Phenological Variants of Terminalia Alata Coexist in a Dry Dipterocarp Forest

Plant Species Biology (2017) doi: 10.1111/1442-1984.12180

NOTES AND COMMENTS Two phenological variants of Terminalia alata coexist in a dry dipterocarp forest

ERIKO ITO ,* SOPHAL CHANN,† BORA TITH,† SAMKOL KETH,† CHANDARARITY LY,† PHALLAPHEARAOTH OP,† NAOYUKI FURUYA,* YASUHIRO OHNUKI,‡ SHIN’ICHI IIDA,§ TAKANORI SHIMIZU,§ KOJI TAMAI,§ NAOKI KABEYA,¶ TAKANOBU YAGI¶ and AKIRA SHIMIZU¶ *Hokkaido Research Center, Forestry and Forest Products Research Institute (FFPRI-HKD), 7 Hitsujigaoka, Toyohira, Sapporo, Hokkaido, 062-8516, ‡Tohoku Research Center, Forestry and Forest Products Research Institute (FFPRI-THK), 92-25 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate, 020-0123, §Forestry and Forest Products Research Institute (FFPRI), 1 Matsunosato, Tsukuba, Ibaraki, 305-8687; and ¶Kyushu Center, Forestry and Forest Products Research Institute (FFPRI-KYS), 4-11-16 Kurokami, Kumamoto, Kumamoto, 860-0862, Japan; and †Institute of Forest and Wildlife Research and Development (IRD), Forestry Administration, Street 1019, Phum Rongchak, Sankat Phnom Penh Thmei, Khan Sen Sok, Phnom Penh, Cambodia

Abstract

Two morphological variants of Terminalia alata (Combretaceae) differed in leaf flushing phenology and spatial distribution in a Cambodian deciduous forest. The hairy-type trees displayed leaf exchange behavior in the middle of the dry season. The glabrous type flushed new leaves 3 months after the wet season started. The leafless period of the hairy type was estimated to be <1 month, whereas that of the glabrous type lasted more than 5 months. The landscape-scale leaf exchange behavior was similar to that of the hairy type. The two types showed clear spatial separation. The hairy type was limited to flat areas with deep soils. The dominance of the glabrous type in hilly areas with shallow soils suggests that it is adapted to water-limited environments. The abundance of the glabrous type in hilly areas and its unique leaf phenology probably influence the carbon, energy and water balance at the landscape level.

Keywords: Cambodia, phenology, seasonal tropical forest, spatial distribution, trichome, water availability. Received 15 December 2016; revision received 8 May 2017; accepted 15 June 2017

Introduction Rivera et al. 2002; Williams et al. 2008). Water availability is strongly affected by soil conditions, microtopography, Temporal variations in total leaf area within forests are precipitation and other meteorological phenomena. All closely related to the leaf phenologies of the component of these parameters can vary in space and time, making species. Leaf phenology is a key biophysical variable that leaf phenology spatially heterogeneous. governs the transpiration and CO2 uptake of forest cano- Tropical deciduous forests are often more water lim- pies, thereby controlling net primary productivity, water ited than evergreen and semi-evergreen forests. Decidu- balance and energy balance (Asner et al. 2003). Leaf phe- ous forests are predominant in Cambodia, where they nology in seasonal tropical zones is governed largely by cover 25% of the land area (Forestry Administration water availability (Ashton 1991), although budburst may 2011). Terminalia alata Heyne ex Roth (Combretaceae) is be triggered by photoperiods (Borchert & Rivera 2001; known as ‘Chhlik’ in the Khmer language. It is one of the dominant species in Cambodian deciduous forests. We found two morphological variants of T. alata (gla- Correspondence: Eriko Ito brous and hairy types) in a hydrological and meteorolog- Email: [email protected] ical observation plot that we established in Kratie (Iida

© 2017 The Society for the Study of Species Biology 2 E. ITO ET AL. et al. 2016). The glabrous-type leaves are covered with as fuel). Most burns were initiated by hunters flushing brownish hairs when young, whereas the mature organs out game. are almost glabrous or slightly hairy underneath; in com- The plot was vegetated with a typical lowland dry parison, the mature leaves of the hairy type retain dense dipterocarp forest, in which three tree species were domi- white hairs. The production of leaves with a dense trich- nant: Dipterocarpus tuberculatus Roxb., Shorea siamensis ome cover has the potential for greater drought tolerance Miq. and S. obtusa Wall. ex Blume. Excluding the diptero- (Benzing & Renfrow 1971; Ennajeh et al. 2006; Rossatto & carps, Terminalia alata was the most common species. The Kolb 2009). The variants also differed in the duration of stem density and basal area of trees with diameter at fl the lea ess period; the glabrous-type T. alata trees had a breast height (DBH) ≥5 cm in the study plot were fi fl −1 2 −1 signi cantly and characteristically longer lea ess period 564 stem ha and 13.6 m ha , respectively (2014 cen- (>4 months) than did a hairy-type T. alata tree and other sus; Appendix). T. alata was one of the major compo- dominant tree species (<1 month, Dipterocarpus tubercula- nents in the stand, accounting for 19 and 17% of stand tus, Shorea obtusa and Xylia xylocarpa; Iida et al. 2016). The tree density and basal area, respectively. Other rarer dry dipterocarp forest studied by Iida et al. (2016) was (<2% cover) deciduous species were found, including located in a heterogeneous landscape, comprised of ele- Dalbergia spp., Pterocarpus macrocarpus Kurz and Xylia fl vated areas with shallow soils and at areas with deep xylocarpa (Roxb.) W. Theob.; these taxa usually occur in soils (Ohnuki et al. 2014). The contrasting topographic dry dipterocarp or deciduous dipterocarp forests (Royal conditions are likely to be related to differences in water Forest Department 1962; Tani et al. 2007; Pin et al. 2013). availability, which probably caused spatial differentia- A full list of tree species occurring in the study plot is tion in two variants of T. alata. In Iida et al. (2016), obser- provided in the Appendix. vations were limited to a plot of 15 × 25 m in a flat area Tertiary and Quaternary sedimentary rocks and including a flux tower, which contained one hairy-type basalts lie under the forests located on the Mekong River tree and two glabrous-type trees, too few to clarify spa- terrace (Ohnuki et al. 2008, 2012; Toriyama et al. 2010). tial patterns. Coarse-rounded quartzite gravels were found on the Here, we describe these two phenologically differen- ground surface along the flow channel. Topography, soil tiated morphologies, which differed in spatial distribution types and soil thickness were associated with one another in relation to topography, soil type and soil depth on a in the study plot (Fig. 1, Ohnuki et al. 2014). Soil types small spatial scale (within a 4-ha plot). Here, we propose and soil thickness were examined at 41 points in and three working hypotheses: (i) the hairy-type T. alata,which around the study plot (adding 17 points to Ohnuki et al. is likely to be drought-tolerant by retaining dense trichome 2014). The boundaries of the soil types were determined cover, grows abundantly in elevated areas; (ii) the glabrous on the spot by soil surface observations (Fig. 1). Soil type, which shows uniquely delayed leaf flushing, suggest- thickness was interpolated based on the field measure- ing a drought-tolerance behavior, is mainly distributed in ments using a handy dynamic cone penetrometer (S06-M; elevated areas; and (iii) both types equivalently grow in all Tsukuba Maruto, Tsukuba, Ohnuki et al. 2008, 2014). locations, suggesting no difference in drought tolerance Some elevated sections (southeastern portion of the plot) between the two types of T. alata. We also provide leaf phe- had thin Leptosols (FAO soil classification) that were nology data of both types of T. alata to support the obser- <1 m deep (mostly <50 cm deep). In the hilly areas, the vations for one hairy-type and two glabrous-type trees of basaltic bedrocks were often exposed. Flat areas (north- Iida et al. (2016). western portion of the plot) had relatively deep Plintho- sols and Arenosols that were 1.0–2.5 m deep. Plinthosols had a large clay content near the plinthite layer with large Study site accumulations of iron (Ohnuki et al. 2012). Water storage capacity in the study plot was assumed to be directly The study was conducted in a 4-ha plot (200 × 200 m) proportionate to soil thickness given an identical effective − with a flux tower in the center. The site was located in porosity of the three soil types (0.15 m3 m 3, Ohnuki Kratie Province, Cambodia (12.9N, 106.2E; elevation, et al. 2008). Leptosols had significantly thinner soils than 74–85 m). We divided the plot into 400 quadrats measur- Plinthosols and Arenosols (Fig. 2). ing 10 × 10 m, each of which contained four sub- quadrats (5 × 5 m). The mean annual temperature was 27C (Iida et al. 2016). The annual rainfall (mean Æ SD) Methods was 1643 Æ 272 mm in the period 2000–2010 (National Tree census Institute of Statistics 2012). The region has a dry season extending from November to April. Part of the plot was In our tree censuses in the study plot, we measured the burned annually (with a plentiful supply of weed grass diameters (to the nearest 1 mm at breast height,

Fig. 1 Physical conditions of the study plot. Soil type is shown with contours of elevation (revised from Ohnuki et al. 2014). Numbers are elevations (m). The square boundary line and the solid black square symbol indicate the 4-ha study plot (200 × 200 m) and the meteorological flux observation tower, respectively. i.e. 1.3 m above ground level [DBH]) of all standing Phenological observation woody stems with DBH values ≥5 cm; complete data We compared the leaf phenologies of the two types of were collected twice in the dry seasons of 2012 and 2014. T. alata through examination of leaf flushing and shed- Preliminary tree censuses were conducted in the period ding phenologies near the tower (i.e. in the center of the 2009–2011. We also identified trees to species, and 4-ha plot) from 26 February 2009 through to 2 May 2012. recorded the position of each individual based on sub- One hairy-type tree and two glabrous-type trees were quadrat location. examined three times per month (ca. day 10, 20 and 30 of each month). Another 14 glabrous-type trees and one hairy-type tree were photographed once per month. To increase the sample size of hairy-type trees to confirm leaf flushing behavior in the middle of the dry season, we made intensive observations. Leaf phenologies were observed directly on 56 and 43 hairy-type trees at sepa- rate times: (i) 8 February 2011 and 16 February 2011, and (ii) 5 February 2012. For reference purposes, glabrous- type trees were observed on the same day (n = 242 on 8 February 2011 and n = 178 on 5 February 2012). Leaf phenology was classified into three phases: (i) flushing, (ii) with mature or senescent leaves and (iii) leafless. Data were summarized as the ratios of observed trees for both types. We compared landscape-scale leaf phenologies with the leaf phenology of both types of T. alata. As indexes Fig. 2 Soil thickness by soil type. Data are shown as box- whisker plots (median, 25 and 75% quartile, range). Values that to landscape-scale leaf phenology, we measured the do not share a common superscript letter are significantly differ- plant area index (plant area per unit area) with a plant ent at P < 0.05 (Tukey-Kramer HSD test). canopy analyzer (LAI-2000; Li-COR, Lincoln, NE, USA)

Fig. 3 Phenological differences between the two types of Terminalia alata. Ratios of leaved trees for (a) the hairy type and (b) the glabrous type, and rainfall (c). Solid lines and open circles refer to data based on direct observations every 10 days and monthly photographic observations, respectively. Bars indicate leaf phenology data obtained by intensive observations. Black, white and gray bars indicate ratios of trees that were flushing leaves, leafless or with senescent leaves, respectively. Direct observations for the hairy type were missing from early March to middle April in 2009. and the leaf area index (leaf area per unit area) by We measured gross rainfall on the flux tower at a hemispherical photography (Tani et al. 2011). Data height of 30.0 m with a 0.2-mm tipping bucket type rain- were collected once per month from February 2009 fall gauge (RG-3; Onset Computer, Bourne, MA, USA; through to May 2012. Measurements were made at Iida et al. 2016) in the period following February 8 2009; 13 fixed points within the plot, including locations we used the correction function of Iida et al. (2012) to used for observations near the tower. Visual inspection take into account the inflow rate during tipping. of hemispherical images captured in February 2012 indicated that all trees were leafless. Although the study plot has a few evergreen species (Appendix), Results and discussion these were not distinguished in the images because the locations of these trees were far from the measurement We found distinct differences in leaf phenology between points. The leafless images were used to calculate stem the two types of T. alata (Fig. 3). Leaf shedding occurred and branch area indexes (stem and branch area per in late January or early February in both types. Hairy- unit area). Leaf area index using hemispherical photog- type trees produced new leaves in early February raphy was calculated by subtracting the stem and (i.e. about the middle of the dry season), in many cases branch area index from the plant area index measured before the first rains. Trees that were shedding leaves, at each measurement point. Because the acquisition of leafless or flushing occurred concurrently within the plot plant canopy analyzer data failed in February 2012, in early or middle February (Fig. 3a, bars). Leaf exchange data were shown as plant area index without subtract- behavior was observed in the hairy type; some trees ing the stem and branch area index. flushed leaves whereas some old leaves remained and

Fig. 4 Temporal changes in landscape-scale plant and leaf area indexes. Plant area index (plant area per unit area) measured with a plant canopy analyzer (a) and leaf area index (leaf area per unit area) measured with hemispherical photography (b). Data are shown as box-whisker plots (median, 25 and 75% quartile, range). were still falling. Such a leaf exchange pattern occasion- in glabrous T. alata. The leaf area index remained high ally prevented detection of a leafless period (in 2010, during the wet season (until early November, Fig. 3c), Fig. 3a). The glabrous type flushed new leaves in June or then gradually decreased during the early dry season, early July, 3 months after the start of the wet season and reached the lowest level again in February (Fig. 4). (Fig. 3c). Thus, the leafless period of the hairy type was We observed intermittent leaf shedding of deciduous estimated to be <1 month, but that of the glabrous type dipterocarps from August or September in the study plot extended over 5 months, in agreement with the observa- (E. Ito, unpublished data). Delayed leaf flushing in gla- tions of Iida et al. (2016). brous T. alata may compensate for the loss of leaves of Iida et al. (2016) reported that most of the tree species the major component species in terms of landscape-level (including the three dominant species, D. tuberculatus, leaf area index. S. obtusa and X. xylocarpa) in our study plot had leaf We found clear spatial separation of the two types of exchange phenologies in the middle of the dry season T. alata (Fig. 5). Among 400 quadrats, the glabrous and similar to that of hairy-type T. alata (Fig. 3a). The leaf hairy types occurred in 181 and 44, respectively. The two area index fell to its lowest value in February, then grad- types co-occurred in only four quadrats. The spatial dis- ually increased and peaked in July (Fig. 4). The leaf area tributions of the two types were likely to be related to index indicated that the greater part of trees in the land- differences in water availability resulting from variations scape display the leaf exchange behavior in the middle of in soil thickness, in which soil thickness was relatively the dry season. The increase in the leaf area index from deep along the flow channel of a shallow valley, and thin February through to June was probably because of in a hilly area (Fig. 5). Contrary to working hypothesis increases in the number of leaves plus individual leaf #1, the hairy type was limited to flat areas of Arenosols expansions in the major component species. Similar grad- or Plinthosols with deep soil. The glabrous type was ual increases in leaf number were found in a seasonal mainly distributed in hilly areas, but also grew in flat tropical forest in India (Devi & Garkoti 2013). Delayed areas, which partially supports working hypothesis #2. leaf flushing was restricted to glabrous-type T. alata. Our The abundance of the glabrous type in elevated areas photographic images did not detect leaf flushing in other indicates that the delayed leaf flushing is adapted to species during the June–July period (data not shown). It water-limited environments. is possible that the increase in the leaf area index after Corresponding to differences in leaf phenology, the July (Fig. 4) was partly caused by delayed leaf flushing seasonal patterns of transpiration (Iida et al. 2016) and

Fig. 5 Spatial distributions of the two types of Terminalia alata and soil thickness shown with contours of elevation in the study plot. Soil thickness was revised from Ohnuki et al. 2014. Numbers are elevations (m). The square boundary line and the inverse white circle indicate the 4-ha study plot (200 × 200 m) and the meteorological flux observation tower, respectively (m-1). photosynthesis (Kenzo et al. 2015) differed between the research coordination system, funded by the Ministry of two types of T. alata. Leaf phenology and related transpi- the Environment Japan, and the emergency project to ration and photosynthesis activities may be decisive fac- develop the structure of promoting REDD action sup- tors regulating carbon and water cycles in the ecosystem. ported by the Forestry Agency Japan. The authors are The abundance of the glabrous type in the elevated area deeply indebted to H. E. Dr Ty Sokhun, Secretariat of and its unique leaf phenology are likely to significantly State, to H. E. Dr Chheng Kimsun, Delegate of the Royal influence the landscape-scale energy transfer. Leaf phe- Government, Head of Forestry Administration at the nology is a key biophysical variable in many process- Ministry of Agriculture, Forestry and Fisheries, and to Dr based forest ecosystem and water cycle global models Sokh Heng, Director of the Institute of Forest and Wildlife (Running & Coughlan 1988; Aber & Federer 1992; Ito & Research and Development Forestry Administration, for Oikawa 2002; Tanaka et al. 2003; Gerten et al. 2004; Kang permission to undertake field research. The authors sin- et al. 2004). Models of Cambodian deciduous forests cerely thank two anonymous reviewers for constructive should incorporate the behavior of the glabrous type as comments on and corrections to the manuscript. an intraspecific variation in feedback between water availability and plant activity. References

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Appendix List of tree species occurring in the study plot Khmer names within quotation marks were provided by the local population.

Scientiﬁc name Family Khmer name Tree density Basal area − − [stems ha 1] [%]† [m2 ha 1] [%]†

Acacia harmanidiana (Pierre) Gagnep. Leguminosae THMEAS TUK 0.25 0.04 0.010 0.08 Aporosa octandra (Buch.-Ham. ex D. Don) Euphorbiaceae KRONG (sp. 1) 0.25 0.04 0.001 0.01 Vickery Aporosa villosa (Lindl.) Baill. Euphorbiaceae KRONG (sp. 2) 0.50 0.09 0.007 0.05 Bridelia retusa (L.) A. Juss. Euphorbiaceae CHHLIK PORK 0.25 0.04 0.001 0.00 Buchanania lanzan Spreng Anacardiaceae KAPRAONG 13.50 2.39 0.201 1.47 Buchanania reticulata Hance Anacardiaceae LEANG CHEY (sp. 1) 1.00 0.18 0.011 0.08 Buchanania siamensis Miq. Anacardiaceae LEANG CHEY (sp. 2) 1.75 0.31 0.045 0.33 Canarium subulatum Guill. Burseraceae TALAT/‘Pon Svar’ 0.25 0.04 0.002 0.01 Careya arborea Roxb./C. sphaerica Roxb. Lecythidaceae KANNDOL 0.75 0.13 0.009 0.07 Catunaregam longispina (Roxb.) Tirveng Rubiaceae LVIENG SOR 2.50 0.44 0.012 0.09 Catunaregam tomentosa (Bl. ex. DC.) Tirv. Rubiaceae LVIENG KROHOM 0.25 0.04 0.002 0.02 Dalbergia cochinchinensis Pierre Leguminosae KRORNHOUNG 0.25 0.04 0.001 0.01 Dalbergia cultrata Grah. ex Benth. Leguminosae ‘Ta Meaek’ 1.75 0.31 0.039 0.29 Dalbergia nigrescens Kurz var. nigrescens Leguminosae SNUOL 1.50 0.27 0.142 1.04 Dalbergia oliveri Gamb. ex Prain (syn. Leguminosae NEANG NOUN 0.25 0.04 0.005 0.03 D. dongnaiensis Pierre, D. bariensis Pierre) Dillenia ovata Wall. ex Hook. f. & Thomson Dilleniaceae LOWEY 1.25 0.22 0.009 0.06 Diospyros ehretioides Wall. ex G. Don Ebenaceae CHHOEU ROMEANG / 1.75 0.31 0.029 0.21 LOMEANG Diospyros pilosanthera Blanco var. helferi Bakh.‡ Ebenaceae TROR YING 0.25 0.04 0.007 0.05 Dipterocarpus obtusifolius Teijsm. ex Miq. Dipterocarpaceae TBENG 0.25 0.04 0.006 0.04 Dipterocarpus tuberculatus Roxb. Dipterocarpaceae KHLONG 112.25 19.91 4.205 30.82 Garcinia cowa Roxb. Guttiferae - 0.75 0.13 0.003 0.02 Gardenia obtusifolia Roxb. Rubiaceae BAKDORNG 4.50 0.80 0.013 0.10 Grewia eriocarpa Juss. Tiliaceae PO PLEAR 0.25 0.04 0.001 0.01 Heterophragma sulfureum Kurz Bignoniaceae TA KUT TAMAT 6.00 1.06 0.073 0.53 Lannea coromandelica (Houtt.) Merr. Anacardiaceae - 0.50 0.09 0.006 0.04 Lophopetalum wallichii Kurz Celastraceae ‘Pon Ta Ley’ 3.75 0.67 0.080 0.59 Madhuca stipulacea Fletcher‡ Sapotaceae SRAKUM 1.00 0.18 0.006 0.05 Melientha suavis Pierre Opiliaceae ‘Pricch’ 0.50 0.09 0.003 0.02 Mitragyna rotundifolia (Roxb.) O. Kuntze Rubiaceae KHTOM/KHTOM 5.75 1.02 0.097 0.71 PHNOM Morinda coreia Ham. Rubiaceae NHOR 0.75 0.13 0.020 0.15 Neonauclea sessilifolia Merr. Rubiaceae ROLEAY 0.50 0.09 0.030 0.22 Pavetta tomentosa Roxb. ex Sm. Rubiaceae PREAH CHHNET/PUK 0.25 0.04 0.001 0.00 CHHMAR Phyllanthus emblica L. Euphorbiaceae KANTOUT PREY 0.25 0.04 0.015 0.11 Pterocarpus macrocarpus Kurz Leguminosae THNONG KRAHAM 0.25 0.04 0.014 0.10 Shorea obtusa Wall. ex Blume Dipterocarpaceae PHCHEK 50.00 8.87 2.490 18.25 Shorea siamensis Miq. Dipterocarpaceae RAING PHNOM 227.00 40.27 2.666 19.54 Spatholobus parviﬂorus Kuntze Leguminosae CHHAR 0.25 0.04 0.001 0.01 Strychnos nux-blanda Hill Loganiaceae PRAVEK 1.75 0.31 0.013 0.09 Syzygium cumini (L.) Skeels‡ Myrtaceae PRING BAI 5.00 0.89 0.272 1.99 Terminalia chebula Retz var. chebula Retz Combretaceae SRORMOR 7.00 1.24 0.266 1.95 Terminalia mucronata Craib & Hutch. Combretaceae PRAM DOMLENG 4.00 0.71 0.221 1.62 Terminalia alata Heyne ex Roth [Hairy type] Combretaceae CHHLIK 15.75 2.79 0.749 5.49 Terminalia alata Heyne ex Roth [Glabrous type] Combretaceae CHHLIK 77.25 13.70 1.761 12.91 Vitex pinnata L. Verbenaceae POPOUL 0.50 0.09 0.009 0.06 (Labiatae) Xylia xylocarpa (Roxb.) W. Theob. Leguminosae SOKROM 9.50 1.69 0.091 0.67 Total 563.8 100.0 13.6 100.0

† The percentage of species-speciﬁc values in the total. ‡ Evergreen trees in the study plot.