Survival of Scots pine after wildfires depending on damage degree Chemical and biological renaturalization of afforested and abandoned arable Arenosols Effects of windthrow disturbance on forest-a northern perspective

Jānis Donis, Guntars Snepsts, Leonids Zdors, Mārtins Bicevskis, Kęstutis Armolaitis, Jūratė Aleinikoviené, Vilma Žékaité, Heikki Kauhanen
During last 2 decades in Latvia forest fires affected in average 1000 ha per year. Most of those fires are in pine forests. Forest managers have to take decision about future management activities in these areas to optimize economical and ecological as well as social considerations. Therefore it is important to predict survival probabilities of trees after such events and research was financed by JSC "Latvijas valsts meži". During 2003 to 2009 totally were established 168 sample plots (500 m 2)
more » ... ple plots (500 m 2) within 28 different fire events, which covered wide range of age groups (20 to 180 years) and forest site types (from dry mineral soils to wet peat soils and drained soils). For each tree (N=3237) was measured DBH, calculated height as well was assessed fire effects (height of bark char, crown scorch, root char) and presence of damage by stem boring insects. Survival as well as presence of stem boring insects was assessed during 2008 to 2009 twice a year. For survival assessment we used Life tables and Cox regression analysis (SPSS14). Survival depends on tree diameter and time since fire. Smaller trees (dbh<14cm) has almost 3 times higher hazard rate than trees of dbh>30cm with similar damage rate. 36 month after forest fire survival probability is higher than 80% for pines with dbh from 6 to 14 cm and max height of bark char less than 1m and no root damage, while pines with dbh of 14 to 22 cm have the same survival probability if max height of bark char does not exceed 3m. Larger trees have survival probability more than 80% if bark char does not exceed 3 m or if no more than ¼ of roots is exposed and max bark char does not exceed 2 m. Comparative study on chemical and biological renaturalization of arable Arenosols were performed in 45-year-old Scots pine plantations and arable land abandoned for 11 years. It was determined that former ploughing Ap horizon was renaturalized according to the pH and the concentrations of organic C, total N and Al 3+ ions in pine plantations. The renaturalization of organic C and both total and mineral N concentrations was found in abandoned arable land as well. The renaturalization of ground vegetation (forest type-Vaccinio-myrtillosa) in pine plantation were explained by the accumulation of organic layer. The changes in species diversity of ground vegetation reflect the leaching, mainly mineral N, in abandoned formerly fertilized arable land. In mineral topsoil of Arenosols the abundance of the microorganisms (soil bacteria prevailed) was in average by 2-5 folds higher in abandoned land than in pine plantations. The microorganisms in abandoned arable land showed the homology to the actinobacterias and proteobacterias, while soil microorganisms in pine plantations were presented only by proteobacterias.