Effects of a broadleaf-oriented transformation of coniferous plantations on the hydrological characteristics of litter layers in subtropical China

As a unique structural level of forest ecosystems, the litter layer has significant ecological effects on soil and water conservation. The broadleaf-oriented transformation of coniferous forests is an effective approach for reducing the degradation of the ecosystem services of subtropical coniferous plantations, but previous studies rarely involved the effects of the change in litter layer structure and ecological hydrology caused by the construction of mixed coniferous and broad-leaved forests. In our study, the litter and hydrological characteristics of 5 kinds of mixed coniferous and broadleaf forests (15 years after their transformation) and nontransformed coniferous plantations at the Longli National Forest Farm, China were studied quantitatively through in situ surveys and laboratory experiments. Compared with the coniferous plantation, the thickness and quantity of undecomposed layer in mixed coniferous and broad-leaved forests ranged from -21.86% similar to 46.05% and -44.91% similar to -18.91%,while that of semidecomposed layer ranged from 82.61% similar to 136.23% and 11.75% similar to 63.49%. A logarithmic function and an exponential function fit the water holding ratio and water absorption rate of the litter very well. The maximum water holding capacity and effective storage capacity of the litter in all the forest types are both greater in the undecomposed layer than in the semidecomposed layer. The introduction of Michelia maudiae Dunn and Bretschneidera sinensis Hemsl into coniferous Pinus massoniana plantations can significantly increase the effective litter water retention capacity, but the introduction of Camellia oleifera Abel will be counterproductive. Leaves are the most important component of litter and provide the most runoff retention. The leaf area increased by 0.01 m(3) on average, and the maximum water capacity increased by 1.68 g/g on average. The density of different plant organs in the litter was as follows: leaf < fruit < branch; the density increased by 0.1 g/cm3 on average, and the maximum water capacity decreased by 0.29 g/g on average. Overall, Michelia maudiae Dunn (Magnoliaceae) and Bretschneidera sinensis Hemsl (Bretschneideraceae) are more suitable than other broad-leaved species for the transformation of subtropical coniferous plantations. We suggest that forest resource managers should take into account the impact of tree species differences on the ecological hydrology of plantations when making management decisions. (c) 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).