K.L. Heong, International Rice Research Institute, Los Baños, Philippines
Ecological engineering methods to increase flora diversity aim to restore and enhance ecosystem services in rice systems. This is done through increasing plant diversity as they are the fundamental resource base for arthropods. They provide food and shelter to the natural enemies that perform the various ecological functions to provide the regulatory ecosystem services, particularly predation and parasitization. When rice fields in China were surrounded with sesame plants, parasitoid biodiversity and densities increased. In Vietnam when bunds were populated with a variety of flowering plants, parasitization of planthopper eggs increased and densities of the egg predator, Cyrtorhinus, increased. In China, Thailand and Vietnam, ecological engineering techniques emphasized increase in floral biodiversity as a practice that farmers can adopt. Researchers (Isbell et al 2011) publishing in NATURE recently concluded that high plant diversity is needed to maintain ecosystem services in grassland ecosystems, where 84% of the plant species contributed towards at least one ecosystem service. This paper is also cited by the European Commission Science for Environment Policy.
In Hainan, rice fields where bunds were treated with herbicides had significantly lower spider biodiversity. Another study published in SCIENCE by Maestre et al (2012) also showed that high plant diversity enhances the ability of ecosystems to maintain multiple functions. They found that ecosystem multifunctionality is positively and significantly related to plant species richness.
Most rice ecosystems in Thailand, Vietnam and the Philippines are surrounded by rich floral diversity, like fruit trees, grasses, shrubs and flowering plants. They are generally well endowed with high diversity of plants, both annuals and perennials that provide food and shelter to numerous predator and parasitoid species. For instance a sample of 6,531 individuals of hymenoptera collected in Hainan rice ecosystems consisted of 816 species and 123 of them or 15% were new and yet to be described in science. Such biodiversity, often not appreciated, indicates the richness and abundance of predators, parasitoids and pollinators that continue to provide essential services to sustain agriculture. However most of these rice fields are also routinely sprayed unnecessarily with pesticides that destroy the biodiversity, related ecological functions and services.
It is urgent for us to implement extra efforts to protect floral and faunal biodiversity in rice ecosystems to safe ecosystems services and enhance managing pests with nature. Enriching non rice habitat with a diversity of plants is thus fundamental to restoring pest regulatory services. But at the same time we also need to practice “smart” herbicide and insecticide use. Prophylactic applications of chemicals are not “smart” as they counter all attempts to restore biodiversity. In addition these are unnecessary and wasteful practices that pollute the water and upland environments.
Isbell, F., Calcagno, V., Hector, A., et al (2011). High plant diversity is needed to maintain ecosystem services. Nature 477: 199-202.
Maestre, F.T., Quero, J.L. Gotelli, N.J. et al (2012) Plant species richness and ecosystem multifunctionality in global drylands. Science 335: 214 –