Macroclimatic Conditions Research Articles

Ordination of land types in the karoo region into reasonably homogeneous farming areas based on vegetation and environmental factors1

The 291 preliminary land types in the Karoo Region formed the basis for the demarcation of the 144 Reasonably Homogeneous Farming Areas (RHFAs). The land types were firstly reduced to 23 Floristic Climatic Regions (FCRs) according to character species for certain macroclimatic conditions. The character species were identified by means of computer classification and ordination techniques (PHYTOTAB, TWINSPAN and DECORANA). About 22 soils forms and numerous soil series were found in the Karoo Region. Based on differences in the inherent veld production potential and erodibility of the different soils, as well as differences in slope nine Veld Soil Potential Classes (VSPCs) were synthesised. The land types in each of the FCRs were, lastly, consolidated according to their similarity in terms of macroclimate and dominant topographical units and VSPCs, into RHFAs.Language: English Keywords: Character species; classification; Computer classification; decorana; Environment; environmental factors; FCRs; floristic climatic regions; Homogeneous farming areas; karoo; Karoo Region; land types; ordination; Ordination techniques; phytotab; production; production potential; Reasonably Homogeneous Farming Areas; RHFAs; slope; soil series; soils; south africa; technique; twinspan; vegetation; veld soil potential classes; VSPCs

Gradient analysis in assessing differences in community pattern of three adjacent sectors within Abitibi, Quebec

Gradient analyses were done for three sectors within the clay belt section of western Quebec, in order to study the differences in plant community distributions caused by macroclimatic conditions and disturbance dynamics. Firstly, indirect ordinations were performed for the data collected in each sector representing a latitudinal and longitudinal gradient within the whole region. The interpretations of these ordinations showed that variations in moisture gradient, trophic level and surficial deposits explained the distribution of plant communities within the three sectors. In contrast to sectors located further south, neither altitude nor exposure have a significant effect.

Predicting physiognomic vegetation types with climate variables

A quantitative terrestrial vegetation model was produced which consists of: The model was applied to a world climatic data-base (1 225 sites) in order to substantiate the hypothesized life-form status of the plant types by accurately predicting their actual world distributions. Particular combinations of forms are interpreted as vegetation formation types by reference to growth-form dominance considerations. Model validation was attempted by comparing predicted and actually occurring vegetation at independent sites on all continents. Prediction accuracy of 85% for individual plant types and 50% for vegetation structure (exact combination of actually occurring dominant forms) suggests that general macroclimatic conditions are much more important than any other factors (such as complex specific interactions) in determining general ecological structure on most sites.

PHENODYNAMIC ANALYSES OF TWO FIRST‐YEAR OLD FIELDS

Phenological spectra from two adjacent first‐year old fields suggest that phenological events may be directed by the biotic influences of associated species as well as by climatic and edaphic conditions of the region. These two fields possessed similar macroclimatic conditions but had differing soil textures and crop histories. Phenological spectra were developed by observations made on all plant species occurring in fixed quadrats during the duration of this study, April 1, 1970, to October 20, 1970. The phenophases observed were initiation of vegetative growth, time of budding, occurrence of flowering, fruiting sequences, and time of seed set and dissemination. Production studies based on short‐term harvest methods indicated the dominance of Erigeron canadensis in the abandoned soybean field, and Erigeron annus in the abandoned corn field.

Competition and Thermoregulatory Behavior of the Namib Desert Tenebrionid Bettle Genus Cardiosis

Tenebrinonid beetles of the genus Cardiosis are confined to sand dunes and other sandby substrates of the Namib Desert in South West Africa and Angola. In the northern Namib the breadth of environments occupied by each species is considerably greater in the southern Namib. This may be due to competition resulting in ecological divergence, since there is sympatry in this genus only in the southern Namib. All species of the genus Cardiosis, including the sympatric C. fairmairei and C. hamiltonuli are diurnal. The daily activity rhythm of these species responds to ambient thermal conditions, and fluctuations in ambient conditions result in differing patterns of activity. Substrate and ambient temperatures are the important microclimatic variables influencing the actual timing of activity. This usually results in a concentration of activity in the least humid hours of the day. On cool days or when winds cool the sand surface, activity may extend through the middle hours of the day. On hot or calm days activity becomes bimodal, with activity limited to intervals when body temperatures can be maintained at levels well above 30 degrees C and substantially below lethal limits. The interval of morning activity is less pronounced than the afternoon activity period and on especially hot days morning activity may be omitted altogether. Unconfined populations of Cardiosis extend their activity over considerably greater intervals than confined populations exposed to identical macroclimatic conditions. This is due to the ability of the unconfined population to utilized a broad spectrum of environments, thus locating favorable thermal conditions as they develop in the course of a daily cycle.

Influence of Macroclimatic Conditions on the Development of Blast and Helminthosporiose of Rice

Influence of Macroclimatic Conditions on the Development of Blast and Helminthosporiose of Rice