**1. Introduction**

The global area of plantation forests exceeds 2.84 hundred million hm2, with plantation forests in China showing the largest area and fastest development worldwide [1]. Many ecological problems occur with the development of plantations [2,3]; thus, close-to-nature managemen<sup>t</sup> (actively or passively developing planted forest communities into more diverse vegetation communities dominated by native species) has recently been used to maintain and improve ecosystem ecological function and stability [4–7]. Indeed, many previous studies have demonstrated that plantation managemen<sup>t</sup> practices (e.g., thinning, strip-cutting, introducing tree species) have increased the diversity of forest species and

**Citation:** Yang, Y.; Yang, H.; Wang, Q.; Dong, Q.; Yang, J.; Wu, L.; You, C.; Hu, J.; Wu, Q. Effects of Two Management Practices on Monthly Litterfall in a Cypress Plantation. *Forests* **2022**, *13*, 1581. https:// doi.org/10.3390/f13101581

Academic Editor: Benjamin L. Turner

Received: 30 August 2022 Accepted: 23 September 2022 Published: 27 September 2022

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improved soil properties [8–11]. However, the mechanisms driving the improvement of these ecological functions involved in managemen<sup>t</sup> practices remain unclear.

Litterfall is one of the major pathways by which organic matter and nutrients return to soils from vegetation [12,13], and the production and patterns of litterfall significantly contribute to the maintenance of soil fertility and nutrient balance in forest ecosystems [14,15]. Its production and its temporal dynamics are strongly influenced by tree density, vegetation composition and climate factors (e.g., temperature, precipitation, wind etc.) [16–18], which are significantly regulated by managemen<sup>t</sup> practices [19,20]. For instance, thinning or strip-cutting can primarily reduce stand density or canopy density. The decrease in stand density or canopy density not only directly reduces total litter production but also indirectly alters the composition of litterfall by affecting the formation and regeneration of light-loving vegetation [8,21]. In contrast, replanting or reconstruction in mixed forests could directly change the composition of litterfall as a result of adding new species. The practices mentioned above can all make the monthly production of litterfall vary. Since the production of litterfall is higher in mixed stands or species-rich forests than it is in monocultures [22–24], we hypothesized that forest managemen<sup>t</sup> practices that increase species richness might be more conducive to litter production. However, although some studies have reported the characteristics of litterfall production at different levels under certain managemen<sup>t</sup> practices [25,26], it is difficult to accurately predict litterfall among these practices, which is not conducive to comprehensively understanding the mechanism of litterfall among managemen<sup>t</sup> practices.

In general, litterfall composed of materials from different organs exhibits allometric relationships [27,28]. The allometric relationship of litterfall production provides a new approach for estimating forest productivity because litterfall is an important contributor to the net primary productivity of forest ecosystems [29]. However, the biomass allocation in litterfall is still under debate. For instance, Ma et al. [27] found that the allometric relationships between total litterfall and litterfall components were approximately the same in evergreen forests and deciduous forests in China. However, Fu et al. [28] found that the allometric relationships of forest litterfall varied with litterfall components, functional types and vertical structures in alpine forests, e.g., evergreen versus deciduous and trees versus shrubs. Thus, additional studies on the allometric relationships of forest litterfall in different climatic zones, at different regional scales and in various forest types are needed. The managemen<sup>t</sup> practice of plantations, as a form of human disturbance, inevitably create heterogeneous habitats and are expected to affect the allocation of litterfall from different organs.

As one of the major tree species in the Yangtze River shelter forests, cypress (*Cupressus funebris*) plays a critical role in regulating the regional climate and conserving water and soil. Cypress plantations have also led to a weak capacity for water storage, low biodiversity, and soil degradation, resulting in a large decrease in ecological services, although they have addressed the demand for high forest coverage. Therefore, a series of experiments implementing forms of managemen<sup>t</sup> practices, such as strip filling (first strip-cutting and then replanting) and ecological thinning, were performed to adjust the structure of cypress plantation monocultures and improve their ecological functions. Although the waterholding capacity, plant diversity, soil microbial diversity and physicochemical properties after implementation of several managemen<sup>t</sup> practices have been widely reported [30–33], little attention has been given to litterfall production. Here, a one-year field study, implementing the litter trap method, was carried out on three cypress plantations, including two managemen<sup>t</sup> practices (strip filling and ecological thinning) and an unmodified pure plantation for comparison. Litter production was investigated monthly to assess the changes in annual total litterfall production and seasonal dynamics, as well as the allometric growth relationships among litter organs under different managemen<sup>t</sup> practices. Specifically, we hypothesized that (1) the total litterfall production and its components would be higher in the plantation with managemen<sup>t</sup> practices than in the pure cypress plantation and (2) managemen<sup>t</sup> practices would alter the monthly dynamics of litterfall and change the allometric relationships in cypress plantations.

#### **2. Materials and Methods**
