Temperature And Betula Disribution On The Holy — страница 2

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are present affecting the growth of Betula on the Holyoke Range. My prediction is that the north face of the mountain will have a higher density of these trees than the south face of the range due to environmental factors such as temperature. Methods On September 20, 2000, the birch tree genus, Betula, density was measured on the north face of the Holyoke Range and on September 27, 2000, Betula??s density was also measured, but on the south face of the Holyoke Range. There were eight sites laid across a 150m transect line running across the slope starting from a subjectively chosen point. The replicates were formed by taking eight random sites above the transect line, and eight below; then counting each as a single replicate giving a sample size of 16. Within these eight sites,

the size, density of adults and saplings of other trees along with Betula. From the transect line, two 10×10m plots were measured, one above the transect line, one below the transect line. In the upper left corner of these plots, a 4×4m plot was also measured. Within the 10×10m plots, the species and the dbh (diameter at breast height, measured at about 1.5 above ground) of each adult tree was recorded. An adult was defined as an individual that had a dbh that was greater than 10cm. For trees with multiple trunks, the dbh of each trunk was recorded separately, noted the values of these as x+y+?K Also within the plot, dead trees were not counted. In the 4×4m plots the number of saplings of each tree species along with Betula was recorded. A sapling was defined as being over 1m

tall and less than 10cm in dbh. Also within these plots shrubs and bushes were not included in the count. Results Mean densities were significantly higher on the north face versus the south face of the mountain range in the case of only one of birch tree species recorded, Betula lenta, (Table 1). Also mean basal area (cm2 m-2) of birch trees found was significantly larger in only Betula lenta (Fig 1). Frequency of Betula lenta was highest on the north face of the mountain range, and overall birch species have a higher frequency on the north face of the mountain (Fig 2). Eight separate t-tests were performed, four on the density (ind ha-1) of adult Betula, and another four on the basal area (cm2 m-2) of the adult Betula. For Betula lenta, the basal area (cm2 m-2) was significantly

higher on the north versus the south face of the mountain range (t = 9.435; P * 0.001). For mean density (ind ha-1) of Betula lenta, the data was significantly higher on the north versus the south face of the mountain range (t = 10.26; P * 0.001). For Betula lutea, mean basal area (cm2 m-2) was higher on the north-facing slope (Fig 1), but was not significant (t = 1.343; 0.1 * P * 0.2). For mean densities of Betula lutea, it was higher on the north face, but was not significant (Table 1) (t = 1.382; 0.1 * P * 0.2). For Betula papyrifera also the mean basal area was higher on the northern-facing slope of the range (Fig 1), but the test found it not significant (t = 1.651; 0.1 * P * 0.2). For the mean density of Betula papyrifera (ind ha-1) the data was marginally significant (t =

1.769; 0.05 * P * 0.1). For Betula populifolia, again the mean basal area (cm2 m-2) was larger on the north face of the range, but the tests of the data found them not significant (t = 1.480; 0.1 * P * 0.2), but like Betula papyrifera, the mean density of Betula populifolia (ind ha-1) was marginally significant (t = 1.896; 0.05 * P * 0.1). Discussion From the results of my data, it cannot be concluded that temperature could be the sole factor in the tree distribution of Betula on the Holyoke range. This is so because the probability of the data occurring by chance is large, the exception of the species Betula lenta, which means that densities recorded at these slopes of the mountain are not an accurate representation of the population as a whole. Two other species of birch tree

densities (ind ha-1) were marginally significant, Betula papyrifera and Betula populifolia, but their mean basal area (cm2 m-2) wasn??t significant. Although these species of Betula are usually found mainly on north facing slopes, there was not enough significant data to support this, suggesting a different reason for the densities of Betula on the Holyoke range. One factor that could contribute to the higher densities of Betula on the Holyoke Range is inter-specific and intra-specific competition. This is a possible explanation of the data because the yellow birch, Betula lutea, is found usually around cherry birch, or Betula lenta. This could induce intra-specific competition between the two birch tree species, which would lower densities of one of the two species of birch