Phytosociological survey of weed plants in soybean culture in the Gurguéia Valley

Phytosociology is a set of ecological assessment methods that aim to provide a view of plant species distributions within a plant assemblage. The objective of the current study was to identify and quantify the plants designated as weeds in a glyphosate-resistant soybean crop, using a phytosociological survey of a conventional planting system on the Fazenda Agrosantos (09°27’4124.4” S and 45º01’00.4” O), Vale do Gurguéia, Monte Alegre municipality Piauí state, Brazil. The site lies at a mean altitude of 652 m. Field collections were made 15 days after initial soya planting. For sampling, a 0.40 x 0.40 m quadrat was used, thrown randomly twenty times within the experimental area. Weeds were identified and quantified using the sum of the samples obtained from the quadrat samples. Plants that lay within the quadrat were identified, counted and collected for identification, which was carried out by comparison with specialist bibliographies and weed identification manuals. Evaluated variables were: frequency, density, abundance, relative frequency, relative density, relative abundance and species importance value index. In the soybean cultivation area, 60% of the sampled species were Eudicotyledons, and a total of 8 botanical families and 10 weed species were identified. The species Cenchrus echinatus, Ipomoea asarifolia (Desr.) Roem. & Schult, Amaranthus retroflexus L. and Zea mays L showed the highest values for the analyzed variables, and should therefore be of special attention to soybean producers in the region of Vale da Gurguéia, Piauí, Brazil.

Changes of Köppen–Trewartha climate types in the Tibetan Plateau during the mid-Holocene, present day, and the future based on high-resolution datasets

<p>Based on the Köppen–Trewartha climate classification schemes, we examined the shifts in terrestrial climate regimes in the Tibetan Plateau (TP) by analyzing the WorldClim high-resolution (~25 km) downscaled climate dataset for the mid-Holocene (MH, 6,000 cal yr BP), the present day (PD, 1970-2000), and in the future (2041-2060, represented by 2050). The climate types of the PD are compared to those of the MH and the future. Our aim was to place ongoing anthropogenic climatic and environmental changes in the TP within the context of changes due to natural forcing in the three selected warm period, and to determine the differences in the spatial expression of ecosystem among these selected periods. The results indicate that the climate of the TP will continue to warm in the future. The intensity of the South Asian monsoon may increase in the future which will affect precipitation in the southern TP. There will be a significant decrease in the areas covered by polar climate, while the spatial coverage of the other climate types will increase. A tropical climate which did not exist in the MH and PD will develop in some areas and the shrinking polar climate indicates that the cryosphere of the TP will change significantly, which in turn may cause the climate system to pass a tipping point and cause irreversible consequences. The large changes in the climate regimes of the TP suggest that there will be a widespread redistribution of the surface vegetation and significant changes in plant species distributions by 2050. Compared to changes in precipitation, increasing temperature is the dominant factor that driving the change of climate types in the TP. The warming alone may cause the climate types to change in more than 20% areas by 2050.</p>