Potential of dendrochronology to assess annual rates of biomass productivity in savanna trees of West Africa

We examined the potential of dendrochronology to assess biomass productivity of individual savanna species from a semi-arid ecosystem in southern Senegal. The 9 tree species examined in this dendrochronologial study included: Acacia macrostachya, Acacia seyal, Balanites aegyptiaca, Combretum glutinosum, Cordyla pinnata, Pterocarpus erinaceus, Terminalia macroptera, Daniellia oliveri, and Combretum nigricans. Dendrochronologial analyses were applied on cross-sectional disks obtained from the tree stem to reconstruct past tree growth (diameter and biomass) histories. Despite challenges with discerning annual tree rings in these savanna species (associated with ring suppression, wedging, indistinct ring boundaries, and fires), tree species (A. macrostachya, A. seyal, and T. macroptera) with the highest dendrochronology potential produced a clear thin band of marginal parenchyma. A. macrostachya had rapid annual diameter and biomass growth increments in the juvenile years (ages 1–10), compared to T. macroptera which showed greater growth past this early juvenile period. Given the same species, generally wetter forests had lower annual and cumulative growth rates that were likely due to increased inter-tree and tree-grass competition for soil moisture in the wetter forests. We concluded that dendrochronology is well suited for retrospective annual biomass assessment in savanna trees of Senegal, West Africa.     

Growth response of Abies georgei to climate increases with elevation in the central Hengduan Mountains,southwestern China

Climatic harshness is expected to increase at higher elevations; however, elevational trends of tree radial growth response of high-elevation forests to climate change need to be investigated at different locations because of existing local variability in site-specific climatic conditions. We developed tree-ring width chronologies of Yunnan fir (Abies georgei) along elevation gradients at two sites in the central Hengduan Mountains (HM). High-elevation forests of A. georgei showed growth synchronicity and common growth signals along elevation gradients, indicating a common climatic forcing, although tree radial growth rates decreased with increasing elevation. Radial growth of Yunnan fir showed positive correlations with summer temperatures and February precipitation and moisture availability, but were negatively correlated with spring temperatures. The strongest positive relationship indicated summer (July) mean and minimum temperatures are the most important growth determining climatic factors for tree radial growth in the cold environment of HM, and this relationship revealed a clear elevational trend with stronger correlations at higher altitudes. In contrast, tree radial growth was negatively correlated with June precipitation and moisture availability. The whole study period 1954–2015 was split in two sub-periods of equal length. Comparing the early sub-period (1954–1984) to the later sub-period (1985–2015), tree growth response to the summer temperatures strongly increased, while it became weaker to June precipitation and moisture availability. High-elevation Yunnan fir forests in the HM currently benefit from elevated growing season temperatures under humid summer conditions. However, increasing temperatures may induce drought stress on tree radial growth if the observed decreasing trend in humidity and precipitation continues.     

Responses of radial growth and stable carbon isotopes to climate in the northern Tianshan Mountains

Climate change has profound effects on forest ecosystems. Schrenk spruce (P. schrenkiana) is a natural conifer species endemic to the arid inland areas of Asia. In this study, the relationship between tree-ring parameters of P. schrenkiana and major meteorological factors were analyzed, and the main limiting factors for tree radial growth and stable carbon isotope fractionation were explored. Our results indicate that moisture stress before and during the growing season have an important influence on radial growth of P. schrenkiana, especially, the correlation coefficient between tree-ring width and vapor pressure deficit (VPD) from previous August to current July is as high as −0.622 (n = 51, p < 0.01). Collinearity analysis further supports the conclusion that the limiting factor for the radial growth of P. schrenkiana is moisture. Although the correlation analysis results show that the tree-ring δ¹³C_corr is significantly positively correlated with sunshine duration (SD), additional analysis based on first order difference variables suggests that the climate factor may not be the only limiting factor for the stable carbon isotope fractionation of tree rings in the Sayram Lake Basin. This lays the foundation for the assessment of forest management practices and carbon sink capacity in light of future climate change.     

Diverging growth and resilience of Pinus tabulaeformis and Pinus massoniana to droughts in north-south transition zone,central China

Climate transition zone is a sensitive area of climate change and ecological transition where forests are vulnerable to climate extremes. Extreme droughts are increasing in frequency and magnitude under climate change, resulting in structure and function changes of forest ecosystems. Here, to analyze climate-growth relationships and quantify tree resilience to extreme droughts, we developed six tree-ring-width chronologies from P. tabulaeformis and P. massoniana sampling sites in Mt. Jigong region, Central China. The results indicated that all chronologies from the two species had good consistency, precipitation in current April and mean temperature in current August or mean minimum temperature from current August to October were the main limiting factors of the two tree species growth, but the responses of P. massoniana ring-width to climatic factors was more complex than that of P. tabulaeformis. The results also showed that tree growth of 1999–2005 was the lowest growing period during 1979–2018, and P. massoniana grew better than P. tabulaeformis before 2005 and vice versa after 2005. Comparing low growth years of trees, we identified to study tree growth resilience. The calculations from 1988, 1999–2005 and 2011 drought years indicated that P. tabulaeformis had more increased resilience to extreme droughts than that of P. massoniana, and the two species had stronger ecological recovery and resilience under global warming and non-extreme drought conditions in the recent 40 years. These results have implications for predicting tree resilience and identifying tree species in heterogeneous forest landscapes vulnerable to future climate change in climatic transition zone.     

Stories hidden in tree rings: A review on the application of stable carbon isotopes to dendrosciences

During the last 25 years, the dendrochronology community has benefited from the application of stable carbon isotopes in tree rings to answer a number of research questions, which has resulted in an exponential burst in the number of publications related to this discipline. Here, we perform a literature review of the most influential topics (scope, methodology, targeted species, and climatic signals) that have shaped the research agenda and its impact on the scholarly output over the recent decades. Based on a total of 550 publications, we observed that: (1) conifers are the most investigated tree functional type, being included in over two-thirds of studies; (2) although being a subject of debate, the material of choice for carbon isotope analyses is still cellulose, for which the extraction procedure has been refined with methodological improvements over the years; (3) a shift in the application of carbon isotopes has occurred from proxies of climatic information for paleoclimatic reconstructions to tools for the understanding of short- and long-term tree functioning; and (4) such shift in research scope is apparently linked to an increasing number of publications showing drought-related signals governing isotope time series in the context of current climate change. Besides, we also assessed the number and outcome of publications analyzing ¹³C-derived intrinsic water-use efficiency (WUE_i) trends within the framework formulated by Saurer et al. (2004). We found that leaf intercellular CO₂ concentration responding proportionally to the increase in atmospheric CO₂ is the most common scenario reported across continents, but with changing importance relative to other scenarios depending on the biome examined. We also detected that climate plays a dominant role over any potential CO₂ fertilization linked to increasing WUE_i. Looking for new and thrilling research avenues, future studies should further examine δ¹³C fluctuations at intra-annual resolution, explore its links to wood characteristics, and disentangle δ¹³C signals of the distinct wood constituents for a better understanding of tree functioning at varying spatiotemporal scales, also benchmarking vegetation models of different complexities.     

Impact of environmental conditions on fruit production patterns of shea tree (Vitellaria paradoxa C.F.Gaertn) in West Africa

A better knowledge of the impact of environmental conditions on shea tree’s fruit production is critical to improve the species management. Fruit production of 237 shea trees was monitored over five successive years (2014–2018) to understand how climatic variables, shea tree population and land use could affect fruit production patterns of the species in Burkina Faso. Data were collected in 12 shea tree populations distributed in three climatic zones with two contrast land use systems. The results showed that fruit production was negatively correlated with mean annual temperature, temperature seasonality, rainfall seasonality and solar radiation, while it was positive with annual rainfall. Therefore, fruiting modelling is needed to predict the impact of future climate change on reproductive ability of the species. In each climatic zone, fruit production was significantly different among shea tree populations (p < 0.05). Within populations, fruit production greatly varies among years with specific patterns of variation. Land use had significant effect on fruit production of shea tree (p < 0.05). Annually, shea trees produced about 12 times more in agroforestry parklands than in protected areas. Interannual variation in fruit production at individual tree level was higher in protected areas. The cultivation of shea tree is recommended to improve its fruit productivity.     

Ecological adaptation of the shea butter tree (Vitellaria paradoxa C.F. Gaertn.) along climatic gradient in Bénin,West Africa

The ecological adaptation of shea butter trees was assessed based on their dendrometric and production traits in four shea butter tree parks occurring in different climatic zones of Bénin. A total of 99 rectangular plots of 50 × 30 m were established within the four parks according to a random sampling scheme. In each plot, all trees with a diameter at breast height (dbh) >10 cm were inventoried and measured for stem and crown diameters, and total height. The production of 120 productive shea butter trees was quantified. Collected data were used to compute structural parameters for each park. Moreover, stem diameter and height structures of the trees were established. Principal component analysis was performed on the dendrometric variables, and the first three components were correlated with the climatic parameters. Results revealed significant differences between parks in most of the dendrometric and production parameters of shea butter trees. For all the four parks, stem diameter and height structures present a Gaussian shape with left dissymmetry. In the Guinean zone, shea butter trees develop large crowns but produce little quantities of fruits, whereas in the Sudanian regions, the opposite trend was observed.     

Regulating effects of climate,net primary productivity,and nitrogen on carbon sequestration rates in temperate wetlands,Northeast China

Temperate wetlands in the Northern Hemisphere have high long-term carbon sequestration rates, and play critical roles in mitigating regional and global atmospheric CO₂ increases at the century timescale. We measured soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP) from 11 typical freshwater wetlands (Heilongjiang Province) and one saline wetland (Jilin Province) in Northeast China, and estimated carbon sequestration rates using ²¹⁰Pb and ¹³⁷Cs dating technology. Effects of climate, net primary productivity, and nutrient availability on carbon sequestration rates (R_carbon) were also evaluated. Chronological results showed that surface soil within the 0–40 cm depth formed during the past 70–205 years. Soil accretion rates ranged from 2.20 to 5.83 mm yr⁻¹, with an average of 3.84 ± 1.25 mm yr⁻¹ (mean ± SD). R_carbon ranged from 61.60 to 318.5 gC m⁻² yr⁻¹ and was significantly different among wetland types. Average R_carbon was 202.7 gC m⁻² yr⁻¹ in the freshwater wetlands and 61.6 gC m⁻² yr⁻¹ in the saline marsh. About 1.04 × 10⁸ tons of carbon was estimated to be captured by temperate wetland soils annually in Heilongjiang Province (in the scope of 45.381–51.085°N, 125.132–132.324°E). Correlation analysis showed little impact of net primary productivity (NPP) and soil nutrient contents on R_carbon, whereas climate, specifically the combined dynamics of temperature and precipitation, was the predominant factor affecting R_carbon. The negative relationship observed between R_carbon and annual mean temperature (T) indicates that warming in Northeast China could reduce R_carbon. Significant positive relationships were observed between annual precipitation (P), the hydrothermal coefficient (defined as P/AT, where AT was accumulative temperature ≥10 °C), and R_carbon, indicating that a cold, humid climate would enhance R_carbon. Current climate change in Northeast China, characterized by warming and drought, may form positive feedbacks with R_carbon in temperate wetlands and accelerate carbon loss from wetland soils.     

Endemic Foci of the Tick-Borne Relapsing Fever Spirochete Borrelia crocidurae in Mali,West Africa,and the Potential for Human Infection

Background

Tick-borne relapsing fever spirochetes are maintained in endemic foci that involve a diversity of small mammals and argasid ticks in the genus Ornithodoros. Most epidemiological studies of tick-borne relapsing fever in West Africa caused by Borrelia crocidurae have been conducted in Senegal. The risk for humans to acquire relapsing fever in Mali is uncertain, as only a few human cases have been identified. Given the high incidence of malaria in Mali, and the potential to confuse the clinical diagnosis of these two diseases, we initiated studies to determine if there were endemic foci of relapsing fever spirochetes that could pose a risk for human infection.

Methodology/Principal Findings

We investigated 20 villages across southern Mali for the presence of relapsing fever spirochetes. Small mammals were captured, thin blood smears were examined microscopically for spirochetes, and serum samples were tested for antibodies to relapsing fever spirochetes. Ornithodoros sonrai ticks were collected and examined for spirochetal infection. In total, 11.0% of the 663 rodents and 14.3% of the 63 shrews tested were seropositive and 2.2% of the animals had active spirochete infections when captured. In the Bandiagara region, the prevalence of infection was higher with 35% of the animals seropositive and 10% infected. Here also Ornithodoros sonrai were abundant and 17.3% of 278 individual ticks tested were infected with Borrelia crocidurae. Fifteen isolates of B. crocidurae were established and characterized by multi-locus sequence typing.

Conclusions/Significance

The potential for human tick-borne relapsing fever exists in many areas of southern Mali.     

Moisture-driven changes in the sensitivity of the radial growth of Picea crassifolia to temperature,northeastern Tibetan Plateau

Precipitation is one of the most important climate factors controlling tree growth, yet it is not fully understood how changes in precipitation affect the relationship between growth and temperature. On the northeastern edge of the Tibetan Plateau, nine tree-ring chronologies of Picea crassifolia were developed along a precipitation gradient from semi-arid (mean annual precipitation, 255 mm) to semi-humid (710 mm). We analyze the growth-climate relationships along this precipitation gradient and assess whether these associations are regulated by local precipitation. From 1960 to 2014, temperature increased significantly while precipitation remained stable at the nine sampling sites. The radial growth of P. crassifolia decreased at the semi-arid sites but increased at the semi-humid sites. Growth-temperature relationships gradually changed from negative to positive along the precipitation gradient (from dry to wet sites), particularly during summer. The moist P. crassifolia sites are also characterized by positive correlations with the Palmer Drought Severity Index. The temporal growth-temperature relationships varied significantly among the different spruce sites over the last five decades. Although temperature remains the main factor controlling the growth of P. crassifolia, local precipitation variability is becoming increasingly important. Our findings indicate that considering species distribution areas supports the analyses of the impact of climate change on tree growth.     

Species-specific climate sensitivity of tree growth in Central-West Germany

Growth responses to twentieth century climate variability of the three main European tree species Fagus sylvatica, Quercus petraea, and Pinus sylvestris within two temperate low mountain forest sites were analyzed, with particular emphasis on their dependence upon ecological factors and temporal stability in the obtained relationships. While site conditions in Central (~51°N, 9°E, KEL) and West (50.5°N, 6.5°E, EIF) Germany are similar, annual precipitation totals of ≅700 mm and ≅1,000 mm describe a maritime-continental gradient. Ring-width samples from 228 trees were collected and PCA used to identify common growth patterns. Chronologies were developed and redundancy analysis and simple correlation coefficients calculated to detect twentieth century temperature, precipitation, and drought fingerprints in the tree-ring data. Summer drought is the dominant driver of forest productivity, but regional and species-specific differences indicate more complex influences upon tree growth. F. sylvatica reveals the highest climate sensitivity, whereas Q. petraea is most drought tolerant. Drier growth conditions in KEL result in climate sensitivity of all species, and Q. petraea shifted from non-significant to significant drought sensitivity during recent decades at EIF. Drought sensitivity dynamics of all species vary over time. An increase of drought sensitivity in tree growth was found in the wetter forest area EIF, whereas a decrease occurred in the middle of the last century for all species in the drier KEL region. Species-specific and regional differences in long-term climate sensitivities, as evidenced by temporal variability in drought sensitivity, are potential indicators for a changing climate that effects Central-West German forest growth, but meanwhile hampers a general assessment of these effects.     

Characterization of Aerosolized Bacteria and Fungi From Desert Dust Events in Mali, West Africa

Millions of metric tons of African desert dust blow across the Atlantic Ocean each year, blanketing the Caribbean and southeastern United States. Previous work in the Caribbean has shown that atmospheric samples collected during dust events contain living microbes, including plant and opportunistic human pathogens. To better understand the potential downwind public health and ecosystem effects of the dust microbes, it is important to characterize the source population. We describe 19 genera of bacteria and 3 genera of fungi isolated from air samples collected in Mali, a known source region for dust storms, and over which large dust storms travel.     

Dendrochronological potential of four neotropical dry-forest tree species: Climate-growth correlations in northeast Brazil

Tropical dry forests (TDF) are highly important tropical forest ecosystems. Yet, these forests are highly threatened, usually neglected and only poorly studied. Understanding the long-term influences of environmental conditions on tree growth in these forests is crucial to understand the functioning, carbon dynamics and potential responses to future climate change of these forests. Dendrochronology can be used as a tool to provide these insights but has only scantly been applied in (dry) tropical forests. Here we evaluate the dendrochronological potential of four Caatinga neotropical dry forest tree species – Aspidosperma pyrifolium, Ziziphus joazeiro, Tabebuia aurea, and Libidibia ferrea – collected in two locations in northeastern Brazil (Sergipe state). We provide an anatomical characterization of the ring boundaries for the four species and investigate correlations of their growth with local and regional climatic variables. All four species form annual rings and show high inter-correlation (up to 0.806) and sensitivity (up to 0.565). Growth of all species correlated with local precipitation as well as with sea-surface temperatures in the tropical Atlantic and/or tropical Pacific oceans. We also show teleconnections between growth and the El Niño South Oscillation. The strong dependence of tree on precipitation is worrisome, considering that climate change scenarios forecast increased drought conditions in the Caatinga dry forest. Including more species and expanding dendrochronological studies to more areas would greatly improve our understanding of tree growth and functioning in TDFs. This type of knowledge is essential to assist the conservation, management and restoration of these critical tropical ecosystems.     

Structural attributes,tree-ring growth and climate sensitivity of Pinus nigra Arn. at high altitude: common patterns of a possible treeline shift in the central Apennines (Italy)

European black pine (Pinus nigra ssp. nigra Arnold) encroachment at increasing elevation has been analyzed at four treeline ecotones of the central Apennines (Italy). The study sites are located along a North-South gradient of 170 km across Marche and Abruzzo regions in Central Italy. The aims of this study were: (i) to detect possible common patterns of structural attributes of black pine regeneration at the treeline ecotone; (ii) to date the seedlings germination and (iii) to assess the climate influence on the pine upward encroachment process also using intra-annual density fluctuations (IADFs) in tree-rings. We sampled 658 encroached black pine trees above the current treeline to the mountain top. All individuals were mapped and their basal stem diameter, total height, annual height increments and other structural attributes measured. One increment core was extracted from stem base of most samples for cambial age determination and detection of intra-annual density fluctuations (IADF). At two sites we also extracted cores at DBH from forest trees to assess climate–growth relationships of black pine. We used multivariate analysis (PCA) to explore the correlation structure of the main tree attributes, regression analysis to relate radial and height increment and dendroclimatic analysis to assess the influence of climate on tree growth and IADF formation.Most black pine trees were located at high altitude and their structural attributes were similar at the four sites where the pine encroachment process started between 30 and 40 years ago featuring similar germination peaks and growth patterns. Black pine is particularly sensitive to maximum temperatures and IADF occurred in mid-late summer with highest frequency peaks between 2003 and 2004. The pine encroachment process, besides the differences of environmental features and land use histories of the four study sites, appears synchronic and spatially diffused. Consistent tree-growth dynamics and the species adaptation to a warming climate are signals envisaging a possible treeline upward shift.     

气候变暖对长白山主要树种的潜在影响

应用LINKAGES模型对长白山自然保护区内主要树种在各斑块类型中对气候变化的潜在响应进行了模拟,模拟时选择了目前和未来变暖2种气候条件,对于目前气候状态,模型使用目前气象参数;而对于未来变暖气候,则按温度增加5℃,降水无明显变化作为模拟假设,温度的增加假定各月都相同,即各月均增加5度,模拟结果表明,对于高山岳桦林,气温变暖后岳桦依然扮演重要角色,但落叶松,云极,冷杉等目前这一林带的伴生树种,在气温上升后,其生物量均有较大辐度的增加,部分占据目前岳桦的位置,即目前下部的云冷杉林带有上移的趋势;对于亚高山云冷杉林,其优势种云杉和冷杉在气温变暖后,生物量有较大幅度的增加,落叶松虽有增加的趋势但幅度较小,即云杉和冷杉在未来气温变暖后依然是这一林带的优势种,但生长会加快,阔叶红松林的主要建群种在气温升高后,其生物量只有较小的增加,其它主要伴生种的生物量随气温上升的增加趋势非常相似,表明阔叶红松林在未来气候变暖情况下仍将维持目前的结构状态。     

Lack of secular change in male adult stature in rural Mali (West Africa)

A study has been carried out on a sample of 2,158 male subjects between 20 and 50 years old representative of the rural Malian population (West Africa), and the results are compared with historic data obtained since 1885. This comparison suggests that there has been no modification in stature during this century. The analysis of each ethnic group does not show any disparity. Our results are in agreement with the theory that certain factors lead to the secular increase of stature in developed countries. These etiologic factors are not found in our West African population.     

Genetic differentiation of Anopheles gambiae s.s. populations in Mali,West Africa,using microsatellite loci

Anopheles gambiae sensu stricto is a principal vector of malaria through much of sub-Saharan Africa, where this disease is a major cause of morbidity and mortality in human populations. Accordingly, population sizes and gene flow in this species have received special attention, as these parameters are important in attempts to control malaria by impacting its mosquito vector. Past measures of genetic differentiation have sometimes yielded conflicting results, in some cases suggesting that gene flow is extensive over vast distances (6000 km) and is disrupted only by major geological disturbances and/or barriers. Using microsatellite DNA loci from populations in Mali, West Africa, we measured genetic differentiation over uniform habitats favorable to the species across distances ranging from 62 to 536 km. Gene flow was strongly correlated with distance (r(2) = 0.77), with no major differences among chromosomes. We conclude that in this part of Africa, at least, genetic differentiation for microsatellite DNA loci is consistent with traditional models of isolation by distance.     

Evidence for indigenous selection and distribution of the shea tree, Vitellaria paradoxa, and its potential significance to prevailing parkland savanna tree patterns in sub-Saharan Africa north of the equator

Aim Woody vegetation patterns in African savannas north of the equator are closely connected to human presence, but the distinctions between natural and anthropogenic landscapes have not been clear to many observers. Criteria for identifying savanna landscapes on a continuum of intensity of anthropic impact are explored. Methods A key savanna tree species, Vitellaria paradoxa (Sapotaceae), was used as model for evaluating anthropic impact. Fruits harvested from tree populations across the species range were analysed for variation in traits valued by indigenous peoples. A simple selection index was used to scale tree populations from a hypothetical wild state to a hypothetical domesticated state. Index values were compared with trait values along climate zone gradients and evaluated in the context of indigenous savanna management practices and historical species distribution reports. Results Trait values such as fruit size and shape, pulp sweetness, and kernel fat content show a significant influence of temperature and rainfall. At the same time, the mean values of groups of traits vary perpendicular to the general climatic zone gradient. Selection index values between Vitellaria populations vary up to sixfold, with highest values in central Burkina Faso. Comparison of present day Vitellaria distribution with historical range limits show range expansion by human migration. Main conclusions The prevalence of major economic tree species in the savannas of Africa north of the equator is a strong indicator of human involvement in tree dispersal. This conclusion is supported by paleobotanical evidence and by recent Vitellaria range expansion as a result of human migration. The presence of high mean values of several Vitellaria fruit traits in central Burkina Faso suggests that selection for desired characteristics has occurred. The impact of indigenous savanna peoples on woody species composition and spatial distribution is probably much greater than usually thought and is the result of a deliberate strategy of altering the landscape to provide needed human resources.     

The effect of individual genetic heterozygosity on general homeostasis,heterosis and resilience in Siberian larch (Larix sibirica Ledeb.) using dendrochronology and microsatellite loci genotyping

The genetic mechanisms underlying the relationship of individual heterozygosity (IndHet) with heterosis and homeostasis are not fully understood. Such an understanding, however, would have enormous value as it could be used to identify trees better adapted to environmental stress. Dendrochronology data, in particular the individual average radial increment growth of wood measured as the average tree ring width (AvTRW) and the variance of tree ring width (VarTRW) were used as proxies for heterosis (growth rate measured as AvTRW) and homeostasis (stability of the radial growth of individual trees measured as VarTRW), respectively. These traits were then used to test the hypothesis that IndHet can be used to predict heterosis and homeostasis of individual trees. Wood core and needle samples were collected from 100 trees of Siberian larch (Larix sibirica Ledeb.) across two populations located in Eastern Siberia. DNA samples were obtained from the needles of each individual tree and genotyped for eight highly polymorphic microsatellite loci. Then mean IndHet calculated based on the genotypes of eight loci for each tree was correlated with the statistical characteristics of the measured radial growth (AvTRW and VarTRW) and the individual standardized chronologies. The analysis did not reveal significant relationships between the studied parameters. In order to account for the strong dependence of the radial growth on tree age the age curves were examined. An original approach was employed to sort trees into groups based on the distance between these age curves. No relationship was found between these groups and the groups formed based on heterozygosity. However, further work with more genetic markers and increased sample sizes is needed to test this novel approach for estimating heterosis and homeostasis.