8/22/2019 Elephant utilization of riparian tree species and the use of TPCs in Mapungubwe National Park

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TEMPLATE DESIGN2008

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Elephant utilization of riparian tree species and the use of TPCs in Mapungubwe

National Park

Diana K. Guzmn Coln1, Matthew Nielsen 2, Elizabeth T. Kane3, Taylor Gullet4

1Universidad de Puerto Rico en Bayamn, Indus trial Minil las 170 Carr 174, Bayamn, PR, 00959, 2 Grinnell College,1115 8th Ave., Grinnell, IA 50112-1670, 3 Rutgers University, 83 Somerset St, New Brunswick,

NJ, 8901, 4Duke University, 2301 Erwin Road, Durh am, NC 27705

Abst ract

Recently, Faidherbia albida, Ficus sycomorus, and Acacia xanthophloea in the gallery forestnear the Limpopo river of Mapungubwe National Park are being heavily impacted by

elephants. Because of the increased impact, MNP has established a Tresholds for Potential

Concern (TPC) measurement for riparian tree species. Annual surveys of the trees are

conducted to determine whether or not they are reaching a TPC level. These trees are

impacted by elephants differently as well as respond differently to the detriment caused by

elephant. Mainly elephant stripping and breakage are the causes of decreased health within

these species populations. Similar to previous surveys F. albida has reached the upper limits

of the TPC due to stripping, while the others seem to be sustaining a stable level of

population health despite stripping. In addition to determining if the TPC is being reached by

any of these species, the cause of death for these trees needs to be determined. Along with

the impact of elephants other pressures exist and could be contributing to ultimate mortality

of the trees. We found that the presence of borers greatly adds to the mortality of the trees

once the bark has been stripped by elephants, and there is a direct association between

borers and percent stripping.

Introduction

Literature cited

Methods

Conclusion

Elephants (Loxodonta africana) have been reintroduced Mapungubwe National Park after

100 years of exclusion, and have added an additional stress to the system, given that from

2005 to 2007 elephant population increased from45 individuals to 219.

Elephant damage is more frequent than the damage caused by other stressors: Stripping of

bark, complete toppling of trees, and the devouring of roots.

Stripping of bark consequently removes phloem, and increases the trees vulnerability to the

weather, borers, and increased loss of water.

The canopy is becoming thinned. This change is capable of changing the species

composition of the gallery forest system; canopy cover is also used as an indicator of forest

degradation that arises fromthe shift fromclosed canopy to open canopy forest

Riverine forests are impacted more heavily because of their proximity to water

Thresholds for Potential Concern (TPC) measures to take action when potential irreversible

changes in systemare detected. Taking into consideration several disturbances: herbivore

damage and changes in the woody and herbaceous component of the system.

In MPN a TPC was established to monitor herbivore impacts on vegetation structure and

composition by measuring bark stripping, caused mainly by elephants

We are evaluating the TPC established for elephant damage: 10%of trees of the indicator

species are 50%ring-barked over any one year period, the TPC for that certain species is

reached .

Questions: 1.) What are the differences in bark removal fromthese different tree species,

2.) What are the relationships between stripping of a trees bark by an elephant and the

occurrence of borers, 3.) What are the responses of the plants to these impacts, and 4) Has

the TPC been reached and at what rate. It needs to be determined whether the trees aredying mainly because of borers and elephants or some other possible factors, such as other

local disturbances that may affect the functioning of the ecosystem.

(a)(b)

Figure 1. Riverine forest systems have stressors which causes themto weaken and possibly succumb to death. (a)

This picture shows the stripping done by an elephant. (b) Possible stressors: browsers and grazers, borers, fungi,

lack of water, floods

Figure 2. In the gallery forest at MNP, Faidherbia albida, Ficus sycomorus, andAcacia xanthophloea have been chosen as

indicator species because they are heavily utili zed by elephants.

Study Site

Experimental Design & Protocol

This study incorporated TPC trees surveyed in 2007 by Aunget al. (2007). The individual trees

were found using GPS coordinates and identified using the metal tags nailed into the trees that

were labeled with unique identification numbers. The surveying took place from11 to 13

November 2008.

For each tree we measured: 1.) Total percentage of bark circumference removed in the single,

largest stripping event within the previous year (11/2007-11/2008). 2.) Percentage of the total

area under three meters that had its bark stripped within the previous year 3.) Percentage of

canopy that was no longer present. 4.)Presence or absence of resprouting. 5.) Presence or

absence of holes caused by boring beetles.

Emphasis was placed on recording the single largest percentage of bark circumference

stripping to examine the impact of elephants on the trees phloemduring the previous year as

well as the fact that this observation is the basis of the TPC. The total area removed within the

past year (11/2007 11/2008) under three meters was recorded to see how large the

cumulative, rather than a single events impact had been on these trees in the past years.

Data Analysis

Data analysis was performed using Statistica 6.1 (Statsoft 2004). The data fromAunget al.s

study in 2007 regarding total percentage of bark circumference removed, percentage of bark

circumference removed in the past year (11/2006-11/2007), and percentage of the total area

under three meters that had its bark stripped were included in our data analysis.

Kruskal-Wallis ANOVA:

Percent circumference of bark stripping done below three meters from 11/2007-11/2008

between the tree species (Mann-Whitney U-Tests to analyze the difference in stripping

incidence between species)

Canopy loss btween three species (Mann-Whitney U-Tests for the difference between them)

Wilcoxon Paired Test

To compare the circumference of the largest continuous patch of bark stripping found last year

pre 2007 and this year 2007-2008

Mann-Whitney U-Tests

To compare boring and percent stripping below three meters.

Spearman Rank Correlation Test

Analyze correlation between canopy loss and area stripped below three meters in the past year

(11/2007-11/2008).

Figure 3. Our study was conducted in the Mapungubwe NationalPark in Limpopo province, South Africa. The sites we surveyed were

in the riparian vegetat ion along the Limpopo River. The sit es were on

the Limpopo near the northern and western border of Mapungubwe

National Park to Botswana

Figure 4. (a) The observations were recorded by three observers that divided the tree into thirds and assessed everything

for their third. Any percentages that were recorded were then averaged to form the percentage for the total tree. (b)

An area recently utilized by elephants

ResultsWe reassessed bark stripping damage for 255 individuals tagged by Aung et al. (2007). Thirteen

of the trees were excluded fromanalysis due to being dead or toppled by elephants. In total, we

surveyed 105 Faidherbia albida, 62Ficus sycomorus, and 78Acacia xanthophloea trees.

For the percent circumference of the single largest patch of bark stripping this year, there was a

significant difference between the tree species (Kruskal-Wallis ANOVA, n=228, H(2)=8.271,

P=0.016)

0

5

10

15

20

25

F ai dh er bi a a lb id a F ic us s yc om or us A ca ci a x an th op hl oe aMean%c

ircumferenceofthelarge

stsingle

patchofofbarkstrippedin2

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Figure 6. Mean percent of bark circumference stripped. Significant difference between F. albida andA. xanthopholea (Mann-Whitney U-test, n=165, U=2512.00, P=0.011), but not between F. albida and F. sycomorus (Mann-Whitney U-test, n=132,

U=1513.50, P=0.427) orF. sycomorus andA. xanthophloea (Mann-Whitney U-test, n=101, U=981.50, P=0.258).

The greatest proportion of all bark stripping below three meters, both old and new, occurred onF.

albida (Kruskal-Wallis ANOVA, n=228, H(2)=32.376, P