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Tree-ring study sites: ecology

WSL tree-ring research: ecology

Dendroecological studies, in which tree-ring analyses are applied to ecological questions, have been an integral part of the tree-ring research at WSL since the early 1970s. Such studies deal with the assessment of a wide range of changes in the local environment, as reflected in different tree-ring and wood-anatomical parameters.

These parameters, often available from intra-annual to Holocene-long time-scales, enable the reconstruction of ecological processes such as defoliation by insect outbreaks; the effects of air, water, and soil pollution on tree growth and forest health; the age, maturity, and successional status of forest stands; and the effects of human disturbances and management on forest vitality.

The Dendroecology Group at WSL uses annually resolved and absolutely dated dendrochronological and wood anatomical information to reconstruct environmental conditions over different spatiotemporal scales. We perform cutting-edge tree-ring research at the interface of archaeology, climatology and ecology, and suggest expanding dendroecology beyond existing disciplinary boundaries.

Our timely dendrochronological and wood anatomical investigations, centered on the emerging interdisciplinary Global Change arena, also consider non-forested Arctic and alpine vegetation. In this regard, the team develops, archives and analyzes globally distributed, high-resolution tree-ring datasets that may range from intra-annual to Holocene-long time scales and cover a variety of spatial domains.

In summary, we aim to better understand how the Earth's climate system changed and still changes and how terrestrial ecosystems were and are responding to such changes on various spatial and temporal scales.

The following examples of dendroecological frontiers emphasize the interdisciplinary character of our investigations.

Life at the frontier
Rhododendron lapponicum A small (<5 cm high) Rhododendron lapponicum plant from coastal Eastern Greenland around 71°N that contains ~240 annual rings and contradicts the life-form paradigm. In fact, age and size are not necessarily correlated.

Schweingruber FH, Hellmann L, Tegel, W, Braun S, Nievergelt D, Büntgen U (2013) Evaluating the wood anatomical and dendroecological potential of Arctic dwarf shrubs. IAWA Journal 34: 485-497. doi:10.1163/22941932-00000039


Reconstructing insect outbreaks

Zeiraphera diniana
A high-resolution thin-section from a historical larch (Larix decidua) timber sampled in the Swiss subalpine Lötschental.

The extremely narrow ring that consists of only one earlywood and two latewood cell rows was caused by a severe defoliation event due to a mass outbreak of the larch bud moth (Zeiraphera diniana).

Esper J, Büntgen U, Frank DC, Nievergelt D, Liebhold A (2007) 1200 years of regular outbreaks in alpine insects. Proceedings of the Royal Society B 274: 671-679. doi:10.1098/rspb.2006.0191


Illuminating the mysterious world of truffles

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Breaking new ground at the interface of dendroecology and mycology:
(a) An excavation of a natural truffle (Tuber aestivum) site in southwest Germany,
(b) a nearby radius dendrometer (Ecomatik DR) measuring radial stem growth of a possible truffle host (Fagus sylvatica) at hourly resolution, and
(c) a microscopically magnified image of a Tuber aestivum peridium (surface) with mycelium extensions. 

New insight on the mycorrhizal fungus-host association, expected to emerge from combining dendrochronology and mycology, may help disentangling biotic, abiotic and combined edaphic factors of the mutualistic relationship between thousands of ectomycorrhizal fungi and their perennial partners.

Büntgen U, Egli S, Tegel W, Stobbe U, Sproll L, Elburg R, Peter M, Nievergelt D, Cherubini P, Stenseth NC (2012) Illuminating the mysterious world of truffles. Frontiers in Ecology and the Environment 10: 462-463. doi:10.1890/12.WB.021


Intra-annual profiles of anatomical traits

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In the top picture of an exemplary cross-section of a tree-ring of Pinus sylvestris (Scots pine), yellow tracheid lumina are displayed after semi-automatic quantification of xylem anatomy using the specialized tool ROXAS. The corresponding changes in tracheid lumen area and tracheid cell-wall thickness within an annual ring as measured with ROXAS are shown at the bottom.

Such intra-annual profiles of anatomical traits show the influence of environmental conditions on tree-ring formation throughout the whole growing season. The analysis of time series of intra-annual profiles help to establish cause-effect relationships between the environment and tree growth. Ultimately, this improves our mechanistic understanding of tree structure-function responses to environmental variability

von Arx G, Carrer M (2014) ROXAS - a new tool to build centuries-long tracheid-lumen chronologies in conifers. Dendrochronologia doi:10.1016/j.dendro.2013.12.001


European springtime temperatures benefits Alpine ibex vitality

Effects of climate change on trophic interactions and subsequent disruptions of seasonal synchrony, together with warming-induced alternations of body size and fitness are particularly severe in Arctic and Alpine ecosystems. Unraveling biotic from abiotic drivers, however, remains challenging because high-resolution animal population data are often limited in space and time.

We showed that year-to-year variation in annual horn growth (an indirect proxy for individual fitness) of 8,043 Alpine male ibexes (Capra ibex) is spatially well synchronized among eight disjunct colonies living in different regions and altitudes in the eastern Swiss Alps. Increasing March-May temperatures, controlling Alpine snowcover, plant phenology and subsequent ibex resource consumption, not only fuelled annual horn growth but also enhanced general body size over the past four decades.

Our results reveal strong dependency of local trophic interactions on large-scale climate dynamics, and provide insight on rapid phenotypic plasticity.

Büntgen U, Liebhold A, Jenny H, Mysterud A, Egli S, Nievergelt D, Stenseth NC, Bollmann K (2013) European springtime temperature synchronises ibex horn growth across the eastern Swiss Alps. Ecology Letters doi:10.1111/ele.12231

News release


Neolithic wooden well
Brunnen Example of early Neolithic craftsmanship from a well construction in Germany dating around 7200 years before present. The picture shows timber bearing tool marks on the surface, a cogging joint, i.e., the base frame with wedged tusk tenon joint with an interlocked corner joint.

Tegel W, Hakelberg D, Elbrug R, Stäuble H, Büntgen U (2012) Early Neolithic water wells reveal the world’s oldest wood architecture. PLoSONE 7(12): e51374. doi:10.1371/journal.pone.0051374