches in the driest garden.

Conclusion

The absence of local adaptation suggests a similar ability of all silver fir populations to develop in the various environments. This result provides favourable conditions for coping with the ongoing climate change without exotic resources enrichment.