Gianluca Piovesan

Structure, dynamics and dendroecology of an old-growth Fagus forest in the Apennines

Abstract Question: Which are the structural attributes and the history of old-growth Fagus forest in Mediterranean montane environments? What are the processes underlying their structural organization? Are these forests stable in time and how does spatial scale affect our assessment of stability? How do these forests compare to other temperate deciduous old-growth forests? Location: 1600–1850 m a.s.l., Fagus forest near the tree line, central Apennines, Italy. Methods: An old-growth Fagus forest was studied following historical, structural and dendroecological approaches. History of forest cover changes was analysed using aerial photographs taken in 1945, 1954, 1985 and 1994. The structural analysis was carried out in the primary old-growth portion of the forest using 18 circular and two rectangular plots. Dendroecological analyses were conducted on 32 dominant or co-dominant trees. Results: These primary old-growth Fagus remnants consist of four patches that escaped logging after World War II. Both living and dead tree components are within the range of structural attributes recognized for old-growth in temperate biomes. Dendroecological analyses revealed the roles of disturbance, competition and climate in structuring the forest. We also identified a persistent Fagus community in which gap-phase regeneration has led to a mono-specific multi-aged stand at spatial scales of a few hectares, characterized by a rotated-sigmoid diameter distribution. Conclusion: Even at the relatively small spatial scale of this study, high-elevation Apennine Fagus forests can maintain structural characteristics consistent with those of old-growth temperate forests. These results are important for managing old-growth forests in the Mediterranean montane biome. Nomenclature: Pignatti (1982). Abbreviations: BAI = Basal area increment; CCTRMD = Computer controlled tree ring measuring device; CV = Coefficient of variation; CWD = Coarse wood debris; DBH = Diameter at breast height; DIB = Diameter inside bark; IGM = Istituto Geografico Militare; OG = Old-growth; PGC = Percentage growth change; PNA = Abruzzo National Park; UTM = Universal transverse Mercator.

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.

A long-term tree ring beech chronology from a high-elevation old-growth forest of Central Italy

Summary This paper describes preliminary dendroecological analyses of tree ring collections from an old-growth beech forest in the Central Apennines (Cervara Valley, Abruzzi National Park). Tree ring series show that at high-elevation sites in Central Italy the potential longevity of beech trees is more than 500 years. A 425 year site chronology spanning the period 1577–2001 was built. Its comparison with other chronologies from the same and other species showed a good connection of tree-ring patterns especially for the contexts of high elevation chronologies. The climatic signals of beech trees were investigated by means of pointer intervals and bootstrapped response functions for the period 1832–2000. Mid summer precipitation (July–August) and May temperature were the prominent climatic signals.

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.

The evolutionary ecology of masting: does the environmental prediction hypothesis also have a role in mesic temperate forests?

The evolutionary advantages of mast seeding in mesic temperate forests are reviewed with reference to the whole plant’s lifecycle. The aim of this article is to give attention to the environmental prediction hypothesis as an evolutionary aspect of closed-forest dynamics that need to be tested in field studies and modelling. It is suggested that the year after a period of water stress (or other suboptimal conditions for growth) trees respond with high seed production. Due to an understory environment favorable for prolific establishment of seedlings (i.e., more light at the forest floor) this may give rise to a pulse of regeneration. Thus, understanding masting may require a multi-faceted approach including the study of the ecology of the trees themselves beyond pollination and seed predation, and including gap ecology and patch dynamics with special attention to patterns of forest regeneration.

Uncertainties in the role of land vegetation in the carbon cycle

Since the late 1950s the CO2 concentration of the atmosphere has been increasing by around 0.5-3 ppm per year. Understanding of carbon sinks is vital to understanding this trend and its future behaviour. Here we examine some of the factors which may affect the proportion of anthropogenic CO2 ending up in the atmosphere in the present and in the future, and variability in the CO2 increase from one year to another. We also examine the evidence for the potential of terrestrial ecosystem carbon sinks to take up or release CO2. In some cases, a careful re-examination of the research methods used to deduce present and future feedbacks may be necessary. The most advanced technology and the most complex models do not necessarily produce reliable results. They should be carefully checked against a general background knowledge of ecological processes before their results are accepted.

Carbon balance gradient in European forests: Interpreting EUROFLUX

. A latitudinal trend in forest carbon uptake across Europe has been described by the EUROFLUX group, suggesting a considerable uptake in Italian Quercus ilex, Fagus sylvatica and Picea abies forests while a much lower C sink is reported in Scandinavian Picea abies forest. These results are discussed on the basis of the existing literature, and considered to be open to considerable doubt.

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.

Ecological behavior of Quercus suber and Quercus ilex inferred by topographic wetness index (TWI)

The ecological behaviors of a network of pure evergreen oak stands (Quercus suber L. and Quercus ilex L.) in the Central-Western Mediterranean Basin were investigated toward climatic and edaphic factors implemented with the application of topographic wetness index (TWI). A Categorical Principal Component Analysis (Catpca) using climatic and soil physico-chemical parameters was performed on 23 cork oak and holm oak pure stands with the aim to understand better the effectiveness of TWI for characterizing soil ecology of the two species. Catpca pointed out that, although cork oak and holm oak are able to growth in similar Mediterranean conditions, they show different behaviors in terms of needs and tolerance to soil water content. TWI confirmed such results at local scale, allowing highlighting some interesting features of the species differential ecology. Although both species confirmed to be drought-tolerant, the heliophilous cork oak revealed to dominate the landscape on wettest soils with high TWI values—indicating the capacity to tolerate stresses due to periods of waterlogging—, while the shade-tolerant holm oak prevails for low-medium TWI values—drier and mesophilous sites. Despite the application of TWI to vegetation science and ecology is relatively recent, results are encouraging and suggest considering this user-friendly and synthetic index in ecological investigations and modeling.

Soil microarthropod communities from Mediterranean forest ecosystems in Central Italy under different disturbances

The aim of this study is to assess soil quality in Mediterranean forests of Central Italy, from evergreen to deciduous, with different types of management (coppice vs. high forest vs. secondary old growth) and compaction impacts (machinery vs. recreational). Soil quality was evaluated studying soil microarthropod communities and applying a biological index (QBS-ar) based on the concept that the higher is the soil quality, the higher will be the number of microarthropod groups well adapted to the soil habitat. Our results confirm that hardwood soils are characterised by the highest biodiversity level among terrestrial communities and by a well-structured and mature microarthropod community, which is typical of stable ecosystems (QBS value, >200). While silvicultural practices and forest composition do not seem to influence QBS-ar values or microarthropod community structure, the index is very efficient in detecting soil impacts (soil compaction due to logging activities). Several taxa (Protura, Diplura, Coleoptera adults, Pauropoda, Diplopoda, Symphyla, Chilopoda, Diptera larvae and Opiliones) react negatively to soil compaction and degradation (QBS value, <150). In particular, Protura, Diplura, Symphyla and Pauropoda, are taxonomic groups linked to undisturbed soil. This index could also be a useful tool in monitoring soil biodiversity in protected areas and in urban forestry to prevent the negative effects of trampling. QBS-ar is a candidate index for biomonitoring of soil microarthropod biodiversity across the landscape to provide guidance for the sustainable management of renewable resource and nature conservation.