Ants,fire, and bark traits affect how African savanna trees recover following damage

Bark damage resulting from elephant feeding is common in African savanna trees with subsequent interactions with fire, insects, and other pathogens often resulting in tree mortality. Yet, surprisingly little is known about how savanna trees respond to bark damage. We addressed this by investigating how the inner bark of marula (Sclerocarya birrea), a widespread tree species favoured by elephants, recovers after bark damage. We used a long‐term fire experiment in the Kruger National Park to measure bark recovery with and without fire. At 24 months post‐damage, mean wound closure was 98, 92, and 72%, respectively, in annual and biennial burns and fire‐exclusion treatments. Fire exclusion resulted in higher rates of ant colonization of bark wounds, and such ant colonization resulted in significantly lower bark recovery. We also investigated how ten common savanna tree species respond to bark damage and tested for relationships between bark damage, bark recovery, and bark traits while accounting for phylogeny. We found phylogenetic signal in bark dry matter content, bark N and bark P, but not in bark thickness. Bark recovery and damage was highest in species which had thick moist inner bark and low wood densities (Anacardiaceae), intermediate in species which had moderate inner bark thickness and wood densities (Fabaceae) and lowest in species which had thin inner bark and high wood densities (Combretaceae). Elephants prefer species with thick, moist inner bark, traits that also appear to result in faster recovery rates.     

Thermal properties and fauna on the bark of trees in two different African ecosystems

Summary The thermal properties of 26 African tree species in two different ecosystems were studied using thermocouples. In a subtropical moist forest were three bark types of trees: species with thin and smooth bark types with low values of insulation across the bark; species with a more structured bark type and medium insulation values; and species with deep-fissured or scaly bark types and high insulation values. Only these latter trees are able to survive openings in the subtropical forest and stand alone on edges of forest gaps. In the savanna all tree species showed adaptations in the structure of their bark in different forms: many tree species shade their trunks. Some have low bark insulation and these are known to be sensitive to fires. Some tree species show high bark insulation and do not shade their trunks. Tree species with white bark avoid overheating of their surface by reflection of the radiation. The arthropod community living exclusively on the bark was investigated for the first time on South African trees, on ten tree species. In the two different ecosystems this habitat is occupied by different arthropod groups. In the subtropical forest Acari, Araneae, Opiliones, Isopoda, Myriopoda, Blattodea, Psocoptera, Heteroptera, Coleoptera, Formicidae, and Nematocera (Diptera) are the main arthropod groups living exclusively on the bark of trees. In the savanna Pseudoscorpiones, Araneae, Collembola, Blattodea, Psocoptera, Coleoptera, Neuroptera, Termites, Formicidae, Hymenoptera and Brachycera (Diptera) are the main arthropod groups living exclusively on the bark of trees. Within one ecosystem on one bark type the dominant species are similar; richly structured bark types have a richer fauna. In the forest, bark arthropod diversity is related to the bark structure of the constituent trees, and the arthropod communities on the bark would reflect changes in the structure of the forest. Forests comprising tree species with different bark types would have a richer total bark arthropod fauna. Specialists on richly structured bark types would die out if tree species composition were altered by man to give stands consisting only of tree species with smooth bark types. Bark arthropods in a subtropical moist forest have different proportions of herbivorous and fungivorous compared to carnivorous species than those on the bark of trees in a savanna.     

Structure and identification of root bark of Quercus robur L.

The root bark structure of Quercus robur L. was analysed at different stages of root development and compared to the structure of stem bark. Root bark thickness varied considerably between different roots. Sclereid quantity decreased with increasing distance from the stem, which means it increased with age. Visible growth increments diminished with increasing distance from the stem. In lateral roots crystal quantity decreased with increasing distance from the stem. In lateral roots secondary phloem fibre length, sieve tube member length, and sieve tube diameter showed no regular trend. There were only a few basic structural differences between root and stem bark. The zone of cell differentiation (cell expansion, lignification) was wider in root bark; sieve tube collapse was delayed. In lateral root bark fewer sclereids were formed. The first-formed periderm often originated from deeper cell layers. Thus, primary elements were lacking after periderm formation. In root bark the phellem cell walls were of equal thickness. Thus, phellem lacked visible growth increments. Root bark phellem cells were slightly larger. The root phelloderm was more distinct. The secondary phloem fibres were slightly shorter than those in stem bark. Sieve tube members of stem and root bark were of similar length and diameter. The qualitative bark anatomical characters of oak root bark are suitable for root identifications. Due to minor structural differences between root and stem bark the characters must be used with care.     

The origins of tannins and flavonoids in black-wattle barks and heartwoods, and their associated "non-tannin" components

1. The distributions of flavonoid, carbohydrate, amino acid and imino acid components in the leaves, twig bark, stem bark, root bark and heartwoods of the black-wattle tree were compared by paper chromatography after their isolation from specific portions of the tree. 2. Wattle leaves contain mainly myricitrin, (+)-gallocatechin, an unknown myricetin glycoside and leuco-delphinidin tannins, together with smaller amounts of (+)-catechin, quercitrin and other flavonol glycosides. These are prominent in the twig bark, but decline progressively with age in the stem bark and are absent from root bark. 3. The non-phenolic components of the mature stem bark were shown to be (+)-pinitol, sucrose, glucose, fructose, l(-)-pipecolic acid, trans-4-hydroxy-l(-)-pipecolic acid, alpha-alanine, arginine, aspartic acid, glutamic acid, l(-)-proline, serine, a ;steroid' alcohol and a long-chain beta-diketone. 4. Wattle bark and heartwood ;tannins' consist of the analogues of closely related prototypes with common origins in the vascular tissues of the bark. Leaf ;tannins' are superimposed on the bark components mainly during the initial stages of bark growth. 5. Origins of the pipecolic acids and the transformations of carbohydrates in the sap- and heart-woods are discussed.     

Using wavelet analysis to examine bark microrelief

Key Message

An improved quantification of variations in bark microrelief is presented that uses wavelets on a circular domain from data acquired using the LaserBark? automated tree measurement system.

Abstract

An important metric of canopy structure, bark microrelief affects both the hydrology and biogeochemistry of forests. Increased bark microrelief leads to reduced stemflow volumes and higher concentrations of stemflow leachates and nutrient-ions. Consequently, an improved representation of bark microrelief would be useful to describe the influence of various tree species on water and solute contributions to the forest floor. Most existing methods to quantify bark microrelief are ‘global’ measures; that is, they provide a single number that represents the overall bark microrelief of the entire perimeter of the tree. To remedy this, wavelet analysis of LaserBark? automated tree measurement system data is proposed and described to quantify variations in bark microrelief around the perimeter of the tree. This measure describes the spatial differences in bark microrelief and allows representation of trees that exhibit directional variability in bark microrelief due to natural or anthropogenic effects. The results show that wavelet analysis is effective in quantifying both bark microrelief and large-scale tree asymmetry. The radial component highlights changes in the depth of bark microrelief while the tangential component relates to the distance between bark furrows in the bark cross section. Thus, wavelet analysis may be a useful tool for comparing bark structure that varies, for example, within- and between-tree species, at different stages of tree growth, and among trees grown under different environmental conditions.     

The bark of trees: thermal properties,microclimate and fauna

Summary The thermal properties of four different types of bark were investigated on twentyfour central European tree species using thermocouples. Tree species with white bark avoid overheating of their surface by reflection of the radiation. Species with fissured and scaly barks shade inner parts of their bark. Some tree species with fissured barks show high insulation across the bark. Smooth and thin barks show no adaptation to avoid overheating. These tree species (in central Europe e.g. Fagus sylvatica) have to form closed stands and are not able to occur in open stands as tree species with structured or white bark types.The arthropod fauna of the same bark types was studied on six tree species using three collecting methods. The microclimate on the bark determines the number per cm² of some species, some are active during winter, and other tend to aptery and reproduce parthenogenetically. On smooth bark one species dominates, whereas a highly diverse fauna lives on fissured barks. The occurrence of species on bark is determined by the microstructure, microclimate and consistence of the epiphyts. If tree species alter within forest ecosystems the dominant species on bark will persist. Specialists of fissured barks will die out if tree species with smooth bark (Fagus sylvatica) form the central European forest.     

Qualitative and quantitative changes in nitrogenous compounds in senescing leaf and bark tissues of the apple

Quantitative and qualitative changes in proteins and ethanol-soluble nitrogen were followed in senescing leaf and bark tissues of ‘Golden Delicious’ apple trees (Malus domestica Borkh.). While senescing leaves lost 46% of their proteins, total bark protein increased 240% during senescence. However, the protein nitrogen gain in bark tissue was about the same as the protein nitrogen loss in leaf tissue per unit fresh weight of tissues. The pattern of bark protein accumulation appears to be gradual from early August to November and sequential from lower to higher molecular weight species of proteins. The final electrophoretic profile of total bark proteins was established at the later stages of senescence. By late November, 89% of the nitrogen in the bark tissue was found in proteins with 11% in the ethanol-soluble fractions. The total protein content of dormant bark tissue was 3.5% per gram dry tissue. Fractionation of the total bark proteins by DEAE-cellulose chromatography indicated that the final upsurge of bark proteins observed in November was associated primarily with one group of proteins (Peak III).     

Fire and drought: Shifts in bark investment across a broad geographical scale for Neotropical savanna trees

Savanna tree communities occurring in confluence zones with other biomes likely experience different environmental pressures, resulting in shifts in the selection of individual traits, the combinations of such traits, and species composition. In seasonally dry fire-prone environments, plant survival is presumably associated with adaptive changes in bark properties related to fire protection and water storage. Here, we integrated the multiple functions of the bark to investigate whether different selective pressures could influence patterns of variation in bark structure and allocation across species in a broad geographical range. We measured thickness, density, and water content of the inner and outer bark in branches and the main stem of the 51 most abundant species in three savanna communities differing in climatic aridity, one located at the core region of Cerrado in Central Brazil and the other two at its periphery, in the transition zones with Amazonia and Atlantic forest biomes. We found no difference in outer bark thickness but markedly difference in inner bark thickness between the three plant communities. In the central region, where dry season is long and fire is frequent, branches and main stem showed thicker inner bark. Contrastingly, in the south periphery region, where dry season is short, species showed thinner inner bark in both branches and main stem. Species from the north periphery region, where mean annual precipitation is higher, but fire is frequent and the dry season is also long, showed similar main stem inner bark thickness, but thinner branch inner bark compared to core region species. Our findings support the idea that investing in inner bark thickness and bark moisture may be the most advantageous strategy in plant communities that suffer from high evaporative demand during a long period and are at a high risk of fire.     

Metabolomic analysis of Strychnos nux-vomica, Strychnos icaja and Strychnos ignatii extracts by 1H nuclear magnetic resonance spectrometry and multivariate analysis techniques

1H Nuclear magnetic resonance spectrometry and multivariate analysis techniques were applied for the metabolic profiling of three Strychnos species: Strychnos nux-vomica (seeds, stem bark, root bark), Strychnos ignatii (seeds), and Strychnos icaja (leaves, stem bark, root bark, collar bark). The principal component analysis (PCA) of the 1H NMR spectra showed a clear discrimination between all samples, using the three first components. The key compounds responsible for the discrimination were brucine, loganin, fatty acids, and Strychnos icaja alkaloids such as icajine and sungucine. The method was then applied to the classification of several "false angostura" samples. These samples were, as expected, identified as S. nux-vomica by PCA, but could not be clearly discriminated as root bark or stem bark samples after further statistical analysis.     

Complementary DNA cloning of poplar bark storage protein and control of its expression by photoperiod

Bark storage proteins accumulate in the bark of many woody plants during autumn and winter. In poplar (Populus deltoides Bartr. ex Marsh), the accumulation of the 32-kilodalton bark storage protein is controlled by photoperiod. We have isolated a full-length cDNA encoding for the poplar 32-kilodalton bark storage protein and determined its nucleotide sequence. The derived amino acid sequence shows that poplar bark storage protein is rich in serine, leucine, phenylalanine, and lysine. Poplar bark storage protein is similar to the poplar wound-induced cDNA clone 4 and clone 16 (TJ Parsons, HD Bradshaw, MP Gordon [1989] Proc Natl Acad Sci USA 86: 7895-7899). DNA gel blot analysis suggests that poplar bark storage protein is encoded by a multigene family of about five genes. Poplar plants grown in long days contained low levels of mRNA for the bark storage protein. Exposure to short days resulted in an increase in bark storage protein mRNA within 7 days. After 21 days of short day exposure, high levels of mRNA were detected. The accumulation of bark storage protein mRNA in response to short days was also observed in plants exposed to natural shortening daylengths. Our results indicate that the accumulation of poplar bark storage protein mRNA is controlled by photoperiod. This finding will provide a useful system for investigating photoperiodism in woody plants.     

Environmental filtering structures fungal endophyte communities in tree bark

The factors that control the assembly and composition of endophyte communities across plant hosts remains poorly understood. This is especially true for endophyte communities inhabiting inner tree bark, one of the least studied components of the plant microbiome. Here, we test the hypothesis that bark of different tree species acts as an environmental filter structuring endophyte communities, as well as the alternative hypothesis, that bark acts as a passive reservoir that accumulates a diverse assemblage of spores and latent fungal life stages. We develop a means of extracting high‐quality DNA from surface sterilized tree bark to compile the first culture‐independent study of inner bark fungal communities. We sampled a total of 120 trees, spanning five dominant overstorey species across multiple sites in a mixed temperate hardwood forest. We find that each of the five tree species harbour unique assemblages of inner bark fungi and that angiosperm and gymnosperm hosts harbour significantly different fungal communities. Chemical components of tree bark (pH, total phenolic content) structure some of the differences detected among fungal communities residing in particular tree species. Inner bark fungal communities were highly diverse (mean of 117–171 operational taxonomic units per tree) and dominated by a range of Ascomycete fungi living asymptomatically as putative endophytes. Together, our evidence supports the hypothesis that tree bark acts as an environmental filter structuring inner bark fungal communities. The role of these potentially ubiquitous and plant‐specific fungal communities remains uncertain and merits further study.     

The Effect of New Bark Pormation After Removal of Tree-Crown in Eucommia Ulmoides

Histogenesis of the newly formed bark and the variation in accumulation of starch grains after removal of tree-crown of Eucommia ulmoides Oliv. were observed. The tree in which the tree-crown was removed only formed incomplete bark after girdling, and eventually died after two months or later. The xylem usually reserved a great amount of starch and also presented a limited quantity of it in the new bark. However, the starch grains of the part of xylem that produced the new bark and that in the new bark ail disappeared at the time of death.     

Hydrological properties of bark of selected forest tree species. Part I: the coefficient of development of the interception surface of bark

Key message

The coefficient of development of the interception surface of bark allows for objective assessment of the degree of bark surface differentiation between different species.

Abstract

Inter-species differentiation of bark morphology and its variability progressing with tree age suggest that the hydrological properties of the bark of particular species depend on the degree of development of the outer bark surface of trees. The aim of the present research was to develop a method of calculating the actual bark surface with the use of the coefficient of development of the interception surface of bark, describing the degree of development of the outer bark surface of trees. The primary aim was to show inter-species differentiation of the coefficient of development of the interception surface of bark at breast height, as well as its variability within a single species, progressing with tree age. The present study shows the results obtained for 77 bark samples collected at the breast height of the following tree species: Pinus sylvestris L., Larix decidua Mill., Abies alba Mill., Picea abies L., Quercus robur L., Fagus sylvatica L., Acer pseudoplatanus L. and Betula pendula Ehrh. In all of the examined species, the coefficient of development of the interception surface of bark shows a distinct relation to the breast-height diameter. The highest values of coefficient of development of the interception surface of bark among the thickest trees are reached by: L. decidua—2.56, Pinus sylvestris—2.28 and B. pendula—2.44, whereas the lowest values are reached by the bark of European beech F. sylvatica—1.07. The coefficient of development of the interception surface of bark describes the morphological differentiation of the outer bark surface of trees in an objective way. Owing to its mathematical form, the coefficient of development of the interception surface of bark may be useful in the modelling of hydrological processes occurring in forest ecosystems.     

Change in the chemical composition of the crust and inner bark of the <Emphasis Type="Italic">Betula pendula</Emphasis> roth. Birch (Betulaceae) with tree height

In this article, the group chemical composition of individual parts of the bark of the Betula pendula (Betulaceae) birch was determined at different tree heights. The part of the bark in the examined birch was found to be 14%, including 5.4% of the outer bark and 8.6% of the inner bark. The content of main groups of substances (cellulose, lignin, extractive and mineral substances, free acids, and carbohydrates) was evaluated in the outer and inner bark depending on the stem height.     

The ancient use ofPinus sylvestris L. (Scots pine) inner bark by Sami people in northern Sweden, related to cultural and ecological factors

A multidisciplinary study of use by Sami people ofPinus sylvestris L. (Scots pine) inner bark was performed in northern Sweden. We combined linguistic, historical and archaeological records with ecological data collected from field studies to investigate important cultural and ecological factors associated with previous use of bark. Our data from bark peeled trees at 313 sites were used to describe patterns in space and time in the land-scape. Sites with bark peeled trees were mainly found in the central and northern part of Lapland (65°00–68°14N). Large numbers of barked trees were found in undisturbed forests in national parks and reserves but few were found in forests under commercial management. The dendroecological analysis revealed a continuous use of inner bark from A.D. 1450 to 1890. Large sheets of bark were taken from trees in the spring, prepared and stored as a staple food resource. Inner bark was eaten fresh, dried or roasted. Smaller bark peelings were used for the wrapping of sinews. The cessation of bark use in the 19th century was driven by several factors, but the availability of other products that could replace traditional use of bark was specifically important. The previous common and varied use of bark, the great age of Sami terminology and a possible association with archaeological remains of potential great age indicate that peeled bark was used long before the historic period. Our study also focused on the ongoing loss of culturally-modified trees in forests outside protected areas.     

Bark thickness determines fire resistance of selected tree species from fire-prone tropical savanna in north Australia

We investigated the fire resistance conferred by bark of seven common tree species in north Australian tropical savannas. We estimated bark thermal conductance and examined the relative importance of bark thickness, density and moisture content for protecting the cambium from lethal fire temperatures. Eucalypt and non-eucalypt species were contrasted, including the fire-sensitive conifer Callitris intratropica. Cambial temperature responses to bark surface heating were measured using a modified wick-fire technique, which simulated a heat pulse comparable to surface fires of moderate intensity. Bark thickness was a better predictor of resistance to cambial injury from fires than either bark moisture or density, accounting for 68% of the deviance in maximum temperature of the cambium. The duration of heating required to kill the cambium of a tree (τ_c) was directly proportional to bark thickness squared. Although species did not differ significantly in their bark thermal conductance (k), the thinner barked eucalypts nevertheless achieved similar or only slightly lower levels of fire resistance than much thicker barked non-eucalypts. Bark thickness alone cannot account for the latter and we suggest that lower bark moisture content among the eucalypts also contributes to their apparent fire resistance. Unique eucalypt meristem anatomy and epicormic structures, combined with their bark traits, probably facilitate resprouting after fire and ensure the dominance of eucalypts in fire-prone savannas. This study emphasises the need to take into account both the thermal properties of bark and the mechanism of bud protection in characterising the resprouting ability of savanna trees.     

Ringing induces the accumulation of vegetative storage proteins in poplar bark

Poplar branches were ringed in late spring to determine whether the interruption of the phloem flow could induce the accumulation of vegetative storage proteins (VSPs) in the bark of adult trees. Eight days after ringing, an increased deposition of starch as well as a premature rise in the soluble-protein level occurred in the bark tissues located 1 cm above the ring. Changes in the SDS-PAGE pattern of bark proteins were characterized by the accumulation of three polypeptides (32, 36 and 38 kDa), which exhibited the same molecular weight as VSPs described in poplar bark during winter, cross-reacted to antibodies raised against a poplar VSP, and bound to several lectins in the same way as poplar bark VSPs. These results indicate that during the vegetative period, ringing induces the accumulation of VSPs in the bark of poplar.     

The protective role of bark against fire damage: a comparative study on selected introduced and indigenous tree species in the Western Cape,South Africa

The objective of this study was to compare the protective role of bark against fire for three selected indigenous and five exotic species in the Western Cape, South Africa. Bark thickness, compass direction, stem diameter at breast height, bark moisture content and relative height of the sample in the stem were tested for their effect on heat insulation capacity of bark. Trees were felled and heating experiments were conducted at 400 ºC on fresh billets with intact bark. Time to heat the cambium to lethal 60 ºC was determined. Statistical analysis based on correlation, multi-model inference and multiple regression revealed no significant influence of compass direction and diameter at breast height. Heat resistance was mainly determined by bark thickness, to a lesser degree by moisture content. In several species relative height at the stem modulated the bark thickness effect. Higher up the stem bark of the same thickness offered less protection against heat. Significant species-specific differences in heat resistance were apparent in the results, which could not be explained by bark thickness thus indicating further need for research in scrutinising these factors, which might help to explain the relative higher fire tolerance of certain species compared to others.     

Taxol content in the bark of Himalayan Yew in relation to tree age and sex

Taxol content in the bark of Taxus baccata trees growing in a homogenous (uniform) environment at Jageshwar, District Almora in Central Himalaya has been quantified. The average taxol concentration in the bark of sampled trees was 0.0558+/-0.008% (of dry wt.) and was about 64% higher for male plants (averaged across tree age) in comparison to female trees. Maximum taxol content was recorded in the bark samples collected from trees of >110 yrs age. ANOVA indicates a significant difference in the taxol content of bark from trees of different ages, however, differences were not significant between sexes. Taxol was quantified by HPLC using a standard curve prepared with authentic taxol; the identification of bark taxol was confirmed by UV and mass spectrometry. The total taxol content of the bark of Taxus trees across an age series was found to range between 0.064 to 8.032 g/tree, and a tree of about 100 yrs age can yield 5.74 kg dry bark.     

Otomi bark paper in Mexico: Commercialization of a pre-hispanic technology

The Otomi village of San Pablito in northern Puebla has preserved the tradition of making bark paper for over 400 yr, and today is the only papermaking center in all of Mexico. In the past 20 yr, bark paper has become highly commercialized and severalaspects of the Otomi papermaking process have changed. Unprecedented production levels have caused the total depletion of traditional sources of raw material. In response to this situation, the Otomi have been forced to change the types of bark that are utilized, the logistics of bark collection, and the treatment of the bark fiber prior to use. The majority of the paper currently produced in San Pablito is made from the bark ofTrema micrantha imported from the state of Veracruz. A plantation of this species is being established near San Pablito to reduce the Otomi dependence on outside sources of raw material.