Table 1.
Water balance components.
Table 2.
(Time) periods and their average climate.
Figure 1.
Effects of tree density on water table (panel A) and mesocosm evapotranspiration (panel B).
Bars represent means +1 SE (n = 5) per birch density treatment. NT = control without trees, LT = low tree density, HT = high tree density. Mesocosm evapotranspiration was averaged over the first summer (period V, calendar week 19–32, 2008). Water table values refer to the situation at the end of period V, as measured at the beginning of week 33. Water table level was measured relative to a fixed point (the overflow outlet), which was 10–15 cm below the moss surface. Different letters above the bars denote statistically significant (P<0.05) differences between tree density treatments based on 2-way ANOVAs with treatment as factor and block as random factor.
Figure 2.
Seasonal changes in tree density effects on mesocosm water table.
Bars represent mean water tables ±1 SE (n = 5) in cm relative to a fixed point per week, from week 38 in 2007 (38) until week 37 in 2008 (37). Positive values indicate a water table closer to the surface. Water table level was measured relative to a fixed point (the overflow outlet), which was 10–15 cm below the moss surface. Birch density treatments are identified by differently shaded bullets. NT = control without trees, LT = low tree density, HT = high tree density. Arrows indicate onsets of leaf senescence in 2007 and leaf emergence in 2008. * = week during which storage coefficient has been determined, ** week in which demineralized water has been added to each mesocosm. ETp periods indicates periods (I-V) differing in solar radiation and potential evapotranspiration, over which evapotranspiration has been averaged for Figures 1, 3 and 4. Note: mesocosm trees were planted in December 2007.
Figure 3.
Seasonal changes in tree density effects on mesocosm evapotranspiration.
Bars represent means +1 SE (n = 5) per birch density treatment averaged over periods (I–V) in order of increasing atmospheric demand for water. Periods I and II cover late autumn -early spring, whereas periods III–V represent mid spring-mid autumn (Table 2). Measurements spanned 1 year from week 38 in 2007 until week 37 in 2008, the only year for which we had water table data for all seasons. NT = control without trees, LT = low tree density, HT = high tree density. Different letters above the bars denote statistically significant (P<0.05) differences between tree density treatments within a period based on five separate 2-way ANOVAs with treatment as factor and block as random factor, one ANOVA for each period.
Figure 4.
Relationship between plot-LAI and mesocosm evapotranspiration (ET) for the summers of 2008, 2009 and 2010.
ET of the mesocosms with trees (LT and HT) were averaged over the summer (period V) for each year separately and standardized by dividing by the ET from mesocosms without trees (NT mesocosms). Symbols above the dashed line indicate a higher evapotranspiration than NT mesocosms, whereas symbols below this line indicate lower evapotranspiration than NT mesocosms. The solid line indicates a weak, but significant, (P<0.05), linear relationship (linear regression, R2 = 0.25, y = 0.1x+1.1).
Table 3.
Vegetation composition understory.