Stem radius fluctuations of trees





Roman Zweifel


Stem radius changes of trees are mainly induced by tree water relations altering the pressure conditions and thus the size of living and woody tissues in the stem, wood and bark growth, the degradation of phloem cells, and thermal expansion and contraction of the stem. These stem radius fluctuations are measured by dendrometers.

Units, terms, definitions

Stem radii can either increase or decrease over time. This change in radius is abbreviated with DRt μm. t defines the time period over which the radius change is integrated.

Origin of stem radius fluctuations

Stem radius changes (DR) are determined by five components:

(i) tree water relations altering the pressure conditions and thus the water content and the size of living and woody tissues in the stem,

(ii) wood and bark growth (cambial activity),

(iii) the degradation of dead phloem cells,

(iv) freeze and thaw induced fluctuations of the stem, and

(v) temperature induced expansion or shrinkage of wood.

Swelling/shrinking or mechanical deformations of the dead outermost layer of the bark and temperature sensitivities of the dendrometers are (vi) artefacts and need to be reduced to a minimum when measuring DR.

(i) Plants in general and trees in particular are hydraulic systems in which all living cells are interconnected with each other by water columns (Lockhart, 1965; Molz & Klepper, 1973; Zweifel et al., 2007). Thus, pressure changes and water deficits in one part of the plant are transmitted into other plant parts and are, depending on water availability and hydraulic resistances, levelled off over time (van den Honert, 1948; Steppe et al., 2006). The living cells of the wood and bark act as a water storage location in the tree’s water flow and storage system and are hydraulically connected to the water flow in the dead conducting elements of the xylem (Perämäkiet al., 2001; Zweifel et al., 2001; Steppe et al., 2006; Sevanto et al., 2008). Negative pressures in the xylem induced by transpiration determine a contraction in the wood (Irvine & Grace, 1997; Sevanto et al., 2002; Daudet et al., 2005), in the cambium (Drew et al., 2010) and in the bark (Breda & Granier, 1996; Steppe et al., 2006; Zweifel et al., 2006; Drew et al., 2008). Depending on the tree species, the biggest fraction of this reversible, pressure induced DR is usually originated in the bark (Zweifel & Häsler, 2001) but also the cambium and the xylem including its cell walls undergo a volume change depending on the actual tree water status at the point of measurement (Sevanto et al., 2002; Daudet et al., 2005; Sevanto et al., 2005; Sevanto et al., 2008). The loss of volume is proportional to the loss of water out of the respective tissues and therefore proportional to the measured DR (Zweifel et al., 2000; Steppe et al., 2006 ).

The reversible fraction of DR, which is induced by tree water relations, lasts from minutes to weeks and can either be positive or negative, depending on the changing turgor of the stem tissues and the respective drought conditions of the plant’s environment (Zweifel et al., 2006; Zweifel et al., 2007; De Swaef & Steppe, 2010; Zweifel et al., 2010). In dry periods, the daily balance between water uptake and water loss can be negative, and therefore lead to tree water deficits lasting several weeks with shrinking stems even during the wood growth period (Zweifel et al., 2005; Drew et al., 2008; De Swaef et al., 2009). On a daily scale, cells lose water during periods of transpiration (daytime) and are replenished during night and rainy or foggy periods. Accordingly, stems shrink during the day and expand at night (Steppe et al., 2006; Steppe et al., 2008b).

(ii) In addition to this rather short-term rhythm of water induced stem radius changes, seasonal growth periods contribute to the dynamics of DR (Kozlowski & Winget, 1964; Downes et al., 2009). New xylem and phloem cells are built and elongated to their predisposed size (Lockhart, 1965). Both processes of cell division and cell elongation are turgor-pressure dependent and therefore also affected by tree water relations (De Schepper & Steppe, 2010). In the succeeding wood formation process, the juvenile xylem cells become lignified and die when mature (Drew et al., 2010) and the stem size is only little altered by these woody structures (see above). By contrast, newly built phloem cells remain living and are not lignified. Thus, phloem cells remain elastic and undergo diurnal water-related size changes even when mature.

(iii) In contrast to the lignified xylem elements, phloem cells shrink, break down, die and, finally, are shed (Lockhart, 1965; Rossi et al., 2008; Gricar et al., 2009). This fraction of DR is not well understood so far but might significantly contribute to shrinking stems particularly during wintertime and in tree species with low (wood) growth rates.

(iv) Freeze and thaw events of tree stems are a special aspect of water induced stem radius changes since the effect on DR is induced by a rapid dehydration of living tissues (mainly phloem cells) short before ice is built in the bark and by a rehydration of these tissues with thawing (Zweifel & Häsler, 2000; Ameglio et al., 2001; Ameglio et al., 2002; Daudet et al., 2005). A potential mechanism assumes that water is withdrawn from living cells to increase the osmotic potential, thus, decreasing the freezing point and therefore protect the living cells from freezing damages. DR strongly decreases during these freezing events and this despite the fact that ice needs more volume than liquid water. This finding indicates that the water removed from living cells freezes in gas-filled inter-cellular spaces with no effects on DR. As soon as the temperature returns above the freezing point the contracted tissues are re-hydrated and DR increases in the same magnitude as it has decreased before.

(v) The coefficient of thermal expansion of dry wood varies between 15-35*10-6 K-1. For a tree stem with 25 cm in diameter, this results in 4-9 μm expansion per K temperature increase, what is mostly relatively small compared to diurnal amplitudes of DR.

(vi) The most common artefact in DR measurements is the temperature sensitivity of the dendrometer itself. The mechanical frame, the anchoring in the stem, and also the electronic devices and their power sources are potentially temperature sensitive. It is therefore essential to test any type of dendrometers for its temperature sensitivity by mounting the device on a stone column or a similar temperature-insensitive object and compare the measurements with the temperature readings. Other sources of measurement artefacts are the swelling or shrinkage of the dead outermost layer of the bark. Generally, any changes in DR induced by dead tissue outside the cork cambium are to be judged as artefacts, e.g. mechanical bending of drying and shed pieces of he bark.

Measurement approaches

Point dendrometers automatically detect stem radius changes on a single point on the stem. There exist different anchoring and frame approaches. Usually a frame with the electronic device attached to it (e.g. a linear variable displacement transducer (LVTD) or a potentiometer) is anchored with three rods in the heartwood of the stem. The sensor head is placed on the bark surface where the dead outermost layer of the bark has been removed. A good point dendrometer has a temperature sensitivity < 1 μm C-1 and a resolution of < 1 μm.

The frame can also enclose the entire stem (often used for small-diameter stems) enabling the mounted sensor (either point dendrometer or LVDT) to measure whole stem diameter variations (Steppe & Lemeur, 2004).

Band dendrometers detect stem circumference changes and are available for manual and automated readings. Since the electronic devices of band dendrometers and the long metal bands are more temperature sensitive than point dendrometers the readings are usually less precise but include the entire circumference and not just a single spot of the stem. Another source of noise of the band dendrometer is the shrinking/swelling or mechanical bending of the dead outermost layer of the bark since it is hard to properly remove this dead layer all around the stem under the band without injuring the living tissue.

Measured fractions and ranges of DR

Picea abies

Pinus sylvestris

Quercus pubescens

Fagus sylvatica (Steppe et al., 2006; Steppe et al., 2008b)

Quercus robur (Steppe et al., 2008b; De Schepper & Steppe, 2010)

Malus domestica (Steppe et al., 2008a; De Swaef et al. 2009)

Solanum lycopersicum (De Swaef & Steppe, 2010)

Related topics

  • Tree water relations (conductance, water flow and storage, tree water deficit, water potentials, winter dehydration = frost shrinkage, etc.)
  • Wood growth (cambial activity, wood anatomy, tree ring development, etc.)


Ameglio T, Bodet C, Lacointe A, Cochard H. 2002. Winter embolism, mechanisms of xylem hydraulic conductivity recovery and springtime growth patterns in walnut and peach trees. Tree Physiology 22(17): 1211-1220.

Ameglio T, Cochard H, Ewers FW. 2001.Stem diameter variations and cold hardiness in walnut trees. Journal of Experimental Botany 52(364): 2135-2142.

Breda N, Granier A. 1996.Intra- and interannual variations of transpiration, leaf area index and radial growth of a sessile oak stand (Quercus petrea). Annales des Sciences Forestieres 53: 521-536.

Daudet FA, Ameglio T, Cochard H, Archilla O, Lacointe A. 2005.Experimental analysis of the role of water and carbon in tree stem diameter variations. Journal of Experimental Botany 56(409): 135-144.

De Schepper V, Steppe K. 2010. Development and verification of a water and sugar transport model using measured stem diameter variations. Journal of Experimental Botany 61 : 2083 – 2099.

De Swaef T, Steppe K. 2010. Linking stem diameter variations to sap flow, turgor and water potential in tomato. Functional Plant Biology 37: 429-43.

De Swaef T, Steppe K, Lemeur R. 2009. Determining reference values for stem water potential and maximum daily trunk shrinkage in young apple trees based on plant responses to water deficit. Agricultural Water Management 96: 541-550.

Downes GM, Drew D, Battaglia M, Schulze D. 2009.Measuring and modelling stem growth and wood formation: An overview. Dendrochronologia 27(2): 147-157.

Drew DM, Downes GM, Battaglia M. 2010.CAMBIUM, a process-based model of daily xylem development in Eucalyptus. Journal of Theoretical Biology 264(2): 395-406.

Drew DM, O’Grady AP, Downes GM, Read J, Worledge D. 2008.Daily patterns of stem size variation in irrigated and unirrigated Eucalyptus globulus. Tree Physiology 28(10): 1573-1581.

Gricar J, Krze L, Cufar K. 2009.Number of cells in xylem, phloem and dormant cambium in Silver fir (Abies alba), in trees of different vitality. IAWA Journal 30(2): 121-133.

Irvine J, Grace J. 1997.Continuous measurements of water tensions in the xylem of tree based on the elastic properties of wood. Planta 202: 455-461.

Kozlowski TT, Winget CH. 1964.Diurnal and seasonal variation in radii of tree stems. Ecology 45: 149-155.

Lockhart JA. 1965.An analysis of irreversible plant cell elongation. Journal of Theoretical Biology 8: 264-275.

Molz FJ, Klepper B. 1973.On the mechanism of water-stress-induced stem deformation. Agron J 65: 304-306.

Perämäki M, Nikinmaa E, Sevanto S, Ilvesniemi H, Siivola E, Hari P, Vesala T. 2001.Tree stem diameter variations and transpiration in Scots pine: an analysis using a dynamic sap flow model. Tree Physiology 21: 889-897.

Rossi S, Deslauriers A, Gricar J, Seo JW, Rathgeber CBK, Anfodillo T, Morin H, Levanic T, Oven P, Jalkanen R. 2008.Critical temperatures for xylogenesis in conifers of cold climates. Global Ecology and Biogeography 17(6): 696-707.

Sevanto S, Holtta T, Markkanen T, Peramaki M, Nikinmaa E, Vesala T. 2005.Relationships between diurnal xylem diameter variation and environmental factors in Scots pine. Boreal Environment Research 10(5): 447-458.

Sevanto S, Nikinmaa E, Riikonen A, Daley M, Pettijohn JC, Mikkelsen TN, Phillips N, Holbrook NM. 2008.Linking xylem diameter variations with sap flow measurements. Plant and Soil 305(1-2): 77-90.

Sevanto S, Vesala T, Peramaki M, Nikinmaa E. 2002.Time lags for xylem and stem diameter variations in a Scots pine tree. Plant Cell and Environment 25(8): 1071-1077.

Steppe K, De Pauw DJW, Lemeur R. 2008a. A step towards new irrigation scheduling strategies using plant-based measurements and mathematical modelling. Irrigation Science 26, 505-517.

Steppe K, De Pauw DJW, Lemeur R. 2008b. Validation of a dynamic stem diameter variation model and the resulting seasonal changes in calibrated parameter values. Ecological Modelling 218, 247-259.

Steppe K, De Pauw DJW, Lemeur R, Vanrolleghem PA. 2006.A mathematical model linking tree sap flow dynamics to daily stem diameter fluctuations and radial stem growth. Tree Physiology 26: 257-273.

Steppe K, Lemeur R. 2004. An experimental system for analysis of the dynamic sap-flow characteristics in young trees: results of a beech tree. Functional Plant Biology 31: 83-92.

van den Honert TH. 1948.Water transport in plants as a caternary process. Faraday Society Discussions 3: 146-153.

Zweifel R, Eugster W, Etzold S, Dobbertin M, Buchmann N, Häsler R. 2010.Link between continuous stem radius changes and net ecosystem productivity of a subalpine Norway spruce forest in the Swiss Alps. New Phytologist 187: 819-830.

Zweifel R, Häsler R. 2000.Frost-induced reversible shrinkage of bark of mature, subalpine conifers. Agricultural and Forest Meteorology 102: 213-222.

Zweifel R, Häsler R. 2001.Dynamics of water storage in mature, subalpine Picea abies: temporal and spatial patterns of change in stem radius. Tree Physiology 21: 561-569.

Zweifel R, Item H, Häsler R. 2000.Stem radius changes and their relation to stored water in stems of young Norway spruce trees. Trees 15: 50-57.

Zweifel R, Item H, Häsler R. 2001.Link between diurnal stem radius changes and tree water relations. Tree Physiology 21: 869-877.

Zweifel R, Steppe K, Sterck FJ. 2007.Stomatal regulation by microclimate and tree water relations: interpreting ecophysiological field data with a hydraulic plant model. Journal of Experimental Botany 58(8): 2113-2131.

Zweifel R, Zeugin F, Zimmermann L, Newbery DM. 2006.Intra-annual radial growth and water relations of trees – implications towards a growth mechanism. Journal of Experimental Botany 57(6): 1445-1459.

Zweifel R, Zimmermann L, Newbery DM. 2005.Modeling tree water deficit from microclimate: an approach to quantifying drought stress. Tree Physiology 25: 147-156.

Leave a Reply