Variations In Climatic Factors Research Articles

ARTISANAL FISHER FOLK’S PERCEPTION OF THE EFFECTS OF VARIABILITY IN CLIMATIC FACTORS ON FISH YIELD IN KAINJI LAKE BASIN, NIGERIA

Abstract. This study assessed the artisanal fisher folk’s perception of the effects of variability in climatic factors on fish yield in Kainji Lake basin. The specific objectives were to: describe the socio-economic characteristics of the respondents; assess the artisanal fisher folk’s perception of the effectsof variability in climatic factors on fish yield; and assess the influence of variability in climatic factors on fish yield. Both primary and secondary data was used for the study. Primary data was collected from 173 respondents using structured questionnaires while secondary data was obtained from the Power Holding Company of Nigeria and the National Institute of Freshwater Fisheries Research (NIFFR), all of them located in New Bussa, Niger State. Once collected, the data was analyzed based on descriptive and inferential statistics involving the use of multiple regression models. As shown by the results, 91.32% of respondents were male; many (75.14%) of them aged between 41 and 60. Most of them (90.18%) were married and had Quranic education (96.62%). 48.74% had a household composed of 6 to 10 members. The respondents perceived all the factors of climate variability (draught, change in the lake’s water levels, variations in the seasonal calendar, change in seasonal rainfall, Harmattan intensity and change in temperatures) as unfavorable developments (with small variations in the mean scores). As an exception, humidity and change in sunlight conditions were believed to be favorable aspects by the respondents. The implication isthat all the variables except humidity and change in sunlight conditions will adversely affect the fish yield, as claimed by the respondents. As shown by the results of a multiple regression study of the influence of variability in climatic factors on fish yield, the temperature had a negative influence on fish yield, whereas water inflow had a positive effect. The study recommends that the local population should attend adult literacy classes and improve their formal education levels. The management of NIFFR and other higher authorities, such as the Ministry of Water Resources and the Ministry of Environment, that are vested with the responsibility of managing the water bodies, should be advised to stock the water bodies with fish species that are resistant to temperature. In turn, the artisanal fisher folk should be encouraged to improve on their management practices, especially as regards overfishing and the use of obnoxious fishing methods. Also, they should extend their livelihood to such areas as crop production, animal breeding, trading/commerce and services as alternativeincome diversification strategies to cushion the effect of declining fish yields as a result of climate change.

Mathematical modelling and numerical simulations of the influence of hygiene and seasons on the spread of cholera

Cholera is a bacterial disease, its spread is strongly influenced by environmental factors and some socio-economic factors such as hygiene standards and nutrition of the population. This paper is devoted to the modelling of the impact of climatic factors and human behaviour on the spread of cholera. The mathematical modelling incorporates the direct transmission and the indirect transmission due to environmental knowledge. Taking into account the effect of the intra-annual variation of climatic factors on the transmission of cholera, a non-autonomous ordinary differential equations is proposed to describe the dynamics of the transmission of cholera. When the intra-annual variation of climate is not incorporated into the model, the latter becomes autonomous. The basic reproductive number is calculated and the stabilities of equilibria are investigated. In the non-autonomous case, the disease extinction and uniform persistence of disease are investigated. The results suggest that the transmission and spread of cholera can be affected by climatic factors, the proportion of the undernourished individuals and the proportion of people who respect the hygiene standards. Finally, some numerical simulations are proposed using the parameters values of climatic factors and socio-economic factors of some localities situated in Lake Chad border between Chad, Cameroon and Nigeria.

Interaction of the fluctuation of the population density of sweet potato pests with changes in farming practices, climate and physical environments: A 11-year preliminary observation from South-Kivu Province, Eastern DRCongo

Interaction of the fluctuation of the population density of sweet potato pests with changes in farming practices, climate and physical environments: A 11-year preliminary observation from South-Kivu Province, Eastern DRCongo

Climate changes affecting biotic interactions, phenology, and reproductive success in a savanna community over a 10-year period

Climatic parameters are able to influence the timing of phenological events affecting the degree of synchrony among plant species, their interactions, and reproductive success. Shrubs of Malpighiaceae family in the Brazilian Tropical Savanna present sequential flowering phenology. We verified variations in climatic factors (temperature and precipitation) over a period of 10 years (2005–2014) and correlated them with the onset of flowering of four of these Malpighiaceae species. Furthermore, we tested whether the phenological synchronization among species has changed over time affecting the herbivory and fruit set. Herbivory and fruit production were recorded during three reproductive seasons (2008/2009, 2011/2012, 2013/2014). We developed a mathematical model to estimate the flower and fruit production in response to phenological changes for the next 5 years. Results show that climatic factors changed, influencing the onset of species flowering. The degree of overlap among species also changed and the effects on species interactions were species specific. The mathematical model successfully presented a tendency on flower and fruit production contributing to the predictions of the outcomes in response to phenological changes. We confirm the effects of climate changes on plant phenological events and the importance of feature plasticity for better performance of species.

Forecasting wheat and barley crop production in arid and semi-arid regions using remotely sensed primary productivity and crop phenology: A case study in Iraq

Crop production and yield estimation using remotely sensed data have been studied widely, but such information is generally scarce in arid and semi-arid regions. In these regions, inter-annual variation in climatic factors (such as rainfall) combined with anthropogenic factors (such as civil war) pose major risks to food security. Thus, an operational crop production estimation and forecasting system is required to help decision-makers to make early estimates of potential food availability. Data from NASA's MODIS with official crop statistics were combined to develop an empirical regression-based model to forecast winter wheat and barley production in Iraq. The study explores remotely sensed indices representing crop productivity over the crop growing season to find the optimal correlation with crop production. The potential of three different remotely sensed indices, and information related to the phenology of crops, for forecasting crop production at the governorate level was tested and their results were validated using the leave-one-year-out approach. Despite testing several methodological approaches, and extensive spatio-temporal analysis, this paper depicts the difficulty in estimating crop yield on an annual base using current satellite low-resolution data. However, more precise estimates of crop production were possible. The result of the current research implies that the date of the maximum vegetation index (VI) offered the most accurate forecast of crop production with an average R2=0.70 compared to the date of MODIS EVI (Avg R2=0.68) and a NPP (Avg R2=0.66). When winter wheat and barley production were forecasted using NDVI, EVI and NPP and compared to official statistics, the relative error ranged from −20 to 20%, −45 to 28% and −48 to 22%, respectively. The research indicated that remotely sensed indices could characterize and forecast crop production more accurately than simple cropping area, which was treated as a null model against which to evaluate the proposed approach.

Variation in the reproductive strategy of a lichenized fungus along a climatic gradient.

Onset of reproduction and reproductive allocation patterns are key components of plant reproductive strategies. Life history theory predicts that plants in adverse environments for juvenile performance start reproduction at smaller sizes and exhibit higher reproductive allocation compared to their counterparts in favourable environments. Life history theory will gain in generality if its predictions are shown to apply to a broad range of organisms and modes of reproduction. This study tested whether the asexual reproductive strategy of a lichenized fungus changed along a climatic gradient. The variation in threshold size for asexual reproduction and asexual reproductive allocation of the lichen Lobarina scrobiculata was assessed in 18 populations (9665 individuals) along a climatic gradient spanning 800 km in latitude in Southern Europe. Using generalized linear models and standardized major axis regressions, the allometric relationships and the associated variation in climatic factors according to the changes in the threshold size for reproduction and reproductive allocation patterns were assessed. The onset of reproduction was size-dependent and the reproductive allocation increased with individual size. Both the threshold size for reproduction and the reproductive allocation varied along the rainfall gradient. A lower threshold size for reproduction and higher reproductive allocation in drier, adverse locations were found. Therefore, populations in drier locations fitted the predictions of life history theory for sexually reproducing organisms in adverse environments for juvenile performance. This study highlights the applicability of the life history theory to fungi and to modes of reproduction other than sexual reproduction. Based on the intraspecific variation in the asexual reproductive strategy of a fungal organism with climatic factors, these findings expand the scope of life history theory predictions and increase our understanding of life history diversity and reproductive strategies across environments.

Can individual variation in phenotypic plasticity enhance population viability?

In response to climatic and other sources of environmental variation, individuals within a population may adjust their behavioral, morphological or physiological responses to varying environmental conditions through phenotypic plasticity. In seasonal environments, time constraints related to seasonality, as well as variation in climatic factors, may affect body mass growth rates. To cope with the consequences of a harsh period, individuals may, for example, compensate for lost body mass by accelerating their growth rate in the following period. Phenotypically plastic responses like this can, therefore, directly affect body mass, which may affect individual fitness and, ultimately, population dynamics. Here, we use a well-studied population of yellow-bellied marmots, Marmota flaviventris, in Colorado to parametrize and develop an individual-based model (IBM) to investigate how phenotypically plastic responses in body mass growth rate may compensate for an individual’s bad start after a harsh period (compensatory growth), and to explore whether individual variation in compensatory growth favors population persistence under less favorable climatic scenarios. A simulation model that allowed marmots with a body mass less than the population’s average body mass to compensate their growth provided the best match with observed population sizes, suggesting the importance of trade-offs in population dynamics. We also found that compensatory growth plays an important role in decreasing the probability of extinction under both less favorable colder and random climate scenarios. Our results lead to a deeper understanding of the mechanisms that govern population fluctuations and highlight the importance of quantifying the fitness cost of phenotypically plastic responses.

Sundarban mangroves: diversity, ecosystem services and climate change impacts

The Bengal delta coast harboring the famous Sundarban mangroves is extremely vulnerable to climate change. Already, salinity intrusion, increasing cyclones and anomalies in rainfall, and temperature, are causing many social and livelihood problems. However, our knowledge on the diversified climate change impacts on Sundarban ecosystems services, providing immense benefits, including foods, shelters, livelihood, and health amenities, is very limited. Therefore, this article has systematically reviewed the major functional aspects, and highlights on biodiversity, ecosystem dynamics, and services of the Sunderban mangroves, with respect to variations in climatic factors. The mangrove ecosystems are highly productive in terms of forest biomass, and nutrient contribution, especially through detritus-based food webs, to support rich biodiversity in the wetlands and adjacent estuaries. Sundarban mangroves also play vital role in atmospheric CO2 sequestration, sediment trapping and nutrient recycling. Sea level rise will engulf a huge portion of the mangroves, while the associated salinity increase is posing immense threats to biodiversity and economic losses. Climate-mediated changes in riverine discharge, tides, temperature, rainfall and evaporation will determine the wetland nutrient variations, influencing the physiological and ecological processes, thus biodiversity and productivity of Sundarban mangroves. Hydrological changes in wetland ecosystems through increased salinity and cyclones will lower the food security, and also induce human vulnerabilities to waterborne diseases. Scientific investigations producing high resolution data to identify Sundarban?s multidimensional vulnerabilities to various climatic regimes are essential. Sustainable plans and actions are required integrating conservation and climate change adaptation strategies, including promotion of alternative livelihoods. Thus, interdisciplinary approaches are required to address the future climatic disasters, and better protection of invaluable ecosystem services of the Sunderban mangroves.Asian J. Med. Biol. Res. December 2016, 2(4): 488-507

Abrupt Intensification and Dissipation of Tropical Cyclones in Indian Ocean: A Case Study of Tropical Cyclone Nilofar – 2014

This study aims to investigate the possible influence of different atmospheric forcing on intensification/dissipation of tropical cyclonic “Nilofar” in Arabian Sea appeared during the last week of October, 2014 which exhibited abrupt intensification and dissipation as well. The cyclone was monitored by the Tropical Cyclone Warning Center (TCWC) of Pakistan Meteorological | department and the Regional Specialized Meteorological Center (RSMC) of Indian Meteorological | department (IMD) continuously, issued warnings and advisories with the help of available synoptic observations, satellite data and numerical models. Almost all the essential ingredients for intensification and tracking of the cyclone were studied and monitored accurately. Although the track forecast of the cyclone remained up to mark; but great errors occurred in intensity forecast. The atmospheric vertical wind shear could not be studied accurately. The intensity of wind shear itself is dependent on both; the local and global atmospheric forcing and climate variables, reoccurring periodically, especially while occurring two or more at the same time. More studies are required for influence of these climate variables while co-occurring at the same time period. This study will help weather forecasters to pay special attention on variation of climate factors affecting the wind shear for proper forecasting of tropical cyclones in the Arabian Sea for the safety of coastal communities along the coast.

Nitrogen deposition does not enhance Sphagnum decomposition

Long-term additions of nitrogen (N) to peatlands have altered bryophyte growth, species dominance, N content in peat and peat water, and often resulted in enhanced Sphagnum decomposition rate. However, these results have mainly been derived from experiments in which N was applied as ammonium nitrate (NH4NO3), neglecting the fact that in polluted areas, wet deposition may be dominated either by NO3− or NH4+. We studied effects of elevated wet deposition of NO3− vs. NH4+ alone (8 or 56kgNha−1yr−1 over and above the background of 8kgNha−1yr−1 for 5 to 11years) or combined with phosphorus (P) and potassium (K) on Sphagnum quality for decomposers, mass loss, and associated changes in hummock pore water in an ombrotrophic bog (Whim). Adding N, especially as NH4+, increased N concentration in Sphagnum, but did not enhance mass loss from Sphagnum. Mass loss seemed to depend mainly on moss species and climatic factors. Only high applications of N affected hummock pore water chemistry, which varied considerably over time. Overall, C and N cycling in this N treated bog appeared to be decoupled. We conclude that moss species, seasonal and annual variation in climatic factors, direct negative effects of N (NH4+ toxicity) on Sphagnum production, and indirect effects (increase in pH and changes in plant species dominance under elevated NO3− alone and with PK) drive Sphagnum decomposition and hummock C and N dynamics at Whim.

Essential oil composition in natural populations of Pistacia lentiscus L. from Tunisia: Effect of ecological factors and incidence on antioxidant and antiacetylcholinesterase activities

Essential oil leaves of 14 Tunisian Pistacia lentiscus L. (Anacardiaceae) populations, growing wild in three bioclimatic zones, were analyzed by GC-FID and GC⿿MS. The species was found to be rich in monoterpene hydrocarbons (41.9%) and sesquiterpene hydrocarbons (40%). α-pinene (9.9%), limonene (8.5%), terpinen-4-ol (5.1%), β-caryophyllene (8.2%), germacrene D (11.9%) and δ-cadinene (8.5%) were found to be the main compounds.Significant variations of essential oil composition, mainly of major compound percentages (α-pinene, limonene, terpinen-4-ol, β-caryophyllene, germacrene D and δ-cadinene), were detected between populations. PCA and CCA analyses showed a substantial chemical differentiation among populations that was mainly attributed to variation of climatic factors (precipitation, Emberger⿿s coefficient, summer precipitation, temperature of the warmest months in the year, evapotranspiration and winter cold stress) and altitude between the analyzed populations.P. lentiscus essential oils were found to possess antioxidant and antiacetylcholinesterase activities. These activities varied significantly among populations. Essential oil of the species collected from the population 1 possessed the highest antiradical (993.4μg TE/g EO) and reducing power (13.8mmol Fe2+/g EO) activities. Essential oil from population 14 exhibited the uppermost capacity to prevent β-carotene bleaching (IC50=557.3μg/ml). The population 13 showed the most important ferrous ion chelating activity (IC50=130.6μg/ml). Essential oil from the population 6 was found to be the most effective inhibitory against acetylcholinesterase. Levels of antioxidant and antiacetylcholinesterase activities varied according to chemical composition of the investigated essential oils.

Xylogenesis: Coniferous Trees of Temperate Forests Are Listening to the Climate Tale during the Growing Season But Only Remember the Last Words!

The complex inner mechanisms that create typical conifer tree-ring structure (i.e. the transition from large, thin-walled earlywood cells to narrow, thick-walled latewood cells) were recently unraveled. However, what physiological or environmental factors drive xylogenesis key processes remain unclear. Here, we aim to quantify the influence of seasonal variations in climatic factors on the spectacular changes in the kinetics of wood cell differentiation and in the resulting tree-ring structure. Wood formation was monitored in three sites over 3 years for three coniferous species (Norway spruce [Picea abies], Scots pine [Pinus sylvestris], and silver fir [Abies alba]). Cell differentiation rates and durations were calculated and related to tracheid final dimensions and corresponding climatic conditions. On the one hand, we found that the kinetics of cell enlargement and the final size of the tracheids were not explained by the seasonal changes in climatic factors. On the other hand, decreasing temperatures strongly constrained cell wall deposition rates during latewood formation. However, the influence of temperature was permanently written into tree-ring structure only for the very last latewood cells, when the collapse of the rate of wall deposition was no longer counterbalanced by the increase of its duration. Our results show that the formation of the typical conifer tree-ring structure, in normal climatic conditions, is only marginally driven by climate, suggesting strong developmental control of xylogenesis. The late breakage of the compensatory mechanism at work in the wall deposition process appears as a clue to understand the capacity of the maximum latewood density to record past temperature conditions.

Rainfall effects on the sap flow of Hedysarum scoparium.

In arid and semi-arid areas, plant physiological responses to water availability depend largely on the intensity and frequency of rain events. Knowledge on the responses of xerophytic plants to rain events is important for predicting the structure and functioning of dryland ecosystems under changing climate. The sap flow of Hedysarum scoparium in the Mu Us Sand Land was continuously measured during the growing season of 2012 and 2013. The objectives were to quantify the dynamics of sap flow under different weather conditions, and to examine the responses of sap flow to rain events of different sizes. The results showed that the daily sap flow rates of H. scoparium were lower on rainy days than on clear days. On clear days, the sap flow of H. scoparium showed a midday plateau, and was positively correlated with solar radiation and relative humidity. On rainy days, the sap flow fluctuated at low levels, and was positively correlated with solar radiation and air temperature. Rain events not only affected the sap flow on rainy days through variations in climatic factors (e.g., solar radiation and air temperature), but also affected post-rainfall sap flow velocities though changes in soil moisture. Small rain events (<20 mm) did not change the sap flow, whereas large rain events (>20 mm) significantly increased the sap flow on days following rainfall. Rain-wetted soil conditions not only resulted in higher sap flow velocities, but also enhanced the sensitivity of sap flow to solar radiation, vapor pressure deficit and air temperature.

Local Perception of Climate Change and Adaptation in Mangrove Areas of the Cameroon Coast

Mangroves supply essential ecosystem services to tropical informal economies. In the Cameroon coastal region, the impacts of various projections on change in temperatures and precipitations sound low compared to the pressure of human activities. This survey evaluated the sensitivity of local population on the impact of climate change and the vulnerability of coastal ecosystems. An investigation carried out on 425 individuals was based on the major income and development activities, the knowledge of the subject, the information sources, the origin of changes, perceptible effects, risks and consequences. More than 90% of interviewees have heard about climate change essentially from radio (20%). Industries (47.53%) are perceived to have major responsibility for temperature (78%) and precipitation (67%) changes and increased inundation (39.07%) was perceived as the highest risk. Compared with Cartesian predictions in the area, the results have shown the sensitivity of population to local variation of climate factors. No efficient endogenous measure has been recorded. Forest and specially mangroves are the most affected ecosystems by local activities. Expected extension of the dry season could affect the natural regeneration and the structure of mangrove forests. Considering the importance of woody species in the local economies, the lack of appropriate actions and adaptation measures will lead to the total degradation of mangroves.

The Impact of Climate Variabilities on the Water Resources of Nyong River (Cameroon) during Few Anterior Decades

The Nyong River is situated in south Cameroon. The study of the impact of climate change on the water resource of the River shows that its precipitations and flow rate are decreasing. This negative effect is reinforcing by the fact that the water of the River is collected to feed the population of Yaounde, the political capital of Cameroon and its environs. Given that no action can stop the variability of climate factors, it is necessary to ameliorate the management of water resource of Nyong River.

English

“Chemlali” is the main olive variety cultivated in Tunisia. Seasonal factors such as rainfall and temperature vary year to year influencing the composition and quality of virgin olive oil. This work aims to investigate the effect of the seasonal climatic variations on the quantity and the quality characteristics (free acidity, specific ultraviolet absorbance K232 and K270, fatty acid composition, chlorophylls and total phenols) of Tunisian “Chemlali” olive oil. Water and oil content increased with increasing rainfall and temperature respectively. The seasonal variations of climatic factors within the growing region did not affect the main legal quality indices of all oil samples. K232, total phenol contents and oxidative stability increased at high temperature, while K270 and chlorophyll content decreased. Key words: Analytical quality parameters, chlorophyll, fatty acid composition, Olea europaea L., rainfall, temperature, total phenols.

Effect of Climatic Factors on Cashew (Anacardium occidentale L.) Productivity in Benin (West Africa)

Cashew production is affected by variability of climatic factors. The present work aims to study the effect these climatic factors on cashew productivity in the Central and North-West areas of Benin. Data related to plant phenology, nut and apple yields were collected in three villages (Adourékoman and Gobé in the Centre and Founga in the North-West) during two production seasons (2013-2014 and 2014-2015). In addition, socioeconomic survey was conductedamong 80 experienced producers (over 50 years aged and over 10 years’ experience in cashew plantation). Quantity of rainfall, temperature, number of rain days, potential evapotranspiration and wind speed from a period of 1981 to 2010 were also collected at the synoptic stations of ASECNA of Savè in the Centre and Natitingou in North-West. The average rainfall and temperature of both areas revealed an upward trend while, wind speed was less violent in the North-West and potential evapotranspiration was high in the Centre. The season and the area of production did affect significantly (from P<0.05 to P<0.001) appearance of flowers and fruits and also nuts and apples production. In general, cashew trees had produced more in the North-West than the Centre. Furthermore, apples and nuts production were higher in 2014-2015 (6.48 ± 0.05 and 50.72 ± 5.86 kg/tree respectively for nut weight and apple weight) than in 2013-2014 (3.95 ± 0.55 and 39.20 ± 6.63 kg/tree respectively for nut weight and apple weight). The agro-climatic stress index and amount of rainfall in September and October (in both areas), and the number of rainy days (at the Centre only) were main factors determining cashew trees’ production.

Effects of seasonal climatic variability on several toxic contaminants in urban lakes: Implications for the impacts of climate change

Climate change is supposed to have influences on water quality and ecosystem. However, only few studies have assessed the effect of climate change on environmental toxic contaminants in urban lakes. In this research, response of several toxic contaminants in twelve urban lakes in Beijing, China, to the seasonal variations in climatic factors was studied. Fluorides, volatile phenols, arsenic, selenium, and other water quality parameters were analyzed monthly from 2009 to 2012. Multivariate statistical methods including principle component analysis, cluster analysis, and multiple regression analysis were performed to study the relationship between contaminants and climatic factors including temperature, precipitation, wind speed, and sunshine duration. Fluoride and arsenic concentrations in most urban lakes exhibited a significant positive correlation with temperature/precipitation, which is mainly caused by rainfall induced diffuse pollution. A negative correlation was observed between volatile phenols and temperature/precipitation, and this could be explained by their enhanced volatilization and biodegradation rates caused by higher temperature. Selenium did not show a significant response to climatic factor variations, which was attributed to low selenium contents in the lakes and soils. Moreover, the response degrees of contaminants to climatic variations differ among lakes with different contamination levels. On average, temperature/precipitation contributed to 8%, 15%, and 12% of the variations in volatile phenols, arsenic, and fluorides, respectively. Beijing is undergoing increased temperature and heavy rainfall frequency during the past five decades. This study suggests that water quality related to fluoride and arsenic concentrations of most urban lakes in Beijing is becoming worse under this climate change trend.

Elevational disease distribution in a natural plant–pathogen system: insights from changes across host populations and climate

Understanding the factors determining the distribution of parasites and pathogens in natural systems is essential for making predictions about the spread of emerging infectious disease. Here, we report the distribution of the fungal anther‐smut disease, caused by Microbotryum spp., on populations of the European wildflower Silene vulgaris over a range of elevations. A survey of several geographically distinct mountains in the southern French alps found that anther‐smut disease was restricted to high elevations, rarely observed below 1300 m despite availability of hosts below this elevation. Anther smut causes host‐sterility, and is recognized as a model system for natural host–pathogen interactions, sharing common features with vector‐borne and sexually‐transmitted disease in animals. In such systems, many biotic and abiotic factors likely to change over ecological gradients can influence disease epidemiology, including host spatial structure, pathogen infectivity, host resistance, and vector behavior. Here, we tested whether host population size, density, or connectivity also declined across elevation, and whether these epidemiologically relevant factors explained the observed disease distribution. We found that while none of these factor means changed across elevation, disease was significantly more likely to occur at both higher elevations and in larger populations, the majority of which were found above 1300 m. The break in disease incidence was also associated with an apparent scarcity of these larger host populations between 1000 and 1300 m in elevation. Examining variation in climatic factors among host populations, we also showed that the probability of disease was higher in areas with historically colder, wetter, and more stable conditions. The restricted distribution of anther‐smut disease in high‐elevation S. vulgaris provides an opportunity for empirical study on range limits and disease distribution in natural alpine communities that are considered particularly sensitive to the effects of climate change.

Potential of tree-ring analysis in a wet tropical forest: A case study on 22 commercial tree species in Central Africa

Implementing sustainable forest management requires basic information on growth, ages, reproduction and survival of exploited tree species. This information is generally derived from permanent sample plots where individual trees are monitored. Accurately estimating growth rates and especially tree ages from plots is however challenging, as plots often contain only few individuals of the exploited species and monitoring periods cover only a fraction of the life-span of most trees.Alternatively, tree-ring analysis is increasingly used to obtain accurate age estimates and growth rates for tropical tree species, especially in regions with seasonally harsh conditions. However, for species from wet tropical forests (>4000mmyear−1 rainfall) few tree-ring studies exist. Under persistent high levels of rainfall, formation of distinct tree rings is uncertain due to the lack of strong seasonal variation in climate factors. Here we evaluated the potential of applying tree-ring analysis on commercial tree species in a wet tropical forest in Central-Africa. For this purpose we screened the wood anatomy of 22 tree species for the presence of tree-ring structures and, on a subset of five species, we assessed crossdating potential and evaluated the annual character of tree-ring formation by radiocarbon dating.A total of 14 of the 22 tree species showed distinct tree-ring boundaries. Radiocarbon proved annual tree-ring formation in four of the five tested species. Crossdating between trees was problematic for all species and impeded exactly dating each detected ring and building tree-ring chronologies. We also show that diameter growth rates vary strongly between and among species, with important consequences for the calculation of future timber yields.Tree-ring analysis can thus be applied on tree species growing in wet tropical forests to obtain growth rates. We argue that tree-ring analysis should actually be applied on more tree species from different areas to obtain accurate, site specific growth data. This data is urgently required to design and improve sustainable forest management practices.