Abnormal Drought Research Articles

Responses of leaf-litter ant communities to tropical forest wildfires vary with season

Fire is an important land-management tool in tropical forest landscapes. However, these fires sometimes escape into surrounding forests (Uhl & Buschbacker 1985), and are one of the most severe disturbances threatening tropical forest biodiversity (Barlowet al2006). These forest fires have become more frequent over the last decades due to the combined effect of selective logging, fragmentation and abnormal droughts that increase the flammability of forests, and agriculture expansion that brings the ignition sources (Aragão & Shimabukuro 2010).

Proposition of Low Flow Management Under Several Scenarios and Application to Abnormal Drought

Proposition of Low Flow Management Under Several Scenarios and Application to Abnormal Drought

Photosynthesis, non‐photochemical pathways and activities of antioxidant enzymes in a resilient evergreen oak under different climatic conditions from a valley‐savanna in Southwest China

Plants in the savanna-valleys in Southwest China are annually exposed to different combinations of multiple stresses from the hot-rainy, to chill-dry, and to warm-dry seasons. This study monitored seasonal changes in photosynthesis and photoprotection in an evergreen oak (Cyclobalanopsis helferiana) from one of these valleys for four years during which usual and abnormal drought occurred. In general, during the study period with decreasing xylem water potential (Psix), photosynthetic gas exchange, quantum yield of photosystem II (PSII) photochemistry and activities of most of the measured antioxidant enzymes decreased, while activities of the xanthophyll cycle and associated non-photochemical energy dissipation and glutathione peroxidase (GP) (EC 1.11.1.9) increased. In a fairly severe chill period, high concentration of reactive oxygen species induced high activities of most of the antioxidant enzymes and relatively stronger decrease in gas exchange. In the most severe dry period, even when predawn Psix decreased down to -4 MPa, considerable Pn (maximum photosynthetic rate) (4 micromol m(-2) s(-1)) was still maintained in midmorning. At this time, most of the antioxidant enzyme activities decreased to the lowest values, whereas the xanthophyll cycle and associated non-photochemical energy dissipation and GP activities increased to their highest levels. High predawn antheraxanthin and zeaxanthin contents were observed in the severe and very severe drought periods. Superoxide dismutase maintained high and fairly constant activity (1500-1800 U mg(-1) protein) and predawn maximum photochemistry efficiency of PSII was always above 0.8 throughout the whole study period. These results indicated that the photosynthetic apparatus of the oak leaves was highly capable of maintaining its function under the multiple stresses in different seasons in the present valley-savanna.

Modification of Vegetative Phenology in a Tropical Semi‐deciduous Forest by Abnormal Drought and Rain1

ABSTRACTThe control of vegetative phenology in tropical trees is not well understood. In dry forest trees, leaf abscission may be enhanced by advanced leaf age, increasing water stress, or declining photoperiod. Normally, it is impossible to dissect the effects of each of these variables because most leaves are shed during the early dry season when day length is near its minimum and leaves are relatively old. The 1997 El‐Niño Southern Oscillation caused a ten‐week long, severe abnormal drought from June to August in the semi‐deciduous forests of Guanacaste, Costa Rica. We monitored the effect of this drought on phenology and water status of trees with young leaves and compared modifications of phenology in trees of different functional types with the pattern observed during the regular dry season. Although deciduous trees at dry sites were severely water stressed (Ψstem < ‐7MPa) and their mesic leaves remained wilted for more than two months, these and all other trees retained all leaves during the abnormal drought. Many trees exchanged leaves three to four months earlier than normal during the wet period after the abnormal drought and shed leaves again during the regular dry season. Irrigation and an exceptional 70 mm rainfall during the mid‐dry season 1998/1999 caused bud break and flushing in all leafless trees except dormant stem succulents. The complex interactions between leaf age and water stress, the principal determinants of leaf abscission, were found to vary widely among trees of different functional types.

Modification of Vegetative Phenology in a Tropical Semi-deciduous Forest by Abnormal Drought and Rain1

The control of vegetative phenology in tropical trees is not well understood. In dry forest trees, leaf abscission may be enhanced by advanced leaf age, increasing water stress, or declining photoperiod. Normally, it is impossible to dissect the effects of each of these variables because most leaves are shed during the early dry season when day length is near its minimum and leaves are relatively old. The 1997 El-Niño Southern Oscillation caused a ten-week long, severe abnormal drought from June to August in the semi-deciduous forests of Guanacaste, Costa Rica. We monitored the effect of this drought on phenology and water status of trees with young leaves and compared modifications of phenology in trees of different functional types with the pattern observed during the regular dry season. Although deciduous trees at dry sites were severely water stressed (ΨSTEM < −7MPa) and their mesic leaves remained wilted for more than two months, these and all other trees retained all leaves during the abnormal drought. Many trees exchanged leaves three to four months earlier than normal during the wet period after the abnormal drought and shed leaves again during the regular dry season. Irrigation and an exceptional 70 mm rainfall during the mid-dry season 1998/1999 caused bud break and flushing in all leafless trees except dormant stem succulents. The complex interactions between leaf age and water stress, the principal determinants of leaf abscission, were found to vary widely among trees of different functional types.

琵琶湖およびその集水域における水問題 平成６年度異常渇水に伴う琵琶湖の水環境

琵琶湖およびその集水域における水問題 平成６年度異常渇水に伴う琵琶湖の水環境

The analysis on the features of the atmospheric circulation in preceding winters for the summer drought and flooding in the Yangtze and Huaihe river valley

Based on the annual variation of the rainfall departure percentage in summer in the lower-middle reaches of the Yangtze River and the Huaihe River valley, 7 cases for the abnormal drought and flooding summers (the drought years: 1981, 1984, 1985; the flooding years: 1980, 1982, 1983, 1987) are selected. First we analyse the general circulation characteristics of the summer drought and flooding, and then the evolution processes of the general circulation patterns from preceding winters to summers are studied. It is found that during the two kinds of preceding winters for the drought and flooding summer, not only the general circulation patterns in the high-mid latitudes, the local Hadley cells in East Asia but also the activities of the cold surge in the lower latitude are different obviously. Spring, especially April, is the turning period of the general circulation in preceding winter for the drought or flooding summer evolution towards opposite direction. Hereafter, the drought or flooding circulation pattern is established and developed.

Drought in South-west Ireland

WHILST all round us have been reports of wintry weather and unceasing rain during the summer months, we in this small south-westerly area of Ireland have been passing through a period of abnormal drought, in fact a record season, accompanied by high temperature throughout.