The geographic origin of old Douglas-fir stands growing in Central Europe

Since the nineteenth century, Douglas-fir seed sources have been widely used for establishment of forest stands outside its natural distribution range. In Europe, some of these old Douglas-fir stands are registered as seed stands and provide seed sources for nurseries, although it is unclear from which region in North America they originate. In recent years, the interest in planting Douglas-fir has increased substantially because the species is seen as a potential adaptation option to climate change. This makes the assignment of European Douglas-fir stands of unknown seed origin to their geographic origin in North America increasingly important, because the genetic quality of these plantations must be guaranteed. In this study, we use 13 nuSSR loci to investigate the origin of 67 Austrian and German Douglas-fir stands of unknown origin. We performed a hierarchical Bayesian cluster analysis using 38 native Douglas-fir populations. The resulting clusters are used as reference populations to assign the 67 Central European Douglas-fir stands from Austria and Germany planted more than 80 years ago. Our results suggest that the majority of our investigated Douglas-fir stands come from central Washington (USA), the recommended seed zones for Central Europe. Some stands were located outside the suggested area, e.g. central Oregon and Santa Fe (New Mexico). The accuracy assessment of our approach revealed the best performance for the highest hierarchical level, e.g. assigning populations either to the coastal or the Rocky Mountain variety. As expected, the uncertainty increases with decreasing hierarchical level. The final assessment, if an admixture of seed sources within the European Douglas-fir stands is evident suggests that 23 of the Douglas-fir stands show an admixture which was not detected in our Douglas-fir reference populations growing in the natural distribution range.     

Genetic diversity and adaptive traits of European versus American Douglas-fir seedlings

Due to its productivity and potential to adapt to the expected climate change, the Douglas-fir is one of the most important commercial non-native forest tree species in Europe. Currently, seeds from both non-native European and native American seed stands are used for plantations. In this study, we investigate European seed lots for their native origin (variety and potential geographic origin in America) and assess the adaptability, growth and survival potential of European versus American Douglas-fir seed lots. We compare the genetic diversity, morphological characteristics such as height (h), root collar diameter (rcd) and the ratio of h/rcd, and the timing of bud burst. We investigate 852 1-year-old seedlings from 10 different US and European seed lots representing 5 provenance regions which are sold in Germany and Austria. Seedlings are genotyped for 13 nuclear SSRs and analysed together with reference data set and standard genetic structuring and assignment methods. Adaptive traits of morphological characteristics and timing of bud burst of the seedlings are recorded and statistically analysed. The results show that the investigated European seedlings originate from recommended American native seed sources and represent both varieties and inter-varietal admixed individuals. European seedlings have a lower genetic diversity versus the American seedlings and native populations. They show significant differences in the adaptive traits such as morphological characteristics and timing of bud burst. According to the genetic diversity indices, certified North American Douglas-fir seed sources should be preferred for planting in Central Europe.     

Native woody species regeneration in exotic tree plantations at Munessa-Shashemene Forest,southern Ethiopia

Regeneration of native woody species was studied in the plantations and the adjacent natural forest at Munessa-Shashemene Forest Project Area, Ethiopia. The aim of the study was to test the hypothesis that tree plantations foster regeneration of native woody species. A total of 60 plots, having 10 × 10 m area each, were studied in monoculture plantations of 4 exotic species (Cupressus lusitanica, Eucalyptus globulus, E. saligna, Pinus patula) and an adjacent natural forest. Ages of the plantations ranged between 9 and 28 years. Soil seed bank analysis was also undertaken from soil samples collected in each of the 60 plots to examine the similarity between the soil seed flora and aboveground vegetation. A total of 56 naturally regenerated woody species were recorded beneath all plantation stands with densities ranging between 2300 and 18650 individuals / ha in different stands. There was a significant difference among plantation stands with regard to understorey density (standard deviation: 4836 ± 1341). Vegetation diversity was assessed through analyses of floristic composition, species richness and abundance. Generally, seedling populations were the most abundant components of the regeneration in most of the plantation stands, forming 68 % of the total regeneration count in all stands. A total of 77 plant species represented by 44 herbs, 13 woody species, 8 grasses and 12 unidentified species were recorded in the soil seed bank from all stands. Similarity between the soil seed bank and aboveground flora was very low implying that the role of soil seed banks is negligible rather dispersal plays an important role in the process of regeneration. These results support the concept that forest plantations can foster the regeneration of native woody species, thereby increasing biological diversity, provided that there are seed sources in the vicinity of the plantations.     

Natural Regeneration in Thinned Douglas-fir Stands in Western Oregon

ABSTRACT

In response to interests by land management agencies to transform even-aged stands to structurally mimic old-growth forests, we evaluated whether thinning in 40- to 80-year-old Douglas-fir (Pseudotsuga menziesii) stands influenced amount and composition of advanced regeneration 5 to 7 years following treatment. We used data from two large-scale management experiments (Density Management Study and Young Stand Thinning and Diversity Study) conducted in western Oregon. Thinning focused on the removal of Douglas-fir, while maintenance of minor species was encouraged. Although both experiments showed higher tree regeneration after thinning, we found that variation in regeneration density was too high (3 orders of magnitude) to find statistical differences among thinning intensities. While seedlings of the major species, Douglas-fir and western hemlock (Tsuga heterophylla), were always present and dominated regeneration on nearly all sites, species trends were driven by high spatial and compositional variation throughout all units, treatments, and sites. Thinning increased the number of species within the regeneration layer. Hereby, species diversity was strongly related to overstory composition, suggesting seed source limitations for minor species. Hence, favoring rare species during thinning operations may be an effective method to increase regeneration species richness. Local conditions, as defined by overstory density appeared more influential than regional climate patterns in determining seedling densities. Shrub and grass competition did not prevent seedling establishment as their cover values were generally not as high as typically found in clearcuts in the region. The high variation in seedling density and species richness within the seedling stratum in the thinned stands may set the stage for development of structural complexity in even-aged Douglas-fir plantations.     

The effects of Douglas-fir on tree-specific arthropod communities in mixed species stands with European beech and Norway spruce

The ecological effects of planting exotic Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] in Central Europe are still poorly understood. The aim of this study was to answer the question of whether Douglas-fir affects tree specific arthropod communities in different mature forest types (Douglas-fir, spruce and beech dominated) in Southern Germany. Therefore, arthropod communities of stem and tree crown strata of Douglas-fir and spruce (Picea abies L.) were sampled in the years 1999–2001 using arboreal photo-eclectors and flight interception traps. Statistical analysis was conducted for all species and focused on conifer specialists at three levels: (1) species diversity, (2) guild structure and (3) community structure. Within the stem stratum, species diversity was significantly higher on spruce than on Douglas-fir independent of year and stand composition. This could not be explained by a single feeding guild, rather by species changing strata during the vegetation period. In contrast, species diversity in tree crowns was approximately the same for both conifer species. However, communities in Douglas-fir crowns were conspicuously different from those in spruce crowns, especially in the Douglas-fir dominated stand type. While zoophagous insects exhibited higher activity on Douglas-fir in 2000, xylophagous beetles were more abundant on spruce in 2001. In European beech stands with widely spaced Douglas-fir trees, the site specific and broad-leaved tree related fauna might be maintained. In addition, Douglas-fir with its resource of Adelges cooleyi and crowns that overtop the broad-leaved tree canopy, offer additional resources for several aphidophagous and thermophile species.     

Magnitude and efficiency of genetic diversity captured from seed stands of <Emphasis Type="Italic">Pinus nigra</Emphasis> (Arnold) subsp. <Emphasis Type="Italic">pallasiana</Emphasis> in established seed orchards and plantations

To test how efficiently plantations and seed orchards captured genetic diversity from natural Anatolian black pine (Pinus nigra Arnold subspecies pallasiana Holmboe) seed stands, seed sources were chosen from 3 different categories (seed stands (SS), seed orchards (SO) and plantations (P)) comprising 4 different breeding zones of the species in Turkey. Twenty-five trees (mother trees) were selected from each SS, SO and P seed sources and were screened with 11 Random Amplified Polymorphic DNA (RAPD) markers. Estimated genetic diversity parameters were found to be generally high in all Anatolian black pine seed sources and the majority of genetic diversity is contained within seed sources (94%). No significant difference in genetic diversity parameters (numbers of effective alleles, % of polymorphic loci and heterozygosity) among seed source categories was found, except for a slight increase in observed heterozygosities in seed orchards. For all seed source categories, observed heterozygosity values were higher (H_o = 0.49 for SS, 0.55 for SO and 0.49 for P) than expected ones (H_e = 0.40 for SS, 0.39 for SO and 0.38 for P) indicating the excess of heterozygotes. In general, genetic diversity in seed stands has been transferred successfully into seed orchards and plantations. However, the use of seeds from seed orchards can increase the amount of genetic diversity in plantations further. The study also demonstrated that number of plus-tree clones (25–38) used in the establishment of seed orchards was adequate to capture the high level of diversity from natural stands.     

Family composition of Douglas-fir nursery stock as influenced by seed characters,mortality, and culling practices

Changes in family composition during nursery production were evaluated by following individual seeds and seedlings of 36 wind-pollinated Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) families sown in mixture in two operational nurseries in western Washington and Oregon. Families differed significantly in emergence and in percent of seedlings culled for being too small. However, differences were small enough that family composition was largely unaffected. The observed changes in family composition did not markedly reduce genetic diversity and did not affect the genetic gain that may be expected from an improved population. The plantable nursery stock was, for the most part, representative of the composition of families originally sown.     

Beech decline in Central Europe driven by the interaction between Phytophthora infections and climatic extremes

During the past decade, and in particular after the wet year 2002 and the dry year 2003, an increasing number of trees and stands of European beech (Fagus sylvatica L.) in Bavaria were showing symptoms typical for Phytophthora diseases: increased transparency and crown dieback, small‐sized and often yellowish foliage, root and collar rot and aerial bleeding cankers up to stem heights of >20 m. Between 2003 and 2007 134 mature beech stands on a broad range of geological substrates were surveyed, and collar rot and aerial bleeding cankers were found in 116 (86.6%) stands. In most stands the majority of beech trees were declining and scattered or clustered mortality occurred. Bark and soil samples were taken from 314 trees in 112 stands, and 11 Phytophthora species were recovered from 253 trees (80.6%) in 104 stands (92.9%). The most frequent species were P. citricola, P. cambivora and P. cactorum. Primary Phytophthora lesions were soon infected by a series of secondary bark pathogens, including Nectria coccinea, and wood decay fungi. In addition, infected trees were often attacked by several bark and wood boring insects leading to rapid mortality. Bark necroses were examined for their probable age in order to determine whether the onset of the current Phytophthora epidemic was correlated to rainfall rates recorded at 22 Bavarian forest ecosystem monitoring stations. A small‐scale survey in nine Bavarian nurseries demonstrated regular infestations of all beech fields with the same range of Phytophthora species. The results indicate that (1) Phytophthora species are regularly associated with beech decline and may also be involved in the complex of ‘Beech Bark Disease’, (2) excessive rainfalls and droughts are triggering the disease, and (3) widespread Phytophthora infestations of nursery stock might endanger current and future silvicultural projects aiming on the replacement of non‐natural conifer stands by beech dominated mixed stands.     

Seedborne Fusarium on Douglas-fir: Pathogenicity and seed stratification method to decrease Fusarium contamination

Twelve Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlots from coastal British Columbia were assayed for seedborne Fusarium. All of the seedlots were contaminated with Fusarium. Percent of nonstratified seeds from individual seedlots harboring Fusarium ranged from 0.3% to 95.4%. Sixty-seven percent of the seedlots had Fusarium on less than 2% of the seeds. Post-stratification seedborne Fusarium levels were significantly less for running water imbibition compared to standing water imbibition. However, seedling growth at a container nursery was not consistently different for stratified seed imbibed initially in standing or running water. Fusarium disease symptoms were not observed in the nursery environment. The species of Fusarium isolated from seed were F. acuminatum, F. avenaceum, F. lateritium, F. moniliforme, F. oxysporum, F. poae and F. sambucinum. Twelve Fusarium isolates, comprising six species, were assessed for pathogenicity. Disease symptoms were observed after four weeks incubation and Fusarium isolates ranged in virulence from low to high. Fusarium oxysporum isolates were the most pathogenic.     

Seedling growth and establishment in natural stands of yellow-cedar (Chamaecyparis nootkatensis) seedlings derived from the use of modified seed dormancy-breaking treatments

Following dispersal from the parent tree, seeds of yellow-cedar (Chamaecyparis nootkatensis[D. Don] Spach) exhibit low germination, primarily as a result of coat-imposed dormancy. Dormancy of the mature (intact) seed is effectively terminated by traditional warm/cold treatments. A chemical treatment using the anaesthetic 1-propanol combined with a three day warm water soak (30 °C), a two day GA₃ treatment and 60 d of moist chilling not only promotes high germinability of yellow-cedar seeds, but also elicits vigorous post-germinative growth following seedling emergence under nursery greenhouse conditions. Here we compare the effectiveness of the more traditional warm/cold treatments with the chemical treatment in terms of their capacity to elicit vigorous growth and establishment in natural stands following transplant of seedlings from a nursery greenhouse environment. Two seed lots (42313 and 43697) and open-pollinated seed from parent trees 13-6 and 19-8 showed equivalent seedling growth in natural stands following the chemical treatment and two traditional warm/cold treatments typically used for dormancy breakage by the forest industry and by the Ministry of Forests in British Columbia. The chemical protocol offers the advantage of reducing the time required to break seed dormancy. We have now demonstrated that it yields seedlings that exhibit vigorous growth and are capable of withstanding the vagaries of the environment.     

Roles of seed and pollen dispersal in natural regeneration of Castanopsis fargesii (Fagaceae): Implications for forest management

Natural regeneration is an important process to reverse the loss of forests. Understanding the process of natural regeneration is crucial for achieving sustainable forest management. In this study, we examined the effects of seed and pollen dispersal in naturally regenerated populations of Castanopsis fargesii. Genetic variation in six populations along two successional series (three successional stages in each series: early, pre-climax, and climax) was assayed using RAPD (random amplified polymorphic DNA) markers. High genetic variability was observed as measured with Shannon's information index. A majority of genetic variation was distributed within populations (Φ_st = 0.1271) and significant isolation by distance existed among populations. A contrasting pattern of genetic variation along these two series was observed, representing different scenarios of natural regeneration processes. The ratio of the number of migrants between the mature populations to the number of migrants from the mature to immature populations was estimated as 1.146 ± 0.099 to 1.981 ± 0.164, implying that comparable seed and pollen dispersal might exist at a fine spatial scale (∼2 km²). The results suggest the critical role of seed dispersal in shaping genetic composition and diversity in the second-growth forests. Barriers to seed dispersal from a variety of genetic sources could result in low genetic diversity in naturally regenerated populations. Management that facilitates the connectivity of newly regenerated stands with mature forests could be effective for natural regeneration given the predominant role of short-distance dispersal of seeds in this species.     

Detection of genetic variation among seed and seedlings ofChamaecyparis obtusa using allozyme markers

The effects of nursery practices on genetic composition and structure were studied inChamaecyparis obtusa by analyzing seeds and one-, two-, and three-year-old seedlings. Enzyme polymorphisms of the6Pgd-2, G6pd, Got, Gk, Shd-2, Pod, Dia-1, andPgm loci were used. OnlyDia-1 indicated significantly different allelic frequencies between seeds and three-year-old seedlings. Most of the genetic diversity of the parental clones in this seed orchard could be transferred to the offsprings. Genetic diversity on the basis of an average expected heterozygosity did not differ between seeds and seedlings. A slight excess of homozygotes in seeds and a significant excess of heterozygotes in seedlings of different ages to the expected panmictic proportions were found. Most of the differences in genotypic distributions among the seed and seedling stages, probably resulted from viability selection favoring outcrosses, and selective removal of inbred offsprings including self-fertilized ones prior to their transplantation in the nursery. A part of this paper was orally presented at the 107th Annual Meeting of the Japanese Forestry Society (1996).     

Estimates of pollen contamination and selfing in a coastal Douglas-fir seed orchard

Seed orchards are the link from tree breeding to reforestation programs and are theoretically expected to function as closed, perfect populations, ensuring gain and diversity are consistently and predictively delivered as improved seed and seedlings. Seed orchard populations often deviate from panmixia due to fertility variation, reproductive asynchrony, and gene flow, leading to reduced seed crops genetic quality. Here, as a part of multiyear monitoring study, we used DNA fingerprinting (simple sequence repeat markers) to assess a Douglas-fir (Pseudotsuga menziesii) seed orchard's seed crop genetic quality (2009 seed crop). The studied seed crop was produced under ambient temperature (i.e. no reproductive phenology manipulation) and pollination was augmented by pollen from within orchard's pollen donors. DNA fingerprinting of the parental population (66 parents) along with 207 gametophyte (1n) – embryo (2n) pairs of random bulk sample of seed allowed parentage (maternal and paternal) assignment and the direct assessment of pollen contamination (0.18 ± 0.027) and selfing (0.17 ± 0.025) rates as well as parental (pollen, ovule and individual parent) gametic contribution was compared to a previous year's crop (2005). The extended reproductive phenology coupled with variable within-orchard pollen availability has created opportunities for both self and foreign pollen to be successful at various times resulting in the seemingly paradoxical scenario of high selfing and gene flow. These results (2005 and 2009) allowed comparison of seed orchard's crop management practices and are expected to provide scientific foundations to effective seed crops genetic quality improvement.     

Prevalence and incidence of the root-inhabiting fungi, Fusarium, Cylindrocarpon and Pythium, on container-grown Douglas-fir and spruce seedlings in British Columbia

Surveys were made at the end of the 1990 and 1991 growing seasons for root-inhabiting fungi in the genera Fusarium, Cylindrocarpon and Pythium from the roots of one year-old container-grown Douglas-fir and spruce seedlings grown under greenhouse conditions. In the 1990 survey of four nurseries, it was found that 61–97% of both Douglas-fir and spruce roots were colonized with Fusarium, Cylindrocarpon or Pythium. There were significantly (p0.05) more Douglas-fir roots than spruce roots colonized by Fusarium at all nurseries, however, there were significantly (p0.05) more spruce roots than Douglas-fir roots colonized by Cylindrocarpon and Pythium. Root colonization of Douglas-fir and spruce by the three fungal genera during 1991 varied from 0–82% at three nurseries, however, only at a south coastal nursery was there significantly (p0.05) more spruce than Douglas-fir roots colonized by Cylindrocarpon. Significantly more seedlings were infected in 1990 than in 1991. In 1991, there were few significant differences between Douglas-fir and spruce, in the percentage of seedlings with colonized roots and in the percentage of growth medium colonized by the fungi. However, there were significant differences between nurseries.     

Tree microhabitat structures as indicators of biodiversity in Douglas-fir forests of different stand ages and management histories in the Pacific Northwest,U.S.A.

The importance of structural complexity in forest ecosystems for ecosystem diversity has been widely acknowledged. Tree microhabitat structures as indicators of biodiversity, however, have only seldom been the focus of diversity research although their occurrence is highly correlated with the abundance of forest species and ecosystem functions. In this study, microhabitat structures in Douglas-fir (Pseudotsuga menziesii) forests were defined and their frequency and abundance in natural stands and stands of varying active management histories and stand ages was compared. Indicator microhabitat structures for natural forests were determined and the relationship of the abundance of microhabitat structures with tree diameter of Douglas-fir trees was analysed.     

Seed rain of ponderosa pine beneath partial overstories

An analysis was conducted of the 1999 ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws.) seed crop at two stands of differing overstory density in each of two sites that differed in productivity (forest community series) on the east slope of the Cascade Range in central Oregon, USA. A total 2,166 viable seeds were collected between 2 September 1999 and 6 June 2000. Total seed quantities varied more by site than by tree density, with the xeric site producing six-fold greater seed yields. Within each site, the stand of higher density produced more viable seed. Per-tree cone yields were also greater at the site of lesser productivity. At three of the four stands, tree fecundity (as measured by cone counts) was positively related to diameter at breast height and height, but not to live crown ratio. A difference in temporal seedfall patterns among the two sites occurred late and was relatively minor: most seedfall occurred within the first month after it started regardless of absolute seed production. Seedfall distribution varied spatially within stands, but no seed trap (of 55) received less than an equivalent 28 thousand seeds per hectare. Seedfall was not perceived to be a limiting factor on natural regeneration at any of the four partial-overstory stands in this study.     

Seed Biology,Stand Characteristics,and Regeneration of Fraxinus rhynchophylla Hance

Fruit size and seed moisture content were measured and seed production and dispersal were monitored to understand the seed biology of the Korean ash (Fraxinus rhynchophylla Hance) in two Korean ash forests. A combination of four ground treatments and four crown closure levels were created in a natural forest to understand the site conditions needed for seedling emergence in natural stands and to determine practical regeneration methods for direct seeding. The seed size of Korean ash increased until late May and its moisture content decreased rapidly in early November. Prolific seed bearing occurred every 3 yr. The distance of seed dispersal by wind was about 30 m, but more than 90% of the seeds dispersed within 10 m from the seed trees. Twenty-five seed trees per hectare provided for successful natural regeneration. The seedling emergence in the natural stands was best with scarification treatment and 25～50% of crown closure.     

Genetic Diversity of RAPD Mark for Natural Davidia involucrata Populations

The genetic diversity and genetic variation within and among populations of five natural Davidia involucrata populations were studied from 13 primers based on random amplified polymorphic DNA (RAPD) analysis. The results show that natural D. involucrata population has a rich genetic diversity, and the differences among populations are significant. Twenty-six percent of genetic variation exists among D. involucrata populations, which is similar to that of the endangered tree species Liriodendron chinense and Cathaya argyrophylla in China, but different from more widely distributed tree species. The analysis of the impacts of sampling method on genetic diversity parameters shows that the number of sampled individuals has little effect on the effective number of alleles and genetic diversity, but has a marked effect on the genetic differentiation among populations and gene flows. This study divides the provenances of D. involucrata into two parts, namely, a southeast and a northwest provenance. Translated from Scientia Silvae Sinicae, 2004, 40(4) (in Chinese)     

Long-term ecological impacts of clear-fell logging on tree species diversity in a subtropical forest,southern Japan

Defining the spatial arrangement and length of the cutting cycle in a logged area is crucial for reconciling potential conflicts between timber yields and maintenance of ecosystem services in natural forests. In this study, we investigated long-term impacts of clear-fell logging on timber production and tree species diversity in a subtropical forest on the Ryukyu Islands, using an individual-based simulation model. We assumed six logging scenarios defined by combinations of forest type and regeneration processes, which acted as surrogates for spatial scales of clear-fell logging. These scenarios were simulated under cutting cycles ranging from 20 to 150 years. Short-cutting cycles resulted in dominance by the sprouting species Castanopsis sieboldii. The compositional shift was accelerated by the lack of seed dispersal from surrounding forest areas. The simulations demonstrated that a sustainable logging regime maintaining both yield and tree species diversity requires a cutting cycle longer than 50 years. The simulation results also suggest that the trade-off between the recovery of tree species diversity and timber production is favored more in stands surrounded by mature forest than in isolated stands or stands surrounded by immature forest. Ecological risk assessments based on model simulations provide an alternative to current forest management practices that rely on empirical knowledge.