Revisiting the use of soil water budget assessment to predict site productivity of sessile oak (<Emphasis Type="Italic">Quercus petraea</Emphasis> Liebl.) in the perspective of climate change

Climate change is expected to increase the frequency and severity of drought events over the next few decades in Western Europe. Consequently, there is a crucial need for an efficient tool for field water budget diagnosis to enable forest managers to estimate tree survival and productivity. Robust estimates of water budget using soil and topography were compared for their ability to predict site yield of Quercus petraea (Matt.) Liebl. Site yield was estimated using site index at 100 years. Ninety-nine even-aged high-forest stands located in northern France were investigated. Water budget was estimated by topographic position and soil water capacity (SWC) calculated for different soil depths down to a maximum 2.0 m. (1) Site index predictions improved when calculating SWC for increasing depths until 1.0 m. (2) Site index predictions did not improve when calculating SWC at depths below 1.0 m, thus confirming that the water contained in deep soil layers is not used for tree growth but probably contributes to tree fitness or survival by maintaining a not too negative in-tree water potential. (3) Topographic position was also a predictor of site index in addition to SWC. Practical recommendations for estimating extractable soil water content are given.     

Fourier transform infrared analyses of bog and modern oak wood (<Emphasis Type="Italic">Quercus petraea</Emphasis>) extractives

Bog and modern oak wood extractives were studied to see the impact of bog conditions upon the nature of extractives using Fourier transform infrared analyses. Except for the ethanol-toluene extracts of modern oak acidic components predominate in the bogwood, ester forms prevail in modern or non-bog wood. In both cases, toluene extractives were mostly fatty acids and their esters, whilst the extracts recovered by the remaining solvents were mainly polar aromatic substances of cyclic nature. Tests revealed these components to be mainly tannins and low molecular polysaccharides.     

Agrobacterium-mediated transformation of cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) somatic embryos

A simple method is presented for the unreported genetic transformation of cork oak (Quercus suber L.). Pro-embryo masses (PEMs) were induced on immature zygotic embryos applied to medium supplemented with 2.3 M 2,4-dichlorophenoxyacetic acid. The established PEMs were inoculated with Agrobacterium tumefaciens LBA4404/p35S GUS INT/pCAMBIA 1301 strain. Transformants were selected on hygromycin (HYG) 94 M-supplemented medium. Viable embryos constituted 13% of those selected on HYG during 4 months. Expression of -glucuronidase at 4 months following co-cultivation confirmed transformation in 5.8% embryos selected on HYG. This method forms a basis for genetic transformation of cork oak somatic embryos.     

Spatial pattern of beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) and oak (<Emphasis Type="Italic">Quercus pubescens</Emphasis> Mill.) seedlings in natural pine (<Emphasis Type="Italic">Pinus sylvestris</Emphasis> L.) woodlands

Spatial pattern of recruitment is an important factor influencing population dynamics of plant communities. The spatial pattern is determined by seed dispersal and by the spatial variability of germination and initial survival. In the process of forest expansion following farmland abandonment, mid- and late-successional species are often dispersed in pioneer forests by birds. This could result in an aggregated spatial pattern of seeds that could influence the dynamics of these species in mixed pioneer forests. In the sub-Mediterranean area, mid- and late-successional species such as Quercus pubescens (downy oak) and Fagus sylvatica (European beech) are expected to replace pioneer Pinus species. Using a point sampling method we demonstrated that beech and oak seedlings (height <2 m) have a clumped distribution in the understorey of pine. This could result from an aggregated dispersal by jays (dispersal effect) or from preferential recruitment in particular habitats (habitat effect). To test these hypotheses we proposed a statistical analysis of spatial patterns of regeneration of beech and oak. Ground cover variables (i.e. cover by rock outcrops, herbs, box shrubs, mosses or pine) did not differ significantly around seedlings as compared with random sample plots. Likewise, clumped seedlings had growth similar to isolated seedlings, thus refuting the hypothesis of preferential location in the most favourable microsites. Aggregated dispersal seems to be involved in the process of regeneration. Since beech and oak seedlings have contrasting ecological demands, we discuss the implication of this pattern for the replacement dynamics of pine by these species.     

Flammability of some companion species in cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) forests

Key message

The high flammability of some companion species in Quercus suber forests, estimated in laboratory tests, could potentially generate an increase in fire vulnerability and in fire risk.

Context

Recurrent wildfire is one of the main causes of forest degradation, especially in the Mediterranean region. Increased fire frequency and severity due to global change could reduce the natural resilience of cork oak to wildfire in the future. Hence, it is important to evaluate the flammability of companion species in cork oak forests in the particularly dry bioclimatic conditions of North Africa.

Aims

This study aimed to assess and compare flammability parameters at laboratory scale among ten companion frequent species in cork oak forests.

Methods

Fuel samples were collected in a cork oak (Quercus suber L) forest in the southern part of the mountains of Tlemcen (Western Algeria). A series of flammability tests were carried out using a Mass Loss Calorimeter device (FTT ®). A cluster analysis to classify flammability of the selected species was conducted using the K-means algorithm.

Results

The results revealed differences in the four flammability parameters (ignitability, sustainability, combustibility and consumability), in both fresh and dried fine fuel samples from Quercus suber, Pinus halepensis, Quercus ilex, Quercus faginea, Erica arborea, Arbutus unedo, Pistacia lentiscus, Calicotome spinosa, Juniperus oxycedrus and Tetraclinis articulata. Application of the K-means clustering algorithm showed that C. spinosa, T. articulata, J. oxycedrus and P. halepensis are highly flammable because of their high combustibility and sustainability.

Conclusion

The findings identify species that could potentially increase the vulnerability of cork oak forests to forest fires.

     

Decay resistance against <Emphasis Type="Italic">Coriolus versicolor</Emphasis> in Sessile oak (<Emphasis Type="Italic"> Quercus petraea </Emphasis>Liebl.): analysis of the between-tree variability and correlations with extractives,tree growth and other basic wood properties

Abstract Weight loss due to fungus Coriolus versicolor has been measured on 614 samples according to the NF EN 113 norm. Up to eight samples were cut at breast height (two opposite radii×four radial positions in heartwood) from 82 mature sessile oaks ( Quercus petraea Liebl.) originating from contrasting regions, silvicultural schedules and site qualities in France. The following points are addressed in the paper: (i) contribution to the total variability for weight loss of the effects tree, position in the tree, as well as their interaction; (ii) percentage of wood samples and trees in each of the five classes of natural durability defined by the norm NF EN 350–2; (iii) test of the effects of region, silvicultural schedule and site quality on weight loss and evaluating their contribution to the total variation; and (iv) correlations at tree level between weight loss and several traits related to tree growth and basic wood properties (density, swelling, grain angle, multiseriate wood rays characteristics, extractives content). The results are discussed with a view to aid the forest manager as well as the log/wood user to take advantage of the high level of between-tree variability observed as natural durability against C. versicolor.     

Variation in the date of budburst in <Emphasis Type="Italic">Quercus robur</Emphasis> and <Emphasis Type="Italic">Q. petraea</Emphasis> across a range of provenances grown in Southern England

The widely observed advance in spring budburst across a range of temperate forest species due to climatic warming has received considerable attention. This change in forest phenology has important implications for the choice of species and provenances currently being planted, which need to be suited to both current and future climatic conditions. Using a provenance trial in the south of England, this study assessed variation in the timing of budburst across 23 different European provenances of oak (Quercus robur L. and Q. petraea (Matt.) Liebl.) over 8 years of observations. The order in which the different provenances reached budburst was related to provenance source latitude: the southern provenances were always earlier than those from more northerly latitudes. The statistical technique partial least squares regression was used to identify critical periods of both chilling and warming. A General Linear Model and three-dimensional temperature response surfaces were used to analyse the temporal trends in budburst. There was a negative correlation between the date of budburst and mean daily air temperature in both the chilling and warming periods for all provenances, which was statistically significant for a majority. Spring warming had a larger effect on budburst than winter chilling with a mean spring temperature-driven advance of 3.61 days/°C (standard error = 0.17 days/°C) and mean winter period temperature-driven advance of 0.99 days/°C (standard error = 0.17 days/°C). Surprisingly, there was no statistically significant interaction between mean air temperatures during the chilling and warming phases on the date of budburst.     

Base-age invariant cork growth model for Spanish cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) forests

A cork growth model for Spanish cork oak forests was developed using data from 432 cork samples. Ten dynamic equations derived from the generalised algebraic difference approach (GADA) were considered for analysis, and both numerical and graphical methods were used to compare alternative models. All of the equations are base-age invariant and directly estimate accumulated cork thickness in complete years at any moment of the cork rotation. The fittings were done using the nested iterative method of the stochastic regression approach. The GADA formulation derived by Krumland and Eng (2005) from the Richards model by considering a ₁ and a ₃ as related to site productivity was finally selected. The cork growth model developed in this study allows the total accumulated cork thickness in complete years to be estimated in the fourth year of cork rotation with close to 80% reliability for any debarking period, increasing to nearly 90% from the eighth year onwards.     

Variation components in leaf morphology of recruits of two hybridising oaks [<Emphasis Type="Italic">Q. petraea</Emphasis> (Matt.) Liebl. and <Emphasis Type="Italic">Q. pyrenaica</Emphasis> Willd.] at small spatial scale

Leaf morphological variation was examined in recruits of two hybridising oaks in a small sympatric area from Central Spain. Nuclear microsatellites were used to identify hybrids and assess the parental lineage. By Bayesian clustering analysis, 5% of hybrids were found. Principal component analysis was used to reduce 15 morphometric variables to four components associated with leaf size, lobation/pubescence and overall shape of the leaf. The percentage of variance due to genetic factors was evaluated through nested analysis of variance. As much as 70% of variance component was due to the factor “species” for lobation/pubescence, suggesting high adaptive value for these traits, possibly related to ecological constraints of the species. The genetic component of variance for leaf size and overall shape of the leaf was below 33%. Age and height of the recruits did not correlate with sun-leaf morphology. Competition indexes and diameter of the recruits showed slight, although significant, correlations with leaf size and lobation/pubescence components, pointing to some trade-offs between competition for light and leaf morphology of Q. petraea and Q. pyrenaica recruits.     

Summer field performance of <Emphasis Type="Italic">Quercus petraea</Emphasis> (Matt.) Liebl and <Emphasis Type="Italic">Quercus pyrenaica</Emphasis> Willd seedlings,planted in three sites with contrasting canopy cover

In 2000, one-year-old seedlings of pyrenean oak (Quercus pyrenaica Willd.) and sessile oak (Quercus petraea [Matt.] Liebl) were planted in a thinned and an unthinned plot in a pinewood (Pinus sylvestris), and in a nearby clearing. In summer 2002 and 2003, water relations and gas exchange parameters were measured to address the impact of drought on the seedlings. Chlorophyll a fluorescence was also measured to explore leaf photochemistry and a possible non-stomatal limitation to photosynthesis (A). Reduction in stomatal conductance (g) in response to the decrease of predawn water potential (Ψ_pd) resulted the main cause affecting net carbon uptake. Water potential at midday (Ψ_md) was similar in both species but Quercus petraea was more sensitive to soil water deployment occurred along summer, showing slightly lower Ψ_pd because worse recover of water potential during night. Rate of photosynthesis was higher in Q.␣pyrenaica probably in relation to its greater leaf mass per area (LMA) and nitrogen content per leaf area (N_a). Mortality was highest in the clearing and lowest in the thinned pinewood. Throughout the summer, soil moisture was higher in the thinned area, possibly because of the reduction in tree transpiring surface and interception of rainfall. Accordingly, Ψ_pd of both species was higher in the thinned site.     

Site quality of pedunculate oak (<Emphasis Type="Italic">Quercus robur</Emphasis> L.) stands in Galicia (northwest Spain)

Accurate estimates of forest productivity are required for sustainable forest management. Height of dominant and codominant trees at a reference age is often used as a measure of site productivity. Eight algebraic difference equations based on the models proposed by Sloboda, Bertalanffy-Richards, Korf, Hossfeld, and McDill-Amateis were tested on the transformed, longitudinal data structure that considers all possible growth intervals. Autocorrelation was modelled by expanding the error term as an autoregressive process according to this data structure. Generalized nonlinear least squares methods were used for model fitting. Several numerical and graphic analyses were used to compare the different candidate models. The relative error in dominant height prediction was used to select 60 years as the best reference age. An algebraic difference equation based on the model proposed by Korf provided the best compromise between biological and statistical aspects and produced the most adequate site index curves. This model is therefore recommended for height growth prediction and site classification of pedunculate oak stands in Galicia. The model is polymorphic and base-age invariant, having only one asymptote. Predictions of height for age intervals between t₁ and t₂ of more than 15 years should be considered with caution because of the associated critical error.     

Leaf-level responses to light in two co-occurring <Emphasis Type="Italic">Quercus</Emphasis> (<Emphasis Type="Italic">Quercus ilex</Emphasis> and <Emphasis Type="Italic">Quercus suber</Emphasis>): leaf structure,chemical composition and photosynthesis

We studied morphological, biochemical and physiological leaf acclimation to incident Photon-Photosynthetic-Flux-Density (PPFD) in Quercus ilex (holm oak) and Quercus suber (cork oak) at Mediterranean evergreen oak woodlands of southern Portugal. Specific leaf area (SLA) decreased exponentially with increasing PPFD in both species. Q. ilex had lower SLA values than Q. suber. Leaf nitrogen, cellulose and lignin concentration (leaf area-based) scaled positively with PPFD. Maximum rate of carboxylation (V_cmax), capacity for maximum photosynthetic electron transport (J_max), rate of triose-P utilization (V_TPU) and the rate of nonphotorespiratory light respiration (Rd) were also positively correlated with PPFD in both Quercus species, when expressed in leaf area but not on leaf mass basis. Q suber showed to have higher photosynthetic potential (V_cmax, J_max^m and V_TPU^m) and a higher nitrogen efficient nitrogen use than Q.ilex. Leaf chlorophyll concentration increased with decreasing PPFD, improving apparent quantum use efficiency (Φ) in both Quercus species. We concluded that, in Q.ilex and Q.suber, leaf structural plasticity is a stronger determinant for leaf acclimation to PPFD than biochemical and physiological plasticity.     

Nutrients return from leaves and litterfall in a mediterranean cork oak (<Emphasis Type="Italic">Quercus suber</Emphasis> L.) forest in southwestern Spain

The knowledge of the cycle of nutrients is fundamental for the correct comprehension of the tree–soil relationship and for an adequate forest management. In order to analyse the nutrients return from leaves and litterfall in a Mediterranean cork oak forest in southwestern Spain, 12 trees were randomly selected and litterfall collected for 2 years. Samples were taken monthly and separated in different fractions (leaves, twigs, catkins, acorns and miscellaneous), then leaves nutrients were analyzed. Simultaneously, we analyzed the nutrient content of living leaves from the same trees in each season during 1 year. The analyzed nutrients were C, N, P, K, Ca, Mg, Fe, Mn, S, Cu, Zn and Mo. Annual patterns of each nutrient in fallen leaves were characterized and compared with seasonal values of these nutrients in living leaves. Leaves fall has two annual maximum, first and most important in spring around April coinciding with renewal of foliar cover and second around October. Main concentration patterns of N, P and K are related with phenological patterns, in consequence minimum concentration in leaves fall were obtained in periods of growing and maximum litterfall. Concentrations of Ca, Fe and Mn increase with the age of the leaves and maximum concentrations were obtained before periods of maximum litterfall while concentrations of Cu, Mo and Mg stay stable. Seasonal analysis of nutrients in living leaves collected from the same trees in four different periods of the year allowed to corroborate the patterns of leaves fall and the probable osmotic function of K.     

Influence of water-stress acclimation and <Emphasis Type="Italic">Tuber melanosporum</Emphasis> mycorrhization on <Emphasis Type="Italic">Quercus ilex</Emphasis> seedlings

Mycorrhizal and non-mycorrhizal holm oak (Quercus ilex L.) seedlings inoculated with black truffle (Tuber melanosporum) were grown under nursery conditions and subjected to drought hardening for 4 months in autumn and winter followed by irrigation for 10 days. Leaf water potential and stomatal conductance were monitored during the 4 months of drought. When the test was completed (March), measurements were made for each treatment (inoculated or non-inoculated), and watering regime (watered and water-stressed). Pressure–volume curves, osmotic potential at full turgor, osmotic potential at zero turgor and the tissue modulus of elasticity near full turgor were calculated. Mycorrhizal colonization and growth, and the content of the main mineral nutrients N, P, K, Ca and Mg were measured. Water stress affected plant growth, caused an elastic adjustment of the plant tissues, and decreased the P and K content, and inoculation improved the nitrogen content. Drought acclimation apparently achieved the goal of improving the drought tolerance of holm oak seedlings, without depressing ectomycorrhizal root colonization by T. melanosporum. José Antonio Rodríguez Barreal—Deceased     

Plant water relations and edaphoclimatic conditions affecting acorn production in a holm oak (<Emphasis Type="Italic">Quercus ilex</Emphasis> L. ssp. <Emphasis Type="Italic">ballota</Emphasis>) open woodland

Acorn production patterns and the annual evolution of water relations parameters of Quercus ilex ssp. ballota (Desf.) Samp. in a dehesa (an open woodland forest) subject to various soil treatments (ploughing, ploughing + sowing, control) were studied in southwest Spain from June 2006 to December 2008. The effects of soil water holding capacity and effective soil depth on soil and plant water status and acorn production were also investigated. Water parameters showed significant differences between the ploughing treatment and the control, and there were also significant temporal differences. Xylem water potential ranged from −3.4 ± 0.1 to −0.7 ± 0.2 MPa, and cuticular transpiration was 62.4–192.9 mmol H₂O kg⁻¹ s⁻¹. Acorn production did not differ significantly according to soil treatment, and showed large intra-specific variability. Individual values ranged from 0 to 1,220 g m⁻² (fresh weight). Positive relationships were found between xylem water potential, cuticular transpiration and relative water content measured at midsummer, and acorn production during the three studied years. These results suggest that climatic conditions and soil water availability have a strong influence on plant water status, and therefore on acorn development during summer. The results also reflect the ability of this species to adapt to the Mediterranean climate by preserving water during dry periods, which to a large extent can be attributed to stomatal closure at high relative water content levels, and low cuticular transpiration during these periods.     

Effect of moisture on physical parameters of timber from Turkey oak (<Emphasis Type="Italic">Quercus cerris</Emphasis> L.) coppice in Central Italy

This study aims to investigate wood density at different levels of moisture, basic density and shrinkage of timber from Turkey oak (Quercus cerris L.) coppice forests growing in Central Italy. We also studied the variability in density in the trees within and among sites. Density shows no significant statistical differences in the tested population. A higher variability in the shrinkage than in the density was found. Wood moisture is referred to as dry mass and fresh mass, which is related to many performance characteristics of wood, i.e., energy production. Trends in moisture and water content were studied because these physical parameters play an important role in the specific area of firewood which requires an accurate estimation of mass, volume and energy content. This work is a contribution to improve xylo-energy estimates of small and medium forestry issues.     

<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.

     

Successful <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of <Emphasis Type="Italic">Populus tomentosa</Emphasis> with apple <Emphasis Type="Italic">SPDS</Emphasis> gene

The problem of salinized soils has become one of the most serious constraints to agricultural and forest productivity. With the purpose of enhancing salt stress tolerance of Populus tomentosa, we transformed this tree species with spermidine synthase （SPDS） genes derived from an apple by an Agrobacterium-mediated method. Four transgenic clones were confu＇med by PCR and Southern blot analysis. As well, the expression of introduced SPDS genes was analyzed by real-time quantitative PCR.