Phenological Variants of Terminalia Alata Coexist in a Dry Dipterocarp Forest
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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, © 2017 The Society for the Study of Species Biology Plant Species Biology PHENOLOGICAL VARIANTS OF TERMINALIA ALATA 3 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 bound- ary line and the solid black square symbol indicate the 4-ha study plot (200 × 200 m) and the meteorologi- cal 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.