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European black pine recolonization at high altitude in the central Apennines (Italy). Spatial and Temporal Patterns
No full textIn Italia gran parte degli studi sulle dinamiche della treeline è stata condotta in ambiente alpino. Pochi sono invece quelli sulle cenosi appenniniche, dove la sinergia tra disturbi naturali e antropici è decisamente più accentuata. Negli Appennini la treeline attuale è caratterizzata in grande prevalenza da cenosi di faggio, situate tra 1500 m e 1900 m di quota. Alcuni studi hanno evidenziato una notevole stazionarietà spazio-temporale di tali cenosi forestali nel settore centrale ed un maggiore dinamismo di formazioni arbustive. Nell’Appennino centro-meridionale le cenosi naturaliformi con Pinus mugo, Pinus laricio, Pinus leucodermis appaiono più dinamiche. Tale fenomeno trova analogie nelle zone calcaree dell’Appennino centrale con la diffusione spontanea di individui di Pinus nigra sopra l’attuale limite superiore del bosco, spesso ma non solo a partire da rimboschimenti di protezione.
La ricolonizzazione di pino nero in ecotoni di treeline è stata analizzata in 5 siti dell’Appennino centrale lungo un gradiente Nord-Sud di circa 170 km compreso fra Marche e Abruzzo.
Obiettivi dello studio erano: i) individuare possibili pattern comuni nell’assetto fisionomico - strutturale e nei dinamismi di diffusione del pino nero; ii) datare accuratamente l’insediamento degli individui arborei; iii) determinare l’influenza dei principali fattori climatici nel processo di ricolonizzazione.
Globalmente sono stati censiti oltre 900 individui arborei di pino nero, tutti localizzati al di sopra della treeline attuale fino alla massima altitudine possibile. E’ stata rilevata la loro posizione mediante GPS, determinato l'habitat di crescita e misurati il diametro del fusto, l’altezza totale, gli accrescimenti longitudinali ed altri caratteri fisionomici e strutturali. Da ogni fusto è stata anche prelevata una carota basale per la determinazione dell’età cambiale, accrescimento radiale e individuazione di fluttuazioni intra-annuali di densità (IADF). Carote legnose sono state estratte anche da 20 individui arborei adulti, per ogni sito, al limite esterno dei rimboschimenti di pino nero presenti, per verificare la sensitività climatica del pino nero. Con l’analisi univariata (regressione) e multivariata (PCA) e con l'analisi dendroecologica sono state esplorate le correlazioni fra i diversi attributi strutturali degli alberi, una possibile influenza delle variabili ambientali, e le analogie o differenze tra i diversi siti, le relazioni fra incrementi radiali e longitudinali e l’influenza di temperature e precipitazioni mensili sull’accrescimento e la formazione delle IADF.
Gran parte dei pini sono ubicati ad altitudini elevate e i loro caratteri fisionomico-strutturali sono molto simili nei cinque siti, dove il processo ricolonizzativo è iniziato circa 30-40 anni fa con picchi di frequenza e dinamismi di accrescimento sincroni.
Il pino nero è particolarmente sensibile alle temperature massime estive periodo in cui si formano preferenzialmente anche le IADF il cui acme di frequenza è nel 2003 e 2004. La diffusione del pino nero, sebbene vi siano differenze nei caratteri ambientali e nell’uso del suolo pregresso dei cinque siti, appare sincronica e spazialmente dispersa. Simili dinamismi di accrescimento e adattamento della specie al riscaldamento climatico sono segnali che potrebbero preludere ad un futuro innalzamento del limite superiore del bosco
Structural attributes, tree-ring growth and climate sensitivity of Pinus nigra Arn. at high altitude: common patterns of a possible treeline shift in the central Apennines (Italy)
Full text linkEuropean black pine (Pious nigra ssp. nigra Arnold) encroachment at increasing elevation has been analyzed at four treeline ecotones of the central Apennines (Italy). The study sites are located along a North-South gradient of 170 km across Marche and Abruzzo regions in Central Italy. The aims of this study were: (i) to detect possible common patterns of structural attributes of black pine regeneration at the treeline ecotone; (ii) to date the seedlings germination and (iii) to assess the climate influence on the pine upward encroachment process also using intra-annual density fluctuations (IADFs) in tree-rings. We sampled 658 encroached black pine trees above the current treeline to the mountain top. All individuals were mapped and their basal stem diameter, total height, annual height increments and other structural attributes measured. One increment core was extracted from stem base of most samples for cambial age determination and detection of intra-annual density fluctuations (IADF). At two sites we also extracted cores at DBH from forest trees to assess climate-growth relationships of black pine. We used multivariate analysis (PCA) to explore the correlation structure of the main tree attributes, regression analysis to relate radial and height increment and dendroclimatic analysis to assess the influence of climate on tree growth and IADF formation.
Most black pine trees were located at high altitude and their structural attributes were similar at the four sites where the pine encroachment process started between 30 and 40 years ago featuring similar germination peaks and growth patterns. Black pine is particularly sensitive to maximum temperatures and IADF occurred in mid-late summer with highest frequency peaks between 2003 and 2004. The pine encroachment process, besides the differences of environmental features and land use histories of the four study sites, appears synchronic and spatially diffused. Consistent tree-growth dynamics and the species adaptation to a warming climate are signals envisaging a possible treeline upward shift
Are young trees suitable for climate-growth analysis? A trial with Pinus nigra in the central Apennines treeline
No full textn the context of ecological research, tree-ring analysis often deals with short time series (< 30 years). Their crossdating and averaging can be difficult but crucial to use such data for ecological modelling, multivariate statistics, and climate-growth analysis. Several studies were conducted in the Central Apennines (Italy) on recent encroachment of European black pine (Pinus nigraJ.F. Arnold) on treeless areas above the current forestline.Growth of young trees is mainly controlled by endogenous or microclimatic factors making usual den-drochronology methods less applicable and crossdating very difficult or even impossible. The potential ecolo-gical information deriving from tree-ring growth in short series is therefore limited by this methodological bias.The aim of this study is to test suitable methods for optimizing the use of short ring series for further analyticaluse. A dataset of 734 tree-ring series of young European black pines (mean cambial age 15 years) growing athigh altitude in 8 sites was used in this analysis. At each site tree-ring series were divided in two groups based on inter-series correlation: the crossdated or selected series (SEL), and non-crossdated or rejected ones (REJ). The following dendrochronological parameters were calculated for SEL and REJ series: mean tree-ring width, mean sensitivity, Gini coefficient,first order autocorrelation, inter-series correlation, and Gleichläufigkeit(GLK). Two methods of pointer years analysis were tested in order to detect years with synchronous growth: i) Normalization in a moving Window (NW) and ii) the RElative growth change method (RE). The two methods were applied to the raw series varying the standard thresholds, in order to detect synchronous growth-years in SEL and REJ group. A sensitivity analysis was included to assess how the threshold choice in the analysis could affect the results obtained. The term“common”was used to indicate years with similar tree growth response. Differences in the detected number of common years within SEL and REJ were obtained using different time windows with the RE and NW methods. The 47 % of all series were classified as SEL, showing more common years than the REJ series. However, a similar result occurred considering all the series together without SEL/REJ discrimination. In general, a significant occurrence of common years could be a tool to select series to be averaged for a site mean chronology. These are preliminary but encouraging results contributing to a more efficient use of the ecological information provided by short time series from young trees
Climate Influence on the Expansion and Tree-Ring Growth of Pinus nigra L. at High Altitude in the Central Apennines
Full text linkScattered expansion of European black pine (Pinus nigra Arnold) has been observed above the current timberline in the central Apennines. We aimed to detect possible common pattern of structure and growth dynamics of pine regeneration in treeline sites. Over 700 black pine samples growing above the timberline were sampled at four sites in the limestone Apennines of Marche and Abruzzo regions. For each tree we measured basal stem diameter, total height and annual height increments; a wooden core was extracted from the stem near the ground for cambial age determination and detection of intra-annual density fluctuations (IADF). We used multivariate analysis to assess patterns of the main tree structural attributes and dendrochronological analysis for age structure and growth dynamics. Expansion of European black pine started about 35 years ago featuring similar germination peaks, tree structure and growth patterns in all the sites. IADF have similar frequencies and peaks and occur in mid-late summer. These similar patterns occur at all sites besides the local differences and grazing histories suggesting the presence of an overall climate driver
Il limite superiore del bosco negli Appennini: dinamismi recenti negli ecotoni con Pinus spp.
No full textThe mountain treeline is an ecological boundary between the closed upper forest and permanent grasslands broadly studied for over a century by geographers, biogeographers, climatologists, glaciologists and ecologists. Spatio-temporal dynamics of its position is an important indicator of climate and land use changes. In Italy an ongoing research on the Appennine treeline reveals the prevailing but stable presence of beech forests and localized altitudinal expansion of pioneering pines
Recent expansion of Pinus nigra Arn. above the timberline in the central Apennines, Italy
Full text linkThe altitude of timberlines in the central Apennines
has lowered over the past few thousand years due to interacting
natural and anthropogenic disturbances. These timberlines
are usually sharp and consist of coppiced beech forests.
We found scattered individuals of European black
pine (Pinus nigra Arn.) at two high elevation sites above the
timberline on limestone slopes. We investigated the spatial
and temporal pattern expansion of black pine and assessed
vigour and growth dynamics of pine trees.
Over 250 individuals were mapped in the two
sites using GPS. Several site and tree parameters were
measured. Tree-ring widths and the frequency of intraannual
density fluctuations were also recorded.
Black pine expansion started around 30 years ago.
Pine trees are randomly distributed at higher elevations with
no visible spatial pattern. Germination peaks were synchronous
in the two sites, and tree growth displayed very similar
chronologies, with synchronous occurrence of intra-annual
density fluctuations.
We hypothesise that the reduced livestock grazing
over the last decades as well as climate warming are the
major driving forces behind the high-altitude expansion of black pine on the central Apennines, where this species was
present in pre-historic times
Pinus nigra anthropogenic treelines in the central Apennines show common pattern of tree recruitment
Full text linkTreeline position, structure, and composition are shaped by natural and anthropogenic factors. At human-disturbed treelines, it is particularly difficult to disentangle the specific role of natural and anthropogenic drivers controlling tree recruitment dynamics following land abandonment. We tested for a possible common regeneration pattern of Pinus nigra Arn. at four upper treeline ecotones in the central Apennines (Italy). The sites were selected based on (1) the occurrence of natural encroachment of P. nigra above 1600 m a.s.l., and (2) the mountain top elevation higher than 2000 m a.s.l. We assessed structure and spatiotemporal patterns of P. nigra advancing regeneration using point and surface pattern analyses. We mapped, measured, and dated 845 trees sampled on a total surface area of 336 ha. P. nigra is the only tree species expanding at high altitude and features a scattered process that started 35–40 years ago, with a maximum recruitment frequency between 1995 and 2003. Pinus regeneration appeared over-dispersed along the slope at a scale range of 12–18 m. We found spatial segregation between saplings and young trees at intermediate distances (8–17 m) and small patches of young trees distributed along the treeline ecotone. The spatial pattern of P. nigra encroachment in the central Apennines revealed a replicable model independent of treeline topography and local disturbance histories
The anatomy of »blue ring« in the wood of Pinus nigra
Full text linkTree-ring features are widely used to identify specific climate, environment and stress events affecting plant life. Cold temperatures can mainly affect the last phase of cell differentiation by interfering in the process of cell wall lignin deposition. Recently, it was found out that the effect of cold temperature on lignification is visible in wood microsections double stained with astra blue which stains cellulose, and red safranin which stains lignin. This new tree-ring feature was called »blue ring«. In this study, we investigated the anatomical morphology of blue rings in transverse and longitudinal wood microsections of three European black pine trees (Pinus nigra Arnold) growing above the treeline. We aim to understand if the lack of lignification is consistent along the entire tracheid length and whether or not pits, responsible for water transport from one tracheid to another, are lignified. The results show that the lack of lignification extends along the entire tracheids cell wall, including bordered pits. Based on our observations we speculate that blue ring occurrence decreases the safety of water transport and wood mechanical properties
Intra-annual density fluctuations (IADFs) inPinus nigra(J. F. Arnold) at high-elevation in the central Apennines (Italy)
Full text linkAlthough wood anatomical features can provide yearly resolved climatic information at sub-seasonal resolution, the occurrence of intra-annual density fluctuations (IADFs) might be triggered by several abiotic factors under different ecological settings. Here, we use information on cambial age and tree-ring width to standardize the frequency of IADFs in European black pines from three different mountain slopes in the central Apennines (Italy). At each site, we sampled isolated 15–30-year pioneer pines above the forest limit, as well as close-grown 40–60-year planted pines at the forest limit. Mainly restricted to the latewood of both pioneer and planted trees, the occurrence of IADFs reveals a significant positive relationship with cambial age and ring width. Although the standardized IADFs are well synchronized between the planted and pioneer pines, the frequency of IADFs in narrow rings was higher in the pioneer pines. Drought conditions in July and August are responsible for the highest IADFs frequency in planted and pioneer pines, respectively. Our study underlines the value of IADFs to obtain a more nuanced understanding of the climatic drivers of wood formation at the intra-annual scale
The “blue ring”: anatomy and formation hypothesis of a new tree-ring anomaly in conifers
No full textKey message: Double-stained microsections from highaltitudePinus nigrawood cores highlighted unlignified latewood cells possibly linked to abrupt temperature reduction at the end of the growing season. More consolidated detection could increase their role in dendroecology. Cambial activity and wood formation are influenced by environmental factors, primarily climate. During cell wall formation the lignification is mainly controlled by temperature. By staining with safranin and astra blue it is possible to distinguish cell walls richer in lignin (stained in red) from those richer in cellulose (stained in blue). Here we show an uncommon phenomenon observed in 41 transverse sections prepared for anatomical studies of young European black pine (Pinus nigra Arnold) individuals. We detected some layers of incompletely lignified cells that appear blue in safranin–astra blue-stained sections. Growth rings showing this anatomical feature were named “blue rings”. The aims of this preliminary study are: (i) to describe the features of this peculiar anatomical trait, (ii) to enhance its visualization, and (iii) to suggest possible drivers of its formation. First results indicate the influence of low air temperature causing a lack of lignification in latewood cells. The added values provided by the identification of “blue rings” within tree-ring series could be (i) their possible use as pointer year, (ii) cross dating improvement, and (iii) finer assessment of tree sensitivity to environmental and climatic factors. © 2014, Springer-Verlag Berlin Heidelberg
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