Tree Growth Rates Research Articles

Growth and flowering of young cocoa plants is promoted by organic and nitrate-based fertiliser amendments

SummaryCocoa (Theobroma cacao) farmers in Sulawesi, Indonesia typically use subsidised, ammonium-based rice fertilisers that in combination with poor agricultural practices have resulted in soil acidification, loss of organic matter, aluminium toxicity and lower soil fertility. As a result, these soils are only marginally appropriate for replanting cocoa to boost production. A field experiment was performed to test alternative soil amendments for successful replanting of cocoa on these deficient soils. In a trial with a randomised block design, 6-month old seedlings, top-grafted with the local MCC02 clone, were planted under light Gliricidia sepium shade and after 3 months treated quarterly with two options of mineral fertilisers: either a customised fertiliser, consisting of Nitrabor (a combination of calcium nitrate and boron), dolomite, rock phosphate and KCl or a NPK/urea mix used by farmers, each supplied with or without ‘micronutrient’ rock salt, organic fertiliser and beneficial microorganisms or their culture medium, a mixture of chitin and amino acids (a total of 20 treatments). Over a 4-year period, the marginal mean rates of stem diameter increment and flowering score were higher in customised fertiliser than NPK/urea treatments. The average growth rate was highest in the first year and was increased by supplying organic fertiliser. A significant correlation (r = 0.22, p < 0.05) occurred between growth and available P, but concentrations of available P were higher in the NPK/urea plots, which also had lower mean growth rates. Combined supply of organic fertiliser and microbes increased available P, as well as growth rates, in both the customised and NPK/urea treatments. In contrast, NPK/urea-treated plots without these amendments demonstrated very low growth rates. The customised formulation was more effective with or without added organic fertiliser or inoculated microbes. Micronutrient supply stimulated flowering. Growth rates in trees supplied with NPK/urea were also promoted by micronutrients. Leaf flush production occurred in regular cycles and was unaffected by the nutrient amendments. After 3 years, the customised and organic fertiliser application increased soil pH and exchangeable Ca and Mg concentrations, although they remained below recommended levels for cocoa production. These treatments had little impact on soil C content (about 1.3%) which was also deficient. Exchangeable Al and total Zn concentrations were higher in soils amended with NPK/urea. The results of the trial provide evidence that utilisation of organic fertiliser in combination with customised nitrate-based formulations improves cocoa establishment, growth and soil properties and should be recommended as a replacement for the NPK/urea fertilisers traditionally used by farmers.

Determinants of fire intensity in working landscapes of an African savanna

BackgroundAn often cited rule of savanna fire ecology is that early dry-season fires burn less intensely than late dry-season ones; however, few studies base their experimental design on the practices of fire managers in working landscapes. The objective of this research was to study the factors influencing fireline intensity, combustion, and patchiness for a West African savanna under common vegetation and land management practices. We conducted 97 experimental fires by selecting burn plots and seasonal timing (early, n = 33; middle, n = 44; or late, n = 20) based on local practices in a typical working landscape. We collected data for biomass consumed, grass type, scorch height, speed of fire front, visual efficiency (patchiness), fire type, and ambient air conditions. We used multiple regression analysis to determine the key factors affecting fire intensity.ResultsMean intensity was lowest for the middle season fires and highest for the late season fires. Minimum fire intensity increased over the fire season except for a sharp drop mid season, while maximum intensity progressively decreased. Seasonal values were highly variable. Fire intensity was moderately positively correlated with scorch height and more modestly correlated with visual efficiency, but only marginally correlated with combustion completeness. Average combustion completeness increased weakly as the dry season progressed. Intensity of back-fires was determined primarily by seasonal timing and the associated ambient humidity and wind and, to a lesser extent, grass characteristics. Head-fire intensity was only feebly responsive to wind speed.ConclusionsWe found that, at the peak time of West African savanna burning, the intensity of fires decreased. Fire behaviors in working West African landscapes were more dependent on fire type and wind than seasonality. Finally, we found that fire intensity values were lower than those reported elsewhere due to the more representative conditions of the fire setting (under lower afternoon winds) and fuel loads (lower biomass on working landscapes). Future research should focus on the ecological impacts of fires set under such conditions on growth and death rates of savanna trees.

The Effect of a Pine Looper Moth Outbreak on the Radial Growth Rate of Pine

This study compares the 1945–2015 time series of the radial growth rate of pine Pinus sylvestris L. damaged by the 1974–1978 outbreak of the pine looper moth Bupalus piniarius L. and those of the undisturbed Krasnoturansk pine forest. It is proposed to employ regulatory characteristics of time series, including the order of autoregression (lag value n) and standard deviation of the amplitude of time series oscillation s (number of the first differences of radial growth s), to estimate differences between radial growth rates of trees in damaged and intact stands. These indicators allow for a quantitative assessment of the lag of the processes regulating the radial growth rate. Only the first differences of the series of radial growth rate are assessed, inasmuch as the regulatory characteristics can be correctly calculated only for the stationery time series. Trees exposed to insect outbreak either have no lag in the dynamics of the first differences of the series in the radial growth rate or they have high values of autoregression order n. At the same time, the oscillations of the current radial growth rate of damaged trees in relation to the age gradient are significantly larger than in undisturbed trees. We estimate the speed of the growth-rate recovery in damaged trees as a function of regulatory characteristics of time series of the radial growth rate before the damage. These data could be used to assess the pest hazard in the stands and recovery rates of forests damaged by insect outbreaks.

Improving predictions of tropical tree survival and growth by incorporating measurements of whole leaf allocation

Abstract Individual‐level demographic outcomes should be predictable upon the basis of traits. However, linking traits to tree performance has proven challenging likely due to a failure to consider physiological traits (i.e. hard‐traits) and the failure to integrate organ‐level and whole plant‐level trait information. Here, we modelled the survival rate and relative growth rate of trees while considering crown allocation, hard‐traits and local‐scale biotic interactions, and compared these models to more traditional trait‐based models of tree performance. We found that an integrative trait, total tree‐level photosynthetic mass (estimated by multiplying specific leaf area and crown area) results in superior models of tree survival and growth. These models had a lower AIC than those including the effect of initial tree size or any other combination of the traits considered. Survival rates were positively related to higher values of crown area and photosynthetic mass, while relative growth rates were negatively related to the photosynthetic mass. Relative growth rates were negatively related to a neighbourhood crowding index. Furthermore, none of the hard‐traits used in this study provided an improvement in tree performance models. Synthesis. Overall, our results highlight that models of tree performance can be greatly improved by including crown area information to generate a better understanding of plant responses to their environment. Additionally, the role of the hard‐traits in improving models of tree performance is likely dependent upon the level of stress (e.g. drought stress), micro‐environmental conditions or short‐term climatic variations that a particular forest experiences.

Stable Allometric Trajectories in Picea abies (L.) Karst. Trees along an Elevational Gradient

The effect of temperature on tree phenology and growth has gained particular attention in relation to climate change. While a number of reports indicate that warming can extend the length of the growing season and enhance tree growth rates, it is still debated whether temperature also affects biomass partitioning. Addressing the question of whether trees grown at different elevations invest similarly in various organs, we established four sites along an elevational gradient (320 to 595 m a.s.l.) in managed Norway spruce (Picea abies (L.) Karts) stands regenerating after clearcuts in central Norway. There, differences in temperature, bud break, tree growth, and allometric scaling were measured in small spruce trees (up to 3 m height). The results showed that bud break and shoot growth are affected by temperature, as lower sites completed the bud break process 5 days earlier than the higher sites did. There was some evidence indicating that the summer drought of 2018 affected tree growth during the season, and the implications of this are discussed. The allometric scaling coefficients did not change for the crown volume (slope value range 2.66–2.84), crown radius (0.77–0.89), and tree diameter (0.89–0.96) against tree height. A slight difference was found in the scaling coefficients of crown length against tree height (slope value range 1.04–1.12), but this did not affect the general scaling of the crown volume with tree height. Our results showed that different local environmental conditions affect both the growth rate and phenology in Norway spruce trees but, on the contrary, that the biomass partitioning among different parts of the tree remains essentially unchanged. This demonstrates that the allometric approach is an important tool for unraveling true vs. apparent plant plasticity, which in turn is an essential awareness for predicting plant responses to environmental changes.

Breakdown failure analysis of 220 kV cable joint with large expanding rate under closing overvoltage

The silicone rubber is subjected to either the mechanical stress or the pulse voltage, making it is easier for initiation and development of electrical tree, which is the main reason for breakdown failure of cable joint. Studying the effect of electrical tree for breakdown failure of cable joint is the valid way to ensure the safety and stability of the cable system. In this paper, a breakdown failure case of 220 kV integral prefabricated silicone rubber cable joint with large expanding rate under closing overvoltage is discussed. Through dissection, it was found that there were electric trees inside the cable joint produced by factory C. Based on the failure characteristics, the mechanical stress model of the cable joint and the closing overvoltage model of the system were established to analyze the influencing factors of electric trees. Furthermore, some sample tests were carried out to discuss the relationship between material performance and electrical tree, including carbon black test, gel content test, thermogravimetric test, tensile test and volume resistivity. The results showed that the large circumferential stress would destroy the physical crosslinking of silicone rubber, leading to a decrease in tensile strength and volume resistivity. This was the main factor affecting the growth of electrical trees. Meanwhile the overvoltage and the poor material characteristics of cable joint would accelerate the growth rate of electrical trees. Eventually the breakdown failure of cable joint occurred when the electric trees running through both polarities. The analytical method and conclusions proposed in this paper can provide suggestions and guidance for the analysis of similar breakdown accidents in the future.

Plant traits controlling growth change in response to a drier climate

Plant traits are increasingly being used to improve prediction of plant function, including plant demography. However, the capability of plant traits to predict demographic rates remains uncertain, particularly in the context of trees experiencing a changing climate. Here we present data combining 17 plant traits associated with plant structure, metabolism and hydraulic status, with measurements of long-term mean, maximum and relative growth rates for 176 trees from the world's longest running tropical forest drought experiment. We demonstrate that plant traits can predict mean annual tree growth rates with moderate explanatory power. However, only combinations of traits associated more directly with plant functional processes, rather than more commonly employed traits like wood density or leaf mass per area, yield the power to predict growth. Critically, we observe a shift from growth being controlled by traits related to carbon cycling (assimilation and respiration) in well-watered trees, to traits relating to plant hydraulic stress in drought-stressed trees. We also demonstrate that even with a very comprehensive set of plant traits and growth data on large numbers of tropical trees, considerable uncertainty remains in directly interpreting the mechanisms through which traits influence performance in tropical forests.

Partner turnover and changes in ectomycorrhizal fungal communities during the early life stages of European beech (Fagus sylvatica L.).

The first life stages of a tree are subject to strong environmental stresses and competition, limiting their chances of survival. Establishing a mutualistic relationship with mycorrhizal fungi during early life stages may increase growth and survival rates of trees, but how mycorrhizal communities assemble during these stages remains unclear. Here, we studied variation in the ectomycorrhizal (EcM) fungal communities in the soil and roots of Fagus sylvatica seedlings and saplings. Fungal DNA was extracted from the soil and seedling and sapling roots collected in 156 plots across the beech-dominated Sonian forest (Belgium) and community composition was determined through metabarcoding. EcM fungal community composition significantly differed between soil, seedlings and saplings. Russula, Amanita and Inocybe were most abundant in soil, while Lactarius and Scleroderma were more abundant in seedling and sapling roots and Xerocomellus and Laccaria were most abundant in sapling roots. Our results provide evidence of partner turnover in EcM fungal community composition with increasing age in the early life stages of F. sylvatica.

Characteristics of Bird Nestling Trees in the Padang State University, West Air Tawar, West Sumatera

The purpose of this research is to describe the characteristic of the tree as birds nesting at State University of Padang , West Air Tawar, West Sumatra. This research conducted on March 2019. Data collection was using survey method. The results showed that found 14 species of tree is using by birds to nesting. The characteristic of tree is preferable by birds to using for nesting are tree and pole growth rate, monopodium and simpodium branching type, with round, oval and fountain canopy type, model leeuwenberg, attims and corner architecture model.

Size dependent associations between tree diameter growth rates and functional traits in an Asian tropical seasonal rainforest.

Many studies focus on the relationships between plant functional traits and tree growth performances. However, little is known about the ontogenetic shifts of the relationships between functional traits and tree growth. This study examined associations between stem and leaf functional traits and growth rates and their ontogenetic shifts across 20 tropical tree species in a tropical seasonal rainforest in Xishuangbanna, south-west China. For each species, physiological active branches of individual trees belonged to three size classes (i.e. small, diameter at breast height (DBH) 5-10 cm; middle, DBH 10-20 cm; big, DBH >20 cm) were sampled respectively. We measured 18 morphological and structural traits, which characterised plant hydraulic properties or leaf economic spectrum. Associations between diameter growth rates and functional traits were analysed across three size classes. Our results revealed that diameter growth rates of big-sized trees were mainly related to traits related to plant hydraulic efficiency (i.e. theoretical hydraulic conductivity (Ktheo) and leaf vein density (Dvein)), which suggests that the growth of large trees is limited mainly by their xylem water transport capacity. For middle-sized trees, growth rates were significantly related to traits representing leaf economic spectrum (i.e. specific leaf area (SLA), individual leaf mass (ILM), palisade thickness (PT) and spongy thickness (SP)). Diameter growth rates of small-sized trees were not correlated with hydraulic or leaf economic traits. Thus, the associations between tree growth rates and functional traits are size dependent. Our results suggest ontogenetic shift of functional traits which could potential contribute to different growth response to climate change.

Temperature controls growth of Pinus taiwanensis along an elevational gradient

Alpine treelines are thought to be controlled by low temperature, which affects tree physiology and limits growth. Irrespective of carbon and nutrient limitations are physiological mechanisms affecting the formation of alpine treelines still needs to be defined. We measured the rates of tree growth (basal area increment, BAI), nutrient concentrations in leaves and roots, foliar concentration of nonstructural carbohydrates (NSCs), and gas exchange in Pinus taiwanensis at five elevations (1200, 1400, 1600, 1800, and 2000 m) in the Wuyi Mountains, China. Leaves and roots were sampled twice (summer and winter). The soil nitrogen (N) and phosphorus (P) concentrations and BAI were measured during the summer. We analyzed the foliar traits in summer and winter. The N:P ratio was also analyzed. BAI decreased significantly as elevation increased, accompanied by increases in foliar NSC, N, and P concentrations in both summer and winter. The root P concentration increased with elevation in summer, but the foliar N:P ratio and root N and P concentrations were not affected by elevation in winter. Foliar photosynthesis and respiration did not change in winter, but increased in summer as elevation increased. These results suggest that C and nutrients may not be limiting resources in P. taiwanensis at this alpine treeline site, which instead may be controlled by temperature. P. taiwanensis at alpine treelines accumulates C and nutrient to increase its rates of biochemical reactions at low temperatures.

A century of pollution in the boreal forest

Forest Decline The environs of Norilsk, in northern Siberia, are among the most heavily polluted in the world as a result of the effects of decades of heavy metal production and sulfur dioxide emissions. Kirdyanov et al. reveal the extent of pollutant effects on the boreal forests of the region through a study of tree-ring patterns in larch and spruce from sites along a 200-kilometer transect on either side of Norilsk. Their results document tree growth rates before the onset of industrialization in the region in the 1930s and show the trajectory of subsequent decline in growth rates that eventually led to dieback of entire forest stands. These effects fit into a wider picture of increasing pollution from multiple sources across the wider boreal and arctic region. Ecol. Lett. 10.1111/ele.13611 (2020).

Differential determinants of growth rates in subtropical evergreen and deciduous juvenile trees: carbon gain, hydraulics and nutrient-use efficiencies.

Growth rate varies across plant species and represents an important ecological strategy for competition, resource-use and fitness. However, empirical studies often show a low predictability of functional traits to tree growth. We measured stem diameter and height growth rates (DGRs and HGRs) of 96 juvenile trees (2-5m tall) of eight evergreen and eight deciduous broadleaf tree species over three consecutive years in a subtropical forest in south-western China. We examined the relationships between tree growth rates and 20 leaf/stem traits that are associated with carbon gain, stem hydraulics and nutrient-use efficiency, as well as the difference between evergreen and deciduous trees. We found that cross-species variations of stem DGR/HGR can be predicted by leaf photosynthetic capacity, leaf mass per area, xylem-theoretical-specific hydraulic conductivity, wood density (WD) and photosynthetic-nutrient-use efficiencies. Higher leaf carbon assimilation and lower leaf/stem constructing costs facilitate deciduous species to be more resource acquisitive and consequently faster growth within a relatively shorter growing season, whereas evergreen species exhibit more conservative strategies and thus slower growth. Furthermore, stem growth rates of evergreen species showed were more dependence on leaf carbon gains, whereas stem hydraulic efficiency was more important for deciduous tree growth. Our results suggest that physiological traits (photosynthesis, hydraulics and nutrient-use efficiency) can predict tree diameter and height growth of subtropical tree species. The differential resource acquisition and use strategies and their associations with tree growth between evergreen and deciduous trees provide insights into explaining the coexistence of evergreen and deciduous tree species in subtropical forests.

Reduced tree density and basal area in Andean forests are associated with bamboo dominance

Forest structure and composition play an essential role in determining the carbon storage capacity of tropical forests. Andean forests, with great potential for carbon accumulation, include large expanses of high-density woody bamboo communities. Woody bamboos can potentially alter forest structure, composition and dynamics and thus can affect carbon storage capacity; however, they are commonly excluded from forest monitoring and modelling. With the aim of documenting patterns of bamboo abundance and disentangling its association with forest structure, we carried out a bamboo census in seven 1-ha long-term forest monitoring plots situated across a large elevation gradient (1000–3600 m a.s.l.) in the Peruvian Andes. We determined that bamboo is a dominant plant group in the study area. In every plot, bamboos were the most common genera in terms of number of stems, and in two of the plots bamboo species were among those with the greatest basal area. We used a combination of Generalized linear mixed models (GLMM) and structural equation modelling (SEM) to hypothesize a causal framework and determine the direction and size of the effects of bamboo abundance (basal area) on number of individual trees, total tree basal area, mean tree basal area, mean tree growth rate and tree mortality rate. We found an overall negative association between bamboo abundance and total tree basal area driven mainly by reduced tree density (directly and indirectly mediated by an increase in tree mortality). However, the decrease in tree density and the increase in tree mortality are also associated with a small increase in tree diameter (mean tree basal area). Overall, the negative association between bamboo abundance and tree basal area suggests a lower biomass accumulation and thus a lower carbon storage capacity of trees in Andean forests where bamboo is dominant. Our results, which show the importance of bamboo in determining forest function, highlight the need for including bamboo in monitoring efforts and modeling studies.

A Unifying Concept for Growth Trends of Trees and Forests – The “Potential Natural Forest”

Changes in the environment will alter the growth rate of trees and forests. Different disciplines assess such growth rates differently, for example with, tree-ring width data, forest inventories or with carbon-flux data from eddy covariance towers. Such data is used to quantify forests biomass increment, forest's carbon sequestration or to reconstruct environmental variables before instrumental records. However, raw measurement data is typically not considered to be representative for the average growth rate of trees or forests. Depending on the research question, the effects of certain environmental variables or effects of tree and forest structure have to be removed first. It can be challenging to define and quantify a growth trend that can answer a specific research question because trees and forests grow and respond to environmental change in multiple ways simultaneously, for example with altered radial increment, height growth and stand density. Further challenges pose time-lagged feedback loops, for example between height and radial increment or between stand density and radial increment. Generally, different environments will lead to different tree and forest structures, but because of tree’s longevity this change will take decades or even centuries. Consequently, there can be an offset between the present forest structure and what we term the potential natural forest (PNF): Similar to the potential natural vegetation (PNV), the potential natural forest represents that forest that would develop under the current environmental conditions in the absence of human intervention. Because growth rates are affected by the tree and forest structure, growth-trend estimates will differ between the present and the potential forest. Consequently, if the legacy effects of the past are not of interest, the potential natural forest is the theoretical baseline to correct and estimate growth trends.

Modeling Self-Thinning Patterns in Loblolly Pine with Provenance and Family Effects

Abstract Size-density trajectories and self-thinning boundary lines were modeled for two diverse provenances of Pinus taeda L. and five open-pollinated families within each provenance. The data used come from a single site with replicated 64-tree block plots measured through age 25 years. The effects of provenance and family were tested using linear and nonlinear mixed-effects self-thinning models. The drought-hardy Lost Pines of Texas provenance displayed a greater predicted carrying capacity (almost 200 more trees per hectare at reference diameter 25.4 cm) and had a more abrupt approach to the self-thinning line than the widely planted Atlantic Coastal Plain provenance. However, the growth rate of the Lost Pines of Texas provenance was considerably slower and stem form was unacceptable for timber production. Families from the Atlantic Coastal Plain differed in their maximum stand density index predictions (from 1,118 to 1,282 trees per hectare at the reference diameter), suggesting there is an opportunity for artificial selection to change maximum stand density index in this breeding population of loblolly pine. A novel method for predicting the self-thinning boundary line using random effects inherent to the experimental design is presented and recommended for repeated measures data. Experimental design considerations for evaluating genetic differences in self-thinning are discussed. Study Implications Genetic improvement of growth rate in forest trees has resulted in large gains in plantation productivity, but the effect on carrying capacity has not been addressed. This study indicated that artificial selection on tolerance to competition in the widely planted Atlantic Coastal Plain provenance of loblolly pine can potentially increase harvest yield without sacrificing growth rate. The drought-hardy Lost Pines of Texas provenance displayed greater carrying capacity but had poor stem form and slow growth. The Lost Pines provenance may be attractive for aboveground carbon sequestration, since it sustained substantially more biomass because of greater maximum stand density and denser wood.

Variation in Tree Growth along Soil Formation and Microtopographic Gradients in Riparian Forests

Policy makers are interested in managing forests to store carbon. Optimizing this strategy requires understanding how carbon storage varies across environmental gradients. We explored variation in tree growth rate, tree longevity, and surface soil organic matter across 135 Connecticut River riparian forest plots. Tree growth rate did not vary significantly with climate but rather increased with sediment accretion rate, soil pH and decreased with plot elevation, where elevation was measured relative to the stage of the 2-year flood. By contrast, surface soil organic matter was negatively related to pH and tree growth rate. Tree species longevities were greater at higher elevations with coarser soils. The faster growth rates at lower elevations allow for restoring forest structure rapidly, whereas flood intolerant but longer-lived tree species allow more durable carbon sequestration at higher elevations. The close associations of growth rate, sediment accretion, and pH suggest that riverine nutrient inputs are important to maintaining the exceptionally high productivity of floodplains. Environmental assessments of river dams should consider impacts of intercepting sediments and reducing flooding on downstream floodplain fertility and productivity. Restoration of riparian locations with high deposition of sediments and associated nutrients may be an opportunity to maximize both nutrient and carbon sequestration.

Light and nutrient limitations for tree growth on young versus old soils in a Bornean tropical montane forest

We examined forest and tree responses to decreasing nutrient availability with soil aging in a species-rich tropical montane rain forest on Mount Kinabalu, Borneo. Community composition and structure and tree growth rates were compared between two 1 ha plots on nutrient-rich young soil versus nutrient-deficient old soil. Myrtaceae and Fagaceae dominated both plots. With soil aging, the dominance of Lauraceae, stem density, basal area and aboveground biomass decreased, and the forest understory became brighter. Some dominant taxa on the old soil (Podocarpaceae and the genus Tristaniopsis in Myrtaceae) were virtually absent on the young soil; this was attributed to light limitation in the understory. Growth rates of understory trees were lower on the young soil, whereas those of canopy trees were lower on the old soil. This suggested that the growth of understory trees was limited by light on the young soil, whereas that of canopy trees was limited by nutrients on the old soil. Of the eight species that were abundant in both plots, the dominance of five species was considerably lower on the old soil, four of which also exhibited decreased maximum sizes and lower growth rates. The remaining three species showed similar dominance across plots without a decline in growth rates, although they exhibited decreased maximum sizes on the old soil. These analyses demonstrated divergent responses of species to the soil-age gradient. We suggest that the differential responses of species to decreasing nutrient availability with a concomitant increase in understory light levels explain floristic turnover with soil aging.

Neighborhood context mediates probability of host tree mortality in a severe bark beetle outbreak

AbstractUnderstanding drivers of disturbances across scales is critical as environmental constraints change in a warming climate. Outbreaks of native bark beetles (Curculionidae: Scolytinae) are key natural disturbances that shape the structure and function of conifer forests across the northern hemisphere. While drivers of bark beetle outbreaks have been studied extensively at spatial scales ranging from stands to continents, within‐stand processes governing individual tree mortality in an outbreak are less well understood. Here, we use a spatially explicit long‐term monitoring dataset of a lodgepole pine (Pinus contorta var. latifolia) forest (>9000 individually mapped trees in three 2‐ha plots) impacted by a severe mountain pine beetle (Dendroctonus ponderosae) outbreak to explore interactions among fine scale drivers of beetle‐caused tree mortality. Using a Bayesian spatial modeling approach, we evaluated how tree scale and tree neighborhood scale characteristics interact with tree size to mediate host tree susceptibility to mountain pine beetle outbreak in the Southern Rocky Mountains (USA). We found evidence that both tree growth rate preceding the outbreak and neighborhood structure (within a 10 meter radius of the host tree) mediate the effect of tree size, and that the direction and magnitude of these mediating effects vary with tree size. Tree scale mortality probability increased with pre‐outbreak growth rate for small to medium sized host trees (~10–25 cm diameter), but that same effect was not detected for large trees. Conversely, tree scale mortality probability increased with greater neighborhood density, with the most pronounced effects for medium to large sized host trees (~15–30 cm diameter). Within‐stand topographic variability was not an important predictor of mortality probability; among stands, however, the stand in the driest topographic position experienced the greatest overall mortality. By explicitly considering how within‐stand heterogeneity mediates individual tree scale susceptibility to bark beetle outbreak, our findings bridge an important gap in understanding multi‐scale drivers of disturbance dynamics.

Timber harvest and frequent prescribed burning interact to affect the demography of Eucalypt species

Ecosystem management can negatively affect the demography of plant communities through the introduction of novel disturbance regimes. Prescribed burning and timber harvesting are two common and widely applied management strategies across forest ecosystems. Despite this, little is known about the long-term effects that these interacting disturbances have on forest demography. This study examined the effect of timber harvesting and frequent prescribed burning on the mortality, growth and regeneration of trees in a temperate eucalypt forest of south-eastern Australia. The study took place at a long-term experimental site, where experimental coupes were subjected to a one-off selective harvesting treatment (harvested, not harvested), followed by regimes of experimental burning (no fire, ~4 year burn intervals or ~2 year burn intervals) over a 22 year period. Tree communities were surveyed at permanent monitoring sites prior to the application of experimental treatments (1985 – 1989), and resurveyed post treatment (2016) to assess mortality, growth rates and ingrowth of trees >10 cm diameter at breast height. Harvesting directly removed ~40% of trees and indirectly increased the mortality of retained trees through damage (e.g. crown and bole breakage) caused during the harvesting operation. The likelihood of harvesting damage was greater for small trees and increased with harvesting intensity (i.e. the amount of timber removed). Frequent burning increased the likelihood of tree mortality on harvested sites, with large, old trees being particularly vulnerable. Growth rate and ingrowth of trees was elevated at harvested sites, increasing almost linearly with harvesting intensity, which suggests that competitive release had occurred. Fire frequency had no effect on growth rates or ingrowth of trees. This study highlights that frequent prescribed burning and selective timber harvesting can have additive effects on the loss of large trees, reducing the availability of these keystone habitat structures in intensively managed forest ecosystems. Although the elevated rates of growth and ingrowth may hasten the replacement of lost large trees, recovery will require long time frames.