Ecosystem services provided by native New Zealand plants in vineyards

Abstract

This thesis investigates the value of native New Zealand plants within the agricultural landscape of the Waipara District, Canterbury Province, New Zealand with regards to their provision of ecosystem services (ES). ES have undergone extensive study with the conclusion that they are vital to maintain and improve the productivity of agricultural systems. Today, as concerns about the continued loss of biodiversity caused by agriculture mount, there is an urgent need to understand further the value of native plants. An appreciation of the ES which native plants provide would give cause for their conservation and restoration; as these services may improve agricultural sustainability. This study assessed several ES that native plants potentially provide. These included conservation biological control (CBC), marketing opportunities, biodiversity conservation, soil health, greenhouse gas sequestration (GHG) and weed suppression. Of these, the first two received greatest attention in this thesis. While the research predominantly focussed on the value native plants may have within vineyards, it also considered agricultural systems in general.

Native plant species were assessed in the laboratory to determine their relative ability to enhance the fitness of pest and agriculturally beneficial invertebrates; helping to assess the potential for these species to enhance CBC. A field trial investigated the ability of different native plant species to provide ES when deployed beneath grapevines. Assessments for survival, growth, flowering characteristics and invertebrate visitation, weed suppression, resident arthropod diversity, soil parameters and agronomic practicalities were undertaken to determine which plant species may be recommended to wine growers for their ES provision. Remnants of native vegetation within the Waipara valley of North Canterbury were also assessed for their provision of resources to sustain arthropods which may in turn contribute ES within the agricultural landscape. The potential for native plants in viticultural landscapes to provide marketing opportunities was evaluated by a survey of winery visitors, while another survey of wine growers clarified the factors influencing their adoption of practices incorporating native plants.

Results identified several native plant species which may be established to provide particular ecosystem services, either around arable crop borders or within vineyards. For CBC enhancement around crop borders, the shrub Muehlenbeckia astonii Petrie (Polygonaceae) may improve the management of the brassica (Brassica spp.) pest Plutella xylostella L. (Lepidoptera: Plutellidae) as the floral resources of this plant significantly enhanced the fitness of this pest’s natural enemy. Other plant species which significantly enhanced the fitness of natural enemies included Leptospermum scoparium Cockayne (Myrtaceae), Kunzea ericoides A.Rich, Joy Thomps. (Myrtaceae) and Hebe salicifolia G.Forst., Pennell (Plantaginaceae).

Of those plant species deployed beneath grapevines Muehlenbeckia axillaris Hook.f., Endl. (Polygonaceae), Leptinella dioica Hook.f. (Asteraceae) and Acaena inermis Hook.f. (Rosaceae) were identified as the most suitable plants for potential CBC enhancement in vineyards. M. axillaris appeared to be the most suitable species with regards to selective floral resource provisioning for leafroller (Lepidoptera: Tortricidae) pest management, while L. dioica may be suitable for enhancing the fitness of Cryptolaemus montrouzieri Mulsant (Coleoptera: Coccinellidae), a natural enemy of another vineyard pest: mealybug (Pseudococcus longispinus (Targioni-Tozzetti)).

The floral resources of matagouri (Discaria toumatou Raoul), the dominant native plant species within remnant shrubland of the Waipara valley, enhanced the fitness of Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae), an important biocontrol agent of brassica pests. Field observations of flowering matagouri suggested that remnants of this habitat support populations of a wide array of arthropod biocontrol agents and pollinators. Although further work is necessary, the findings support conservation of native remnants in agricultural landscapes, on the basis that they are enhancing the ecosystem services of pest control and crop pollination.

Assessment of arthropod diversity within the vineyard found diversity was positively affected by native plant establishment. For certain plant species, this increased diversity was maintained during the winter. This may result in cumulative enhancement of biodiversity within the vineyard over time as beneficial invertebrates are retained within the system, rather than arriving seasonally from refuges surrounding the crop. While an increase in diversity may bring with it improved ES, this will rely on the identity of the species and their function. Therefore while this study has found that native plants do indeed preserve biodiversity, the implications of this for the provision of other ES are yet to be resolved.

Native plants deployed within the vineyard varied in their effect on tested soil parameters, which included microbial populations and activity, soil moisture, total organic carbon and GHG sequestration. Indirect assessments of microbial activity revealed that it was heightened in soil directly beneath the native plant L. dioica while little evidence was found for the native plants affecting soil moisture levels. No significant effects of the plants on vineyard soil total organic carbon, microbial populations or GHG sequestration were observed. These findings are likely to have been due to the short time over which plants had been established.

Weed management was a major concern of vineyard operators in Waipara. This study found that native plant species L. dioica and A. inermis were capable of suppressing weeds in a Waipara vineyard. These species may provide vineyard managers with an alternative form of weed control, capable of reducing the currently prevalent mechanical and chemical methods.

Findings suggest wine growers can create marketing opportunities by establishing native plants within their properties. Native plants deployed within biodiversity trails at winery cellar doors provided wine consumers with an experience which may strengthen their brand loyalty to a winery. Additionally, establishing native plants within a regional project which aims to improve the sustainability of agricultural production may also provide marketing opportunities. Waipara winegrowers participating within ‘Greening Waipara’ (http://bioprotection.org.nz/greening-waipara) mostly agreed that this project provided point of difference marketing opportunities and generated greater regional brand recognition. For practices incorporating native plants to be adopted by growers, the practice must meet a demand, be financially viable and logistically feasible. Projects such as Greening Waipara provide a model by which native plants may be established. This project, an example of agro-ecological extension, increased the awareness of ES that native plants may provide; and consequently facilitated grower adoption of practices utilizing these plants.

These findings have implications for conservation on private land, sustainable agriculture and the wine industry. Although further research is needed to more fully understand the ES provided by native plants in agricultural landscapes, especially in an economic sense, this study offers strong evidence that native plants may indeed provide ES which contribute towards greater agricultural sustainability. In doing so, they provide tangible incentives for their conservation and restoration on farmland.