Above- and below-ground biomass, surface and volume, and stored water in a mature Scots pine stand

J. Urban 0 1 2 J. C ermak 0 1 2 R. Ceulemans 0 1 2 0 J. Urban (&) J. C ermak Faculty of Forestry and Wood Technology, Mendel University in Brno , Zemedelska 3, 61300 Brno, Czech Republic 1 Communicated by Agustn Merino 2 R. Ceulemans Department of Biology, University of Antwerp, Universiteitsplein 1 , 2610 Wilrijk, Belgium This study describes the amount and the spatial distribution of the above- and below-ground tree skeletondefined as the woody structure of stem, branches and rootsin a mature Scots pine (Pinus sylvestris L.) stand in Belgium. Tree skeleton data were linked to the respective needle area, and as such, this work provides the background framework for modeling the tree hydraulic architecture and the carbon balance of the forest stand. Using validated allometric equations, we were able to calculate the amount of the volume, of the biomass and of the corresponding surface areas of individual trees in the stand. Total woody biomass of the 66-year-old forest stand was 155 Mg ha-1, i.e., 126 Mg ha-1 above ground and 29 Mg ha-1 below ground. The total bio-volume of the woody mass of the stand was 314 m3 ha-1. The highest fraction of this value was the stem bio-volume, i.e., 236 m3 ha-1 or 75 % of the total. The total volume of all roots was 57 m3 ha-1 (18 % of the total volume), and the volume of branches was 20 m3 ha-1 (7 % of the total volume). The surface area of the roots ranged from 38,000 m2 ha-1 in the winter to 68,000 m2 ha-1 in the spring. The surface area of the stems was 2,700 m2 ha-1, and the surface area of all branches reached 4,400 m2 ha-1. The total above-ground water storage in the xylem was 94 m3 ha-1 (or 9.4 mm), while the accessible stored water was 2 mm of that quantity. A comparative analysis of the biometric parameters showed the balance between the different functionally connected, operational surface areas of the trees. The needle surface area was similar to the root surface area and in the same order of magnitude as the surface area of woody cambium. The results allow to link water uptake with transpiration and assimilation with respiration. - Forests contain about 90 % of the carbon stored in the terrestrial vegetation and account for 40 % of the carbon exchange between the atmosphere and the terrestrial biome (Schlesinger 1997). Forest stands contribute to the terrestrial carbon balance in two different ways. First, forest stands are the principal pools of the stored carbon. It is therefore of interest to quantify tree biomass and its increment to enable the quantification of the carbon pool size. Secondly, forest trees exchange carbon with the atmosphere, not only through the uptake of carbon in photosynthesis, but also through the release of carbon dioxide via the respiration of living cells. The amount of carbon released by the woody skeleton (stem and branches) is usually quantified on a surface area basis (Edwards and Hanson 1996; Damesin et al. 2002; Kim et al. 2007; Acosta et al. 2008). For a proper extrapolation to the tree and the stand levels, the tree surface area should be known. Scots pine (Pinus sylvestris L.) is the most widely spread pine species across Eurasia, covering 24 % of Europes forested area (Stanners and Bourdeau 1995) and growing in a wide range of ecotypes (Richardson 1998). Scots pine stands are thus an important factor affecting the carbon and water balances in Europe and Asia (Richardson 1998; Poyatos et al. 2007). Although there is a good knowledge of the stems of Scots pine (e.g., Claesson et al. 2001; Landsberg et al. 2005), much less is known about the surface area and the biomass of branches and roots. The vertical distribution of roots and branches plays an important role in the competitiveness of an individual tree (Stoll and Schmid 1998). The branches hold the needles, exposing them to incoming radiation, and thus affect photosynthesis and transpiration of the individual tree (Sala and Tenhunen 1996; Peters et al. 2008). With their high surface area, branches significantly contribute to the overall tree respiration (Damesin et al. 2002). Therefore, an optimal needle to branch (and stem) surface area improves the carbon economy of the tree. Similarly, the rate and the structure of colonization of the soil by roots affect both water and nutrient uptake. Usually, most of the roots grow in the topsoil layers, exploiting the most fertile soil horizons and acquiring rain water (Jackson et al. 1996; Monserud et al. 1996; Janssens et al. 1999; Xiao et al. 2003; Konopka et al. 2005, 2006). However, in sites with easily accessible groundwater and low precipitation, a significant fraction of the roots grow in deeper soil layers, as, e.g., observed in Scots pine (Nadezhdina et al. 2007; C ermak et al. 2008a) and in oak trees (Vyskot 1976; Tatarinov et al. 2008), among others. The distribution of biomass and biosurface area (i.e., the surface area of the plant/tree parts) is similar in roots and branches: The highest amount of biomass is located in the coarse roots and in the coarse branches, whereas the highest surface area is generally found in the fine roots and in the thin branches (Helmisaari et al. 2002). Tree allometry reflects the environmental conditions and stand properties as well as individual tree statusespecially age, social position and tree health (Cannell 1982; Bartelink 1997; Kono pka et al. 2010; Wang et al. 2011; Poorter et al. 2012). Theoretically, allometric equations describing tree dimensions are affected by the physiological requirements of the tree; i.e., form and function are related. The most important of these requirements are water transport, light interception, and mechanical support against gravity or wind (Niklas 1994). The present allometric study provides the necessary background information and knowledge for more detailed studies on water relations of Scots pines of different social positions. From the hydraulic point of view, a tree may be viewed as a network of interconnected pipes (Zimmerman 1983). According to the pipe model theory (Shinozaki et al. 1964), the quantity of roots is proportional to the conductive stem cross-sectional area of a tree (i.e., sapwood), while the sapwood area is linked to the amount of foliage. Any disproportion in this balance will affect tree function. For example, larger crowns relative to the sapwood area resultif other tree parameters of the overall hydraulic conductivity remain the samein lower water potentials and in a higher risk of cavitation (Maherali and de Lucia 2000; Cochard 2006; Ogasa et al. 2013). The Huber value (HV, Huber 1928; Tyree and Ewers 1991)defined as the sapwood area supporting a unit amount of foliageis therefore a good measure of tree adaptation to the environment and of the susceptibility of a tree to stress (e.g., Berninger et al. 1995; Poyatos et al. 2007, Martnez-Vilalta et al. 2009). Sapwood water storage is a key feature that helps the tree to cope with diurnal peaks in water demand as well as with a (...truncated)