Planted Riparian Buffer Zones in New Zealand: Do They Live Up to Expectations?

Abstract

River and stream rehabilitation projects are increasing in number, but the success or failure of these projects has rarely been evaluated, and the extent to which buffers can restore riparian and stream function and species composition is not well understood. In New Zealand the widespread conversion of forest to agricultural land has caused degradation of streams and riparian ecosystems. We assessed nine riparian buffer zone schemes in North Island, New Zealand that had been fenced and planted (age range from 2 to 24 years) and compared them with unbuffered control reaches upstream or nearby. Macroinvertebrate community composition was our prime indicator of water and habitat quality and ecological functioning, but we also assessed a range of physical and water quality variables within the stream and in the riparian zone. Generally, streams within buffer zones showed rapid improvements in visual water clarity and channel stability, but nutrient and fecal contamination responses were variable. Significant changes in macroinvertebrate communities toward “clean water” or native forest communities did not occur at most of the study sites. Improvement in invertebrate communities appeared to be most strongly linked to decreases in water temperature, suggesting that restoration of in‐stream communities would only be achieved after canopy closure, with long buffer lengths, and protection of headwater tributaries. Expectations of riparian restoration efforts should be tempered by (1) time scales and (2) spatial arrangement of planted reaches, either within a catchment or with consideration of their proximity to source areas of recolonists.

Longitudinal changes in biota along four New Zealand streams: Declines and improvements in stream health related to land use

“…in a recent study, Harding et al (2006) did not find significant improvements in macroinvertebrate metrics as third order streams passed through short (250-350 m) forested corridors along agricultural streams in Canterbury, New Zealand. in their study of planted riparian zones, Parkyn et al (2003) concluded that riparian rehabilitation from the headwaters down to higher order streams may be necessary for restoration of stream health.…”

“…High amounts of agricultural development in catchments usually lead to declines in biodiversity and biotic indices used as measures of stream health compared with streams in less developed or pristine catchments. More recently, studies have also examined the effects of restoration of native vegetation in catchments, particularly in riparian zones, on stream physicochemistry and biology (Parkyn et al 2003).…”

“…The effects of pastoral agriculture on streams, whether from nutrients or sediments, can be mitigated by management practices (Quinn 2000;Parkyn et al 2003;wilcock et al 2006). These include fencing to keep stock from streams, and planting of vegetation in riparian zones between pastures and streams.…”

Setting the bar: an international comparison of public and private forest policy specifications and implications for explaining policy trends

“…A comprehensive review of this literature is well beyond the scope of this paper, but numerous studies from around the world have investigated the impacts of forest management on riparian ecosystems (Iwata et al 2003;Parkyn et al 2003;Semlitsch and Bodie 2003;Olson et al 2007). These studies have variously demonstrated the importance of maintaining the integrity of riparian structural features such as shade and coarse woody debris, and of maintaining water quality parameters, to both riparian zone and in-stream values.…”

Benefits of riparian forest for the aquatic ecosystem assessed at a large geographic scale

“…Such benefits may include the following: addition of organic matter, diversifying the trophic conditions; thermal regulation by forest canopy cover; structuring of habitat and provision of microhabitat; and buffer for nutrients and pollutant influx to the water course (Lowrance et al, 1984;Lowrance et al, 1997;Wenger et al, 1999). These functions have been evidenced only from local studies with field measurements (Storey and Cowley, 1997;Wallace et al, 1997;Parkyn et al, 2003;Dodds and Oakes, 2006;Rios and Bailey, 2006) and from some larger scale studies in strictly agricultural watersheds (Stewart et al, 2001;Wilson et al, 2008;Arnaiz et al, 2011). The cumulative watershed impact of forested riparian zones on stream nutrient levels is also acknowledged (Newbold et al, 2010;Curie et al, 2011;Wang et al, 2011), but remains poorly understood (Weller et al, 2011).…”