Preserving multicentennial climate variability in long tree-ring records is critically important for reconstructing the full range of temperature variability over the past 1000 years. This allows the ...putative "Medieval Warm Period" (MWP) to be described and to be compared with 20th-century warming in modeling and attribution studies. We demonstrate that carefully selected tree-ring chronologies from 14 sites in the Northern Hemisphere (NH) extratropics can preserve such coherent large-scale, multicentennial temperature trends if proper methods of analysis are used. In addition, we show that the average of these chronologies supports the large-scale occurrence of the MWP over the NH extratropics.
The effects of climate change on Arctic ecosystems can range between various spatiotemporal scales and may include shifts in population distribution, community composition, plant phenology, primary ...productivity and species biodiversity. The growth rates and age structure of tundra vegetation as well as its response to temperature variation, however, remain poorly understood because high‐resolution data are limited in space and time. Anatomical and morphological stem characteristics were recorded to assess the growth behaviour and age structure of 871 dwarf shrubs from 10 species at 30 sites in coastal East Greenland at ˜70°N. Recruitment pulses were linked with changes in mean annual and summer temperature back to the 19th century, and a literature review was conducted to place our findings in a pan‐Arctic context. Low cambial activity translates into estimated average/maximum plant ages of 59/204 years, suggesting relatively small turnover rates and stable community composition. Decade‐long changes in the recruitment intensity were found to lag temperature variability by 2 and 6 years during warmer and colder periods, respectively (r = 0.85₁₉₆₁–₂₀₀₀ ₐₙd ₁₈₈₁–₁₉₂₀). Synthesis. Our results reveal a strong temperature dependency of Arctic dwarf shrub reproduction, a high vulnerability of circumpolar tundra ecosystems to climatic changes, and the ability of evaluating historical vegetation dynamics well beyond the northern treeline. The combined wood anatomical and plant ecological approach, considering insights from micro‐sections to community assemblages, indicates that model predictions of rapid tundra expansion (i.e. shrub growth) following intense warming might underestimate plant longevity and persistence but overestimate the sensitivity and reaction time of Arctic vegetation.
Identifying to what degree inherent characteristics of plant species and their variation in response to their environment regulate the temporal stability of plant populations is important to ...understand patterns of species coexistence and the stability of ecosystems. Longevity is a key characteristic of plant life history and an important component of demographic storage, but age is usually unknown for herbaceous species.
In a 12‐year‐old biodiversity experiment (Jena Experiment) comprising 80 grassland communities with six levels of plant species richness (1, 2, 4, 8, 16 and 60 species) and four levels of functional groups richness (1, 2, 3 and 4 functional groups), we studied populations of 38 dicotyledonous forb species (N = 1,683 plant individuals). The sampled individuals represented three plant functional groups (legumes, small herbs and tall herbs) and two different growth forms (species with long‐lived primary roots and clonal species with rhizomes/stolons). We assessed the age of plant individuals by means of growth ring analysis and related the age of plant populations to their temporal stability in terms of peak biomass production.
On average, plant species richness did not affect the mean age of the populations or the maximum age of individuals found in a population. Age of herbs with taproots increased and age of herbs with clonal growth decreased with increasing species richness, cancelling out each other when growth forms were analysed together. Mean population age was lowest for small herbs and highest for tall herbs, while legumes had an intermediate population age. Herbs with a taproot were on average older than herbs with a rhizome. Across all species‐richness levels, populations with older individuals were more stable in terms of biomass production over time.
Synthesis. Our study shows for the first time across multiple species that the longevity of forbs is affected by the diversity of the surrounding plant community, and that plant longevity as an important component of demographic storage increases the temporal stability of populations of grassland forb species.
Our study shows for the first time across multiple species that the longevity of forbs is affected by the diversity of the surrounding plant community, and that plant longevity as an important component of demographic storage increases the temporal stability of populations of grassland forb species.
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Fine roots support the water and nutrient demands of plants and supply carbon to soils. Quantifying turnover times of fine roots is crucial for modeling soil organic matter dynamics and constraining ...carbon cycle-climate feedbacks. Here we challenge widely used isotope-based estimates suggesting the turnover of fine roots of trees to be as slow as a decade. By recording annual growth rings of roots from woody plant species, we show that mean chronological ages of fine roots vary from <1 to 12 years in temperate, boreal and sub-arctic forests. Radiocarbon dating reveals the same roots to be constructed from 10 ± 1 year (mean ± 1 SE) older carbon. This dramatic difference provides evidence for a time lag between plant carbon assimilation and production of fine roots, most likely due to internal carbon storage. The high root turnover documented here implies greater carbon inputs into soils than previously thought which has wide-ranging implications for quantifying ecosystem carbon allocation.
We investigated the response of conifer trees in northern Eurasia to climate change and increasing CO2 over the last century by measuring the carbon isotope ratio in tree rings. Samples from Larix, ...Pinus and Picea trees growing at 26 high‐latitude sites (59–71°N) from Norway to Eastern Siberia were analysed. When comparing the periods 1861–1890 and 1961–1990, the isotope discrimination and the ratio of the intercellular to ambient CO2 concentration (ci/ca) remained constant for trees growing in mild oceanic climate and under extremely cold and dry continental conditions. This shows a strong coordination of gas‐exchange processes, consisting in a biochemical acclimation and a reduction of the stomatal conductance. The correlation for ci/ca between the two investigated periods was particularly strong for Larix (r2=0.90) and Pinus (r2=0.94), but less pronounced for Picea (r2=0.47). Constant ci/ca under increasing CO2 in the atmosphere resulted in improved intrinsic water‐use efficiency (Wi), the amount of water loss at the leaf level per unit carbon gain. We found that 125 out of 126 trees showed increasing Wi from 1861 to 1890 to 1961 to 1990, with an average improvement of 19.2±0.9% (mean±SE). The adaptation in gas exchange and reduced transpiration of trees growing in this region must have had a strong impact on the water and energy budget, resulting in a drier and warmer surface air layer today than would exist without this vegetation–climate feedback.
The persistence of plant populations depends on the ability of individuals to cope with the conditions provided by the community. So far, it is not known whether differences in the diversity and ...composition of plant communities affect the age structure of plant populations or the expression of stem anatomical traits reflecting investment into plant growth and storage. We analyzed annual growth rings in the secondary xylem and measured stem anatomical traits in individuals from 18 populations of Plantago lanceolata growing in a 12‐year old grassland biodiversity experiment (Jena Experiment). Plant individuals of P. lanceolata were on average older and reproduced later with increasing species richness. Individuals of P. lanceolata were slightly younger and the age distribution within populations skewed to younger individuals in the presence of grasses. The presence of legumes did not affect mean age, but led to a more even age distribution within populations. The width of growth‐related tissues (xylem, phloem, phellem) decreased with increasing species richness. Plant diversity‐effects on storage‐related tissues (pith, cortex) were less consistent, as pith showed increasing width with species richness, while cortex did not change with plant diversity. Our results imply that plant diversity effects on population age structure and the expression of stem anatomical traits of P. lanceolata reflect a tradeoff: growth and turnover is fast at low diversity (younger age, higher allocation to growth‐related tissue, faster generative reproduction), while it is slow at high diversity (older age, higher allocation to storage‐related tissue, later generative reproduction).
Age‐dependence of the demographic rates survival, fecundity and individual growth is a fundamental aspect of population biological theory. Knowledge about plant ageing can also be important for ...conservation and agriculture as it will improve the accuracy of population viability assessments and long‐term performance assessments in perennial crops. Recent studies show age effects on demographic rates for several plant species, yet much remains to be learned about the patterns and mechanisms of plant ageing, particularly about how age effects interact with the environment and with plant size.
We collected age‐and‐size‐based demographic data, as well as individual‐based environmental data, for the perennial herb Plantago lanceolata in Denmark over three annual transitions (4 years). We combined frequent field monitoring of carefully mapped individuals with the underused technique of root histology to determine age of herbaceous plants. We used generalized linear mixed effects models to assess how age, soil properties and year influenced survival, growth and reproduction.
Our results show no strong evidence of consistent age declines, rather, we found mostly positive effects of age on vital rates. For all vital rates, i.e. survival, growth, flowering and reproductive output, age effects also differed significantly among years. Additionally, we detected an interactive effect of age and size in the growth model. Size, and temporal and spatial environmental variation also affected vital rates independently of age.
Synthesis. Our study shows that age‐dependence of demographic rates can depend both on individual size and environmental variation. These results suggest that a consideration of potential age‐interactions may improve the accuracy of comparative studies of ageing and population projections. Moreover, this study shows that much is still unknown about how plant ageing can be affected by the environment.
Our study shows that age‐dependence of demographic rates can depend both on individual size and environmental variation. These results suggest that a consideration of potential age‐interactions may improve the accuracy of comparative studies of ageing and population projections. Moreover, this study shows that much is still unknown about how plant ageing can be affected by the environment.
The area covered by boreal forests accounts for ∼16% of the global and 22% of the Northern Hemisphere landmass. Changes in the productivity and functioning of this circumpolar biome not only have ...strong effects on species composition and diversity at regional to larger scales, but also on the Earth's carbon cycle. Although temporal inconsistency in the response of tree growth to temperature has been reported from some locations at the higher northern latitudes, a systematic dendroecological network assessment is still missing for most of the boreal zone. Here, we analyze the geographical patterns of changes in summer temperature and precipitation across northern Eurasia >60 °N since 1951 AD, as well as the growth trends and climate responses of 445 Pinus, Larix and Picea ring width chronologies in the same area and period. In contrast to widespread summer warming, fluctuations in precipitation and tree growth are spatially more diverse and overall less distinct. Although the influence of summer temperature on ring formation is increasing with latitude and distinct moisture effects are restricted to a few southern locations, growth sensitivity to June-July temperature variability is only significant at 16.6% of all sites (p ≤ 0.01). By revealing complex climate constraints on the productivity of Eurasia's northern forests, our results question the a priori suitability of boreal tree-ring width chronologies for reconstructing summer temperatures. This study further emphasizes regional climate differences and their role on the dynamics of boreal ecosystems, and also underlines the importance of free data access to facilitate the compilation and evaluation of massively replicated and updated dendroecological networks.
Trait variation across species plays a fundamental role in ecology and evolution, but quantitative analyses of key life-history traits under natural conditions generally do not include a large number ...of species. In a comparative study, we analyzed interspecific variation in adult age as a minimum estimate of the lifespan of 708 vascular plant species along elevational gradients from 263–3175 m a.s.l. and compared this variation with predictions from r-K selection theory and the metabolic theory of ecology (MTE). Age data based on annual ring counts of root collars and rhizomes were combined with a systematic sample of current species distributions in Switzerland (453 plots, each 1 km2). Elevation and temperature trends were investigated by regression analyses of the variation in adult age across species and species assemblages (median adult age) at the landscape level. We included climate, land use and geology as environmental predictors in multiple regressions and considered phylogeny by eigenvector filtering. We found a general increase in adult age towards higher elevations at the level of overall interspecific variation, and this trend was also detectable within individual plant families. Species generally had a shorter lifespan under warmer climates and, in agreement with r-K prediction, in lowland agricultural landscapes. We found an exponential adult age-temperature relationship that is consistent with MTE. The estimate of the MTE parameter ‘activation energy’ for median adult age in multiple regression was 0.65 eV (95% CI 0.62–0.69 eV) which coincided with the predicted range of 0.60–0.70 eV. Our results imply that climate warming could accelerate species turnover rates by favoring short-lived species over the whole range of life histories and species assemblages. Besides the strong temperature relationship, residual variability and confounding factors demonstrate the need for additional research about interactions between broad-scale constraints and more local drivers of life-history variation.
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