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Using databases of previously published primers, we optimised six nuclear microsatellite markers for Prunus africana for the purposes of studying spatial genetic structure and gene flow. To assess variability, these and three previously transferred loci were screened in populations from Kenya and South Africa. Across both populations most loci were polymorphic, with the exception of a single locus which failed to amplify in the South African samples, exhibiting between 2 and 22 alleles and levels of expected heterozygosity (He) ranged from 0.059 to 0.932. Departures from Hardy-Weinberg equilibrium were detected for all loci but not for all populations. The estimated null allele frequency was very low to moderate and no evidence for linkage disequilibrium was detected.

The spread of arbuscular mycorrhizal (AM) fungi from tree to crop roots was examined by molecular and microscopic methods in a glasshouse study. Growth of Calliandra calothyrsus Meissner trees inoculated with isolates of the AM fungi Glomus etunicatum Becker and Gerdemann and Gigaspora albida Schenck and Smith was monitored over an 18-month period. Three successive ‘intercrops’ of beans or maize were sown at 25, 50 and 75 cm distances from the tree and harvested during this period. At each crop harvest, the distribution of tree and crop roots and the spread of the inoculant fungi were determined using traditional microscopic methods and fungal specific primers. Both inoculants greatly improved the growth of the trees and colonization spread to the crops once the trees were 6 months old. However, benefits of inoculation to crop growth were not observed due to increased competition from the larger inoculated trees growing in a restricted soil volume. Of the two inoculant fungi, Glomus etunicatum appeared to be more mobile as it spread more rapidly, formed higher levels of colonization at increasing distances from the tree and was responsible for most of the mycorrhizal cross-contamination. In contrast, colonization of tree and crop roots by Gigaspora albida was higher nearest the tree. This work demonstrated the benefits of mycorrhizal fungus inoculation for tree growth and confirmed that trees and crops share the same AM fungi. Trees may therefore act as reservoirs of mycorrhizal fungi, either inoculant or indigenous, for surrounding crops or other annual vegetation. It was also shown that tree pruning, the normal practice in agroforestry systems, did not reduce mycorrhizal colonization or prevent spread to crops. However, the slow rates of inoculant spread found here suggest that it may take years before inoculants benefit the growth of crops sown several metres from the tree. The work also demonstrated that microscopic quantification of mycorrhizal colonization and the use of molecular probes to identify specific fungi within roots can complement each other effectively. Molecular probes were more sensitive at detecting mycorrhizal fungi than microscopic methods, but did not discriminate between full mycorrhizal structures and traces of hyphae.

Aim Agroforestry systems incorporating N-fixing trees have been shown to be socially beneficial and are thought to be environmentally friendly, both enriching and stabilizing soil. However, the effect of such systems on the emissions of the important greenhouse gas nitrous oxide (N 2 O) and the tropospheric ozone precursor nitric oxide (NO) is largely unknown. Location Soil was collected from the research plots of Institut Senegalais de Recherches Agricoles at Bandia and Bambey, Senegal, West Africa, and from neighbouring farmers' fields. Trace gas flux measurements and chemical analysis of the soil were carried out at the Centre for Ecology and Hydrology (CEH), Edinburgh, UK. Methods Nitric oxide (NO) and nitrous oxide (N 2 O) emissions were measured following simulated rainfall events (10 and 20 mm equivalents) from repacked soil cores collected under two tree species (Acacia raddiana) and Eucalyptus camaldulensis) in each of two provenance trails. In addition, soil samples were collected in local fields growing peanut (Arachis hypogaea) and Sorghum (Sorghum vulgare), close to the species trials in Bambey. NO was measured using a flow through system and was analysed by chemiluminescence. Nitrous oxide was measured from the repacked soil core headspace and was analysed by electron capture gas chromatography. Soil mineral N was extracted with KCl and analysed by colorimetric methods on separate soil columns. Results Light rainfall, which increased the gravimetric soil moisture content to 20%, stimulated an increase in NO emission but there was no detectable N 2 O emission. A heavy rainfall event, which increased the gravimetric soil moisture to 30%, stimulated N 2 O emission with a subsequent peak in NO emissions when the soils became drier. Soil collected under the N-fixing tree species emitted significantly more N 2 O than soil collected under the N-fixing crop species (P < 0.01). NO and N 2 O emissions significantly correlated with soil available N (NH 4 and NO 3 ) (P < 0.05). Main conclusions Rainfall intensity, supply of mineral N from organic matter and N fixation were the prime drivers of NO and N 2 O emissions from seasonally dry tropical soils. The improved soil fertility underneath the trees provided a larger pool of mineral N and yielded larger rates of NO and N 2 O emissions.

Nitrate in the unsaturated zone between the soil surface and the water table was studied in agroforestry Parklands in north western Senegal by examination of samples obtained by hand auger. Depending on location, water tables existed at depths between 10 and 35m below ground. Previous studies of groundwater in this region had found that large concentrations of nitrate were unconnected with anthropogenic activity. The objective of this study was to determine whether nitrogen fixing vegetation had a role in groundwater nitrate accumulation and whether roots of trees were located deeply enough to access the nitrate. Accordingly, sample profiles were augered close to stems of nitrogen fixing trees, non-nitrogen fixing trees and also in adjacent areas that were unaffected by tree presence. These adjacent areas were typically open pasture or cultivated fields. Tree fine roots were quantified in the samples and examined for the presence of mycorrhizas. Similarly, sand/soil samples were examined and tested for the presence of nitrogen fixing rhizobia that were capable of forming functional nodules on appropriate host plants. Concentrations of nitrate were greatest in soils beneath nitrogen fixing trees and nitrate was more plentiful in profiles augered beneath nitrogen fixing crops than it was elsewhere suggesting that N-fixation was the source of the nitrate. The concentrrations of nitrate that were found in the unsaturated zone were greatly in excess of the WHO recommended limit for nitrate in drinking water. High NO3-N/Cl ratios confirm insitu production of nitrate, and indicate that this is a natural baseline occurrence related to N-fixation. The nitrate is moving down the profile and impacts the groundwater unless it can be intercepted by plant roots. NO3-N amounts in solution in the soil profile varied between 75 and 1000kg ha−1 beneath trees and between 120 and 400kg ha−1 in areas outwith tree crowns. Although these quantities of N occupy the lower end of the range of N values obtained in north American deserts, they comprise a considerable dryland resource where amounts of organic fertilizer are limited and where cost prohibits the use of commercial fertilizers. Roots of both nitrogen fixing and non-nitrogen fixing trees were deep enough to access the nitrate but the small amounts of available water at intermediate depths suggest that large scale uptake of nitrate will only be possible in the wetter zones located close to the water table. Shallow roots tended to be more heavily colonized by mycorrhizas than deeper roots but mycorrhizas were recovered from roots located 22m below ground. Tree roots and rhizobia had similar patterns of distribution. They were commonest close to the soil surface, less frequent at intermediate depths and tended to increase in frequency close to the water table.

Summary This paper describes the route, speed and mode of colonisation of oaks by integrating a number of independent analyses using molecular ecology, palaeoecology and simulation modelling approaches. Using a synthetic map of the contemporary distribution of chloroplast DNA (integrating several published and unpublished data sets and describing variation in 1468 trees from 313 autochthonous stands of Q. robur and Q. petraea from Britain and Ireland), and considering the postglacial topographic landscape, the most likely routes of postglacial colonisation across the British Isles are suggested. The overall pattern of these directions agrees with previous interpretations, but several routes, particularly those into Ireland, differ from previous interpretations and benefit here from using a single synthesised data set. Interestingly, the Atlantic oakwoods appear to have been colonised by individuals bearing a single haplotype (type 12). Two palaeoecology data sets, published separately for Britain and Irel...

We report a method using variation in the chloroplast genome (cpDNA) to test whether oak stands of unknown provenance are of native and/or local origin. As an example, a sample of test oaks, of mostly unknown status in relation to nativeness and localness, were surveyed for cpDNA type. The sample comprised 126 selected trees, derived from 16 British seed stands, and 75 trees, selected for their superior phenotype (201 tree samples in total). To establish whether these two test groups are native and local, their cpDNA type was compared with that of material from known autochthonous origin (results of a previous study which examined variation in 1076 trees from 224 populations distributed across Great Britain). In the previous survey of autochthonous material, four cpDNA types were identified as native; thus if a test sample possessed a new haplotype then it could be classed as non-native. Every one of the 201 test samples possessed one of the four cpDNA types found within the autochthonous sample. Therefore none could be proven to be introduced and, on this basis, was considered likely to be native. The previous study of autochthonous material also found that cpDNA variation was highly structured geographically and, therefore, if the cpDNA type of the test sample did not match that of neighbouring autochthonous trees then it could be considered to be non-local. A high proportion of the seed stand group (44.2 per cent) and the phenotypically superior trees (58.7 per cent) possessed a cpDNA haplotype which matched that of the neighbouring autochthonous trees and, therefore, can be considered as local, or at least cannot be proven to be introduced. The remainder of the test sample could be divided into those which did not grow in an area of overall dominance (18.7 per cent of seed stand trees and 28 per cent of phenotypically superior) and those which failed to match the neighbouring autochthonous haplotype (37.1 per cent and 13.3 per cent, respectively). Most of the non-matching test samples were located within 50 km of an area dominated by a matching autochthonous haplotype (96.0 per cent and 93.5 per cent, respectively), and potentially indicates only local transfer. Whilst such genetic fingerprinting tests have proven useful for assessing the origin of stands of unknown provenance, there are potential limitations to using a marker from the chloroplast genome (mostly adaptively neutral) for classifying seed material into categories which have adaptive implications. These limitations are discussed, particularly within the context of selecting adaptively superior material for restocking native forests.

Despite the clear evidence of competition for water between trees and crops, there have been very few studies comparing simultaneous water use by differing tree species in drylands. Comparative water use by dryland trees was measured in Senegal using heat balance gauges at the end of the wet season and in the dry season. Significant differences between tree species were found for maximum rates of water use per unit leaf area. Indigenous species may be better adapted to the dry environment than exotic species but the indigenous species Acacia seyal Del. used more water per unit leaf area than all other species. The exotic species Azadirachta indica Adr. Juss. consistently used less water per unit leaf area than most other species. There were significant differences in amounts of water used per unit leaf area by differing provenances of the same tree species. Water use in the dry season varied by a factor of three between two provenances of Acacia aneura F. Muell ex Benth. indicating potential to select provenances for drylands based on their water use characteristics. Absolute rates of water use as well as differences in sapflow between species were greatest when soils were moist suggesting that comparative sapflow studies will be most informative when carried out during the wet season. Water use rankings of the differing tree species were broadly maintained irrespective of season.

Two oak woods in northern Britain which contained both Quercus robur and Quercus petraea were selected for study. The woods differed in the degree of human interference they had experienced; Roudsea, in the Lake District, is a native wood with no record of planting but has experienced coppicing; Dalkeith, in southern Scotland, has experienced extensive planting and management. All the trees in a selected area of each wood (nearly 700 trees) were mapped and genotyped using six nuclear microsatellite loci. A range of statistical methods was used to assess the diversity and degree of spatial genetic structure present in each wood, and results are compared with published results for a natural oakwood in central France (Petite Charnie). For the unplanted wood at Roudsea, significantly higher genetic diversity and greater spatial genetic structure, at relatively short distances, was detected in the Q. petraea component of the wood relative to that of Q. robur. These observations agree with those from Petit Charnie and indicate that native oak woods across Europe maintain similar levels and structure of genetic variation, and is probably due to differences in seed dispersal mechanism and regeneration dynamics of the species. At Dalkeith, however, significant spatial structure of genetic variation occurred in both species examined, and the additional influence of planting is offered to account for increased genetic structure within this wood. At Roudsea, the influence of coppicing is also discussed to explain the lack of population genetic equilibrium and increased genetic diversity at this site.

Survival, biomass production, nutrient use and fertility of soil were examined in experimental stands of 10-year-old N-fixing indigenous Acacia nilotica (L.) Del. (eight provenances), A. senegal (L.) Willd. (one provenance), Acacia tortilis (Forsskal) Hayne (six provenances), Acacia raddiana syn A. tortilis (Forssk.) Hayne ssp. raddiana (Savi) Brenan (three provenances) and exotic N-fixing A. holosericea A. Cunn. ex G. Don (one provenance), A. cowleana Tate (one provenance), Acacia aneura F. Muell. ex Benth. (twelve provenances), Prosopis juliflora (Sw.) DC. (one naturalised provenance), Prosopis cineraria (L.) Druce (five provenances) and P. chilensis (Molina) Stuntz (two provenances) growing on a coastal site in semi-arid Senegal. Similar data were obtained for the non-N-fixing fast-growing exotic species Azadirachta indica Adr. Juss. and Eucalyptus camaldulensis Dehnh. of the same age that were growing on adjacent plots. P. juliflora produced more biomass than the other species and showed the greatest potential for use as a multipurpose tree. A. aneura showed the greatest potential for fodder production and despite its small stature, it ranked second for biomass among the N-fixing species. Of the indigenous species, A. nilotica was the most efficient user of non-renewable elements in biomass production. A. raddiana seemed profligate in its consumption of both N and P in wood production. E. camaldulensis was efficient in its use of N in wood but its wood contained large concentrations of P and K. A. aneura, P. juliflora and A. nilotica had the smallest concentrations of P in wood. A. raddiana and A. indica contained large concentrations of K in their wood in contrast to A. aneura and A. nilotica which were the most efficient users of K in wood production. There were few significant differences in fertility in soils beneath the differing tree species. Nevertheless, plots containing P. juliflora and P. cineraria tended to be the most fertile. Soil beneath A. indica was more fertile than soil beneath some N-fixing species. The extent of removal of plant nutrients in biomass suggests that without inputs of nutrient elements, harvest of wood and foliage is unlikely to be sustainable at the measured rate of production for more than two tree rotations of 10 years duration.

International audience; Leaf morphology was assessed in nine mixed oak stands (Quercus petraea and Q. robur) located in eight European countries. Exhaustive sampling was used in an area of each stand where the two species coexisted in approximately equal proportions (about 170 trees/species/stand). Fourteen leaf characters were assessed on each of 5 to10 leaves collected from the upper part of each tree. Three multivariate statistical techniques (CDA, canonical discriminant analysis; PCA, principal component analysis; MCA, multiple correspondence analysis) were used in two different ways: first on the total set of leaves over all stands (global analysis) and second, separately within each stand (local analysis). There was a general agreement of the results among the statistical methods used and between the analyses conducted (global and local). The first synthetic variable derived by each multivariate analysis exhibited a clear and sharp bimodal distribution, with overlapping in the central part. The two modes were interpreted as the two species, and the overlapping region was interpreted as an area where the within-species variations were superimposed. There was no discontinuity in the distribution or no visible evidence of a third mode which would have indicated the existence of a third population composed of trees with intermediate morphologies. Based on petiole length and number of intercalary veins, an "easy to use" discriminant function applicable to a major part of the natural distribution of the species was constructed. Validation on an independent set of trees provided a 98% rate of correct identification. The results were interpreted in the light of earlier reports about extensive hybridization occurring in mixed oak stands. Maternal effects on morphological characters, as well as a lower frequency or fitness of hybrids in comparison with parent species could explain the maintenance of two modes, which might be composed of either pure species or pure species and introgressed forms.; La différenciation morphologique des feuilles entre Quercus robur et Quercus petraea est stable à travers les peuplements mélangés de chênes de l'ouest européen. La variabilité de la morphologie foliaire a été etudiée dans neuf peuplements mélangés de chênes (Quercus petraea et Q. robur) en Europe sur la base d'un échantillon exhaustif moyen de 170 arbres/espèce/peuplement. Trois méthodes d'analyses multivariables ont été utilisées (ACD : analyse canonique discriminante ; ACP : analyse en composantes principales ; AFC : analyse factorielle des correspondances). Les trois méthodes aboutissent à des résultats congruents. La première variable synthétique de chaque méthode se caractérise par une distribution bimodale, chaque mode correspondant à une espèce. La distribution de la première variable ne manisfeste pas de discontiunuité pouvant indiquer l'existence d'un troisième groupe, correspondant à des arbres avec des morphologies de type intermédiaire. Une méthode d'identification rapide basée sur les deux caractères les plus discriminants (nombre de veines intercalaires et longueur du pétiole) a été proposée et validée sur un autre jeu de données (98 % d'identifications correctes). La structure de la variation morphologique entre les deux espèces résulte sans doute de l'hybridation entre elles, et de l'hérédité des caractères morphologiques.

The aim of this work was to investigate whether a correlation exists between maternal lineage, assessed by variation in maternally inherited chloroplast DNA (cpDNA) and nuclear controlled variation (phenotypic traits and gene markers). Variation in cpDNA and nuclear controlled traits (62 phenotypic traits, eight isozyme and 31 RAPD loci) was studied in deciduous oak trees (mostly Q. petraea) growing in 16 provenance tests. Results from two nuclear diversity studies were also included. The test for correlation was performed using two methods by: (1) comparing provenance mean values (or allele frequencies) among different lineages using ANOVA, (2) making pairwise comparisons of chloroplastic genetic distances (CGDs) with phenotypic differentiation index (DI) (or nuclear genetic distances (GD)) among all provenances using the Mantel test. Among the 62 phenotypic traits, only seven exhibited significant associations with maternal lineages when tested using ANOVA (six using Mantel test). This number decreased to two once correction for geographic distance was introduced in the calculation for Mantel test. There were stronger correlations between maternal lineage and nuclear gene markers. The existence of cytonuclear disequilibrium was shown by the significant differences in allozyme frequencies between the four maternal lineages (at least one allele for each locus). These associations were confirmed by significant correlations between CGD and GD. Finally associations were also found between levels of diversity in nuclear markers and maternal lineages. These results are discussed in the context of the glacial and postglacial history of oak populations in Europe. The analysis suggests that the processes which led to the current structure of chloroplastic diversity and variation for phenotypic traits can be subdivided into four major phases. (1) During the last long glacial period, deciduous oaks were probably confined to three major refugia which were genetically differentiated for chloroplastic and nuclear genes. (2) At the end of the glacial period, oaks migrated northwards and established a spatial pattern of distribution for chloroplastic genes which remains largely intact to this day. (3) As oaks progressively occupied the mid and northern parts of Europe, pollen flow established communication between stands originating from eastern and western refugia. This resulted in the gradual erosion of the original nuclear differentiation while conserving the chloroplastic variation installed during colonization. (4) Local selection pressures acting on the established populations eventually caused their genetic differentiation gradually to increase with time. New patterns of differentiation now exist which are totally different from those in place immediately following colonization. During this time, chloroplastic divergence remained unchanged. These processes led to the loss of any association between chloroplastic divergence and phenotypic traits, although some association with gene markers which are less affected by selection has been retained.

Chloroplast DNA (cpDNA) variation was studied in the white oak species, Quercus robur and Quercus petraea , from Denmark, Norway, Sweden and Finland. A total of 474 trees from 91 populations were screened within the region for a set of previously characterised cpDNA haplotypes. Within the sample, haplotype 1, known to have originated from an Italian Pleistocene forest refugium, was the most common (55%), and was well-distributed across all Scandinavian countries and dominated in Sweden. We propose that material of Italian origin was part of the first wave of post-glacial migration of oak into Scandinavia, and that the Italian haplotype migrated into Finland from Sweden across the Baltic Sea. In Finland, a sharply defined transition zone between the haplotype of Italian origin and haplotype 5, originating from an eastern European refugium in the Balkans, was observed in southern Finland, and confirms the findings of a previous study [Heredity 80 (1998) 584]. Evidence from the study of Csaikl et al. [For. Ecol. Manage., this issue] confirms that this haplotype migrated into Finland via an eastern route through the Baltic States. Another haplotype of Balkan origin (haplotype 7) was only common in southern Denmark and known to be present throughout the native German forests [For. Ecol. Manage., this issue], from where we believe it migrated into Denmark. It appears probable that this haplotype reached Denmark later than the Italian lineage as its progress towards north appears to have been hindered by a bottlenecking in central Denmark. Finally, three haplotypes originally of Iberian origin (haplotypes 10–12) were also found at intermediate frequency throughout the Nordic countries sampled, except Finland. This pattern of distribution suggests that migration occurred concurrently or just behind that of the Italian lineage. One of the Iberian haplotypes (haplotype 12) is rare in autochthonous stands, but found at a frequency of 24% in planted non-autochthonous stands in Denmark. Overall, the proportion of populations fixed for a single haplotype was high in natural, autochthonous stands (77%) and lower in artificial stands (54%). In addition, population subdivision was higher ( G ST =0.87) and diversity lower ( h S =0.075 and h T =0.6) in autochthonous stands than in artificial stands ( G ST =0.69, h S =0.22, h T =0.72). The pattern of haplotype distribution across Scandinavia and Finland appears fairly clumped and is discussed in relation to natural gene flow, leptokurtic post-glacial dispersal and human influences. Finally, no relation between cpDNA haplotype and six quantitative traits measured on autochthonous stands in Denmark was found. The potential for cpDNA haplotype screening for setting gene conservation and seed certification priorities is discussed.

The geographic distribution throughout Europe of each of 32 chloroplast DNA variants belonging to eight white oak species sampled from 2613 populations is presented. Clear-cut geographic patterns were revealed by the survey. These distributions, together with the available palynological information, were used to infer colonisation routes out of the glacial period refugia. In western Europe in particular, movements out of the Iberian and the Italian Peninsulas can be clearly identified. Separate refugia are also present in eastern Balkans, whereas further west in this peninsula similarities with Italy were evident. Movements resulting in the exchange of haplotypes between refugia both during the present interglacial and probably also during earlier glacial cycles were therefore inferred. The consequences of these past exchanges is that phylogenetically divergent haplotypes have sometimes followed very similar colonisation routes, limiting somewhat the phylogeographic structure. Cases of geographic disjunction in the present-day distribution of haplotypes are also apparent and could have been induced by the existence of rapid climatic changes at the end of the glacial period (specifically the Younger Dryas cold period), which resulted in range restriction following an early warm period during which oak first expanded from its primary refugia. This cold phase was followed by a new period of expansion at the outset of the Holocene, involving in some cases ‘secondary’ refugia. It is expected that these short climate oscillations would have led to a partial reshuffling of haplotype distribution. Early association between haplotypes and oak species are also suggested by the data, although extensive introgression among species has ultimately largely blurred the pattern. This implies that colonisation routes may have been initially constrained by the ecological characteristics of the species hosting each chloroplast variant. We suggest for instance that two oak species distributed in the north of the Iberian Peninsula ( Quercus petraea and Q. pubescens ) are recent post-glacial immigrants there. When considered together, conclusions on the location of glacial period refugia and the colonisation routes derived from molecular information and fossil pollen data appear to be both largely compatible and complementary.

A consortium of 16 laboratories have studied chloroplast DNA (cpDNA) variation in European white oaks. A common strategy for molecular screening, based on restriction analysis of four PCR-amplified cpDNA fragments, was used to allow comparison among the different laboratories. A total of 2613 oak populations (12,214 individual trees from eight species) were sampled from 37 countries, and analysed with the four fragments. They belong to eight related oak species: Quercus robur, Q. petraea, Q. pubescens, Q. frainetto, Q. faginea, Q. pyrenaica, Q. canariensis and Q. macranthera. During this survey, 45 chloroplast variants were detected and are described together with their phylogenetic relationships, but several of these haplotypes were pooled when there were some risks of confusion across laboratories during the survey, and finally 32 remained that were mapped and used in diversity analyses. A strong phylogeographic structure is apparent from the data, where related haplotypes have broadly similar geographic distributions. In total, six cpDNA lineages are identified, which have distinct geographic distributions, mainly along a longitudinal gradient. Most haplotypes found in northern Europe are also present in the south, whereas the converse is not true, suggesting that the majority of mutations observed were generated prior to postglacial recolonisation, corroborating the conclusions of earlier studies. The description of a new western European lineage constitutes a major finding, compared to earlier phylogenetic treatments. Although the eight oak species studied systematically share cpDNA variants when in sympatry, they partition cpDNA diversity differently, as a consequence of their different ecology and life history attributes. Regional differences in levels of differentiation also exist (either species-specific or general); these seem to be related to the intensity of past and present management of the forests across Europe but also to the level of fragmentation of the range within these regions.

Variation in the non-coding region of chloroplast DNA (cpDNA) was studied to determine the route and pattern of postglacial recolonisation of native oak throughout mainland Britain. In total, 1076 mature oak trees of either Quercus petraea (Matt.) Liebl. or Quercus robur L. from 224 British ancient woodland sites were analysed, and represent the largest and most saturating molecular analysis of British oak undertaken to date. The majority of oaks (98%) possessed one of the three cpDNA haplotypes from lineage B that are commonly found in Spain and western regions of France. Thus, our findings strongly support the hypothesis that most native British Q. robur and Q. petraea originate from a Pleistocene refugium in the Iberian Peninsula. A haplotype previously thought to be the result of a de novo postglacial mutation in East Anglia, Native and Non-native in British Forestry. Proceedings of a Discussion Meeting, March 31–April 2, 1995. University of Warwick, pp. 38–55] was found at several sites in eastern Britain, including major population clusters in East Anglia, Tyneside and northeast Scotland. We propose that this haplotype was introduced to Britain via normal postglacial colonisation processes. Less than 2% of oak trees sampled possessed haplotypes from lineages which originate from more eastern refugia (Italy and Balkans). Whilst human-mediated translocation may be responsible for the occurrence of these haplotypes in Britain, single long distance dispersal events (of between 300 and 500 km from France) cannot be excluded for at least one case. The majority of populations sampled (including those where both species are present) were fixed for a single haplotype (69%). However, significant areas of mixed haplotype woods occurred in the Welsh Marches and Scotland and the proportion of population fixation was lower and intra-population diversity higher for Q. robur (GST=0.661; hS=0.224) than for Q. petraea (GST=0.884; hS=0.089). The distribution of cpDNA variation in British oak populations is discussed and interpreted in the light of hypothesised recolonisation routes and dynamics, inter-specific hybridisation and chloroplast capture, and human impacts due to the management of ancient woodland.

As Eucalyptus globulus (Labill.) seedlings are being widely outplanted to sites characterised by both high and low rainfall, this study describes the effect of soil moisture availability on mycorrhizal development and growth of seedlings inoculated with three different fungi. The information generated by this study should enable the nurseryman to target which mycorrhizal fungi to select as suitable inoculants for dry and wet sites. Mycorrhizal and non-mycorrhizal seedlings of E . globulus , grown under non-nutrient limiting conditions, were subjected to two different watering regimes from nine weeks after inoculation. During the following eight weeks, weekly measurements of stomatal conductance were made. All fruit bodies were collected, as they were formed, and the plants were harvested at 17 weeks. Of the three fungi used as inoculants, an isolate of Laccaria fraterna (Cooke and Mass.) Peg. formed the highest level of infection on seedlings that were watered normally whereas, on seedlings that were water-stressed, Pisolithus tinctorius (Pers.) Coker and Couch (syn. P . arhizus (Pers.) Raus.) achieved greatest mycorrhizal development. However, this isolate of L . fraterna sustained high levels of infection (>50%) on E . globulus seedlings in both `wet' and `dry' regimes. Seedlings subjected to drought conditions possessed significantly less stem and leaf biomass. Although there was a negative correlation between mycorrhizal development and shoot growth on seedlings watered normally, for those raised in the drier regime, benefits attributable to mycorrhizal inoculation were detected. In particular, the stomatal conductances of inoculated plants, raised in the `dry' regime, were found to be greater than those of non-inoculated plants growing in the same conditions.

In order to improve the procedure for selecting effective mycorrhizal inoculants for fast-growing eucalypts, a wide range of isolates associated with Eucalyptus globulus Labill. was tested at two contrasting nutrient regimes, representative of that present following outplanting (i.e, post-fertilization) and that likely to occur one or two years later when soil nutrient concentrations will have returned to a much lower level. It was felt that this would provide a more accurate prediction of a selected isolate's potential performance during early plantation establishment. As a consequence, during an initial 12-week period, representative of the nursery phase, seedlings of Eucalyptus globulus, pre-inoculated with 10 different mycorrhizal fungi, were given optimal nutrients to encourage the development of mycorrhizas. At the end of this period, six of the 18 replicate plants were harvested and assessed for shoot growth and mycorrhizal infection while the remainder received for a further 12 weeks two different nutrient solutions (10 and 3 mg l(-1) phosphorus (P)). When these plants were harvested at 24 weeks, shoot growth and mycorrhizal development were again assessed. At the end of the first phase (0-12 weeks), all seedlings, irrespective of fungal inoculant, had become mycorrhizal. However, the extent of mycorrhizal infection achieved by the 10 different fungi ranged from 1.4% to 40.7%. Significant differences were also found between the fungi in their effect on stem diameter, stem dry weight, and shoot dry weight but not stem height or leaf dry weight. When assessed at 24 weeks, mycorrhizal development ranged from 22.3% to 77.7% on seedlings given 10 mg l(-1) P and 23.1-77.3% for those given 3 mg l(-1) P. Three of the 10 fungi formed >50% infection on seedlings, irrespective of the nutrient regime applied. Most of the fungi formed higher levels of infection on seedlings given 10 mg l(-1) P; however, two isolates formed higher levels of infection on seedlings given 3 mg l(-1) P. Infection by nine of the 10 isolates led to a significant increase in leaf and shoot dry weight by seedlings given 10 mg l(-1) P in comparison to those which received 3 mg l(-1) P. However. inoculation with the remaining fungus, an isolate of Pisolithus tinctorius, led to seedlings given 3 mg l(-1) P forming shoots as large as those attained by plants given the higher P regime. The results indicate that isolates can be selected with the potential to achieve significant gains over a broad spectrum of nutrient concentrations. The implications for improving the establishment of E. globulus plantations at a wide spectrum of outplanting sites is discussed.

A number of investigations have demonstrated that balanced fertilizer applications can improve shoot growth of E. globulus plantations. Similar information on the impact of balanced N + P fertilizers on mycorrhizal development is lacking. This study was thus undertaken to determine the combinations of N and P which promote greatest mycorrhizal development and growth of seedlings of E. globulus. The overall objective was to generate information which might be translated into protocols for improved nursery and plantation management. Factorial combinations of two ectomycorrhizal fungi (Hydnangeum carneum Wall. apud Klotz. and Laccaria fraterna (Cooke and Mass.) Peg.) and eight fertilizer regimes containing different combinations of nitrogen (N) and phosphorus (P) were applied to Eucalyptus globulus seedlings. The four concentrations of nitrogen in the solutions ranged from 62.5 up to 250 mg l(-1) while those of phosphorus were 10 and 25 mg l(-1). Plants were harvested 12 weeks after inoculation. When given the lower P regime (10 mg l(-1) P), increasing amounts of applied N resulted in increasing percentages of infected roots, irrespective of fungal inoculant. Maximum colonization, including frequency of mycorrhizal branching, was observed at 250 mg l(-1) N/10 mg l(-1) P, with no indication that mycorrhizal infection had peaked. For seedlings given the higher P (25 mg l(-1)) concentration, increasing amounts of nitrogen tended to decrease per cent root infection. Seedlings given 25 mg l(-1) P grew larger (leaf, stem and shoot dry weight) with increasing concentrations of nitrogen. Those that were given the lower P concentration responded less to N. With the exception of leaf number, a strong positive relationship was found between seedling growth variables and percentage mycorrhizal infection at 10 mg l(-1) P. No such relationship was found at 25 mg l(-1) P. The implications of these findings for the development of a balanced N:P fertilizer regime in eucalypt nurseries and plantations are discussed.

A pot experiment in Kenya examined the effects of mycorrhizal and rhizobial inoculation on the growth and symbiont infection of Acacia tortilis seedlings in unsterile soil, in comparison with sterile and unsterile soil controls. Three mixed, arbuscular mycorrhizal inocula, originating from A. tortilis, Terminalia brownii, T. spinosa and Prosopis juliflora (produced under nursery conditions), were used to inoculate the seedlings, which also received a standard, mixed, rhizobial inoculum. Mycorrhizal infection and plant growth were significantly affected by experimental treatment ( p A. tortilis origin were 105 mm tall and their roots were 56% mycorrhizal, whereas the controls most representative of normal nursery treatment were only 77 mm tall and 29% mycorrhizal. Nodulation was erratic and poor in all treatments. The results suggest that mycorrhizal inoculation can improve both mycorrhizal infection and growth of tree seedlings in unsterile nursery soil. The methods of culture and inoculation described here could easily be adopted by nurseries at little cost.

Nine months after logging, seedlings of S. parvifolia were sampled from beneath open, closed and partially closed canopies, which resulted from the different logging treatments. Logging was done manually with minimal soil disturbance, compaction or damage to the vegetation. Assessments were made of seedling growth and ectomycorrhizal populations present on the roots. Seedlings growing under the closed canopy were smaller and possessed lower levels of mycorrhizal infection than those under open or partially closed canopies. Twenty-six ectomycorrhizal types were distinguished, with diversity greatest on seedlings growing under open and partially closed canopies. Although most mycorrhizal types occurred in less than half of the samples, occurrence of individual types was related to canopy type. Based on their frequency (number of seedlings having a mycorrhizal type) and abundance (% infection of a mycorrhizal type if present), mycorrhizal types were categorized into two main groups; those which occurred predominantly under the closed canopy and those which occurred under both open and partially closed canopies. Many of the fungi which dominated under the open and partially closed canopies are thought of as pioneer fungi and their occurrence is discussed in relation to their methods of dispersal and sensitivity to disturbance. Implications for forest management are considered.

Measurements of atmospheric ammonia concentration along a gradient of decreasing concentration, species composition and tissue nitrogen content of a range of plant species were made in woodland in the vicinity of four intensive animal units in Scotland. Ammonia concentrations were large at woodland edges close to the livestock buildings (annual means 20–60 μg m−3) and exceed critical levels for NH3 (8 μg m−3 annual mean). Surveys of species composition of ground flora along an 0.5 km transect from livestock buildings show marked changes within 300 m downwind of the buildings. Species such as Deschampsia flexuosa, Holcus lanatus, Rubus idaeus and Urtica dioica were abundant close to livestock units and their percentage cover decreased rapidly with distance from source, while the more N-sensitive species such as Oxalis acetosella, Galium odoratum, mosses and ferns which are found upwind and outside the influence of the NH3 source, were scarce at all sites receiving >25 kg ha−1 N year−1. Visible injury to pine and spruce needles was observed immediately downwind of the buildings. Foliar nitrogen concentration of a number of species was large close to the buildings and declined with distance. Total nitrogen deposition at the woodland boundaries is estimated to range from 40 to 80 kg N ha−1 year−1 at the 4 sites and exceeds critical loads for acidic coniferous forest, i.e. 15–20 kg N ha−1 year−1 to protect ground flora, and is also often in excess of that (11–50 kg N ha−1 year−1) proposed to protect tree health. Foliar nitrogen content of mosses, (LN, % dry weight) is related to nitrogen deposition (FN, kg N ha−1 year−1) according to LN = 3.81(1-e−0.04FN).

The water status of Terminalia brownii seedlings was assessed in relation to incident microclimate and initial irrigation treatments, during establishment at Olorgesailie in the Rift Valley of Kenya. Experimental treatments involved incorporation of a water-absorbing polymer with the root systems of the plants during establishment, and repeated irrigation, in a factorial design. The maximum photosynthetically active radiation of over 2500 μmol/m 2 /s recorded during the first 9 days after outplanting was associated with air temperatures of up to 47·4°C, and leaf-to-air vapour pressure deficits (VPDs) of up to 8·04 kPa. Water potentials declined to a minimum of -3·7 MPa, 9 days after outplanting, indicating severe water deficits. Stomatal conductances were generally below 0·2 cm/s, reflecting a high degree of stomatal closure. However, conductances of over 1·3 cm/s were observed on the 6th day after outplanting, associated with VPDs below 1·5 kPa. These relatively high conductances were restricted to plants which had received irrigation; overall, irrigation was found to significantly increase stomatal conductance on three of the four measurement days. Although the application of synthetic polymers increased stomatal conductances on two of the measurement days, the effects were very slight (treated means 0·02-0·03 cm/s higher than controls). These results indicate the severity of the transplant shock in semi-arid sites for seedling water status, and imply that initial irrigation treatments are more likely to increase establishment rates of tree seedlings than application of synthetic polymers.

Effects of vesicular-arbuscular mycorrhizal inoculation and the incorporation of water-holding polymer to the rooting zone, on tree survival and early growth have been assessed at two semi-arid sites in Kenya. Mycorrhizal inoculation was generally beneficial to plant growth in the nursery while polymer had few effects. Survival 30 weeks after planting was significantly affected by the experimental treatments in three out of four tree species at each site; inoculation enhanced survival, while polymer reduced it. Improvements in survival of up to 80% were achieved. Mycorrhizal effects on growth of Acacia tortilis and Prosopis juliflora after outplanting occurred with increases of up to 36% being obtained. The detrimental effects of polymer were unexpected.

The marker variables, Ellenberg Nitrogen Index, nitrous oxide and nitric oxide fluxes and foliar nitrogen, were used to define the impacts of NH3 deposition from nearby livestock buildings on species composition of woodland ground flora, using a woodland site close to a major poultry complex in the UK. The study centred on 2 units in close proximity to each other, containing 350,000 birds, and estimated to emit around 140,000 kg N year(-1) as NH3. Annual mean concentrations of NH3 close to the buildings were very large (60 microg m(-3)) and declined to 3 microg m(-3) at a distance of 650 m from the buildings. Estimated total N deposition ranged from 80 kg N ha(-1) year(-1) at a distance of 30 m to 14 kg N ha(-1) year(-1) at 650 m downwind. Emissions of N2O and NO were 56 and 131 microg N m(-2) h(-1), respectively at 30 m and 13 and 80 microg N m(-2) h(-1), respectively at 250 m downwind of the livestock buildings. Species number in woodland ground flora downwind of the buildings remained fairly constant for a distance of 200 m from the units then increased considerably, doubling at a distance of 650 m. Within the first 200 m downwind, trends in plant species composition were hard to discern because of variations in tree canopy composition and cover. The mean Ellenberg N Index ranged from 6.0 immediately downwind of the livestock buildings to 4.8 at 650 m downwind. The mean abundance weighted Ellenberg N Index also declined with distance from the buildings. Tissue N concentrations in trees, herbs and mosses were all large, reflecting the substantial ammonia emissions at this site. Tissue N content of ectohydric mosses ranged from approximately 4% at 30 m downwind to 1.6% at 650 m downwind. An assessment of the relative merits of the three marker variables concludes, that while Ellenberg Index and trace gas fluxes of N2O and NO give broad indications of impacts of ammonia emissions on woodland vegetation, the application of a critical foliar N content for ectohydric mosses is the most useful method for providing spatial information which could be of value to policy developers and planners.

The emissions of ammonia from point sources close to the ground and the rapid deposition to vegetation lead to very large horizontal gradients in both concentration and deposition close to sources. The sources are primarily livestock related and some of the largest terrestrial N inputs occur in the proximity of intensive production facilities. This study quantifies the local fate of livestock NH3 emissions from a poultry farm using measured NH3 concentrations and the relationship between canopy resistance (rc) and ambient NH3 concentration from intensive flux measurements. The results of the measured concentrations and deposition are compared with those obtained using a dispersion model of the emission, transport and deposition close to point sources. The results of the measurements showed annual mean concentrations in the range 23 μg m−3 to 63 μg m−3 at a distance of 15 m from the source, declining to background concentrations for the region of 1 to 2 μg m−3 at a distance of 276 m and in reasonable agreement with the model. The deposition of NH3N estimated from the measurements, declined from 42 kg N ha−1 at 15 m to 5 kg N ha−1 at 270 m and was smaller than the deposition estimated using the dispersion model by about a factor of two. Annual deposition within 270 m of the source to the woodland amounted to 155 kg N, and represented 3.2% of annual emissions from the poultry unit. The comparison between measurements and the model indicated substantial uncertainty in the deposition budget values, but supports the overall conclusion that local deposition of NH3 to woodland within 300 m of the source represents a small fraction (3% to 10%) of the local emission source.

Amenity trees, defined as all trees excluding those in Forestry Commission and grant-aided woodlands, worked coppice, commercial orchards and hardy-stock nurseries, were surveyed in the Lothian Region between 1972 and 1975. The Region (c. 188,000 ha or 1,877 km2) was stratified into three land categories-(i) burghs (Scottish equivalent of English boroughs), (ii) lowland rural and (iii) upland rural, parts of at least 10% of the 1 km squares (vide Ordnance Survey maps) of each land category being surveyed; the surveyed squares were selected randomly. Numbers of trees per ha ranged from 59 in burghs to 43 and 24 in lowland and upland (above 150m) rural areas respectively. In total there were 6·7 ± 1·9 million amenity trees in the Region divided as follows: 1·4 ± 0·4, 3·2 ± 0·9 and 2·1 ± 0·6 millions between the burghs and lowland and upland rural areas respectively; c. 1·0 m of the 1·4 million trees in burghs were located in Edinburgh. Approximately 70% of trees were deciduous with a larger proportion of conifers in upland areas than elsewhere; sycamore (Acer pseudoplatanus L.), hawthorn (Crataegus spp.) and Scots pine (Pinus sylvestris L.) were the commonest of 76 species or generic groupings recorded, accounting for 11·6, 11·1 and 10·5% respectively of the regional total. Birch (Betula spp.) was the commonest deciduous tree in upland areas where ash (Fraxinus excelsior L.) and beech (Fagus sylvatica L.) were more abundant than sycamore. In the burghs wych elm (Ulmus glabra Huds.) was more numerous than hawthorn and less than sycamore. Trees in Edinburgh differed greatly from those in the smaller towns (burghs) with more rural atmospheres, where sycamore, wych elm, hawthorn, elder and birch contrasted with apple, lilac, flowering cherry, sycamore and rowan occurring abundantly in Edinburgh. Excluding Edinburgh, over 50% of the Region's trees were identified in broadleaved (26·7%), coniferous (21·4%) and mixed (13·6%) woodlands, with 12·0% and 8·1% occurring in shelterbelts and hedgerows respectively; gardens and parks, of all sorts, only accounted for 4·5% and 1·1% respectively. Size class distribution ssuggest that there are sufficient developing saplings to maintain the existing number of mature trees but that wych elm (Ulmus glabra Huds.), unless devastated by Dutch elm disease, sycamore and ash are likely to increase at the expense of oak (Quercus spp.), lime (Tilia spp.), Scots pine and beech. In some situations, however, the resourse seems to be seriously deficient in saplings, e.g. oaks in parks.