4 Discussion
Our findings support the first hypothesis that the vertical depth of fine roots in woody species increases with increasing RFC. Plants distributed more than 60% of fine root biomass in a soil depth above 30 cm and their presence reduced exponentially with soil depth. With an increase in RFC, fine root biomass and length density in most soil layers showed increasing trends, and this increase was highly noticeable in soil layers below 30 cm. The increase in fine root depth, average biomass, and length density range of woody species with increasing RFC were maximum in the second year, but minimum in the fourth year, which is consistent with our second hypothesis. Fine root diameter in all species decreased with increasing plant age, and the thinnest roots were found in soil profiles with 75% RFC. We also found that fine root depth, biomass, and length density ofA. vestita decreased with increasing RFC and age, whereas the other three woody species presented maximum values under 75% RFC and in the last year.