| Range, Massachusetts Essay, Research Paper
Temperature and Betula distribution on the Holyoke Range, Massachusetts
Abstract
In this study, it will be tested whether temperature affects tree densities in the genus Betula on different slopes of the Holyoke Range, specifically the north and south faces of the mountain 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 because of the temperature differences of the north slope being warmer than south slope for the range of growth for these trees. This experiment can be used to predict patterns of vegetation in other similar latitudes and slopes around the world. 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. Based on the data collected on the Holyoke Range, the birch trees densities were not significantly higher on the north face than on the south face of the mountain range. Eight separate t-tests were performed, four on the density of the adult birch trees, and another four on the basal density of adult birch trees. From this data analysis it was possible to determine that the results were due to chance, not congruent with my prediction. From the results of my data, it can be concluded that temperature is not a factor in the tree density of Betula. In fact, temperature is not the only factor that can determine the growth of Betula, or other species of trees. Certain biotic and abiotic factors that can explain vegetation patterns of similar areas compared to this study.
Introduction
In this study, it will be tested whether temperature is one of the factors that affect tree densities in the genus Betula on different slopes of the Holyoke Range, specifically the north and south faces of the mountain range. In mid-latitudes in the Northern Hemisphere, northern-facing slopes are cooler than south-facing slopes because they receive less direct solar radiation. R. B. Livingston found that slope variation on the range exerts marked influence on all environmental factors (Livingston 1982). The upper, north-facing slopes are steep and abrupt (35?a to 40?a), while the south-facing slopes are more moderate (20?a). Accordingly, the angle of mid-day insolation is typically 55?a to 60?a greater on the south slopes than on the north slopes, except in late fall and winter when no direct light strikes the steep north-facing hill (Livingston 1982). Even though the area this experiment took place in does not exactly exhibit the same temperature variations discussed by Livingston, this can be still be used as a representation of north-facing slopes being warmer than south-facing slopes around the world.
On the Holyoke Range there are various species of Betula that have similar areas of optimal growth. The cherry birch, Betula lenta, can be found both in woods and in open and uplands on moist, protected, north-or east-facing slopes (Elias 1980). The yellow birch, Betula lutea, can also be found among cherry birch, but in the southern portion of its range, it can grow in cooler marshlands. The paper birch, Betula papyrifera, is found at lower elevations and often on north and east-facing slopes. Also the paper birch is one of the first species to occupy areas devastated by fire. Another species with similar traits to the paper birch is the gray birch, Betula populifolia, which occupies wide areas of abandoned fields and burned-over lands (Elias, 1980). These characteristics of these four Betula species are important because sometimes these trees are not in their optimal growth area, so implying that other factors 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 trees. Also birch trees grow in areas that other trees occupy and this could either help or hinder the growth of Betula on either side of the range, or inter-specific competition between trees. Another possible reason for Betula densities to change is herbivory. Wilsey (1998) describes the effects that herbivorous insects and fungi have on leaf asymmetry by increasing it, which would increase productivity of the leaves of the trees (Betula). While discussing some of the certain biotic factors, abiotic factors must also be considered for possible reasons of birch tree densities. A study on hurricane disturbance on a forest was done in the Harvard Forest in north-central Massachusetts, and it was found that after this massive disturbance, there is a reorganization of biomass and openings into the forest canopy (Cooper-Ellis et al. 1999). In this experiment, disturbance had little effect on composition of the forest, but does lead to a possible explanation for the densities differences of Betula. Possibly the irregular growth of Betula on the Holyoke range can be contributed to the, or the lack of a major disturbance (i.e. hurricane) in the area. With the combination of both biotic and abiotic factors, it is best explained by Claus (1999): ??Compositions and structure of a community are shaped by both abiotic factor and interaction among organisms.??
Figure Legend
Fig 1. Mean basal area (cm2 m-2) of adult Betula species on Holyoke range
Fig 2. Frequency of adult Betula species on the Holyoke range
Betula Betula Betula Betula
lenta lutea papyrifera populifolia
Adults
North side 110.9 (10.7) 4.7 (3.4) 2.3 (1.3) 5.5 (2.9)
South side .8 (.8) 0.0 (0.0) 0.0 (0.0) 0.0 (0.0)
Table 1. Mean adult densities (ind ha-1) and standard error in parerthses. Betula species
on the Holyoke Range, Massachusetts. (Sept 20 and Sept 27, 2000)
1. Elias, T. E. 1980 The Complete Trees of North America, Outdoor Life/Nature Books
New York, USA
2. Livingston, R. B. 1982. Microclimates and Vegetation of the Holyoke Range, Dept of
Biology, University of Massachusetts
3. Cooper-Ellis, .S, Foster D. R., Carlton, D., Lezberg, A., 1999. Forest response to catastrophic wind: results from an experimental hurricane, Ecology
4. Wilsey, B. J. 1998 Leaf fluctuating asymmetry increase with hybridization and elevation in tree line birches, Ecology
5. Holzapfel, C., Mahall, B., 1999 Bidirection facilitation and interference between shrubs and annuals in the Mojave Desert, Ecology
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