Phytomass and Soil Temperature in Herbaceous Communities of the Central Forest Reserve

Plant communities sufficiently change microclimate under their canopy. To reveal the effects of different types of herbaceous communities on the soil thermal regime, phytomass and soil temperature were measured in four plant communities of the Central Forest State Nature Biosphere Reserve and its surroundings (Tver oblast). The productivity of the studied communities increased in a row: abandoned meadows (930 ± 53 g/m²) → managed meadows (1111 ± 40 g/m² ) → meadowsweet Filipendula ulmaria communities (1357 ± 155 g/m²) → subruderal tall-herb communities (1726 ± 188 g/m²). The belowground phytomass in the 0–5 cm layer ranged on average from 614 ± 102 g/m² in the subruderal community to 1756 ± 448 g/m² in the Filipendula ulmaria community. The total phytomass was positively correlated with the soil pH (R = 0.814, p < 0.001, n = 16), as well as with nutrient availability indicator values (R = 0.528, p = 0.029). In all the communities the temperature maximum coincided with that of air temperature and occurs in June–July. In winter, soils at the depth of 8 cm did not freeze, but some days surface temperatures dropped below zero. Soil water capacity was significantly negatively correlated with mean temperatures at the depth of 8 cm in July, August, and September. The correlation with soil surface temperature was similar, but less pronounced. Soil temperatures at the peak of the growing season and in the following months were not significantly correlated with the aboveground phytomass values. Thus, in the forest zone, even within a relatively small area, the phytomass of herbaceous communities differs greatly. Soil temperature under a herbaceous vegetation canopy mostly depends on the soil physical properties, but not on the aboveground biomass.