Examensarbeten 2008:8 Institutionen för skogens ekologi och skötsel - PDF

Examensarbeten 2008:8 1 Institutionen för skogens ekologi och skötsel Institutionen för skogens ekologi och skötsel Tropical Rain Forest Recovery after Cyclone and Human Activity on Savai i, Samoa -A field

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Examensarbeten 2008:8 1 Institutionen för skogens ekologi och skötsel Institutionen för skogens ekologi och skötsel Tropical Rain Forest Recovery after Cyclone and Human Activity on Savai i, Samoa -A field study of tree species composition and distribution View from the crater in Tafua-Tai taken by Sakura Netterling Sakura Netterling Examensarbete i skogshushållning, 30 hp, D-nivå Handledare: Henrik Hedenås, Umeå Universitet, Olle Forshed, SLU ISSN Examinator: Arne Albrektson Umeå 2008 MFS report 30 ECTS points at D-level with a Major in Forest Management. Mälardalens Högskola, International Office, Stefan Boegård Examiner: Professor Arne Albrektson Supervisor: Dr. Henrik Hedenås at Umeå University Assisting supervisor: Dr. Olle Forshed Supervisor in Samoa: Chief Moelagi Jackson President of Faasao Savai'i Society Umeå, February 2008 I denna rapport redovisas ett examensarbete utfört vid Institutionen för skogens ekologi och skötsel, Skogsvetenskapliga fakulteten, SLU. Arbetet har handletts och granskats av handledaren, och godkänts av examinator. För rapportens slutliga innehåll är dock författaren ensam ansvarig. This report presents an MSc thesis at the Department of Forest Ecology and Management, Faculty of Forest Sciences, SLU. The work has been supervised and reviewed by the supervisor, and been approved by the examinator. However, the author is the sole responsible for the content. SLU Institutionen för skogens ekologi och skötsel / Department of Forest Ecology and Management UMEÅ PREFACE This study was initiated by Henrik Hedenås 2004 based on former studies by Thomas Elmqvist at Umeå University in 1990 and 1992 and Johan Hjerpe and Henrik Hedenås in1996 and The study was funded by the Swedish International Development Cooperation Agency (Sida) 2004 by authority from Mälardalens högskola and was carried out as a Minor Field Study The field work was conducted in Samoa during March May 2005 with the assistance from Chief Moelagi Jackson President of Faasao Savai'i Society and local people in the area of villages Tafua-Tai and Taga. ~ 3 ~ ABSTRACT Keywords: Samoa, disturbance, cyclone, logging, rain forest, species diversity. This MFS study was conducted in the island of Savai i of State Samoa, performed as a follow up to a ten years previous study. The aim was to estimate the recovery of forest species diversity following two sequential cyclones that passed over the forest reserve of Tafua-Tai 1990 and We compared this natural disturbance to a cumulative natural disturbance as an extensive area suffered from a fire one month after the cyclone Ofa. To broaden the work and to include a forestry aspect a comparison of human afflicted disturbance a survey was made in the area near Taga village. Here a substantial area had been clear-felled in the same time interval as the cyclones, and one harvested and logged just five years ago. We performed relative abundance analysis and compared the status of the forests as well as climber and vines ratio between the disturbance regimes. It was found that cumulative disturbance severely affected the area and opened it up to secondary forest species and vines which arrest crown growth. The severest damage was still found in the clear-felled area that during the fifteen years interval has not recovered and was significantly worse in all aspects to the other disturbed areas. One can interpret that the logged and harvested area which was five years old was as good as the cumulative natural disturbance area due to a more selective logging. However, both are still not as diverse and some of the most important mature forest species are missing. Invasive species such as Funtumia elastica, a shadow tolerant exotic species and a late introduction, show an alarming dominance in the naturally disturbed area. SAMMANFATTNING Nyckelord: Samoa, störning, cyklon, avverkning, regnskog, artrikedom. Den här MFS studien utfördes på ön Savai i i Samoa. Den är en uppföljande studie till en långtidsstudie som utfördes senast för 10 år sen (1995). Målsättningen var att uppskatta återhämtningen av den tropiska skogens artdiversitet efter två stora cykloner som passerade Tafua-Tai området 1990 respektive Vi jämförde den här naturliga störningen med en kumulativ störning som innebar en brand som drabbade delar av det cyclondrabbade området en månad efter cyklonen, Ofa. Arbetet innefattar också en jämförelse med områden nära byn Taga där omfattande mänsklig störning i form av avverkning och sedemera boskapsskötsel skedde i samma tidsrymd som cyklonerna. Ett område avverkades totalt för år sen och ett annat avverkades selektivt för 5 år sen. Vi utförde relativ artrrikedoms analyser och jämförde skogens uppbyggnad och antalet lianer och krypväxter i alla områden. Vi fann att den kumulativa störningen med cykloner och brand påverkade området kraftigt och öppnande upp det för sekundära arter. Den svåraste påverkan fanns i kalhygge området som efter 15 år inte hade återhämtat sig och var signifikant sämre i alla aspekter. Man kan tolka data från den selektiva avverkningen som att den är likvärdig som den kumulativa störningen av två stora cykloner och en brand men den är mycket mer påverkad än den naturliga störningen i det icke brända området. Många viktiga primära skogsarter saknas i dessa områden och diversiteten har inte återhämtat sig efter cykloner samt brand eller i det selektivt avverkade området. En skuggtålig exot, Funtumia elastica, har dessutom etablerat sin dominans inom det naturligt störda området. ~ 4 ~ TABLE OF CONTENTS PREFACE... 3 ABSTRACT... 4 SAMMANFATTNING... 4 BACKGROUND OF SAMOA... 6 Cyclones... 6 Soil structure... 7 Flora and fauna... 7 Samoan forests... 8 INTRODUCTION Disturbance variation Tree species composition in relation to resilience and recovery Regrowth requirements Aspect of the distribution of pioneer trees versus shade tolerant climax species before and after the different disturbances Anthropogenic influences on forest diversity and recovery Fire as a disturbance regime Lianas and invasive species Anthropogenic vs. natural Objective MATERIALS AND METHODS Study sites Location Sampling DATA ANALYSIS Stand characteristics Species abundance and diversity indices RESULTS Stand characteristics Species abundance and diversity DISCUSSION Forest dynamics in the natural disturbed forest and the cumulative disturbed forest Comparing forest structures and tree diversity among forests affected by different disturbance regimes Invasive species and lianas Conclusions and implications for management ACKNOWLEDGEMENTS REFERENCES Internet references: APPENDIX APPENDIX ~ 5 ~ BACKGROUND OF SAMOA The independent State of Samoa, formerly known as Western Samoa, formed 1st January 1962 is a South Pacific group of islands located in Oceania (13 35 S, W), south of the equator about 800 km from Tonga and 2400 km northeast from New Zealand, nearly half way to Hawaii. The country land area is a total of 2,944 sq km. Samoa consists of two large islands Upolu and Savai'i (96% of the land area) together with eight smaller islands and uninhabited islets. (CIA -the World Factbook 2007) The climate is tropical with a mean annual temperature of 26.5 C, with little variation as the temperatures seldom rise above 29º C or fall below 24º C, with abundant rainfall (Samoan Sensation, NOAA, The Global Historical Climatology Network). There is a slight seasonal variation with rainy season from November to April and a dry season from May to October. Mean rainfall is about 2,900 mm per annum, but due to the rocky interior average annual rainfall varies from 5,000 to 7,000 mm on the southern windward side and 2,500 to 3,000 mm on the leeward side (Samoan Sensation; NOAA, The Global Historical Climatology Network). Humidity is high averaging about 80%. The terrain on the two large islands is a rocky rugged mountain interior with civilization mostly located on the surrounding lowlands of the narrow coastal plain (CIA -the World Factbook 2007). Mostly the landscape is an almost flat coastal plain, gradually passes into a region of gently rolling slopes, these in turn merge with the more strongly sloping (5-15º) foothills, which continue upwards until an upland or plateau. The highest point of Mauga Silisili 1,857 m a s is found on Savai'i (CIA - the World Factbook 2007). It is estimated that Samoa has been inhabited for over three thousand years. Samoa has a population of 214,265 (2007 est.) with a density of 73 individuals per km 2. The population growth rates are 1.3% (2007 est.) with a fertility rate of 4.21 children born per woman. The population of Samoa consist of mainly the ethnic group Samoans (Polynesians), 92.6%. The languages spoken are Samoan (Polynesian) and English. Government type is a mix of parliamentary democracy and constitutional monarchy. The capital of Samoa is Apia and has an estimated inhabitants. The GDP per capita is $ 2,100 (2005) % of the land area is arable land and 24.3% are used for permanent crops. Natural resources are considered to be hardwood forests, fish and hydropower. The agricultural products are coconuts, bananas, taro, yams, coffee, and cocoa. Samoa s export commodities are fish, coconut oil and cream, copra, taro, automotive parts, garments and beer. The economy of Samoa has traditionally been dependent on development aid, family remittances from overseas, agriculture and fishing. The country is vulnerable to devastating storms due to its concentration of economy to the coastlands. Tourism is an expanding sector and in 2005 it accounted for 25% of GDP. (CIA -the World Factbook 2007) CYCLONES Samoa is located in the South Pacific cyclone belt. Ofa and Val ravaged terrestrial and marine environments in February 1990 respectively December 1991 (ReliefWeb). The cyclone Ofa caused 90% damage to tree crops (UNDRO 90/0301) and the subsequent Val destroyed nearly 90% of the vegetation on the northern side of Savai i (UNDRO 91/1855) and destroyed 60% of the forests (UNDRO 91/1869). The cyclones had vast economic and public health effects as causes of ecological problems such as devastated coral reefs, marine life reduction, rain forest destruction and a following draught spell leading to prolonged shortage of staple foods (personal communication with natives). Ofa killed 8 people and left people homeless, with 50% of the homes destroyed on Savai i (ReliefWeb). The eye of the cyclone passed ~ 6 ~ about 60 nautical miles south of the Samoa, bringing the most destructive quadrant of the cyclone over the islands which sustained winds of 260 km/h (UNESCAP 2001). Ofa formed high storm waves causing serious reef damage along the western and northern shores. The cyclone Val was smaller with the eye of the cyclone passing over Savai i with wind speeds on average of 170 km/h, but the impact of the cyclone was intense and worsened the damage done by Ofa (ReliefWeb, UNDRO 91/1841; The New York Times, 22 December 1991). Cyclone Val raged for approximately four days and hit 90% of the island, causing 13 deaths, leaving 95% homeless on Savai i and resulting in a huge blow to Samoa s economy. On the 16 th of February 2005, the cyclone Olaf, with winds of up to 250 km/h made a close pass of Samoa but luckily did not inflict any large visible damage to the forest or other ecological and economical assets (BBC, 6 February 2005). The impact of the cyclones has been a severe influence on Samoa s fragile ecology and the complex Polynesian culture. SOIL STRUCTURE All of Samoan islands are of volcanic oceanic origin and consist of basalt derived from magmatic material normal to the Pacific basin, only Savai'i could be considered volcanically active since in the beginning of the 18 th century (between 1905 and 1911) there was a volcanic eruption from Mount Matavan where lava flowed down to the village Salealua (CIA -the World Factbook 2007, Bennett 2003). According to FAO Samoa s soil consist of low fertile volcanic latosols, which contain % titanium oxides (FAO, Land and Water Information, Samoa National Report 2002). The most extensive soil order in Samoa is that derived from recent volcanic ash called Andisols found in the uplands. Inceptisols, together with Oxisols are also found in great areas in Samoa. Significant areas of Mollisols and Entisols are cultivated. Most Samoan soils have a ph between 5.5 and 7.5. The alkaline soils with ph above 7.5 include the coral sands along the coast. Soils of Samoa are generally extremely porous and excessively drained so vegetation may suffer from water shortage if there is no rain a week. FLORA AND FAUNA The environment of Samoa with its tropical climate supports a wide range of flora from tropical rain forests to scrublands, marshes, swamps and mangrove. Samoa is predominated by higher plants of which 90% of the 550 flowering plants; 95 plant families about 300 genera, are indigenous or native (Whistler 2002) about 30% are endemic to the archipelago (Whistler 2004). There are about 250 native and naturalized tree species. There is also a threat of invasive alien vegetative species which often have negative impact on both the economy and the environment. Invasive species is a threat through the reduction of grazing areas, reduction of crop yield, risk of threat to biodiversity, disruption of water flow, livestock poisoning and the formation of impenetrable thickets. Forest quality is further reduced by the subsequent invasion of highly aggressive non-native trees, not including the 22 tree species that have been naturalized over the past 170 years (Whistler 2004). Samoa has a limited land fauna of larger animals where flying foxes, land and sea birds, skinks and geckos play an important role to the forest community (Hjerpe et al. 2001). There is of course other fauna such as various insects and land crustaceans inhabiting the land of Samoa. Flying foxes are the major pollinators and seed dispersers in these forests and both flying foxes and resident birds were affected by starvation as seed and fruit production was low in the cyclone devastated areas (Elmqvist 1994; Hjerpe et al. 2001). Since the cyclones 1990 and 1991 there has been increased effort within Samoa to rehabilitate and conserve the endangered flying fox population of Samoa and efforts to conserve endangered birds such as Tooth Billed pigeons and others. The avian community is also of high importance to the seed dispersal of the Samoan flora (Elmqvist 1994; Hjerpe et al. 2001). Samoa supports a total of ~ 7 ~ 49 bird species of which 11 are endemic species and 7 are threatened by extinction (Government of Samoa 1998). Tooth Billed pigeon is threatened by deforestation for agriculture particularly combined with the severe effects of cyclones, e.g. in 1990 and 1991, when canopy cover was reduced from 100% to 27% (Elmqvist et al. 1994). Extractions of timber lead to further habitat losses due to the forest areas being converted to agriculture (Elmqvist et al. 1994). Hunting is also a further threat and although hunting is now illegal, birds are still shot in the seasonal harvest of unprotected pigeon species. Poaching was and is a towering problem to solve as food availability was scarce after the cyclones and Flying foxes and pigeons are thought of as delicacies and therefore are still hunted (personal communication; Government of Samoa 1998). Other current environmental issue is excessive fishing (Government of Samoa 1998). SAMOAN FORESTS In a global perspective the tropical forest of the world is now shrinking with about 5% each decade. A gross deforestation of 2.8 million hectares a year is estimated in Asia alone. FAO Global Forest Resources Assessment 2005 data shows that primary forests are being replaced by less diverse plantations and secondary forests (FAO Global Forest Resources Assessment ). Samoa consists of 100% tropical rain forest with a high degree of endemism making it one of the biodiversity hotspots for conservation priorities (Myers et al. 2000). About 171,000 hectares or 60.4% of the land area of Samoa is forested (FAO State of the World's Forests 2007). Historically the rate of deforestation is high in Samoa and of great concern to the government. In % of the land area was covered by closed forests canopy compared to 47% in 1992, directly after the two cyclones and 74% in1954 prior to the extensive timber-export-times between 1974 and 1987 (FAO State of the World's Forests 2001; Whistler 2002; Government of Samoa Sustainable forest management programmes in Samoa 2002). In contrast to this, according to FAO State of the World's Forests (2007), between 1990 and 2000, Samoa gained an average of 4,000 hectares of forest per year. This amounts to an average annual reforestation rate of 2.8% (FAO State of the World's Forests 2007). Between 2000 and 2005, the rate of forest change decreased to 0% per annum, all data conceived by remote sensing (FAO State of the World's Forests 2007, 2001, and 1999). In total, between 1995 and 2005, Samoa gained 31.5% of its forest cover, or around 41,000 hectares. However 32,000 of those hectares are forest plantations making it 78% of the gained forest during the intervals (FAO State of the World's Forests 2007, 2001, and 1999). Samoa in 2005 consists of 171,000 hectares of primary forest in total with 64.3% modified natural forest (110,000 hectares), 17.0% semi-natural forests (29,000 hectares) and 18,7% (32,000 hectares) forest plantations (FAO State of the World's Forests 2007, 2001, and 1999). Ownership of forestland 2000 was 98.2 % publically owned and 1.8% privately owned. Still over 70% of the land in Western Samoa is held in customary ownership (FAO Asia-Pacific Forestry Sector Outlook Study: Commentary on Forest Policy in the Asia- Pacific Region 1997). Nevertheless, the remaining lowland forest from sea level to 600 m a s has been severely fragmented and the forest has mostly been converted to agricultural land. About 77% of the total land area of land holdings is under some form of cultivation. The remaining 23% comprises land under fallow (3%), bush (3%) or under non-agricultural use (17%). Thus any forest policy must be aware of this intricate political system, in which families strive for status and power, making a flexible customary land-tenure system mostly inflexible and less controllable by intricate country laws. Preceding 1992 the rain forests of Samoa were threatened by extensive logging operation by foreign operation contractors and most of the lowland forest and foothill forest on Savai'i and Upolu have been highly modified (FAO Sustainable Production, Intensification and Diversification of Agriculture, Forestry and Fisheries in Small Island Developing States ~ 8 ~ 1999). In 1993 the government banned export of logged unprocessed timber and banned all logging operations on the island of Upolu. In 1994 the government had approved some documents of legislation to improve the status of the forest management; those were the National Forest Policy 1995, Watershed Protection and Management Regulations 1992 and National Environment and Management Strategies (NEMS) In the same time period drafts on Code of Logging Practice (COLP) and the Reduced Impact Logging Guidelines (RIL) were made but have not yet been agreed on (FAO Asia and the Pacific National Forestry Programmes: Update ; Government of Samoa Sustainable forest management programmes in Samoa 2002). By these documents one constraint to logging licence was made; that no tree less than 30 cm dbh were allowed to be cut (Government of Samoa What every potential investor needs to know 2000). Still between 1977 and % of the merchantable forest of Savaii was cleared at an average rate of 987 hectares per year. Though counted from 1978 to 1990 approximately 20% of the deforestation on Samoa was due to logging operation, but most 97% of logging was concentrated to the island of Savai
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