Hydraulic properties of mor layers in Finland

Mor, which is the most common humus form in Finnish forests., is an importa nt interface between the mineral soil and the atmosphere through which hydr aulic processes, e.g. infiltration and evaporation. take place. Hydraulic p roperties, Le. water-retention characteristics and the unsaturated hydrauli c conductivity K(psi) in the mor lavers of low-fertility (CT) Scots pine (P inus sylvestris L.) sites and medium-fertility (MT) Norway spruce (Picea ab ies (L.) Karst.) sites were measured on undisturbed samples. Samples were c ollected from four clusters. each of which contained 3-5 stands of CT and M T sites. Water retention and K(psi) were slightly higher on MT than on CT s ites. With a decrease in matric potential (psi) from -4 to -60 kPa. the mea n K decreased from 8.8 x 10(-3) to 1.4 x 10(-6) m d(-1) and from 6.9 x 10(- 3) to 4.9 x 10(-7) m d(-1) at the MT and CT sites, respectively. The main s ource of variation both in water retention characteristics and K(psi), was the spatial heterogeneity within a stand. K(psi) did not differ statistical ly between stands or between clusters within either of the site types studi ed.