Oak Plantations Research Articles

Формирование лесных фитоценозов правобережья реки Волги

The coastal forests, presented by valuable deciduous and coniferous forests, grow in the northeastern and eastern parts of the Volga region of the Republic of Tatarstan, skirting the high right bank of the Volga River. They contribute to the maintenance of biological diversity in nature. The study of the formation of coastal forest phytocenoses, their species diversity and the modern state is now urgent work, and development activities for the conservation of natural habitats of plants, improve the sustainability of forest ecosystems are perspective direction. According to research of the forests of the right bank of the river Volga, we present the structure of coastal forest ecosystems. The association of forest ecosystems to the various elements of the relief was installed. The types of soil and litter were presented. The estimation of α-diversity of vascular herbaceous plants and ß-diversity of the studied forest ecosystems were reported. The largest number of species of vascular plants in coastal forests are: oak plant communities; a second group includes birch plants, pine and willow; the third group - the lime and larch; the fourth group - maple plant communitie. The ß-diversity index (Whittaker’s index) of plants in the studied forests varies between 2.2-6.8. The Jaccard coefficient of floristic similarity between forest ecosystems varies from 0.01 to 0.30, which confirms the diversity of generated by coastal forest ecosystems. The greatest diversity of plants was found in forests of ash and mixed grass, mixed grass willow, oak and lime-grove, maple, ash and mixed grass larches, birch wood. The forestry activities in coastal areas should be aimed at creating productive, sustainable forest ecosystems with a rich biodiversity of flora and fauna.

Macromycetes of oak forests in the Jurassic Landscape Park (Częstochowa Upland) - monitoring studies

Mycological observations were carried out between 1994-1996 in two representative plots (1000 m<sup>2</sup> each) in 80-year-old oak plantation (<i>Quercus robur</i> and <i>Qu. petraea</i>) on calcareous hill in the Mstów village in the Jurassic Landscape Park. The project was carried out in the frame of international network of the „Mycological monitoring in European oak forests". During 24 visits in the plots a total of 190 species of macromycetes was recorded: 80 mycorrhizal and 110 saprobic fungi. Among them 2 species are new to Poland and 16 are inscribed in the Red List of threatened macromycetes in Poland (Wojewoda and Ławrynowicz 1992).

Factors affecting the bird diversity of planted and semi-natural oak forests in Ireland

Capsule In Ireland, which has relatively low diversity of bird species, commercially mature plantation oak forests (aged 72–151 years old) have similar bird diversity to typical semi-natural oak woodlands, and higher bird diversity than over-browsed semi-natural oak woodland, with bird diversity related to habitat complexity.Aims To investigate whether oak plantations can support comparable bird assemblages to semi-natural oak woodlands, and to assess if high levels of ungulate browsing and grazing impact on the quality of semi-natural oak woodland habitat for birds.Methods Bird and vegetation surveys were conducted in commercially mature oak plantations (n = 4), semi-natural oak woodlands (n = 10) and intensively browsed semi-natural oak woodland (n = 4). Species richness, total bird density, warbler density and density of parids were compared between oak forest types. Variation in bird communities between sites was investigated using ordination, and relationships between bird and vegetation metrics were assessed using general linear models.Results Bird diversity in plantation oak and the semi-natural forests subject to low levels of ungulate browsing, was similar, with no difference in species richness, total bird density or density of warbler and density of parids. However, browsed semi-natural oak woods had lower species richness than either of the other two study site types, and lower density of warblers than oak plantations. These observed differences in bird communities appear to be a result of browsing mediated differences in habitat complexity between the forest types.Conclusions Plantation forests of native tree species may support comparable bird communities to semi-natural woodlands in areas that lack forest specialists. Bird diversity in woodlands subject to high levels of browsing and grazing is likely to be limited, unless ungulate populations and their access to these woodlands are managed to promote the development of a more complex understorey.

Planting stock type and seasonality of simulated browsing affect regeneration establishment ofQuercus rubra

Animal herbivory is a major limiting factor to successful oak (Quercus spp.) regeneration. Although bare-root seedlings are the most commonly used nursery stock type for oak plantings in the eastern United States, container seedlings may better resist planting stress and help enable seedlings to overcome browsing pressure. Four stock types (1 + 0 bare-root seedlings and seedlings in 164, 336, and 520 mL containers) of northern red oak (Quercus rubra L.) were planted on two reforestation sites in Indiana, USA, which were fenced to exclude white-tailed deer (Odocoileus virginianus Zimmerman). Seedlings were then subjected to three simulated browsing treatments (control unclipped, dormant clipped, and summer clipped). Container seedlings exhibited higher relative growth rates on both sites; for example, at one site, control seedlings in 336 mL containers had relative height growth of 558% compared with 79% for bare-root control seedlings. On both sites, summer-browsed seedlings of all stock types had negligible height growth, and summer browsing reduced survival at one site by 23% for all stock types compared with control seedlings. Browsing of seedlings during the dormant period did not affect growth for any stock type. Container seedlings may help facilitate rapid establishment of planted oak seedlings, but browse protection is necessary to ensure oak regeneration success in areas of large populations of deer.

The silent shareholder in deterioration of oak growth: common planting practices affect the long-term response of oaks to periodic drought

Oaks play an important role in forest ecosystems and are of great economic value. Therefore, the increasing frequency of oak decline incidents in recent decades is of outstanding interest to foresters and researchers in many fields. Despite the general agreement that drought is of major importance in oak decline, very little attention has been devoted to the condition of root systems during drought. In this paper we tested whether cutting the taproot of oak seedlings, a common forest nursery practice, or coppicing, a common management strategy, play a pivotal role in drought-related weakening of oak plantations. Using dendrochronological methods we analyzed whether Quercus robur stands originating from acorns sown directly in the ground, planted seedlings and coppice managed stands differ in response to drought. All studied stands have shown growth depression as a result of prolonged drought conditions. However, stands originating from direct seeding were less severely affected than those from planted seedlings and stands regrown from sprouts after coppicing. In addition, stands established by direct acorns sowing were characterized by lower 13C/12C isotope ratios (δ13C) in wood, indicating better access to water during its deficit. Therefore, it is likely that intact taproot systems of trees developed from direct seeding are able to reach deeper levels of ground water, and as a result oaks are able to cope more effectively with the difficulties created by prolonged drought conditions. Our study has indicated that common forestry practices may exacerbate drought stress in oak stands, which is considered a major factor causing or predisposing oak decline.

Modeling the long-term natural regeneration potential of woodlands in semi-arid regions to guide restoration efforts

Understanding forest regeneration at sites previously used for agriculture underlies the establishment of science-based woodlands management policies. This is especially relevant in semi-arid areas, where the tree cover is critical in ameliorating the effects of aridity and in preventing desertification and land degradation. Natural regeneration in semi-arid areas occurs very slowly, which in part explains why it has hardly been studied. In the present work, we sought to devise a method to predict the natural regeneration potential of woodlands in semi-arid areas, to be used in guiding restoration efforts. Specifically, we evaluated holm oak coverage at a long-term ecological research site and then designed and validated a model to predict the natural regeneration of holm oak based on a few environmental variables. Unlike available studies, we obtained long-term information on tree regeneration (making use of >60 years of aerial photography) and climate (using long-term climate and microclimate data). We found that microclimate, measured using the potential solar radiation as a proxy, was a key driver of natural regeneration: after 60 years of agricultural abandonment, less sun-exposed areas attained a tree cover >90 %, whereas in more sun-exposed areas it remained below 20 %. We then used the model to map the natural regeneration potential, first in the study area and then in an area where holm oak plantations had been unsuccessfully introduced. In the latter case, the model successfully predicted the failure of this reforestation effort. Our results support the use of this model by decision makers to optimize management practices, as it will encourage the concentration of efforts in areas more prone to successful reforestation and allow the identification of areas more likely to benefit from natural regeneration processes.

Environmental risk assessment of carbosulfan on target and non-target beetles when used as white grub larvicide in the cork oak forest of Mamora (Morocco)

The protection of new cork oak plantations against the larvae of the beetle Sphodroxia maroccana (Melolonthidae), which destroy the roots of newly planted trees, was provided for many years in the forest of Mamora in Morocco by the use of carbosulfan, usually formulated as dry granules for direct incorporation into the soil at planting. Ecotoxicological tests were conducted in the laboratory on S. maroccana and on two non-target beetle species, namely Pachychila obtusecostata and Pimelia platynota (Tenebrionidae), to measure the acute effects of carbosulfan and evaluate the potential risk associated with inappropriate practices. The mortality was measured at both 4 d and 7 d after ingestion of a known quantity of carbosulfan. The recommended dose by the manufacturer was exceeded by at least four-fold in the Mamora Forest, with obvious environmental risks. Risks were identified for wildlife when the pesticide is misused and spread on the soil around the plants.

Noble biomass: restore, recycle, profit using cork oak (Quercus suber L.)

Land use changes over recent decades have led to serious decline in natural ecosystems, in particular the Mediterranean forests. This is due mainly to uncontrolled urbanisation causing agricultural land to be abandoned or to become partially polluted. In such areas, forest restoration appears the most appropriate remedy, in particular, by using native species with high ecological and economic values, such as cork oak. This species can be used for noble biomass production, that is biomass not addressed for energy production but mainly for industrial purposes. This work describes a case study located in central Italy, which is characterised by the integration of forest restoration with water-saving management for irrigation purposes, based on the use of effluents from a phytodepuration plant. By joining thematic maps with a map of topographic wetness index (TWI) a suitable site was selected in the municipality of Tuscania for a cork oak plantation. An irrigation scheme, useful for maximising the growth rate of cork oak and consequently for maximising the economic profits retrievable from the plantation, was determined based on the estimated potential evapotranspiration using Thornthwaite’s equation, the soil type and the available wastewater. An economic analysis showed that the total cost of the works might be amortised within the first stripping of gentle cork or even before, for example, if cork oak was cultivated in conjunction with an economically relevant non-food species. In this case study, the advantages of dyeing species were analysed. Results show that an integrated forest restoration and wastewater

Assessing the effect of late-season fertilization on Holm oak plant quality: insights from morpho–nutritional characterizations and water relations parameters

Forest restoration projects with Holm oak (Quercus ilex) have had limited success, mostly due to water stress after planting and poor plant quality. Recent studies indicated that large and nutrient rich plants perform better in Mediterranean areas, suggesting that late-season fertilization may improve plant quality and field performance. The purpose of this study was to assess the effect of late-season fertilization on the quality of Holm oak seedlings, as determined by morphological, nutritional, and water relations analyses. We grew Holm oak nursery seedlings under 5 different late-season fertilization regimes and then analyzed morphological characteristics, nutritional status, and water relations parameters of the fertilization groups at the end of the nursery period. We also analyzed the effect of fertilization on nutritional status by use of vector nomograms. Our results indicated that late-season NPK fertilization improved shoot and root growth, and the overall nutritional status of seedlings. The lack of late-season fertilization leads to nutrient deficiency in plants, whilst the application of imbalanced fertilization treatments may trigger nutrient luxury consumption and nutrient dilution, pointing out the importance of NPK proportions in the fertilizer. Moreover, late-season fertilization with nitrogen might improve the drought resistance of seedling by enhancing their osmotic adjustment.

Is nitrogen fertilization in the nursery a suitable tool for enhancing the performance of Mediterranean oak plantations?

Mediterranean oaks frequently have poor performance in forest restoration projects. We analyzed if nitrogen (N) fertilization during nursery cultivation enhances the outplanting performance of two ecologically distinct oaks, Quercus coccifera L. an evergreen shrub, and Quercus faginea L., a deciduous tree. Additionally, we compared the sufficiency N levels of both oaks and if root growth capacity (RGC) and photosynthesis testing at low air temperature better discriminated among fertilization treatments than testing at mild temperature. Plants were cultivated under five N fertilization rates (0, 30, 75, 150 and 200 mg N plant−1) for one growing season. At the end of the cultivation period several plant material and performance attributes were measured. RGC and photosynthesis were assessed at mild temperature and cool conditions in Q. coccifera, while in Q. faginea these attributes were only analyzed at mild temperature conditions. Q. coccifera seedlings were transplanted into four terraces that imposed increasing drought stress, while Q. faginea seedlings were transplanted into an abandoned wheat cropland. Sufficiency level was higher for the tree (150 mg N plant−1) than for the shrub (75 mg N plant−1) Nitrogen-deprived Q. coccifera plants had higher frost damage than remaining treatments, which did not differ among them. Fertilization in Q. faginea did not affect photosynthesis rate but it delayed leaf senescence and abscission. RGC increased with fertilization in both species. Testing temperature did not change the effect of fertilization on RGC in Q. coccifera. Photosynthesis in cool conditions discriminated N-deprived seedlings from the remaining treatments, but treatments did not differ in photosynthesis at mild temperature. Fertilization enhanced outplanting survival in Q. coccifera, primarily in the terraces imposing stronger drought stress, while fertilization only increased growth in the terraces imposing mild drought stress. Overall, survival and growth was positively related to seedling size at planting in both oaks. Additionally, Q. coccifera survival was also positively related to RGC in the harsh planting conditions. Field growth was positively related to RGC and plant N concentration in both oaks but the relation was weak or nonexistent under harsh conditions in Q. coccifera. We conclude that fertilization in the nursery is an important tool for improving the success of oak plantations in Mediterranean continental sites, and that large and N-rich seedling have greater field performance than small and low tissue N concentration seedlings, especially in harsh field sites.

A short-term mineral amendment impacts the mineral weathering bacterial communities in an acidic forest soil

Mineral amendment (i.e. calcium, phosphorous, potassium and/or magnesium) is a management practice used in forestry to improve nutrient availability and recover soil fertility, especially in nutrient-poor forest ecosystems. However, whether this amendment can lead to modifications of the soil characteristics and an improvement in tree growth, and its impact on the soil bacterial communities, especially the mineral weathering bacterial communities, remains poorly documented. In this study, we investigated the short-term impact of a mineral amendment on the taxonomic and functional structure of the mineral weathering bacterial communities. To do this, a plantation of four-year old oak (Quercus petraea) trees amended with or without dolomite [CaMg(CO3)2] was established in the experimental forest site of Breuil-Chenue, which is characterized by an acidic soil and a low availability of calcium and magnesium. Three years after amendment, soil samples were used to isolate bacteria as well as to determine the soil characteristics and the metabolic potentials of these soil microbial communities. Based on a bioassay for quantifying the solubilisation of inorganic phosphorous, we demonstrate that the bacterial isolates coming from the non-amended bulk soil were significantly more efficient than those from the amended bulk soil. No difference was observed between the bacterial isolates coming from the amended and non-amended rhizospheres. Notably, the taxonomic analyses revealed a dominance of bacterial isolates belonging to the Burkholderia genus in both samples. Overall, our results suggest that the bioavailability of nutritive cations into soil impacts the distribution and the efficacy of mineral weathering bacterial communities coming from the soil but not those coming from the rhizosphere.

Shifting bottom-up and top-down regulation of oak recruitment across a regional resource gradient

Aim Questions about the relative importance of top-down and bottom-up regulation of populations have long occupied ecologists. Recent work has explored how the strength of consumer- versus resourced-based limitation can shift in strength across both time and space, and indicates the need for larger scales of study across spatial resource gradients. A better understanding of how climate gradients affect population regulation is integral to conservation ecology, particularly in the context of global change. Location California. Methods We examined the effects of bottom-up (water limitation) and top-down (small mammal herbivory) forces on valley oak (Quercus lobata) sapling recruitment. We used existing literature on valley oak planting experiments and field data on natural populations at 26 sites across the species' distribution to explore how the factors regulating oak populations shift along a regional precipitation gradient. This approach allowed us to study time-integrated ecological processes in a long-lived system that would be impossible to manipulate in a strictly experimental setting. Results We found that the relative importance of top-down and bottom-up forces in limiting oak recruitment shifted across the precipitation gradient, with small mammalian herbivory (top-down) more important as long-term mean site precipitation increased, and factors related to moisture stress (bottom-up) increasingly important at lower precipitation levels. Main conclusions Our findings emphasize the importance of expanding the spatial scale of studies on population and community dynamics in order to better understand patterned variation in the multiple factors regulating them across resource gradients.

Inter-annual variation of carbon uptake by a plantation oak woodland in south-eastern England

Abstract. The carbon balance of an 80-yr-old deciduous oak plantation in the temperate oceanic climate of the south-east of Great Britain was measured by eddy covariance over 12 yr (1999–2010). The mean annual net ecosystem productivity (NEP) was 486 g C m−2 yr−1 (95% CI of ±73 g C m−2 yr−1), and this was partitioned into a gross primary productivity (GPP) of 2034 ± 145 g C m−2 yr−1, over a 165 (±6) day growing season, and an annual loss of carbon through respiration and decomposition (ecosystem respiration, Reco) of 1548 ± 122 g C m−2 yr−1. Although the maximum variation of NEP between years was large (333 g C m−2 yr−1), the ratio of Reco/GPP remained relatively constant (0.76 ± 0.02 CI). Some anomalies in the annual patterns of the carbon balance could be linked to particular weather events, such as low summer solar radiation and low soil moisture content (values below 30% by volume). The European-wide heat wave and drought of 2003 did not reduce the NEP of this woodland because of good water supply from the surface-water gley soil. The inter-annual variation in estimated intercepted radiation only accounted for ~ 47% of the variation in GPP, although a significant relationship (p < 0.001) was found between peak leaf area index and annual GPP, which modified the efficiency with which incident radiation was used in net CO2 uptake. Whilst the spring start and late autumn end of the net CO2 uptake period varied substantially (range of 24 and 27 days respectively), annual GPP was not related to growing season length. Severe outbreaks of defoliating moth caterpillars, mostly Tortrix viridana L. and Operophtera brumata L., caused considerable damage to the forest canopy in 2009 and 2010, resulting in reduced GPP in these two years. Inter-annual variation in the sensitivity of Reco to temperature was found to be strongly related to summer soil moisture content. The eddy covariance estimates of NEP closely matched mensuration-based estimates, demonstrating that this forest was a substantial sink of carbon over the 12-yr measurement period.

Consequences of faster growth for wood density in northern red oak (Quercus rubra Liebl.)

The objective of this study was to establish whether the relationships between wood density, growth rate and ring number from the pith were equivalent in the contrasting conditions of a natural forest and an intensively managed plantation of northern red oak (Quercus rubra Liebl.). The radial X-ray densitometry profiles of 14 natural forest trees and 18 plantation trees growing in the southwest of Quebec, Canada, were studied in detail using a linear mixed-effects modelling approach. In the natural stand, the effect of faster growth on overall ring density changed from a slightly negative relationship at a ring number 5 to a strongly positive effect at ring 40. In the plantation trees, the overall ring density remained almost constant along the range of observed ring widths. For the range of ring numbers common to both stand types (i.e. rings 1–15) the relationship was almost equivalent. Overall, our results suggest that because trees are harvested at a target diameter, silvicultural interventions specifically designed to improve radial growth rate in northern red oak will not be detrimental to overall wood density.

Quantification of Quercus petraea Liebl. forking based on a 23-year-long longitudinal survey

For Quercus petraea (sessile oak), the origin of forks is either traumatic or related to crown base formation (“metamorphosis”). The objectives of this study were to quantify forking, distinguish the two origins and test the effect of initial stocking density and tree attributes on the number of forks and height to the lowest one.The experiment took place in a 23-year-old sessile oak plantation in Normandy, France, where three initial planting densities were compared (1333, 2667 and 5333seedlings per ha). The forks were observed every 3years after the plantation. Fork number was modelled with a system of simultaneous linear equations that respectively predicted tree girth, height and the log-transformed fork frequency, with age and initial stocking density as explanatory variables. This model 1 was fitted as a seemingly unrelated regression with random effects to account for the tree and plot clustering. For trees having at least one fork, lowest fork height was quantified using a linear mixed model including predictors compatible with the response variables of model 1, age and stocking.The results showed that the number of forks can be predicted using the expected explanatory variables and it is significantly correlated with height and girth as well. Traumatic and metamorphosis-related origins were not clearly distinguished, but significant differences between the initial seedling densities were found, with the lowest density showing the highest number of forks. Lowest fork height depended on response variables of model 1, age and stocking. The stocking effect was significant but small.This study presents the first statistical quantification of tree forking ever made. From this quantification, it seemed obvious that the initial density of 2667 seedlings per ha could be a relevant initial density to avoid the emergence of too many forks and the insertion of the lowest forks too low down.

Diverging effects of two contrasting tree species on soil and herb layer development in a chronosequence of post-agricultural forest

The restoration of forest ecosystems on former agricultural land faces numerous problems. Recolonisation of forest species is hampered by the modified habitat quality and by the isolation from source populations. Tree species are ecosystem engineers that can modify soil and light conditions and can therefore act as a possible catalyst for understory recovery.Therefore, we set out to study the effects of tree species on herb layer development. For this purpose, a chronosequence of post-agricultural oak (Quercus robur and Quercus petraea) and poplar (Populus x euramericana and Populus x interamericana) plantations on silt and sandy silt soils was selected. The selected tree species are frequently planted and have contrasting characteristics (e.g. in terms of litter quality, shade casting ability and growth rate).Under plantations of oak, soils acidified with increasing stand age and dropped into the aluminium buffer range after only 20–30y, whereas soil pH hardly changed under poplar plantations. Carbon (C) and nitrogen (N) soil content increased with stand age, while C/N ratio depended on tree species but remained constant in time. Multivariate analysis revealed that vegetation development depended on tree species, isolation and stand age. Poplar stands were characterised by rough Arrhenaterion grassland species while oaks had low understory cover and consequently had no indicator herb species. No tree species effect was found on the cover of strict forest species and ancient forest species. Oak favoured acid tolerant forest species, while poplars favoured light demanding and acid intolerant forest species.Our results lead to the conclusion that tree species can be important drivers of vegetation development in post-agricultural forests, in particular through their impact on soil development and light availability for the understory. Therefore it is important that goals for soil development and understory restoration are taken into account when tree species are selected for afforestations. Acidifying tree species may have irreversible effects, permanently excluding acid intolerant species. This is especially important when aiming to safeguard acid intolerant forest species from acidification in ancient forest by creating post-agricultural forest as refugee zones.When a species rich herb layer with acid intolerant species are aimed at, selecting a tree species with a good decomposable litter like poplar is a necessity and suppressing competitors by a shady overstory of the tree or shrub layer. Soil acidifying species like oak might be more suitable to enlarge forest habitats that mainly contain acid and shade tolerant species.

Effects of microsite conditions and early pruning on growth and health status of holm oak plantations in Central-Western Spain

The aim of this study was to examine the influences of early pruning and microsite conditions on the growth and health status of holm oak plantations on former agricultural land in Central-Western Spain. With that purpose, we designed a cross-sectional study to examine the effects of topographic position, gravel surface cover and accompanying vegetation cover on holm oak plantations density, growth (height and basal diameter) and health status. We surveyed three technically identical and multi-patched holm oak plantations dating from 1995, 1998 and 2003, aged 15, 12 and 7 respectively, covering an homogeneous climate and soil area of about 500 ha located in Central-Western Spain. Six hundred and seventy-two pruned and unpruned trees were sampled in 107 systematically sampled plots covering a wide range of site conditions in the studied area. At the tree level, two linear mixed effect models were adjusted for each year under study to explore the influence of pruning and microsite factors on height and diameter. Also at a tree level, a linear mixed effect model was fitted in order to analyze the influence of microsite factors and pruning on the health status of trees. At plot level, we performed a Multifactor Analysis of variance model to explore the influence of the microsite predictor variables and of the age of plantations on stocking. The results revealed that both basal diameter and height were increased by early pruning in all plantations under study. The effects on height and basal diameter of the three microsite parameters analysed varied with the age of plantations. The oldest plantations (15 years old), were affected by the surface gravel cover, while vegetation cover was significant in 12 years old plantations. Slope position was near relevant (p < 0.1) only in the youngest plantations. When significant, a high surface gravel cover was directly related to higher trees and larger basal diameters. Plantations density was significantly affected by the topographic position and, in all the plantations studied, pruned trees were associated with a better health status. Overall, our results show that early pruning and microsite conditions significantly influence the growth of holm oak seedlings. These results suggest that the management and growth modelling of holm oak should take into consideration the spatial distribution of the different microsites represented. Moreover, early- pruning should be considered as a positive practice affecting not only final tree form but also the growth and health status of trees. Finally, our results should lead to for further studies and help for improving future projects in areas with similar conditions.

Frost-Acclimation of Photosynthesis in Overwintering Mediterranean Holm Oak, Grown in Central Europe

As a consequence of global change, forestry in Central Europe has to expect and be prepared for an increase of hot and dry summers in the near future. In two model plantations of the Mediterranean holm oak (Quercus ilex L.) in Central Europe (Rhine-Main basin) we tested its potential as a future forestry tree for drought-threatened stands by studying its overwintering strategy under harsh winter conditions. During prolonged frost periods, chronic photoinhibition was developed, which lasted until the end of the frost period. Nearly all plants survived minimum temperatures of −16 to −18 °C and their photosynthetic apparatus recovered completely during late winter. A detailed study of the temperature dependence of chlorophyll (chl) fluorescence parameters of the OJIP test revealed statistically significant correlations between minimum temperature and maximum quantum yield of primary photochemistry (Fv/Fm), absorption rate/reaction centre (ABS/RC), dissipation rate/reaction centre (DI0/RC) and electron transport rate/reaction centre (ET0/RC) as well as with the deepoxidation state (DES) of the xanthophyll pigments. The DES correlated with Fv/Fm, ABS/RC, DI0/RC and ET0/RC. It is concluded, that from the point of view of the winter hardiness of the photosynthetic apparatus, Q. ilex should be further investigated as a potential future forestry tree also for very dry and warm stands in Central Europe under the scenarios of climate change.

Contribution of cork oak plantations installed after 1990 in Portugal to the Kyoto commitments and to the landowners economy

Cork oak stands are a part of the agroforestry ecosystem in Portugal, characterized by a low crown cover from cork oak trees, managed towards cork production, and sometimes in combination with grazing. In recent years, European Union policies gave impetus to a large area of new cork oak plantations, which have been established mainly for cork production purposes, and consequently with higher stand density than traditional agroforestry systems. These plantations are important not only for cork production but also for the carbon sequestered by these slow growing forests that won't be harvested for wood production. Thinning operations will be needed to avoid excessive inter-tree competition and wood extracted from these thinning may also provide income for the owners. In the present study, carbon sequestered and wood volumes resulting from thinning were estimated for the next 70years. Three scenarios of different annual afforestation rates and different site indexes were tested. The resulting values for the considered scenarios show that, if the plantation rates are maintained, new cork oak plantations will have an important contribution to the Portuguese commitments to providing CO2 offsets under the Kyoto protocol. Additionally, due to the increasing values of initial density in new cork plantations, cork oak forests will produce a significant volume of wood that may become an important contribution to the landowners' income.

Growth and nutrition of Quercus petraea underplanted in artificial

This study presents results on the growth and nutritional status of Quercus petraea trees underplanted in an artificial pine stand as a conversion strategy. A total of 162 plots of 400 to 800 m2 were established in underplanted pine stands (130 plots), naturally regenerated oaks in pine stands (23 plots) and pure oak plantations (9 plots). The age of the oak stands was 7 to 14 years where they were planted, and 25 to 60 years in the natural regenerations. Biomass growth and nutrition of the oaks was studied by means of foliar analysis, soil analysis, biomass evaluation and regression techniques, considering site variables, meteorological parameters and pine cover as explicative variables. The vegetation structure of the stands in the forest-transforming areas is still dominated by the species spectrum of the original pure pine stands. As the quality of a site decreases, so the dominance of a few species increases and the diversity decreases. The manipulative effect upon the vegetation of underplanting with oaks is less severe than that of underplanting with beeches. With the progressing development of the ecological system, more demanding deciduous tree types replace the undemanding pine forest vegetation. On principle, the pine-tree canopy influences the supply of nutritional elements to the under-planted oaks. However, neither in average weather periods nor during droughts could any symptoms of nutrient deficiency or growth-impeding nutritional element disharmonies be detected by the naked eye. Only in the «Summer of the Century», 2003, did the laboratory analysed macro-element leaf-index reveal slight deficiencies of Ca- und S. The modelling of the above-ground increase in oak biomass growth, differentiated according to site and depending on time and the canopy of pine trees revealed increasing increment losses the greater the canopy cover, which even lead to stagnation in growth as the quality of the site deteriorates.