Alfredo Di Filippo

Plasticity in Dendroclimatic Response across the Distribution Range of Aleppo Pine (Pinus halepensis)

We investigated the variability of the climate-growth relationship of Aleppo pine across its distribution range in the Mediterranean Basin. We constructed a network of tree-ring index chronologies from 63 sites across the region. Correlation function analysis identified the relationships of tree-ring index to climate factors for each site. We also estimated the dominant climatic gradients of the region using principal component analysis of monthly, seasonal, and annual mean temperature and total precipitation from 1,068 climatic gridpoints. Variation in ring width index was primarily related to precipitation and secondarily to temperature. However, we found that the dendroclimatic relationship depended on the position of the site along the climatic gradient. In the southern part of the distribution range, where temperature was generally higher and precipitation lower than the regional average, reduced growth was also associated with warm and dry conditions. In the northern part, where the average temperature was lower and the precipitation more abundant than the regional average, reduced growth was associated with cool conditions. Thus, our study highlights the substantial plasticity of Aleppo pine in response to different climatic conditions. These results do not resolve the source of response variability as being due to either genetic variation in provenance, to phenotypic plasticity, or a combination of factors. However, as current growth responses to inter-annual climate variability vary spatially across existing climate gradients, future climate-growth relationships will also likely be determined by differential adaptation and/or acclimation responses to spatial climatic variation. The contribution of local adaptation and/or phenotypic plasticity across populations to the persistence of species under global warming could be decisive for prediction of climate change impacts across populations. In this sense, a more complex forest dynamics modeling approach that includes the contribution of genetic variation and phenotypic plasticity can improve the reliability of the ecological inferences derived from the climate-growth relationships.

Climate change and oak growth decline: Dendroecology and stand productivity of a Turkey oak (Quercus cerris L.) old stored coppice in Central Italy

Abstract• We combined stem volume increment analysis with dendroecological tools to address two unresolved issues concerning oak dieback in Mediterranean areas: early detection of changes in stand growth, and identification of mechanisms for observed growth declines.• We reconstructed productivity of a stored coppice formed by Turkey oak (Quercus cerris) to test if its growth decline was linked to climatic variability, while also accounting for age-related and sociological factors.• Drought in May–June and in prior-year late summer-autumn was negatively correlated with current growth during 1974–2006. Previous November water balance was the strongest signal. Moving Correlation Functions (11 y windows) indicated that the May–June signal remained dominant until 1996, thereafter falling to non-significant values in parallel with the May–June water balance drying trend; at the same time the previous autumn correlations reached significant values. Since 1994 there was a two-year lagged response to June water balance, suggesting that, when growth declined, loss of current-year climate signals was accompanied by the emergence of previous-year ones.• Growth and productivity of deciduous oaks in Mediterranean environments is linked to late spring-early summer hydrologic balance; at both annual and decadal timescales, oak growth decline was associated with a delayed response to climate.

Structure and function of intra–annual density fluctuations: Mind the gaps

Tree rings are natural archives of climate and environmental information with a yearly resolution. Indeed, wood anatomical, chemical, and other properties of tree rings are a synthesis of several intrinsic and external factors, and their interaction during tree growth. In particular, Intra-Annual Density Fluctuations (IADFs) can be considered as tree-ring anomalies that can be used to better understand tree growth and to reconstruct past climate conditions with intra-annual resolution. However, the ecophysiological processes behind IADF formation, as well as their functional impact, remain unclear. Are IADFs resulting from a prompt adjustment to fluctuations in environmental conditions to avoid stressful conditions and/or to take advantage from favorable conditions? In this paper we discuss: (1) the influence of climatic factors on the formation of IADFs; (2) the occurrence of IADFs in different species and environments; (3) the potential of new approaches to study IADFs and identify their triggering factors. Our final aim is to underscore the advantages offered by network analyses of data and the importance of high-resolution measurements to gain insight into IADFs formation processes and their relations with climatic conditions, including extreme weather events.

The longevity of broadleaf deciduous trees in Northern Hemisphere temperate forests: insights from tree-ring series

Understanding the factors controlling the expression of longevity in trees is still an outstanding challenge for tree biologists and forest ecologists. We gathered tree-ring data and literature for broadleaf deciduous (BD) temperate trees growing in closed-canopy old-growth forests in the Northern Hemisphere to explore the role of geographic patterns, climate variability, and growth rates on longevity. Our pan-continental analysis, covering 32 species from 12 genera, showed that 300-400 years can be considered a baseline threshold for maximum tree lifespan in many temperate deciduous forests. Maximum age varies greatly in relation to environmental features, even within the same species. Tree longevity is generally promoted by reduced growth rates across large genetic differences and environmental gradients. We argue that slower growth rates, and the associated smaller size, provide trees with an advantage against biotic and abiotic disturbance agents, supporting the idea that size, not age, is the main constraint to tree longevity. The oldest trees were living most of their life in subordinate canopy conditions and/or within primary forests in cool temperate environments and outside major storm tracks. Very old trees are thus characterized by slow growth and often live in forests with harsh site conditions and infrequent disturbance events that kill much of the trees. Temperature inversely controls the expression of longevity in mesophilous species (Fagus spp.), but its role in Quercus spp. is more complex and warrants further research in disturbance ecology. Biological, ecological and historical drivers must be considered to understand the constraints imposed to longevity within different forest landscapes.

Climatic Signals from Intra-annual Density Fluctuation Frequency in Mediterranean Pines at a Regional Scale

Tree rings provide information about the climatic conditions during the growing season by recording them in different anatomical features, such as intra-annual density fluctuations (IADFs). IADFs are intra-annual changes of wood density appearing as latewood-like cells within earlywood, or earlywood-like cells within latewood. The occurrence of IADFs is dependent on the age and size of the tree, and it is triggered by climatic drivers. The variations of IADF frequency of different species and their dependence on climate across a wide geographical range have still to be explored. The objective of this study is to investigate the effect of age, tree-ring width and climate on IADF formation and frequency at a regional scale across the Mediterranean Basin in Pinus halepensis Mill., Pinus pinaster Ait., and Pinus pinea L. The analyzed tree-ring network was composed of P. pinea trees growing at 10 sites (2 in Italy, 4 in Spain, and 4 in Portugal), P. pinaster from 19 sites (2 in Italy, 13 in Spain, and 4 in Portugal), and P. halepensis from 38 sites in Spain. The correlations between IADF frequency and monthly minimum, mean and maximum temperatures, as well as between IADF frequency and total precipitation, were analyzed. A significant negative relationship between IADF frequency and tree-ring age was found for the three Mediterranean pines. Moreover, IADFs were more frequent in wider rings than in narrower ones, although the widest rings showed a reduced IADF frequency. Wet conditions during late summer/early autumn triggered the formation of IADFs in the three species. Our results suggest the existence of a common climatic driver for the formation of IADFs in Mediterranean pines, highlighting the potential use of IADF frequency as a proxy for climate reconstructions with geographical resolution.

Missing Rings in Pinus halepensis - The Missing Link to Relate the Tree-Ring Record to Extreme Climatic Events.

Climate predictions for the Mediterranean Basin include increased temperatures, decreased precipitation, and increased frequency of extreme climatic events (ECE). These conditions are associated with decreased tree growth and increased vulnerability to pests and diseases. The anatomy of tree rings responds to these environmental conditions. Quantitatively, the width of a tree ring is largely determined by the rate and duration of cell division by the vascular cambium. In the Mediterranean climate, this division may occur throughout almost the entire year. Alternatively, cell division may cease during relatively cool and dry winters, only to resume in the same calendar year with milder temperatures and increased availability of water. Under particularly adverse conditions, no xylem may be produced in parts of the stem, resulting in a missing ring (MR). A dendrochronological network of Pinus halepensis was used to determine the relationship of MR to ECE. The network consisted of 113 sites, 1,509 trees, 2,593 cores, and 225,428 tree rings throughout the distribution range of the species. A total of 4,150 MR were identified. Binomial logistic regression analysis determined that MR frequency increased with increased cambial age. Spatial analysis indicated that the geographic areas of south-eastern Spain and northern Algeria contained the greatest frequency of MR. Dendroclimatic regression analysis indicated a non-linear relationship of MR to total monthly precipitation and mean temperature. MR are strongly associated with the combination of monthly mean temperature from previous October till current February and total precipitation from previous September till current May. They are likely to occur with total precipitation lower than 50 mm and temperatures higher than 5°C. This conclusion is global and can be applied to every site across the distribution area. Rather than simply being a complication for dendrochronology, MR formation is a fundamental response of trees to adverse environmental conditions. The demonstrated relationship of MR formation to ECE across this dendrochronological network in the Mediterranean basin shows the potential of MR analysis to reconstruct the history of past climatic extremes and to predict future forest dynamics in a changing climate.

Tree ring‐based metrics for assessing old‐growth forest naturalness

Summary Old-growth studies commonly emphasize structural and age conditions, selecting proxy indicators of long-term ecological processes. Transition dynamics from mature to old-growth status reveal how natural legacies are progressively accumulated in forests after major disturbances, including human ones. In late-successional, multi-aged forests, the chronosequential ranking of developmental stages is a difficult task, as stand age provides little information, and time since last stand-replacing disturbance cannot be easily determined. Canopy age features, disturbance/suppression history, and growth trajectories were reconstructed from ring-width series of canopy trees in a network of 19 old-growth and managed European beech forests in the eastern Alps and central Apennines. A set of tree-ring metrics able to describe the intensity and time distribution of biological and ecological processes (e.g. understorey suppression, canopy accession age), were used to describe the advancement of old-growth status, and compared to established metrics of forest structure. Tree-ring metrics were site dependent, as biogeoclimate affects turnover rates and constrains the onset and recovery rate of old-growth attributes. Under the same environmental conditions (high-mountain, limestone-bedrock beech forests), values of the best indicators (number/duration of growth suppression phases; synchronicity of first release; maximum and range of canopy tree age; canopy accession age of the slowest-growing trees) increased monotonically (2 to 5 times) from managed to secondary and primary old-growth forests. Trees in well-conserved primary old-growth forests experienced several and long suppressions, showing the highest complexity in recruitment history, canopy accession, and growth trajectories. The best tree-ring metrics, condensed in a Naturalness Score to provide a synthetic functional ranking of forests, varied coherently with structural complexity, which represented stand dynamics more closely than biomass-related metrics. Synthesis and applications. We propose a synthetic ranking of forest functional naturalness based on the ecological processes experienced by trees. This ranking helps to overcome the limitations associated with the use of arbitrary size- or age-related thresholds of old-growth status and provides a functional approach to establish chronosequences in ecological studies. The quantitative description of complex processes underpinning the unique biological and ecological features (e.g. extreme tree longevity) found in primary old-growth forests enhances their irreplaceable value in nature conservation. The proposed framework of tree-ring indicators describes functional traits tightly related to forest naturalness, and may thus become a tool to identify and protect old-growth forests, benchmark the impact of silvicultural practices, prescribe targets or evaluate the effectiveness of restoration programs. This article is protected by copyright. All rights reserved.

A dendrochronological analysis of Pinus pinea L. on the Italian mid-Tyrrhenian coast

In order to assess the response of the radial growth of Pinus pinea L. to climatic variability in Central Italy, dendrochronological and dendroclimatological analyses were carried out on five different populations scattered along the Tyrrhenian coasts of the peninsula. The aim of this study is to contribute to the understanding of the ecological demands of this species, particularly in the study area.For each site total ring, early-, and late-wood width chronologies were developed.Multidimensional analyses were performed for the three tree-ring datasets in order to analyze the relations between sites chronologies. Both Principal Component Analyses and hierarchical classifications highlighted an important difference of one site in respect to the other, probably due to site characteristics.Correlation functions were performed to infer the main climatic factors controlling the radial growth of the species. For a comparative study, we limited our attention to the common interval 1926–2003 (78 years) in which the response of the tree-ring chronologies to climate at both local and regional scale was investigated.Positive moisture balance in the late spring-summer period of the year of growth is the climatic driver of P. pinea radial growth in the study area. Moreover, this study shows how low summer temperatures strongly favor the radial growth of the species.

La hêtraie pluri-séculaire de la vallée Cervara (Parc national des Abruzzes, Italie)

Abstract The oldest beech forest of Europe was found in the Apennines. The stand is located in valle Cervara (Abruzzo national Park) and it covers about fifty hectares from 1 400 to 1 800 m a.s.l. The forest is characterized by a mosaic of patches in different phases of development from seedlings to senescent and dead trees. Some trees reach five hundred years, two fold the maximum age reported for the species. The dendrochronological analysis of the tree-ring series showed tree growth variations which occurred in the forest since the Little Ice Age (1600–1850). The reconstruction of the past climate is an important step to understand the role of human activities in the present climatic global change. This study will be also useful to define a model of forest management that take into consideration the natural cycle of beech forests.

The oldest dated tree of Europe lives in the wild Pollino massif: Italus, a strip‐bark Heldreich's pine

How long do the oldest trees in Europe live? And where do they live? Recently, Konter et al. (2017) documented the discovery in Greece of Adonis, a Pinus heldreichii H.Christ with at least 1,075 tree rings, thus the oldest tree so far scientifically dated in Europe. An area of extreme interest to further explore these questions is the Pollino National Park (southern Italy, see Appendix S2), where maximum crossdated age of Heldreich’s pine had been previously reported as approaching a thousand years (Serre-Bachet 1985, Biondi 1992). After a 3-yr sampling campaign, we discovered a few millennium-old trees living on high-mountain cliffs (1,850– 2,150 m a.s.l.) in the Pollino Massif. The oldest sampled tree, which we called Italus (Fig. 1), became the subject of further investigation to determine its actual age. Italus has the typical shape of extremely old conifers, with dead spike top, strip-bark formation, and few live crown patches in the lower-middle part of the stem (Swetnam and Brown 1992). This Heldreich’s pine has diameter at breast height of 160 cm and is located on a steep rocky slope with cliff ledges. The stand is open, with little or no understory, generally undeveloped soils, and plenty of exposed dolomitic bedrock, hence the risk of wildfire spread is minimized. The Heldreich’s pine population occupies the vegetation zone just above beech forests that include old-growth stands with 500-yr old individuals, approaching the maximum longevity for this deciduous species (Di Filippo et al. 2015). Wood cores 5-mm in diameter were extracted using increment borers from the lower stem, which was hollow, and from exposed roots. Thanks to the particular configuration of the stem, straddling rocky and steep terrain that had eroded away, it was possible to collect increment cores from the root system close to the germination pith. To obtain a scientifically validated age for this old hollow tree, we developed a specific multistep dating procedure that combines tree-ring and radiocarbon analyses to match samples from a hollow stem and from exposed roots of a living tree. Increment cores extracted from the Italus stem revealed an innermost ring date of 955 CE, giving a total chronology length of 1,062 yr (955 CE–2,016 CE) (Fig. 2). Overall, ring-width patterns of Italus follow the typical features of isolated old trees, with relatively large increments in the first few cambial years, followed by a rapid decline towards a very long series of extremely small rings (Biondi and Qeadan 2008). Xylem increment is extremely low because of difficult environmental conditions, which typically lead to presence of extremely old individuals, as is the case with Pinus longaeva in Great Basin mountains of north America (Schulman 1954). A potential age estimate was then calculated using the increment core length and the stem diameter at the coring location. Given a 23.8 cm distance between the end of the core and the stem center (assuming a circular trunk), we used the average ring width for the innermost 20-50 rings (Di Filippo et al. 2017) to derive an estimate of 205–227 rings between the pith and the first dated ring. With this estimate, the pith date could fall in the 727–749 CE time interval. The total estimated stem age, obtained by adding the number of crossdated tree rings with the estimated missing ones, could therefore be 1,267–1,289 yr. Improving the age determination for Italus required analyzing the increment cores collected from the exposed roots. Anatomical features of root samples, such as the clear presence of latewood, indicated that those roots had been exposed for quite some time. Exposed roots often contain ring patterns that are not synchronous with rings in buried roots, and in our case there was also no clear correlation with the stem ring-width patterns. An abrupt growth decline was evident in the stem ring widths (Fig. 2) between 1,016