We investigated several aspects of windthrow that are relevant to our understanding and management of forest ecosystems. As an example, we used an extreme event in December 2017, when the strongest storm in recent history occurred in the Slovenian Dinaric High Karst. We examined influential factors such as soil properties, wind speed, precipitation and ecological consequences for the affected forests. Soil properties were measured around standing and fallen silver fir trees at all three research sites. Tree species composition in the regeneration was observed on plots with chemical and acoustic ungulate deterrents and on control plots without deterrents. Economic estimates of yield loss due to damage were calculated at the national level. A model of the potential threat from windthrow was also developed based on data collected from windthrow events and meteorological data over the past 20 years. Our results indicate that soil depth and mineral fraction depth were similar at sites with and without damaged trees and were not the determining factors for tree toppling. Plots with acoustic deterrents showed the most effective regeneration development, the least decline in silver fir and the greatest increase in noble hardwood seedlings, while plots with chemical deterrents showed the least browsing damage. The estimated economic loss of €16.1 million is 6.6% less than the harvest under normal conditions. The economic loss was relatively low due to the nature of the storm, with the predominant type of damage being uprooted trees with no damaged trunks. The windthrow hazard model revealed that a large number of consecutive events with strong winds in each section weakened the stand, which was subsequently knocked down during the next extreme wind and rainfall event.
The monitoring of seasonal radial growth of woody plants addresses the ultimate question of when, how and why trees grow. Assessing the growth dynamics is important to quantify the effect of environmental drivers and understand how woody species will deal with the ongoing climatic changes. One of the crucial steps in the analyses of seasonal radial growth is to model the dynamics of xylem and phloem formation based on increment measurements on samples taken at relatively short intervals during the growing season. The most common approach is the use of the Gompertz equation, while other approaches, such as general additive models (GAMs) and generalised linear models (GLMs), have also been tested in recent years. For the first time, we explored artificial neural networks with Bayesian regularisation algorithm (BRNNs) and show that this method is easy to use, resistant to overfitting, tends to yield s‐shaped curves and is therefore suitable for deriving temporal dynamics of secondary tree growth. We propose two data processing algorithms that allow more flexible fits. The main result of our work is the XPSgrowth() function implemented in the radial Tree Growth (rTG) R package, that can be used to evaluate and compare three modelling approaches: BRNN, GAM and the Gompertz function. The newly developed function, tested on intra‐seasonal xylem and phloem formation data, has potential applications in many ecological and environmental disciplines where growth is expressed as a function of time. Different approaches were evaluated in terms of prediction error, while fitted curves were visually compared to derive their main characteristics. Our results suggest that there is no single best fitting method, therefore we recommend testing different fitting methods and selection of the optimal one.
Abstract Using a unique 8‐year data set (2010–2017) of phloem data, we studied the effect of temperature and precipitation on the phloem anatomy (conduit area, widths of ring, early and late phloem) and xylem‐ring width in two coexisting temperate tree species, Picea abies and Fagus sylvatica , from three contrasting European temperate forest sites. Histometric analyses were performed on microcores taken from tree stems in autumn. We found high interannual variability and sensitivity of phloem anatomy and xylem‐ring widths to precipitation and temperature; however, the responses were species‐ and site‐specific. The contrasting response of xylem and phloem‐ring widths of the same tree species to weather conditions was found at the two Slovenian sites generally well supplied with precipitation, while at the driest Czech site, the influence of weather factors on xylem and phloem ring widths was synchronised. Since widths of mean annual xylem and phloem increments were narrowest at the Czech site, this site is suggested to be most restrictive for the radial growth of both species. By influencing the seasonal patterns of xylem and phloem development, water availability appears to be the most important determinant of tissue‐ and species‐specific responses to local weather conditions.
<p>Radial growth, wood density and climate-growth relationship of four Douglas fir provenances were analysed separately for the juvenile and the adult phase. Two pairs of provenances were selected from an existing IUFRO provenance trial planted in 1971 based on their diameter at breast height and vitality. Increment cores were extracted from individual trees, on which we measured tree-ring widths (RW), earlywood widths (EWW) and latewood widths (LWW). Wood density was assessed in standing trees using resistance drilling. The climate-growth correlations were calculated between provenance chronologies of RW, EWW, LWW and latewood share, and day-wise aggregated Standardised Precipitation-Evapotranspiration Index (SPEI). We calculated the accumulated drought effects by aggregating climatic water deficits into a log-logistic probability distribution to obtain the SPEI index series of different seasons, starting from three weeks to nine months, including the effect of previous growing season. In all provenances, RW, and consequently EWW and LWW, were wider in juvenile period than in adult period. Share of latewood was in all cases higher in juvenile wood then in mature wood. All four provenances have similar wood density in both analysed growth phases. The general effect of wet conditions in current growing season was positive, indicating that Douglass fir&#8217;s radial growth was favoured in moist years, and reduced in dry years. The significant positive effect of SPEI on LW was observed also at the beginning of previous growing season. Our analysis showed that when selecting the most promising provenance for planting, it needs to be considered that growth rate may change from juvenile to adult period. Only by combining climate-growth analysis with measurements of external tree features we can compare and assess the suitability of certain provenances for planting in current and future climate.</p>
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