Soil d13C and d15N as a good indicator for predicting the site index of Galician pine forests (Pinus pinaster Ait. and Pinus sylvestris L.)

Abstract

Stable isotopes natural abundance (13C, 15N) was studied in soils from P. pinaster Ait. and P. sylvestris L. plantations located in Galicia, NW Spain, to evaluate the use of isotopic techniques for stand quality estimation. Combinations of old/young forest plantations of high/low site index, growing on acidic soils over two different parent materials (granite/schists) were studied. Significantly lower 13C in soils under P. pinaster (–27.03‰) as compared with soils under P. sylvestris (–26.13‰) were found (P < 0.001). However, soil 15N of both species did not differ significantly. Significant linear regressions between soil 13C and site index for P. pinaster were found, pointing at the 13C signature of the soil as a good stand quality indicator, especially over schists. For P. sylvestris over schists, linear regression between soil 15N and site index suggests that 15N could be used as a complementary tool in quality determinations. As a general trend for both tree species, stands with high site index showed more depleted soils in 13C and 15N as compared with low site index stands.

Soil microbial biomass under pine forests in the north-western Spain: influence of stand age, site index and parent material

“…The site index is defined as the dominant height of the stand, in meters, at the age of 20 years for P. pinaster (Álvarez González et al, 1999) and at the age of 40 years for P. sylvestris (Diéguez Aranda, 2004). A detailed description of the plots as well as their exact location throughout Galicia have been given by Fernández et al (2006). The plots were subjectively selected to represent the whole range of stand densities, undergrowth types and growing conditions in Galician pine forests but restricted to two different ranges of age and site index.…”