Trees and Mistletoes in Australia Report

One interesting observation in landscape ecology is that natural environments occur heterogeneously or exhibit patchiness. This case study examined this hypothesis by evaluating the occurrences of trees and mistletoes in a large remnant area of natural vegetation in Australia.

Mistletoes are generally hemiparasites that feed on trees and shrubs. Therefore, this study provided an opportunity to examine the distribution of species and the ecological relationship between hosts and parasites. In Australian forests and woodlands, Mistletoes and host plants had a fascinating form of relationship in two main ways.

First, Mistletoes are hemiparasites that obtain their nutrients and water from their host plants. Second, a mutualistic relationship exists between the birds and the mistletoes. Specifically, the Mistletoebird is responsible for dispersing seeds of mistletoes while the mistletoe offers its fleshy fruits as food to the bird. In addition to the Mistletoebird, mistletoes also provide food and shelter to other various species of birds in Australian forests and woodlands.

Study Objectives
This study aimed to examine the distribution of the Drooping Mistletoe Amyema pendulum across an urban bushland landscape in relation to variation in vegetation type and the abundance of host tree species. Specifically, the study focused on the following questions:

Does the density of trees (stems) differ between vegetation types in the study landscape?
Does the proportion of trees with mistletoe infestation differ between vegetation types?
What is the spatial pattern of mistletoe parasitism at the level of individual trees?
Study Area
This study was undertaken in the Royal Botanic Gardens, Cranbourne. This is a large area of heathland and heathy woodland at Cranbourne, Australia. In the past, the Royal Botanic Gardens has acted as a study area for many ecological studies, such as a floristic vegetation study, studies of the ecology of Swamp Rats and Southern Brown Bandicoots, resource partitioning by small mammals, the foraging ecology of New Holland Honeyeaters, and studies of frogs.

Study Methodology
There were many types of vegetation identified in the study area. However, this study concentrated on Heathy Woodland (drier vegetation on sandy areas) and Wet Heath (lower lying areas, drainage lines) areas as indicated on the map. There were two major species of trees found in these areas, which included Coast Manna Gum E. pryoriana and Mealy Stringybark E. cephalocarpa.

Stratification of transects
All data were gathered on a single field trip referred to as a snap shot survey. Transects were stratified across the landscape to sample Heathy Woodland and Wet Heath vegetation types. All student groups collected data from all the allocated transects in order to conduct a joint sampling of a number of replicate transects in every vegetation type. All these collected data were later cleaned, classified in classes and analyzed.

Researchers were cautious not to damage the vegetation in the study area.

Data collection
Each group collected data in transect measured at a 100 m by using a tape, which represented 0.4 ha. They collected data from a belt of 20 m wide from all sides of transects. Researchers also methodically gathered data along the transect line. This process involved checking and counting all tree stems, including cases in which a tree had more than one trunk.

Data elements recorded on the data sheet included:

The total number of tree stems within the transect area
For each stem that had mistletoes present, record details of
The number of mistletoe plants present
Whether the mistletoe plants were alive or dead
The level of branch on which the mistletoe plant was located (primary, secondary, tertiary)
The Drooping Mistletoe Amyema pendulum was the most common type of mistletoe in the bushland under studies. Researchers observed the foliage of the mistletoe and noted the similarities and the differences between the leaves of the mistletoe and eucalypts. They also checked for any signs of dead trees and possible causes of identified cases and attachment of mistletoes on eucalypt branches.

Another area of interest in this study involved data related to variations across the landscape attributes, such as topography, soils, density of trees, moisture availability and vegetation types.

Collation and analysis of data
Data were cleaned, categorized and analyzed using SPSS.

The proportion of trees with mistletoe infestation
The proportion of trees (stems) in each transect that had mistletoe present (i.e. number of stems with mistletoe / total number of stems)
Statistics
Dry Wet
N Valid 12 10
Missing 0 2
Mean 67.25 123.70
Std. Error of Kurtosis 1.232 1.334
Sum 807 1237
The observed mean for the dry heath was 67.25 while the mean for the wet heath was 123.7 with standard error of 1.23 and 1.33 respectively.

Independent Samples Test
Levenes Test for Equality of for Equality of Means
95% Confidence Interval of the Difference
F Sig. . (2-tailed) Mean Difference Std. Error Difference Lower Upper
Total number of stems Equal variances assumed 4.665 .043 -2.669 20 .015 -56.450 21.153 -100.575 -12.325
Equal variances not assumed -2.539 13.614 .024 -56.450 22.229 -104.253 -8.647
The for the dry heath and the wet heath was p =.015. This indicated a significant difference between the two heaths (p value standard =.05).

Does the proportion of trees with mistletoe infestation differ between vegetation types?
The proportion of trees (stems) in each transect that had mistletoe

Statistics
Number of stems with mistletoe Total number of stems
N Valid 22 22
Missing 0 0
Mean 10.05 92.91
Std. Error of Mean 1.228 11.970
Median 10.00 74.00
Mode 11 49
Std. Deviation 5.761 56.144
Std. Error of Kurtosis .953 .953
Sum 221 2044
There was a significant variation in the proportion of trees (stems) in each transect that had mistletoe present (221) and to the total number of stems recorded (2044).

T-test

Independent Samples Test
Levenes Test for Equality of Variances t-test for Equality of Means
95% Confidence Interval of the Difference
F Sig. t Df Sig. (2-tailed) Mean Difference Std. Error Difference Lower Upper
Number of stems with mistletoe Equal variances assumed 2.658 .119 -1.086 20 .291 -2.667 2.456 -7.790 2.457
Equal variances not assumed -1.039 14.251 .316 -2.667 2.568 -8.165 2.831
The for the number of stems with mistletoes in dry heath and wet heath was p =.29. Therefore, the p value indicated that there was no statistically significant difference between the numbers of stems with mistletoes in both dry and wet heaths.

What is the spatial pattern of mistletoe parasitism at the level of individual trees?
The proportion of live mistletoes vs. dead mistletoes

Statistics
Alive Dead
N Valid 22 22
Sum 72 214
A total of 72 mistletoes were alive whereas 214 were dead.

Uneven distribution in alive mistletoesUneven distribution in dead mistletoes
The histograms depicted uneven distribution in alive and dead mistletoes.

The proportion of mistletoe plants that were on primary vs. secondary vs. tertiary or smaller branches
Statistics
Primary Branch Secondary Branch Tertiary Branch
N Valid 22 22 22
Sum 10 135 137
Mistletoe plants that observed on primary branches were 10, secondary branches 135 while tertiary branches were 137.

Spatial occurrences of mistletoes in primary branches across treesSpatial occurrences of mistletoes in secondary branches across treesSpatial occurrences of mistletoes in tertiary branches across trees
The histograms indicated that spatial occurrences of mistletoes differed in primary, secondary and tertiary branches across trees.

Discussion
Results from the study confirmed that hypothesis that mistletoe distribution was heterogeneous or depicted patchiness. Thus, the researchers accepted the study hypothesis. The significant difference in the distributions of mistletoes between the dry heath and wet heath showed patchiness in a natural environment.

Past studies have established such patchiness in distributions of mistletoes in Australia (Turner, 1991). Parkes, Newell, and Cheal observed that patches of native vegetation were often heterogeneous and could consist of other several species of plants (Parkes, Newell and Cheal, 2003). In addition, Turner, Clarke, Lewis, and Ostendorf observed variations in vegetation covers and noted that some areas were highly fragmented (Turner, Clarke, Lewis and Ostendorf, 2013).

Several factors could have influenced the distribution of mistletoes at the landscape scale and at the tree level. For example, abiotic factors, such as soils, water, light and biotic factors (dispersal vector) influenced the distribution of the Drooping Mistletoe across the landscape. From the study, several mistletoes were observed in the wet heath (1237) than in the dry heath (807). This indicated that abiotic factors had critical influences on the distribution of mistletoes in natural vegetation.

Some studies also noted that seed dispersal by marsupials altered the spatial distribution patterns of mistletoes (Garca, Rodrguez-Cabal and Amico, 2009). Thus, biotic factors affected the distribution patterns of mistletoes. Such mammals were responsible for spatial distribution and patchiness in mistletoe offspring at a larger scale (Garca et al, 2009).

Therefore, both abiotic and biotic factors created distribution and dispersal processes that could significantly change the mistletoe spatial distribution in natural vegetation. A mutualistic relationship was observed between mistletoes and other animals. They depended on animals for both pollination and fruit dispersal, and this leads to a broad range of mistletoe-animal interactions (Watson, 2001).

Thus, fruit eating birds, such as Mistletoebirds were responsible for wide dispersion of mistletoe seeds while the preference of birds for infected trees influenced the spread of mistletoes and the spatiotemporal pattern formation of mistletoes (Ward and Paton, 2007). Overall, Watson noted that mistletoes were important resources in forests and woodlands where they were present (Watson, 2001). They offered shelter for both animals and birds in woodlands and forests.

Variations in mistletoe distributions were also observed in the stems of the tree. For instance, primary branches had 10 mistletoes, secondary branches had 135 mistletoes and tertiary branches had 137 mistletoes. Mistletoes survived better in protected areas of the trees such as secondary and tertiary branches. Hence, the use of hosts among mistletoes was also heterogeneously distributed.

In conclusion, this study supported previous observations, which had indicated that vegetations had heterogeneous occurrences in natural environments. The distribution of mistletoes differed significantly in dry and wet heaths and on stems of trees. Variations could have resulted from both abiotic and biotic factors. Overall, mistletoes acted as important resources in their natural habitats.