Bark Moisture Content Research Articles

Vertical variation in swelling properties of Norway spruce bark depending on tree age and bark moisture content

AbstractIn forest ecosystems, interception of rainwater on foliar and woody surfaces and the subsequent partitioning into stemflow is largely controlled by physical and hydrological properties of bark. Few forest ecohydrology studies have explored the role of bark properties (e.g., thickness, density) on bark water storage capacity and stemflow production. Even fewer have explored how different phases of water (e.g., liquid, vapor) may affect bark through bark swelling properties across the stem and how the degree of swelling affects tradeoffs between bark water storage and stemflow generation. Thus, the objective of this study was to analyze changes in a bark swelling index (BSI) vertically along stems of Picea abies (Norway spruce) after exposure to both water vapor and liquid water, as a function of tree age and bark moisture content. We found that tree age influenced BSI and bark moisture content, wherein BSI was ∼ 6.5% lower in older trees (70 years) compared to younger trees (35 and 50 years), and average moisture content was 10.4–13.2% lower. BSI increased when bark was exposed to hygroscopic water vapor and reached maximum swelling after 1 day of water saturation. BSI also increased from the base of the tree to 20–30% of total tree height, beyond which BSI remained relatively stable across all age classes. Enhanced understanding of bark swelling mechanisms as a result of stem position, age, and moisture content and exposure provide stronger foundations for understanding canopy hydrologic partitioning and the fate of rainwater moving through forest canopies.

Stem moisture content prediction model for Larix olgensis based on beta regression.

To investigate the longitudinal variation patterns of sapwood, heartwood, bark and stem moisture content along the trunk of artificial Larix olgensis, we constructed mixed effect models of moisture content based on beta regression by combining the effects of sampling plot and sample trees. We used two sampling schemes to calibrate the model, without limiting the relative height (Scheme Ⅰ) and with a limiting height of less than 2 m (Scheme II). The results showed that sapwood and stem moisture content increased gradually along the trunk, heartwood moisture content decreased slightly and then increased along the trunk, and bark moisture content increased along the trunk and then levelled off before increasing. Relative height, height to crown base, stand area at breast height per hectare, age, and stand dominant height were main factors driving moisture content of L. olgensis. Scheme Ⅰ showed the stable prediction accuracy when randomly sampling moisture content measurements from 2-3 discs to calibrate the model, with the mean absolute percentage error (MAPE) of up to 7.2% for stem moisture content (randomly selected 2 discs), and the MAPE of up to 7.4%, 10.5% and 10.5% for sapwood, heartwood and bark moisture content (randomly selected 3 discs), respectively. Scheme Ⅱ was appropriate when sampling moisture content measurements from discs of 1.3 and 2 m height and the MAPE of sapwood, heartwood, bark and stem moisture content reached 7.8%, 11.0%, 10.4% and 7.1%, respectively. The prediction accuracies of all mixed effect beta regression models were better than the base model. The two-level mixed effect beta regression models, considering both plot effect and tree effect, would be suitable for predicting moisture content of each part of L. olgensis well.

Pine Bark Particle Separation Improves as Moisture Content Decreases at Time of Screening

Bark particle screening is a critical secondary processing stage when engineering bark-based horticultural substrates. There are several factors that can influence bark screening efficiency; however, the bark moisture content immediately before screening may have the largest impact. The objectives of this study were to determine the effect bark moisture content has on bark particle separation across two commonly used screen apertures and the subsequent static physical properties of the screened bark. The moisture contents examined herein ranged from 50%, 55%, 60%, 65%, and 70% and were gravimetrically determined. The screen apertures used were 6.3 mm and 9.5 mm. The results showed that moisture content has a considerable effect on both screening yield and the physical properties. Generally, as moisture content increased, bark yield (i.e., bark processed through the aperture) decreased. Moreover, as moisture content increased, the proportions of fine bark particles adhered to coarse bark increased, shifting the air-filled porosity: water-holding capacity of the substrate. In summation, the drier moisture content had the greatest (i.e., most equal) separation, regardless of screen aperture. Future research should identify the interaction between feed rate and moisture content.

Effect of bark properties on the cambium cell viability of Eucalyptus species under low radiative heat exposure

Tree bark reduces energy transfer from the bark surface towards the cambium during fires. To date, the heat reflection, absorption, and transmission properties of bark has been interpreted mainly in terms of elapsed time to increase temperature in the region of the cambium in response to external heating. To better understand bark protective properties, this study combines a known energy input and a cambium cell viability measure of heat impact, to develop an understanding in terms of characteristics that alter the heat capacity of bark. In this way three Eucalyptus species with different bark types are compared in terms of their heat absorption and transmission responses to heating.Stem sections from freshly felled trees of the three Eucalyptus species with contrasting bark types were exposed to a heat source that produced a constant 10 kWm−2 at the bark surface, that was applied until the cambium reached 60 °C. After stems cooled the viability of cambial cells from both the heated and non-heated sides of the stem were tested to determine the extent of heat impairment of cell function. Radiant heat between 3.5 and 13.6 MJ m−2 was required for the cambium to reach 60 °C, with more heat required for thicker and wetter bark, among the stem sections tested.The capacity of bark to protect the viability of cambium cells was strongly associated with bark moisture content, as well as with bark thickness. Bark with higher moisture content required more energy to heat the cambium to 60 °C, but once heated the moist bark retained the heat for longer than drier bark, resulting in a higher degree of cambial cell impairment. The critical specific heat capacity of bark varied between 3444 and 4657 J kg−1 °C−1 depending on the bark type. When exposed to a constant 10 kWm−2 heat source the critical exposure time for loss of cambium cell viability was between 20 and 40 min depending on bark type. This study provides a strong scientific basis to predict the tree impacts of heat released from fuels during planned fire and during wildfire over a range of fireground conditions – with applications to limit tree damage and increase survival.

Impact of Storage Conditions on Shear Strength of Beech (Fagus sylvatica L.) and Sessile Oak (Quercus petraea (Matt.) Liebl.)

The structure of a bark as a component of a living tree is completely different from wood. Different structures significantly influence the physical and mechanical properties of the bark. In the processing of logs, it is in most cases necessary to separate the bark from the wood. Problems can arise mainly in the pulp and paper industry. The research focused on the impact of storage conditions on shear strength, showing that the value of shear strength decreased remarkably due to the storage. A decrease in strength can mainly be explained by the changes in the moisture content of bark, remarkably affected by the surrounding environment (climate). The research showed that three months of storage seemed to be the most appropriate and effective period for removing the bark in the case of beech logs and that a storage time of up to five months was the best in the case of oak logs.

Influence of temperature and moisture content on bark/wood shear strength of black spruce and balsam fir logs

The effects of temperature (T) and moisture content (MC) on bark/wood shear strength (BWSS) were studied. Fifteen stems of black spruce (Picea mariana (Mill.) B.S.P.) and balsam fir (Abies balsamea (L.) Mill.) logs were selected and cross-cut into three 1.25 m log sections, corresponding to bottom (1.3 m), middle (3.8 m), and top (6.3 m) positions. BWSS was measured at five temperatures, ranging from 10 to − 30 °C, and at five levels of sapwood moisture contents (SMC), obtained by air-drying, from green state to near to the fiber saturation point (FSP). Bark and sapwood properties, MC and basic density (BD) were also determined. Temperature had a significant effect on BWSS for both species. This property was similar between 10 and 0 °C, and significantly increased as temperature decreased below 0 °C. However, the influence of temperature on BWSS depended on SMC and it varied between the two species. For black spruce, for each temperature between 0 and − 20 °C, BWSS showed similar values for SMC between 157 and 62%. At − 30 °C, BWSS showed a tendency to increase with SMC. For balsam fir, the BWSS increase due to the decrease in temperature was more important as the SMC increased. BWSS increased as SMC approached the FSP of wood for both species. Among the studied covariates, inner bark MC and inner and outer bark BDs significantly affected BWSS. Inner bark MC and SMC affected BWSS similarly. Multiple regressions were developed for prediction purposes, which explained 68 and 69% of BWSS variability for black spruce and balsam fir, respectively.

Evaluation of Changes in Tree Morphology Parameters, Biomass Yield, Chemical and Energy Properties at Three Spacings of Short Rotation Energy Plantations of Gmelina arborea in Costa Rica, from 1 to 2 Years of Age

Tree diameter and height, yield and chemical and energy properties increment throughout two different ages (1- and 2-year-old) were evaluated in Gmelina arborea trees growing in short rotation woody crops at three sites and three spacings (0.5 × 1.0, 1.0 × 1.0 and 2.0 × 1.0 m). The results showed great variation in parameters evaluated in relation to site, whereas for spacing the results were regular. Diameter, height and biomass yield increased in 2-year-old trees at all sites and spacings. The higher increments were observed in the 0.5 × 1.0 m spacing at sites 2 and 3. Biomass distribution in the different parts of 2-year-old trees showed increased biomass in the trunk and branches, and reduced biomass in leaves. The study of biomass properties showed increments in the specific gravity and reductions in the moisture content (MC) of trunk and branches, but MC of bark was regular. The increment in specific gravity and volatile contents was highest in the 0.5 × 1.0 m spacing, while MC of trunk, branches and bark, heat calorific value and ash content decreased. Carbon and nitrogen contents were irregular throughout spacing and sites. It was determined that at 2 years of age, Sites 1 and 2 presented normal behavior of Gmelina arborea in SRWC conditions, and in the Site 3 the changes produced improved the quality of biomass for energy purposes.

Solid Bioenergy Properties of Paulownia tomentosa Grown in Korea

Paulownia tomentosa is one of fast-growing wood species in Korea. In order to evaluate the solid bioenergy properties of Paulownia tree, this study examined the heating value, moisture content (MC), pH and proximate analysis of stem, branch, root, bark and leaf. The heating values of wood parts were slightly higher than those of bark and leaf, and that of branch was the highest among all the samples. The higher moisture content of bark and leaf referred to their lower heating value. Also, the pH of stem, branch and root was similar and lower than those of bark and leaf. The ash content of bark and leaf was much higher than that of wood parts, which is the one of the reasons for effect on the lower heating value and higher pH. While, the volatile matter content (VMC) of bark and leaf was lower than those of wood parts. The bark showed the highest fixed carbon content (FCC), while the FCC of stem was the lowest among all the samples. The obtained results are encouraging that the Paulownia tree could be totally utilized as alternative fuels for bioenergy production.

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.

Longleaf Pine Inner Bark and Outer Bark Thicknesses: Measurement and Relevance

Measurements of bark thickness generally ignore the fact that bark is comprised of both living inner bark (phloem) and essentially dead outer bark (rhytidome). Discerning between them has ramifications for the utility of bark as a byproduct of timber harvesting and its functionality on a living tree. Inner bark and outer bark thicknesses for longleaf pine (Pinus palustris Mill.) were investigated using disks collected from trees harvested on a 70-year-old plantation. Inner bark thickness was relatively constant up the bole of each tree whereas outer bark thickness rapidly declined from its thickest point at stump height; at relative heights above 20%, the decrease in outer bark thickness was more gradual. The proportion of inner bark, therefore, increased up the bole, from an average of 15% at stump height to above 40% toward the top of the tree. Since inner bark is a richer source of extractives than old outer bark, tree tops may be preferable in terms of bark abundance and quality as feedstock for extractive-based products. Reductions in the inner and outer bark thicknesses on disk drying, with averages of roughly 20 and 10%, respectively, differed when the data were pooled by cardinal direction. Thus, variability in bark thickness around the circumference of a standing tree may actually be a manifestation of differences in bark moisture content.

Which traits determine shifts in the abundance of tree species in a fire‐prone savanna?

Summary Fire is a process that shapes the structure and composition of vegetation in many regions. Species in these regions have presumably evolved life‐history strategies that allow success in fire‐prone environments. In this study, we examine the extent to which the ecological success of savanna trees is determined by traits that enhance the capacity to tolerate fire and/or traits indicative of an ecophysiological capacity for rapid growth. We define ecological success as the relative change in stem density over the course of a long‐term (circa 40 year) fire experiment conducted in the Kruger National Park, South Africa. We first examine the extent to which differences in the capacity of trees to tolerate fire can be explained by allometries describing bark traits and tree size. We then examine whether these differences in fire tolerance traits can explain observed shifts in abundance. We show that species differ in their topkill responses (probability of above‐ground mortality) and that these differences are explained in part by differences in bark moisture content and the allometry between height and diameter. Contrary to previous studies, we find no evidence that bark thickness is important in explaining susceptibility to topkill. Synthesis. Fire tolerance traits did explain a significant component of the variance in observed shifts in the abundance of tree species. However, traits related to the carbon economy of photosynthesis were also important.

Host Selection and Colonization Strategies With Evidence for a Female-Produced Oviposition Attractant in a Longhorn Beetle

In longhorn beetles and many other internally feeding insects, oviposition choice by females is critical to the survival of their offspring because their larvae are incapable of moving between hosts. Here we report on the complex host selection and colonization strategies of a longhorn beetle, Glenea cantor (F.) (Coleoptera: Cerambycidae), which is an important pest of kapok trees [Bombax ceiba L.=Gossampinus malabaricus (DC.) Merr.] in southern Asia. It attacks weakened trees, eventually killing them. The typical oviposition behavioral sequence in the laboratory includes the following: oviposition site search and recognition using antennae and palpi, oviposition slit preparation with mandibles, turning body direction 180°, egg deposition with the ovipositor, and oviposition wound covering with a jelly-like material from the ovipositor. Bark moisture content significantly increases from the upper to lower sections in kapok trees. In accordance with this variation female adults select the upper section of trees first for oviposition. As infestation continues and the host becomes more weakened, ovipositing females move further down the tree for oviposition. Consequently, the larvae kill the hosts from the top down. We show that the jelly-like material or eggs or both have an olfactory role in attracting females to oviposit nearby. Our findings are important in terms of increasing our understanding of host selection and colonization mechanisms of internally feeding insects, particularly cerambycids, and the development of environmentally friendly pest management measures.

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 (τc) 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.

Fire resistance of tree species explains historical gallery forest community composition

Fire, climatic variability, and grazing by large herbivores have historically limited woody vegetation in the tallgrass prairie region of North America to gallery forests in protected areas along rivers and streams. Fire, in particular, has been a strong selective pressure against woody vegetation. Consequently, we expect that dominant tree species in these forests have developed mechanisms for tolerating periodic surface fires. Susceptibility of trees to fire damage depends in part on key properties of bark which influence heat transfer to the vascular cambium, including thickness, density, and moisture content. An historical (1983) survey of Konza Prairie Biological Station in northeast Kansas, USA indicated that gallery forests were co-dominated by Quercus macrocarpa and Quercus muehlenbergii, while Celtis occidentalis occurred as an important sub-dominant species. Populus deltoides, Gleditsia triacanthos, and Juniperus virginiana were relatively uncommon. To test the hypothesis that historically dominant gallery forest tree species are more resistant to fire damage than uncommon species, fire was applied to the bark of 10 individuals of each of these six species under conditions mimicking surface fires (400 °C for 120 s). Maximum temperature at the vascular cambium, bark thickness, bark moisture content, and bark density were measured. Trees were considered fire-resistant if the vascular cambium temperature remained below the thermal cell death threshold, 60 °C, throughout the treatment. Using logistic regression, bark thickness was found to be a significant predictor of lethal cambium temperatures ( P = 0.002), while neither bark density nor moisture content were significantly related to lethal cambium temperature ( P = 0.279 and P = 0.131, respectively). Across species, a minimum bark thickness of approximately 8.6 mm was necessary to maintain the vascular cambium temperature below 60 °C. Trees that produce thick bark quickly in juvenile size classes ( P. deltoides, Q. macrocarpa, and Q. muehlenbergii) experienced lower temperatures at the vascular cambium than those which do not develop thick bark with increasing diameter ( C. occidentalis, G. triacanthos, and J. virginiana). Ranking these tree species by either the DBH or age needed to develop the minimum protective bark thickness largely agreed with ranking based on historical relative importance. As fire frequency and intensity decrease in remnant tallgrass prairie of North America as a result of habitat fragmentation, fire suppression, and changing land management, fire-sensitive species may increase in relative importance in gallery forests because of increased juvenile survival.

Insulation capability of the bark of trees with different fire adaptation

When exposed to a surface fire, the probability of a tree to survive widely varies, depending on its capability to protect the cambium from lethal temperatures above 60 °C. Thereby, the bark, the entirety of all tissues outside the cambium, serves as an insulation layer. In laboratory experiments, the heat production of a surface fire was simulated and the time span τ60 until the temperature of 60 °C is reached in the inner bark surface was measured. Thereby, τ60—as a measure of the fire resistance—was quantitatively determined for seven tree species. In addition, the influence of bark thickness and moisture content on bark heat insulation capacities was examined. Independent of the tree species and bark moisture content a power function correlation between bark thickness and τ60 was found. Our results also show that fire resistance increases with decreasing bark density. The seven tree species examined can be classified in two groups differing highly significant in their bark structure: (1) tree species with a faintly structured bark, which show a low fire resistance, and (2) tree species with an intensely structured bark, showing a high fire resistance. Furthermore a mathematical model simulating heat conduction was applied to describe the experimental results, and some ideas for a transfer into biomimetic materials are presented.

Phenological and chemical differences among hybrid poplar clones (Salicaceae) varying in resistance to Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae)

Hybrid poplars with Populus maximowiczii parentage have demonstrated antixenotic resistance against adult poplar-and-willow borers, Cryptorhynchus lapathi (L.) (Coleoptera: Curculionidae), in the summer, and antibiosis against C. lapathi larvae in the spring. We examined phenological and biochemical differences among hybrid poplars with and without P. maximowiczii parentage that are resistant and susceptible, respectively, to C. lapathi, to test the hypotheses that resistance was due to physical hydraulic forces, inadequate nutrition, or abundant secondary metabolites. The hybrids with P. maximowiczii parentage flushed earlier than susceptible hybrids, but no differences were found between hybrids with respect to sap flow or bark moisture content that could explain larval mortality in the spring. Similarly, constitutive levels of nutritive compounds (sitosterol, nitrogen, linoleic and linolenic acids, and carbohydrates) were lower or not different in the most susceptible hybrid TN 302-9. Thus, all hybrids appear to be nutritionally sound. TN 302-9 contained the highest constitutive levels of condensed tannins and catechin, but overall phenolic glycoside levels (salicin and salicortin) were similar among all hybrids, with the exception of one sampling date; however, this difference would not likely explain resistance. Neither induced or constitutive polyphenol oxidase (PPO) activity nor induced levels of secondary metabolites could explain resistance. Thus, we conclude hybrids that contain P. maximowiczii parentage have a novel mechanism for resistance.

Influence of the larval environment on performance and adult body size of the wood‐boring beetle Phoracantha semipunctata

AbstractLarge body size confers a reproductive advantage to adults of the wood‐boring beetle Phoracantha semipunctata (F.) (Cerambycidae: Cerambycinae: Phoracanthini). Larvae of this species feed subcortically in stressed and dying eucalypt trees and logs. We evaluated the influence of the larval environment on larval performance and adult body size by manipulating the post‐felling age of host logs (from freshly cut to 2‐weeks‐old) and the density of colonizing neonates (low density with minimal competition for resources vs. high density with intense competition). Adult beetles emerged in greater numbers from logs that had been subjected to the aging treatment which reduced bark moisture content and favored colonization by neonates. Survival was greatest in larger logs having lower densities of neonates, but was greatly diminished in all treatments by mortality during pupation. Development time varied from 2 months to more than a year and was shortest in smaller logs having high densities of larvae. The size of adult beetles emerging from a log was not influenced by larval density, but was positively correlated with the age of logs when the neonates colonized, and log size. These findings suggest that the optimal developmental conditions for P. semipunctata larvae, in terms of larval performance and adult body size, are available in large, aged host logs having low densities of larvae. Manipulation of the larval environment in this study resulted in a considerable variation in adult body size, but large individuals were relatively more common in the wild population that was the source of neonates for the experiment. Potential body size may have been constrained by our use of only one host species and a narrow range of log dimensions.

Evaluation of a hand-held burner for the control of woody weeds by flaming

A hand-held burner (Atarus Ranger) was evaluated as a method for controlling woody weeds by flaming in sensitive or riparian areas where traditional methods, such as chemical or mechanical control, have limited usefulness. The equipment was trialled on 3 North Queensland weed species: bellyache bush (Jatropha gossypiifolia), parkinsonia (Parkinsonia aculeata) and rubber vine (Cryptostegia grandiflora), at 5 different heat durations (0, 10, 30, 60 and 120 s) and on 3 plant size classes based on basal diameter (15–25, >25–50 and >50 mm).No significant difference in percentage mortality was recorded between a 10 s treatment and longer heat treatments for bellyache bush and parkinsonia plants, or between a 60 s treatment and longer heat treatments for rubber vine. A 10 s treatment killed 92% of the treated bellyache bush plants and 83% of the parkinsonia plants, while a 60 s treatment killed 76% of the treated rubber vine plants (values are the means of all size classes combined).Flaming was least effective on rubber vine, which had the thickest bark, but was highly effective on bellyache bush, which had the highest bark moisture content. Weeds with a low capacity for root suckering, thin bark, high bark moisture content and low bark density appear the best candidates for flaming. Flaming is an effective technique for the control of woody weeds with efficacy varying among species. Individual plants are targeted, and the technique is accepted by organic farming groups.

Pathogenetic and physiological mechanisms of poplar ice nucleation active bacterial canker

Using the methods introduced by Bier, X.H., Buchinock, Wang Jing-wen, Shi Riheet al., different varieties of poplar (poplar-MeixQing, Poplar-A100, Poplar-Xiaohe14 et al.) were inoculated with poplar ice nucleation active (INA) bacteria respectively in 1997–1999. The water content, relative turgidity, lignin content, phenylalanine ammonialyase (PAL) activity, electrolyte effusion rate, and inorganic element content of poplar bark were measured before and after inoculating. The results showed that after the poplar trees were inoculated with INA bacteria, the moisture content of bark decreased but relative turgidity increased, electrolyte effusion rate increased and had a peak at temperatures of −4 and 5°C, lignin content increased and positively correlated with poplars’ disease-resistance and the plenylalanine ammonialyase activity increased and also showed a significant positive correlation with poplars' disease-resistance. For the contents of inorganic element, Cu and Fe decreased but K and Zn increased obviously, while Mn, Ca and Mg changed little.

Fire resistance and bark properties of trees in a seasonally dry forest in eastern Bolivia

ABSTRACTAs forest fragmentation and intentional burning of grasslands increase, the frequency of fires penetrating the dry and subhumid tropical forests of Bolivia is also likely to increase. To expand our understanding of the role of fire in tropical dry forest, the physical and thermal properties of barks of tree species were studied to determine their relative resistances to cambial damage by fire. For 16 tree species found in the dry forest of the Lomerío region of eastern Bolivia, bark thickness, moisture content, and specific gravity were measured. Insulating capabilities of bark were measured by obtaining cambial and surface temperatures during experimental wick fires. Bark thickness on trees 5-100 cm dbh (diameter at 1.4 m) ranged from 2–51 mm and both thick- and thin-barked species were represented. For all species, bark thickness increased as stem diameter increased. Bark thickness explained more (63%) of the variation in peak cambial temperatures during fires than did bark moisture content (4%) or specific gravity (1%). A threshold bark thickness of 18 mm was associated with the ability to withstand lethal cambial temperatures during the experimental, low intensity fires. For 13 of the 16 species included in this study, trees ≤20 cm dbh have bark thickness below the threshold 18 mm and, therefore, are likely to experience cambial injury from low intensity fires. Our results suggest that the forest presently characteristic of the Lomerío region did not develop with frequent fires and that species composition is likely to be substantially affected by an increase in fire frequency.