Abstract

Arrested succession may lead to losses of productivity and biodiversity in forests after disturbance. In this condition, recalcitrant understory vegetation often dominates over long periods of time and delays forest recovery and succession. Arrested succession has been defined as a type of forest degradation because ecosystem processes and functions that underlie successional dynamics are dramatically reduced. We used the Hutchinson' niche concept to understand the relative importance of environmental variables that define niche axes of species leading to arrested succession (recalcitrant understory vegetation) and to identify a shift along niche axes that promote the successional progression of long-lived early- and late-seral tree regeneration after partial disturbance due to restoration treatments. We studied Nothofagus old-growth forests in the Chilean Andes, where after selective harvests (i.e., a partial overstory disturbance) the understory is commonly dominated by dense thickets of native bamboo (Chusquea spp.), which has been shown to arrest succession by preventing tree regeneration. To overcome this, sites are typically partially scarified (24 to 45% of the area) following harvest to control bamboo and to encourage early-seral tree regeneration. The partial overstory and ground disturbance leaves a wide array of conditions (environmental gradient) that allowed us to investigate the factors under which a given plant group may regenerate, grow, and dominate the forest. Ordination and niche modeling were used to investigate the niche breadths for bamboo and regenerating tree species, as well as the environmental niche axes at this early successional stage, i.e., eight years after disturbance. The results showed different trends in the shift of centroid and extent of realized niches among three plant groups. For instance, performance of the early-seral group was related to litter cover (-), exposed mineral soil (+) and soil water content (+), which resulted in a niche expansion. In contrast, soil water content affected bamboo (-) and may be responsible for the reduction in realized niche space. Light had less influence on defining niches for tree regeneration during early successional stages. Linking the niche concept to succession provided a simple display of multifaceted issues and thus a better understanding of underlying processes and mechanisms. It provides an example of how application of this concept can help to determine situations in which such regeneration can (or cannot) be established successfully and promote the progression of succession following disturbance. This knowledge provides important insights for designing management and restoration practices based on strong ecological foundations.