Reiichi Miura

Short-term effects of fire intensity on soil organic matter and nutrient release after slash-and-burn in Eastern Province, Zambia

Abstract According to the slash-and-burn technique used in Eastern Province, Zambia, cut trees are piled and burned in only a part of the cleared fields, because adequate tree biomass is not available to burn the entire field. Due to a recent decrease in emergent trees, not only emergent tree piles but also bush tree piles may exist. Therefore, our objective was to evaluate the changes in soil organic matter followed by nutrient release occurring immediately after burning in spots unburned and burned with emergent and bush trees. Fire intensity was significantly higher where emergent tree piles were present. Total carbon (C) decreased by 25.1% and 14.7% in spots burned with emergent and brush tree piles, respectively, while total nitrogen (N) decreased by 15.0% only at spots burned with emergent tree piles and did not change significantly elsewhere. Additionally, the mortality of microbes with soil heating caused an increase in C mineralization after fire. The levels of available nutrients, such as ammonium nitrogen (NH4-N), available phosphorus (P), and exchangeable potassium (K) and calcium (Ca), increased following the decomposition of soil organic matter and microbial mortality that occurred with an increase in fire intensity. Net N mineralization did not occur, especially in spots burned with emergent tree piles, because the N content of labile organic matter decreased. Maize (Zea mays L.) grain yield increased with fire intensity, because fire increased nutrient availability and limited weed biomass. Although the burned emergent and bush tree piles occupied only 6.9 and 7.5% of total cleared field, respectively, the grain yield in spots burned with emergent and bush trees accounted for 21% and 15% of the total yield, respectively. Therefore, the burning of bush trees, which is increasing because of the decreased number of emergent trees, could result in a decrease in grain yield but could also alleviate the overall severe loss of soil organic matter.

Preliminary Observations of Insect Visitation to Flowers of Vincetoxicum pycnostelma (Apocynaceae: Asclepiadoideae), an Endangered Species in Japan

Abstract Vincetoxicum pycnostelma Kitag. (Apocynaceae) is a perennial herb that grows in grassland habitats in East Asia and the western part of Amur. Urbanization, land development, abandonment of traditional management of grasslands, or any combination of these factors are rapidly reducing grassland habitats, and V. pycnostelma is now ranked as a “Near Threatened” species on the Red List of Japan. Identification and characterization of pollinators of this endangered species are important in its conservation. We observed and collected insect visitors to the flowers at night and in the morning in the populations of V. pycnostelma on the banks of the Kidzu River, Kyoto, Japan from June to August in 2011. Pollinators were characterized as those insects on which flower pollinaria were attached. Twenty-seven species (9 families; 3 orders) were observed visiting the flowers; individuals of 14 lepidopteran species (6 families) had pollinaria attached to their bodies and most visited the flowers at night. Adult lepidopterans with a proboscis length of 0.9 - 4.5 mm were the primary carriers of pollinaria. Examination of stigmatic chambers of randomly selected flowers showed that the percentage of flowers in which pollinaria was inserted was much higher than the percentage of fruit set observed. Reasons for the observed low fruit set may be self-incompatibility or resource limitation. These preliminary observations were conducted at only 1 site and were restricted to a short period of time; yet, these data could be useful for elucidation of effective pollinators of this species and, thus, its conservation.