Abstract:

Coarse woody debris (CWD) consists mainly of log, snag, large branch, stump and coarse root. CWD is widely distributed on the forest floor and especially valuable in most of forest ecosystems because it is vital to the global carbon cycling and biodiversity conservation. In particular, increasingly extreme climatic events, such as persistent high temperature, prolonged drought, and tropical cyclones are greatly affecting forest ecosystem function and stability by accelerating tree death, changing the sources of CWD inputs and decomposition processes. Thus, research about CWD decomposition has becoming an ecological hotspot. More and more ecologists have contributed greatly in disentangling the mechanisms on how factors control decomposition process and how CWD nurses biodiversity, which have greatly stimulated the development of CWD ecology. In this review, firstly, we summarized the dominant methodology used in the CWD decomposition study. Then we introduced the scenarios which could be applied for each method. Secondly, we described the morphological, physical and chemical properties of CWD during decomposition, respectively. Thirdly, we overviewed previous studies disentangling factors affecting decomposition dynamics. Briefly, substrate quality, decomposer community and environmental conditions are the main control factors of CWD decomposition. Substrate quality and decomposer community dominate the CWD decomposition process at site scale, with substrate quality regulating the decomposer community with bottom-up effects, while environmental conditions functioning at regional or broad scales. Fourthly, huge amount and diverse types of organisms use decaying CWD as a habitat, many of which are endangered species. It is fundamental to maintain the biodiversity in the CWD ecosystem. Epixylic plants (especially for bryophytes), bacteria, fungi and invertebrates are the common species living on/in the CWD. Invertebrates can utilize CWD in different ways, such as habitat, nourishment and foraging sites, which are species specific. The community composition changed along with decomposition process. The succession of epixylic plants is correlated with the duration of decomposition, while the succession of other types of organisms is mainly driven by the changing substrate quality of decaying CWD. Additionally, we summarized the decomposition dynamics of different structural components (bark vs. xylem) and the interaction between bark and xylem during CWD decomposition which have been overlooked. Finally, as the long decomposition time and the limitation of methodology impeded the progress of revealing the mechanism of CWD decomposition, we made an outlook of future research in the area of decomposition mechanism and biodiversity conservation, and provided methodology that could be of help in stimulating the further development in CWD ecology.

Key words: decay rate, bark, xylem, decay stage, functional trait, size effect