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It has been hypothesized that as soil fertility increases, the amount of carbon allocated to below-ground production (fine roots) should decrease. To evaluate this hypothesis, we measured the standing crop fine root mass and the production of fine roots (−1 yr−1, method 1 and 2, respectively) as much as for the more fertile loamy soil forest (1.51±0.14, method 1, and from 1.03±0.31 to 1.36±0.23 Mg C ha−1 yr−1, method 2). Similarly, the average of standing crop fine root mass was higher in the white-sands forest (10.94±0.33 Mg C ha−1) as compared to the forest on the more fertile soil (from 3.04±0.15 to 3.64±0.18 Mg C ha−1). The standing crop fine root mass also showed a temporal pattern related to rainfall, with the production of fine roots decreasing substantially in the dry period of the year 2005. These results suggest that soil resources may play an important role in patterns of carbon allocation to the production of fine roots in these forests as the proportion of carbon allocated to above- and below-ground organs is different between forest types. Thus, a trade-off between above- and below-ground growth seems to exist with our results also suggesting that there are no differences in total net primary productivity between these two forests, but with higher below-ground production and lower above-ground production for the forest on the nutrient poor soil.