Transcript Investigating the relationship between species richness and

Investigating the relationship between species
richness and wilderness in the coastal temperate
rainforest of Southeast Alaska.
This poster represents part of a study of Prince
of Wales Island (PoW), Tongass National Forest,
Southeast Alaska. This work investigates how
species richness changes with distance from
human features, as an index of wilderness quality.
Such features include roads and forest tracks.
This has been facilitated by access to the 1998
USDA Forest Service Southeast Alaska Inventory
and associated digital coverages such as roads
for the island. In addition, primary field data
collection enables a more detailed analysis of the
impact of recreational trails on species richness at
the micro scale and is the focus of this poster.
Prince of Wales Island. From One Duck Trail
looking towards the Karta River Wilderness
In spite of a wide range in latitude in the
Pacific Northwest, a similarity in climate,
habitat structure and composition is found
throughout the regiona. In the global study,
climate was found to be a major determinant
of the distribution of species richness and
wilderness. Here, if there is any change in
species richness with wilderness quality we
must look towards explanations other than
climate.
by Crewenna Dymond, School of Geography,
University of Leeds, UK
Trampling impact
Trails are one of the few
‘permitted’
impacts
in
designated wilderness areas.
Previous
research
has
investigated
how
trampling
effects native flora but this has
not been done specifically for
PoW. It has been suggested
that within short distances from
the trail there is little discernible
impact on species richness or
compositionb, but what is the
form of this pattern on Prince of
Wales Island?
Collecting field data from trails on Prince of Wales Island
Data collection took place in June-July 2001 on PoW. In total six Forest Service
trails were surveyed and a total of 80 transects were taken. All tree, shrub and
herbaceous species were identified within the transects. Four 1 m2 quadrats
were taken at distances of 0, 2, 5 and 10 m from the trail and the abundance of
herbaceous plants was recorded. Shrubs, and by default, small trees (< 5m in
height) were also identified within a 2 m wide transect to 10 m from the trail.
Distance of each individual shrub from the trail was measured. Trees (diameter
>12.5 cm) were identified within a 10 m wide transect to 10 m from the trail and
again the distance of each individual tree from the trail was measured.
Change in species richness
In the field a difference in composition was observed
between trails at low elevation, for example on river
corridors, and those that climbed up into the hills.
Analysis of the herb quadrats revealed that at sites
adjacent to the trail (0 m), the mean species richness
was higher in the upland sites (2.56) than in valley
ones (1.877).
Figure 1. Change in herb species
richness with distance from trail
All trails
Upland trails
Valley trails
Mean species
richness
3
2.5
2
1.5
1
0.5
0
0
2
5
10
Distance from trail (metres)
Slender bog orchid,
Platanthera strictab.
Found throughout SE Alaska.
Figure 1 shows that the general trend is for species
richness to decline away from the trail (all trails) and
this pattern is also exhibited by the valley trails.
In contrast, upland trails are more species rich to begin with and the trail has less
impact on the species richness. If we accept that the effect of trampling is not
transmitted very far into the forest, perhaps no more than 2 mb, we can assume
that at 10 m species richness is no longer effected by the trail. At this distance,
unaffected by human impact, species richness is lower than at the trail-side, in
particular in valley locations. The trail serves to unnaturally increase the number
of species that occupy the site.
Analysing composition with distance from trail edge
A Kruskal-Wallis test (non-parametric one-way ANOVA) was used to determine
difference in the composition of herbaceous species with distance from the trail.
The test analyses the medians of the populations at each of the quadrat
distances. If they are significantly different they could be from different parent
populations. A significant difference (p = 0.005) was found between the sites. The
z values indicate that quadrats at 2, 5 and 10m are from the same population
whereas the population in 0 m quadrats are statistically different. Furthermore,
the composition of 0 m quadrats in the valley locations is different to those at 2
and 5 m and that the 10 m quadrats were also distinct from the others. As
suggested by the analysis of species richness, there was no significant
difference between the populations in the quadrats of the upland trails.
Collecting data on One Duck, an upland trail
Summary Trails in valley locations have
been found to positively influence the species
richness of the surrounding vegetation.
Upland trail corridors do not seem to effect the species richness of the
surrounding vegetation to the same extent. Further research using ordination
techniques is underway to further examine compositional difference between the
valley and upland locations. On Prince of Wales Island elevation has been found
to contribute towards the fluctuation in the response of species richness to
recreational trails. Minimal lateral spread (<10 m) in species richness from the
trail has been found to occur, but linear effects should not be underestimated.
Work is underway to investigate the impact of clear cut forestry on species
richness to determine the relative importance of trails as an impact in wilderness.
aPojar,
J.; MacKinnon, A. (Eds). 1994. Plants of the Pacific Northwest Coast: Washington,
Oregon, British Columbia and Alaska. BC Ministry of Forests and Lone Pine Publishing,
Vancouver.
bDale, D.; Weaver, T. 1974, Trampling effects on vegetation of the trail corridors of North
Rocky Mountain Forests. Journal of Applied Ecology. 11: 767-772.