Effects of simulated defoliation on physiology and growth of Abies alba trees
Rationale
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Scientists checking out a Christmas tree
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Crown transparency of trees in Switzerland has been monitored annually since 1984. An increasing trend of defoliation in Swiss forests was detected (Brang 1998). The knowledge of the defoliation effects on the physiological processes resulting in tree growth is still lacking. Although several studies found that a severe defoliation leads to a significant reduction in mobile carbohydrates and growth of trees (e.g., Li et al. 2002), no studies investigated the effects of an age-dependent defoliation. Defoliation observed in the Swiss forests by the Sanasilva-inventory usually starts from the older needles going on to the youngest (Dobbertin 1998). How important is the contribution of the oldest needles to the whole plant photosynthesis? To what a defoliation extent can a crown compensate the effect without a significant reduction in tree growth/productivity?
Project aims
Our working hypothesis is that a moderate defoliation due to the shedding of the oldest needles has no significant effect, whereas a severe defoliation decreases the availability of carbohydrates and therefore causes an abrupt decrease in growth (both needle length and biomass). The effects caused by a severe defoliation will be detected for several years. The capability for a photosynthetic compensation of defoliated trees depends on light conditions, being easier a compensation in the gap rather than in the shadow of old trees. Following questions will be answered:
- How are the responses of the photosynthetic activity and the coresponding available carbohydrates to defoliation?
- What are the effects on height and diameter growth?
- What effects can be found in the wood anatomical characteristics of tree rings?
- How are the stable isotope ratios in foliage and wood affected?
Methods
We used one in situ experiment close to one of the Swiss Long-Term Forest Ecosystem Research (LWF) plots, Vordemwald (AG), to simulate such a defoliation (removal of the older needles) with different intensities (5 treatments) in trees (Abies alba) growing in a stand (shadow) and in a gap, i.e. open field (more light).
We use the content of total non-structural carbohydrates (TNC), N, K, Mg and Mn as internal indicators of the defoliation effects on tree physiology, and annual height and tree-ring growth as external indicators for the final actual effects on tree productivity. In order to understand the possible changes in TNC content in defoliated trees, we also measure photosynthetic activity each year during the vegetative season. The rationale behind this method is that TNC concentrations are related to needle age and to source activity (more light, more TNC). The availability of TNC controls tree growth.
Work plan
2003
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Selection and establishment of experimental plots: 25 young
Abies alba trees (ca. 2 m in height) in the stand, 25 in a gap.
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2003
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Artificial defoliation, 5 classes:
I - 0%;
II - removal of >=5-year-old needles;
III - removal of >=4-year-old needles;
IV - removal of >=3-year-old needles;
V - removal of >=2-year-old needles.
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2003
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Measuring of light intensity at each tree/site (PAR).
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2003-2005
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Three samplings each year (1-yr old needles, bark and wood)
(April, July, September). Measuring of photosynthetic activity each
year (each tree, July) (LI-COR). Measuring of starch and mobile sugars.
Measuring of N, K, Mg, Mn in 1-yr old needles (Atom absorption
spectrometer). 13C and 18O analysis of total organic matter and sucrose.
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2005
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Measuring of cambium respiration (TTC test), height growth,
ring-width measurement, image analyses on tree-ring structure at the
end of the experiment.
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Participants
Contact
Publications
- Li M.H., Cherubini P. , 2002. Der Kronenverlichtung auf der Spur. Informationsblatt Forschungsbereich Wald 11:4.
- Li M.H., Uehre P., Körner Ch., Matschke J., 2000. Einfluss der Grünästung auf das kurzfristige Dickenwachstum und die Wachstumsdynamik. AFZ-Der Wald 25: 1348-1350.
- Li M.H., Uehre P., Matschke J. 2001. Dickenzuwachs und Stammform von jungen Bäumen in Abhängigkeit von Entastungsintensitäten. Schweiz. Z. Forstwes.152(9): 389-393.
- Li M.H., Hoch G., Körner Ch. 2001. Spatial Variability of Mobile Carbohydrates within Pinus cembra Trees at the Alpine Treeline. Phyton 41(2): 203-213.
- Li M.H., Hoch G., Körner Ch. 2002. Source/sink removal affects mobile carbohydrates in Pinus cembra at the Swiss treeline. Trees 16: 331-337.
Links
| Keywords: |
Defoliation, Abies alba, carbohydrate, photosynthesis, isotope, height, radial growth, wood anatomy |
