Combining Participatory Mapping and Geospatial Analysis Techniques to Assess Wildfire Risk in Rural North Vietnam.

Participatory mapping (PM) is a valuable research tool for assessing fire risk, especially in regions where data are difficult to collect or inconsistent; in such areas, the integration between crowdsourced data and geospatial techniques plays a fundamental role in gathering more consistent and reliable information. This study combines a participatory (community-based) mapping approach with geospatial techniques to assess fire risk in Van Chan district, northern Vietnam, an area where the economy relies mainly on forestry activities. Local stakeholders designed a map of wildfires, which was modelled as a function of a set of physical and socio-economic variables. A fire-probability map of the district was obtained and compared with MODIS data (2000-2020). The results suggest that higher fire probability occurs in areas with lower human pressure, and they provide information on related socio-economic drivers that affect this phenomenon. This study highlights the importance of combining participatory approaches and geospatial techniques to assess fire dynamics and prevent wildfires in terms of understanding and predicting the risks. The involvement of local communities is fundamental to this innovative participatory approach with regard to better supporting decision-making and prevention actions and to developing fire control management guidelines.

Individual reproductive success in Norway spruce natural populations depends on growth rate, age and sensitivity to temperature.

Quantifying the individual reproductive success and understanding its determinants is a central issue in evolutionary research for the major consequences that the transmission of genetic variation from parents to offspring has on the adaptive potential of populations. Here, we propose to distil the myriad of information embedded in tree-ring time series into a set of tree-ring-based phenotypic traits to be investigated as potential drivers of reproductive success in forest trees. By using a cross-disciplinary approach that combines parentage analysis and a thorough dendrophenotypic characterisation of putative parents, we assessed sex-specific relationships between such dendrophenotypic traits (i.e., age, growth rate and parameters describing sensitivity to climate and to extreme climatic events) and reproductive success in Norway spruce. We applied a full probability method for reconstructing parent-offspring relationships between 604 seedlings and 518 adult trees sampled within five populations from southern and central Europe. We found that individual female and male reproductive success was positively associated with tree growth rate and age. Female reproductive success was also positively influenced by the correlation between growth and the mean temperature of the previous vegetative season. Overall, our results showed that Norway spruce individuals with the highest fitness are those who are able to keep high-growth rates despite potential growth limitations caused by reproductive costs and climatic limiting conditions. Identifying such functional links between the individual ecophysiological behaviour and its evolutionary gain would increase our understanding on how natural selection shapes the genetic composition of forest tree populations over time.

Tree-ring and remote sensing analyses uncover the role played by elevation on European beech sensitivity to late spring frost.

Extreme climate events such as late spring frosts (LSFs) negatively affect productivity and tree growth in temperate beech forests. However, detailed information on how these forests recover after such events are still missing. We investigated how LSFs affected forest cover and radial growth in European beech (Fagus sylvatica L.) populations located at different elevations at four sites in the Italian Apennines, where LSFs have been recorded. We combined tree-ring and remote-sensing data to analyse the sensitivity and recovery capacity of beech populations to LSFs. Using daily temperature records, we reconstructed LSF events and assessed legacy effects on growth. We also evaluated the role played by elevation and stand structure as modulators of LSFs impacts. Finally, using satellite images we computed Normalized Difference Vegetation Index (NDVI), Enhanced Vegetation Index (EVI) and LAI (Leaf Area Index) to evaluate the post-LSF canopy recovery. The growth reduction in LSF-affected trees ranged from 36 % to 84 %. We detected a negative impact of LSF on growth only during the LSF year, with growth recovery occurring within 1-2 years after the event. LSF-affected stands featured low vegetation indices until late June, i.e. on average 75 days after the frost events. We did not find a clear relationship between beech forest elevation and occurrence of LSFs defoliations. Our results indicate a high recovery capacity of common beech and no legacy effects of LSFs.

Functional Relationships of Wood Anatomical Traits in Norway Spruce.

The quantitative assessment of wood anatomical traits offers important insights into those factors that shape tree growth. While it is known that conduit diameter, cell wall thickness, and wood density vary substantially between and within species, the interconnection between wood anatomical traits, tree-ring width, tree height and age, as well as environment effects on wood anatomy remain unclear. Here, we measure and derived 65 wood anatomical traits in cross-sections of the five outermost tree rings (2008-2012) of 30 Norway spruce [Picea abies (L.) H. Karst.] trees growing along an altitudinal gradient (1,400-1,750 m a.s.l.) in the northern Apennines (Italy). We assess the relationship among each anatomical trait and between anatomical trait groups according to their function for (i) tree-ring growth, (ii) cell growth, (iii) hydraulic traits, and (iv) mechanical traits. The results show that tree height significantly affects wood hydraulic traits, as well as number and tangential diameter of tracheids, and ultimately the total ring width. Moreover, the amount of earlywood and latewood percentage influence wood hydraulic safety and efficiency, as well as mechanical traits. Mechanically relevant wood anatomical traits are mainly influenced by tree age, not necessarily correlated with tree height. An additional level of complexity is also indicated by some anatomical traits, such as latewood lumen diameter and the cell wall reinforcement index, showing large inter-annual variation as a proxy of phenotypic plasticity. This study unravels the complex interconnection of tree-ring tracheid structure and identifies anatomical traits showing a large inter-individual variation and a strong interannual coherency. Knowing and quantifying anatomical variation in cells of plant stem is crucial in ecological and biological studies for an appropriate interpretation of abiotic drivers of wood formation often related to tree height and/or tree age.

Three centuries of insect outbreaks across the European Alps.

Knowledge of the persistence of regular larch budmoth outbreaks is limited in space and time. Although dendrochronological methods have been used to reconstruct insect outbreaks, their presence may be obscured by climatic influences. More than 5000 tree-ring series from 70 larch host and 73 spruce nonhost sites within the European Alps and Tatra Mountains were compiled. Site-specific assessment of growth-climate responses and the application of six larch budmoth detection methods considering host, nonhost and instrumental time-series revealed spatiotemporal patterns of insect defoliation across the Alpine arc. Annual maps of reconstructed defoliation showed historical persistence of cyclic outbreaks at the site level, recurring c. every 8-9 yr. Larch budmoth outbreaks occurred independently of rising temperatures from the Little Ice Age until recent warmth. Although no collapse in outbreak periodicity was recorded at the local scale, synchronized Alpine-wide defoliation has ceased during recent decades. Our study demonstrates the persistence of recurring insect outbreaks during AD 1700-2000 and emphasizes that a widely distributed tree-ring network and novel analysis methods can contribute towards an understanding of the changes in outbreak amplitude, synchrony and climate dependence.

Disentangling the effects of spatial proximity and genetic similarity on individual growth performances in Norway spruce natural populations.

Cambial growth is a phenotypic trait influenced by various physiological processes, numerous biotic and abiotic drivers, as well as by the genetic background. By archiving the outcome of such complex interplay, tree-rings are an exceptional resource for addressing individual long-term growth responses to changing environments and climate. Disentangling the effects of the different drivers of tree growth, however, remains challenging because of the lack of multidisciplinary data. Here, we combine individual dendrochronological, genetic and spatial data to assess the relative importance of genetic similarity and spatial proximity on Norway spruce (Picea abies (L.) Karst.) growth performances. We intensively sampled five plots from two populations in southern and central Europe, characterizing a total of 482 trees. A two-step analytical framework was developed. First, the effects of climate and tree age on tree-ring width (TRW) were estimated for each individual using a random slope linear mixed-effects model. Individual parameters were then tested against genetic and spatial variables by Mantel tests, partial redundancy analyses and variance partitioning. Our modelling approach successfully captured a large fraction of variance in TRW (conditional R2 values up to 0.94) which was largely embedded in inter-individual differences. All statistical approaches consistently showed that genetic similarity was not related to variation in the individual parameters describing growth responses. In contrast, up to 29% of the variance of individual parameters was accounted by spatial variables, revealing that microenvironmental features are more relevant than genetic similarity in determining similar growth patterns. Our study highlights both the advantages of modelling dendrochronological data at the individual level and the relevance of microenvironmental variation on individual growth patterns. These two aspects should be carefully considered in future multidisciplinary studies on growth dynamics in natural populations.

Long-term change in the sensitivity of tree-ring growth to climate forcing in Larix decidua.

Tree rings are widely used long-term proxy data which, if combined with long-term instrumental climate records, can provide excellent information on global climate variability. This research aimed to determine whether interannual climate-growth responses in Alpine treeline forests are stationary over time. We used tree-ring width chronologies of Larix decidua (European larch) from 17 sites and monthly temperatures and precipitation data for the period 1800-1999. Climate-growth relationships were assessed with correlation and response functions, and their stationarity and consistency over time were measured using moving correlation. Tree-ring chronologies showed similar interannual variations over the last two centuries, suggesting that the same climatic factors synchronously limited growth at most sites. The most sensitive variables showed significant transient responses varying within the time period, indicating a possible deviation from the uniformitarian principle applied to dendroclimatology. If these findings are confirmed in future studies on other species and in other regions, we suggest that time-dependent variables should be taken into account to avoid overestimation of treeline advance, future forest carbon storage in temperature-limited environments and inaccurate reconstruction of past climate variability.