Seed size, seedling morphology, and response to deep shade and damage in neotropical rain forest trees

To investigate the existence of coordinated sets of seedling traits adapted to contrasting establishment conditions, we examined evolutionary convergence in seedling traits for 299 French Guianan woody plant species and the stress response in a shadehouse of species representing seed size gradients within five major cotyledon morphology types. The French Guianan woody plant community has larger seeds than other tropical forest communities and the largest proportion of hypogeal cotyledon type (59.2%) reported for tropical forests. Yet the community includes many species with intermediate size seeds that produce seedlings with different cotyledonal morphologies. A split-plot factorial design with two light levels (0.8% and 16.1% PAR) and four damage treatments (control, seed damage, leaf damage, stem damage) was used in the shadehouse experiment. Although larger-seeded species had higher survival and slower growth, these patterns were better explained by cotyledon type than by seed mass. Even larger-seeded species with foliar cotyledons grew faster than species with reserve-type cotyledons, and survival after stem grazing was five times higher in seedlings with hypogeal cotyledons than with epigeal cotyledons. Thus, to predict seedling performance using seed size, seedling morphology must also be considered.     

Inter- and intraspecific relationships between shade tolerance and shade avoidance in temperate trees

Patterns of physiological and architectural adaptation and acclimation to decreasing light availability were investigated along a light gradient for saplings of 12 common species of temperate deciduous trees in southeastern Ontario, Canada. Physiological adaptation and acclimation (shade tolerance physiology) were quantified at the leaf level by measuring leaf mass per unit area (LMA), dark respiration per unit leaf nitrogen, chlorophyll per unit leaf nitrogen and the chlorophyll a:b ratio for the newest fully expanded leaf on the leader. Architectural adaptation and acclimation (shade avoidance) were quantified by measuring branching intensity and side shoot:main shoot length ratios for the most recent three years of growth on the leader and selected side branches. Within species, increases in LMA, chlorophyll a:b ratio and respiration per unit nitrogen and decreases in chlorophyll per unit nitrogen indicated that shade tolerance physiology generally increased with decreasing canopy openness. Increases in the branching intensity and side shoot:main shoot ratios of the leader and side branches indicated that shade avoidance also increased with decreasing canopy openness for the majority of species; however, in some species, stem bending under deep shade resulted in lateral growth. Interspecific variation in shade tolerance physiology was minimal when species were compared under equal amounts of canopy openness. In contrast, interspecific variation in shade avoidance variables was relatively high under equal canopy openness, with saplings of shade tolerant canopy species exhibiting higher shade avoidance than saplings of shade tolerant understory species.     

population dynamics of some tropical trees that yield non-timber forest products

The population biology ofAquilaria malaccensis, one source of gharu, and Cinnamomum mollissimum, one source of wild cinnamon, was studied in a 50 ha permanent plot of primary rain forest in Malaysia. Median diameter growth rates of 0.22 cm yr^-1 and 0.1 cm yr^-1 should not be prohibitive of economic exploitation, and suggest that the trees could be grown commercially. However, the natural densities were between 2 and 3 trees over 1 cm d.b.h. per ha, which is roughly the median for all trees in the plot, would preclude economic exploitation of these natural populations. The economics of harvesting natural populations is considered in a preliminary fashion by allowing favorable assumptions of quantity and quality of production. The price likely to be fetched from either a first time extraction (on the order of US$10.00 per ha) or from sustained production (on the order of USThe population biology ofAquilaria malaccensis, one source of gharu, and Cinnamomum mollissimum, one source of wild cinnamon, was studied in a 50 ha permanent plot of primary rain forest in Malaysia. Median diameter growth rates of 0.22 cm yr^-1 and 0.1 cm yr^-1 should not be prohibitive of economic exploitation, and suggest that the trees could be grown commercially. However, the natural densities were between 2 and 3 trees over 1 cm d.b.h. per ha, which is roughly the median for all trees in the plot, would preclude economic exploitation of these natural populations. The economics of harvesting natural populations is considered in a preliminary fashion by allowing favorable assumptions of quantity and quality of production. The price likely to be fetched from either a first time extraction (on the order of US10.00 per ha) or from sustained production (on the order of US10.00 per ha) or from sustained production (on the order of US0.10 per ha per yr), are too small to be of interest as single-product schemes, and are negligible compared to the extraction of multi-species crops of timber. However, it is possible that by combining multiple products under a “High Diversity Forestry” scheme, one could increase the density of harvestable products, reduce the unit cost of labor and improve the economic portrait. La poblacion dinamica de algunos arboles tropicales. La población biológica deAquilaria malaccensis, un original de gharu, yCinnamomum mollissimum, un original del cinnamon salvage, ha sido estudiado en 50 ha en un terreno primario permanente de lluvia tropical en. Con un índice de crecimiento de medio dimetro 0.22 cm yr^-1 0.1 cm yr^-1 no deberia prohibirse la explotación económica, y se segiuere que los árboles pueden ser cultivados comercialmente. De cualquier manera, la densidad natural siendo aproximadamente entre 2 y 3 árboles per encima de 1 cm dbh per ha, lo cúal es un promedio de todos los árboles en el terreno, esto representa un impedimento a la explotacion económica de la población natural. La economía de la población natural de recolección de la cosecha está considerada como una moad preliminar por permitirse favorablemente la supuesta cantidad y calidad de productión. Los precios problemente alcanzen, bien sea, la primera vex de su extracción sobre el pedido de US10.00 per ha o desde una continua productión ininterrumpida, (sobre un pedido US10.00 per ha o desde una continua productión ininterrumpida, (sobre un pedido US0.10 per ha per yr), siendo demassiado peque?o para ser de interés tal proyecto comoproducto-unico, y son insignificantes comparados con la extracción de multiples especies de semillas de madera. De caulquier manera esposible que sepueda combinar los multiple productos en el proyecto de “Alta Diversidad Forestal,” uno puede la un puede incrementar la densidad de la productión de la cosecha, reduciendo el costo de mano de obra por unidad y mejorando la imagen económica.     

Selection of shade trees in forest restoration plantings should not be based on crown tree architecture alone

The planting of tree seedlings is a common restoration technique in the tropics, and using large‐crowned, fast‐growing shade species is recommended to suppress invasive grasses and accelerate forest succession. We analyzed the effectiveness of shade species in shading the forest floor during the rainy and dry seasons at young forest restoration sites, whether shade changes according to site for a given species, and whether crown architecture can predict the shade level. We measured the photosynthetically active radiation (PAR) intercepted by the tree crowns of 14 species in two 3‐year‐old restoration plantings. The ability to predict shade based on crown architecture traits was evaluated using multiple linear regressions. The interception of PAR varied according to species, site, and season for seven species and was generally higher during the rainy season. Low values of tree and first branch height and high values of trunk diameter and mean area of a leaf predicted greater light interception. For the dry season, the ability to predict PAR interception was weaker than that for the rainy season and affected by a shorter tree height and a greater crown area. The crown architecture of shade species did not completely predict their shading ability, and the preselection of shade species for forest restoration purposes based only on crown architecture traits is not effective. Therefore, it is important to consider other factors, such as how long trees retain their leaves throughout the year and the soil and management conditions of the sites undergoing restoration, during the selection of species.     

Nitrogen cycle of tropical perennial crops under shade trees

The distribution and fluxes of nitrogen in some parts of a coffee plantation under shade were studied at a typical mountain (1380 m a sl) location in Venezuela. The amounts of nitrogen in the soil to 60 cm depth are by far the largest nitrogen store, reaching a total of 49 000 kg ha^?1. The nitrogen flow associated with litterfall was dominated by the shade-tree fraction accounting for a transfer of 86 kg ha^?1 yr^?1 of the total 189 kg ha^?1 yr^?1. The rapid decomposition of this litter, although showing a phase of nitrogen accumulation, is an important source of nitrogen to the roots of coffee which occupy preferentially the upper 30 cm of soil and even the litter layer itself. Some evidence of synchrony was found between the peaks of nitrogen transfer to the soil by litter and the periods of high nitrogen demand by the crop plants. It is proposed that the system can amply compensate the nitrogen outputs by harvest (17 kg ha^?1 yr^?1) with a subsidy from the shade trees.Erythrina sp. andInga sp. are potential nitrogen fixers although we found no active sites during the dry period sampled. The average litter decomposition constant, k, expressed in terms of nitrogen, was estimated as 4.5, equivalent to a half-life of approximately two months.     

Neuroimaging: seeing the trees for the forest

New functional imaging studies demonstrate that it is possible to decode a sensory visual pattern, and even an internal perceptual state, by combining seemingly insignificant feature selective signal biases present in a large number of voxels.     

Stacking transgenes in forest trees

Huge potential exists for improving plant raw materials and foodstuffs via metabolic engineering. To date, progress has mostly been limited to modulating the expression of single genes of well-studied pathways, such as the lignin biosynthetic pathway, in model species. However, a recent report illustrates a new level of sophistication in metabolic engineering by overexpressing one lignin enzyme while simultaneously suppressing the expression of another lignin gene in a tree, aspen. This novel approach to multi-gene manipulation has succeeded in concurrently improving several wood-quality traits.     

Molecular cytogenetics of forest trees

The economic and ecological importance of forest trees, as well as their unique biological features, has recently raised the level of interest in studies on their genomes, including sequencing of the entire poplar genome. However, cytogenetic studies have not moved in parallel with developments in genomics. This is especially true for hardwood species characterized by small genomes and relatively high numbers of small chromosomes. Molecular cytogenetic studies have mainly been focused on coniferous species, owing to the larger size of their chromosomes, and have been applied exclusively for chromosome identification and comparative karyotyping in an attempt to understand genome evolution and phylogenetic relationships. In this context, rRNA genes physical mapped by FISH reveal particularly useful chromosomal landmarks with variable distribution patterns between species. Here we present a contribution of DNA markers used for chromosome analysis, which already allowed a deeper characterization and understanding of the processes underlying genome diversity of forest trees. The use of advanced cytogenetic techniques and other potential important methods for genome analysis of forest trees is also discussed.     

Spatial pattern of trees in kerangas forest,Sarawak

The 64 most abundant species (10 cm dbh) in a 400×480 m plot of predominantly kerangas forest in Sarawak were individually investigated for two-dimensional pattern by spectral analysis using the basal areas of trees in 20×20 m contiguous quadrats. All species had individuals in the upper canopy.30 species showed pattern with clumps. The most frequent scales of clump size were between 35 and 55 m across. Patterned species were less abundant in the plot, had a greater proportion of smaller (10–20 cm dbh) trees and had a lower ratio of upper to lower canopy trees than species without pattern.Trend across the plot between dipterocarp and kerangas forest types matched the change in soil from red-yellow podzol (oxisol and ultisol) to medium gleyic and bleached sand podzols (spodosol). However, soil differences and small scale (ca. 50 m) changes in topography did not account for patterns.The scale of pattern matches the size of gaps produced by windthrow. It is suggested that patterned species are light-demanding and grow from seeds in gaps, whereas non-patterned species are shade tolerant, growing within closed forest to sapling size and eventually maturing by filling smaller single tree gaps.D. McC. N. thanks the Deutsche Akademische Austauschdienst for a scholarship and the British Council for travel funds to work at Hamburg. We are grateful to A. Weiscke for entry of the 1963 field records on the computer, T. W. Schneider for helpful discussions and T. C. Whitmore for commenting on earlier drafts.Nomenclature for three species follows Whitmore (1972, 1973), Ng (1978) and Ashton (1982).     

Natural history, biogeography, and endangerment of Hawaiian dry forest trees

We describe the floristic composition of Hawaiian dry forest trees and identify natural history characteristics and biogeographic variables that are associated with risk of endangerment. Hawaiian dry forests are comprised of 109 tree species in 29 families, with 90% of all species endemic, 10% indigenous, and 37% single-island endemics. Forty-five percent of Hawaiian dry forest taxa are at risk of endangerment. Dry forest taxa at risk have a significantly larger range size compared to taxa from other Hawaiian forest types. Dispersal mechanism was a significant predictor of a species occurrence in dry forest compared to other forest types based on logistic regressions clustered by lineage. Among dry forest taxa, hermaphroditic breeding systems, autochorous dispersal mechanisms, conspicuous flowers, and dry fruit were all more likely to be at risk of endangerment. When analyses were clustered by lineage using logistic regressions, only dispersal mechanism and flower size were significant predictors of risk and taxa with autochorous dispersal and conspicuous flowers were more likely to be at risk. The Big Island, Maui, Oahu, and Kauai all have remarkably similar numbers of dry forest taxa (63–65 species) and dry forest taxa at risk of endangerment. However, Big Island and Kauai have the highest number and percentage of single-island endemics. These results demonstrate patterns of endangerment specific to Hawaiian dry forests, the high levels of endangerment in this forest type, and the importance of prioritizing conservation in dry forest regions.     

Linking forest shade tolerance and soil moisture in North America

Increasing occurrence of droughts is a major environmental concern, however its consequences on forested ecosystems are not fully understood at the landscape level. Here we link the forest shade tolerance index to soil moisture in the North America using the U.S. and Quebec forest inventories. We report a significant decrease of shade tolerance index along the hydric–mesic–xeric soil transition in most of the area considered except three subtropical/tropical ecoregions of the Southeastern U.S. We conclude that droughts may alter forest succession, and in particular decrease the role of forest gap dynamics and dominance of the shade-tolerant species in mature forests.     

Growth strategies of main trees and forest architecture of aFagus-Magnolia forest in Florida, USA

Growth strategies of six species of trees are compared and used to analyze forest architecture. They included the overstory speciesFagus grandifolia, Magnolia grandiflora, Pinus glabra andLiquidambar styraciflua, and the understory speciesOstrya virginiana andIlex opaca. The six species were abundant in Woodyard Hammock, an old-growth forest in northern Florida, USA. Height, stem diameter, crown projection and radial growth were measured in trees between 5 and 35 m tall. Three different, but non-exclusive, growth strategies were identified for the tree species: survival (Fagus grandifolia, Magnolia grandiflora, Ilex opaca), occupy open space (Fagus grandifolia, Ostrya virginiana, Ilex opaca), and reach above competitors (Liquidambar styraciflua, Pinus glabra). In two transects (0.42 ha) and one quadrat (1 ha), heights of dominant trees were used to distinguish different phases of forest development, which were mapped. In the quadrat, juvenile canopy trees in the undergrowth were mapped. The combination of presence of different developmental phases, presence of juveniles in the undergrowth, growth strategies of main tree species, and disturbance regime was used to assess forest development in the near future.Fagus grandifolia is predicted to become the main dominant species, but the frequent hurricanes open the forest canopy and provide opportunities for understory species (Ostrya virginiana andIlex opaca), and light-demanding overstory species (Liquidambar styraciflua andPinus glabra).     

Genomic diversity in forest trees

Forest trees in general are out-crossing, long-lived, and at early stages of domestication. Molecular evolution at neutral sites is very slow because of the long generation times. Transferring information between closely related conifer species is facilitated by high sequence similarity. At the nucleotide level, trees have at most intermediate levels of variation relative to other plants. Importantly, in many species linkage disequilibrium within genes declines within less than 1000 bp. In contrast to the slow rate of neutral evolution, large tree populations respond rapidly to natural selection. Detecting traces of selection may be easier in tree populations than in many other species. Association studies between genotypes and phenotypes are proving to be useful tools for functional genomics.     

Some ecophysiological features in sun and shade leaves of tall beech trees

Some ecophysiological features in sun and shade leaves of tall European beech trees (Fagus sylvatica L.) growing in a natural forest stand were investigated. Quantitative leaf characteristics were followed in the field and under controlled conditions. In the sun leaves significantly higher rates of photosynthesis, photorespiration and dark respiration, and also photosynthetic CO₂ fixation capacity, photosynthetic productivity, and saturating, adaptation and compensating irradiances were found. Specific leaf mass, mean leaf area, stomata density and size as well as the chlorophyll content per unit dry mass were also significantly different in both types of the leaves. Higher photosynthetic efficiency in the shade leaves allows them a better utilization of the lower irradiance for carbon dioxide uptake. The importance of these findings for annual carbon gain of the shade tolerant European beech species is also discussed.