Forest biotechnology: Innovative methods, emerging opportunities

Summary The productivity of plantation forests is essential to meet the future world demand for wood and wood products in a sustainable fashion and in a manner that preserves natural stands and biodiversity. Plantation forestry has enormously benefited from development and implementation of improved silvicultural and forest management practices during the past century. A second wave of improvements has been brought about by the introduction of new germplasm developed through genetics and breeding efforts for both hardwood and conifer tree species. Coupled with the genetic gains achieved through tree breeding, the emergence of new biotechnological approaches that span the fields of plant developmental biology, genetic transformation, and discovery of genes associated with complex multigenic traits have added a new dimension to forest tree improvement programs. Significant progress has been made during the past five years in the area of plant regeneration via organogenesis and somatic embryogenesis (SE) for economically important tree species. These advances have not only helped the development of efficient gene transfer techniques, but also have opened up avenues for deployment of new high-performance clonally replicated planting stocks in forest plantations. One of the greatest challenges today is the ability to extend this technology to the most elite germplasm, such that it becomes an, economically feasible means for large-scale production and delivery of improved planting stock. Another challenge will be the ability of the forestry research community to capitalize rapidly on current and future genomics-based elucidation of the underlying mechanisms for important but complex phenotypes. Advancements in gene cloning and genomics technology in forest trees have enabled the discovery and introduction of value-added traits for wood quality and resistance to biotic and abiotic stresses into improved genotypes. With these technical advancements, it will be necessary for reliable regulatory infrastructures and processes to be in place worldwide for testing and release of trees improved through biotechnology. Commercialization of planting stocks, as new varieties generated through clonal propagation and advanced breeding programs or as transgenic trees with high-value traits, is expected in the near future, and these trees will enhance the quality and productivity of our plantation forests.     

Fruit production is influenced by tree size and size‐asymmetric crowding in a wet tropical forest

In tropical forest communities, seedling recruitment can be limited by the number of fruit produced by adults. Fruit production tends to be highly unequal among trees of the same species, which may be due to environmental factors. We observed fruit production for ~2,000 trees of 17 species across 3 years in a wet tropical forest in Costa Rica. Fruit production was modeled as a function of tree size, nutrient availability, and neighborhood crowding. Following model selection, tree size and neighborhood crowding predicted both the probability of reproduction and the number of fruit produced. Nutrient availability only predicted only the probability of reproduction. In all species, larger trees were more likely to be reproductive and produce more fruit. In addition, number of fruit was strongly negatively related to presence of larger neighboring trees in 13 species; presence of all neighboring trees had a weak‐to‐moderate negative influence on reproductive status in 16 species. Among various metrics of soil nutrient availability, only sum of base cations was positively associated with reproductive status, and for only four species. Synthesis Overall, these results suggest that direct influences on fruit production tend to be mediated through tree size and crowding from neighboring trees, rather than soil nutrients. However, we found variation in the effects of neighbors and nutrients among species; mechanistic studies of allocation to fruit production are needed to explain these differences.     

Trends of genetic study of forest tree and development of useful traits for apple Biotechnology

Conclusion  Forest trees have long generation times and arc highly heterogeneous, so few extended pedigrees are available. Because of these limitations, there is a greater potential for DNA-markers to improve genetic analysis and to accelerate breeding in forest trees. In deciduous fruit plants, the most important traits are fruit qualities such as acidity, sugar content, fruit size, and total yield. As these are quantitative traits that appear to be controlled by a number of loci, it is difficult to make progress in the quick improvement of fruit quality, requiring the elucidation of the position and function of QTLs affecting these traits. Although QTL analysis is important for genetic enhancement, it is time consuming work. Also, for many years until now, DNA-markers have not been applied to practical tree improvement because of technical and theoretical limitations. High levels of heterozygosity and linkage equilibrium of markers in populations were considered to be serious limitations. Now, it is carefully suggested that molecular breeding should be primarily based on the cloning and characterization of useful agronomic traits for direct application to forest tree plants.For example, a monogenic trait that specifically contributes to flower and fruit development is useful for control of thinning. Biotechnology is likely to give valuable genetic improvement of tree species and the adopted strategy based upon biotechnology provides a model system in similar studies for other fruit and woody species. This paper was presented at the 11th Symposium on Plant Biotechnology entitled “Plant Genes and Genetic Resources” organized by Gynheung An, held July 4–5, 1997, by the Botanical Society of Korea     

Densities of Two Frugivorous Primates with Respect to Forest and Fragment Tree Species Composition and Fruit Availability

Conservation of wildlife populations requires extensive knowledge of their habitat requirements, efficient methods to evaluate habitat quality, and an understanding of the value of fragments and edges. Kibale National Park, Uganda has areas that differ in the densities of 2 species of frugivorous monkeys—Cercopithecus mitis and Lophocebus albigena—including one on an edge and forest fragments outside the park that lack both species. We compared the basal area densities of important food trees with primate densities. The density of Cercopithecus mitis correlates most strongly with the basal area density of all types of food trees combined. The density of Lophocebus albigena does not correlate with the basal area densities of any category of food trees or with fruit availability. An index of their density—number of groups seen per km walked—correlates to fruit availability but with marginal significance. Lack of a relationship between the basal area densities of food trees and density of Lophocebus albigena may be the result of a mismatch in scale between the forest area measured and their large home ranges. We compared the unused area of forest to the other areas of the forest and the fragments and found it had higher basal area densities in all food tree categories for both species than the fragments and lower basal area densities of most categories than the other parts of the forest, indicating that the fragments are poor quality and would probably be unused even if dispersal were likely.     

In vitro culture and genetic engineering of Populus spp.: synergy for forest tree improvement

Populus species and hybrids are intensively cultivated as sources of woody biomass for the forest products industry and for reforestation of lowlands in temperate regions of the world. However, the long generation time of trees, the presence of seasonal dormancy and the prolonged period required for evaluation of mature traits are strong limitations for classical breeding and selection. The development of methods for in vitro culture and genetic engineering has increased the possibility of producing poplar genotypes improved in insect pest resistance, herbicide tolerance, growth rate and wood quality, or reduction in undesirable traits. Poplar has become a model system in forest tree biotechnology due to several useful features: small genome size, short rotation cycle, rapid growth rate and ease of vegetative propagation. The combination of molecular techniques and classical breeding will help create forest trees with positive effects on the environment. However, risks associated with the biotechnological applications (concerning the impact on biodiversity, long-term adaptation, transgene inheritance and stability) should be carefully evaluated and field tests performed with transgenic poplar.     

Technological advances in temperate hardwood tree improvement including breeding and molecular marker applications

Hardwood forests and plantations are an important economic resource for the forest products industry worldwide and to the international trade of lumber and logs. Hardwood trees are also planted for ecological reasons, for example, wildlife habitat, native woodland restoration, and riparian buffers. The demand for quality hardwood from tree plantations will continue to rise as the worldwide consumption of forest products increases. Tree improvement of temperate hardwoods has lagged behind that of coniferous species and hardwoods of the genera Populus and Eucalyptus. The development of marker systems has become an almost necessary complement to the classical breeding and improvement of hardwood tree populations for superior growth, form, and timber characteristics. Molecular markers are especially valuable for determining the reproductive biology and population structure of natural forests and plantations, and the identity of genes affecting quantitative traits. Clonal reproduction of commercially important hardwood tree species provides improved planting stock for use in progeny testing and production forestry. Development of in vitro and conventional vegetative propagation methods allows mass production of clones of mature, elite genotypes or genetically improved genotypes. Genetic modification of hardwood tree species could potentially produce trees with herbicide tolerance, disease and pest resistance, improved wood quality, and reproductive manipulations for commercial plantations. This review concentrates on recent advances in conventional breeding and selection, molecular marker application, in vitro culture, and genetic transformation, and discusses the future challenges and opportunities for valuable temperate (or “fine”) hardwood tree improvement.     

Nurse Trees as a Forest Restoration Tool for Mixed Plantations: Effects on Competing Vegetation and Performance in Target Tree Species

Multi‐species mixed plantations can be designed to meet social, economic, and environmental objectives during forest restoration. This paper reports results from an experiment in southern Sweden concerning the influence of three different fast growing nurse tree species on the cover of herbaceous vegetation and on the performance of several target tree species. After 10 years, the nurse trees had reduced the competing herbaceous vegetation but the effect was weak and it may take more than a decade to achieve effective vegetation control. The nurse tree species Betula pendula and Larix x eurolepis did improve stem form in some target tree species, but had a minor effect on survival and growth. The open conditions before crown closure of nurse trees strongly influence seedling performance and so delayed planting of target tree species may provide a means to avoid those conditions. Survival and growth differed greatly among the tree species. Besides the two nurse tree species mentioned above, high survival was found in Picea abies and Quercus robur and intermediate survival in Fagus sylvatica, Tilia cordata, and in the N‐fixing nurse tree Alnus glutinosa. Survival was low in the target tree species Fraxinus excelsior L. and Prunus avium. For restoration practitioners, our results illustrate the potential of using nurse trees for rapidly building a new forest structure and simultaneously increase productivity, which might be a cost‐effective strategy for forest restoration.     

Use of Fruiting Trees by Birds in Continuous Forest and Riparian Forest Remnants in Los Tuxtlas,Veracruz, Mexico1

The composition of plant species in fragmented landscapes may be influenced by the pattern of visitation by birds to fruiting trees and by the movement of seeds among and within fragments. We compared bird visitation patterns to two tree species (Dendropanax arboreus, Araliaceae; Bursera simaruba, Burseraceae) in continuous forest and remnants of riparian vegetation in a region dominated by pasture in Los Tuxtlas, Veracruz, Mexico. We quantified frequency of visitation, fruit consumption, consistency of visitation (percentage of total tree observation periods during which a given bird species was recorded), and species composition of birds at individuals of both tree species in continuous forest and riparian remnants. Bird visitation rate, species richness, and fruit consumption rates were similar within both tree species in the two habitats. Species assemblages at D. arboreus were different between continuous forest and remnants. Species assemblages at B. simaruba did not differ by habitat. Our results demonstrate that habitat disturbance may influence avian visitation patterns, which may in turn affect subsequent recruitment patterns in some tree species. Our results, however, were not consistent between the tree species, suggesting that it is difficult to generalize concerning the effects of forest disturbance on avian species assemblages in fruiting trees.     

Report on the 31st Southern Forest Tree Improvement Conference (SFTIC)

The 31st Southern Forest Tree Improvement Conference was held 14–16 June 2011 in Biloxi, MS, USA. This marks 60 years of biennial technical conferences supported by the Southern Forest Tree Improvement Committee. The theme of the conference was tree improvement opportunities and challenges in the economy emerging around cellulosic biomass, bioproducts, and biofuels. Invited speakers from the industry, academia, and government challenged scientists and students to employ robust technologies for developing and deploying improved trees for the emerging biomass markets as well as for the existing forest products markets. Opportunities for integrating genomics into breeding and selection programs and somatic embryogenesis into deployment practices look promising for loblolly pine (Pinus taeda); the main industrial forest tree in the southeastern USA. Advances in enabling technologies such as DNA sequencing and genotyping open new opportunities for accelerating and achieving tree improvement in all forest tree species. Of the 109 attendees, 47 were first time conference participants and 27 were students, an encouraging sign for the future of forest genetics and tree improvement.     

Biotechnological advances in guava (Psidium guajava L.): recent developments and prospects for further research

Guava (Psidium guajava L.), an important fruit crop of several tropical and sub-tropical countries, is facing several agronomic and horticultural problems such as susceptibility to many pathogens, particularly guava wilting caused by Fusarium oxysporium psidii, low fruit growth, short shelf life of fruits, high seed content, and stress sensitivity. Conventional breeding techniques have limited scope in improvement of guava owing to long juvenile period, self incompatibility, and heterozygous nature. Conventional propagation methods, i.e., cutting, grafting or stool layering, for improvement of guava already exist, but the long juvenile period has made them time consuming and cumbersome. Several biotechnological approaches such as genetic transformation may be effective practical solutions for such problems and improvement of guava. The improvement of fruit trees through genetic transformation requires an efficient regeneration system. During the past 2–3 decades, different approaches have been made for in vitro propagation of guava. An overview on the in vitro regeneration of guava via organogenesis, somatic embryogenesis, and synthetic seeds is presented. Organogenesis in several different genotypes through various explant selection from mature tree and seedling plants has been achieved. Factors affecting somatic embryogenesis in guava have been reviewed. Production of synthetic seeds using embryogenic propagules, i.e., somatic embryos and non-embryogenic vegetative propagules, i.e., shoot tips and nodal segments have also been achieved. Development of synthetic seed in guava may be applicable for propagation, short-term storage, and germplasm exchange, and distribution. An initial attempt for genetic transformation has also been reported. The purpose of this review is to focus upon the current information on in vitro propagation and biotechnological advances made in guava.     

Fruiting Phenology and the Conservation of the Great Pied Hornbill (Buceros bicornis) in the Western Ghats of Southern India1

The phenology of principal fruits consumed by the endangered Great Pied Hornbill (Buceros bicornis) was monitored for two years in a wet forest habitat in southern India. Lipid–rich fruits, produced by several interior forest trees mainly of the family Lauraceae, were highly seasonal in their availability, and their production in the dry, hot season coincided with the breeding of the hornbill. Sugary fruits, produced mainly by several species of Ficus, were available year–round due to aseasonal fruiting patterns. Because Ficus fruited even at times of low fruit resource availability, and was heavily utilized by hornbills and other frugivores, it played a keystone role in the maintenance of the avian frugivore community. Overall fruit production was scarce between July and January during the southwest and northeast monsoon seasons. Vitex altissima produced berries abundantly during much of this time (September–December) and thus was another important fruit resource for avian frugivores. To safeguard the fruit resource base for the Great Pied Hornbill, we recommend: (1) The protection of Ficus and Vitex trees from overexploitation, and (2) the conservation of forest integrity to maintain compositions and densities of the lipid–rich fruit tree species utilized by the hornbill.     

Reproductive ecology of tropical forest trees in logged and fragmented habitats in Thailand and Costa Rica

Invertebrates mediate several important ecological processes, including pollination and seed predation, and events that affect invertebrate diversity or behaviour can potentially disrupt forest regeneration processes. This study investigates the impact of logging in Thailand and forest fragmentation in Costa Rica on the pollination and seed production of two self-incompatible forest trees. Logging in a dry deciduous dipterocarp forest in Thailand resulted in reduced densities of the common dipterocarp treeShorea siamensis and variably isolated individual trees. The number of flower visits to S. siamensis by pollinating Trigona bees was not affected by logging disturbance. However, pollinators did spend longer periods of time foraging in the canopies of isolated trees which were more prevalent in logged areas where tree density had been reduced. Consequently, at the logged site few cross-pollinations were effected and fruit set of S. siamensis was considerably lower than at nearby unlogged sites where distances between flowering conspecifics were smaller. Reduced fruit set has long-term implications for the recovery of S. siamensis populations in disturbed areas, and local population genetic structure is likely to be affected as reduced outcrossing rates among trees in disturbed regions results in relatively inbred seed. In Costa Rica forest fragmentation has restricted the once widespread tree Anacardium excelsum to forest patches located in an agriculturally-dominated landscape. As with S. siamensis, the abundance of pollinators, also Trigona bees, in the canopies of A. excelsum was largely unaffected by fragment size. Nevertheless, pollination success and seed production was positively correlated with fragment size. We propose that small bees rarely move between forest fragments and gene exchange through pollination occurs predominantly among trees within fragments and, together with likely low genetic variability in small fragments, that this contributes to the observed reduced fertilisation and seed set of A. excelsum. Thus increased tree isolation tree through selective logging or habitat fragmentation by forest clearance can result in reduced seed set due to changes in the foraging patterns of poorly mobile pollinators. Even if population sizes of the pollinators are maintained following environmental perturbation, this study shows that disturbance may disrupt pollination processes through changes in pollinator foraging behaviour. More attention needs to be focussed on changes in the behaviour of species involved in key ecological interactions following disturbance events in tropical forests.     

Genomics to tree breeding and forest health

Genomic discovery in forest trees follows paradigms from both agricultural crop and livestock improvement and human medicine. Forest trees in a domesticated state can be improved using genomic-based breeding technologies, whereas the health of trees in a natural and undomesticated state might be managed using those same technologies. These applications begin by first dissecting complex traits in trees to their individual gene components and for that the association genetics approach is quite powerful in trees. This is true for several reasons including large, random mating, and unstructured populations and the rapid decay of linkage disequilibrium in many tree species. Once marker by trait associations are discovered, they can be used in genomic-based breeding and forest health diagnostics. Initial studies in trees have found ample nucleotide diversity in candidate genes to perform association studies and single nucleotide polymorphisms have been associated with economic and adaptive traits. Population genetic neutrality tests have been applied to identify genes probably under natural selection and thus make good candidates for developing forest health diagnostic tools.     

Selection of Nest Trees by Cavity‐nesting Birds in the Neotropical Atlantic Forest

One of the five most important global biodiversity hotspots, the Neotropical Atlantic forest supports a diverse community of birds that nest in tree cavities. Cavity‐nesting birds may be particularly sensitive to forestry and agricultural practices that remove potential nest trees; however, there have been few efforts to determine what constitutes a potential nest tree in Neotropical forests. We aimed to determine the characteristics of trees and cavities used in nesting by excavators (species that excavate their own nest cavity) and secondary cavity‐nesters (species that rely on existing cavities), and to identify the characteristics of trees most likely to contain suitable cavities in the Atlantic forest of Argentina. We used univariate analyses and conditional logistic regression models to compare characteristics of nest trees paired with unused trees found over three breeding seasons (2006–2008). Excavators selected dead or unhealthy trees. Secondary cavity‐nesters primarily selected cavities that were deep and high on the tree, using live and dead cavity‐bearing trees in proportion to their availability. Nonexcavated cavities suitable for birds occurred primarily in live trees. They were most likely to develop in large‐diameter trees, especially grapia Apuleia leiocarpa and trees in co‐dominant or suppressed crown classes. To conserve cavity‐nesting birds of the Atlantic forest, we recommend a combination of policies, economic assistance, environmental education, and technical support for forest managers and small‐scale farmers, to maintain large healthy and unhealthy trees in commercial logging operations and on farms.     

Masting in a temperate tree: Evidence for environmental prediction?

Many plant species produce large fruit crops in some years and then produce few or no fruits in others. Synchronous, inter‐annual variation in plant reproduction is known as ‘masting’ and its adaptive significance has yet to be fully resolved. For 8 consecutive years, I quantified every fruit produced by 22 females of a New Zealand tree species (Dysoxylum spectabile), which has an unusual habit of taking a full calendar year to mature fruits after flowering. Fruit production varied strongly among years and was tightly synchronized among trees. Annual variability in fruit production declined with total reproductive output, indicating trees with lower fecundity exhibited a stronger tendency to mast. Although unrelated to temperature, annual fruit production was positively related to precipitation during annual periods of fruit development, and negatively related to fruit production in the previous year. Seedlings had higher rates of survivorship in a wet, high‐seed year than in a dry, low‐seed year, suggesting that seedlings might be drought sensitive. Therefore, D. spectabile produced large fruit crops during periods of high rainfall prior to fruit maturation, which may enhance survivorship of drought‐intolerant seeds. Results were inconsistent with several hypotheses that are widely believed to be the most likely explanations for masting. Instead, results were consistent with the environmental prediction hypothesis, suggesting that this hypothesis may be more important than previously appreciated.     

Recruitment of Black Howler Fruit Trees in Fragmented Forests of Northern Belize

We examined recruitment of trees whose seeds are dispersed by black howler monkeys (Alouatta pigra) in forest fragments within the Community Baboon Sanctuary in north-central Belize. In the fragments, most other large frugivores are absent and howlers dominate the large frugivore community. Consequently, we expected to observe an increased representation of howler fruit trees among the sapling community. To test this prediction preliminarily we observed howler feeding behavior for one year and conducted adult tree and sapling transects in 6 locations where howlers were present. We sampled a seventh site where howlers were absent for vegetation only. We found that in 4 of 6 sites there were proportionately fewer howler fruit saplings when compared to adult tree samples. However, when recruitment of howler fruit trees in the 6 sites was compared to a site where howlers were absent, 11 of 12 species had relatively higher recruitment. The lack of recruitment among howler fruit trees in general likely reflects differences in responses of individual species, as well as disruptions from human activities to natural processes within the forests. The observed lower recruitment patterns of howler trees suggest that over time, the abundance of the trees will likely decline and thus affect the foraging behavior and possibly survival of howlers in the fragmented forests.     

Transgenic trees for a new era

Summary Traditional breeding has been widely used in forestry. However, this technique is inefficient because trees have a long and complex life cycle that is not amenable to strict control by man. Fortunately, the development of genetic engineering is offering new ways of breeding and allowing the incorporation of new traits in plant species through the introduction of foreign genes (transgenes). The introduction of selected traits can be used to increase the productivity and commercial value of trees and other plants. For example, some species have been endowed with resistance to herbicide and pathogens such as insects and fungi. Also, it has been possible to introduce genes that modify development and wood quality, and induce sexual sterility. The development of transgenic trees has required the implementation of in vitro regeneration techniques such as organogenesis and somatic embryogenesis. Release of transgenic species into the agricultural market requires a standardized biosafety regulatory frame and effective communication between the scientific community and society to dissipate the suspicions associated with transgenic products.     

Epigenetic regulation of adaptive responses of forest tree species to the environment

Epigenetic variation is likely to contribute to the phenotypic plasticity and adaptative capacity of plant species, and may be especially important for long‐lived organisms with complex life cycles, including forest trees. Diverse environmental stresses and hybridization/polyploidization events can create reversible heritable epigenetic marks that can be transmitted to subsequent generations as a form of molecular “memory”. Epigenetic changes might also contribute to the ability of plants to colonize or persist in variable environments. In this review, we provide an overview of recent data on epigenetic mechanisms involved in developmental processes and responses to environmental cues in plant, with a focus on forest tree species. We consider the possible role of forest tree epigenetics as a new source of adaptive traits in plant breeding, biotechnology, and ecosystem conservation under rapid climate change.     

Landscape patterns of species-level association between ground-beetles and overstory trees in boreal forests of western Canada (Coleoptera, Carabidae)

Spatial associations between species of trees and ground-beetles (Coleoptera: Carabidae) involve many indirect ecological processes, likely reflecting the function of numerous forest ecosystem components. Describing and quantifying these associations at the landscape scale is basic to the development of a surrogate-based framework for biodiversity monitoring and conservation. In this study, we used a systematic sampling grid covering 84 km(2) of boreal mixedwood forest to characterize the ground-beetle assemblage associated with each tree species occurring on this landscape. Projecting the distribution of relative basal area of each tree species on the beetle ordination diagram suggests that the carabid community is structured by the same environmental factors that affects the distribution of trees, or perhaps even by trees per se. Interestingly beetle species are associated with tree species of the same rank order of abundance on this landscape, suggesting that conservation of less abundant trees will concomitantly foster conservation of less abundant beetle species. Landscape patterns of association described here are based on characteristics that can be directly linked to provincial forest inventories, providing a basis that is already available for use of tree species as biodiversity surrogates in boreal forest land management.