Soil Available Phosphorus Loss Caused by Periodical Understory Management Reduce Understory Plant Diversity in a Northern Subtropical Pinus massoniana Plantation Chronosequence

Dong Dai,Changguang Wu,Xin Huang,Yu Liu,Zhixiang Zhou,Ashfaq Ali,Mingjun Teng

doi:10.3390/f11020231

Dong Dai, Changguang Wu + Show 5 more

Open Access

https://doi.org/10.3390/f11020231

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Abstract

Clearing of understory plants is a common management method in plantation forests, but its long-term impact on soil properties and understory plant diversity is still poorly understood. In order to uncover the potential relationship between understory diversity and soil properties, we categorized understory plants into herbs and shrubs, and took soil depth into consideration. We measured the soil variables and investigated the understory plant diversity in four stand age-classes (9-year-old for young, 18-year-old for intermediate, 28-year-old for near-mature, and 48-year-old for mature) in a Pinus massoniana plantation. We aimed to examine how the diversity of herbs and shrubs changed with stand succession and to determine which of the three soil depths (0–10 cm, 10–20 cm, 20–40 cm) had the strongest explanation for the understory plant diversity. Furthermore, structural equation modeling (SEM) was performed to assess the direct and indirect effect of understory clearing and stand age on understory diversity. We found that understory clearing influenced the trend of diversity of herbs and shrubs with stand age, and understory diversity showed a strong correlation with soil physical properties in all three soil layers. The soil properties in the 10–20 cm soil layer related with the diversity of herbs and shrubs most, while the 20–40 cm soil layer properties related with them the least. Understory clearing reduced soil available phosphorus (AP). Understory clearing and stand age were found to benefit understory plant diversity directly and decreased the understory diversity indirectly via AP. Consequently, to improve our understanding of the impact of understory clearing and stand age on biodiversity, we should take into account its direct and indirect effects.

Highlights

Plantation forests are one of the main types of forests in China, and they have been expanding rapidly in recent decades [1]
We proposed the following three hypotheses: (1) understory plant diversity will increase with stand age in plots in which vegetation is not removed but will not increase in plots in which vegetation is cleared; (2) soil properties in different depth have different relation with understory diversity, while herb diversity is more related to 0–10 cm soil depth while shrub is more related to 10–20 cm soil depth according to our observations of their root length; and (3) understory clearing will influence the understory plant diversity indirectly via changing the soil P or N content
In plots with understory clearing, there were no significant differences in shrub diversity between the all four age classes

Summary

Introduction

Plantation forests are one of the main types of forests in China, and they have been expanding rapidly in recent decades [1]. The plantation forest area is expected to triple worldwide by the end of the century [2]. As plantation forests are typically composed of one tree species, the plant diversity of these forests mainly consists of understory plants [6]. These understory plants are important for water and soil conservation [7], energy flow, and material cycling [6,8,9]. There is a need to understand the potential factors that could affect the understory plant diversity in the plantation forest ecosystem

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