Plant Functional Traits in Succession Gradient in the Grasslands of Khao Yai National Park

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1 Plant Functional Traits in Succession Gradient in the Grasslands of Khao Yai National Park Chatchawan Genarkarn 1, Anuttara Nathalang 2 and Wirong Chanthorn 1* ABSTRACT Plant functional traits can be a potential indicator of ecosystem processes besides species diversity. In the tropical grassland such as Khao Yai National Park, it has a succession gradient, because of the Park management by non-systematic prescribed burning or mowing. It generates grassland patches with a time gradient influencing different species-trait composition among sites. To compare plant functional traits among these grassland succession gradient is the main aim of our study. We measured plant functional traits in the landscape and community levels to analyze species composition via three essential functional traits, i.e. specific leaf area (SLA), leaf dry matter content (LDMC), and maximum height. The results showed that trait composition had similar patterns, while ignoring species similarity in each trait. The succession gradient is likely to be associated with the functional redundancy of SLA. Consequently, we suggest that these grasslands can maintain ecosystem functions and resilience along with a succession time. Key words : ecological succession, ecosystem function, plant functional trait, redundancy, tropical grassland * Corresponding Authors; address: fsciwrc@ku.ac.th 1 Department of Environmental Technology and Management, Faculty of Environment, Kasetsart University, Jatujak, Bangkok Ecology Laboratory, Bioresources Technology Unit, 113 Science Park, Paholyothin Road, Klong Luang, Pathumthani 12120

2 INTRODUCTION Plant functional traits are biological characteristics of plants which link to ecosystem functions. They have responses and effects to environmental changes. Because of their association with ecosystem functions and services, functional traits can be a potential indicator to predict ecosystem functions (Lavorel and Garnier 2002; Garnier et al. 2004; Hooper et al. 2005; de Bello et al. 2010). Many researchers suggest that variation changes depending on a scale of species and community composition in a landscape (Lavorel and Garnier 2002; Garnier et al. 2004; Quétier et al. 2007; Lavorel et al. 2011). According to Hooper et al. (2005), biodiversity loss and habitat degradation can proportionally reduce ecosystem functions that can be revealed by functional traits. Furthermore, similarity of functional trait among species leads to functional redundancy, consequently providing similarity of ecosystem functions. Therefore, understanding of functional redundancy helps to manage ecosystem functioning in a community (Hooper et al. 2005). In grassland ecosystems, succession not only changes in community structures performed by plant life histories, population, species interaction but also changes in functional traits (Garnier et al. 2007). Possibly, plant functional traits in both community and species levels may differently respond to times since disturbance (succession time). In a tropical grassland of Southeast Asia such as Khao Yai National Park, ecological succession is an essential process naturally occurred by foraging endangered large herbivores i.e. gaur (Bos frontalis), elephant (Elephas maximus), and sambar (Rusa unicolor) (Chanthorn and Brockelman, 2008; Lynam et al., 2006). However, the grassland is maintained by a park policy that is non-systematic prescribed burning and mowing. The anthropogenic management causes gradient in time of succession among grassland patches. These gradients may affect plant functional traits and community composition. Henceforth, we aim to compare plant functional traits along succession gradient among grassland patches in order to understand species composition and their trait values. We also predict the tendency of ecosystem function remaining via functional redundancy. MATERIALS AND METHODS The study sites are in the central landscape of Khao Yai National Park in Thailand, the UNESCO World Heritage Site. Comprising of grassland and pristine forests, the park locates on longitude and latitude Its elevation ranges from 600 1,351 m above sea level with 1,200 2,000 mm annual rainfall. (Lynam et al., 2006) The central landscape becomes forest-grassland mosaic patches with different times of succession (1 4 years) causing from non-systematic management by fire

3 disturbance and mowing. We divided them into seven grassland communities, which are Nhong Puk Chi 1 (NP1), Nhong Puk Chi 2 (NP2), Sai Sorn Reservoir (WT), Old golf course (GC), Kao Keaw (KK), Tung Kwang (TK) and Training center (TC) Species diversity and trait measurement For species richness and abundance, we used the data of species diversity from the previous work of Kasornbua et al. unpublished, in which all data were collected from 48 (60 60 m) randomly sampled grids in all areas in They were estimated the percent cover from four 1 1m-quadrats per grid. Numbers of grids in each site were standardized by size. Furthermore, each species biomass (10 cm above ground) in one-third grids of each quadrat was quantified by hand-cutting and oven-dried weighing. We collected plant functional traits in November 2012 after the last burning time. These traits are relative maximum height, specific leaf area (SLA), and leaf dry matter content (LDMC). For each trait, we selected ten individuals per species in each site to evaluate functional traits following standard protocols of functional trait measurement (Cornelissen et al., 2003). We sampled mature plants with sunlight exposure to measure three functional traits. First of all, we measured relative maximum height of each plant in the field study using a tape measurement. After that, we collected plant leaves of those samples and kept in moist papers and zip lock bags to maintain freshness for leaf trait assessments both SLA and LDMC in laboratory. We weighed their fresh and dry weights and scanned leaf areas. For all statistical analyses and calculations, we used the R-statistics software version (R develop core team 2013). Data analyses Leaf traits e.g. specific leaf area (SLA) and leaf dry matter content (LDMC) relate to resource richness in leaves, primary productivity, and relative growth rate. It relates to positively photosysthetic rate in SLA (Cornelissen et al., 2003). We calculated from area of a fresh leaf in (mm 2 ) divided by leaf oven-dry mass (mg) shown in the equation (1). LDMC is negative with leaf life span linking ability to conserve nutrients in plants. It correlates with physical resistance. We calculated from leaf oven-dry mass (mg) divided by leaf water-saturated fresh mass (g) following the equation (2). eaf area mm eaf dr mass mg (1) C eaf dr mass mg eaf fresh mass g (2)

4 RESULTS Trait values were ranked by median of species in each grassland site using different colors which indicated in Figure 1.1. Boxplot ranges revealed variation within species which may overlap among each other. It referred to functional redundancy occurring within site. For plant maximum height (Figure 1.1 (a)), there were mature plants as the pioneer species. The lowest maximum heights occurred at the youngest grassland communities (TC). The species composed of Blumeopsis flava, Mimosa pudica, Chrysopogon aciculatus, Sacciplepis indica, Ophiuros exaltatus, Axonopus compressus, Desmodium triflorum, and Centella asiatica. At the older sites (one year old succession grasslands; GC, WT, TK, NP1), we found a few dominant species with upper levels of maximum height which were Eupatorium odoratum and Imperata cylindrica. Howover, these communities were covered by a few nearly aboveground forbs and graminoids e.g. M. pudica, O. exaltatus, Fimbristylis dichotoma, Fimbristylis actinoschoenus, Cyperus halpan, Cynodon dactylon, Euphorbia hirta, and Spilanthes paniculata. When the succession time was increased, the number of species were reduced, for example in NP2, E. odoratum, Melastoma malabathricum and I. cylindrica were dominant as highest species. At the oldest site in KK (4 years), the equal range of the highest maximum species presented in two species, Pennisetum polystachyon and E. odoratum. The medium range was found in I. cylindrica, whereas O. exaltatus had lowest height. For assessing of SLA, in TC site, the species with high SLA were O. exaltatus, D. triflorum, and C. asiatica which had equal range of medians and high variation. Then A. compressus, M. pudica and B. flava were the same range of values. S. indica was the lowest rank species with lowest SLA in this site. For one-year old grasslands (GC, WT, TK, NP1), there was the groups of overlapping boxplots referred to redundancy. In GC, the highest SLA were found in O. exaltatus and M. pudica with high variation, while E. odoratum did not overlap with any species except in M. pudica. There was the same range between I. cylindrica and Eragrostis brownii. Differently, all of species in WT had similar SLA values, which were I. cylindrica, F. dichotoma, E. brownii band F. actinoschoenus. In TK, the ranges of boxplots were separated into two groups. The first group comprises C. aciculatus, E. odoratum and A. compressus, and the one includes I. cylindrica and F. dichotoma. Similar to TK, NP1 had a few groups of redundancy divided by SLA values. S. paniculata and E. hirta were the top range species. C. halpan. had the same values with E. odoratum, and it linked to another groups of C. dactylon, I. cylindrica and F. dichotoma. Nevertheless, we found different results in NP2 because there was no overlapping between I. cylindrica, E. odoratum and M. malabathricum. However, we found a little overlap in oldest KK among I. cylindrica, P. polystachyon and E. odoratum, but I. cylindrica was obviously separated from E.

5 odoratum. From this result, we found the decreasing of redundancy when the stage of succession was increased. Each site always had a few species who kept the top function, and the others stayed on below values splitting out of the first rank. In contrast to SLA, LDMC values among species were almost similar to each other without considering of site separation or time gradient. They were less overlapping of boxplots among species within site. In TC, O. exaltatus had the higher values of SLA than D. triflorum, S. indica, M. pudica, A. compressus, B. flava, and C. asiatica, respectively. In one-year sites, GC, TK and NP1, the ranges of boxplots were organized in similar patterns with small overlapping among species. In contrast, WT had apparent two groups of LDMC values among four species between E. brownii, I. cylindrica, and both Fimbistylis sp. At NP2, I. cylindrica was the highest value and did not overlap with M. malabathricum coincided with E. odoratum. For KK, I. cylindrica, E. odoratum and P. polystachyon did not overlap at all. a) b)

6 c) Figure 1.1 Variation of maximum height (m) (a), SLA (mm 2 mg -1 ) (b), LDMC (mg g -1 ) (c) among sites: the graphs show trait values ranked by median of species in each grassland site via different colors. The grassland sites were ranked by succession times from young to old (left to right). DISCUSSIONS Effects of the succession gradient on functional traits The ability of plant functional traits was useful to predict ecosystem functioning (Lavorel and Garnier 2002; Hooper et al. 2005; de Bello et al. 2010), especially in grassland, where needed fire regime to regenerate ecosystem process via succession. In our study, succession gradient indirectly affected maximum height. We found that plant height increased in the older patches, which had E. odoratum and I. cylindrica as the dominant species after the time was increasing. E. odoratum was outstanding height which strong competition. There was separation of height explicitly among tall and aboveground plants. The differentiation responded to light competition. Although succession time slightly affected SLA and LDMC values, we found the similar patterns of trait composition, whereas the species composition was different. Interestingly, the results showed in similar patterns of boxplot implying maintenance of functional trait structures in the ecosystem. This is an effect of I. cylindrica. They could strongly compete with other species when the succession time is increasing, meanwhile performing high values of SLA and LDMC in the older grassland sites,. According to the niche partitioning theory, we could explain the patterns of functional traits in our results which showed resource separation among species that avoided niche overlapping. Trait variation within species might result from filtering processes in a community known as ecological filters (Violle et

7 al., 2012). Therefore, understanding of variation should focus on both environmental characteristics as external filters and internal processes e.g. competition along with time gradient. Redundancy of functional traits Functional redundancy referred to compensation of ecosystem functioning among species. After species richness was affected from environmental changes, the ecosystem was restored as ecological resilience by redundancy (Wellnitz and Poff, 2001). Many species had similar degree of functional traits, and they could be functioning replaceable with each other. Although two species could not coexist with the same resource-use competition according to the Competitive Exclusive Principle, they could play equivalently functional roles in the community as a redundancy influencing from different times of succession. In our result, similar functional roles among two or three species could be co-occurring at short succession time and decreased by increasing time scales obviously in SLA. Possibly, the functional redundancy was negatively related to change of species composition during increasing succession time. CONCLUSIONS Plant functional traits had indirectly been influenced on succession time via change in species composition. The species which had strong values of function were alternated among sites, whereas the degree of functional traits were maintained constantly. Filtering processes of ecosystem leaded to the variation of trait values within species. Also, differentiating of them resulted from avoiding of niche overlapping among species. However, longer succession times influenced negatively to functional redundancy occurring in SLA. We suggested that the trait-based management in these grasslands needed more other trait information and might focus on one two years of succession times approximately because they could provide functional redundancy resulting from changed species composition. ACKNOWLEDGEMENTS This thesis was supported research funds from Thailand Graduated Institutes of Science and Technology (TGIST) by National Science and Technology Development Agency (NSTDA): TG M. We thank the Department of National Parks, Wildlife and Plant Conservation for permission and supporting to conduct this research. REFERENCES Cornelissen, J.H.C., S. Lavorel, E. Garnier, S. Díaz, N. Buchmann, D.E. Gurvich, P.B. Reich, H. ter Steege, H.D. Morgan, M.G.A. van der Heijden, J.G. Pausas and H. Poorter A handbook of protocols for standardized and easy measurement of plant functional traits worldwide. Australian Journal of Botany 51: Chanthorn, W. and W.Y. Brockelman Seed dispersal and seedling recruitment in the light demanding

8 tree Choerospondias axillaris in old-growth forest in Thailand. ScienceAsia 34: De Bello, F., S. Lavorel, S. Díaz, R. Harrington, J.H.C. Cornelissen, R.D. Bardgatt, M.P. Berg, P. Cipriotti, C.K. Feld, D. Haring, P.M. da Silva, S.G. Potts, L. Sandin, J.P. Sousa, J. Storkey, D.A. Wardle and P.A. Harrison Towards an assessment of multiple ecosystem processes and services via functional traits. Biodiversity Conservation 19: Garnier E., J. Cortez, G. Billès, M.L. Navas, C. Roumet, M. Debussche, G. Laurent, A. Blanchard, D. Aubry, A. Bellmann, C. Neill, J.P. Toussaint Plant functional markers capture ecosystem properties during secondary succession. Ecology 85(9): Garnier E., S. Lavorel, P. Ansquer, H. Castro, P. Cruz, J. Dolezal, O. Eriksson, C. Fortunel, H. Freitas, C. Golodets, K. Grigulis, C. Jouany, E. Kazakou, J. Kigel, M. Kleyer, V. Lehsten, J. epš, T. Meier, R. Pakeman, M. Papadimitriou, V. Papanastasis, H. Quested, F. Quétier, M. Robson, C. Roumet, G. Rusch, C. Skarpe, M. Sternberg, J.P. Theau, A. Thèbault, D. Vile, M.P. Zarovali Assessing the effects of land-use change on plant traits, communities, and ecosystem functioning in grasslands: a standard methodology and lessons from an application to 11 European sites. Annals of Botany 99: Hooper D.U., F.S. Chapin III, J.J. Ewel, A. Hector, P. Inchausti, S. Lavorel, J.H. Lawton, D.M. Lodge, M. Loreau, S. Naeem, B. Schmid, H. Setälä, A.J. Symstad, J. Vandermeer, D.A. Wardle Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecological Monographs 75(1): Lavorel S. and E. Garnier Predicting changes in community composotion and ecosystem functioning from plant traits: revisiting the Holy Grail. Functional Ecology 16: Lavorel, S., K. Grigulis, P. Lamarque, M.P. Colace, D. Garden, J. Girel, G. Pellet, and R. Douzet Using plant functional traits to understand the landscape distribution of multiple ecosystem services. Journal of Ecology 99: Lynam, A.J., P.D. Round, and W.Y. Brockelman Status of birds and large mammals in Thailand s Dong Phayayen Khao Yai forest complex. Wildlife Conservation Society and Biodiversity Research and Training (BRT) Programme, Bangkok. 244pp. Quétier, F., A. Thébault, and S. Lavorel Plant traits in a state and transition framework as markers of ecosystem response to land-use change. Ecological Monographs 77(1): Violle, C., B.J. Enquist, B.J. McGill, L. Jiang, C.H. Albert, C. Hulshof, V. Jung, and J. Messier The return of the variance: intraspecific variability in community ecology. Trends in Ecology and Evolution 27(4): Wellnitz T. and N.L. Poff Functional redundancy in heterogeneous environments: implications for conservation. Ecology Letters 4: