How Forest Gap and Elevation Shaped Abies faxoniana Rehd. et Wils. Regeneration in a Subalpine Coniferous Forest, Southwestern China

Li Chen,Dan Liu,Guohua Liu

doi:10.3390/f9050271

Abstract

Focusing on the underlying ecological mechanisms of dominant species regeneration in forest gaps at a landscape scale can provide detailed understanding for gap-based forest management. The individual effects of forest gaps or elevation on the regeneration of Abies faxoniana Rehd. et Wils. are well known, although elucidating how gap characteristics and elevation concurrently influence regeneration remains an important challenge. In this paper, we present an explorative study using structural equation models (SEMs) to assess the direct and indirect effects of forest gaps and elevation on Abies faxoniana Rehd. et Wils. regeneration. Four of the predicted SEMs showed the following results: (1) Temperature, photosynthetic photon flux density (PPFD), soil total carbon, gap openness, shrub layer cover, herb layer cover, and moss layer thickness in forest gaps were associated with Abies faxoniana regeneration along an elevation gradient in subalpine coniferous forest. (2) Elevation had a generally negative and indirect effect on Abies faxoniana regeneration. Forest gaps positively affected regeneration when compared with non-gap plots and gap size was positively related to small tree regeneration density and the ratio of height to diameter at breast height (HD ratio) of the tallest Abies faxoniana small trees but was negatively related to Abies faxoniana sapling regeneration density. (3) In forest gaps, the Abies faxoniana sapling density and HD ratio of the tallest Abies faxoniana small trees were mainly indirectly influenced by elevation, and Abies faxoniana small tree regeneration density was directly associated with the dominance of the sapling regeneration density. In summary, Abies faxoniana regeneration was negatively and largely affected by elevation (total effect), although forest gaps enhanced Abies faxoniana regeneration by multiple pathways (direct and indirect effects).

Highlights

Forest gaps create important spaces for forest regeneration by modifying microclimate and resource availability [1,2]
Despite the limited attributes used for predicting regeneration variables and such complex and involved ecological processes in subalpine coniferous forest gaps along an elevation gradient, our study tentatively demonstrates how forest gaps and elevation affect Abies faxoniana regeneration, both directly and indirectly, through the simplified classification of influencing factors and factors associated with important and typical regeneration indices in structural equation models (SEMs)
Our study showed that gap heterogeneity, gap size, and elevation favored Abies faxoniana regeneration by promoting abiotic factors and positive interactions of biotic factors by imposing different effects on the various factors

Summary

Introduction

Forest gaps create important spaces for forest regeneration by modifying microclimate and resource availability [1,2]. In many forests, these gaps play the role of resource “hot spots”. To meet sustainable forest ecosystem functions (e.g., diversity and resilience) and silvan economic benefits (e.g., timber production) [4,5], forest ecologists and managers have increasingly emphasized new silvicultural concepts that imitate natural disturbances for forest management [6,7]. In this way, forest gaps are thought to play an important role in the natural regeneration and sustainable development of forest ecosystems. Gap-based silviculture is an intuitive and effective approach for promoting plant regeneration in the majority of mature forests and has been extensively documented in proposals for forest management [8,9].

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Conclusion