Exotic tree species displace indigenous ones on farms at intermediate altitudes around Mount Kenya

Agroforestry systems are potentially suitable for conservation of tree genetic resources. Farmers around Mt. Kenya usually integrate trees into their farm. Large parts of these trees seem to be of exotic origin, whereas indigenous species have priority for conservation. This study aimed at determining on-farm richness, composition and frequency of indigenous and exotic woody species around Mount Kenya to assess the suitability of farms for the conservation of indigenous tree species. 265 on-farm plots of 0.5 ha size each were selected in 18 different agro-ecological zones by using a stratified sampling scheme. All woody species within the plot were recorded with their local and scientific names. Total species richness was 424 (including 306 indigenous ones), mean richness per plot 16.5 species (including 8.8 indigenous ones). Eight out of the 10 most frequent species were exotic ones with Grevillea robusta from Australia ranking first (found on almost 76% of the surveyed farms). The proportion of indigenous species increased with increasing aridity and temperature. Dominance of exotic species was found at farms of humid mid- and highlands. Ordination analysis revealed that mostly exotic species contributed to separation of farms in the highlands and upper midlands, whereas indigenous species in the lower midlands and lowlands. As the frequencies of most indigenous trees were low, only parts of the surveyed farms can contribute to conservation of tree genetic resources, particularly the less intensively managed farms of the more arid lands. Farmers’ access to knowledge on valuable indigenous tree species and to quality seedlings of these trees need to be improved to increase indigenous species’ frequencies on farms and possibly to replace some of the exotic species in the future.     

Post-fire attractiveness of maritime pines (<Emphasis Type="Italic">Pinus pinaster</Emphasis> Ait.) to xylophagous insects

The spectrum and dynamics of xylophagous insects infesting Pinus pinaster after a fire event were studied from November 2007 to December 2008 at Sierra de Outes (Galicia, NW Spain). Insects were collected within and outside the fire area. Relationships among species status, species abundance, tree parameters and tree injury were assessed. Mortality of injured trees was also recorded. Insect colonization built up consistently during the first year after the fire, although the pests did not colonize unburned trees in nearby areas. Thirteen insect species from six xylophagous families were collected. Tomicus spp., Buprestis novenmaculata, Anobium punctatum and Pissodes castaneus were the first species detected. Tomicus spp. (29%) and Ips sexdentatus (23%) were the dominant taxa. Bole char height and soil burn severity were positively correlated with insect presence. Trees with short stem diameter and thinner bark were also preferred. B. novenmaculata presence was positively correlated with crown scorch. Loss of cambium hydration was negatively related to the occurrence of pests, likely because sapwood desiccation and loss of nutrient impede brood development. About 33.3% of the fire-scorched pines died. The results recommend the removal of injured and dying pines after fire, to avoid the rise of pest population threatening recovering trees in the burned areas.     

Relating genetic variation of ecologically important tree traits to associated organisms in full-sib aspen families

Knowledge on phenological, morphometric, and phytochemical variation of local progenies of European aspen (Populus tremula, L.) is limited. The goal of this study was to characterize variation in growth and ecologically important leaf properties in aspen full-sib families in relation to interacting organisms (mycorrhiza, endophytes, and insects) and to determine whether these interactions were affected by soil application of a systemic fungicide. In local progenies, within-family variation of neutral molecular genetic markers (nuclear microsatellites) was higher than between families. Significant variation in growth, production of phenolic defensive compounds and other phytochemical leaf traits was found between families. Phenolic compounds showed clear negative correlation with generalist herbivores, but did not result in negative trade-off with biomass production. Differences in mycorrhizal colonization were not found among full-sib families and application of a systemic fungicide suppressed neither mycorrhizal colonization nor infestation with insects. However, a strong suppression of endophytes occurred, whose long-term consequences may require attention when fungicides are used in agroforestry plantations.     

Impacts of tree canopy structure on wind flows and fire propagation simulated with FIRETEC

Introduction   

Forest fuel management in the context of fire prevention generally induces heterogeneous spatial patterns of vegetation. However, the impact of the canopy structure on both wind flows and fire behavior is not well understood.     

Carbon in heartwood,sapwood and bark along the stem profile in three Mediterranean <Emphasis Type="Italic">Pinus</Emphasis> species

• Context   

Understanding biological processes in forests is necessary to orientate ecosystem management towards potential C sequestration. To achieve this, information is required about changes in forest biomass C pools, including the stem components (bark, sapwood and heartwood).     

Do mature pine plantations resemble deciduous natural forests regarding understory plant diversity and canopy structure in historically modified landscapes?

We compared the structure of the arboreal layer and the diversity and species composition of the understory vegetation of three types of mature forest communities: oak (Quercus pyrenaica) and beech (Fagus sylvatica) forests and Scots pine (Pinus sylvestris) plantations. Our main aim was to determine whether differences in these variables existed and were due to the identity of the dominant tree species. We selected four stands or replicates per forest type located geographically close and with relatively similar conditions. We found no differences in the arboreal structure of oak and beech forests, which were characterised by great variability in tree size, while in case of plantations, this variability was lower at both the intra-stand (estimated by the coefficient of variation) and inter-stand (i.e. the four replicates harboured trees of similar sizes) scales. However, the highest variability in the canopy layer of natural forests was not consistently linked to greater understory species richness. Indeed, the lowest plant species richness was found in beech forests, while oak forests harboured the highest value at either the sampling unit (per m²) or stand scales. The greatest negative correlation between plant diversity and the environmental variables measured was found for litter depth, which was the highest in beech forests. The results obtained by the CCA indicated that the four replicates of each forest type clustered together, due to the presence of characteristic species. We concluded that pine plantations did not approach the environmental conditions of native forests, as plantations were characterised by singular understory species composition and low arboreal layer variability, compared to natural woodlands.     

Diameter distribution of trees in natural stands managed on polycyclic cutting system

Diameter frequency distribution in a specific stand provides basic information for forest resources management.In this study,four probability models were applied to analyze diameter distribution of natural forests after selective cutting with different intensities (low intensity of 13.0% in volume,medium intensity of 29.1%,high intensity of 45.8%,and extra-high intensity of 67.1%).The results show that the skewness and kurtosis of the four models are positive except that of low intensity selective cutting,which suggest that the number of small-size trees dominate the stand.The more intensity of selective cutting,the wider range of diameter distributions.The diameter structure of selective cutting with low intensity met Weibull and Beta distributions;that of medium intensity met Weibull,negative exponential as well as Gamma distributions;that of high intensity cutting met Weibull and negative exponential distributions,but that of extra-high intensity could not meet any above model.Weibull distribution model fits better than others regarding the structure of diameter distribution in natural forests managed on polycyclic cutting system.The results will provide basic information for sustainable management for mixed natural stands managed on a polycyclic cutting system.     

Shrinkage and swelling behavior of archaeological waterlogged wood preserved with slightly crosslinked sodium polyacrylate

In this article, the conservation of archaeological waterlogged wood (WW) of Afzelia sp. (medium degraded: U_max = 385%) was impregnated in vacuum with an aqueous solution of acrylic acid (AA), sodium acrylate monomer (AANa), crosslinking agent (MBA) and catalyst (V-501). The simultaneous in situ polymerization and crosslinking resulted in slightly crosslinked sodium polyacrylate (PAANa) in the wood structure. The results showed that untreated WW had only a very limited ability to re-swell to recover its original dimensions from a collapsed condition, while WW protected by crosslinked PAANa could almost fully recover its original shape and size even after several drying–rewetting cycles. From microscopic observations, treated wood was found to maintain its original cell structure, form and shape even after repeated drying–rewetting cycles. PAANa was observed to be densely localized near the middle lamella, the cell corners, and the cell lumina by transmission electron microscopy observation. These observations suggest that our PAANa treatment provides reasonable strength as well as favorable hydrophilicity to avoid hornification of the cell wall upon drying, thus providing unique shape recovery properties.