The decline in primary natural forests worldwide has intensified research on the effects of forest transformation on soil carbon (C), nitrogen (N), and phosphorus (P) cycles and stocks. However, the extent to which soil C, N, and P stocks and stoichiometry are affected by forest conversion remains unclear. Here, we examined the effects of forest transformation on soil nutrient storage capacity and stoichiometric characteristics in native broadleaf forests (BFs), plantation forests (PFs), tea gardens (TGs), cultivated lands (CLs), and urban artificial green spaces (GSs) at a county scale in subtropical China. The results showed that the other forest types exhibited significantly reduced soil C and N contents and stocks but increased soil P content and stock compared to BFs. The soil C:N:P stoichiometric ratios for BFs and the converted PFs, TGs, GSs, and CLs were sequentially decreased as follows: 444.8:24.2:1, 95.0:10.0:1, 30.2:3.9:1, 23.1:3.7:1, and 19.4:1.9:1, respectively. Within the altitude (AL) span of 180 to 1200 m surveyed, the AL decided the type of forest conversion and significantly influenced the stock levels and stoichiometric ratios of soil C, N, and P. The results of this study highlight the importance of the ecological management of TGs and the optimization of soil P production in CLs, TGs, and GSs.