Research Network in Biodiversity and Evolutionary Biology

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Dendrochronological potential of the Azorean endemic gymnosperm Juniperus brevifolia (Seub.) Antoine

Publication . Pavão, Diogo Cláudio; Jevšenak, Jernej; Petrillo, M.; Camarinho, Ricardo; Rodrigues, Armindo; Silva, L. Borges; Elias, Rui B.; Silva, Luís

Tree-ring inter-annual pattern variation is crucial in dendrochronology, allowing the identification of possible limiting factors on growth. Thus, trees exposed to subtropical or tropical climates without a marked seasonality may show a low degree of interannual variation, impeding a straightforward dendroclimatological approach. Meanwhile, subtropical regions, and areas in transitional climates such as the Azores archipelago, are widely unexplored in terms of dendroclimatology, providing opportunities to work with endemic trees, including the dominant Azorean tree Juniperus brevifolia (Seub.) Antoine. To evaluate the dendrochronological potential of J. brevifolia, we analyzed tree-ring patterns, crossdating capabilities, and correlation with climate parameters. We sampled 48 individual trees from two natural populations (São Miguel and Terceira islands) using an increment borer. Besides, a Trephor tool was used to obtain wood microcores for micro-anatomical analysis. Although the transition between early and latewood was evident, partially indistinct ring boundaries and wedging rings were present in some cases, affecting the crossdating process, but not impeding the establishment of reliable ring-width chronologies. Following detrending, master chronologies were built and correlated with monthly temperature and precipitation data using the treeclim R package. The climate-growth relationships indicated negative correlations with late summer temperature in both populations. Considering our results and the importance of J. brevifolia as a dominant tree in the Azores natural forests, we conclude that it shows an acceptable potential for dendrochronological research. Thus, this study provides baseline information to help fill the knowledge gap regarding the climate-growth relationship of Azorean trees.

2022-02Journal article

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Tree growth-climate relationship in the Azorean holly in a temperate humid forest with low thermal amplitude

Publication . Pavão, Diogo Cláudio; Jevšenak, Jernej; Engblom, J.; Borges Silva, L. Borges; Elias, Rui B.; Silva, Luís

Dendroclimatic records in areas with high relative humidity and low thermal amplitude are manifestly scarcer and only a few studies are applied to species that are present in areas with weak seasonality. The Azores archipelago with temperate climate, with low thermal amplitude, has unique biodiversity, including the Azorean holly, Ilex azorica Gand., that is dominant in most extant natural forests. Hence, the importance of understanding its behavior and relation with climate. In this study, we try to understand tree-ring patterns of this species and examine the relationship between radial tree growth and main climatic drivers. For this purpose, we sampled four populations from São Miguel Island and two from Terceira Island. We found a diffuse-ring porous wood with a common layer of vessels associated to the ring boundary, which was critical to identify annual tree-rings. Generalized linear models were used to relate different variations of temperature and precipitation parameters, resulting into a diverse climate-growth relationships of different populations, while the composite population exhibited pronounced effect of temperature. We conclude that, I. azorica forms reliable annual tree-rings, which can be statistically related to climate, mostly temperature. However, there are differences among specific sites, thus the climate sensitivity depends on other site characteristics, such as soil and slope, but probable also to other ecological drivers, such as the competition, water drainage, among others.

2022-12Journal article

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