Interannual environmental-soil thawing rate variation and its control on transpiration from Larix cajanderi, Central Yakutia, Eastern Siberia

Abstract

Sapflow measurements were carried out in a larch forest in eastern Siberia, an area of wide permafrost distribution. Canopy transpiration and canopy conductance were scaled up from these values.The objective was to analyze the relationship between environmental variables, mainly vapour pressure deficit (D), soil moisture and soil thawing rate with canopy transpiration and canopy conductance. the forest. By comparison with other studies in this region, canopy transpiration is estimated to contribute to almost 50 % of the total forest evaporation, highlighting the important role of understorey transpiration in permafrost regions. Our results show that it is not only the impermeability of permafrost with the property of keeping soil moisture in the thin active layer but it is also the slow soil thawing rate that plays the important role of controlling the amount of water available for trees roots in the upper soil layers during dry years.Interannual environmental-soil thawing rate variation and its control on transpiration from Larix cajanderi, Central Yakutia, Eastern Siberia. Permafrost regions occurring presumably in the Northern hemisphere are of special hydrological interest because of seemingly strange features of local soils and associated behavior of forest tree species, mostly larch. The authors focused on water loss of boreal forests, in Eastern Siberia typical with low precipitation, where water from thawed permafrost is important for tree survival. They applied sap flow technique and usual meteorological and soil moisture equipment for this purpose over two growing seasons (July-Sept. 2003 and 2004). Authors: Here I would like to make something very clear. Water thawed from permafrost is not used by trees, unless there has been a disturbance that has severely broken the stability of permafrost. As it can be observed in figure 4 (of the original manuscript) the active layer (soil layer that freezes in winter and thaws in summer) reaches its maximum thickness at the end of September when leave shedding has already started or water uptake from trees is already very low. Furthermore, root density below 1 meter is close to zero and thus importance of permafrost for tree survival lies not as a water source but as an impermeable layer that avoids water filtration downward. The most important point that I have probably not conveyed properly is the fact that gradual soil layers thawing (Fig. 4) allows the retention of water in the upper layers were the bulk of tree roots distribute and that this deepening shows an inter-annual variation, being slower when water supply is low so as to make more water available for (in the upper layers) tree survival.Unfortunately neither methodical nor instrumental information is provided. Authors: My deepest apologies for this. I make myself (first author) responsible for not providing the proper information. In the revised text all the methodical and instrumental information is provided.So it is not clear e.g., how solar radiation was measured (e.g. by a home-made sol...

Forest decline caused by high soil water conditions in a permafrost region

“…Soil water content values measured in the present study were high compared to those obtained in previous studies in the same forest. Soil at shallow depths is not normally saturated except in the snowmelt season (Sugimoto et al, 2003;Lopez et al, 2007;Ohta et al, 2008) respectively (Fig. 3).…”

“…), with cowberry (Vaccinium vitis-idaea L.) in the understory, extends over the gently undulating eastern terrace of the Lena River. Growing at a density of 1000 ha −1 the larch trees were 13 m tall and 160 years old, on average (Lopez et al, 2007). Larch roots are shallow and mainly limited to a depth of 0.40 m (Kuwada et al, 2002).…”

Effet de la longueur de la portée des sondes de dissipation thermique de type Granier sur des mesures de densité de flux de sève

“…However, particularly in warm seasons (e.g., from spring to autumn), sap movement continued from evening to the predawn and stopped just before sunrise. This phenomenon has been confirmed for tropical broadleaved trees (Granier et al, 1996a;Lu et al, 2004), temperate coniferous trees (Delzon and Loustau, 2005;Granier et al, 1996b;Kobayashi and Tanaka, 2001;Köstner et al, 1998;Kumagai et al, 2005;Phillips et al, 1996;, temperate broadleaved trees (Bréda et al, 1993;Granier et al, 1996b;Phillips et al, 1996), and boreal conifers (Lopez et al, 2007;Zimmerman et al, 2000). Taken together, these data strongly suggest that the heat was not transferred to the lower part of the stem due to the remaining u during the predawn period and the underestimation of u by the TDP does not occur during the warm seasons.…”

The GRENE-TEA model intercomparison project (GTMIP) Stage 1 forcing data set

“…1): Fairbanks in Alaska (Nakai et al, 2013), Tiksi (Kodama et al, 2007;Yabuki et al, 2011;Watanabe et al, 2000) and Chokurdakh (Iwahana et al, 2014) in northeast Siberia, Yakutsk in central east Siberia (Ohta et al, 2001(Ohta et al, , 2008(Ohta et al, , 2014Kotani et al, 2013;Lopez et al, 2007;Yabuki et al, 2011), Tura in central Siberia , and Kevo in northern Europe (Sato et al, 2001; precipitation and air pressure in Kevo are provided by Finnish Meteorological Institute). The longitudes and latitudes of the sites are summarized in Table 1, as well as the observational periods for data collection.…”

“…tic conditions at those sites. It is very difficult, however, to create a complete data set for driving a model solely from observations, which are prone to data gaps due to instrument problems, human mistakes, or other reasons (Nakai et al, 2013;Kodama et al, 2007;Watanabe et al, 2000;Iwahana et al, 2014;Ohta et al, 2001Ohta et al, , 2008Ohta et al, , 2014Kotani et al, 2013;Lopez et al, 2007;Nakai et al, 2008;Sato et al, 2001). Despite efforts to maintain and improve our observational network, data gaps are unavoidable, as the availability of instrumentation is often limited by logistical or funding issues.…”