We are currently analyzing the drivers of wood growth of Swiss forest trees over the past five years (preliminary results).
Figure 1 Growth trends of the main tree species in Switzerland. Radial growth: radial increment per year; Cross section area growth: annual increment of the trees’ cross section area; Relative growth: Annual increment divided by the stem radius (preliminary results).
Wood growth is the result of determining factors at the time of growing but also a response to environmental conditions in the past (carry-over effects). Carry-over effects include conditions of hours, days or even years ago. It includes e.g., the determination of buds in autumn of the past year but also the life-span of different organs of a tree like the sapwood, the leaves or the carbon storage pool.
No general growth trend was found (Fig. 1). However, there appear decreasing trends for some species over the past four years (2012-2015). Generally, the standard deviation from the respective means is large and there appear different patterns for different species.
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Publication in New Phytologist about separating stem radius measurements into growth and tree water deficit
Separating continuously measured stem radius (SR) fluctuations into growth-induced irreversible stem expansion (GRO) and tree water deficit-induced reversible stem shrinkage (TWD) requires a conceptualization of potential growth processes that may occur during periods of shrinking and expanding SR below a precedent maximum. Here, we investigated two physiological concepts: the linear growth (LG) concept, assuming linear growth, versus the zero growth (ZG) concept, assuming no growth during periods of stem shrinkage.
We evaluated the physiological mechanisms underlying these two concepts and assessed their respective plausibilities using SR data obtained from 15 deciduous and evergreen trees.
The application of the LG concept produced steady growth rates, whereas growth rates varied strongly under the ZG concept, more in accordance with mechanistic expectations. Further, growth increased for a maximum of 120 min after periods of stem shrinkage, indicating limited growth activity during those periods. However, this extra growth was found to be a small fraction of total growth only. Furthermore, TWD under the ZG concept was better explained by a hydraulic plant model than TWD under the LG concept.
We conclude that periods of stem shrinkage allow for very little growth in the four tree species investigated. However, further studies should focus on obtaining independent growth data to ultimately validate these findings.
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Wie man die Bäume wachsen hört – Das faszinierende Universum Wald bietet viele Geheimnisse: Seiner komplexen Natur sind Wissenschaftler nun auch mit Hörgeräten auf der Spur.
Artikel in der Sonntagszeitung, 24. Januar 2016
by Simone Kühn-Bühlmann