Interspecific variation in resistance and tolerance to herbicide drift reveals potential consequences for plant community co-flowering interactions and structure at the agro-eco interface.

BACKGROUND AND AIMS: When plant communities are exposed to herbicide 'drift', wherein particles containing the active ingredient travel off-target, interspecific variation in resistance or tolerance may scale up to affect community dynamics. In turn, these alterations could threaten the diversity and stability of agro-ecosystems. We investigated the effects of herbicide drift on the growth and reproduction of 25 wild plant species to make predictions about the consequences of drift exposure on plant-plant interactions and the broader ecological community. METHODS: We exposed potted plants from species that commonly occur in agricultural areas to a drift-level dose of the widely used herbicide dicamba or a control solution in the glasshouse. We evaluated species-level variation in resistance and tolerance for vegetative and floral traits. We assessed community-level impacts of drift by comparing the species evenness and flowering networks of glasshouse synthetic communities comprised of drift-exposed and control plants. KEY RESULTS: Species varied significantly in resistance and tolerance to dicamba drift: some were negatively impacted while others showed overcompensatory responses. Species also differed in the way they deployed flowers over time following drift exposure. While drift had negligible effects on community evenness based on vegetative biomass, it caused salient differences in the structure of co-flowering networks within communities. Drift reduced the degree and intensity of flowering overlap among species, altered the composition of groups of species that were more likely to co-flower with each other than with others and shifted species roles (e.g. from dominant to inferior floral producers, and vice versa). CONCLUSIONS: These results demonstrate that even low levels of herbicide exposure can significantly alter plant growth and reproduction, particularly flowering phenology. If field-grown plants respond similarly, then these changes would probably impact plant-plant competitive dynamics and potentially plant-pollinator interactions occurring within plant communities at the agro-ecological interface.

Deforestation Dynamics on an Amazonian Peri-Urban Frontier: Simulating the Influence of the Rio Negro Bridge in Manaus, Brazil.

Peri-urban expansion is an increasingly important source of tropical deforestation, and a bridge over the Rio Negro in Brazil's state of Amazonas provides an unusual opportunity to quantify these impacts with clear "before" and "after" periods. Inaugurated in 2011, the bridge connects Manaus to forest areas on the right bank of the river, thus opening a new frontier for peri-urban expansion. We used the AGROECO model in the Dinamica-EGO software to simulate "Bridge" and "No-bridge" scenarios to evaluate the spatial dynamics of deforestation in the municipalities (counties) of Iranduba, Manacapuru and Novo Airão. Simulated deforestation between 2011 and 2030 for the study area as a whole was 106% higher with the bridge. The portion of the study area with expansion of roads had four times more deforestation in the Bridge scenario than in the No-bridge scenario. A change in the spatial distribution of the deforested area was detected, with an advance of deforestation in the municipality closest to the bridge. Deforestation also expanded in more distant regions. Peri-urbanization in the Bridge scenario demonstrates the possible increase in the spatial distribution of deforestation activity beyond the already-consolidated frontier, making the deforestation pattern more diffuse and leaving the remaining forest even more vulnerable. Impact of the bridge could further increase due to additional factors, such as the planned opening of a highway (BR-319) connecting Manaus to Brazil's "arc of deforestation."

Simulating deforestation and carbon loss in Amazonia: impacts in Brazil's Roraima state from reconstructing Highway BR-319 (Manaus-Porto Velho).

Reconstruction of Highway BR-319 (Manaus-Porto Velho) would allow for access from the "arc of deforestation" in the southern part of Brazil's Amazon region to vast blocks of forests in central and northern Amazonia. Building roads is known to be a major driver of deforestation, allowing entry of squatters, and other actors. Rather than deforestation along the highway route, here we consider the road's potential for stimulating deforestation in a separate location, approximately 550 km north of BR-319's endpoint in Manaus. Reconstructing BR-319 has great potential impact to start a new wave of migration to this remote region. The southern portion of the state of Roraima, the focus of our study, is already connected to Manaus by Highway BR-174. We modeled deforestation in southern Roraima and simulated carbon emissions between 2007 and 2030 under four scenarios. Simulations used the AGROECO model in DINAMICA-EGO © software. Two scenarios were considered with reconstruction of BR-319 and two without this road connection. For each of the two possibilities regarding BR-319, simulations were developed for (1) a "conservation" (CONSERV) scenario that assumes the creation of a series of protected areas, and (2) a "business-as-usual" (BAU) scenario that assumes no additional protected areas. Results show that by 2030, with BR-319 rebuilt, deforestation carbon emissions would increase between 19% (CONSERV) and 42% (BAU) over and above those corresponding to no-road scenarios.

Wood-nesting ants and their parasites in forests and coffee agroecosystems.

Agricultural intensification is linked to reduced species richness and may limit the effectiveness of predators in agricultural systems. We studied the abundance, diversity, and species composition of wood-nesting ants and frequency of parasitism of poneromorph ants in coffee agroeco systems and a forest fragment in Chiapas, Mexico. In three farms differing in shade management and in a nearby forest fragment, we surveyed ants nesting in rotten wood. We collected pupae of all poneromorph ants encountered, and incubated pupae for 15 d to recover emerging ant parasites. If no parasites emerged, we dissected pupae to examine for parasitism. Overall, we found 63 ant morphospecies, 29 genera, and 7 subfamilies from 520 colonies. There were no significant differences in ant richness or abundance between the different sites. However, there were significant differences in the species composition of ants sampled in the four different sites. The parasitism rates of ants differed according to site; in the forest 77.7% of species were parasitized, and this number declined with increasing intensification in traditional polyculture (40%),commercial polyculture (25%), and shade monoculture (16.6%). For three of four poneromorph species found in >1 habitat, parasitism rates were higher in the more vegetatively complex sites. The result that both ant species composition and ant parasitism differed among by site indicates that coffee management intensification affects wood-nesting ant communities. Further, coffee intensification may significantly alter interactions between ants and their parasites, with possible implications for biological control in coffee agroecosystems.

Copro-necrophagous beetle (Coleoptera: Scarabaeidae) diversity in an agroecosystem in Yucatan, Mexico

Scarabaeinae are sensitive to structural habitat changes caused by disturbance. We compared copronecrophagous beetle (Scarabaeinae) community structure in three differently managed zones within an agroeco-system of the northern Yucatan Peninsula, Mexico. We placed dung and carrion traps once a month from June 2004 through May 2005. The beetle community included 17 species from the genera Canthon, Canthidium, Deltochilum, Pseudocanthon, Malagoniella, Onthophagus, Phanaeus, Copris, Uroxys, Sisyphus and Ateuchus. The secondary vegetation had a higher beetle diversity than the other two zones. Species richness was highest in the Brosimum alicastrum plantation. The pasture had the lowest species diversity and richness, but exhibited the highest abundance of Scarabaeinae in the dry season. The two zones with extensive tree cover were the most diverse. Roller beetles were dominant over burrower species and small-sized species outnumbered large species. Our data show two important issues: beetle species in the pasture extended their activity to the beginning of the dry season, while abundances dropped in the other, unirrigated zones; and the possibility that the Scarabaeinae living in neotropical forests are opportunistic saprophages and have specialized habits for resources other than dung. The B. alicastrum plantation is beneficial to the entire ranch production system because it functions as a dispersion and development area for stenotopic species limited to tree cover.

Copro-necrophagous beetle (Coleoptera: Scarabaeidae) diversity in an agroecosystem in Yucatan, Mexico.

Scarabaeinae are sensitive to structural habitat changes caused by disturbance. We compared copronecrophagous beetle (Scarabaeinae) community structure in three differently managed zones within an agroeco-system of the northern Yucatan Peninsula, Mexico. We placed dung and carrion traps once a month from June 2004 through May 2005. The beetle community included 17 species from the genera Canthon, Canthidium, Deltochilum, Pseudocanthon, Malagoniella, Onthophagus, Phanaeus, Copris, Uroxys, Sisyphus and Ateuchus. The secondary vegetation had a higher beetle diversity than the other two zones. Species richness was highest in the Brosimum alicastrum plantation. The pasture had the lowest species diversity and richness, but exhibited the highest abundance of Scarabaeinae in the dry season. The two zones with extensive tree cover were the most diverse. Roller beetles were dominant over burrower species and small-sized species outnumbered large species. Our data show two important issues: beetle species in the pasture extended their activity to the beginning of the dry season, while abundances dropped in the other, unirrigated zones; and the possibility that the Scarabaeinae living in neotropical forests are opportunistic saprophages and have specialized habits for resources other than dung. The B. alicastrum plantation is beneficial to the entire ranch production system because it functions as a dispersion and development area for stenotopic species limited to tree cover.

Soil nitrogen balance assessment and its application for sustainable agriculture and environment.

Soil nitrogen balance assessment (SNBA) serves as an effective tool for estimating the magnitude of nitrogen loss/gain of the agro-eco systems and to appraise their sustainability. SNBA brings forth awareness of soil fertility problems, besides providing information relating to the resultant release of nitrogen into the environment consequent to agricultural practices. Quantitative information relating to nitrogen escape into the environment through such exercises can be gainfully utilized for identification of causative factors, enhancing fertilizer use efficiency and formulating programmes aimed at plugging N leakages. An overview of nitrogen balance approaches and methodologies is presented. A deeper understanding and insight into the agro-eco systems provided by the SNBA exercises can lay the basis for the formulation of effective agronomic interventions and policies aimed at promoting sustainable agriculture and a benign environment.

Soil nitrogen balance assessment and its application for sustainable agriculture and environment.

Soil nitrogen balance assessment (SNBA) serves as an effective tool for estimating the magnitude of nitrogen loss/gain of the agro-eco systems and to appraise their sustainability. SNBA brings forth awareness of soil fertility problems, besides providing information relating to the resultant release of nitrogen into the environment consequent to agricultural practices. Quantitative information relating to nitrogen escape into the environment through such exercises can be gainfully utilized for identification of causative factors, enhancing fertilizer use efficiency and formulating programmes aimed at plugging N leakages. An overview of nitrogen balance approaches and methodologies is presented. A deeper understanding and insight into the agro-eco systems provided by the SNBA exercises can lay the basis for the formulation of effective agronomic interventions and policies aimed at promoting sustainable agriculture and a benign environment.