Relationships between trunk radial growth and fruit yield in apple and pear trees on size-controlling rootstocks.

BACKGROUND AND AIMS: Understanding the mutual co-ordination of vegetative and reproductive growth is important in both agricultural and ecological settings. A competitive relationship between vegetative growth and fruiting is often highlighted, resulting in an apparent trade-off between structural growth and fruit production. However, our understanding of factors driving this relationship is limited. METHODS: We used four scions grafted onto a series of size-controlling rootstocks to evaluate the relationships between the annual fruit yield and radial growth of trunks, branches and roots. To assess tree radial growth, we measured ring widths on extracted tree cores, which is an approach not frequently used in a horticultural setting. KEY RESULTS: We found that the yield and radial growth were negatively related when plotted in absolute terms or as detrended and normalized indices. The relationship was stronger in low vigour trees, but only after the age-related trend was removed. In contrast, when trunk radial growth was expressed as basal area increment, the negative relationship disappeared, suggesting that the relationship between trunk radial growth and fruit yield might not be a true trade-off related to the competition between the two sinks. The effect of low yield was associated with increased secondary growth not only in trunks but also in branches and roots. In trunks, we observed that overcropping was associated with reduced secondary growth in a subsequent year, possibly due to the depletion of reserves. CONCLUSIONS: Our results show that variation in annual fruit yield due to tree ageing, weather cueing and inherent alternate bearing behaviour is reflected in the magnitude of secondary growth of fruit trees. We found little support for the competition/architecture theory of rootstock-induced growth vigour control. More broadly, our study aimed at bridging the gap between forest ecology and horticulture.

Regional flood occurrence in the culmination zone of medium-high mountain ranges by tree-ring based reconstruction: Frequency, triggers, dynamics.

Floods are among the most dangerous geohazards in Central Europe. Their occurrence is often the result of the cumulative contribution of sub-catchments in the culmination zone of a mountain range, which subsequently has a devastating effect in the foreland. However, data on discharges from gauging stations are mostly missing from these sites (high-gradient streams), which are crucial to understanding the origin of floods in low-lying populated areas where they can cause significant damage. Therefore, this study focuses on an extensive reconstruction of flood events in 13 sub-catchments in the culmination zone of the Orlicke hory Mts. Flood events were reconstructed using dendrogeomorphic approaches, currently the most accurate absolute dating method. The analysis revealed 111 floods in all sub-catchments during the 34 to 84 year period by dating 844 growth disturbances in a tree-ring series of 632 trees (Picea abies (L.) Karst.) damaged during the floods. Regional reconstruction across the mountain range revealed events of regional and local significance, with no direct link between event magnitude and areal extent. This is consistent with the two dominant rainfall patterns identified that likely triggered the floods (short-term extreme rainfall and medium-term above-average rainfall). In particular, however, the study revealed several patterns of spatial transformation of flood events from source sub-catchments to their form captured at gauging stations in the foreland. The combination of various lines of evidence (geomorphic mapping, growth disturbance patterns, spatial pattern of flooding) suggests a limited erosional effect of most of the reconstructed events. The findings thus shed new light on the overall dynamics of floods in the mountain massif and their impact on flood discharges in the foreland.

Historical activity of debris flows in the medium-high mountains: Regional reconstruction using dendrogeomorphic approach.

Detailed knowledge of the occurrence of debris flows in the past is key to understanding their linkage to changing climatic variables and their occurrence in the future. For a comprehensive understanding of the origin of these processes, regional reconstruction is optimal rather than detailed analysis of isolated catchments. This study presents the results of a dendrogeomorphic reconstruction of debris flows across an entire medium-high mountain range in Central Europe covering more than 500 km2. The tree-ring data allowed the reconstruction of 96 debris flow events at 21 sites. The average frequency of events was 6.8 per decade, which is comparable or higher compared to alpine valleys. A detailed analysis of potential precipitation triggers was also performed in the paper, whose magnitude significantly influenced not only the number of debris flows but also their magnitude. Debris flows occur in two forms in the study area, with channelized debris flows showing significantly higher magnitude but lower frequency than fan debris flows. The differences between the two types are probably due to the different source of material that is reactivated during precipitation events of different duration and magnitude.

Anatomical growth response of Fagus sylvatica L. to landslide movements.

Determining the age of landslide events is crucial for determining landslide risk, triggers, and also for predicting future landslide occurrence. Currently, the most accurate method for dating historical landslide events is dendrogeomorphic analysis. Unfortunately, the standard use of macroscopic growth responses of damaged trees for dating landslide activity suffers from many shortcomings. Thus, the aim of this study is to analyze in detail the growth response of trees to landslide movements at the anatomical level, a completely groundbreaking methodological approach. Ten specimens of European beech (Fagus sylvatica L.) were analyzed at two sampling heights, growing in two morphologically contrasting zones of the landslide area. Detailed anatomical analysis was focused on changes in morphometric parameters of the vessels and in the number of radial rays. The period (2008-2012) with the occurrence of the largest landslide movement (2010) recorded by long-term monitoring was analyzed. The results obtained revealed different anatomical responses in trees growing in different morphological zones of landslide. The tree responses on the ridge corresponded to the manifestations of tension wood formation, which corresponded to the stem tilting due to the landslide block movement. In the case of the trees in the trenches, root damage due to the subsidence of the landslide block blocked the flux of phytohormones, and their accumulation caused a significant reduction in the parameters of vessels and an increase in the number of rays. The study also includes recommendations in the future application of anatomical analyses in landslide research resulting from the obtained results. Thus, the obtained findings will improve the acquisition of chronological data for the purpose of landslide risk assessment.

The age-dependent sensitivity of Picea abies (L.) H. Karst. to landslide movements.

Dendrogeomorphic dating of past landslide events is a valuable tool for the assessment of landslide activity, providing unique data for the analysis of triggers or the modelling of landslide behaviour in the future. Unfortunately, tree-ring-based methods as well as dating approaches suffer from some limitations. One of the less frequently addressed limits of dendrogeomorphic analysis concerns the changing capacity of trees to record landslide events in their tree-ring series with increasing age. This study uses, to date, the most extensive database of tree-ring series (1736) of 868 disturbed individuals of Picea abies (L.) H. Karst. subjected to 20 landslides in the Outer Wester Carpathians for the assessment of their age-dependent sensitivity. The distribution of the total number of 1485 growth disturbances (reaction wood - RW and abrupt growth suppression - GS) throughout all decades of tree life shows evidence of distinct changes in the capacity for trees to record landslide signals with increasing age. The occurrence of RW dominated in the juvenile decades of tree life and then increased again in the 9th decade. The frequency of GS gradually increased and culminated during the 7th and 8th decades. The two intensities of growth disturbance (strong and moderate) expressed temporally balanced ratios, suggesting an effect of disturbance intensity rather than changing tree age. The important factors controlling age-dependent tree sensitivity to landslide movements based on the results seem to be changing stem elasticity, decreasing annual increment rates, root system development and increasing tree body weight. Moreover, this study demonstrates that landslide type (e.g., rigid block vs. plastic flow-like landslides) and bedrock geology distinctly modify age-dependent sensitivity that should be taken into account during the sampling of trees for landslide dating.

Understanding complex slope deformation through tree-ring analyses.

Dendrogeomorphic methods are frequently used for the analysis of past landslide behaviour and have become the standard approach used to date landslide activity. Unfortunately, many questions related to the application of tree-rings to landslide analysis remain unsolved. This study points to the significance of dividing a large complex slope deformation area into homogenous zones to obtain as much relevant chronological data as possible and to help with a more precise landslide hazard assessment. The multidisciplinary approach included geophysical measurement and geomorphic mapping. The clay mineral content in weathered slope sediments was analysed to verify the presence of expanding minerals contributing to slope instability. Furthermore, 713 samples from 271 trees and 18 tree roots were analysed to create event chronologies for each zone. The results provided evidence about the different behaviours of each zone. The intensity of tree responses to slope movement significantly changed even within one isolated zone. Chronological data were used to identify landslide triggers using rainfall characteristics and indices for climate variability and extremes. The results suggested a significant contribution of spring rainfall to landslide activity. In addition, shallow landslides movement was dependent on above-average rainfall characteristics compared to the movement of deep-seated blocks. Tree-ring-based chronologies of individual zones were used to characterise the general concept of complex slope deformation development.

Dry Spells and Extreme Precipitation are The Main Trigger of Landslides in Central Europe.

Landslides are frequently triggered by extreme meteorological events which has led to concern and debate about their activity in a future greenhouse climate. It is also hypothesized that dry spells preceding triggering rainfall may increase slope predisposition to sliding, especially in the case of clay-rich soils. Here we combined dendrogeomorphic time series of landslides and climatic records to test the possible role of dry spells and extreme downpours on process activity in the Outer Western Carpathians (Central Europe). To this end, we tested time series of past frequencies and return periods of landslide reactivations at the regional scale with a Generalized Linear Mixed (GLM) model to explore linkages between landslide occurrences and triggering climate variables. Results show that landslide reactivations are concentrated during years in which spring and summer precipitation sums were significantly higher than usual, and that triggering mechanisms vary between different types of landslides (i.e. complex, shallow or flow-like). The GLM model also points to the susceptibility of landslide bodies to the combined occurrence of long, dry spells followed by large precipitation. Such situations are likely to increase in frequency in the future as climate models predict an enhancement of heatwaves and dry spells in future summers, that would be interrupted by less frequent, yet more intense storms, especially also in mountain regions.

Tree ring-based chronology of hydro-geomorphic processes as a fundament for identification of hydro-meteorological triggers in the Hrubý Jeseník Mountains (Central Europe).

Hydro-geomorphic processes have significantly influenced the recent development of valley floors, river banks and depositional forms in mountain environments, have caused considerable damage to manmade developments and have disrupted forest management. Trees growing along streams are affected by the transported debris mass and provide valuable records of debris flow/flood histories in their tree-ring series. Dendrogeomorphic approaches are currently the most accurate methods for creating a chronology of the debris flow/flood events in forested catchments without any field-monitoring or a stream-gauging station. Comprehensive studies focusing on the detailed chronology of hydro-geomorphic events and analysis of meteorological triggers and weather circulation patterns are still lacking for the studied area. We provide a spatio-temporal reconstruction of hydro-geomorphic events in four catchments of the Hrubý Jeseník Mountains, Czech Republic, with an analysis of their triggering factors using meteorological data from four nearby rain gauges. Increment cores from 794 coniferous trees (Picea abies [L.] Karst.) allowed the identification of 40 hydro-geomorphic events during the period of 1889-2013. Most of the events can be explained by extreme daily rainfalls (≥50mm) occurring in at least one rain gauge. However, in several cases, there was no record of extreme precipitation at rain gauges during the debris flow/flood event year, suggesting extremely localised rainstorms at the mountain summits. We concluded that the localisation, intensity and duration of rainstorms; antecedent moisture conditions; and amount of available sediments all influenced the initiation, spatial distribution and characteristics of hydro-geomorphic events. The most frequent synoptic situations responsible for the extreme rainfalls (1946-2015) were related to the meridional atmospheric circulation pattern. Our results enhance current knowledge of the occurrences and triggers of debris flows/floods in the Central European mountains in transition between temperate oceanic and continental climatic conditions and may prompt further research of these phenomena in the Eastern Sudetes in general.