Nutritional analysis of natural oak forests in Galicia in relation to soil properties

Resumo

In this study, we analyzed different edaphic and nutritional factors that affect soil conservation in natural forest stands dominated by Quercus robur L. in Galicia (NW Spain). Oak forests in the northwest Iberian Peninsula represent climax communities with a high diversity of vascular plants. Oak occurs in mixed stands, known as "fragas�, along with other trees species such as Castanea sativa Mill., Betula alba L., Corylus avellana L.,... Other oaks that hybridize easily may also be present: Q. petraea Matts. and Q. pyrenaica Willd. These forests are particularly vulnerable as a result of the human pressure to which they are subjected. Poor soil conditions and nutrient removal as a result of fire or the application of short rotations may limit nutrition and thus affect the conservation of these forests. Therefore, in this study, we characterized the types of soil on which the stands are located and their main properties. We also assessed nutritional status from the results of foliar analyses. Most of the soils on which the stands are established are acidic and rich in organic matter. The foliar analyses showed that the main nutritional limitation for the oaks was generally the low concentration of macronutrients, although in some cases there were also insufficient levels of nitrogen. These deficiencies may to be related to the low availability of these nutrients in the soil. Such limitations may reduce the potential for their conservation, which should be taken into account in future silvicultural treatments aimed at conservation.