| dc.description.abstract | Vernal pools are small, ephemeral wetlands that provide critical breeding habitat for
amphibian populations, increase biodiversity on a landscape scale, and influence local and
regional hydrography. They have unique annual hydroperiods, typically going from full
inundation to full desiccation within a single growing season. This project addresses the current
lack of research on vernal pools in specifically Nova Scotian landscapes. A cross-sectional,
systematically random pool survey has been conducted within Halifax County, NS. Differences
in pool features and dominant land-cover were compared among three ecoregions (Atlantic
Coastal Ecoregion (800), Western Ecoregion (700), Eastern Ecoregion (400)), and between two
ecodistricts within Ecoregion 400 (Eastern Granite Uplands Ecodistrict (430), Eastern Interior
Ecodistrict (440)). Differences in pool features were additionally compared among well-sampled
ecosections within each ecoregion, and between well-sampled ecosections in each ecodistrict.
Systematic sampling at the ecosection level was not possible due to logistical constraints. This
project aims to provide baseline data on the distribution and characteristics of vernal pools within
Halifax County, to investigate possible landscape influences on pool features among ecoregions
and between ecodistricts, and to evaluate the efficiency and reliability of the survey methods in
the context of future provincial vernal pool surveys.
A total of 156 pools were surveyed in the field. The percent canopy per pool, pool surface
area, and pool density per site (# pools/site) were recorded for survey sites in each ecoregion and
ecodistrict. Pool pH levels were also recorded within Ecodistricts 430 and 440. The total means
for all recorded values were: percent canopy = 46.9, surface area = 46.1m2, density = 1.3, and pH
= 5.1. The dominant land-cover (forest, wetland, open) was also recorded for each site. Pool
features and land-cover were tested in Minitab (Minitab 16) for significant differences among
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ecoregions (ANOVA) and between ecodistricts (2 sample t-test). Pairwise comparisons were
conducted (Tukey HSD) among ecoregions for pool features that differed significantly. Among
ecoregions there were significant differences in percent canopy levels (p=0.014), forest land
cover (p=0.033), and open-land cover (p=0.000). Between ecodistricts there was a significant
difference in pH (p=0.000). The type of ecosection each survey site occurred in was determined
retroactively in a GIS (ArcGIS 10.1) through visually analyzing the overlay of survey site
locations (input from a Garmin eTrex Legend GPS) on the Halifax County ecosection layer. Pool
features were tested for significant differences among the dominant ecosections within each
ecoregion (ANOVA) and between the dominant ecosections of each ecodistrict (2 sample t-test).
All results were insignificant.
The total mean values of recorded pool features were compared to relevant literature, and
it was found that all means fell within expected ranges. Pool density per km2 was relatively high
when compared with a small amount of literature.
Both the barren heath/shrub ecosystem typical of Ecoregion 800 and the high abundance
of forest cover in Ecoregions 700 and 400 contributed to significant differences in percent
canopy levels, forest land-cover, and open land-cover among ecoregions. Differences in wetland
abundance, exposed granite bedrock, and possibly pool substrate contributed to a significant
difference in pool pH between ecodistricts. Differences in pool surface area and pool density
were insignificant at all geographic scales, indicating that a) variation in vernal pool site density
and surface area are not significantly affected by variation in geographic landscape features at
the ecosection, ecodistrict, or ecoregion scale or b) that the sample size of this study was not
large enough to reflect significant variation in pool site density and surface area among distinct
landscape settings. There were no significant differences in pool density or pool surface area at
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the ecosection, ecodistrict or ecoregion scales. Tentative relationships between landscape factors
and Ecodistrict 440’s high pool density and Ecoregion 700’s large pool surface were suggested,
however the significance of these relationships will remain in question until an increased survey
sample size is obtained.
Data trends in pool features on the ecosection scale mimicked trends on the ecodistrict
scale but not the ecoregion scale. This indicates that sites within well-sampled ecosections
provide similar depictions of landscape variability in pool features as those stratified within
ecodistricts, and that sites surveyed in well-sampled ecosections may allow for the determination
of landscape trends that are not apparent at the ecoregion scale. However, if a pool survey
obtained adequate sample sizes from all ecosections within an ecodistrict or ecoregion, the
recorded pool features are likely to reflect a finer level of local landscape variation than that
attained on both ecodistrict and ecoregion scales.
The survey methods were expected to be efficient and reliable. However, designating
area as the control variable for each transect decreased efficiency, as the uniform transect route
was inflexible to variations in terrain difficulty. The uniform transect route was also inflexible to
changes in visibility levels. This increased the potential of false negatives in areas with low
visibility and diminished the overall reliability of the survey. An alternative survey method has
been suggested that uses survey time as the control variable for each transect, which increases
flexibility in response to difficult terrain, changes in visibility, and habitat variability. The
benefits of incorporating remote sensing into the survey methods depends on the quality of the
images, the training of the analyst, and the time of year the images were taken, however benefits
remain minimal if the survey area is heavily forested.
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Finding relatively high density of vernal pools in Halifax County suggests that other
counties in NS may have high densities of vernal pools as well. This provides scientific rationale
for the initiation of a provincial vernal pool assessment project, as well as the development of a
vernal pool conservation plan within Halifax County. This project has provided baseline data on
the characteristics and features of vernal pools in Halifax County, which lays the groundwork for
future research in other geographic regions in NS. Ultimately, it provides some first steps
towards protecting vernal pool ecosystems from anthropogenic impact within NS. | en_US |
