Multiple Regression Models of the Distribution of Helianthemum chamaecistus In Relation to Aspect and Slope at Barnack, England
1982; Wiley; Volume: 19; Issue: 2 Linguagem: Inglês
10.2307/2403494
ISSN1365-2664
AutoresK. H. Lakhani, B. N. K. Davis,
Tópico(s)Forest ecology and management
ResumoSUMMARY (1) Data from a survey of sites where Helianthemum chamaecistus was common were analysed to identify the factors which might control the occurrence of the plant. (2) The main patterns in the plant distribution are adequately described by multiple regression models using transformations of aspect and slope values. Aspect and slope are obviously related to insolation and play a significant role in influencing distribution. (3) The study is of direct significance for other plant species, and indirectly for the dependent fauna. A stratified random sampling method was used to locate 311 m2 quadrats at Barnack Hills and Holes. The number of Helianthemum chamaecistus Mill. plants (P1) within each quadrat was recorded, together with the aspect (A1) and slope (S1) of the ground and the presence/absence of trees. There were sixty-eight quadrats with zero slope and therefore with no aspect value. Such quadrats had to be excluded from the multiple regression studies requiring simultaneous observations on both the aspect and slope variables. However, the relationship between H. chamaecistus and slope shown in Figs 2 and 5 include the data from flat quadrats. A grouped bivariate classification of the remaining 249 quadrats by aspect and slope is given in Table 1. This shows, for each combination of aspect and slope class, the total number of quadrats, the total number of quadrats occupied by H. chamaecistus, the total number of H. chamaecistus plants and the mean number of H. chamaecistus plants per quadrat + one standard error (S.E.) of the mean. The table shows a marked effect of aspect on the abundance of H. chamaecistus. Thus, out of the observed total of 249 quadrats, ninety-seven quadrats (39%) had aspect values between 1200 and 2400, but these contained 625 out of a total of 935 observed plants
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