Examensarbeten 2013:13 Institutionen för skogens ekologi och skötsel - PDF

Examensarbeten 2013:13 Institutionen för skogens ekologi och skötsel The effects of mother trees and site conditions on the distribution of natural regeneration establishment in a Bornean rainforest disturbed

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Examensarbeten 2013:13 Institutionen för skogens ekologi och skötsel The effects of mother trees and site conditions on the distribution of natural regeneration establishment in a Bornean rainforest disturbed by logging and fire Effekterna av moderträd och ståndortsfaktorer på spridningen gällande etablering av naturlig föryngring i en regnskog störd av avverkning och brand på Borneo Sebastian Backlund Sveriges Lantbruksuniversitet Jägmästarprogrammet Examensarbete i skogshushållning, 30 hp, avancerad nivå A2E ISSN Handledare: Ulrik Ilstedt, SLU, Inst för skogens ekologi och skötsel Bitr handledare: Malin Gustafsson, SLU, Inst för skogens ekologi och skötsel Examinator: Anders Karlsson, SLU, Inst för skogens ekologi och skötsel Umeå 2013 Examensarbeten 2013:13 Institutionen för skogens ekologi och skötsel The effects of mother trees and site conditions on the distribution of natural regeneration establishment in a Bornean rainforest disturbed by logging and fire Effekterna av moderträd och ståndortsfaktorer på spridningen gällande etablering av naturlig föryngring i en regnskog störd av avverkning och brand på Borneo Sebastian Backlund Nyckelord / Keywords: Dipterocarpaceae, Dipterocarps, dispersal, mother trees, natural regeneration, site factors, tropical rainforest / Dipterocarpaceae, Dipterocarper, moderträd, naturlig föryngring, spridning, ståndortsfaktorer, tropisk regnskog ISSN Umeå 2013 Sveriges Lantbruksuniversitet / Swedish University of Agricultural Sciences Fakulteten för skogsvetenskap / Faculty of Forest Sciences Jägmästarprogrammet / Master of Science in Forestry Examensarbete i skogshushållning / Master degree thesis in Forest Management EX0746, 30 hp, avancerad nivå A2E/ advanced level A2E Handledare / Supervisor: Ulrik Ilstedt SLU, Inst för skogens ekologi och skötsel / SLU, Dept of Forest Ecology and Management Biträdande handledare /Assistant supervisor: Malin Gustafsson SLU, Inst för skogens ekologi och skötsel / SLU, Dept of Forest Ecology and Management Examinator / Examiner: Anders Karlsson SLU, Inst för skogens ekologi och skötsel / SLU, Dept of Forest Ecology and Management 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/BSc 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 examiner. However, the author is the sole responsible for the content. FOREWORD This is a master thesis about tropical tree ecology in Sabah, Borneo. The opportunity was offered to me by Ulrik Ilstedt (Associate Professor) and Jan Falck (Assistant Professor) from the Department of Forest Ecology and Management, SLU. They are both involved in the INIKEA Forest Rehabilitation Project in Sabah, Borneo, which had an opportunity for a student to perform a master thesis. I thought the idea sounded very interesting for several reasons, first I wanted to go abroad to widen my senses and step outside of my safe zone. As well, the subject of tropical forest ecology appeals to me and I believe it is an important topic. I would like to thank my supervisor Ulrik Ilstedt for his great competence, inspiration and for always being welcoming. Also Malin Gustafsson (PhD Student) my assistant supervisor, for your professional support, both in the field and in the writing, for your always welcoming attitude and interesting discussions over the dinners in Luasong. Jan Falck, thank you for the opportunity to be a part of this project and for giving me the chance of adding a piece to the puzzle. The Torsten Wangenbergs scholarship fund and SHS donation fund have a big part in the possibility of performing this thesis and are gratefully thanked for the funding s. Others stationed in Sweden that has been contributing are Daniel Lussetti (PhD Student), for ideas, interesting discussions and good jokes. As well Kristi Kuljus (Visiting Teacher) and Bo Ranneby (Researcher) from Department of Forest Economics, SLU for statistical parts of the method, advice and statistical discussions. Also, thank you Ebba Okfors (Student) for helping me with the correction reading. Employees of the INIKEA Forest Rehabilitation Project have been most helpful and welcoming. Especially I would like to thank David Alloysius (Manager of the INIKEA project), Elisa Linda Laiman (Research Officer) and Albert Lojingi (Research Team Leader); you have truly been of great support in planning and performing the field work. Also a great thanks to the guys in the research team, without your hard work it would not have been possible. And finally a great thanks to the ladies in the kitchen at the Luasong rest house, you provided needed food and laughter. Because of and for Göran, Marie, Jonathan, Daniela, Erica, Åsa, Elsa and others who feel met, dedicated to Bengt. I believe in progress, I believe in making better, I believe in the future Do you and I share the same vision? 1 ABSTRACT In the tropics, logging and wild fire can result in degraded secondary forests with lower biodiversity than in the natural forest. One way to limit forest degradation is to rehabilitate the present large areas of secondary forests. However, there is a lack of knowledge concerning the ecology of tropical tree species and further studies would be advantageous for future rehabilitation efforts of degraded rainforest. The objective of this study was to investigate how mother trees in secondary forest and different site factors affect the abundance and spatial distribution of natural regeneration of non-pioneer tree species in a tropical rainforest in Sabah, Malaysia. The study took place in the INIKEA Forest Rehabilitation Project area, which suffered from wild fire in 1983 and has been selectively logged over both before and after the fire. Natural regeneration and site variables were inventoried in plots, while mother trees were inventoried in the whole survey area. Species were divided into groups used in the INIKEA enrichment planting; Dipterocarps, Non-Dipterocarps and Fruit trees while remaining species were set as Other timber. ArcGIS was used for positioning natural regeneration and mother trees while the Spearman Rank Correlation Coefficient was used for the statistical analysis. All groups analyzed had a positive correlation between the number of naturally regenerated plants per hectare and the number of mother trees per hectare. The species group Dipterocarps had a generally lower regeneration capability than Other timber. Shorea generally had a lower regeneration capability compared to other Dipterocarp genera analyzed in the study. Dryobalanops spp. and Dryobalanops keithii Sym had fewer naturally regenerated plants on sites which had a lot of natural regeneration from other species. D. keithii also had more natural regeneration located to creeks or areas were water flow during heavy rains than on dryer locations, indicating adaptation for more open areas or disturbed locations. Parashorea tomentella (Sym) Meijer on the other hand had more natural regeneration located to sites which had a lot of natural regeneration from other species. This may indicate that P. tomentella has more shade tolerant properties. Dryobalanops indicated longer dispersal ability for natural regeneration than earlier studies have shown. Parashorea spp. and Shorea spp. showed short dispersal abilities for natural regeneration, a pattern in conformity with earlier studies. An exception was P. tomentella, showing dispersal ability up to 75 m. Comparing seed weights and dispersal abilities indicated that shorter dispersal capability is not due to heavier seeds. An indication that the regeneration process in Sabah s rainforests are worthy of further studies is that in an area of nearly 20 ha 119 species were recorded, which had various regeneration success. Of these, 47 species were found only as mother trees which probably had not regenerated after the wild fire of 1983 and 21 species that had established without any mother trees found within the area of inventory. The result of the present study has contributed to better understanding of the regeneration dynamics of tropical tree species and this new knowledge can be used for improvement of rehabilitation methods. Keywords: Dipterocarpaceae, Dipterocarps, dispersal, mother trees, natural regeneration, site factors, tropical rainforest. 2 SAMMANFATTNING I tropikerna kan skogsavverkning och skogsbrand resultera i degraderade sekundära skogar med lägre biologisk mångfald än i naturskogen. Ett sätt att begränsa skogsdegradering är att skydda och rehabilitera de idag vanligt förekommande stora områdena av sekundära skogar. Det finns dock en brist på kunskap gällande tropiska trädslags ekologi och ytterligare studier skulle förbättra framtida rehabiliteringar av skadad regnskog. Syftet med denna studie var att undersöka hur moderträd i sekundär skog och olika ståndortsfaktorer påverkar förekomst och spridning av naturlig föryngring av icke pionjärträdslag i en tropisk regnskog i Sabah, Malaysia. Studien utfördes i ett område som tillhör INIKEA Forest Rehabilitation Project. Detta område drabbades av skogsbrand 1983 och har skogsavverkats selektivt både före och efter branden. Naturlig föryngring och ståndortsfaktorer inventerades i provytor, medan moderträd inventerades i hela experimentområdet. Arter delades in i grupper som används i INIKEA:s rehabiliterings-plantering; Dipterocarps, Non-Dipterocarps och Fruit trees medan övriga arter placerades i gruppen Other timber. ArcGIS användes för att positionera naturlig föryngring och moderträd medan Spearman Rank Correlation Coefficient användes för den statistiska analysen. Alla grupper som analyserats hade en positiv korrelation mellan antalet naturligt föryngrade plantor och mindre träd per hektar och antalet moderträd per hektar. Artgruppen Dipterocarps hade en generellt lägre föryngringskapacitet än Other timber. Shorea hade en lägre föryngringskapacitet jämfört med andra Dipterokarp-släkten som analyserats i studien. Dryobalanops spp. och Dryobalanops keithii Sym hade färre naturligt föryngrade plantor på platser där naturlig föryngring från andra arter förekom i större utsträckning. D. keithii hade också mer naturlig föryngring vid bäckar eller områden där vatten flödar vid kraftigt regn än på torrare platser, vilket indikerar en anpassning till mer öppna områden eller störda platser. Parashorea tomentella (Sym) Meijer däremot hade mer naturlig föryngring på platser som har mycket naturlig föryngring från andra arter. Detta kan tyda på att P. tomentella har mer skuggtoleranta egenskaper. Dryobalanops indikerade en längre spridningsförmåga för föryngring än tidigare studier har visat. Parashorea spp. och Shorea spp. visade sig ha en kort spridningsförmåga för föryngring, mer i likhet med tidigare studier. Ett undantag var P. tomentella som hade en spridningsförmåga på upp till 75 meter. En jämförelse mellan frövikt och spridningsförmåga visade att kortare spridningskapacitet inte beror på tyngre frön. En indikation på att föryngringsprocessen i Sabahs regnskogar är värd fördjupade studier är att det på en yta av nästan 20 ha registrerades 119 arter, som hade varierande föryngringsframgång. Av dessa fanns 47 arter bestående av endast moderträd som troligtvis inte hade föryngrat sig efter skogsbranden 1983 och 21 arter som etablerat sig utan att några moderträd hittades inom området. Resultatet från denna studie har bidragit till bättre förståelse av föryngringsdynamik för tropiska trädslag och denna nya kunskap kan användas för att förbättra rehabiliteringsmetoder. Nyckelord: Dipterocarpaceae, Dipterocarper, moderträd, naturlig föryngring, spridning, ståndortsfaktorer, tropisk regnskog. 3 TABLE OF CONTENTS FOREWORD... 1 ABSTRACT... 2 SAMMANFATTNING... 3 INTRODUCTION... 5 Objectives... 7 MATERIAL AND METHODS... 8 Study area... 8 Data collection... 8 Experimental design for natural regeneration and site variables... 9 Site variables Experimental design for mother tree inventory Structuring of data Statistical analysis RESULTS Natural regeneration and mother trees Spatial distribution of mother trees and regeneration Correlation between natural regeneration and site variables DISCUSSION The contribution of mother trees to abundance of natural regeneration Spatial association between natural regeneration and mother trees The contribution of site variables to abundance of natural regeneration Results uncertainties and improvements CONCLUSIONS LITERATURE APPENDICES INTRODUCTION The current rate of biodiversity loss is higher than the assumed natural frequency and it is increasing (Purvis & Hector, 2000). The main causes for biodiversity decline are e.g. climate change, habitat loss and fragmentation, invasive species and land-use change (Thomas, et al., 2004). Biological diversity is valued for several reasons. For example it supplies free ecosystem services like drinkable water, clean air, fertile soils, providing for human civilization and life overall (Ehrlich & Ehrlich, 1992). Human activities as deforestation, one reason for habitat loss, contribute to threaten this diversity (Grainger, 1993). Except the direct threat to species, deforestation cause soil degradation, changes in water flows and increased sedimentation of rivers (Grainger, 1993). This in itself can obstruct regeneration of forests (Grainger, 1993). In the tropics, instead of clear-cutting, other logging methods are often used like selective logging, but these still have an impact on the ecosystem (Buschbacher, 1990); soils are damaged and there are changes in biomass and species composition (Grainger, 1993). The amount of non-pioneers (long-lived and slow-growing) species decreases (Ashton, et al., 2001). Instead of deforestation, we use the terms degraded or secondary forests for a forest with a lower biodiversity (Chokkalingam & De Jong, 2001). After logging, a forest is in a stage of regeneration, largely through natural processes (Chokkalingam & De Jong, 2001). When performing selective logging the stems most valuable as timber are cut down while others are not harvested. For the tropical forests of Southeast Asia it generally means that it is only allowed cutting down trees with a diameter breast height (dbh) of 60 cm or more, usually trees with a dbh of 120 or more are also forbidden to logging (FAO Forestry Papers, 1989). If the intervals between selective logging are too short, this kind of forestry is unsustainable leading to accumulative disturbances with insufficient time for regeneration (Whitmore, 1998; Meijaard, et al., 2005). Also disturbed forests are more prone to suffer from wild fire (Beaman, et al., 1985), which can severely degenerate the pool of seedlings at the forest floor (Woods, 1989). One way to limit forest degradation and deforestation is to protect and rehabilitate the present large areas of secondary or regrowth forests (Lamb, et al., 2005). Factors that have negative impact on recovery are among others soil compaction, low density of and long distance to non-pioneer mother trees (Whitmore, 1998). Dipterocarpaceae (Dipterocarps) are evergreen non-pioneer trees dominating the biomass of Southeast Asian tropical rainforests (Appanah & Turnbull, 1998). The family contains of 15 to 19 genera and 470 to 580 species (Appanah & Turnbull, 1998), and the Dipterocarp forests are among the richest globally when it comes to flora and fauna (Whitmore, 1975). Luc (2010) recently showed that enrichment planting together with maintenance significantly increase the number of Dipterocarp species in degraded areas. This indicates that enrichment planting is a good way to rehabilitate secondary Dipterocarp forests and increase tree diversity. She also found that in some areas there might already be enough natural Dipterocarp regeneration for the forest to recover. Soil properties and topography have shown to be of importance for the spatial distribution of tropical forest trees (Itoh, et al., 2003a; Baldeck, et al., 2012) and specific site conditions are more favorable to some tropical tree species than others (Ashton, et al., 1995; Palmiotto, et al., 2004). Studies have shown that spatial variation in water availability in tropical forests results in different seedling mortality across habitats (Ashton, et al., 1995; Comita & Engelbrecht, 2009). According to the studies, location in the topography has an impact on how much moisture the soil holds. Ridges for example tend to be drier than other parts of the topography, especially during droughts (Ashton, et al., 1995). In one study some Dipterocarp 5 species showed soil-related habitat specializations (Palmiotto, et al., 2004). It was suggested that the different responses were not related to nutrient status but rather to water-holding capacity. One possible theory is that nutrient poor soils often contain more sand, also giving the soil lesser water-holding properties (Palmiotto, et al., 2004). A contrasting view is that nutrient availability is a major factor limiting the establishment of tropical tree seedlings on soils degraded by heavy machinery (Nussbaum, et al., 1995). It has also been shown that soil compaction of logging machines disturbs the soil adversely. Tree growth, soil pore distribution (important for water properties), soil nutrient contents and microbial properties are negatively affected by heavy machinery used for skidding (Ilstedt, 2002). There is support that higher light intensities can increase tree seedling growth and survival of tropical tree species (Romell, 2011). Itoh, et al. (1997) showed results supporting the importance of canopy gaps for survival of two natural regenerated Dipterocarp species as both saplings (1 dbh 5 centimeters (cm)) and as poles (5 dbh 30 cm). Apparently increased shading had no negative effect on seedling survival in this study but light may be important for seedlings to evolve into saplings. Another study found that lateral light available in all directions is favorable for Dipterocarp seedlings (Bebber, et al., 2002), further emphasizing the importance of light. An earlier study (Itoh, et al., 1997) showed that for the Dipterocarp species Dryobalanops lanceolata Burck and Dryobalanops aromatica Gaertn. F the relationship between seedling density and mother trees were constant within the closest 10 meters (m). After a distance of 10 m the seedling density decreased rapidly and at 30 to 40 m from mother trees it was basically zero. The mean density of saplings and poles peaked at 15 to 20 m from closest mother tree (Itoh, et al., 1997). For D. aromatica it has also been shown that the size of trees up to a dbh of 60 cm are positively related to fruiting, while a larger dbh has no further effect on fruiting (Itoh, et al., 2003b). In addition to dbh, fruiting was also correlated to site conditions, such as elevation, slope inclination and soil texture (Itoh, et al., 2003b). More knowledge about tropical tree species is needed, and further studies investigating the relationship between natural regeneration, mother trees and site factors would be advantageous for rehabilitation. One biodiversity hotspot is the Island of Borneo (Figure 1), located in Southeast Asia (Myers, et al., 2000). Previously the whole Island was covered with a rich and diverse tropical rain forest, where the tree layer was dominated by Dipterocarps (Falck & Wai, 2010). Today a majority of the forests have been selectively logged over or converted into other uses like oil-palm plantations, also almost a m
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