Effects of prescribed fire on vegetation structure and breeding birds in young Pinus pinaster stands of northern Portugal

The effects of prescribed fire on understory vegetation structure and bird populations of Pinus pinaster stands in northern Portugal were assessed by using a synchronic sampling approach. During the spring of 1998 and 1999, 49 plots (of which 40 had been burned from 0.5 to 5 years ago) were characterised in terms of vegetation structure, surrounding landscape composition and breeding bird populations. Linear regression analysis and ANOVA were used to evaluate the effects of prescribed fire on vegetation and birds. Herbaceous vegetation showed a modal growth with a maximum development ca. 3 years after fire. Shrub development increased linearly with time since fire. Understory vegetation structure 5 years after fire was similar to control plots. Bird abundance and richness were influenced by plot variables (increased with stand age) and landscape variables (decreased with the amount of shrublands and eucalyptus stands surrounding the plot). After controlling for the effect of these variables, time since fire affected bird abundance, particularly for shrub/ground nesters. Minimum abundance occurred in the second or third breeding season after fire, possibly due to site tenacity or increased food availability. Prescribed bums did not affect bird richness. The size of the burned plots did not affect bird abundance or richness, probably because most bums were very small. Measures to increase bird diversity in these forests include maintaining other tree species and snags, avoiding the use of eucalyptus, and keeping a 5-year interval between consecutive prescribed burns in a given stand. The average size of burns could probably be increased without detrimental effects on bird populations. (C) 2003 Elsevier B.V. All rights reserved.