What are the consequences of being a downy oak (quercus pubescens) or a holm oak (Q. ilex) for breeding blue tits (Parus caeruleus)?

By comparison with deciduous oaks, the lower yearly production of new leaves in sclerophyllous oaks is hypothesized to have several consequences on animal communities. In particular, the production of arthropod communities that feed upon the leaves should be lower in sclerophyllous than in deciduous oaks, this causing changes in breeding patterns and the demographic balance in insectivorous birds. Studies in both deciduous and sclerophyllous habitats in southern France have shown that: 1) the spring development of new leaves occurs later and more slowly in sclerophyllous than in deciduous oaks, 2) the biomass of caterpillars is much lower in sclerophyllous oak forests, and 3) there is a large variation in life history traits of the Blue Tit depending in which type of habitat they breed. Laying date occurs later and clutch size is lower in sclerophyllous habitats than in deciduous habitats. The evolution of life history traits is discussed according to whether poor sclerophyllous habitats are isolated (e.g. on Corsica) or are parts of landscapes including both habitat types.     

The effect of drought stress on heterozygosity–fitness correlations in pedunculate oak (Quercus robur)

Background and Aims

The interaction between forest fragmentation and predicted climate change may pose a serious threat to tree populations. In small and spatially isolated forest fragments, increased homozygosity may directly affect individual tree fitness through the expression of deleterious alleles. Climate change-induced drought stress may exacerbate these detrimental genetic consequences of forest fragmentation, as the fitness response to low levels of individual heterozygosity is generally thought to be stronger under environmental stress than under optimal conditions.

Methods

To test this hypothesis, a greenhouse experiment was performed in which various transpiration and growth traits of 6-month-old seedlings of Quercus robur differing in multilocus heterozygosity (MLH) were recorded for 3 months under a well-watered and a drought stress treatment. Heterozygosity–fitness correlations (HFC) were examined by correlating the recorded traits of individual seedlings to their MLH and by studying their response to drought stress.

Key Results

Weak, but significant, effects of MLH on several fitness traits were obtained, which were stronger for transpiration variables than for the recorded growth traits. High atmospheric stress (measured as vapour pressure deficit) influenced the strength of the HFCs of the transpiration variables, whereas only a limited effect of the irrigation treatment on the HFCs was observed.

Conclusions

Under ongoing climate change, increased atmospheric stress in the future may strengthen the negative fitness responses of trees to low MLH. This indicates the necessity to maximize individual multilocus heterozygosity in forest tree breeding programmes.     

Morphological and ecophysiological variation of the hybrid oak Quercus subpyrenaica (Q. faginea × Q. pubescens)

Natural hybridization is common among oaks. We studied the variability of morphological and ecophysiological variables in the hybrid Quercus subpyrenaica and its assumed parental species Q. faginea and Q. pubescens, which co-occur in NE Spain. To assess the fitness of these taxa we studied several ecophysiological variables (hydraulic conductivity, K_h; hydraulic specific conductivity, K_s; leaf specific conductivity, LSC; water potential corresponding to a 50% loss of conductivity, PLC₅₀; efficiency of light absorption, E_a). We performed a correspondence analysis (CA) to ordinate seedlings, grown under homogeneous environmental conditions, according to their plant and leaf morphology. The CA axis 1 synthesized intra-taxon variability, while the CA axis 2 summarized inter-taxa variability. Q. subpyrenaica showed a wide spectrum of forms, but they were overall closer to those of Q. faginea. We defined three phenotypes within the hybrid based on morphology, which were: (i) the robur group (Qs-r; auriculate leaf base, rounded lobe apex); (ii) Q. pubescens (Qs-p; rounded leaf base, acute lobe apex); and (iii) Q. faginea (Qs-f; acute leaf base, acute-spiny lobe apex). The mean values of K_s and PLC₅₀ arranged the hybrid groups in the same order as the ordination based on leaf morphology. The Qs-r group showed the highest values of K_s and PLC₅₀, while the Qs-f group showed the lowest. Both morphologically and ecophysiologically, the hybrids showed a wide range of values, which spanned and even exceeded the variation of parental taxa.     

A 781-year oak tree-ring chronology for the Middle Ages archaeological dating in Maramureș (Eastern Europe)

From 1997 to the present, a sustained project in the Maramureș region in Romania was completed with the construction of a 781-year oak tree-ring chronology. A total of 395 samples from living trees and 429 from archaeological wood were analysed with dendrochronological methods. The study aimed to provide the scientific community with a new oak chronology that could be applied in dendroarchaeology, dendroclimatology and dendroecology studies and also for interpreting past socio-economic events. Furthermore, we studied the number of sapwood rings and the growth pattern for different time periods. The chronology covered the continuous period of A.D. 1236‒2016. From the 824 samples collected, we separated 271 tree-ring series into a new chronology (A.D. 1406–2016), which fulfilled all the criteria necessary to reconstruct past climate and environmental changes. The resulting new tree-ring chronology indicated robust signal series intercorrelation (r = 0.55) and an average mean sensitivity of 0.21. Based on an analysis of the sapwood, we recommend estimating a number between 8 and 32 rings to the date of final ring for 95% confidence range of mean on the for felling in the Maramureș region. Additionally, we observed that the number of sapwood rings was not correlated with altitude or oak tree species.     

Conservation and fruit biology of Sichou oak (Quercus sichourensis,Fagaceae) – A critically endangered species in China

Several conservation programs have been started for the critically endangered Sichou oak (Quercus sichourensis) since 2007. These programs include detailed field investigations, seedling cultivation and research on the fruit biology of the species. In this study, we first report on the five mature individual trees found in our 9-year field investigation. Thus far, a total of 10 mature individuals have been recorded. All Q. sichourensis trees are healthy and most produce healthy acorns. Acorns of Q. sichourensis are large with dry masses of 8.0–14.0 g. These acorns had high moisture contents at collection and died shortly after (7–28 d) when dried with silica gel. Characteristics of Q. sichourensis acorns varied between populations. Compared with the acorns from Funing, the acorns collected from Ceheng were bigger, more viable (germination percentage was up to 96%), less sensitive to desiccation, and germinated faster. Q. sichourensis occurs in regions with a distinct 5–6 month dry season. Habitat degradation is largely responsible for the rareness of Quercus sichorensis, but desiccation sensitivity of the acorns may also limit the regeneration of the species and potentially lead to its continued rareness. As a species with extremely small populations (PSESP), Q. sichourensis is facing high risk of extinction and should be defined as a Critically Endangered species in the global IUCN Red List.     

Phytosociological typology and phytoindicator value of young oak and larch forest communities near Pinczów (southern Poland)

Oak (Quercus petraea Liebl.) and larch (Larix decidua Mill.) forest plantations of the study area Mlodzawy in Poland were analysed. Changes in the syntaxonomic composition and of Ellenberg's indices (light, continentality, moisture, reaction and nitrogen index) were determinated. The results obtained mostly conform to the assumption that the herb layer of both plantations becomes, gradually with tree growth, more similar to each other and to that of mature oak-hornbeam forests. Such statement is justified by: an increase in the share of species common to both plantation types, a significant increase in the number and cover of the Querco-Fagetea character-species, accompanied by a decrease in the number and cover of other character-species, a general decrease in the share of species with extreme climatic and edaphic requirements, accompanied by a gradual increase in the share of number and cover of species with average demands. From the studies it may be concluded that the developmental mechanisms w which determine the direction and trends of changes in the herb layer are mainly common to both plantation types, whereas tree stand species, in spite of different habit, ecological demands, and effect on soil properties, have only slight modification influence.     

Impacts of the exotic,nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen-cycling in a pine–oak ecosystem

We investigated the influence of the exotic nitrogen-fixing black locust (Robinia pseudoacacia) on nitrogen cycling in a pitch pine (Pinus rigida) −scrub oak (Quercus ilicifolia, Q. prinoides) ecosystem. Within paired pine-oak and adjacent black locust stands that were the result of a 20-35 year-old invasion, we evaluated soil nutrient contents, soil nitrogen transformation rates, and annual litterfall biomass and nitrogen concentrations. In the A horizon, black locust soils had 1.3-3.2 times greater nitrogen concentration relative to soils within pine-oak stands. Black locust soils also had elevated levels of P and Ca, net nitrification rates and total net N-mineralization rates. Net nitrification rates were 25-120 times greater in black locust than in pine-oak stands. Elevated net N-mineralization rates in black locust stands were associated with an abundance of high nitrogen, low lignin leaf litter, with 86 kg N ha^–1 yr^–1 in leaf litter returned compared with 19 kg N ha^–1 yr^–1 in pine-oak stands. This difference resulted from a two-fold greater litterfall mass combined with increased litter nitrogen concentration in black locust stands (1.1% and 2.6% N for scrub oak and black locust litter, respectively). Thus, black locust supplements soil nitrogen pools, increases nitrogen return in litterfall, and enhances soil nitrogen mineralization rates when it invades nutrient poor, pine-oak ecosystems. This revised version was published online in June 2006 with corrections to the Cover Date.     

Is primary production in holm oak forests nutrient limited?

Correlations between primary production and patterns of nutrient use and nutrient availability were investigated in 18 plots in closed holm oak (Quercus ilex L.) stands in the Montseny mountains (NE Spain), searching for evidence of nutrient limitation on primary production. The plots spanned a range of altitudes and slope aspects within a catchment. Nutrients considered were nitrogen (N), phosphorus (P), potassium (K) and magnesium (Mg) in plant samples, and the above plus calcium (Ca) and sodium (Na) in the soil. Primary production was found by summing the annual aboveground biomass increment to the annual litterfall. Across plots, primary production was correlated with the annual return of nutrients in litterfall, but this relationship probably arose from the common effects of the amount of litterfall on both primary production and nutrient return, and not from any nutrient limitation. Primary production was not significantly correlated with nutrient concentrations in mature leaves nor leaf litterfall, nor with absolute or relative foliar retranslocation of nutrients before leaf abscission, nor with the concentration and content (kg/ha) of total N, extractable P, and exchangeable K, Mg, Ca and Na in the upper mineral soil. We conclude that there is no correlational evidence that primary production is nutrient limited in this holm oak forest.     

Rodents as seed dispersers in a heath — oak wood succession

Summary In a Danish heathland invasion of oak shrub has taken place, the succession rate being approximately 300 m during the last 100 years. The colonisation has occurred in steps related to the delay time between seedling stage and fertility stage. Seedlings are often found in clusters originating from caches probably made by seed-eating rodents. Apodemus sylvaticus, A. flavicollis and Clethrionomys glareoles. These rodents reached autumn densities of 25–50 individuals per ha. Radioactive acorns were scatterhoarded by the rodents, which mainly deposited the acorns singly up to at least 34 m from the oak shrub (mean 15.3±8.2 m), and preferably under Empetrum nigrum mats in the walls of runways Seedlings originating from radioactive acorns were found next summer at distances of 4–37 m from the oak shrub. In early summer caches containing new seedlings had a mean size of 2.0±2.2 acorns, range 1–16; mean distance of seedlings to nearest crown projection was 24.0±23.6 m, range 1–137. Thus, rodent acorn dispersal can explain the observed succession rate of oaks into the heathland     

A preliminary reconstruction (A.D. 1635–2000) of spring precipitation using oak tree rings in the western Black Sea region of Turkey

Tree-ring data for Turkey are crucial to the understanding of the climatological effect of drought and rainfall from one era to the next. To this end, the present study reconstructed precipitation patterns in the western Black Sea region of Turkey. Tree-ring widths of oak trees were used to reconstruct March–June precipitation patterns for the years A.D. 1635–2000. According to the findings, during the past four centuries drought events in this region persisted for no more than 2 years, and extreme dry and wet events occurred generally in 1-year intervals. Historical records of droughts in Anatolia and neighboring countries corroborate the data furnished by tree-ring widths to indicate that major droughts and famine events occurred in 1725, 1757, 1887, 1890–1891, 1893–1894 and 1927–1928.     

Altitudinal variation in ant–aphid mutualism in nitrogen transfer of oak (<Emphasis Type="Italic">Quercus liaotungensis</Emphasis>)

Ant–plant relationship is a model for the study of the ecology and evolution of interspecific interactions. In direct ant–plant mutualism (i.e., plants providing food or nesting places for ants, and ants protecting the plants in return) ants provide nutrients to plants. However, whether a similar mechanism exists in indirect ant–plant mutualism (i.e., an ant–aphid–plant system) remains unknown. In this work, we used the ¹⁵N stable isotope method to study altitudinal variations in the roles of ants in the nutrient transfer of oak (Quercus liaotungensis). Our work shows that ants deliver nitrogen in indirect ant–plant interactions, and that the effect of nutrient transfer differed significantly with altitude. Ants’ trophic level at high altitudes was significantly lower than that at low altitudes, indicating that the degree of ant–aphid mutualism was greater at high altitudes, which may be beneficial in nitrogen transfer. Our work suggests that ant–aphid mutualism might be context dependent, such that it affects nutrient transfer in the food web, and that this context dependency is an important factor that influences altitudinal variation in nutrient transfer.     

Is forest certification targeting areas of high biodiversity in cork oak savannas?

Over the last four decades the world has been losing biodiversity at an alarming rate despite the increasing number of protected areas (PAs). Certified forest management may complement the role of PAs in protecting biodiversity. Forest certification aims to promote sustainable forest management and to maintain or enhance the conservation value of certified forests. The area of forest under certified forest management has grown quickly over the past decade. Forest Stewardship Council (FSC) certification, for example, currently covers 148 million hectares, i.e., 3.7 % of the world’s forests. In spite of such increase there is, however, a dearth of information on how forest certification is related to biodiversity. In this study we assessed if FSC certification is being applied in high biodiversity areas in cork oak savannas in Portugal by comparing biodiversity values of certified and non-certified areas for birds, reptiles and amphibians. We calculated the relative species richness and irreplaceability value for each group of species in certified and non-certified areas and compared them using randomization tests. The biodiversity value of certified areas was not significantly greater than that of non-certified areas. Since FSC certification is expanding quickly in cork oak savannas it is important to consider the biodiversity value of these areas during this process. Prioritizing areas of high biodiversity value would enhance the conservation value of forest certification and facilitate integrating certification with other conservation initiatives.     

Do litter-mediated plant-soil feedbacks influence Mediterranean oak regeneration? A two-year pot experiment

Background & Aims

Oak seedling establishment is difficult and may be partly explained by litter-mediated interactions with neighbors. Litter effects can be physical or chemical and result in positive or negative feedback effects for seedlings. Mediterranean species leaves contain high levels of secondary metabolites which suggest that negative litter effects could be important.

Methods

Seedlings of Quercus ilex and Quercus pubescens were grown for two years in pots with natural soil and litter inputs from 6 Mediterranean woody species, artificial litter (only physical effect) or bare soil.

Results

Litter types had highly different mass loss (41–80%), which correlated with soil organic C, total N and microbial activity. Litter of Q. pubescens increased soil humidity and oak seedlings aerial biomass. Litters of Cotinus coggygria and Rosmarinus officinalis, containing high quantities of phenolics and terpenes respectively, decomposed fast and led to specific soil microbial catabolic profiles but did not influence oak seedling growth, chemistry or mycorrhization rates.

Conclusions

Physical litter effects through improved soil humidity seem to be predominant for oak seedling development. Despite high litter phenolics content, we detected no chemical effects on oak seedlings. Litter traits conferring a higher ability to retain soil moisture in dry periods deserve further attention as they may be critical to explain plant-soil feedbacks in Mediterranean ecosystems.

     

Temporary immersion systems (RITA®) for the improvement of cork oak somatic embryogenic culture proliferation and somatic embryo production

Somatic embryogenesis in cork oak (Quercus suber L.) is an efficient tool that allows the production of large number of embryos from selected quality and productive trees. Temporary immersion systems (TIS) are an alternative to semi-solid or liquid culture that combine the advantages of liquid culture and avoid the associated problems. Parameters that affect the TIS multiplication efficiency of Q. suber L. embryogenic cultures were evaluated. Immersion frequencies of 1 min every 6 or 4 h increased the fresh weight 3.7 or 7.5-fold compared with an immersion frequency of 1 min every 12 h or cultures on semi-solid medium, respectively. The cellular fate of embryogenic cultures was also affected by the immersion frequency, 1 min every 6 h was the best for mass propagation of proliferative developmental stages (embryogenic calli and embryo clusters) while 1 min every 4 h promoted the formation of single, fully developed cotyledonary embryos. An initial amount of 1.5 g fresh weight of proliferative tissues produced the best results in RITA^® containers while 0.5 g of embryogenic callus was the best for semi-solid cultures.     

Syntheses of (±)-Epoformin (Desoxyepoxydon) and (±)-Epiepoformin (Desoxyepiepoxydon)

Boron is an essential nutrient for plants, but it is toxic in excess. Transgenic rice plants expressing an Arabidopsis thaliana borate efflux transporter gene, AtBOR4, at a low level exhibited increased tolerance to excess boron. Those lines with high levels of expression exhibited reduced growth. These findings suggest a potential of the borate transporter BOR4 for the generation of high-boron tolerant rice.     

Is variation in susceptibility to Phytophthora ramorum correlated with population genetic structure in coast live oak (Quercus agrifolia)?

California coastal woodlands are suffering severe disease and mortality as a result of infection from Phytophthora ramorum. Quercus agrifolia is one of the major woodland species at risk. This study investigated within- and among-population variation in host susceptibility to inoculation with P. ramorum and compared this with population genetic structure using molecular markers. Susceptibility was assessed using a branch-cutting inoculation test. Trees were selected from seven natural populations in California. Amplified fragment length polymorphism molecular markers were analysed for all trees used in the trials. Lesion sizes varied quantitatively among individuals within populations, with up to an eightfold difference. There was little support for population differences in susceptibility. Molecular structure also showed a strong within-population, and weaker among-population, pattern of variation. Our data suggest that susceptibility of Q. agrifolia to P. ramorum is variable and is under the control of several gene loci. This variation exists within populations, so that less susceptible local genotypes may provide the gene pool for regeneration of woodlands where mortality is high.     

Are climatic factors responsible for the process of oak decline in Poland?

Oak decline, a complex process leading to increased mortality of this species, has been observed in Europe for many years. Previous studies suggest that climate conditions, especially drought, may be one of the most important factors that trigger this phenomenon. The paper investigates the radial growth and wood anatomy features of pedunculate oak (Quercus robur) trees of various health status as well as their response to climate conditions. Wood samples including all annual increments were taken at two sites (western and central Poland, 15 trees each). Based on the crown defoliation level, three health groups (healthy, weakened and dead oaks) were distinguished. Cross-sections were prepared with sliding microtome and Cell P image analysis software was used for the measurements. Tree-ring width (TRW), earlywood vessels density (VDen) and non-weighted vessels diameter (VD) were determined and correlated with mean monthly values of temperature, precipitation, vapour pressure, and Palmer Drought Severity Index (PDSI). Radial increment and anatomical parameters were significantly higher for the healthy oaks than for the weakened and the dead trees. TRW showed smaller dependence on climate than analysed anatomical attributes. No obvious pattern of relationship was found between oak radial growth and climate regarding tree health status. Our results revealed that the drought has a weak impact on the process of oak decline on investigated sites in Poland.