Past crops yield dynamics reconstruction from tree-ring chronologies in the forest-steppe zone based on low- and high-frequency components

Interrelations of the yield variability of the main crops (wheat, barley, and oats) with hydrothermal regime and growth of conifer trees (Pinus sylvestris and Larix sibirica) in forest-steppes were investigated in Khakassia, South Siberia. An attempt has been made to understand the role and mechanisms of climatic impact on plants productivity. It was found that amongst variables describing moisture supply, wetness index had maximum impact. Strength of climatic response and correlations with tree growth are different for rain-fed and irrigated crops yield. Separated high-frequency variability components of yield and tree-ring width have more pronounced relationships between each other and with climatic variables than their chronologies per se. Corresponding low-frequency variability components are strongly correlated with maxima observed after 1- to 5-year time shift of tree-ring width. Results of analysis allowed us to develop original approach of crops yield dynamics reconstruction on the base of high-frequency variability component of the growth of pine and low-frequency one of larch

Species- and Age-Specific Growth Reactions to Extreme Droughts of the Keystone Tree Species across Forest-Steppe and Sub-Taiga Habitats of South Siberia

Over the coming decades, climate change can decrease forest productivity and stability in many semiarid regions. Tree-ring width (TRW) analysis allows estimation of tree sensitivity to droughts, including resistance (Rt) and resilience (Rc) indexes. It helps to find adaptive potential of individual trees and forest populations. On a forest stand scale, it is affected by habitat conditions and species’ ecophysiological characteristics, and on individual scale by tree genotype, age, and size. This study investigated TRW response to droughts in forest-steppe and sub-taiga of southern Siberia for keystone species Scots pine (Pinus sylvestris L.), Siberian larch (Larix sibirica Ledeb.), and silver birch (Betula pendula Roth.). Chronologies reacted positively to the Standardized Precipitation-Evapotranspiration Index (SPEI) of the previous July–September and current April–July. Depressed tree growth across region and droughts lasting over both intra-seasonal intervals were registered in 1965, 1974, and 1999. TRW-based Rt and Rc for these droughts did not reveal age- or size-related patterns. Higher growth stability indexes were observed for birch in sub-taiga and for conifers in forest-steppe. Larch at all sites had disadvantage against pine for 1965 and 1999 droughts aggravated by pest outbreaks, but adapted better to drought in 1974. Site aridity affected both tree growth stability and intensity of climatic response

Evidences of Different Drought Sensitivity in Xylem Cell Developmental Processes in South Siberia Scots Pines

Research Highlights: This study emphasized the importance of multi-parameter analyses along ecological gradients for a more holistic understanding of the complex mechanism of tree-ring formation. Background and Objectives: The analysis of climatic signals from cell anatomical features measured along series of tree-rings provides mechanistic details on how environmental drivers rule tree-ring formation. However, the processes of cell development might not be independent, limiting the interpretation of the cell-based climatic signal. In this study, we investigated the variability, intercorrelations and climatic drivers of wood anatomical parameters, resulting from consequent cell developmental processes. Materials and Methods: The study was performed on thin cross-sections from wood cores sampled at ~1.3 m stem height from mature trees of Pinus sylvestris L. growing at five sampling sites along an ecological gradient from cold and wet to hot and dry within continental Southern Siberia. Tracheid number per radial file, their diameters and wall thicknesses were measured along the radial direction from microphotographs for five trees per site. These parameters were then averaged at each site for earlywood and latewood over the last 50 tree rings to build site chronologies. Their correlations among themselves and with 21-day moving climatic series were calculated. Results: Our findings showed that wood formation was not simply the result of environmentally driven independent subprocesses of cell division, enlargement and wall deposition. These processes appear to be interconnected within each zone of the ring, as well as between earlywood and latewood. However, earlywood parameters tend to have more distinctive climatic responses and lower intercorrelations. On the other hand, there are clear indications that the mechanisms of cell division and enlargement share similar climatic drivers and are more sensitive to water limitation than the process of wall deposition. Conclusions: Indications were provided that (i) earlywood formation left a legacy on latewood formation, (ii) cell division and enlargement shared more similar drivers between each other than with wall deposition, and (iii) the mechanism of cell division and enlargement along the gradient switch from water to heat limitations at different thresholds than wall deposition

Warming induced changes in wood matter accumulation in tracheid walls of spruce

The warming-driven increase of the vegetation season length impacts both net productivity and phenology of plants, changing an annual carbon cycle of terrestrial ecosystems. To evaluate this influence, tree growth along the temperature gradients can be investigated on various organization levels, beginning from detailed climatic records in xylem cells’ number and morphometric parameters. In this study, the Borus Ridge of the Western Sayan Mountains (South Siberia) was considered as a forest area under rapid climate change caused by massive Sayano-Shushenskoe reservoir. Several parameters of the xylem anatomical structure in Siberian spruce (Picea obovata Ledeb.) were derived from normalized tracheidograms of cell radial diameter and cell wall thickness and analyzed during 50 years across elevational gradient (at 520, 960, and 1320 m a.s.l.). On the regional scale, the main warming by 0.42°C per decade occurs during cold period (November–March). Construction of the reservoir accelerated local warming substantially since 1980, when abrupt shift of the cold season temperature by 2.6°C occurred. It led to the vegetation season beginning 3–6 days earlier and ending 4–10 day later with more stable summer heat supply. Two spatial patterns were found in climatic response of maximal cell wall thickness: (1) temperature has maximal impact during 21-day period, and its seasonality shifts with elevation in tune with temperature gradient; (2) response to the date of temperature passing +9.5°C threshold is observed at two higher sites. Climate change yielded significantly bigger early wood spruce tracheids at all sites, but its impact on cell wall deposition process had elevational gradient: maximal wall thickness increased by 7.9% at the treeline, by 18.2% mid-range, and decreased by 4.9% at the lower boundary of spruce growth; normalized total cell wall area increased by 6.2%–6.8% at two higher sites but remained stable at the lowest one. We believe that these patterns are caused by two mechanisms of spruce secondary growth cessation: “emergency” induced by temperature drop versus “regular” one in warmer conditions. Therefore, autumn lengthening of growth season stimulated wood matter accumulation in tracheid walls mainly in cold environment, increasing role of boreal and mountain forests in carbon cycle

Precipitation reconstruction for the Khakassia region, Siberia, from tree rings

A nested July–June precipitation reconstruction for the period AD 1777–2012 was developed from multi-century tree-ring records of Pinus sylvestris L. (Scots pine) for the Republic of Khakassia in Siberia, Russia. Calibration and verification statistics for the period 1948–2012 show a high level of skill and account for a significant portion of the observed variance (>50%) irrespective of which period is used to develop or verify the regression model. Split-sample validation supports our use of a reconstruction model based on the full period of reliable observational data (1948–2012). Thresholds (25th and 75th percentiles) based on the empirical cumulative distribution of 1948–2012 observed precipitation were used to delineate dry years and wet years of the long-term reconstruction. The longest reconstructed dry period, defined as consecutive years with less than 25th percentile of observed July–June precipitation, was 3 years (1861–1863). There was no significant difference in the number dry and wet periods during the 236 years of the reconstructed precipitation. Maps of geopotential height anomalies indicate that dry years differ from wet years primarily in the location of an anomalous 500-mb ridge approximately over the study area

Small fluctuations in cell wall thickness in pine and spruce xylem: Signal from cambium?

In the conifer tree rings, each tracheid goes through three phases of differentiation before becoming an element of the stem water-conducting structure: division, extension, and cell wall thickening. These phases are long-lasting and separated temporally, especially cell wall thickening. Despite the numerous lines of evidence that external conditions affect the rate of growth processes and the final anatomical dimensions during the respective phases of tracheid differentiation, the influence of the environment on anatomical dimensions during the cell division phase (cambial activity) has not yet been experimentally confirmed. In this communication, we provide indirect evidence of such an effect through observations of the small fluctuations in the latewood cell wall thickness of rapidly growing tree rings, which exhibit a high cell production rate (more than 0.4 cells per day on average). Such small fluctuations in the cell wall thickness cannot be driven by variations in external factors during the secondary wall deposition phase, since this phase overlaps for several tens of latewood cells in the rings of fast-growing trees due to its long duration

Climatically driven yield variability of major crops in Khakassia (South Siberia)

We investigated the variability of yield of the three main crop cultures in the Khakassia Republic: spring wheat, spring barley and oats. In terms of yield values, variability characteristics, and climatic response, the agricultural territory of Khakassia can be divided into three zones: 1) the Northern Zone, where crops yield has a high positive response to the amount of precipitation, May-July, and a moderately negative one to the temperatures of the same period; 2) the Central Zone, where crops yield depends mainly on temperatures; and 3) the Southern Zone, where climate has the least expressed impact on yield. The dominant pattern in the crops yield is caused by water stress during periods of high temperatures and low moisture supply with heat stress as additional reason. Differences between zones are due to combinations of temperature latitudinal gradient, precipitation altitudinal gradient and presence of a well-developed hydrological network and the irrigational system as moisture sources in the Central Zone. More detailed analysis shows differences in the climatic sensitivity of crops during phases of their vegetative growth and grain development and, to a lesser extent, during harvesting period. Multifactor linear regression models were constructed to estimate climate- and autocorrelation-induced variability of the crops yield. These models allowed prediction of the possibility of yield decreasing by at least 2-11% in the next decade due to increasing of the regional summer temperatures

What prevails in climatic response of Pinus sylvestris in-between its range limits in mountains: slope aspect or elevation?

The roles of slope orientation and elevational temperature gradient were investigated for Scots pine (Pinus sylvestris L.) growth in the middle of its growth range, where these factors can significantly modulate microclimate and thus plant growth. We assumed that slope orientation causes more complex and severe effects than elevation because it influences all three main factors of plant growth: light, heat, and moisture. In addition to the total ring width, the earlywood and latewood width and latewood ratio were considered variables that contain information about tree ring growth during the season and wood structure over all tree life span on three sampling sites at different elevations and opposite slopes. Despite the observed dependence of pine growth rate on temperature and solar radiation, the mean latewood ratio is stable and similar between all sampling sites, being presumably defined by the genotype of individual trees. The seasonality of the climatic response of tree growth is bound to spatiotemporal variation of the vegetative season timing due to the elevational temperature lapse and local warming. However, its direction is primarily defined by slope orientation, where southern slope is moisture-limited, even at adjacent sites, and divergent climatic reactions of earlywood (weak moisture-limited in the last decades) and latewood growth (temperature-limited) were revealed on the northern slope

Tree Rings Reveal the Impact of Soil Temperature on Larch Growth in the Forest-Steppe of Siberia

Dendroclimatology has focused mainly on the tree growth response to atmospheric variables. However, the roots of trees directly sense the “underground climate,” which can be expected to be no less important to tree growth. Data from two meteorological stations approximately 140 km apart in southern Siberia were applied to characterize the spatiotemporal dynamics of soil temperature and the statistical relationships of soil temperature to the aboveground climate and tree-ring width (TRW) chronologies of Larix sibirica Ledeb. from three forest–steppe stands. Correlation analysis revealed a depth-dependent delay in the maximum correlation of TRW with soil temperature. Temperatures of both the air and soil (depths 20–80 cm) were shown to have strong and temporally stable correlations between stations. The maximum air temperature is inferred to have the most substantial impact during July–September (R = −0.46–−0.64) and early winter (R = 0.39–0.52). Tree-ring indices reached a maximum correlation with soil temperature at a depth of 40 cm (R = −0.49–−0.59 at 40 cm) during April–August. High correlations are favored by similar soil characteristics at meteorological stations and tree-ring sites. Cluster analysis of climate correlations for individual trees based on the K-means revealed groupings of trees driven by microsite conditions, competition, and age. The results support a possible advantage of soil temperature over air temperature for dendroclimatic analysis of larch growth in semiarid conditions during specific seasons

Variation of the hydrological regime of Bele-Shira closed basin in Southern Siberia and its reflection in the radial growth of Larix sibirica

This study analyses dynamics of the hydrological regime of Bele-Shira closed basin and evaluates the potential for using radial growth of Siberian larch (Larix sibirica) for its assessment. We investigated the relationships between different characteristics of the water level variation of Lake Shira, precipitation amount and long-term regional chronologies developed from 56 living trees and 32 dead trees on three sites across this basin. Graphical and correlation analysis indicate that the interannual change (June minus previous June) of the water level of Lake Shira is strongly positively related to the annual sum of precipitation from July to June and the radial growth of larch. It was shown that this hydrological characteristic integrates the current dynamics of the regional precipitation and moisture regime as a whole of the Bele-Shira closed basin on interannual and decadal scales. The water level of Lake Shira fluctuates on a multi-year timescale in synchrony with the cumulative sum of the tree-ring chronology and also has strong positive long-term trend, probably driven by the continual groundwater inflow from neighboring Lake Itkul. Delayed relationships of precipitation and radial growth with the Lake Shira level change are interpreted with reference to a water balance model of the closed basin. Results offer the possibility of reconstructing interannual and decadal variation of the hydrological regime during the last few centuries through regression models using tree-ring chronologies or the dynamics of climatic variables recovered from them