Variation of heartwood phenolics and oak lactones between the species and phenological types of Quercus petraea and Q. robur

Pressler cores were taken of Quercus petraea and Q. robur treesfrom young German provenance stands and mature mixed plantationsin England. The concentration of total phenolics extracted fromthe outer heartwood was measured and significant differencesfound between the two species. Concentrations of oak lactones,measured from provenance samples, also varied significantlybetween the species. However, the difference in total phenolicsbetween species was much lower among the trees from the mixedplantations than from the provenance trials. Q. petraea wascharacterized by lower levels of total phenolics but greaterconcentrations of oak lactones than Q. robur. A comparison betweenlate and early flushing Q. petraea trees found no significantdifference in total phenolics between these phenological types.     

Growth stimulation of young oak plantations inoculated with the ectomycorrhizal fungus Paxillus involutus with special reference to summer drought

Nursery-grown Quercus petraea and Q. robur seedlings were inoculated with the ectomycorrhizal fungi Paxillus involutus, Hebeloma crustuliniforme or Laccaria laccata. At the end of the first growing season, the seedlings with roots colonized with the inoculated fungi were outplanted at two sites in northeastern France in 1985 or 1988. P. involutus was found to be the most competitive and efficient of the three fungi tested; its mycorrhizas were present 7 yrs after outplanting and it markedly improved the growth of both oak species. In the case of Q. robur, the growth stimulation was more marked on years with a dry summer. These results are discussed in terms of water relations and of competitiveness of the introduced versus resident symbiotic fungi.     

The reproductive success of a Quercus petraea × Q. robur F1-hybrid in back-crossing situations

A 56 year old Quercus petraea × Q. robur F1-hybrid was back-crossed to both parental species. Pollen mixes were applied and paternity assigned to offspring based on microsatellite markers. The studied Q. petraea × Q. robur hybrid proved highly fertile and back-crossed well with both Q. robur and Q. petraea with slight but not significant preference for Q. robur. The results do not support the hypothesis about highly unidirectional gene flow between Q. robur and Q. petraea towards Q. robur as the observed back-crossing ability of the hybrid opens a route for nuclear gene flow from Q. robur to Q. petraea. However, Q. petraea × Q. robur hybrids may be rare in nature and the results do not tell us if the (probably more common) reciprocal hybrid also back-crosses easily to Q. petraea.     

Oak in Wessex An Account of Field Studies 1982-4

The Wessex Silvicultural Group spent three years studying themanagement and silviculture of the oaks (Quercus robur L andQ petraea (Matt) Leibl) in the Wessex area. Low input methodsof establishment including the use of tree shelters and thetending and thinning of younger oak stands together with controlof timber quality were examined in twenty-one forests and estates.Environmental values were acknowledged. While Q robur has previouslypredominated, Q petraea is now generally preferred.     

OAK

Four basic stages in the life of the oak wood (Quercus roburand Q. petraea) are defined and the factors which should influencethe manager's mind when he weighs density of stocking and lengthof bole against rotation to meet his particular requirementsare considered briefly in non-technical language.     

The effect of heavy or 'free growth' thinning on oak (Quercus petraea and Q. robur)

Free growth is a type of heavy thinning which aims to maximizediameter increment and produce valuable timber on a relativelyshort rotation. An experiment is described which investigatedthe application of free growth to a stand of oak {Quercus petraeaand Q. robur) planted in 1930. At age 58 free growth thinninghad resulted in a mean diameter at breast height of 39.0 cmwith an estimated mean tree volume of 0.98 m³, compared with29.3 cm and 0.52 m³ for equivalent crown thinned trees. Discountedcash flow calculations showed that free growth thinning of oakcould be justified using a 3 per cent discount rate assumingthat the increased intensity of pruning results in a large proportionof veneer quality timber; an independent assessment indicatedthis may be possible. Free growth thinning of oak is not a commonpractice in British broadleaved silviculture probably becauseof the cost of controlling epicormic shoots. It is suggestedthat it may be more appropriate to other species such as ash,sycamore and wild cherry.     

PRELIMINARY LIGHT-INTENSITY STUDY UNDER SESSILE AND PEDUNCULATE OAK

While study by continental and American workers has continuedover a considerable period, little has been published in connexionwith forestry. A method is described using photoelectric cellphotometers and the results given of measurements made undercomparable stands of sessile and pedunculate oak (Quercus petraeaLiebe and Q. robur L.). These results confirm that sessile oakcasts more shade than pedunculate oak.     

Hybridization between Quercus robur and Q. petraea in a mixed oak stand in Denmark

? Hybridization and mating pattern between Quercus robur and Q. petraea was studied in a 5.8 ha mixed forest stand in Jutland, Denmark which comprises in total 135 Quercus robur and 230 Q. petraea trees. Classification of the oak trees into species was performed using canonical discriminant analysis of a range of leaf morphological traits. Adult trees (365) and offspring (582) were genotyped with eight microsatellite markers. Seedlings were sampled in 2003 and acorns were collected in 2004.

? Mating patterns of Q. robur and Q. petraea are expected to be different in the northern range of the distribution area and a larger hybridization rate is expected. It is further expected, that pollination from outside sources will be relatively less in small fragmented forest management systems compared to large scale oak forest. The conclusions should be verified through repeated year to year analysis of the mating pattern.

? Phenological studies revealed that there was no difference in flowering time between species. Data for the adult trees revealed no significant departures from Hardy-Weinberg proportions and there was weak, but significant spatial genetic structure, which supports the idea that the stand is of natural origin. Spatial genetic structure in the first distance class is stronger for Q. petraea. The genetic composition of the offspring was remarkably consistent from year to year. Paternity analysis revealed that, on average, 85% pollination came from fathers within the stand. The direction of the pollen flow varied from year to year. Inter-specific hybridization was high and ranged from 15–17% and from 48–55% for Q. petraea and Q. robur mothers respectively. Paternity analysis revealed that the population was basically outcrossing and only 3.7% of the analysed progeny were the product of selfing. Over the two years of study, approximately 200 trees contributed to the paternity of the next generations.

? The study confirms earlier studies with a greater tendency for Q. robur mothers to produce hybrid seeds than Q. petraea mothers. The rate of hybridization is higher in this Danish stand than in comparable studies elsewhere in Europe. Gene flow from outside sources are relatively low.

     

Intrapopulation and Interpopulation Genetic Variation of Quercus in Denmark

Native Danish oak stands are fragmented and decreasing because of the extensive use of foreign seed sources. Therefore, the population structure of natural Danish oak stands was analysed by means of six polymorphic enzyme loci. A total of 17 stands of Quercus robur L. (including an ''outgroup'' sample from The Netherlands), seven Quercus petraea [Matt.] Liebl. and two putative hybrid stands were included in the study. The average genetic diversity was similar for the two species as well as for the putative hybrid stands: 0.25 for Q. robur, 0.27 for Q. petraea and 0.26 for the hybrid stands. The genotypic proportions at two (Pgm and Mnr) of the six loci showed many significant deviations from Hardy-Weinberg expectations, always with an excess of homozygotes, whereas the remaining four loci accorded to Hardy-Weinberg proportions, suggesting a low level of inbreeding. The differentiation of the Q. petraea and Q. robur populations was quantified with Wright's F-statistics. The within-species component was low, 0.022, reflecting the wind-pollinated reproductive mode of the two species. The betweenspecies component was 10-fold higher, 0.235, indicating two separate groups. A phylogenetic tree estimated from allele frequencies also supported the presence of these two groups. Despite the two well-separated groups in the tree, it was not possible to assign all individuals to the species to which they supposedly belonged. In total, 10% of the Q. robur individuals and 14% of the Q. petraea individuals were assigned to the other species, suggesting a limited amount of introgression between the two species.     

Genetic control of wood colour, density and heartwood ellagitannin concentration in European oak (Quercus petraea and Q. robur)

Pressler cores of young clones of Quercus petraea and Q. roburwere analysed from two sites in Germany. Variation of wood colour(defined by the CIELAB system), density and heartwood ellagitanninswas examined between clones, species and sites. Similar studieswere made of cores from another trial of 20 half-sib familiesof parent trees deriving from five German forests. The resultsfrom both the clonal and progeny trials indicate that heartwoodellagitannin content and wood density are under strong geneticcontrol, while sapwood and heartwood colour are less so. A largeproportion of between-clone variation in wood density and ellagitanninlevels occurred between the two species, while these propertiesvaried little among ramets of the same clone grown on two contrastingsites, despite a difference in growth rates. A large proportionof the total variation among progeny was attributed to forestorigins and could not be attributed clearly to either geneticor environmental causes because of limitations of the samplingdesign     

AN ENUMERATION OF THE MATURE OAK IN THE FOREST OF BERE

The paper describes the methods used in the field and in theoffice to determine the standing volumes and increments of 100-and 130-year old oak in the Forest of Bere, Hampshire, duringworking-plan revision. The figures obtained show that the standingvolumes and increments of sessile oak (Quercus petraea Liebe)are considerably higher than those of pedunculate oak {Q. roburL.) on the three sites investigated, namely, clays, sands, andgravels, while for both species sands appear to be the mostfavourable and gravels the least favourable soil types. Therewas little difference in the mean values for increment and standingvolume between the 100- and the 130-year old pedunculate oak.     

THE STORAGE OF ACORNS IN WATER

Acorns of sessile oak (Quercus petraea) will not tolerate prolongedsubmergence, but those of pedunculate oak (Quercus robur) survivevery well in regularly changed distilled water or tap-water.Survival is considerably worse in basic river water; the differencefrom tap-water is likely to be due either to the greater activityof organisms promoting decay, or to the prevalence of loweroxygen-tensions in river water. Storage in water under suitablycontrolled conditions might be a useful practical procedurewith pedunculate acorns.     

A comparison of the autecology of Quercus robur L. and Q. pyrenaica Wild.: present habitat in Galicia, NW Spain

The biotopes occupied by pedunculate oak (Quercus robur L.)and rebollo oak (Quercus pyrenaica Willd.) in Galicia were characterizedusing different parameters, enabling a comparative analysisof its habitats. Thirty-nine plots of pedunculate oak and 40of rebollo oak were inventoried and 25 ecological parameters(physiographic, climatic and edaphic) were measured to describethe biotopes, along with 14 stand parameters to characterizethe structure and the silviculture of these forests; some ofthem were used in previous works about the autecology of bothspecies. Quercus robur was found to occupy a wider range ofecological habitats and their distribution is oceanic; Q. pyrenaicapresents a more Mediterranean phytoclimatic position. The resultsindicated that the distribution of oak forests in Galicia ismore closely related to physiographic and climatic featuresthan to edaphic, because the nature of the substrates that theyoccupy is similar. Analysis of fragility/aggressiveness betweenboth species and chestnut shows that the aggressiveness of bothoaks, mainly pedunculate, was much higher, except at high altitudes,and in areas with a high mean temperature, where rebollo ismore aggressiveness. Comparison of the two Quercus shows formost of the parameters that Q. robur is the more aggressivespecies.     

Variation in wood volatile compounds in a mixed oak stand: strong species and spatial differentiation in whisky-lactone content

The effect of species and ecological conditions on oak volatile extractive content was investigated in an evenaged (100 years) stand located in western France. The sample included a total of 286 trees (118 sessile, 158 pedunculate and 10 oaks with an intermediate morphology) growing in contrasted environments (plateau, intermediate slope, small valley). The main factor influencing oak extractives level is species. The effect of the local environment appears negligible. No correlation between ring width and volatile extractive content was found. Q. petraea is significantly richer than Q. robur in eugenol and whisky-lactone (10.8 vs. 0.6 μg/g). However, two groups of sessile oaks could be identified, one poor and one rich in whisky-lactone. Among the latter, either the cis or the trans stereoisomer was predominant, suggesting that their production is not independent. A strong spatial structure was detected for whisky-lactone (cis-, trans- and total whisky-lactone, for the two species combined but also for Q. petraea alone in the case of the cis isomer).     

Effects of flooding duration, -frequency and -depth on the presence of saplings of six woody species in north-west Europe

Under natural conditions the zonation of woody species in floodplains is to a large extent determined by hydrological conditions. Flood survival varies even among closely related species of the same genus. Most studies that quantify flood survival of seedlings and saplings of European floodplain species focus on species of the genera Salix and Populus, while few studies on saplings of Quercus robur, Fraxinus excelsior, Crataegus monogyna have been carried out, and even less on comparing these species groups. We performed a comparative observational study on the presence of saplings (<150 cm) of Quercus robur, Fraxinus excelsior, Crataegus monogyna (hardwood species), Salix alba, Salix viminalis and Populus nigra (softwood species) in nature reserves along the Lower Rhine in the Netherlands. For each plot (n = 1178) the duration, frequency and depth of inundation was determined. This was done for both the entire year (January–December) and the growing season (March–October).We found that the presence of the hardwoods decreased with increasing inundation duration and even more so if the inundation occurred during the growing season. Contrary to what is generally assumed, the negative effects of flooding were stronger for F. excelsior than for Q. robur. For the hardwood group the total annual inundation duration was the best explanatory variable.The presence of the softwood species increased with increasing inundation duration and more so if the inundation occurred during the growing season. The average duration per inundation event was the best explanatory variable for this group, especially for both Salix species. The presence of P. nigra was best explained by the average inundation depth. A canonical correspondence analysis on species composition was consistent with these findings.Overall, our results agree with the general perspective of tree zonation along rivers. This is the first study that shows the singular and combined effects of several flooding characteristics on both presence, and species composition, of softwood and hardwood species from riparian woodlands. We outline an approach indicating how the results can be used for the selection of sections in retention areas suitable for the recruitment of the studied tree species.     

The effect of roots and litter of Calamagrostis canadensis on root sucker regeneration of Populus tremuloides

Marsh reed grass (Calamagrostis canadensis (Michx.) Beauv.)is a common, highly competitive grass native to the boreal mixedwoodforest. This grass increases in abundance after clear-cut loggingbut little is known about its effects on trembling aspen (Populustremuloides Michx.) sucker regeneration. The effects of Calamagrostissod and its litter on aspen regeneration were studied in twoseparate greenhouse studies. Calamagrostis sod did not affectthe initiation of suckers, but resulted in 30 per cent fewersuckers emerging above the soil that were smaller and had 40per cent less leaf area. Calamagrostis litter had little effecton the initiation and number of emerged suckers; however, itdelayed emergence by 10 days. The physical barrier by rootsand litter of Calamagrostis reduced or delayed the expansionof suckers and therefore prolonged their dependence on rootreserves. By the time the suckers reached the surface, theyhad to compete for light with Calamagrostis shoots that hademerged a week earlier. This, coupled with low soil temperaturesassociated with Calamagrostis in other experiments, will significantlyreduce the number and growth of suckers. Any reduction and delayin sucker emergence will decrease aspen regeneration and productivitysince the growing season in the boreal forest region is short.     

Species-specific drought effects on flower and fruit production in a Mediterranean holm oak forest

A holm oak forest was exposed to an experimental drought (reductionof 15 per cent soil moisture as predicted for this area forthe next decades by General Circulation Models and ecophysiologicalmodels) during 7 years to elucidate the reproductive responsesof the dominant species Quercus ilex L., Arbutus unedo L. andPhillyrea latifolia L. Soil moisture was partially reduced byplastic strips intercepting rainfall and by ditch exclusionof water runoff. During the period studied, meteorological conditionsand soil moisture were continuously monitored, together withflower and fruit production in the three dominant species. InQ. ilex and A. unedo, flower and specially fruit productionwere strongly correlated with annual rainfall, but not in P.latifolia. The experimental drought reduced flower and fruitproduction in Q. ilex by 30 per cent and 45 per cent, respectively.Reductions in flower and fruit production were not significantin A. unedo and were not observed in P. latifolia. A decreasein production of reproductive structures and the different responseof the species studied to a decrease in water availability couldinduce important changes in the competitive ability of the differentspecies and in the long term in the community species compositionand future distribution of these Mediterranean species.     

The Economics of a Private Forestry Enterprise in South-east Scotland

The annual income and expenditure accounts have been summarizedfor the period 1949–61. The woods had not previously beenunder regular management and due to war fellings were only 60per cent, stocked in 1949. The treatment policy has been restockingand rehabilitation with minimum cash investment. The local conditions,management history, and growing stock are briefly described,and a book valuation is presented to show value of land plusgrowing stock at the beginning and at the end of the period.The book profit on 806 acres averaged ?5. 6s. per acre per annum,of which ?3 per acre is increase in book valuation. This isequivalent to a yield of 6.4 per cent, on an average book valueof the land plus growing stock of ?70,000. The yield per cent,is expected to fall as the capital value of the growing stockincreases. Although these figures may give a reasonably accurateaccount of the financial results, it is considered that theyunderestimate the true value of the woodlands to the estateeconomy.     

A Comparison Between European Continental and British Provenances of Some British Native Trees: Growth, Survival and Stem Form

Data describing the growth, survival and stem form of: a) Europeancontinental, and b) British provenances of trees native to Britainwere collated from Forestry Commission records. The growth ratesof European continental provenances of Scots pine (Pinus sylvestris),silver birch (Betulo pendula), sessile oak (Quercus petraea)and common alder (Alnus glutinosa) were inferior to those ofBritish provenances in 90 per cent of cases. European provenancesof these species also showed inferior survival. The growth ratesof continental provenances of beech (Fagus sylvatica) were superiorto British provenances in about 50 per cent of cases, provenancesfrom northern France, Belgium and Holland being the fastestgrowing. Relationships between the relative height growth offoreign provenances and latitude were demonstrated for Scotspine, silver birch and beech (relative height growth = the heightgrowth of a foreign provenance expressed relative to that ofBritish provenances at the same site). The continental provenancesthat grew best originated at 0–4° south of the latitudesof the planting sites. Relative height growth decreased bothnorth and south of these latitudes. In the case of oak, relativeheight growth did not vary widely between origins. The survivalof continental provenances of Scots pine was particularly pooron exposed upland sites. The stem form of British provenancesof Scots pine was intermediate between Fennoscandian provenancesand provenances from the rest of Europe. In oak and beech therewas generally little difference in stem form between Britishand continental provenances, but the best continental provenances(Belgian beech; French oak) were most reliable. The growth andsurvival of native trees is interpreted in the light of thepost-glacial history of these species. The implications regardingthe continued use of seed of native hardwoods imported fromcontinental Europe are discussed.     

Growing Oaks at Closer Spacing

The reasons for the scarcity of tall straight oaks (Quercusrobur L. and Q. petraea (Mattuschka) Liebl.) in Great Britainare discussed in this paper. It is argued that the historicalpractice of growing timber at very wide spacings in coppice-with-standardssystems rather than high forest, coupled with generations ofselection for crookedness rather than straightness, has resultedin a dearth of tall, well-formed trees. Evidence is presentedthat oak produced in conditions of quite severe competitionwill grow much taller than widely spaced trees. It is concludedthat the current practice of planting at densities of 1100 treesper hectare is unlikely to lead to the government's stated objectiveof encouraging an 'increase [in] the quality and value of timberproduced by broadleaved woodlands as a whole' (Forestry Commission,1985). The economic and other implications of considerably closerspacing are discussed. Received 15 October 1990.