My latest paper is out. It’s a leftover from my last postdoc at Charles Sturt Uni where I was working on ecosystem services in SE Australian apple orchards with Gary Luck and PhD student Rebecca Peisley – see her blog posts on her work here.
Our main research question for the project was to calculate the net outcome, in terms of yield, of all the positive and negative effects of animal interactions across a growing season. You can read our previous paper on those results here.
In this new paper we looked at another interaction, the influence of landscape vegetation and orchard ground cover on different invertebrate groups. I really enjoyed this project as it was an opportunity to explore an idea I had been thinking about for a while. I first got interested in orchard ground cover during my PhD, comparing wild pollinators in almond orchards with and without living ground cover.
Unlike almond plantations, most Australian apple orchards maintain living ground cover across the orchard, with varying degrees of coverage and plant diversity. Flowering non-crop plants are important on farms to support the beneficial insects that enhance crop yields, like pollinators and natural enemies. These flowers can be maintained as ground cover throughout orchards, as well as unmanaged meadows and patches of woodland around farms.
An increasing amount of research has found that local (e.g. crop type or ground cover diversity) and landscape (e.g. amount of native vegetation in the landscape) factors interact to influence what beneficial insects are found on farms.
This is important, because the myriad wild pollinator and natural enemy species that are needed to provide ecosystem services to improve crop yields all have different life cycles and home ranges. Some are flightless, some will fly hundreds of metres across the landscape during their life. Some need dead wood to nest in, some lay their eggs in the ground. Nearly all of them need a diverse range of flowering plants for pollen and nectar, others also feed on other animals. No farm is an island, so complementary strategies at both farm and landscape scale are needed to enhance beneficial insect populations.
Interactions between local and landscape characteristics affect wild bee populations and some natural enemies. But we couldn’t find any studies that had looked at simultaneous effects on pests, pollinators, natural enemies and fruit yield within the same system.
We explored this interaction (number of flowering plants in ground cover X proximity to native woodland) at our apple orchard sites and found that floral diversity within orchards may be buffering the negative effects of orchards being far from woodland. This suggests that both attributes, flowering plant diversity in orchards and more areas of native woodland around farms, are important for increasing beneficial insects and reducing pests. But higher flowering plant diversity may be even more important within orchards situated in intensive, highly-cleared landscapes.
As with most field ecology studies, our data are noisy because of all the natural variability going on. The random effect variance in some of our models was relatively high, which suggests that those random effects (in this case, orchard and region) were also having a big influence over the data. It appeared that orchard identity had a greater influence over pests, syrphid flies and large predatory wasps, while geographical region had a greater influence over wild bees and parasitoid wasps.
This complexity needs to be explored, not ignored. It’s impossible to make definitive assumptions about how to manage a crop system based on data from one crop stage, or one plant-animal interaction. Studies that look at interactions between multiple pollinators, pests and natural enemies within a system are valuable for science and agriculture – and they’re great fun to do!
© Manu Saunders 2017