âReserva Natural Laipunaâ. Tree species: Bursera graveolens. Conclusions. â. At both study sites, two groups of element concentrations in tree rings are evident.
Elemental analysis in tree rings from two different forests in southern Ecuador Darwin Pucha Cofrep 1,2, Achim Bräuning1, Wolfgang Wilcke3 1. Friedrich-Alexander-Universität Erlangen-Nürnberg. 2. Universidad Nacional de Loja. 3. Karlsruhe Institute of Technology
Platform for Biodiversity and Ecosystem Monitoring and Research in South Ecuador
Methodology
The aims of this study were to
Dated annual tree-rings from two different ecosystems were individually digested in 4 mL of HNO3 in a MLS-ETHOS microwave system. Element concentrations in digests were measured with an Inductively-coupled Plasma Mass Spectrometer (ICP-MS)* and an Atomic Absorption Spectrometer (AAS)**. We analyzed six trees of Cedrela montana (63 yr old) from the humid forest and three trees of Bursera graveolens (100 yr old) from the dry forest.
1) detect element patterns in tree rings and to explore their relationship with climate and
Climate data: Throsten Peters
2) explore differences in nutrient accretion in wood between two ecosystems with distinct climate (Fig. 1), a humid and a dry forest.
HUMID FOREST “Reserva Biológica San Francisco” Tree species: Cedrela montana
Results
Climate data: Throsten Peters
Aims
Fig. 1a. Monthly mean climate diagram
Fig. 1b. Monthly mean climate diagram
from the RBSF. The blue area indicates the rainy months.
from Laipuna. The blue area indicates the rainy months, and the red area indicates the dry months.
We ran a Principal Component Analysis (PCA) to identify the elements that explained most of the variance (Fig. 2) and then complemented the PCA with a Hierarchical Cluster Analysis (HCA) (Fig. 3). Our results illustrate a high heterogeneity of the element patterns among individual trees of the same species. Nevertheless, there were distinctly different patterns between the tree rings from the two different forest ecosystems (Fig. 4).
DRY FOREST “Reserva Natural Laipuna” Tree species: Bursera graveolens
Two well defined groups of elements were identified. The first group included Sr, Ca, Ga, Ba, and the second group K, P, and Rb. The two groups showed opposite radial concentration trends across the trunk (Fig. 4). Concentrations of Group 1 elements increased towards the younger tissue and those of Group 2 decreased illustrating that the Group 2 elements were comparatively mobile. The humid forest showed clearer patterns than the dry forest.
Fig. 2a PCA of element concentrations in tree rings of individual trees of C. montana showing the first two Principal Components (PCs). The % value represent the explained part of the total variance by the respective PC. Elements are in black colour and supplementary variables in blue ( TRW: Tree-Ring Width, PRE: Precipitation, TEMP: Temperature and the Weight of rings before the digestion process).
Fig. 2b Similar to the description in the Fig. 2a, PCA of individual trees of B. graveolens showing the first two Principal Components.
Fig. 3a Classification of element concentration patterns in individual trees of C. montana by dendrograms based on HCA. The nutrients are grouped and arranged by their similarity. The colored boxes represent the main two main groups of nutrients. A third group of elements including Cu, Zn and Pb – the classical pollution elements - became apparent. Note that the element grouping and arranging is similar to the PCA.
Fig. 3b Similar to the description in the Fig. 3a, classification of element patterns in tree rings of individual trees of B. graveolens by dendrograms based on HCA.
Scale: Low
Scale: High
Low
Concentration (Index)
High
Concentration (Index)
Cedrela montana
Bursera graveolens
Fig. 4a Left: “Heat map” showing the annual nutrient concentration and distribution across a radial wood section of C. montana. Displayed are median values of the six individual trees. Left of the heat map the dendrogram grouping of the elements (see Fig. 3) is indicated. The long rectangles in the heatmap indicate the elements with the clearest trends (Group 1: Sr, Ca, Ba, Ga and Group 2 Rb, K, P). Right: Median radial distribution of the concentrations of Group 1 (top) and Group 2 (bottom) elements in tree rings of six C. montana trees.
Fig. 4b Similar to the description in the Fig. 4a, a heat map showing the element patterns in tree rings and distribution across a radial wood section of B. graveolens. Note that now the Group 1 elements Ca, Sr, Ba and Ga are separated into two clusters, and their radial trends are less clear than in the humid forest.
Conclusions
Acknowledgements
At both study sites, two groups of element concentrations in tree rings are evident (Group 1: Ba, Ca, Ga, and Sr; Group 2: K, P, and Rb) which show opposite radial trends, presumably as a consequence of their different mobilities in the tree (Group 1 immobile, Group 2 mobile). Although overall patterns of element concentrations are similar at both study sites, the strength of the observed patterns seems to be weaker in the dry forest. The influence of the different climatic and soil conditions and species still needs to be explored in detail.
The authors thank DFG for funding the Project in the framework of the research unit FOR816/PAK823-825, the MAE Ecuador for the research permission, and the NCI-Loja for their help in accessing to the Laipuna Nature Reserve.
* ICP-MS: Be, B, Na, Al, S, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, As, Se, Rb, Sr, Mo, Ag, Cd, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Ho, Er, Tm, Yb, Lu, Re, Tl, Pb, Th and U. ** AAS: Ca, K, Mg and P.
