Annual Diameter Growth Research Articles

Changing role of water table and weather conditions in diameter growth of Scots pine on drained peatlands

We investigated the impact of water table (WT), monthly temperature, and precipitation of current and previous growing seasons on annual diameter growth of Scots pine in boreal drained peatlands. The data were collected from six sites across Finland. WT was monitored during 5-8 growing seasons depending on site during 2007-2014. The sites contained altogether 19 sample plots, where diameter growth from 339 trees was measured, resulting in 1,599 growth observations. Tree-level diameter growth was analysed using mixed linear models, including variables describing tree size, competition, and environment. The higher precipitation in June of the previous year and May of the current year increased diameter growth, whereas the higher temperature in July of the current year and the deeper WT in August of the previous year decreased growth. The results suggest that Scots pine grows better at shallow than deep WT in drained peatlands. This contradicts earlier findings that a deep WT is needed to support tree growth in drained peatlands. We suggest that the development of a mor layer on the peat is changing nutrient cycling and hydrology. The results encourage the avoidance of intensive drainage in forested peatlands, which may also diminish the adverse environmental impacts of peatland forestry.

Growth rate of Clethra mexicana, Juglans pyriformis, Liquidambar styraciflua, and Trema micrantha in secondary cloud forest

Secondary cloud forests (SCF) play a valuable role in regulating the hydrological cycle, providing habitat for biodiversity and resources for local livelihoods in cloud forest landscapes. At present, there is limited information on the potential of SCF for timber production. In this study, we determined the growth rates of 4 common SCF tree species, relative to tree size, crown exposure to light, and basal area of neighbouring trees. We used dendrometric bands to measure annual diameter growth in 375 individuals for 2 years, in SCF in Veracruz, Mexico. Average diameter growth rates were: Clethra mexicana = 0.53 ± 0.04 cm y-1, Juglans pyriformis = 0.41 ± 0.03 cm y-1, Liquidambar styraciflua = 0.41 ± 0.03 cm y-1, and Trema micrantha = 0.22 ± 0.04 cm y-1. Tree size was a significant predictor of diameter growth rate; diameter growth rate increased with tree size in all 4 species. Trees with crown laterally illuminated showed higher growth than trees without direct illumination in L. styraciflua. The basal area of neighbouring trees did not affect diameter growth in any species. The results indicate that young trees have high growth potential.

Limited effects of biochar application and periodic irrigation on jack pine (Pinus banksiana) seedling growth in northern Minnesota, USA

We tested the effect of biochar application on growth of planted jack pine on a sandy soil in northern Minnesota. Biochar was applied in combination with compost and with or without manual irrigation in a factorial design to isolate possible effects associated with nutrient or water availability. There were no differences among treatments in seedling annual diameter or height growth after 4 years. Watering increased mean needle mass, indicating the treatment was somewhat effective at increasing water availability and seedling performance. Watering increased foliage Mg and K concentrations and content, possibly indicating that these elements are limiting to jack pine growth on sandy soils. Biochar-only application decreased foliage Ca concentration relative to controls, likely due to increased nutrient immobilization when biochar is applied without a nutrient source. These findings and others from the region highlight that biochar does not increase planted jack pine seedling survival or growth on sandy soils.

Tree species growth response to climate in mixtures of Quercus robur/Quercus petraea and Pinus sylvestris across Europe - a dynamic, sensitive equilibrium

Quercus robur/Quercus petraea and Pinus sylvestris are widely distributed and economically important tree species in Europe co-occurring on mesotrophic, xeric and mesic sites. Increasing dry conditions may reduce their growth, but growth reductions may be modified by mixture, competition and site conditions. The annual diameter growth in monospecific and mixed stands along an ecological gradient with mean annual temperatures ranging from 5.5 °C to 11.5 °C was investigated in this study. On 36 triplets (108 plots), trees were cored and the year-ring series were cross-dated, resulting in year-ring series of 785 and 804 trees for Q. spp. and P. sylvestris, respectively. A generalized additive model with a logarithmic link was fit to the data with random effects for the intercept at the triplet, year and tree level and a random slope for the covariate age for each tree; the Tweedie-distribution was used. The final model explained 87 % of the total variation in diameter increment for both tree species. Significant covariates were age, climate variables (long-term mean, monthly), local competition variables, relative dbh, mixture, stand structure and interactions thereof. Tree growth declined with age and local density and increased with social position. It was positively influenced by mixture and structural diversity (Gini coefficient); mixture effects were significant for P. sylvestris only. The influence of potential evapotranspiration (PET) in spring and autumn on tree growth was positive and non-linear, whereas tree growth sharply decreased with increasing PET in June, which proved to be the most influential month on tree growth along the whole ecological gradient. Interactions of PET with tree social position (relative dbh) were significant in July and September for Q. spp. and in April for P. sylvestris. Interactions of climate with density or mixture were not significant. Climatic effects found agree well with previous results from intra-annual growth studies and indicate that the model captures the causal factors for tree growth well. Furthermore, the interaction between climate and relative dbh might indicate a longer growth duration for trees of higher social classes. Analysis of random effects across time and space showed highly dynamic patterns, with competitive advantages changing annually between species and spatial patterns showing no large-scale trends but pointing to the prevalence of local site factors. In mixed-species stands, the tree species have the same competitivity in the long-term, which is modified by climate each year. Climate warming will shift the competitive advantages, but the direction will be highly site-specific.

Effects of stand factors on tree growth of Chinese fir in the subtropics of China depends on climate conditions from predictions of a deep learning algorithm: A long-term spacing trial

Stand and climate related variables are the main driving forces controlling individual tree growth. Two machine learning algorithms called deep learning and random forest were used to explore how annual diameter growth varied with stand and climatic variables. Data was obtained from a long-term spacing trail of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations in four provinces of southern China. Results from model comparisons showed the deep learning model with 8 hidden layers and 90 neurons in each hidden layer achieved the best performance, and the RF model ranked 4th among 9 selected models. In addition, sensitivity analysis showed that individual tree growth increased with an increase in Gini coefficient, while growth decreased with an increase in stand age (A) and the basal area of larger trees (BAL). The relationships between diameter growth and summer mean maximum temperature (SMMT), as well as winter mean minimum temperature (WMMT) and annual precipitation (AP) were not constant, which depended on the range of values of each climate factor. BAL had the greatest influence on diameter growth among all the variables. From an interaction analysis, we found that climate factors exacerbated the negative effects of competition on growth. Climate change promoted the growth of younger trees but restrained the growth of older trees. With climate variables considered, tree growth under high and middle stand structural heterogeneity were similar, and observably higher than that with low stand structural heterogeneity. Positive influences of climate tended to promote tree growth under lower competition and older individuals were more vulnerable to WMMT changes. Our findings enhance our understanding of the mechanisms driving individual Chinese fir growth in southern China in the face of future climate uncertainty.

Peak radial growth of diffuse-porous species occurs during periods of lower water availability than for ring-porous and coniferous trees.

Climate models project warmer summer temperatures will increase the frequency and heat severity of droughts in temperate forests of Eastern North America. Hotter droughts are increasingly documented to affect tree growth and forest dynamics, with critical impacts on tree mortality, carbon sequestration and timber provision. The growing acknowledgement of the dominant role of drought timing on tree vulnerability to water deficit raises the issue of our limited understanding of radial growth phenology for most temperate tree species. Here, we use well-replicated dendrometer band data sampled frequently during the growing season to assess the growth phenology of 610 trees from 15 temperate species over 6 years. Patterns of diameter growth follow a typical logistic shape, with growth rates reaching a maximum in June, and then decreasing until process termination. On average, we find that diffuse-porous species take 16–18 days less than other wood-structure types to put on 50% of their annual diameter growth. However, their peak growth rate occurs almost a full month later than ring-porous and conifer species (ca. 24 ± 4 days; mean ± 95% credible interval). Unlike other species, the growth phenology of diffuse-porous species in our dataset is highly correlated with their spring foliar phenology. We also find that the later window of growth in diffuse-porous species, coinciding with peak evapotranspiration and lower water availability, exposes them to a higher water deficit of 88 ± 19 mm (mean ± SE) during their peak growth than ring-porous and coniferous species (15 ± 35 mm and 30 ± 30 mm, respectively). Given the high climatic sensitivity of wood formation, our findings highlight the importance of wood porosity as one predictor of species climatic sensitivity to the projected intensification of the drought regime in the coming decades.

Assessment of the effects of thinnings in scots pine plantations in Mongolia: a comparative analysis of tree growth and crown development based on dominant trees

The post-thinning stand density and spacing in forest plantations influence individual tree growth and crown development, and the changes detected in dominant tree growth are a good indication of the thinning effect. The objective of this study was to determine the effects of different thinning intensities on diameter and height growth in a Scots pine (Pinus sylvestris L.) plantation. The field measurements were carried out between 2016 and 2020 on a Scots pine plantation, growing in Selenge province of northern Mongolia. Following this, experimental thinnings were carried out with different intensities. Thinning treatments comprised thinning with very low, low, medium, and high intensities, as well as an unthinned control stand. Stem analyses were performed to calculate the annual and cumulative diameter, height, and volume growth. For tree crown measurements several parameters were analyzed: crown diameter, crown projection area, and crown index. A total of 300 trees (5 treatments*3 replications*20 dominant trees from each plot) were subjected to the comparative analyses. This study revealed that thinning showed a stronger positive effect on diameter and volume growth of dominant trees in the plantation. Our results showed a gradual increase in diameter, basal area, and volume growth depending on the thinning intensity. An ANOVA test for growth analyses of dominant trees showed a significant difference in diameter (p < 0.0001) and height (p < 0.0001) growth performance following experimental felling with different thinning intensities. Finally we elaborated linear mixed effect models (LMM) for tree growth between 2016 and 2020 of selected dominant trees. With the help of the LMM we analyzed and described the thinning impact on DBH, BA, height, volume and crown diameter. The models confirmed that higher thinning intensity triggered growth of the response variables except for height. A greater height growth was found in very low (10%) and low (15%) intensity treatments. Due to reduction of competition and optimization of the distance between individuals, thinnings contributed to a relatively faster development of the tree crown in radial directions. Based on our analysis results and comparative graphs representing post-thinning dominant tree growth in diameter, height, basal area, and volume, we recommend medium- (30%) and high-intensity (45%) thinnings as at the beginning stage of plantation establishment.

Growth and mortality of Norway spruce and European beech in monospecific and mixed-species stands under natural episodic and experimentally extended drought. Results of the KROOF throughfall exclusion experiment

Key messageUnder severe drought, growth of Norway spruce suffered much more than European beech. Norway spruce benefited from growing in the environment of beech, and both species acclimated slightly to 5 years of experimentally extended drought.Recent studies show that the detrimental effects of drought on stand growth are mitigated when the stand contains mixed tree species. We analysed the growth responses of Norway spruce and European beech to episodic and experimentally extended drought in intra- and inter-specific mature stands. We used annual diameter growth records dating back to 1998 to determine the impact of the natural episodic drought in 2003 and 2015. To analyse extended drought, spruce and beech trees were exposed to extreme drought under automatic throughfall exclusion roofs from 2014 to 2018. The growth of spruce in an inter-specific environment with beech was 20–50% less affected by natural episodic drought compared with an intra-specific constellation. When beech grew in an inter-specific environment, it was by 23% more affected by drought compared to intra-specific conditions, but seemed to recover faster. The induced drought from 2014 to 2018 resulted in a strong growth reduction in the first year particularly for spruce, followed by a slight acclimation to the dry conditions. Beech acclimated and recovered faster than spruce across all growing conditions, while spruce only acclimatized faster in the environment of beech. Both species showed a higher mortality under induced drought compared with the controls; for spruce, the mortality rate was fivefold higher compared to the long-term mortality. The long-term moderate-growth stabilization and the growth increase after the 5-year exposure to drought suggest a gradual acclimation to drought by beech. The resistance and acclimation to drought of spruce when growing in mixture should be considered when designing resource efficient and productive mixed conifer-broadleaved stands for future climates.

Growth rates of valuable tree species in secondary tropical montane cloud forests in Mexico: influence of tree size, crown position and competition

Tropical montane cloud forests (TMCF) are under severe threat from deforestation, fragmentation and degradation. Several tree species are harvested and commercialized by local communities through unplanned selective logging. Lack of information regarding the growth rates of the most economically valuable timber species hampers the design of effective sustainable management schemes for TMCF. The objective of this study was to determine the diameter growth rates and evaluate the influence of tree size, crown class and neighbouring tree basal area on the growth of common and valuable TMCF timber species. Annual diameter growth was measured during two years in 60 trees (10 to 45 cm in diameter at breast height; dbh) each of Alnus acuminata, Liquidambar styraciflua and Quercus xalapensis, located in two unmanaged secondary TMCF sites in Veracruz, Mexico. High diameter growth rates (centimeter per year [cm yr-1]; mean ± SE) were recorded in the three species; the highest was recorded in A. acuminata (1.62 cm yr-1 ± 0.08 cm yr-1), followed by Q. xalapensis (0.91 cm yr-1 ± 0.07 cm yr-1) and L. styraciflua (0.71 cm yr-1 ± 0.08 cm yr-1). Diameter growth rate was inversely related to the basal area of the neighbouring trees, indicating a negative effect of competition in the three species. Dominant trees had higher growth rates than supressed trees in the three species. The high growth rates recorded in forests with no previous management and the negative effect of basal area of neighbouring trees support the potential for silvicultural management in secondary TMCF.

Modeled diameter growth response to intermediate treatments of planted white spruce (Picea glauca) affected by eastern spruce budworm (Choristoneura fumiferana) in Minnesota, U.S.A.

White spruce (Picea glauca (Moench) Voss) plantations have historically been an important source of high-quality forest products in the Great Lakes Region of North America. Thinning in spruce plantations is a common silvicultural practice for reducing competition and promoting resiliency to forest health threats such as eastern spruce budworm (Choristoneura fumiferana Clemens), a native forest pest of eastern North America. Spruce budworm larvae feed on the foliage of trees, which reduces growth and potentially causes mortality during an outbreak. There has been continual spruce budworm defoliation in northern Minnesota, U.S.A., since the mid-1950s, with higher levels of defoliation in the late 1990s. This research modeled the diameter growth response of white spruce 18 years after initial thinning in stands that presently range between 44 and 64 years old. Some stands received a second thinning in recent years. We used generalized nonlinear least squares and nonlinear mixed-effects models to estimate annual diameter growth using common tree and stand metrics. Growth model performance was improved by including thinning and frequency of spruce budworm defoliation as modifiers of diameter growth. Results of this study highlight how thinning in combination with insect disturbance affect diameter growth in white spruce plantations of northern Minnesota.

Influence of Cambial Age and Axial Height on the Spatial Patterns of Xylem Traits in Catalpa bungei, a Ring-Porous Tree Species Native to China

Studying how cambial age and axial height affects wood anatomical traits may improve our understanding of xylem hydraulics, heartwood formation and axial growth. Radial strips were collected from six different heights (0–11.3 m) along the main trunk of three Manchurian catalpa (Catalpa bungei) trees, yielding 88 samples. In total, thirteen wood anatomical vessel and fiber traits were observed usinglight microscopy (LM) and scanning electron microscopy (SEM), and linear models were used to analyse the combined effect of axial height, cambial age and their interaction. Vessel diameter differed by about one order of magnitude between early- and latewood, and increased significantly with both cambial age and axial height in latewood, while it was positively affected by cambial age and independent of height in earlywood. Vertical position further had a positive effect on earlywood vessel density, and negative effects on fibre wall thickness, wall thickness to diameter ratio and length. Cambial age had positive effects on the pit membrane diameter and vessel element length, while the annual diameter growth decreased with both cambial age and axial position. In contrast, early- and latewood fiber diameter were unaffected by both cambial age and axial height. We further observed an increasing amount of tyloses from sapwood to heartwood, accompanied by an increase of warty layers and amorphous deposits on cell walls, bordered pit membranes and pit apertures. This study highlights the significant effects of cambial age and vertical position on xylem anatomical traits, and confirms earlier work that cautions to take into account xylem spatial position when interpreting wood anatomical structures, and thus, xylem hydraulic functioning.

Time shifts in height and diameter growth allocation in understory European beech (Fagus sylvatica L.) following canopy release

In understory trees, height–diameter allocation is subject several constraints: maximal height growth is limited, height growth is never null and, in terms of time dependency, diameter growth always precedes height growth. Understory trees experience a succession of canopy opening and closure events during their lifetime. Preferential allocation of their biomass to height or diameter growth is part of the acclimation process to their immediate environment. In this study, we investigated annual height and diameter increments in Fagus sylvatica understory trees submitted to canopy release. Annual height and diameter increments were obtained from retrospective stem analysis from the top of the tree to the stump on 39 understory trees. The relationship between height and diameter increments was investigated and temporal correlations among successive annual height and diameter increments were analyzed. An asymptotic relationship between annual height and diameter increment indicates that stem height growth was limited in understory trees. The intercept significantly differed from zero suggesting that height growth never stopped even when diameter growth was null. Following canopy release events, immediate diameter growth increase was observed while the height growth response was delayed, resulting in a time shift in the growth allocation strategy. Strong and asymmetric temporal correlations between annual height and diameter increments were observed: past annual diameter growth was positively correlated to present height growth. In understory trees, tree height is the main factor determining their potential growth since it determines their access to above-canopy light. However, the precedence of diameter growth over height growth suggests that tree growth is driven by diameter instead of height. This apparent discrepancy may be explained by the fact that, under closed canopy conditions, stem allometry reaches a functional threshold that forces tree to grow in diameter before growing in height.

Healing ability and diameter growth of lime-trees (Tilia begonifolia Stev.) following logging wounds

Lime-trees (Tilia begonifolia Stev.) have countless ecological and economical values in the northern forests of Iran. Bole wounds on residual trees are commonly caused by logging. The healing ability of bole wounds and the effect of bole wounds on diameter growth in lime-trees were assessed in a natural mixed uneven-age stand. The susceptibility to decay in relation to the wound severity was also evaluated. Condition and location of lime-trees before and after selective logging were determined through systematic plot sampling. The position of each lime-tree was identified on a topographical map using the global positioning system. After 10 years from wound occurrence, tree and wound characteristics were also re-measured. Overall, 68 stems (9.7 stem ha−1) of lime-trees were found in the sampled area, 25 stems (36.8%) were damaged in the form of bole wound, and 43 stems (63.2%) were undamaged. Statistical differences between wounded or non-wounded lime-trees in terms of diameter and height were not found. Most of the wounds occurred at the height of < 1 m; the average wound size was 370.5 cm2. Wound severity was related to wound size and wound position. Wound width healing rate was 6.2 mm year−1. The wound shape was found to be a healing factor as the healing rate by width was higher than that by length. Healed wounds were only 12, 60% of bole wounds resulted in decay. Diameter growth of wounded trees was 43.5% lower than undamaged trees. The average annual diameter growth decreased by increasing wound severity. The results indicated the lime-tree is a very sensitive species to damage caused by logging (bole wound). Single-tree selection cutting needs more careful logging operations to reduce damage on residual lime-trees in order to safeguard this species, valuable in ecologic and economic terms.

Assessing the impacts of topographic and climatic factors on radial growth of major forest forming tree species of South Korea

Although the annual diameter growth of trees is vital for assessing site suitability in terms of potential timber yield, the effects of climatic and topographic factors on this variable are poorly understood. The main objective of this study was to develop a tree-level radial growth model incorporating topographic and climatic factors for four major temperate tree species [red pine (Pinus densiflora), oak (Quercus spp.), Japanese larch (Larix kaempferi), and Korean pine (Pinus koraiensis)] in South Korea. The model was developed and then validated using increment cores sampled from permanent plots in the Korean National Forest Inventory country wide. The Standard Growth (SG) of each increment core, which eliminated the effect of tree age on radial growth, was derived using a SG model. Spatial autocorrelation was detected for the SGs of every species, but not for the original radial growth data. The results showed that using the SG model to standardize radial growth for age was successful for explaining the impact of topographic and climatic factors on radial growth. The influence of climatic (warmth index and precipitation effectiveness index) and topographic (topographic wetness index) factors on the SG of each species was evaluated by the estimated SG (eSG) model. Results show that for all species each variable was correlated to SG. The mean R2 of the final radial growth model for red pine, oak, Japanese larch, and Korean pine during 2001–2009 were estimated to be 0.71, 0.73, 0.67, and 0.65, respectively. In addition, for every tree species the time sequence of estimated annual radial growth exhibited similar characteristics to that of the observed annual radial growth on an individual tree scale. Thus, this growth model can contribute to an understanding of the impacts of topographic and climatic factors on tree radial growth and predict the annual growth changes of major tree species in South Korea, given climate change.

Variation in stand density, black spruce individual growth and plant community following 20 years of drainage in post-harvest boreal peatlands

Drainage can help restore hydrological conditions conducive to the growth of black spruce (Picea mariana) seedlings on logged forested peatlands. The impact of drainage was assessed by analysing the variation in stand density at stump height, black spruce seedling annual diameter growth and composition of plant communities on 20 of the oldest operationally drained sites in Quebec’s James Bay region. These sites, each consisting of a drained, post-harvest area and a corresponding undrained, post-harvest control area, were classified into five ecosites based on soil characteristics and plant communities. The ecosites studied varied from those with rich mineral soils covered with a shallow organic layer to very poor, deep, organic soils. Results showed that the growth response of black spruce seedlings following drainage was strongly dependent on the ecosite. Ecosites RE37 and rich RE39 showed a substantial and steady growth response of black spruce to drainage over time. Therefore, drainage caused a significant increase in stand density and growth rate of black spruce seedlings in moderately rich ecosites. In the other ecosites studied, the peat layer was either too thick (poor RE39 and very poor RE39) or too shallow (RE26) for black spruce stand densities and individual stems growth to increase with drainage, compared to those of the control areas.

Fenología, incremento en diámetro y periodicidad de anillos de crecimiento de Enterolobium cyclocarpum (Jacq.) Griseb (Leguminosae) en Costa Grande, Guerrero, México

In this paper were evaluated the phenological events, the diameter increment and periodicity of growth rings of Enterolobium cyclocarpum (Jacq.) Griseb in Costa Grande, Guerrero, Mexico. Every two months for two years they were studied. At the same time and periods growth diameter was measured using dendrometer bands, the crowns of the trees were measured according to their symmetry and lighting. The periodicity of growth was determined by marks on its vascular cambium and confirming the formation of growth rings. E. cyclocarpum presented its leaves fall late November to late March, flowering from January to May, fruiting from March to May and leaves flushing occurred from March to September. The outbreak of leaves was significantly correlated (P < 0.01) with high temperature. The annual diameter growth was, related to the seasonality of precipitation. The largest increases occurring in categories 25 and 30 cm (P < 0.001), on trees with partially symmetric-symmetrical crowns (P < 0.001) and partially lighting (P < 0.001). As a result of seasonality, an annual growth ring delimited parenchyma and fibers are formed.

Allometric projections of time-related growth trajectories of two coexisting dipterocarp canopy species in India

Background: The Western Ghats of India contain the westernmost dipterocarp forests of Asia. However, only a few dipterocarp tree species actually coexist in the forest canopy among which Vateria indica and Dipterocarpus indicus are the most common. The mechanisms contributing to the coexistence of these phylogenetically closely related species have not been identified.Aims: We investigated the time-related growth trajectories in diameter, height and crown size of these two species in the Uppangala Permanent Sample Plot to determine if trade-offs in their three-dimensional developmental strategies could contribute to their long-term coexistence.Methods: From annual diameter growth data of 692 trees >9.55 cm in diameter at breast height over a 21-year period, we developed time-related diameter growth models for the two species, accounting for local density-dependent competition effects and topography. Combining the diameter growth models with static stem and crown allometries, we projected time-related tree growth trajectories in height and crown size.Results: While both species can reach similar dimensions, V. indica grows much faster, or at least as fast as D. indicus in diameter, height and crown size in all the observed situations. Both species respond similarly to topography, but V. indica appears to be more responsive to local density-dependent competition than D. indicus. Finally, V. indica shows higher mortality and recruitment rates and a greater basal area increase than D. indicus.Conclusions: These results refute our hypothesis that D. indicus coexists with the outperformer V. indica by a growth strategy allowing selected individuals in favourable conditions to reach the canopy more quickly than their competitors. The current coexistence of the two dipterocarp species at Uppangala appears not to be at a static equilibrium; V. indica probably being in a phase of canopy stand colonisation.

Determination of Growth Rate and Age Structure of &lt;i&gt;Boswellia papyrifera&lt;/i&gt; from Tree Ring Analysis: Implications for Sustainable Harvest Scheduling

Boswellia papyrifera is a multipurpose deciduous species that grows in Combretum – Terminalia deciduous woodlands of Ethiopia. It is widely known for its commercial frankincense production. The B. papyrifera woodland is under a problematic state of population decline due to heavy encroachment and unsustainable tapping. To sustainably manage such a sensitive ecosystem needs exact knowledge of growth rates and age structure of trees where such information on tropical trees under natural condition is rather poor. In this study growth rate and age of B. papyrifera was determined from tree ring analysis. The study was carried out in Lemlem Terara, Metema district, Ethiopia. The mean annual diameter growth rate of B. papyrifera derived from the mean ring-width is 2.32mm and varies among sample trees. All sampled trees showed a comparable general growth trend which can be divided into three phases – i) good growth in the beginning, ii) phase with depression in middle and iii) increase in ring width. The average age of B. papyrifera trees growing in the study site is estimated to be about 75 years. Although there is strong correlation between diameter of a tree and age, the result from this study highlighted that age-size relations should be used cautiously as the diameter may not reflect the true age. The result from this study is important input to develop strategic plan for the species regarding tapping frequency and intensity as per the annual increment of the species. For further dendrochronological studies of the species, it is recommended to take samples from different size classes and slope gradients for better and reliable results. In future, the use of tree ring analysis as a tool to understand growth dynamics and age structure of trees species, and their response to climate variability should be strengthen in Ethiopian. Keywords: Boswellia papyrifera, Annual growth rings, Diameter growth rate, Age structure, Ethiopia.

Enrichment of Central African logged forests with high-value tree species: testing a new approach to regenerating degraded forests

ABSTRACTIn natural forests of Central Africa, several studies indicate a dramatic decrease in commercial trees, including species of concern for conservation. Enrichment planting with these species will favor both the long-term recovery of their populations and biodiversity conservation in logged forests. In this study, we analyzed the survival and growth of 23 species in plantations. Fourteen 0.2–1.1 ha mixed species plantations consisting of single-species 15 × 15 m blocks were studied for 5 years in a logging concession of southeastern Cameroon. The plantation design considered both species light requirements and sensitivity to damage by pests. To identify the best species for enrichment planting, we assessed both species performance and plantation costs. We also tested for relationships between species traits and species performance. Mean annual diameter growth increments ranged from 1.67 to 42.9 mm. No significant relationship was found between growth and survival. Herbivory by wild Bovidae was the main cause of mortality and should be carefully considered in rehabilitation efforts. We found a significant negative relationship between wood density and maximum growth rate. The other traits tested were not good predictors of species performance in plantations. The two best-performing species, Triplochiton scleroxylon and Terminalia superba, could reach the minimum cutting diameter during a 30-year cutting cycle. Costs were high and mechanized site preparation is suggested to reduce them. Widespread adoption of such plantations will only occur if financial incentives or national regulations for assuring regeneration are implemented.EDITED BY Nicholas Brokaw

Investigating the Impact of Climate Changes on Qualitative and Quantitative Growth of Oak Trees (Case Study: Central Zagros)

The present study is an attempt to investigate the impact of climate changes on quantitative and qualitative growth of oak trees in central Zagros region. After we selected the study region, 35 discs were taken from trees felled in each height class (e.g. 1400 - 1600, 1600 - 1800, 1800 - 2000 m above the sea level). We used climate index spi. For the data analysis, we employed SPSS software and inferential statistics tests of Kolmogroff Smirnov and the one-way ANOVA. During the recent 15 years, rainfall has shown a decreasing trend and amount of haze and frequency of occurring haze has been increased. The ANOVA results indicated that diameter growth of trees in three height classes revealed a significant difference. The average annual diameter growth in the first, second and third classes were 1.8 mm, 2.5 mm, and 2.2 mm, respectively. Additionally, the results indicated that hillsides and slope aspect has a statistically meaningful effect on the size of canopy area, basal area and number per hectare. Several different studies have reported that during the recent 15 years, qualitative and quantitative growth of central Zagros oak trees strongly correlate with climate parameters in the three habitats.