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Liana Abundance and Diversity in Cameroon's Korup National Park

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Liana Abundance and Diversity in Cameroon's Korup National Park Trim Size: 189mm x 246mm Schnitzer p02.tex V2 - September 3, 2014 9:59 P.M. P. 11 Part II Patterns of Liana Demography and Distribution: From local to Global 11 Trim Size: 189mm x 246mm Schnitzer c02.tex V3 - September 11, 2014 2:18 P.M. P. 13 Chapter 2 LIANA ABUNDANCE AND DIVERSITY IN CAMEROON’S KORUP NATIONAL PARK Duncan Thomas,1 Robyn J. Burnham,2 George Chuyong,3 David Kenfack,4 and Moses Nsanyi Sainge5 1School of Biological Sciences, Washington State University, Vancouver, Washington, USA 2University of Michigan, Ann Arbor, MI, USA 3University of Buea, Buea, Cameroon 4Center for Tropical Forest Science, Smithsonian Institution Global Earth Observatory, Smithsonian National Museum of Natural History, Washington, DC, USA 5Tropical Plant Exploration Group, Mundemba, Southwest Region, Cameroon Ecology of Lianas, First Edition. Edited by Stefan A. Schnitzer, Frans Bongers, Robyn J. Burnham, and Francis E. Putz. © 2015 John Wiley & Sons, Ltd. Published 2015 by John Wiley & Sons, Ltd. Companion Website: www.wiley.com/go/schnitzer/lianas 13 Trim Size: 189mm x 246mm Schnitzer c02.tex V3 - September 11, 2014 2:18 P.M. P. 14 14 Patterns of liana demography and distribution: from local to global OVERVIEW defined as climbers that develop secondary wood and are rooted in the soil. Rattan palms, hemiepi- The lianas (≥1 cm stem diameter) in an 18-ha plot phytes/stranglers, and other categories of climbing of lowland rainforest in southern Cameroon were plants that do not meet the narrow definition were surveyed to document the structure and species included in the census in Korup but excluded from composition of the liana flora, and to compare the this account. abundance and diversity of lianas to that of trees in the The study site is near the town of Mundemba at same area. The liana crowns were concentrated in the 160 m a.s.l, 5.074o N, 8.855o E, 30 km inland from middle and lower canopy of the forest. We found a total estuarine mangrove swamps, and 70 km from the of 256 species in 77 genera and 31 families. When Atlantic Ocean in the Bight of Bonny. Following botan- compared to trees of the same diameter, lianas are ical and primatological studies in Korup National both less abundant than trees (9023 versus 119,027) Park in the 1970s and 1980s (Gartlan & Struhsaker and less speciose (256 versus 409). We also found 1972; Gartlan et al. 1986; Newbery & Gartlan 1996; that the tree community in the mid/lower canopy is Usongo & Amubode 2000), a long-term forest mon- fairly strongly dominated by a single species (Oubanguia itoring plot was established in 1996. Each census alata), while several liana species share dominance, of the 50-hectare plot (1000 × 500 m) includes all each comprising a smaller portion of the dominance trees and saplings at least 1-cm diameter at breast structure. As a result, liana diversity measured by height (dbh): all tagged, measured, mapped, and several commonly used indices equals or exceeds that identified (Thomas et al. 2003; Kenfack et al. 2007; of the trees. This creates a forest canopy where trees http://www.ctfs.si.edu/site/Korup/). Two complete and lianas both make large but different contributions tree censuses have been conducted, in 1997–1999 to fruit and pollen/nectar resources. The liana com- and in 2008–2009. In 2000–2002 and 2011–2012, munity adds at least ten angiosperm families that are two liana censuses for stems ≥1 cm were conducted in not represented in the Korup tree flora, broadening 18 ha of the 50-ha plot. The 18-ha liana census area the phylogenetic diversity of the forest. About 80% is in lower elevation forest on gentle topography at the of the 77 liana genera in the plot are unknown as southern end of the 50-ha plot, in a mosaic of swampy trees, adding further to diversity above the species creeks and uplands (Figs. 2.1B, 2.1C). level. Lianas in Korup are overwhelmingly dispersed by Proximity to the ocean, the presence of surround- animals or by ballistic means, which contrasts with the ing hills, and the onshore wet winds during much high incidence of wind dispersal among neotropical of the year create a very wet climate, with a mean liana species. annual rainfall of 5272 mm (1973–1994 data), as measured 20 km away (Chuyong et al. 2004). Korup experiences a short dry season with 3 months INTRODUCTION (December–February) averaging less than 100 mm precipitation. The remaining 9 months all aver- Data on liana density have become more common age well over 100 mm precipitation, with average from forests worldwide. However, it still remains a monthly rainfall peaking at over 900 mm in July challenge to find accurate or extensive data on the and August. Because of the 3-month dry season, species comprising the liana community in tropical Korup vegetation is classified as moist tropical ever- forests. While comparisons among tree communi- green forest. However, the length and intensity of ties are slowly emerging from large-plot consortia the wet season are unusual among tropical moist (DeCáceres et al. 2012), liana data are still largely forests, and “wet seasonal evergreen forest” might lacking and this is especially true for African forests. be a better description. Mean daily maximum tem- ∘ Here, we describe a study of lianas conducted in perature is 32.6 C, with a diurnal range of about ∘ the Korup National Park, located in Cameroon’s 10 C. Month-to-month and season-to-season vari- Southwest Region, adjacent to the Nigerian border ation is less than the diurnal range. Mean daily (Fig. 2.1). We focus on liana abundance, species maximum temperatures are highest in February ∘ richness, dominance, and diversity, with compar- (32.8 C), a dry season month with low cloud cover, isons to these attributes for the tree community in and lowest in August in the middle of the wet season ∘ the same area. For our study, lianas are narrowly (27.8 C). Trim Size: 189mm x 246mm Schnitzer c02.tex V3 - September 11, 2014 2:18 P.M. P. 15 Liana abundance and diversity in Cameroon’s Korup National Park 15 A B 90 m 1000 m Liana census area m 500 × 360 m 500 500 m 0 m 500 m 18 ha liana census area 1000 m C Fig. 2.1 (A) Africa, showing study area in western Cameroon (arrow); additional dot is Ituri Plot in DR Congo. (B) 3-D map of the Korup Forest Dynamics Plot showing the location of the liana census area at the flatter south end. (C) 50-ha Korup Forest Dynamics Plot showing the location of the 18-ha liana census area (right of vertical line) and pale areas of sparse tree cover, including rock outcrops (lower left) and creeks/swamps elsewhere. (Source: Fig. 2.1 A, adapted from United States Geological Survey vegetation map. Reproduced with permission.) Distribution patterns of the Korup tree species have Lower Guinea forest and the tree flora shows strong been studied relative to the major African phytochoria floristic affinities with this forest block. Approximately (Kenfack et al. 2007), based on the three main blocks of 33% of the tree species in the plot are known only African moist tropical forest described by White (1979, from the Lower Guinea forest (Kenfack et al. 2007), 1983). The large Congolian forest block falls largely and though we have not yet completed this analysis in the basin of the Congo River, the Lower Guinean for lianas, we expect to find similar affinities for the forest covers the coastal belt from southeastern Nigeria liana flora. through Gabon, and the Upper Guinea forest is dis- Trees are less dense in the wetlands (Fig. 2.1C) and tributed mostly in Liberia, the Ivory Coast, and Ghana. in treefall gaps. Korup experiences thunderstorms, The 50-ha plot is located at the western end of the especially during the onset of the wet season, resulting Trim Size: 189mm x 246mm Schnitzer c02.tex V3 - September 11, 2014 2:18 P.M. P. 16 16 Patterns of liana demography and distribution: from local to global in blow-downs or lightning strikes. These disturbances ex Engl.) Pierre ex Dubard (Sapotaceae), with 10.3% of tend to be small, limited to a few trees or large branches, the trees ≥50 cm dbh. The largest tree is an individual and the large tropical storms that cause widespread of Desbordesia glaucescens (Engl.) Tiegh. (Irvingiaceae) forest damage in other parts of the tropics are unknown at 197 cm diameter. However, five of the ten largest in Korup (Thomas et al. 2003; Egbe et al. 2012). In the trees are Lecomtedoxa klaineana, so this species is one of general area of Korup, large gaps result from shifting the major dominants in terms of biomass. cultivation, rather than from storms. The Korup plot The liana data presented here are based on the sec- shows no signs of former cultivation, and is currently ond (2011–2012) census in Korup, which includes protected within a national park, so large canopy the most accurate identifications of the largest number gaps favoring the establishment and growth of lianas of individuals. Comparisons with data from the first and pioneer tree species are absent. Consequently, 2001–2002 liana census are made where appropri- conditions in the plot are less conducive to the estab- ate. The tree data reported here are drawn from the lishment of lianas than in most other tropical forests. 2008/2009 second tree census. Analyses are pre- Many liana species in Korup produce shade-tolerant sented as summary statistics for the complete set of tree-like saplings, which survive in the dark, forest 18 hectares that were censused, with all calculations understory, where they compete with tree saplings and performed with software available in Microsoft Excel or with understory trees (unpublished data).
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