Post-fire changes in the biological properties of the brown soils in the Utrish State Nature Reserve (Russia)

Abstract

The unique ecosystems of the Abraus peninsula on the Caucasian Black Sea coast persisted in the Utrish State Nature Reserve (Russia), are represented by dry Eastern Mediterranean subtropics with a large number of endemics and relics that have been persisted from the Tertiary period. This is one of the few places in Russia where juniper pistachio (Pistacia atlantica, Juniperus excelsa, J. foetidissima, J. oxycedrus) woodlands grow. In 2016–2018, a study was conducted on the content of the biological properties of brown soils in two areas of the Abraus peninsula. The main focus is on the monitoring of Vodopadnaya shchel' on the Utrish State Nature Reserve monitoring site, located in the post-fire area of juniper woodland (Pistacia atlantica, Juniperus excelsa, J. foetidissima, J. oxycedrus) at an altitude of 110–140 m a.s.l. on the southern spurs of the Ridge Navagir. The fire happened in 2009. Additionally, in April 2018, the site of the burnt area of 2013 was investigated in the immediate vicinity of the Sukhaya shchel' of the Utrish State Nature Reserve. The area of the burnt site was several hectares including violation of terrestrial vegetation and changes in the ecological state of the soil. We have demonstrated that brown soils are rare for Russia (Cromic Cambisol and Cromi-Leptic Luvisol according to the WRB international classification). But these are widespread in most parts of the Abraus peninsula, including the Utrish State Nature Reserve. The main features of brown soils include the brown colour of the soil profile; intense textural lining of the middle part of the soil profile; eluvial-illuvial type of decarbonisation closed to neutral reaction of the environment; soil richness with elements of mineral nutrition. The studied soils in the Utrish State Nature Reserve are characterised by higher stoniness and rubble, no carbonate growths, fragmentation of the forest floor due to the low-mountain dissected relief of the territory. We have studied the ecological and biological properties of these soils in response to fire (e.g. temperature, moisture, soil bulk density, organic carbon and carbonate content, bacteria abundance, catalase, peroxidase, dehydrogenase, and invertase activities). In the grass-shrub stage, the restorative succession was in both burnt areas. The fire had a significant effect on the ecological and biological properties of brown soils 5–9 years after the fire impact. Many of the biological properties of post-fire soils differed significantly in comparison with the properties of control areas of juniper light forest. The organic carbon content and biological activity of post-fire soils as a whole are reduced as compared with the soils of control areas of juniper light forest. In this case, a high variation of the biological parameters of the soil was noted in different parts of the same burnt area. The variation is associated both with the peculiarities of the mountain relief, and with the nature of the vegetation, which forms refugia different in the number of plant residues. The rate of carbon dioxide production in the surface horizons of the burnt area soil is more than 2 times lower than the values in control areas. Five years after the fire, the post-fire soil of the Sukhaya shchel' area contained almost half of the humus content at the 5 cm surface layer compared to the soil of the control area of juniper woodlands. At a depth of 15–25 cm, the difference between the soils areas remained at the same level as for the upper horizons. Thus, we demonstrated a significant effect of fires on the biological parameters of the subtropical soils in the Utrish State Nature Reserve, which has been persisted for many years.

Keywords

• biological activity
• extracellular enzyme activities
• pyrogenic effect
• soil organic carbon
• wildfire