Data sources

Taylor (1960), Hall & Swaine (1981), De Koning (1983), Hawthorne (1994, 1995a), Swaine (1996)

Altitude

River

Coast

Mean Annual Rainfall

Soil CMK

Soil WHC

>500m

>500m

<2km

<5km

Zanthoxylum psammophilum (Aké Assi) Waterman

Rutaceae

Phenology

Guild: pi

Life form: woody climber

Max. diameter: 2 cm (Ake Assi 1960)

Leaf: imparipinnately compound, 30-40 cm long,

7-15 alternate leaflets, ovate to oblong, notophyll

(4-6 x 6-13 cm), glabrous, shiny below; petiole and rachis not so spiny

Inflorescence: dioecious; terminal, branched (panicle), male inflorescence 21-30 cm long; female inflorescence 3-5 cm long Flower: male and female flowers small (2.5 mm long), 5-merous, white

Fruit: dry dehiscent (capsule), globose (approx. 0.5 cm in diameter); 1 seed

Seed: medium-sized (0.4 cm in diameter); black or bluish

Other: Zanthoxylum spp. are easily recognised from their bark and slash alone. The bark is covered with broad-based woody prickles. The slash is yellow-orange, fibrous, and with a characteristic very fruity-acidic taste.

Data sources

Ake Assi (1960), IUCN Red List (2000), Hawthorne & Jongkind (2004)

Distribution

Continent: Upper Guinea endemic

Upper Guinea: Cöte d'Ivoire (herbarium, Ake Assi

1960)

Distribution type: continuous, very local, present in 2 30' cells, distribution range is 87 km, Red List species (Endangered)

Forest type: coastal forest (Ake Assi 1960)

Habitat

Data unavailable.

5°30'

5°00'

4°30'

ra1

3°30'

3°00'

spp

n

Open (n)

Altitude

River

Coast

Mean Annual Rainfall

Soil CMK

Soil WHC

>500m

<2km

<5km

D

M

W

II

L

M

H

L

M

H

Z.p.

0

0

0

0

100

0

0

100

0

0

0

100

0

All

1146333

37

4

39

7

37

29

24

10

6

69

25

36

13

39

Introduction

A. Siepel, L. Poorter and W.D. Hawthorne

Ecological profiles of large timber species

Introduction

Large tree species fulfil an ecologically and economically important role in West African forests. Because of their sheer size, they determine to a large extent forest structure and functioning. From a commercial point of view, there is a longstanding interest in forest exploitation in West Africa, not in the least because of the proximity to European markets. The timber trade began as early as 1816, with the shipment of Khaya logs to London (Harcourt et al. 1992, Parren & de Graaf 1995). From a regional point of view, timber exploitation really took off in the 1950s to peak in the 1970s in Côte d'Ivoire (Chatelain et al., chapter 2), and a little bit later in the neighbouring countries. Especially in Sierra Leone and Côte d'Ivoire commercial species have been overexploited or forests have disappeared (Harcourt et al. 1992, Parren & de Graaf 1995, Chatelain et al., chapter 2). There is a strong awareness that a more sustainable forest management is needed, be it through forest plantations, recuperation of degraded areas, line plantation or assistance of natural regeneration (Bongers et al., chapter 8, Parren & de Graaf 1995). For an effective management information is needed on the distribution, ecology, and growth requirements of these large timber species. Over the past century, such information has gradually been accumulated by the foresters and botanists active in the region (Aubréville 1959, Taylor 1960, Voorhoeve 1965, Hall & Swaine 1981, Hawthorne 1995a, Kasparek 2000).

In this chapter we present ecological profiles for 56 large timber species. We have made an effort to summarise the existing knowledge on these species, and to give an idea of their environmental requirements by combining data on species abundance with GIS layers on the environment. In the following pages, we describe the metadata behind the ecological profiles. First we present information on species selection and abundance, then on the environmental data and the analyses used, and finally we describe the format of the ecological profiles.

Princess Diana Dead Body
Figure 10.1 A large tree of a large timber species; an Entandrophragma candollei of 7m dbh in Forêt Classée Haut Sassandra in Côte d'Ivoire.

Species data

Species selection

The focus of this chapter is on the large commercial tree species of Sierra Leone, Liberia, Côte d'Ivoire and Ghana. These countries contain most of the forest in Upper Guinea and are relatively well studied. To compare the different areas we selected 56 species that were inventoried in all countries. For some genera the species are pooled because in some countries the species were identified to genus only (this is the case for Afzelia, Berlinia, Celtis, Entandrophragma, Erythrophleum, Khaya, Milicia, Parinari). In addition some species were added that occur in one country and are absent in the others (for instance Tetraberlinia tubmaniana is only found in Liberia). Most of the species have maximum sizes of over 40m in height and over 100cm in diameter. The 56 selected species represent the most important current and potential timber species in West Africa. Most of these species were used to make the forest map of Upper Guinea (Bongers et al., chapter 4). Synecological information on these species can therefore be found in chapter 4.

Species abundance

In total, species abundance data were collected for 171 forest sites; 3 for Sierra Leone, 26 for Liberia, 37 for Côte d'Ivoire and 105 for Ghana. For some species data were available for 5 additional sites in Sierra Leone. The data were collected by various organisations. For Sierra Leone data were used from Small (1952), Savill & Fox (1967) and Davies (1987). For Liberia data were used from the German Forestry Mission to Liberia (GFML 1967a, 1976b, Sachtler & Hamer 1967a, 1967b and Sachtler 1968) and the Liberian Forest Service. For Côte d'Ivoire we drew largely on data collected by SODEFOR (Clément & Guinaudeau 1973, SODEFOR 1978, 1979) and for Ghana the national forest inventory data were used (Wong 1989, Hawthorne 1995a). In Liberia and Côte d'Ivoire only a number of large timber tree species have been surveyed (in each country c. 60 species), whereas in Ghana all species with a diameter at breast height (dbh) over 30 cm were taken into account. The inventoried area of each site is variable and ranges from 10 to 4500 ha (Appendix 2). Inventories vary from complete inventories to strip inventories. The 171 sites cover a wide range in environmental conditions (Table 4.2).

For the abundance data the number of trees > 30cm dbh per square km was used. In Ghana all trees > 30cm dbh were inventoried and data are available on individual trees. All Liberian and Sierra Leonean sites had data for trees over 40 cm dbh and for Côte d'Ivoire various lower limits were available (> 10 cm, > 15 cm, > 20 cm, > 40 cm and > 60 cm). To be able to compare all sites we estimated for each of the sites the number of trees > 30 cm dbh per km2. Transformation values were based on the Ghanaian data. For the Ghanaian data, for each species (thus the pooled data for all sites together) frequency distribution diagrams for size classes were constructed. Such a frequency distribution shows an idealised population structure. Most species then show a negative exponential pattern with size. For each species a negative exponential curve was fitted on the frequencies by size class. The regression was used to estimate numbers of trees > 30cm for each of the sites in Sierra Leone, Liberia and Côte d'Ivoire. This assumes that in the sites studied the frequency distributions would be similar to the idealised population structure. For the large sample sizes this is a reasonable supposition.

Environmental data

Species distributions are strongly shaped by water availability (rainfall, soil water holding capacity), soil fertility (expressed as sum of exchangeable cations, CMK; Ca2+, Mg2*, K+) and altitude. Maps of these environmental variables were prepared and included in a Geographical

Information System (ArcView, ESRI 1995). In the introduction to chapter 9 a more extensive description is given of the metadata behind these maps.

Species responses to the environment

A multiple regression was carried out to model species abundance as a function of four environmental factors; altitude, annual rainfall, soil water holding capacity, and available cations. A stepwise forward regression was used, with the simple and quadratic variables, but without including interaction terms. A significant simple variable indicates an increasing or decreasing probability to find the species with an increase in the environmental variable. A significant quadratic variable indicates that the species shows a bell-shaped response curve towards that environmental variable (Jongman et a/.1987).

Explanation of the species descriptions

In the following section of the atlas ecological profiles of the species are presented, covering one species per page. Each species account includes a distribution map, a photo and/or drawing, and an environmental table. First a short botanical description of the species is given. The aim of the description is to give the reader an impression of the species. For a more detailed, taxonomical description we refer the reader to the Flora of West Tropical Africa (Keay 1954, 1958a, 1963, Hepper 1968, 1972), the newly published The Woody Plants of Western African Forests (Hawthorne & Jongkind 2004) or other publications (Aubreville 1959, Taylor 1960, Voorhoeve 1965, Savill & Fox 1967, Keay 1989). The botanical description is followed by information on its chorology and its rarity. The environmental requirements of the species are described in terms of light, water and nutrient availability. Finally, regeneration, growth characteristics and main uses of the species are discussed. Each description is accompanied by a table with a quantitative summary of the environmental requirements and the most relevant literature references. For the ecological profiles we drew largely on information given by Voorhoeve (1965) and Hawthorne (1995a). For a detailed description of the format of the species accounts, see the introduction to the ecological profiles of the rare and endemic species (Holmgren et al., chapter 9).

The ecological profiles of the large timber species deviate from those of the rare and endemic species at some points. For example, the wood density is given if available, and there is an extra guild "sw" for species that grow in swamps. The description of countries of occurrence and forest types is less extensive, and largely based on Voorhoeve (1965). The habitat requirements are based on the literature, and inferred from the multiple regression analyses (see above). The description of regeneration characteristics is more extensive, and includes information on growth rates. For only a few species histograms are presented on the reproductive phenology as in general few herbarium collections were available for large species.

Species distribution maps

Information on species distribution is only presented in one distribution map. For some genera the species were identified to genus only (e.g., Celtis, Entandrophragma, Erythrophleum, Khaya, Milicia). For these genera only one map is available, representing the pooled abundance of the species. In some cases this results in an indistinct pattern, because both dry and wet sister taxa are pooled. For example, Khaya grandifoliola occurs mainly in dry semi-deciduous forest whereas Khaya ivorensis occurs mainly in the wetter forest types. The species abundance, expressed as number of stems larger than 30 cm dbh per km2, is given for each of the 171 forest sites. The size of the symbols indicates the log-transformed abundance of the species. A large symbol indicates a high abundance, a small symbol a low abundance or absence. Based on these data an interpolation map was made, using the inverse distance weighting interpolation method in ArcView, and taking the 12 nearest forest sites into account. The interpolated abundance is shown in 8 classes; 0-1, 1-10, 10-20, 20-40, 40-80, 80-160, > 160 individuals per km2. Interpolation was only done for the potential forest zone of Upper Guinea (see chapter 9). One should realise that these maps are likely to present only the potential distribution of the species, as the data are largely based on pre-logging forest inventories carried out in the 1960s and 1970s. The exception is Ghana, were inventories have been carried out in the 1990s. In reality, much of the forest cover, and many large individuals have disappeared in the meanwhile, because of forest exploitation or forest conversion (see also Chatelain et al., chapter 2).

Environmental table

The environmental table provides a quantitative summary of the environmental requirements of the species. It indicates in what percentage of the forests a species if found, where the species is present, and if the species is found above 400 m altitude. The rainfall gradient is divided in 4 classes; Dry (< 1500), Medium (1500-2000), Wet (2000-2500) and Very Wet (> 2500 mm/yr). The total available cations (CMK) of the soil is divided in the classes Low (0-4), Medium (4-8) and high (> 8 cmolc/kg) and the Water Holding Capacity (WHC) of the soil is divided in Low (< 50), Medium (50-85) and High (> 85mm water/m soil).

Information on the environmental conditions where the species is found, is only interesting when comparing it to the full range of environments in which all forests are found. To this end information on the focal species is presented in the first line, and the environmental conditions of all 198 forest sites (the 171 analysed plus 27 additional ones) included in the analysis are presented in the second line.

to symbols in maps and tables of chapter 10

Predicted species abundance (# stems >30 cm diameter at breast height/km2)

0 -1 1 -10 10 - 20 20 - 40 40 - 80 80 -160 > 160

area outside potential forest zone

Observed species abundance (# stems >30 cm diameter at breast height/km2)

0

0,5

1,25

6,25

25

100

o

400

O

> 2240

Environmental tables

Spp species n number of forests in which the species is found

Altitude % of records found at altitudes > 400 m Mean annual rainfall

% of records found in (D) relatively dry areas: < 1500 mm/yr, (M) intermediate areas: 1500-2000 mm/yr, (W) wet areas: 2000-2500 mm/yr, and (VW) very wet areas: > 2500 mm/yr Soil CMK % of records found on soils with (L) low availability of cation: 0-4 cmolc/kg,

(M) intermediate availability of cation: 4-8 cmolc/kg, and (H) high availability of cation: > 8 cmolc/kg Soil WHC % of records found on soils with (L) low water holding capacities: < 50 mm water/m soil, (M) intermediate water holding capacities: 50-85 mm water/m soil, and (H) high water holding capacities: > 85 mm water/m soil sea

Albizia ferruginea (Guill. & Perr.) Benth.

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