Li Yuanfa, Li Muxuan, Li Xian, Liu Zhilong, Ming Angang, Lan Huangxu, Ye Shaoming
College of Forestry, Guangxi Key Laboratory of Forest Ecology and Conservation, Guangxi University, Nanning, China.
Department of Renewable Resources, University of Alberta, Edmonton, AB, Canada.
Front Plant Sci. 2021 Mar 3;12:614695. doi: 10.3389/fpls.2021.614695. eCollection 2021.
The sustainability of coniferous monoculture plantations is facing challenges with respect to yields, ecology, and biodiversity. Conversion of monocultural coniferous plantations into mixed stands using thinning or direct mixed planting is widely considered to be a key strategy for overcoming these challenges and transforming the characteristics of plantations on a regional scale. Substantial amounts of deadwood may be produced in mixed forests (MFs); this material is important for evaluating and modifying forest management methods, understanding the dynamics of forest stands, and achieving biodiversity conservation. We assessed the quantitative characters and diameter distributions of deadwood in mixed and thinned Chinese fir [ (Lamb.) Hook.] forests over one rotation. We used the () function and spatial parameters to analyze the spatial structure of deadwood, and used logistic regression and Hegyi's competition index (HCI) to explore competition and mortality. Our results indicate that: (1) Chinese fir dominated in all groups of deadwood (snags, broken wood, and fallen wood), and the abundance, volume, and mortality rates of deadwood were much lower in the thinning forest compared to the MF. (2) Later coming populations (LCPs) comprised the majority of the small diameter classes in the thinning forest, but only accounted for a small proportion of the MF. (3) Broken wood in the thinning forest was randomly distributed, while the other types of deadwood were clustered at most spatial scales. In contrast, the spatial patterns in the MF were random at most spatial scales. (4) Total deadwood in both stands was in a status of intermediate and was randomly surrounded by its four nearest neighbors. All types of deadwood were highly mixed in the thinning forest and moderately mixed in the MF. Our case study suggests that thinning and mixing result in different stand development processes and thus influence the type, amount, and structure of deadwood. Thinning significantly reduces competition, which is the main driver of tree mortality. Converting pure Chinese fir plantations into mixed stands by thinning should be taken in future. Understanding tree mortality after conversion is essential to select appropriate silvicultural treatments and achieve ultimately sustainable forest management.
针叶纯林人工林的可持续性在产量、生态和生物多样性方面面临挑战。利用间伐或直接混交种植将单一针叶人工林转变为混交林，被广泛认为是克服这些挑战并在区域尺度上改变人工林特征的关键策略。混交林（MFs）可能会产生大量枯立木；这种材料对于评估和修改森林经营方法、理解林分动态以及实现生物多样性保护非常重要。我们评估了一轮生长周期内间伐和未间伐的杉木[（Lamb.）Hook.]混交林中枯立木的数量特征和直径分布。我们使用（）函数和空间参数分析枯立木的空间结构，并使用逻辑回归和赫吉竞争指数（HCI）来探讨竞争和死亡率。我们的结果表明：（1）在所有枯立木组（枯立木、折断木和倒木）中杉木占主导地位，与混交林相比，间伐林中枯立木的丰度、体积和死亡率要低得多。（2）后发种群（LCPs）在间伐林中占小直径级别的大多数，但在混交林中只占一小部分。（3）间伐林中的折断木呈随机分布，而其他类型的枯立木在大多数空间尺度上呈聚集分布。相比之下，混交林在大多数空间尺度上的空间格局是随机的。（4）两个林分中的总枯立木处于中间状态，并且被其四个最近邻随机包围。所有类型的枯立木在间伐林中高度混合，在混交林中适度混合。我们的案例研究表明，间伐和混交导致不同的林分发育过程，从而影响枯立木的类型、数量和结构。间伐显著降低了竞争，而竞争是树木死亡的主要驱动因素。未来应通过间伐将纯杉木人工林转变为混交林。了解转变后的树木死亡率对于选择合适的营林措施并最终实现可持续森林经营至关重要。
