“Hold the line! The invasives are coming!”
“Captain, we’re losing ground! The phosphate is encroaching.”
“Retreat to higher ground! It’s safer up there.”
“Send in the spiders and beetles! Earthworms, you stay here.”
“Defend the Buffer!!!” [insert battle cry]
If the plants and insects at Bankside Scientific Reserve could talk, they would probably sound something like that. While this 2.6 ha protected area is home to important communities of native species, it is under threat of phosphate intrusion and the breaking-up of the local habitat. Humans have greatly altered the lowland Canterbury Plains of Aotearoa/New Zealand. With the recent switch to irrigated dairy farming, very few patches of undisturbed native dryland vegetation are left in the region. This change in land-use has led to a higher reliance on fertilizers as well as water for irrigation, which has come with its own set of challenges.
Aggressive introduced weeds, pasture grasses and forbs, have also begun to dramatically alter the functioning of native plant communities. Remnant areas are both vulnerable and essential to maintaining native ecosystems (hence the need to defend the buffer). Mike Bowie and his team investigated one of these remnant areas, looking at soil chemistry, plant distribution, and soil invertebrates along transects at the Bankside Scientific Reserve. Their study identified the current conservation value of the reserve, assessed how persistence of native biodiversity changed along the pasture-reserve gradient, and evaluated the effects of the likely infringement of irrigation water and nutrients from adjacent farmland.
The vegetation of Bankside Scientific Reserve had been studied previously by Malloy (1970), who provided a detailed catalogue of the flora, listing 66 native vascular plant species. Jenson & Shanks (2005 – unpublished DOC Report) also completed a one-day reassessment of the site, but recorded only 14 native species. Today, the vegetation at the reserve can be described as a patchwork of native woody shrubs, made up mainly of makahikatoa, matagouri, and dry grassland. As Mike and his team point out, the modified soil conditions seem to have made the reserve not as well suited for native species, and better for the invasion by exotic plants. Compared with detailed surveys prior to the dairy conversion, only 31% of the original 65 native vascular plant species were found in the current study, and 27 new exotic species had arrived since the original survey.
As for the underground conditions, soil nutrient concentrations and pH were lower in the reserve than in the surrounding farmland, with peaks of nitrate and ammonium being recorded at the boundary. Meanwhile, soil phosphate was higher in lower-lying areas within the reserve. Four species of endemic (Megasolecidae) earthworms were found in the reserve, but not in the neighbouring pasture.
Other cool finds included ground wētā (Hemiandrus sp.) and trap door spider (Cantuaria dendyi). A 2011 survey by Emberson et al. (2011) also found the large rare rove beetle, Hadrotes wakefieldi, and several species of long-horn beetles. As opposed to the earthworms, the diversity and abundance of beetles and spiders in the reserve was similar to that recorded at least 10 m into surrounding farmland.
Another interesting take-away from this research, is the importance of areas of higher elevation. Although elevational differences between highest and lowest contours were <5 m in the study, the higher areas were very important in avoiding environmental change from agricultural drainage and effluents. They helped to maintain environmental conditions that were closest to the original habitat, providing the best-suited habitat for native plants and animals.
The work of Mike Bowie and his team, along with previous studies, points out the significance of small remnant reserves for the conservation of indigenous invertebrates found in these rare dryland ecosystems. Their findings also suggest that lime and phosphate fertilisers may represent the main threats to dryland nature reserves in irrigated dairy landscapes. Above all, their research underlines the importance of the soil environment in sustaining the variety of plant, animal, and insect life in this unique environment.
Taking the team’s findings into consideration, the maintenance of a buffer zone – a protected zone established around sensitive or critical areas – could be beneficial in lessening the impacts of human activity and land disturbance around remnants, such as Bankside Scientific Reserve. To do this, native species can be planted between agricultural and conservation areas, to help protect sensitive habitat. The key take-away: Defend the Buffer!
This article was prepared by Master of International Nature Conservation student Catherine Priemer as part of the ECOL608 Research Methods in Ecology course.