Abstract: Understory vegetation is an important component of forest ecosystem. Restoring understory biodiversity is one of the primary objectives in forest management. The specialgeographic environment on the Loess Plateau has resulted in poor availability of effectiveunderstory tending measures. Furthermore, previous studies on changes of understory vegetation diversity in post-tending forests have mostly focused upon species diversity, but rarely uponfunctional diversity. The present study investigated the differences of the functional diversity in the understory between the tended and untendedPinus tabuliformis plantations on the Loess Plateau. The results showed that: (1) Soil temperature, moisture, salinity and indirect site factor significantly increasedunder the tended forest. (2) The tended forest was significantly higher than the untended forest in leaf area (LA), leaf dry matter content (LDMC) and leaf thickness (L_th) of the herb layer, but was significantly lower in specific leaf area (SLA). L_th  of the shrub layer was significantly higher in the tended forest than that in the untended forest. (3) Forsingle-trait functional diversity indices, the tended forest exhibited significantly higher functional richness (FR_ci) of LA, SLA andL_th of the herb layer, lower functional regularity (FRO) of SLA and LDMC of the herb layer and higher functional divergence (FD_var) of SLA andFR_ci of L_th of the shrub layer than did the untended forest. (4) For multitrait functional diversity indices, the tended forest displayed significantly higher functional richness (FR_ic) of the herb layer,significantly lower functional evenness (FE_ve) and functional divergence (FD_iv) of the herblayer, and significantly higherFE_ve of the shrub layer than the untended forest. These findings suggested that forest tending improved the understory environmental conditions. Tending exerted obviously greater effects upon the herb layer than upon the shrub layer. Properly raising theintensity of tending may further improve the functional diversity of understory vegetation.

Key words: biological soil crust, vegetation restoration, greenhouse gas, global warming potential, desert ecosystem