juniperus thurifera
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The morphological features of plants, which were the basis of taxonomic solutions in the past, are now sometimes less appreciated due to the intensive development of genetic methods. The present review looks at the results of the research on the taxonomy of plants carried out by the team led by A. Boratyński. The team characterized the taxonomic and geographical differentiation of some species of the genera Abies, Juniperus, Pinus, Cupressus, Cedrus, as well as several others. Many of these studies were carried out in the Mediterranean area due to its importance for biodiversity. The results allowed unravelling taxonomic ambiguities, emphasizing the importance of geographic barriers in shaping variability, e.g., the Strait of Gibraltar or the Aegean Sea, and highlighting the role of mountain ranges as refuges, e.g., the Taurus and Anti-Taurus Mountains. All of the results obtained with biometrics were confirmed by genetic methods by different authors. Detailed research allowed the publication of a new name, Juniperus thurifera subsp. africana (Maire) Romo & Boratyński, stat. nov., and restoration of species status for the dubious taxon Juniperus canariensis. The review shows that relying on the research of a large number of correctly sampled populations and correctly selected differentiated characteristics of plants allows the generation of reliable results.

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.

Research Highlights: Water use efficiency (WUE) varied along a gradient of Juniperus thurifera (L.) forest expansion, being higher in recently colonised areas. Background and Objectives: WUE is a classic physiological process of plants that reflects the compromise between carbon assimilation and water loss and has a profound influence on their performance in water-limited environments. Forest expansion in Mediterranean regions associated with land abandonment can influence the WUE of plants due to the existence of two opposing gradients: one of favourable–unfavourable environmental conditions and another one of increased–decreased intraspecific competition, the former increasing and the latter decreasing towards the expanding front. The main objective of this study was to elucidate how the WUE of Juniperus thurifera varied along the stages of forest expansion and to provide insight on how this variation is influenced by intraspecific competition and abiotic factors. Materials and Methods: Seventeen plots at different distances from the mature forest core were selected at three sites located in the centre of the Iberian Peninsula. For 30 individuals within each plot, we measured biometric characteristics, age, tree vigour, and C/N ratio in leaves, and the leaf carbon isotope signature (δ13C (‰)) as a proxy for WUE. Around each individual, we scored the percentage cover of bare soil, stoniness, conspecifics, and other woody species. Results: WUE of J. thurifera individuals varied along the forest expansion gradient, being greater for the individuals at the expanding front than for those at the mature forest. WUE was influenced by the cover of conspecifics, tree age, and C/N ratio in leaves. This pattern reveals that less favourable environmental conditions (i.e., rocky soils and higher radiation due to lower vegetation cover) and younger trees at the expanding front are associated with increased WUE. The increased cover of conspecifics decreases irradiance at the mature forest, involving milder stress conditions than at the expanding front. Conclusions: Lower WUE in mature forests due to more favourable conditions and higher WUE due to abiotic stress at expanding fronts revealed high constraints on water economy of this tree species in these two contrasting situations. Climate change scenarios bringing increased aridity are a serious threat to Juniperus thurifera forests, affecting both mature and juvenile populations although in different ways, which deserve further research to fully unveil.

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.

Abstract As the global climate warms, increased aridity is expected to become a major determinant of forest productivity and tree growth. In gymnosperms, wood density quantified at seasonal to annual scales can be related to changes in tracheid lumen size due to alterations in soil water availability. In this way, minimum wood density (MND) has been shown to respond negatively to early growing-season precipitation in several conifers because dry conditions reduce tracheid lumen size and consequently increase MND. We investigated if this relationship between spring precipitation and MND applies to four conifer species (Abies alba, Pinus sylvestris, Pinus nigra, Juniperus thurifera) in NE Spain from mesic (A. alba, P. sylvestris) to xeric (P. nigra, J. thurifera) conditions. We further assessed how climate, precipitation, and drought-affected tree-ring width (TRW) and MND at several time scales to test if water shortage in spring increases MND and decreases TRW over time and seasonally. Lastly, we quantified the post-drought MND recovery. We found the strongest negative correlations between MND and spring precipitation in P. nigra followed by J. thurifera. In these two species, the associations between MND and 9-month long droughts peaked in early spring (P. nigra, ; J. thurifera, ). Juniperus thurifera presented a better post-drought recovery (decrease in MND), followed by P. nigra and P. sylvestris. We conclude that MND is a reliable and accurate proxy of drought severity during spring in conifers subjected to seasonal water shortage. MND can be used as an early-warning indicator of short- and long-term changes in the responses of trees to water shortage.