Restoration of rice ecosystem services: Ecological engineering for pest management incentives and practices in the Mekong Delta Region of Vietnam

In southern Vietnam, government support has facilitated the adoption of ecological engineering for pest management by thousands of rice farmers. Despite this, there is still little information on the evolving knowledge, attitudes, and practices of rice farmers regarding ecological engineering and little understanding of the potential social sustainability of ecological engineering in Vietnam

The contributions from pesticides to rice yield increases are far from clear. For example, rice production in Southeast Asia increased by <30% between 2000 and 2015, at a time when pesticide imports to the region had increased by over 300%. Furthermore, certain region-wide pest problems, including frequent and sometimes devastating outbreaks of planthoppers and leafhoppers, are clearly associated with excessive pesticide use

Evidence suggests that outbreaks of pests, such as planthoppers, in rice, are at least partly due to insecticide-related reductions in the diversity, abundance, and regulatory efficiency of natural enemies, including spiders, mirid bugs, and parasitoid wasps.

Such outbreaks are a clear indicator of disruption to the regulating services provided by Asian rice ecosystems. Habitat diversification is proposed as a method to counter these outbreaks in rice by increasing rice ecosystem resilience against damaging pesticides and by restoring regulatory ecosystem services.

In particular, diversification by including flowering plants in rice ecosystems can provide supplementary food or refuge for natural enemies. These functional plants can be conveniently deployed as linear strips on the bunds (levees) that transverse rice landscapes. Because this approach is based on a sound knowledge of ecological interactions, it has been categorized as an ecological engineering approach to pest management. The approach has been used with notable success in a range of other agricultural systems.

A growing interest in ecological engineering (EE) for rice pest management is apparent through a number of recent case studies from across Asia. Based on these studies, ecological engineering can be regarded as a primarily restorative practice because it responds to the ‘state’ of the rice ecosystem vis-á-vis the reduced effectiveness of natural enemies and consequent insect pest outbreaks. Ecological restoration is one of a number of ‘human services to ecosystems’

These services, which also include enhancing and protecting services, are frequently combined in community actions for biodiversity conservation under the influence of associated supporting services to ecosystems.

Supporting services to ecosystems include policies, legislation, or directives around the sustainable management of the ecosystem, as well as community-held knowledge, beliefs, and attitudes concerning components of the ecosystem or concerning the ecosystem as a whole.

Cultural ecosystem services as defined during the Millennium Ecosystem Assessment are closely linked to supporting services to ecosystems and are largely determined by stakeholder interpretations of scientific knowledge and evolving beliefs with respect to the value of ecosystem components. The nature of these cultural ecosystem services (i.e., whether they are predominantly positive or negative) can determine whether supporting services to ecosystems ultimately facilitate or obstruct the enhancing, protecting, or restoring services from human societies to ecosystems.

Therefore, by exploring stakeholder appreciation of ecosystem services and their attitudes toward the implementation of conservation actions, assessments can be made regarding the sustainability and impact of restorative practices such as ecological engineering.

We conducted a survey of ecological engineering and conventional rice farmers from five provinces in the Mekong Delta Region (MDR). In particular, we wished to document the diversity of practices implemented by farmers under the umbrella of ecological engineering.

We assessed farmer satisfaction with these practices and whether the adoption of ecological engineering was associated with reductions in insecticide applications and/or increased yields as part of a strategy to enhance regulating and provisioning ecosystem services.

We further assessed whether the adoption of ecological engineering was associated with a greater appreciation of ‘nature’ and/or ‘ecological balance’ or was associated with an appreciation of recent changes to the state of the rice ecosystem as indicators of declining ecosystem services.

We linked these appreciations to provisioning, regulating, and cultural ecosystem services and evaluated their role in ultimately determining the nature of support for the continued implementation of ecological engineering. We discuss our results in terms of the social sustainability of implementing ecological engineering and make recommendations to adjust ecological engineering research and practices for improved adoption among rice farmers.

Our results indicate that ecological engineering generated a series of positive feedback loops to further support participation. For example, significantly more current-EE farmers (40.6%) than former-EE farmers indicated that they perceived ecological engineering as improving their farm economies by increasing rice yields, providing supplementary goods such as fruits and vegetables for home consumption, producing flowers that they could sell at local markets and producing forage for animals or materials for construction.

Furthermore, significantly more current-EE farmers (47.1%) than former-EE farmers perceived more favorable cost/benefit ratios associated with rice farming. Possibilities for the provisioning of supplementary goods through ecological engineering have been observed in previous studies. Indeed, a recognition of the provisioning services provided by flower and vegetable strips distinguished current-EE farmers from former-EE farmers in our study, thereby highlighting the role of this feedback in sustaining the practice.

Farmers did not report landscape aesthetics as governing their decisions to participate in the ecological engineering movement. However, a large number of farmers (42.9%) mentioned that their planted bunds were aesthetically pleasing, thereby constituting a further feedback loop that promotes the social sustainability of the intervention.

Although the main purpose of ecological engineering is to promote herbivore regulation services by natural enemies in rice ecosystems, this service was rarely mentioned by farmers (only 6.8%) as a factor to stimulate their participation and was not mentioned as an outcome of establishing flower or vegetable strips. Nevertheless, 49.6% of current-EE farmers perceived lower pest, disease, and/or weed damage to their rice crops.

This perception that declining pest damage is linked to planted bunds reveals an understanding by farmers of pest–natural enemy interactions through the visible consequences of those interactions. This specific response by farmers during the listing of ecological engineering outcomes suggests that the farmers largely based their perceptions on direct observations and were not simply repeating concepts they learned during training/extension.

Finally, the observation that current-EE farmers reported fewer insecticide applications to their rice fields than both conventional and former-EE farmers, and that their reduction in insecticide use was related to fewer applications during early crop stages, strongly suggests that current-EE farmers see the intervention as an effective pest management option.

Furthermore, current-EE farmers reported higher yields than conventional farmers. We did not verify these reports of higher yields; however, a study indicated that ecological engineering in An Giang reduced pesticide inputs while delivering similar or higher rice yields. It is also reported that ecological engineering reduced pesticide inputs at sites in the MDR while delivering higher rice yields.

The adoption of ecological engineering in the MDR has occurred despite relatively poor knowledge of the interactions between flower or vegetable strips, insect herbivores, and natural enemies. This may have affected the efficacy of the intervention. For example, many of the flower species that farmers planted on their bunds do not have any documented association with natural enemies.

Most of the species were non-native plants, and some, such as lantana and Macroptilium lathyroides (L.) Urb. (wild pea), are recognized invasive species in Southeast Asia. Indeed, many of the weeds that the farmers had cleared from the bunds might be superior as forage or refuge plants for natural enemies than some of the ornamental flowers that were subsequently planted.

Furthermore, many of the farmers indicated that it was difficult to grow plants on the bunds, particularly during dryer months. Although a large number of farmers reported that they sold flowers to local markets, this was not regarded as a profitable activity, and the demand for bund-grown flowers is probably much lower than the supply.

Among the current-EE and former-EE farmers, 48.5% had planted vegetables on their rice bunds, with more than half of these farmers also growing flowers. Vegetable species included ladyfinger, sesame, mung bean, and cucumbers, all associated with natural enemy abundance in rice production systems.

In many cases, vegetable plants, such as sesame, may be superior to ornamental flowers for sustaining natural enemy populations. Nevertheless, our results indicate that vegetable growers were less compliant with recommended ecological engineering practices. For example, compared to flower growers, farmers planted bund vegetables later (69.3% planted too late for the plants to have any effect on early-stage rice pests, and 23.9% of current-EE farmers applied insecticides to their planted bunds.

Indeed, there was a significant association between insecticide applications to bund vegetables by farmers and the declared profitability of supplementary crops. By advising farmers to only plant selected, tolerant vegetables, a trajectory toward chemical-dependent intensification of bund production might be avoided.

Farmers were almost unanimous in their belief that insecticides are effective in reducing pest damage and thereby contribute to higher yields. This represents a significant undermining service (i.e., supporting disservice) to the restoration of rice ecosystems, particularly since there were indications that insecticides may already have had a negative impact on rice production in some of the farmers’ fields.

For example, farmers that were ‘somewhat satisfied’ with insecticides, or were ‘not satisfied’, tended to make multiple insecticide applications (>5) per season. Furthermore, panicle mites were among the greatest of concerns for conventional farmers and were significantly more problematic than for current-EE or former-EE farmers. Insecticide-induced outbreaks of mites have been reported across a range of agricultural systems, particularly in response to pyrethroid insecticides.

Among the ecological engineering farmers we interviewed, 23.8% had abandoned the intervention. A large proportion of these farmers indicated that the practice was difficult (because of narrow bunds, a lack of experience in growing plants on bunds, and problems with synchronization) and that the practice was costly or labor-intensive. This dissatisfaction with ecological engineering indicates an underlying risk associated with the strong incentives from the government for farmers to participate in the movement without considering the possible consequences of related drudgery.

Because most of the species that farmers planted on the bunds were annual plants, any relaxing of the government incentives might result in further declines in farmer participation. In contrast, although only 19 of the farmers we interviewed also produced fish or crabs, information from these farmers suggests that, by promoting rice-fish systems, farmers might be further encouraged to avoid insecticides and adopt ecological engineering practices.

Based on our analyses, we believe that ecological engineering in the MDR requires further research to optimize practices. The heuristic approach to developing ecological engineering for rice ecosystems has been tremendously successful in promoting the technology among farmers; however, without further attention to the ecology of the system and basic research regarding the best ornamental or vegetable species to plant on bunds, the experience could represent a significant loss of opportunity.

Worrisome indicators of farmer dissatisfaction with the intervention due to labor and material costs, and a shift toward insecticide use on the planted bunds, suggest that simpler and more insect-resilient ecological engineering practices are urgently required. Issues around the social sustainability of the intervention also need to be addressed. At the time of our interviews, farmers relied heavily on government support to transition toward ecological engineering.

Because the nature and extent of government support are subject to changing policies, positive feedback derived from provisioning, regulating, or cultural services should be encouraged to enhance the social supporting services associated with ecological engineering.

Ecological engineering has evolved into a diversity of practices among farmers in the MDR of Vietnam. This includes the planting of various ornamental flowers and vegetables on rice bunds and the incorporation of fish into ecologically engineered paddy fields. To further enhance the provisioning services of the rice ecosystem, many farmers have opted to grow vegetables on their rice bunds. This practice can augment farm profitability and represents a sustainable feedback loop to further support continued restoration actions.

However, a strong dependency on government support, widespread satisfaction with insecticides, and a significant presence of agrochemical agents in rice-producing areas risk depleting the restoration value of ecological engineering practices and threatening the social sustainability of the ecological engineering movement.

Nevertheless, at the time of our study, farmers were still largely satisfied with the intervention, and participating farmers indicated that they made significantly fewer insecticide applications to their rice fields, that they applied insecticides later to the crop and that they attained higher yields than conventional farmers.

Read the study:
Horgan FG, Vu Q, Mundaca EA, Crisol-Martínez E. (2022) Restoration of Rice Ecosystem Services: ‘Ecological Engineering for Pest Management’ Incentives and Practices in the Mekong Delta Region of Vietnam. Agronomy. 2022; 12(5):1042.