The age of monumental trees. A case study of Juniperus thurifera L. in Spain
Abstract and Figures
Aim of the study: To provide tree-age estimation of monumental Juniperus thurifera trees based on dendrochronological methods.
Area of study: “Sabinar de Calatañazor” Nature Reserve (Calatañazor, Soria, Spain), a monumental forest of Juniperus thurifera traditionally used for grazing.
Material and methods: Tree-ring width analysis of increment cores and four different methods for estimating the age of each of the trees analysed.
Main results: Our estimates suggest that most of the trees in this Nature Reserve with a radius greater than 30 cm are over 300 years old. Moreover, the discussion on the constraints and accuracy of each of the four tree-age estimation methods employed can be helpful in future studies of age in many monumental trees. A well-replicated local chronology, ranging from 1738 to 2012 (275 years), was also established for its use in reconstruction studies related to management, past events and climate change.
Research highlights: This study involved analyzing many trees with high percentages of rings that had disappeared as a result of rot. In this case, the age estimation models based on the classical hypotheses of constant growth in radius or basal area, as well as a new estimation method based upon biological behavior and considering two growth stages (juvenile and mature), are the ones that provided the most reliable estimates. On the contrary, regression models are less recommendable, due to being less accurate.
Keywords: Dendrochronology; tree-age estimate; rot, growth stages; management and conservation measures.
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... Ambos enfoques presentan limitaciones al implicar un hipotético crecimiento radial concéntrico y/o no tener en cuenta la variabilidad de los patrones de crecimiento individual en cada periodo vital (Clark y Hallgren, 2004). Otros modelos más complejos sí que tienen en cuenta numerosos datos de la especie y acerca de las diferencias entre las distintas etapas de crecimiento (Stephenson, 2000;Génova y Sadornil, 2020). ...
... En la Dehesa de Carrillo se seleccionaron para su estudio 25 grandes árboles con un solo eje y de apariencia saludable, con el fin de evitar las frecuentes pudriciones y ahuecamientos en el tronco (figura 3). Las series de anchura de anillos de crecimiento obtenidas se sincronizaron entre sí para asegurar que cada valor se correspondiera de forma exacta con el año de su formación (Génova y Sadornil, 2020). A pesar de su aspecto exterior saludable, en numerosos árboles las muestras obtenidas fueron incompletas a causa de pudriciones internas y, además, algunos árboles tenían un radio mayor que la barrena estándar utilizada para extraer las muestras. ...
Uno de los métodos más precisos y fiables para conocer la edad de los árboles
es el análisis dendrocronológico de las series o secuencias de anillos de crecimiento,
pero en muchos casos únicamente se cuenta con secuencias parciales
o incompletas. En este trabajo se presentan algunos estudios que han utilizado
distintas metodologías para realizar estimaciones dendrocronológicas de la edad.
Se pretende divulgar estas técnicas y los resultados obtenidos con los objetivos
de contribuir a la protección y conservación de árboles longevos y, también, de
determinados paisajes forestales.
... The age of monumental and veteran trees is usually not always easy to establish, and the degree of accuracy of tree-age estimates can vary depending upon the previously available data on each tree species and upon the methods used (Altman & al. 2016;Ehrlich & al. 2017;Génova Fuster & Sadornil 2020). Annual growth rates of the trunk for some combinations of species and sites in Sardinia might be very low, and age estimation in evergreen species presents additional issues. ...
Old, veteran and notable trees are ecologically important keystone organisms, have tangible connections to folklore, history and, sociocultural practices, and functional characteristics fundamental for sustaining complex and unique assemblages of species. These trees can be found in different landscapes, ranging from remote mountain areas to cities, historical gardens and, agricultural areas.
In Italy, an official list of monumental trees was recently published under the national law no. 10/2013 and the ministerial Decree 23 October 2014. A number of criteria can be used to identify these trees such as age and/or size, shape and growth habit, ecological value, floristic rarity, interest for its architectural structure, landscape quality, and historical, cultural and religious value.
In this article we aim to provide some general information on monumental and notable trees in Sardinia, as well as on old-growth forest, based on the recent monograph published for Sardinia by I. Camarda.
... The obtained coordinates were digitized in a digital cartography using Quantum GIS software (QGIS). The basal diameter of the trunk was measured as an indicator of the age of the individuals, and although the relationship will not be completely linear since the juniper species have a very irregular growth in semi-arid environments, we can assume diameter as an indicator of growth throughout the life of the individual, and therefore its longevity (Génova & Sadornil, 2020). A forestry caliper with a range of 0 to 600 mm was used for basal diameter measurements and a digital caliper with a range of 0 to 15 mm was used for smaller individuals. ...
Aims of the study: To characterize the southernmost Spanish Juniper (Juniperus thurifera L.) population in Europe, a relict species of the tertiary flora.
Area of study: El Peñón de Alamedilla, Los Montes region (Granada, Spain).
Material and Methods: A census and geo-referencing of the individuals in the population was carried out, together with the determination of the population structure, inference of the potential extension of the population, and discussion of the risk faced by the population.
Main results: A total of 899 individuals were located in mainly 128 ha from 806 to 888 m a.s.l. We found 50.6% adults, 35.7% saplings and 13.6% juveniles. Sexing on the adults showed a 60% of male feet compared to 39.1% of females (0.9% undifferentiated). 47% of the population has a basal diameter less than or equal to 50 mm. A 74.11% of the population was in grasslands + scrubs, and only 5.3% of the specimens were in arable lands. All individuals are on privately owned land.
Research highlights: The characterization of this southernmost Spanish Juniper population suggests a good viability and resilience, though there is also a high risk of inbreeding, with the population being able to go into genetic drift, which is critical for successful reproduction and may easily jeopardize its conservation efforts. This species is not protected enough in Andalusia and conservation measures should be taken.
Keywords: Juniperus thurifera, SE Iberian Peninsula, relict population, Natura 2000 Network.
Aim and area of study: In the present paper we estimated the age of four monumental Pinus canariensis of Gran Canaria (Canary Islands, Spain) by means of tree-ring analysis. Many tree-ring series have been accurately studied and many missing rings have been determined.
Material and methods: The trees were dead and the samples analysed were big disks. We measured numerous radii and crossdated the individual tree-ring series, paying particular attention to the existence and location of missing rings. We have distinguished between missing outer rings (MORs) and missing inner rings (MIRs) and analysed the possible causes of both.
Main results: We determined an average of 8.8% total missing rings (MRs) for these long-lived trees, with a maximum of 96 MRs in a series of over 500. We have tried to establish a tree-ring chronology on Gran Canaria Island, also having the tree-ring series from Inagua site, but the long individual tree-ring series analysed do not crossdate between them.
Research highlights: We consider the Canary pine a species hard to conducting dendroecological studies, especially if the samples come from managed old trees, in which a large amount of known and potentially unknown missing rings can hampered dating. Even knowing the difficulties involved in dendrochronological analyses of P. canariensis, we can confirm that it is a long-lived species, which can grow to over 500 years, and some of whose growth changes could be associated with certain historical and ecological events.
Mediterranean plants cope with cold wet winters and dry hot summers, with a drought gradient from northwest to southeast. Limiting climatic conditions have become more pronounced in the last decades due to the warming trend and rainfall decrease. Juniperus thurifera L., a long-lived conifer tree endemic to the western Mediterranean region, has a disjunct distribution in Europe and Africa, making it a suitable species to study sensitivity to climate in both sides of the Mediterranean Basin. Tree-ring width chronologies were built for three J. thurifera stands at Spain (Europe) and three in Morocco (Africa) and correlated with monthly temperature and precipitation. The temporal stability of climate-growth relationships was assessed using moving correlations; the drought effect on growth was calculated using the monthly standardized precipitation-evapotranspiration index (SPEI) at different temporal scales. In the wettest stands, increasing spring temperature and summer precipitation enhanced growth, while in the driest stands, growth was enhanced by higher spring precipitation and lower summer temperature. The climate-growth correlations shifted during the twentieth century, especially since the 1970s. Particularly noticeable is the recent negative correlation with previous autumn and winter precipitation in the wettest stands of J. thurifera, probably related with an effect of cloud cover or flooding on carbon storage depletion for next year growth. The driest stands were affected by drought at long time scales, while the wettest stands respond to drought at short time scales. This reveals a different strategy to cope with drought conditions, with populations from drier sites able to cope with short periods of water deficit.
Knowledge about tree age is critical to forestry, nature conservation and ecological studies. Direct age determination of large diameter trees through increment cores is complicated by various obstacles, primarily because of rot and insufficient borer length. Here, we aim to (1) test the accuracy of various methods (tree-ring width, basal area increment, age-size relationship) for tree age estimation, (2) select the most accurate approach and (3) enable age estimation of large individuals of Quercus robur. This was done through increment cores collected in an alluvial forest in the Czech Republic. We achieved 75 age estimates for each tree, including our novel approach, which reduces the effect of decreasing tree-ring width and increasing basal area increment during tree life. The extrapolation of mean ring width to missing radius generally overestimates the number of missing rings (by up to 27.5% of actual age) and the level of overestimation increases with decreasing partial core length, while the application of basal area increment largely underestimates the age estimation (by up to 20.5%). Thus, to eliminate the over- and underestimation caused by natural tree ring width decrease and basal area increase during the tree senescence and increasing size, we averaged the number of estimated rings by these two methods. This technique obtained the most reliable age estimates, with an error up to 3.5%. Thus it is suggested here that this technique provides a relatively accurate age estimate for trees where it is impossible to directly determine the age; at least for light-demanding species. Moreover, the proposed technique does not require complicated analysis and is not time consuming. However, future research should test the applicability of this technique for tree species with various ecological strategies, i.e. shade-tolerant species. Finally, we estimate that the age of large oaks in our study area does not exceed 400 years. Due to such fast growth, it is possible to keep the continuity of these keystone structures in a given landscape and thus preserve the associated biodiversity.
Juniperus thurifera L. (Cupressaceae) is a dioecious tree inhabiting the Western Mediterranean Basin in areas under Mediterranean continental climate. Spain (95.1%) and Morocco (4.8%) host the largest populations. Diverse dendroecological research developed during the last years has improved our knowledge about this species functioning and its forest dynamics. This review approaches the advances produced on several topics including xylogenesis, climate forcing of secondary growth and xylem anatomy, regional variability on climate control, water-use efficiency, non-structural carbohydrates dynamics and present and future dynamics of its Iberian forests. A special point is paid on sex-related differences between male and female junipers, including non-structural carbohydrate accumulation patterns, secondary growth and response to summer drought, the main climatic factor limiting growth. This review aims to synthesize the available knowledge about this species at multiple spatio-temporal scales, being particularly useful for researchers and managers interested in the investigation, management and conservation of Iberian Juniperus thurifera woodlands.
Atlantic and Mediterranean air masses influence the climate over the Iberian System mountain range. The relatively short instrumental records in central Spain though limit any long-term assessment of these synoptic systems. We here evaluate the potential to analyze such changes using ring width data from Juniperus thurifera trees growing in the northwestern and southeastern regions of the Iberian System, exposed to Atlantic and Mediterranean cyclonic activity, respectively. Comparison of tree rings with regional precipitation, temperature, and Palmer Drought Severity Index (PDSI) data indicates that juniper trees contain information on late spring and early summer drought conditions. Calibration trials using spatially resolved, gridded climate data reveal that the northwestern sampling site is predominantly controlled by Atlantic weather, while the southeastern site mainly reflects Mediterranean climate patterns. The strength and position of the blocking Azores high during spring to early summer is of particular importance for the distinct growth reactions in the Iberian System. The climate signal is remarkably strong in the southeastern site, where we developed the longest and best-replicated juniper tree ring record of the Iberian Peninsula. Data from this site allowed the reconstruction of May-June PDSI variability back to the early eighteenth century, indicating severe drought (PDSI < −9) in southeastern Spain in 1782, 1828, 1869, 1981, and 2005. The new PDSI record coheres well with historical rogation ceremony data from eastern Spain, indicating that common information on past drought events is inherent in both proxy archives.
• Aim. The Mediterranean Basin is considered to be a climate-change hotspot, for which rising temperatures and associated aridification have been forecast. Such trends could affect the performance and growth of conifers in these drought-prone areas. We evaluated whether radial growth and wood density can act as proxy measures of precipitation and drought in a Mediterranean conifer.
• Location. Iberian Juniperus thurifera forests in northern and eastern Spain.
• Methods. We sampled 10 stands encompassing J. thurifera's distributional area. We related four annually resolved tree-ring variables (earlywood and latewood width, and maximum and minimum wood density) to climatic factors (temperature, precipitation and drought index) for the period 1951–2000. We then analysed the spatial and temporal patterns of those associations.
• Results. Of all the four tree-ring variables analysed, minimum wood density presented the strongest response to climate. Higher values of minimum wood density were related to drier spring conditions, particularly in the most xeric sites, confirming that a drought-induced reduction in the radial expansion of tracheids increases earlywood density.
• Main conclusions. Minimum wood density is a biogeographically meaningful proxy of spring water availability for the Mediterranean conifer J. thurifera.