Decreasing “edge effect” by introducing native species to outcompete invasive plant species in Singapore Chermaine Lim Si Ling (Leader), Sahana Bala Subramaniam, Grace Lam En Ling , Tammy Koh Rui Wen St. Margaret’s Secondary School Little Green Dot Student Research Grant PROJECT REPORT submitted to Nature Society (Singapore) Secondary School Category 2012 1714 words Teacher mentor: Miss Ong Lin Jin Research mentor: Dr Shawn Lum 1 Contents 1. Introduction • Hypothesis statement • Aims 2. Background information • Rationale for study • Lists of suitable native plant species • Locating native plants cultivated in Singapore 3. Methodology 4. Results 5. Discussion 6. Conclusion 7. Bibliography 2 1. Introduction 1.1. Hypothesis statement The introduction of native species Planchonella obovata Pierra and Cyanotis cristata D. Don to the perimeter of secondary forests can decrease edge effect. 1.2. Aims • To discover a native plant species that can survive and thrive well in parts of the forest that experience edge effect • To cultivate and introduce the native plant species to the edge of the forest in order to out-compete alien plant species and minimise edge effect 2. Background information 2.1. Rationale for study As our society processes and more buildings are constructed, there is a constant struggle between forest conservation and economic development. Edge effect occurs along boundaries between developed land and ecological communities. Along these boundaries, ecological communities are exposed to unfavourable environmental conditions such as loose soil, high wind speed, high light intensity and high temperature. Thus, in Singapore, the plant species along the edge of the tropical rainforest are unable to thrive in such harsh environmental conditions resulting in depletion and death. The death of native plants give way to opportunistic alien plant species that thrive well under such environmental conditions, minimising the actual area of the tropical rainforest, e.g. Bukit Timah Nature Reserve. Edge effect results in a loss of natural plant species diversity and variation as it creates a habitat that is unsuitable for the original ecosystem. Typically, shrubs and vines such as an invasive plant species known as rattan are able to tolerate dry environmental conditions and thrive well under high light intensity and temperature. However, there are also native 3 plant species that can be considered such as the Aloe Vera and certain species of orchids. This project increases the viable ecological size of the tropical rainforest in Singapore without actual increase in the physical land space. In Singapore, places such as the Central catchment area require a certain land size in order to be an ecologically sustainable tropical rainforest. By reducing the detrimental effects of edge effect, we can prevent the occurrence of “islands of the living dead” in Singapore, whereby once there is any discontinuation of the deliberate interventional human efforts in the maintenance of the secondary rainforest, the forest will cease to exist. 2.2. List of suitable native plant species The team conducted a dry research on potential native plant species that are able to tolerate and thrive well under harsh conditions; loose soil, high wind speed, high light intensity and high temperature and shortlisted five top native plant species. Plant species Description 1. Planchonella obovata Pierre This plant is a native plant from the tropical rainforest. a.k.a Yellow Boxwood It is able to tolerate 4 out of 4 conditions of the edge effect. It is able to tolerate growing in the presence of poor, infertile soil and is thus able to stand soil erosion. It is also able to withstand full sun, with high temperature and high light intensity.Lastly, it requires moderate amount of water for growth thus enabling it to survive in harsh conditions of drought and flood. Its growth rate is moderate and it requires moderate attention and maintenance. This is a flowering plant. 2. Eulophia graminea Lindi This plant is from the tropical rainforest. It is able to 4 a.k.a Grass orchid tolerate 4 out of 4 conditions of edge effect. This plant is able to tolerate poor, infertile soil and is thus able to withstand soil erosion. It is also able to withstand full sun with high temperature and high light intensity. Lastly, it requires a moderate amount of water and is hence able to adapt to droughts and floods. It requires moderate attention and maintenance. This is a flowering plant. 3. Bromheadia finlaysoniana This is a native plant from the tropical rainforest. It is (Lindl.) Miq. a.k.a Finlayson's able to sustain all the conditions of edge effect. It Bromheadia grows up to 2m max. in height. It grows in full sun and hence able to withstand high light intensity and temperature. It needs a moderate amount of water and hence able to adapt to conditions when there are drought and floods, and lastly, it grows well in the presence of infertile soil. The plant needs moderate attention and maintenance and it has a moderate plant growth rate. This plant is a flowering plant and it bears orchids. It is native to Singapore. 4. Lygodium microphyllum This plant is native to Singapore. It is a fern. It is able (Cav.) R. Br. a.k.a Maidenhair to withstand 3 out of 4 conditions of the edge effect. It fern can withstand full sun, needs moderate water, and it grows fast. It does not grow as well in the presence of infertile soil. This is not a flowering plant. 5. Cyanotis cristata D.Don a.k.a This plant is native to Singapore. It can sustain 3 out 5 Nabhali, Netha Kina of 4 conditions of edge effect. It needs moderate of little amount of water and hence it can tolerate droughts and floods and it can sustain full sun hence being able to tolerate high light intensity and high temperature. The growth rate of the plant is fast. It is a flowering plant. 2.3. Locating native plants cultivated in Singapore Upon meeting with Dr Shawn Lum, research mentor, we were advised to continue the dry research and locate the regions in Singapore in which the five top native plants, Planchonella obovata Pierre a.k.a Yellow Boxwood, Eulophia graminea Lindi a.k.a Grass orchid, Bromheadia finlaysoniana (Lindl.) Miq. a.k.a Finlayson's Bromheadia, Lygodium microphyllum (Cav.) R. Br. a.k.a Maidenhair fern and Cyanotis cristata D.Don a.k.a Nabhali, Netha Kina, are cultivated as opposed to purchasing and cultivating the plants. This method would help to minimise cost in cultivating new plants and allowed us to perform the experiment in situ. While some of the plants species are not locally cultivated in Singapore, the Yellow Boxwood and Cyanotis Cristata are cultivated in the Botanic Gardens. The Yellow Boxwood is planted near the Raffles Building and along Cluny road and there is a small patch of Cyanotis Cristata growing in the car park lot near the Raffles Building. 3. Methodology The initial phase of the group’s task involved a literature research to short-list the potential native plant species that can thrive well under the harsh conditions of edge effect. Subsequently, further literature research was conducted to short-list the plant species that are currently cultivated in Singapore to carry out the experiment in situ. 6 Methodology of cultivating respective plants in situ: • Yellow Boxwood: 1. Measure the diameter of the girth of the tree at a height of 1 m every odd week 2. Measure the height of the tree every even week 3. Estimate the percentage of yellow leaves on the tree weekly • Cyanotis Cristata: 1. Measure the surface area occupied by the patch of plant growth in m2 2. Count the number of flowers in each patch 3. Measure the height of the tallest stem 4. Measure the height of the smallest stem 5. Find the average height for the patches *the following measurements were performed weekly 4. Results Cyanotis Cristata Patch 2 Patch 1 7 Yellow Boxwood (along Nassim Gate) Date: 22nd Nov Date: 29th Nov Date: 6th Dec 8 Date: 20th Dec Date: 27th Dec 9 Yellow Boxwood (next to Raffles Building) 10 5. Discussion In this two-month study, the growth rate of Planchonella obovata Pierre a.k.a Yellow Boxwood, and Cyanotis Cristata were observed. The aim of this study was to measure the growth rates of native plant species and determine if they are capable of minimizing the negative impact of edge effect on the primary and secondary forests in Singapore. Among these two native plants, we found that the Planchonella obovata Pierre a.k.a Yellow Boxwood is more suitable to be planted as compared to the Cyanotis Cristata. The various reasons are stated below. • Height Firstly, height plays an important role to minimise edge effect. The Planchonella obovata Pierre a.k.a Yellow Boxwood next to the Raffles Building, and the series of Yellow boxwoods near the Nassim gate has an average height of 7m compared to the Cyanotis Cristata, which has a height ranging from 16cm to 3cm. The Yellow Boxwood being greater in height would be able to withstand full sun, thus being able to withstand high temperature and high light intensity in addition to being able to tolerate soil erosion, and needing moderate amount of water for growth, enabling it to survive harsh conditions of drought and flood. Although the Cyanotis Cristata is able to withstand moderate amount of water, high temperature, and light intensity, it has a height less than a metre would not be able to shelter the other plants that cannot withstand high light intensity from the sun. Thus, Planchonella obovata Pierre a.k.a Yellow Boxwood would be a better plant to be planted at the edge.