TROPICS Vol. 21 (3) Issued November 30, 2012

Colonization of tree species along an interior-exterior gradient across the forest edge in a tropical montane forest, northwest Thailand

Lamthai Asanok1,2,＊, Dokrak Marod3, Anak Pattanavibool4, Tohru Nakashizuka1

1 Graduate School of Life Sciences, Tohoku University, Sendai 980-8578, Japan. 2 Department of Agroforestry, Maejo University, Phrae Campus, Phrae 54140, Thailand. 3 Department of Forest Biology, Faculty of Forestry, Kasetsart University, Bangkok 10900, Thailand. 4 Wildlife Conservation Society (WCS) Thailand Program, Nonthaburi 11120, Thailand. ＊Corresponding author: E-mail: [email protected]

ABSTRACT We investigated the environmental factors and tree species characteristics that are important for colonization of an interior-exterior gradient across the forest edge, for application to the restoration of abandoned shifting-cultivation areas in tropical montane forests in the Umphang Wildlife Sanctuary, northwest Thailand. The relative importance of physical environment and recruit limitation was evaluated in relation to the regeneration traits of tree species. Three belt transect plots (150 m x 20 m) were established at the transition from secondary forest (edge interior) to open areas (edge exterior) of different ages (1, 3, and 5 years) after abandonment of shifting cultivation. We also set three belts (20 m x 50 m each) in a primary forest remnant. The species composition of canopy trees, regenerated seedlings, and saplings was studied, together with aspects of the physical environment. We found that it was difficult for primary forest species to effectively colonize the forest edge exterior, mostly due to recruitment limitations rather than the physical environment. Many of secondary forest species and generalists were also affected by recruitment limitation (significant negative correlation with the distance from forest edge), though they were also affected by factors related to the physical environment and forest structure and more abundant in open area. Only a few species, like Choerospondias axillaris (primary forest species), Wendlandia tinctoria (secondary forest species), Colona elobata, and Ficus hispida (generalist species) did not suggest recruitment limitation. These results suggested that natural regeneration of secondary forest and generalist species could be utilized as a first step in restoration expecting their facilitation effects for primary forest species.

Key words: forest edge; forest restoration after shifting cultivation; recruitment limitation; tree species traits; tropical montane forest.

INTRODUCTION Shifting cultivation is the main cause of tropical forest loss and fragmentation in many countries of Tropical montane forests host high biodiversity, although Southeast Asia and South America (Fukushima et al. human activities are leading to their decrease and 2008, Harttera et al. 2008, Do et al. 2010, Klemick 2011). fragmentation (Tabarelli et al. 1999, Garcia et al. 2005, Both fragmentation and decreases in forest area have Zang et al. 2005, Cayuela et al. 2006, Toledo-Aceves et al. caused serious losses of biological diversity (Sole et al. 2011). In human-dominated agricultural landscapes in 2004, Bailey 2007, Conceicao and Oliveira 2010). The tropical highland regions throughout the world much of forest edge is the line dividing edge interior and edge the original forest cover has been converted into cropland exterior, and the structure and species composition and pastures, including shifting cultivation with cultivated differs between the interior and exterior of the forest temporarily crops and abandoned after harvesting (Mertz edge (Thomas et al. 1979, Oosterhoorn and Kappelle 2009), or semi-permanent land-use systems were crop- 2000, Lopez-Barrera et al. 2006, Marchand and Houle fallow cycle (Manlay et al. 2001), resulting in mosaics of 2006), which increases with increasing fragmentation. agricultural land, secondary forest (SF) with re-growth of Vegetation at the forest edge interior consists mainly of vegetation that covers land (Perz and Skole 2003), and secondar y shrub and tree species; edge effects are primary forest (PF) patches (Mottet et al. 2006, Soliva et sometimes expressed as a reduction in canopy height and al. 2008, Calvo-Iglesias et al. 2009). an increase in subcanopy stature from the forest interior 68 Lamthai Asanok, Dokrak Marod, Anak Pattanavibool, Tohru Nakashizuka towards the edge (Oosterhoorn and Kappelle 2000). tropical forest. However, forest edges may play an important role in Most mountainous areas of northern Thailand restoration of forests (Park 2001, Asbjornsen et al. 2004), covered by lower montane forest (Bunavejchewin et al. and much more information on interior-exterior the edge 2011), long history of shifting cultivation by local and hill- vegetation and tree regeneration is required. tribe people has also caused gradual fragmentation of PFs Edge-related responses of tree species and their (Buergin 2003, Barnaud et al. 2008, Fukushima et al. consequences for plant community composition can be 2008) and increases forest edge especially, in protected ameliorated or exacerbated as a result of differences in area such as wildlife sanctuary and national park (Royal edge type, which is determined by the type of vegetation Forest Department 2010). Local people cultivated rice, adjoining the forest fragment (Lopez-Barrera et al. 2006, maize, cabbages, and fruit crops after slash-and-burn Pauchard and Alaback 2006) and the age of open land clearing of forest areas, though some of them have been after abandonment (Landenberger and Ostergren 2002, abandoned. So, the restoration of abandoned areas Wulder et al. 2009). Forest structure can also affect these especially, the area transition forest is now urgently gradients. Edge contrast (the difference in canopy height required for biodiversity conservation in the vicinity of between cleared and intact forest) and edge closure (the protected areas. The previous study in tropical forest density and vertical distribution of foliage along the edge) found that important factor of tree colonization around can affect light penetration and air movement and thus the edge. There could be many factors af fecting gradients in temperature, humidity, and other colonization around forest edge, the types of forest edge microclimate variables at the area connection of forest (vegetation adjoining the forest fragment and age of open edge (Heithecker and Halpern 2007, Li et al. 2007, Wright land after abandonment) and distance from the edge to et al. 2010). These interior-edge-exterior environment open areas outside the forest (Lopez-Barrera et al. 2006, changes substantially, especially when abrupt transitions Landenberger and Ostergren 2002, Wulder et al. 2009), occur between vegetation communities with distinct forest structure changing on high-low disturbance regime structures and compositions (Asbjornsen et al. 2004, (Kennard et al. 2002), and interior-edge-exterior Heithecker and Halpern 2007). environmental factors such as light intensity and soil In tropical forest, seedling survival and growth can conditions (organic, moisture and bulk density) differ be enhanced at around forest edges or in the understory along the forest edges (Williams-Linera et al. 1998), and due to the ameliorating effects of mature trees and increasing rates of tree mortality (Laurance et al. 2002). shrubs on abiotic microsite conditions (Murcia 1995, However, both environmental factors and recruitment Sizer and Tanner 1999, Piessens et al. 2006). limitations depend on the specific traits of tree species, Environments around the edge may provide critical and studies to separate these components are necessary regeneration sites in fragmented landscapes (Park 2001, to understand mechanisms of tree regeneration at Asbjornsen et al. 2004), while aggregated forests are interior-exterior gradient across the forest edge. Although sufficiently buffered to maintain species that are sensitive regeneration of light-demanding tree species is high to environmental changes (Hewitt and Kellman 2004). around forest edges, the goal of restoration and Soil moisture availability is often the most important regeneration of PFs, rather than disturbance-dependent factor affecting plant establishment and growth following forest (Elliott et al. 2003, Dent and Wright 2009), and the disturbance (Kolka and Smidt 2004, Fay and Schultz 2009, traits related to PF species are of particular concern in Gaduno et al. 2010, Yang et al. 2010). A high light restoration practice. environment after a large canopy disturbance can In this study, we conducted in Umphang Wildlife promote growth of seedlings of some species (Ashton Sanctuary forested fragmentation, which has been caused 1995), while other species grow better in smaller canopy by shifting and permanent cultivation activities by local openings (Brown 1996). The light regime of the forest hill tribes. We investigated the recruitment limitations, understory and gap edges favors seedling growth of the environmental factors and tree species characteristics more shade-tolerant species (Saldana-Acosta et al. 2009, that are important for colonization of interior-exterior Chazdon et al. 2010). Thus, understanding the potential gradient across the forest edge, for application to the responses of tree species to environmental of interior- restoration of abandoned shifting-cultivation areas in edge-exterior gradient is critical to designing systems tropical montane forests. Specifically, we aimed to answer that maintain and facilitate recovery of biological diversity two questions. 1) Can PF species effectively colonize at interior-exterior gradient across the forest edge of along interior-exterior gradient across the forest edge? 2) Colonization of tree species along an interior-exterior gradient across the forest edge in a tropical montane forest, northwest Thailand 69

If not, what factor(s) prevents regeneration: the physical Field studies environment or recruitment limitations? From July 2005 to June 2006, four study sites were selected: one typical remnant of primary montane forest MATERIALS AND METHODS and three plots at interior-edge-exterior gradient. We selected three study sites at the transition from secondary Study area forests into maize crop land with different time after The study was conducted in montane evergreen forests abandonment (1, 3, and 5 years). They were distant about of Umphang Wildlife Sanctuary, Tak province, northwest one kilometer each other. Maize was cultivated before the Thailand (98˚ 55′–99˚ 05′ E, 16˚ 10′–16˚ 15′ N; 1265–1420 fields were abandoned in all these area. This information m a.s.l.; Fig. 1). Mean annual air temperature and was confirmed by the interview of the wildlife sanctuary precipitation are about 27ºC and 1392.4 mm, respectively. officer. The interior-edge-exterior gradient plots were The climate is seasonal, with three distinct seasons, a established at the transition from SF (edge interior) to cool dry season from November to February, a hot dry agricultural land (edge exterior) of different ages (1, 3, season from March to May, and a rainy season from May and 5 years) after abandonment (AA1, AA3, and AA5, to October (WEFCOM 2003). respectively). All transects (PF and SF) were established The original vegetation at the site is tropical montane at similar altitudes of 1300 m a.s.l., with 40 percentage on forest, dominated by trees in the families Fagaceae, a steep slope, and about five km from a village (Fig. 1). Myrtaceae, Lauraceae, Theaceae, and Magnoliaceae. At the PF site, we established three 20 m x 50 m belt Some large remnant patches of relatively undisturbed plots, divided into ten 10 m x 10 m quadrats, giving a total montane forest still remain in this area (WEFCOM 2003). of 30 quadrats. For each an across forest edge site, we Forest fragmentation has been caused by shifting and established a 20 m x 150 m belt transect, running from permanent cultivation activities by local hill tribes. They the forest interior (50 m long) through the edge to the cultivate rice, maize, cabbages, and fruit crops after slash- outside of the forest (100 m long), perpendicular to the and-burn clearing of forest areas. Some areas are edge line. These transects were divided into 30 abandoned after the harvest, leaving a mosaic of scattered contiguous 10 m x 10 m quadrats, 10 inside and 20 forest patches and abandoned fallow fields. outside the forest (Fig. 1). We enumerated all mature

PF

AA5 10 m 50 m AA3 4 m AA1 10 m 20 m 1 m 4 m 1 m PF AA1

Village

1 km AA3 SF (edge interior) Agricultural land (edge exterior) 150 m

AA5

Fig. 1. The location and study sites. Study sites (white dot) and three sampling plots (20 m x 50 m) were established in primary forest and forest edge plots (20 m x 150 m) was established at the transition from secondary forest (edge interior) to agricultural land (edge exterior) of different ages (1, 3, and 5 years) after abandonment (AA1, AA3, and AA5, respectively). 70 Lamthai Asanok, Dokrak Marod, Anak Pattanavibool, Tohru Nakashizuka trees (those of 1.3 m height, with a diameter at breast plot) in PF (30 plots), SF (30 plots), and open areas (60 height [DBH] greater than or equal to 5 cm) in the 10 m plots). We grouped species into (1) PF species that had a x 10 m quadrats. At a corner of ever y 10 m x 10 m significantly high density in PFs; (2) SF species with a quadrat, we established 1 m x 1 m and 4 m x 4 m sub- significantly high density in SFs; (3) generalist species quadrats, a total of 30 sub-quadrats in each transect (Fig. without any significant density bias; and (4) infrequent 1). The saplings (DBH < 5 cm, but height > 1.30 m) in the species with inadequate densities for statistical analysis. 4 m x 4 m sub-quadrats, and the seedlings (height < 1.30 We analyzed the regeneration characteristics by included m) in 1 m x 1 m quadrats were also enumerated. DBH number of seedling (in 1 m x 1 m plot) and sapling (in 4 was measured for all trees, but we only counted the m x 4 m plot) of each species in the both subplot as number of saplings and seedlings of each species. All of located at same position on each transect site, the total 30 the trees, saplings, and seedlings were identified to sample for PF and SF, and 60 sample for open area. We species by collecting specimens and comparing them to applied the Kruskal–Wallis test for sapling and seedling standard specimens in the herbarium of department of density in primary and SFs and in open areas, and applied the National Park, Wildlife and Plant Conservation. The for testing the difference of each environment factor nomenclature followed The Forest Herbarium (2001) and between PF and SF and in open area too. To analyze Gardner et al. (2000). factors affecting regeneration, we applied generalized Soil samples were collected from the top soil layer linear mixed models (GLMMs) in a step-wise regression (0–15 cm) in October 2005, using a soil core sampler with analysis for seedling and sapling density of species with a volume of 100 cm3, at the center of each 1 m x 1 m sub- sufficient density for statistical analyses (species with quadrat, on the same day when 10 days after the last rain. greater than or equal to 20 stems). The independent This is the season close to the beginning of dry season in variables adopted were: (1) the physical environmental this area, with infrequent rain though still relatively factors RLI, SMC, and SDb; (2) forest structure, i.e., humid soil. However, it seems the soil condition in this forest type (FT), basal area (BA), and tree stem density season may reflect the variations among the quadrats (D); and (3) factors relating to recruitment, distance from better than mid rainy nor mid dry seasons. Soil bulk edge (DE), and age after abandonment (AA). All of these density (SDb, g/cm3) was estimated for each soil sample variables were obtained for each 10 m x 10 m quadrat. as the proportion of mass of oven-dried soil to the total Most of species found in edge exterior had their volume, and soil moisture content (SMC, %) was conspecific seeding trees in edge interior. All factors had determined from the ratio of fresh weight to dry weight correlation coefficients less than 0.7. Transect site was (Kissling et al. 2009). We also took a hemispherical included as a random factor, and the model with the photograph with a Nikon FM and fish-eye lens (8 mm lowest Akaike’s information criterion (AIC) was focal distance) by setting the camera at the center of the selected for each species (Hamberg et al. 2009). All 1 m x 1 m quadrat. We took photos at two heights, just statistical analyses were performed using the software R above ground level (0.1 m) and 1.3 m above ground level, v 2.11.1 (R Core Development Team, Vienna, Austria). on a sunny day (09:00–11:00 h) in December 2005 to estimate relative light intensity (RLI). We avoided the direct sunlight at edge interior not to have over- RESULTS contrasted images. The RLIs were analyzed with the Gap Environmental factors along the forest edge Light Analyzer (GLA) version 2.0 software program (Frazer 1999). RLI in each frame quadrat was estimated Environmental factors showed higher contrast between as the percentage of standard overcast sky distribution. inside and outside the forest at the site just after These soil and light factors were used to analyze abandonment than at sites after a longer period of seedlings and saplings, representing the environment in abandonment (Fig. 2A). In the open areas of AA5 and both 1 m x 1 m and 4 m x 4 m quadrats. AA3, RLI 1.3 m above ground level was higher than at ground level (significant difference between interior and exterior, p <0.05 and p <0.01, respectively), while AA1 had Data analysis similar and high RLI values at both levels. Relative light To classify tree species into primary or secondary forest intensity inside PFs were low, similar to those deep more species, we used the Kruskal–Wallis test (Ruxton and than 20 m inside the SFs. RLI values in open areas Beauchamp 2008) for mature tree density (per 0.01 ha increased with distance from the forest edge in AA5 and Colonization of tree species along an interior-exterior gradient across the forest edge in a tropical montane forest, northwest Thailand 71

Secondary forest Open land 120 AA5 1.3 m (A) 100 AA5 0.1 m AA3 1.3 m 80 AA3 0.1 m ) AA1 1.3 m ) % ( %

( m AA1 0.1 I 60

L m LI

R PF R 40

20

0 PF -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

1.4 (B) 1.2

) 1.0 3

cm 0.8 / g ( 0.6 b

D PF S 0.4 AA5 AA3 0.2 AA1

0.0 PF -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100

60.0 (C) AA5 50.0 50 AA3

) AA1 40.0 % 40 PF ( )

% ( C

C 3030.0 M S SM 20

10.0

00.0 PF -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 Distance across forest edge (m)

Fig. 2. Changes in the physical environment from the inside to the outside of the forests. (A) the relative light intensity (RLI) at 0.1 m and 1.3 m above the ground, (B) soil bulk density (SDb), and (C) soil moisture content (SMC) measured in primary forest (PF) and transects from the inside of secondary forests to the areas of open land that have been abandoned for different time periods: AA1, 1 year; AA3, 3 years; AA5, 5 years. Mean±SD, N = 2 (AA1, AA3, AA5), N = 30 (PF).

AA3. distance from the forest edge to the outside. While, the Soil bulk density in AA5 and AA3 (including PFs) trend of AA5 seem increased when distance far from the was similar, while AA1 lower than both former sites. edge. Soil moisture in PFs was rather low. However all site slightly higher in open areas (no significant: Fig. 2B). Soil moisture content in AA3 and Species composition AA1 was high in quadrats inside SFs and declined in open areas, while AA5 looked similar in both areas (Fig. 2C). Mature trees comprised 929 stems of 121 species in total. The SMC of AA3 and AA1 were contrast between inside The dominant species in PFs were Syzygium fruiticosum, and outside the forest (p <0.05), by decreased with Nephelium hypoleucum, Walsura trichostemon, and 72 Lamthai Asanok, Dokrak Marod, Anak Pattanavibool, Tohru Nakashizuka

PF SF OA No. Species Mean ± SD Mean ± SD Mean ± SD Sig. (stem/0.01 ha) (stem/0.01 ha) (stem/0.01 ha) N = 30 N = 30 N = 60 Primary forest species 1 Syzygium fruiticosum 0.70±2.69 0 0 2 Nephelium hypoleucum 0.63±3.11 0 0 3 Walsura trichostemon 0.53±2.10 0 0 4 Anacolosa ilicoides 0.40±1.67 0 0 5 Beilschmiedia elegantissima 0.33±1.37 0 0 6 Litsea laeta 0.33±1.30 0 0 7 Chionanthus sp. 0.30±1.32 0 0 8 Gironniera nervosa 0.27±1.05 0 0 9 Polyalthia sp. 0.23±1.10 0 0 10 Calophyllum polyanthum 0.20±0.92 0 0 11 Elaeocarpus sphaericus 0.20±0.76 0 0 12 Canthium glabrum 0.10±0.40 0 0 13 Memecylon plebejum 0.10±0.31 0 0 14 Choerospondias axillaris 0.10±0.31 0.03±0.18 0 15 Cryptocarya impressa 0.07±0.25 0 0 16 Garcinia pedunculata 0.07±0.25 0 0 17 Lithocarpus elegans 0.07±0.25 0 0 18 Randia fusca 0.07±0.25 0 0 Total primary forest species 4.70±14.57 0.03±0.18 0 * Secondary forest species 1 Castanopsis tribuloides 0 1.47±5.24 0.20±1.09 2 Styrax benzoides 0 1.37±5.03 0 3 Litsea martabarnica 0 1.33±3.54 0.08±0.65 4 0 1.00±3.26 0.03±0.26 5 Wendlandia tinctoria 0.07±0.25 0.83±1.58 0.10±0.35 6 Archidendron clypearia 0 0.70±1.74 0.23±1.81 7 Baliospermum solanifolium 0 0.43±1.33 0 8 Trichilai connaroides 0 0.33±0.99 0.10±0.48 9 Lithocarpus grandifolius 0 0.27±1.05 0 10 Arytera littoralis 0 0.27±0.94 0 11 Betula alnoides 0 0.27±0.69 0.02±0.13 12 Euodia meliaefolia 0 0.23±0.82 0 13 Aporosa octandra 0 0.23±0.77 0 14 Balakata baccata 0 0.20±0.66 0 15 Archidendron jiringa 0 0.17±0.75 0 16 Trema orientalis 0 0.17±0.59 0 17 Mallotus paniculatus 0 0.07±0.25 0 18 0 0.07±0.25 0 19 Vitex quinata 0 0.07±0.25 0 Total secondary forest species 0.07±0.25 9.47±18.67 0.77±2.68 * Generalist species 1 Castanopsis acuminatissima 0.10±0.55 1.77±5.50 0.10±0.48 NS 2 Schima wallichii 0.07±0.37 0.97±3.71 0.28±1.51 NS 3 Eurya acuminata 0 0.80±2.41 0.20±0.71 NS 4 Colona elobata 0 0.37±1.25 0.07±0.41 NS 5 Diospyros glandulosa 0.60±2.93 0.37±1.25 0 NS 6 Meliosma pinnata 0.07±0.25 0.37±1.25 0 NS 7 Cordia mhaya 0 0.30±1.32 0.18±0.81 NS 8 Micromelum minutum 0 0.30±0.95 0.08±0.46 NS 9 Ficus hispida 0.20±1.10 0.30±0.84 0.02±0.13 NS 10 Macaranga kurzii 0 0.20±1.10 0.02±0.13 NS 11 Rhus chinensis 0 0.20±0.76 0.12±0.58 NS 12 Alangium chinense 0.03±0.18 0.17±0.75 0 NS 13 Glochidion rubrum 0 0.13±0.43 0.07±0.36 NS 14 Vernonia volkameriifolia 0 0.10±0.55 0.02±0.13 NS 15 Macaranga indica 0 0.10±0.40 0.02±0.13 NS 16 0.10±0.40 0.10±0.40 0 NS 17 Syzygium pyrifolium 0.03±0.18 0.10±0.40 0 NS 18 Albizia chinensis 0 0.10±0.31 0.13±0.39 NS 19 Erythrina subumbrans 0 0.07±0.37 0.02±0.13 NS 20 Apodytes dimidiata 0.10±0.55 0.07±0.25 0.05±0.29 NS 21 Broussonetia papyrifera 0 0.07±0.25 0.02±0.13 NS 22 Ailanthus triphysa 0 0.03±0.18 0.02±0.13 NS 23 Alstonia rostrata 0.30±1.64 0.03±0.18 0 NS 24 Ardisia colorata 0.07±0.38 0.03±0.18 0 NS Total generalist species 1.67±5.18 6.43±11.67 1.40±3.59 NS Total for all species 6.43±19.90 15.93±28.24 2.17±5.77 NS Colonization of tree species along an interior-exterior gradient across the forest edge in a tropical montane forest, northwest Thailand 73

Anacolosa ilicoides (Table 1). Dominant secondar y mature trees in the PFs (not statistically significant). species were Castanopsis tribuloides, Styrax benzoides, Choerospondias axillaris and Anacolosa ilicoides had Litsea mar tabarnica, and Michelia floribunda, and higher seedlings and sapling density in SFs than in PFs dominant generalist species were Castanopsis (including significant and no significant). All other PF acuminatissima, Schima wallichii, Eurya acuminata, species had higher seedling and sapling density in PFs Colona elobata, and Diospyros glandulosa. We classified than in SFs or open areas (including some species the species into 18 PF species, 19 SF species, and 24 without significant differences). In particular, Calophyllum generalists (Table 1). The other 60 species were classified polyanthum, Cryptocarya impressa, and Nephelium as infrequent species. hypoleucum had high abundant seedlings and saplings in PFs (Table 2). The seedling and sapling density of most SF species Composition of seedlings and saplings were higher in SFs than in PFs and open areas (Fig. 3, Seedling densities had different patterns among the Table 2). In par ticular, Archidendron clypearia, species types (Fig. 3). The PF species had the highest Wendlandia tinctoria, Castanopsis tribuloides and Styrax density in PFs, followed by SF species, with very few in benzoides had high abundant in SFs (including some open areas. Seedlings of SF species had the highest species without significant differences). Baliospermum density in SFs, and decreased towards the open area in solanifolium and Vitex quinata showed seedling and relation to distance from the forest edge, but were also sapling only in PFs (including significant and no distributed within PFs, although at lower densities than in significant), while Aporosa octandra and Trema orientalis SFs. Seedling of generalist species had the lowest density appeared in open area only, although the difference was in PFs and showed an intermediate pattern between not significant because the seedlings and saplings had an those of PF and SF species in SFs, but had the highest aggregated distribution. Wendlandia tinctoria, Styrax density in the open area closely the edge, and also a benzoides and Arytera littoralis also had relatively high decrease in relation to distance from the forest edge. densities in open areas (Table 2). The seedlings and saplings of most species (include; Most generalist seedlings and saplings occurred primar y, secondar y and generalist species) were more in SFs and open areas (Table 2). Many of their observed not in PFs, but in SFs and open areas (Table 2), densities were slightly higher in SFs than in open areas, even though the density of seedlings of PF species in SFs especially, Castanopsis acuminatissima, Macaranga kurzii and open areas was low. Randia fusca had no seedlings and Eurya acuminata. Rhus chinensis had a higher and saplings in PFs, even though these species had density significant in open areas, while Colona elobata

Secondary forest Open land 16 ) 2 14 Psp 1 m /

m Ssp

e 12 t s (

Gsp 10 ngs i l

d 8 e e s

f 6 o r e

b 4 m u

N 2 0 PF -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 Distance across forest edge (m)

Fig. 3. Seedling densities of primary forest species (Psp), secondary forest species (Ssp), and generalist species (Gsp) in the primary forest (PF) and in transects from secondary forest to abandoned, open land. Mean±SD, N = 6 (AA1, AA3, AA5), N = 30 (PF). 74 Lamthai Asanok, Dokrak Marod, Anak Pattanavibool, Tohru Nakashizuka

Table 2. Mean ± standard deviation of the sum stem density of seedling (in 1 m x 1 m subplot) and sapling (in 4 m x 4 m subplot), as located at the same position on each transect inside the primary (PF) and secondary forest (SF), and in the open area PF SF OA No. Species Mean ± SD Mean ± SD Mean ± SD Sig. N = 30 N = 30 N = 60 Primary forest species 1 Calophyllum polyanthum 1.00±02.26 0 0 2 Cryptocarya impressa 0.63±1.81 0.57±1.33 0.13±0.60 NS 3 Nephelium hypoleucum 0.60±1.35 0.17±0.46 0.13±0.43 NS 4 Gironniera nervosa 0.30±1.47 0 0 5 Syzygium fruiticosum 0.23±1.28 0 0 NS 6 Beilschmiedia elegantissima 0.17±0.91 0 0 NS 7 Chionanthus sp. 0.13±0.73 0 0 NS 8 Polyalthia sp. 0.13±0.73 0 0 NS 9 Anacolosa ilicoides 0.10±0.40 0.13±0.73 0 NS 10 Litsea laeta 0.10±0.40 0 0 11 Walsura trichostemon 0.10±0.40 0 0 12 Choerospondias axillaris 0.03±0.18 1.77±4.25 0.35±1.58 13 Elaeocarpus sphaericus 0.03±0.18 0.03±0.18 0 NS 14 Randia fusca 0 0 0.05±0.39 NS Total primary forest species 3.57±8.48 2.67±5.26 0.67±2.09 ** Secondary forest species 1 Archidendron clypearia 0 3.13±11.22 0.12±0.67 NS 2 Wendlandia tinctoria 0 2.77±8.54 1.90±8.13 NS 3 Castanopsis tribuloides 0 1.40±4.84 0.05±0.39 NS 4 Styrax benzoides 0.03±0.18 1.03±3.35 0.28±1.61 5 Litsea martabarnica 0.20±1.10 0.80±2.81 0 6 Arytera littoralis 0 0.40±1.50 0.25±0.84 NS 7 Euodia meliaefolia 0.07±0.37 0.37±0.89 0.02±0.13 8 0.17±0.53 0.37±0.67 0.17±0.56 NS 9 Archidendron jiringa 0 0.10±0.55 0 NS 10 Balakata baccata 0 0.03±0.18 0 NS 11 Aporosa octandra 0 0 0.03±0.26 NS 12 Baliospermum solanifolium 0.13±0.57 0 0 13 Trema orientalis 0 0 0.05±0.39 NS 14 Vitex quinata 0.03±0.18 0 0 NS Total secondary forest species 0.63±2.47 10.40±25.74 2.87±9.51 ** Generalist species 1 Castanopsis acuminatissima 0 4.30±20.61 0.02±0.13 2 Macaranga kurzii 0 1.87±5.09 0.33±1.82 3 Eurya acuminata 0 1.53±5.82 0.93±3.46 NS 4 Rhus chinensis 0 1.30±3.81 7.88±28.27 5 Diospyros glandulosa 0.10±0.40 0.67±1.47 0.22±0.96 6 Micromelum minutum 0 0.63±2.14 0.23±1.03 NS 7 Ficus hispida 0 0.63±1.45 0.28±0.85 8 Glochidion rubrum 0 0.47±1.53 0.27±0.84 NS 9 Alangium chinense 0.10±0.40 0.37±1.19 0.15±0.48 NS 10 Colona elobata 0 0.27±0.64 0.33±1.35 NS 11 Alstonia rostrata 0.03±0.18 0.17±0.91 0 NS 12 Broussonetia papyrifera 0 0.17±0.75 0.03±0.26 NS 13 Schima wallichii 0.07±0.37 0.13±0.57 0.30±1.15 NS 14 Erythrina subumbrans 0 0.10±0.31 0 15 0 0.07±0.37 0 NS 16 Macaranga indica 0 0.07±0.25 0 17 Albizia chinensis 0 0.03±0.18 0.03±0.18 NS 18 Ardisia colorata 0.03±0.18 0 0 NS Total generalist species 0.33±0.80 12.77±27.56 11.02±31.89 *** Total for all species 4.53±11.20 25.83±50.54 14.55±34.81 NS Colonization of tree species along an interior-exterior gradient across the forest edge in a tropical montane forest, northwest Thailand 75 and Schima wallichii had high abundant in open area, but Seven out of 19 SF species showed distance the difference was not significant. Species such as (negative) and/or time (positive or negative) dependency Diospyros glandulosa, Alangium chinense, Alstonia (Table 3), while most of them also had a significant rostrata, Schima wallichii, and Ardisia colorata were also relationship with the physical environment, light, or soil found in PFs, and all generalist species also had mature moisture. Castanopsis tribuloides and Michelia floribunda trees in PFs (Table 1). had a positive relationship with RLI and negative with SMC. Only Litsea mar tabarnica did not have any significant relationship with environmental factors. Some Factors determining regeneration species, e.g., Archidendron clypearia and Litsea The factors related to recruitment limitations were more martabarnica, had a negative relationship with BA. important, and the physical environment and forest The distribution patterns of seedlings and saplings of structure were less important for PF species than for SF generalist species were appeared between those of PF and generalist species, which they were affected by all and SF species. Some species, e.g., Micromelum categories (physical environment, forest structure, and minutum, Schima wallichii, and Alangium chinense, recruitment; Table 3). The importance of the factors showed a significant relationship only with distance differed according to species. (negative) and/or time since abandonment (positive or Four PF species were significantly affected by negative), while Colona elobata had a significant distance from the forest and/or the time since relationship with physical environmental and forest abandonment, but only one PF species was affected by structure factors. Ficus hispida showed a significant RLI and soil moisture. Three PF species showed a positive correlation with distance and a negative negative effect of distance from the forest, and two correlation with time since abandonment. Other species showed a positive effect of the time since abandonment of depended both on physical environment and recruitment an open area. factors. Rhus chinensis and Diospyros glandulosa had a

factors are shown. FT is the forest type: primary forest (1), secondary forest (0). AA is age after abandonment of open land Physical environment Forest structure Recruitment Factor No. Species 3 2 RLI (%) SMC (%) SDb (g/cm ) Ba (m /ha) D (stem/ha) FT DE (m) AA Primary forest species 1 Calophyllum polyanthum 2 Choerospondias axillaris 3 Cryptocarya impressa 4 Nephelium hypoleucum Secondary forest species 1 Archidendron clypearia 2 Arytera littoralis 3 Castanopsis tribuloides 4 Litsea martabarnica 5 6 Styrax benzoides 7 Wendlandia tinctoria Generalist species 1 Alangium chinense 2 Castanopsis acuminatissima 3 Colona elobata 4 Diospyros glandulosa 5 Eurya acuminata 6 Ficus hispida 7 Glochidion rubrum 8 Macaranga kurzii 9 Micromelum minutum 10 Rhus chinensis 11 Schima wallichii 76 Lamthai Asanok, Dokrak Marod, Anak Pattanavibool, Tohru Nakashizuka significant negative relationship with BA, while several their edges (Li et al. 2010). Increased time since species had significant positive relationships with tree abandonment enhances seedling establishment density. (Fukushima et al. 2008; Groeneveld et al. 2009). Three of 4 PF species had a significant (negative) relationship with distance from the forest edge, although DISCUSSION some of the SF and generalist species did not appear to have recruitment limitations. Colona elobata and Ficus Regeneration of primary forest species hispida did not have a negative relationship with distance, PF composition is an expected goal of natural forest suggesting their high ability to reach disturbed sites. restoration, though the seedling and sapling compositions Colona species (Tiliaceae) have winged fruits that are outside the forest are generally much different from dispersed by wind (Gardner et al. 2000) and fig (Ficus those inside PFs (Tables 1 and 2). Seedlings and saplings spp.) is an important food of frugivorous birds in tropical of a few PF species were found in abandoned open areas, forests (Lambert 1991) that can disperse seed over large but their densities were very low (Table 2), suggesting distances from a mother tree. Some secondar y and that they have some difficulty colonizing the open areas. generalist species (e.g., Arytera littoralis, Diospyros The seedlings and saplings that regenerated in open glandulosa, Ficus hispida, and Schima wallichii) can areas outside forests were mainly those of SF species and establish in a short time after land abandonment, and generalists, thus, any restored forests will more closely have characteristics of early successional species resemble SFs than PFs. Disturbances cause losses of (Chazdon et al. 2010). Canopy gap promoted germination primary species from the canopy layer (Oosterhoorn and of soil seed banks and seedling growing of some of these Kappelle 2000) and also influence seedling sur vival species, might effectively they can colonize in open areas (Lopez-Barrera et al. 2006). Only a few PF species, such (Zhu et al. 2003, Martins and Engel 2007, Dupuy and as Choerospondias axillaris and Anacolosa ilicoides, had Chazdon 2008). established seedlings success in secondary forest (inside PF species did not tend to have significant edge) in our study. This is consistent with the observation relationships with the measured physical environmental of Elliott et al. (2003) that Choerospondias axillaris was factors, while many SF and generalist species did. None excellent in terms of sur vival and growth rate in of the PF species had a significant positive relationship restoration areas. However, it is not realistic to expect with RLI, suggesting that they can establish seedlings in effective restoration of PFs just by leaving abandoned low light conditions. Choerospondias axillaris had a degraded areas. negative relationship with RLI, suggesting it might not be On the other hand, we found that some SF and able to establish well in high-light sites. Suggesting, PF generalist species can establish well along an interior- species showed characteristics looked like shade-tolerant exterior gradient across the forest edge. In particular, species (Chazdon et al. 2010). Among SF and generalist Archidendron clypearia, Wendlandia tinctoria, Styrax species, Michelia floribunda and Castanopsis tribuloides benzoides, Arytera littoralis, Macaranga kurzii, Eurya had significant positive relationships with RLI and acuminata, and Rhus chinensis, successfully established negative with SMC, and Colona elobata had positive seedlings in our study areas. Suggesting, these species significant with RLI, showing that they are especially should be utilized in forest edge restoration, because the light-demanding species, as also found by Chazdon et al. surroundings of any given restoration area are more (2010). However, we found the soil moisture decreased, likely to be SFs than PFs. and RLI increased gradually from the forest interior to the outside edge (Fig. 2), resulted open area had high- light condition and soil moisture was low. Suggesting, SF Factors affecting regeneration in open areas and generalist species can responses with soil moisture Recruitment limitations seemed to be important for most and light condition outside edge (open area) more than of the studied species, irrespective of species group. Sites PF species. distant from the forest edge (open areas) are less likely to receive seeds from mother trees in the forest interior Implications for forest edge management (Lopez-Barrera et al. 2006), and PF species sometimes cannot effectively disperse seeds far from mother trees We found that it was difficult for PF species to colonize into open area due to buffering by areas of SF around the open areas outside the secondary forests, mostly Colonization of tree species along an interior-exterior gradient across the forest edge in a tropical montane forest, northwest Thailand 77 because of recruitment limitations rather than effects ACKNOWLEDGMENTS This research would not related to the physical environment of the abandoned have been possible without the assistance of forestry land outside the edge. Thus, reducing recruitment students from the Faculty of Forestr y, Kasetsar t limitations is the most impor tant factor for rapid University. We are much indebted to the Umpang Wildlife restoration of PF species. Only a few species, such as Sanctuary, Department of National Parks, Wildlife and Choerospondias axillaris, could regenerate in open sites, Plant Conservation, for allowing us to conduct this study. but this was the exception. Rather, to more rapidly This study was funded by the Hornbill Project Thailand, recover the forest, the first step is to consider using the the Wildlife Conser vation Society (WCS) Thailand natural regeneration of SF and generalist species, such as Program, and partly by the Strategic Environmental Michelia floribunda, Castanopsis tribuloides, Colona Research Program (S9) of the Ministry of Environment, elobata, and Diospyros glandulosa. These species Japan. regenerate better in high-light conditions and/or low soil moisture, although they may still experience some recruitment limitations. 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Received 23 Jan. 2012 Accepted 11 Aug. 2012