Drying and soaking pretreatments affect germination in pedunculate oak

? Pedunculate oak (Quercus robur L.) acorns are recalcitrant so they are difficult to store. Therefore, deterioration in quality during storage may reduce seedling yield and quality. In an attempt to address this, the effects of drying and soaking treatments on acorn germination were assessed.

? After harvesting on two occasions in October, the moisture content (MC) of acorns were adjusted using the following treatments: (1) fresh state or control (46–48% MC); (2) soaked in fresh state (46–48%); (3) dried (40–42%) (standard method); and (4) dried and then soaked (46–48%). The treated acorns were allowed to germinate at 15 °C, both before and after storage at ?3 °C.

? Treatment effects were generally consistent for each harvest date. Compared to the untreated controls, soaking alone and drying followed by soaking significantly increased germination both before and after storage. Storage reduced germination, except for the dried and soaked acorns.

? The results confirmed that drying and soaking improved acorn germination, but this was not mediated through an effect on acorn MC. In a separate nursery experiment, acorns given this treatment resulted in higher seedling yields and better quality plants than those given the standard treatment (dried to 40–42% MC).

     

Influence of annual weather on growth of pedunculate oak in southern Sweden

? A network of oak (Quercus robur L.) chronologies containing 49 sites and 635 single trees was analysed to identify weather variables affecting annual tree-ring increment dynamics in southern Sweden during 1860–2000.

? We analysed (1) the growth response of oak to non-extreme weather, and (2) the temporal and spatial patterns of regional growth anomalies (pointer years) and associated climatic extremes resolved on a monthly scale.

? Growth was controlled by precipitation in the current (June–July) and the previous growing season (August) in 48% and 22% of all sites, respectively. Temperature during July of the current year and August of the previous year was negatively correlated with growth in 29% and 43% of the sites, respectively. Growth was positively correlated with temperature in October of the previous season in 72% of the sites. The most extensive growth anomaly occurred in 1965 and was probably caused by intrusion of cold Arctic air masses into the region at the end of March that year.

? During climatically non-extreme years, oak growth is driven mostly by the dynamics of summer precipitation. Many of the negative growth anomalies, however, were associated with temperature extremes. Southern Swedish oak pointer years tend not to coincide with the pan-European oak pointer years.

     

Dendroclimatic signals of pedunculate oak (Quercus robur L.) in Estonia

This study investigates the climate impact on the radial increment of pedunculate oak (Quercus robur L.) in Estonia at the species’ northern distribution limit. Tree-ring width series of 162 living oaks were compiled into three regional chronologies—western (1646–2008), northeastern (1736–2011), and southeastern Estonia (1912–2011). Although these regional growth patterns are similar to each other and even to the growth patterns in adjacent regions, spatial differences in growth responses to climate were established. Thus, oaks growing on shallow soil in western Estonia are positively influenced by summer (June–August) precipitation, and oaks on the deeper soil in northeastern Estonia are favoured by June temperature, while oaks in the southeastern part of the country depend on both July precipitation and temperature. These relationships are pronounced especially in pointer years. However, due to the impact of regional weather fluctuations on tree growth, there is a lack of correspondence between the local and the pan-European pointer years. In addition, our research presents the first tree-ring-based palaeoclimatic reconstruction for the country. Although the created model has relatively low predictive skill describing less than a quarter of the variance in actual summer precipitation in western Estonia, it has passable capacity of detecting past rainfall extremes.     

Development of tree hollows in pedunculate oak (Quercus robur)

Many invertebrates, birds and mammals are dependent on hollow trees. For landscape planning that aims at persistence of species inhabiting hollow trees it is crucial to understand the development of such trees. In this study we constructed an individual-based simulation model to predict diameter distribution and formation of hollows in oak tree populations. Based on tree ring data from individual trees, we estimated the ages when hollow formation commences for pedunculate oak (Quercus robur) in southeast Sweden. At ages of about 200–300 years, 50% of the trees had hollows. Among trees <100 years old, less than 1% had hollows, while all >400-year-old trees had hollows. Hollows formed at earlier ages in fast-growing trees than in slow-growing trees, which may be because hollows are formed when big branches shed, and branches are thicker on fast-growing trees in comparison to slow-growing trees of the same age. The simulation model was evaluated by predicting the frequency of presence of hollows in relation to tree size in seven oak stands in the study area. The evaluation suggested that future studies should focus on tree mortality at different conditions. Tree ring methods on individual trees are useful in studies on development of hollow trees as they allow analysis of the variability in time for hollow formation among trees.     

Etiology of oak decline in Spain

In different areas of Extremadura, Western Spain, soil samples were taken at the bottom of holm oak (Quercus ilex) trees that were showing decline symptoms. Half of each sample was sterilized, and acorns were sown in both sterilized and nonsterilized soil samples. The resulting seedlings were used as baits for the isolation of fungi. Seedlings growing on the natural, nonsterilized substrate were characterized by having a lower vegetative growth than the ones growing on the sterilized soil samples, and most of them died. Phytophthora dnnamomi was consistently isolated from their roots. Fusarium oxysporum was also isolated as well as different species of Pythium, although to a lesser extent. Pathogenicity tests were performed on holm oak seedlings with five different isolates of P. chinnamomi, with F. oxysporum, Pythium and with a mixture of the three fungi. All the inoculated seedlings with P. chinnamomi developed root rot and grew slowly, and 35.7% of them died up to the end of the experiments. P. chinnamomi was consistently isolated from their roots, indicating that this fungus is the causal agent of holm oak decline. However, F. oxysporum caused similar symptoms on oak seedlings as P. chinnamomi, and was isolated also from the roots, although its frequency was lower than that of. P. cinnamomi.     

Sewage sludge fertilisation of a silvopastoral system with pines in northwestern Spain

The use of municipal sewage sludge as a fertiliser could be a more adequate means of disposal of this residue than its transport to the dump. The objective of this experiment was to evaluate the effects of different doses of sludge and sowing a mixture of cocksfoot (Dactylis glomerata) and clover (Trifolium repens) on pasture production, botanical composition of the pasture, forage quality, and changes in soil chemical properties. Treatments applied were: (1) no fertilisation (L0), (2) fertilisation with 26 Mg ha^–1 of sewage sludge with no sowing (L40), (3) fertilisation with 26 Mg ha^–1 of sewage sludge and sowing with 25 kg of Dactylis glomerata L. cv Artabro (Dg) and 3 kg Trifolium repens cv Huia per hectare and (4) 52 Mg ha^–1 of sewage sludge with no herbage sowing (L80). Plots were established in a silvopastoral system with Pinus radiata D. Don at a density of 1666 trees ha^–1 (3 × 2 m). The improvement of soil fertility due to organic fertiliser application and the use of Dactylis glomerata increased the production and quality of pasture as well as reduced the risk of fire and erosion, as grasses dominated shrubs. Fertilisation with sewage sludge in soils of acid origin increased the concentration of copper in the pasture and, if cocksfoot was not sown, the levels of this element exceeded the maximum tolerable dietary levels for sheep. On the other hand, fertilisation also increased the levels of zinc in pasture, but values were not above toxic limits for sheep, horses and cattle.This revised version was published online in November 2005 with corrections to the Cover Date.     

Studies on insects causing galls on the leaves of pedunculate oak Quercus robur in southern Poland

Analytical studies concerning the species composition of galls occurring on the leaves of Quercus robur L. were conducted in 2000 in three localities: near an urban agglomeration of Kraków – the Wolski Forest, in a protected area – the Ojców National Park and in a managed forest – the Andrychów Forest District. In each of the selected localities 2000 leaves (a total of 6000 leaves) were randomly collected. A total of 2246 galls, including 1028 in the Andrychhów FD, were found. The galls represented 12 insect species. The species composition of galls in the Ojców NP (11 species) distinctly differed from those of the remaining two areas (7 species each). Neuroterus quercusbaccarum (L.) ♀♀ was the most abundant species in the managed forest. The index of occurrence frequency and the Agrell's index of species co-existence have been calculated. The frequency of gall occurrence varied considerably in the investigated localities. On the basis of the Agrell's index of species co-existence it was shown that the strongest bond existed between Neuroterus laeviusculus Schenck ♀♀ and Andricus ostrea (Hartig) ♀♀ in the managed forest.     

Genetic variation of pedunculate oak (Quercus robur L.) in the urban woodlands of Helsinki

We present a genetic profile of pedunculate oak (Quercus robur L.) in three woodlands of the Helsinki region. We genotyped all mature trees and samples of seedlings to evaluate patterns of genetic variation and gene flow, and evaluate the long-term stability and natural regeneration of these stands. Although five microsatellite loci showed no significant differences in heterozygosity between generations in most locations, significant (p?per se does not interfere with gene flow over the distances represented here. Based on our findings, a minimal-maintenance program reliant upon natural regeneration of oak in the public parks of Helsinki seems plausible.     

Biotic and abiotic factors affecting the dying back of pedunculate oak Quercus robur L.

Episodes of dying back of pedunculate oak Quercus roburhaveoccurred in Europe. In this article, produced to mark the 70thvolume of Forestry, the 1920s episode, as described by contemporaryresearch workers, is evaluated. The second part of the paperis concerned with an accountof the 1989–1994 episode inGreat Britain and comparisons are made with occurrences elsewherein Europe. In Britain, one feature not previously recorded,was attack on declining trees by the buprestid beetle, Agriluspannonicus.     

Development of a stand density management diagram for even-aged pedunculate oak stands and its use in designing thinning schedules

Density management is the usual method used by silviculturiststo achieve a desired future stand condition, and one of themost effective methods of design, display and evaluation ofalternative density management regimes in even-aged stands isthe use of stand density management diagrams. In the presentstudy, we describe a method for developing thinning schedulesfor even-aged pedunculate oak (Quercus robur L.) stands in Galicia(north-western Spain), using a density management diagram. Thediagram integrates the relationships among stand density, dominantheight, quadratic mean diameter and stand volume in a singlegraph. The data used in its construction were obtained from172 sample plots located throughout Galicia. The diagram isbasically composed of two equations: the first relates the quadraticmean diameter to the stand density and dominant height; thesecond relates the stand volume to the quadratic mean diameter,stand density and dominant height. These equations were fittedsimultaneously using full information maximum likelihood. Therelative spacing index is used to characterize the growing stockand the diagram provides isolines for dominant height, numberof trees per hectare, quadratic mean diameter and stand volume.Dominant height isolines together with the site index curvesallow specification of the timing of thinnings while intermediateand final harvest volumes are calculated using the stand volumesisolines.     

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.     

Degradability of soils under oak and pine in Central Spain

The purpose of this research was to study the influence of the vegetation on the soil C pool of forests of pines (Pinus sylvestris) and oaks (Quercus pyrenaica), located in Central-Western Spain. Horizons from selected soils located in these forests were sampled, and the soil organic C (SOC) was determined. In addition, in vitro incubation experiments were carried out, under controlled conditions, to monitor the stability of SOC against the microbial activity. Soil humus fractions were isolated following a classical procedure of chemical fractionation using alkaline solutions, before and after the incubation experiment. A deeper O horizon was found under the pine forest than under oak one; however, higher SOC content was found in the oak site than that under pine one. During the in vitro mineralization process, a lower CO₂ production by the soil sample from pine forest was observed, in relation to that emitted by the oak soil. In addition, a lower humification degree was estimated for the soil humus under pines than for that under oaks. In conclusion, replacement of oaks by pines produced a decrease in SOC accumulation and a lower quality of humus in the forest soils.     

Modeling non-catastrophic individual-tree mortality for Pinus radiata plantations in northwestern Spain

An individual-tree mortality model for radiata pine (Pinus radiata D. Don) plantations in northwestern Spain was developed. The model relies on data from three inventories of a network of 130 permanent plots. The equation that predicts the probability of complete survival is a logistic function, which depends on tree size and competition (diameter, mean-squared diameter, stand basal area, dominant height and BALMOD competition index). Several methods of implementing the mortality model were tested (deterministic versus stochastic threshold selection and the use of expansion factors). The best results were obtained when using a fixed cut-off value to decide which trees would survive to the next growing period. When a cut-off value of 0.55 was applied, the model correctly classified 99% of the live trees and 25% of the dead trees. A cut-off of 0.71 provided an estimated mortality rate that was closest to the observed rate. With this cut-off value, the model correctly classified 95% of the live trees and 47% of the dead trees. This cut-off value is recommended when using the model to predict radiata pine individual-tree mortality in the study area.     

Ingrowth model for pyrenean oak stands in north-western Spain using continuous forest inventory data

In this paper, a two stage ingrowth model is presented for predicting periodic, 10 years ingrowth for pyrenean oak (Quercus pyrenaica Willd.) grown in medium to fully stocked coppice stands in north-western Spain. Data from the Spanish National Forest Inventory was used to develop the model, extracting the information from two inventories taken in 222 permanent plots. The first stage of the model predicts the probability of ingrowth occurrence, and in the second stage, the number of recruits is predicted using a conditional model. Both models were biologically realistic and presented logical behaviour. The ingrowth occurrence probability model was dependent on quadratic mean diameter and average height. The recruitment quantification model included stand density and average diameter as explanatory variables. Although the occurrence probability of ingrowth was predicted correctly in 71.7% of cases, the predictions of the number of recruitment are poorer, yielding a coefficient of determination of 0.358. The evaluation criteria included qualitative and quantitative examinations and a testing with independent data from another region. The proposed ingrowth model is the first to be developed for mediterranean oak species in Spain and is an essential feature in any stand growth system.     

A merchantable volume system for Pinus sylvestris L. in the major mountain ranges of Spain

? Accurate estimation of stem volume makes it possible to estimate the monetary value of one of the many commodities and services that forests provide to society, i.e. timber.

? In the present study a compatible volume system for Scots pine in the major mountain ranges of Spain (the Pyrenees, Southern Iberian Range, Northern Iberian Range, Soria and Burgos Mountains, Central Range and Galician Mountains) was developed with data from 2 682 destructively sampled trees. Several well-known taper functions were evaluated. A second-order continuous-time autoregressive error structure was used to correct the inherent autocorrelation in the hierarchical data, allowing the model to be applied to irregularly spaced and unbalanced data.

? The compatible segmented model of Fang et al. (2000) best described the experimental data. It is therefore recommended for estimating diameter at a specific height, height to a specific diameter, merchantable volume, and total volume for the six mountain ranges analyzed.

? The non-linear extra sum of squares method indicated differences in mountain range-specific taper functions. A different taper function should therefore be used for each mountain range in Spain.

     

墨西哥瓦瓦州州东北部橡树商品材材积核算系统

比较了Kozak（1988）,Bi（2000）和Fang等（2000）的削度模型,形成了橡树商品材材积核算系统。在所研究的不同树龄、不同密度的松树．橡树混交林内,采集了298株橡树削度数据。结果表明,Fang等（2000）建立的可兼容分段模型可以很好地描述实验数据,可用于估测树木在指定树高的直径、树高一指定直径比、商品材材积量和总体积。本研究建立的公式可作为该研究区内森林调查的基本工具,简便、易于操作。统计分析结果表明,尽管本研究所建立的公式具有局地适应性,但仍可应用于其他区域。图4表4参53。     

Impact of targeted sheep grazing on herbage and holm oak saplings in a silvopastoral wildfire prevention system in south-eastern Spain

Several wildfire prevention programs in southern Europe are currently using livestock grazing for the maintenance of fuelbreaks. This silvopastoral management is valued for being sustainable and effective in reducing fuel loads, but few studies have analyzed other impacts linked to fuelbreak grazing. This paper reports on an experiment performed within the wildfire prevention program in Andalusia (southern Spain) with the aim of clarifying and quantifying the effect of fuelbreak grazing on herbage biomass, ground cover, herbage species composition, and growth of holm oak saplings. The study site, located in a semiarid Mediterranean environment, was grazed by a shepherded sheep flock from February to June in three consecutive years at a similar stocking rate. Livestock consumed between 33 and 68 % of herbage production in the different years, and the greatest fuel reduction (remaining dry matter of 200?kg?ha^?1) was registered in Year 2, when rainfall and herbage production was lowest. Ground cover was significantly affected by grazing: on average, the percentage of bare soil increased three-fold, while herbage cover was reduced by a quarter. The botanical composition of herbage varied remarkably between years, but very little between Grazed and Non-Grazed areas within each year. Non-browsed holm oak saplings became progressively larger than browsed ones, differences only reaching clear statistical significance at the end of the three experimental years. At this time, the volume of browsed saplings was 47–56 % smaller than that of non-browsed holm oaks, even though the former had also grown significantly in the course of the experiment.