Hidden Effects: the Belowground Consequences of Introduced Browsing Mammals in New Zealand Forests

Abstract

Over the past decade, there has been an increasing interest in understanding the linkages between aboveground and belowground components of ecosystems. This includes consideration of how the producer and decomposer subsystems influence one another, and the consequences of this for ecosystem properties (van der Putten et al. 2001; Wardle 2002). The organisms of both the aboveground and belowground components are organized into food webs, and there has been growing recent recognition of both the aboveground consequences of belowground food web relationships (e.g., Laakso and Setala 1999; Scheu et al. 1999), and the belowground consequences of aboveground food web associations (reviewed in Wardle 2002; Bardgett and Wardle 2003). Foliar herbivory represents the primary trophic relationship in the aboveground food web, and has been shown in several ecosystems to operate as an important ecosystem driver (e.g., McNaughton et al. 1988; Pastor et al. 1988). Appreciation of how foliar herbivory affects the decomposer subsystem may increase our understanding of the controls of decomposition and nutrient supply in ecosystems. Several species of browsing mammals were liberated throughout New Zealand between the 1770s and 1920s, including feral goats (Capra hircus) and deer (particularly European red deer, Cervus elaphus scoticus; see Chap. 4). Prior to this, no browsing mammals were present in New Zealand. New Zealand’s native megaherbivores, moas (Aves, Dinornithiformes), became extinct following Polynesian colonization of New Zealand 800–1,000 years ago. New Zealand presents an almost unique opportunity to investigate the ecosystem consequences of the introduction of an entire functional group of alien organisms (forest-dwelling browsing mammals) to an ecosystem from which that group was previously absent.