Impact of fire severity on soil properties and the development of tree and shrub species in a Scots pine moist forest site in southern Poland

Abstract

We studied the effect of fire severity on soil properties and on post-fire regeneration and dynamics of vegetation over a period of 14years after a wildfire in moist pine forest on muck-peat soil with a thick layer of organic matter. We found that the fire markedly altered soil properties and, depending on its severity, differentially affected tree and shrub colonisation and development. Total N was most reduced in more severely burned areas, where it did not change even after 14years. A fire-severity-dependent increase of Ca, P, K, Mg and the sum of basic cations persisted two or three years after the fire. This short-term pulse was the principal reason for rapid and abundant vegetation development during the first three years after the fire. From the beginning of succession, silver birch (Betula pendula) was dominant at all sites while Scots pine (Pinus sylvestris) was of minor importance. The rates of tree species colonisation, birch development, and cover of all trees and shrubs were highest on more severely burned sites and lowest on slightly burned sites. Seedlings of anemochorous trees and shrubs emerged first (within 3–5years after the fire); zoochorous species appeared much later, after the shrub layer developed. Seedling recruitment and development of tree species were inhibited on slightly burned sites by strong competition from herbaceous plants that survived the fire. The results indicate that distance from the source of pioneer tree species and the soil conditions prevailing in the first years after a fire can determine the composition and structure of vegetation in the early stages of post-fire succession. On moister and richer soil, the colonisation success of pioneer tree species increased with increasing fire-caused consumption of the organic soil layer. Early post-fire recruits may form the major source of canopy trees in late successional stands.