Tanzania Wildlife Discussion Paper No. 33
Dr. R.D. Baldus and Dr. L. Siege (Eds.)
THE VEGETATION OF THE SAADANI NATIONAL PARK AND POSSIBLE
CONSERVATION- AND MANAGEMENT STRATEGIES
Dr. Urs Blösch and Prof. Dr. Frank Klötzli
Deutsche Gesellschaft für Technische Zusammenarbeit Selous, Saadani and Katavi Rukwa Conservation Programmes, Community Based
Dar es Salaam 2002
The Saadani Game Reserve together with the Mkwaja Cattle Ranch and some other areas is being transformed into Tanzania’s 13th National Park. Germany has been supporting this process under the joint Technical Cooperation Programme.
One of the major objectives of the National Park will be the conservation of the unique coastal vegetation and forests. Very little is known about the Saadani ecosystem and this little paper serves as a first step of presenting some facts on the National Park’s vegetation. It also proposes possible conservation strategies to the management.
Rolf D. Baldus, Ludwig Siege
Map of Saadani National Park
The Discussion papers may contain authors’ views and positions which do not necessarily correspond with the official position of the Wildlife Division, TANAPA, GTZ and the editors
Address: Deutsche Gesellschaft für Technische Zusammenarbeit
Community Based Wildlife Conservation Programme
P.O.Box 1519, Dar Es Salaam, Tanzania
1. Introduction 4
2. Study area 4
3. The main ecosystems of Saadani, their conservation values and threats 5
3.1 Forest-savanna-grassland mosaic 6
3.1.1 Savanna formations and grassland 9
3.1.2 Small forest formations 11
3.2 Zaraninge coastal forest 12
3.3 Shoreline 15
4. Management of the National Park and its surroundings 16
4.1 Management objective 16
4.2 Management strategies 16
4.2.1 Community Based Conservation approach 16
4.2.2 Fire policy 17
4.2.3 Suggestions 18
5. Proposed applied research activities 19
6. References 20
A: Brief history of the applied research programme at Mkwaja 23
A brief biogeographical description of the Saadani ecosystem is given. The terrestrial vegetation units are defined and their dominant plant species and soil types listed. The biodiversity and conservation values of the vegetation units are assessed. A transect from the sea westward towards the inland shows the typical topographic position of the vegetation units. The dynamics of the vegetation units is briefly outlined regarding mainly the impact of fire, herbivory and cutting. Based on the vegetational description of the Saadani ecosystem management suggestions are presented stressing in particular the importance of community participation and fire. In view of a sustainable management of the Saadani National Park and its surroundings additional applied research activities are proposed. A summary of the savanna research programme at the former Mkwaja cattle ranch is attached.
Location of Saadani National Park
Other National Parks Game Reserves RubondoSerengeti NPMain Roads
Main Cities Kilimanjaro NPNgorongoro CA
Saadani NPTarangire NP
Gombe NP TaboraTanga
Mahale NPZanzibar DodomaDar es Salaam Katavi NP Mikumi NPRuaha NP Udzungwa NP
250 kmMtwara Songea
Recently the ranch of Mkwaja North has been handed over officially to Tanzania National Parks (TANAPA) for the inclusion in the proposed upgraded Saadani National Park. The thgazettement of the 13 National Park in Tanzania should be finalised in the coming months. The reserve thus could become the nucleus of nature and beach tourism along the coast between Bagamoyo and Pangani (GTZ 1999).
The goal of this report is to describe the terrestrial vegetation of the Saadani ecosystem in view of defining the respective conservation objectives and management strategies. In particular the following aspects are stressed:
a) Compilation of major ecological baseline-data from the long term savanna research
programme of the Geobotanical Institute (Swiss Federal Institute of Technology, Zurich)
at Mkwaja Ranch including ecological data about the coastal forests from the literature; b) Description of the biodiversity and conservation values of the different terrestrial
ecosystems and of their main threats;
c) Definition of the conservation objectives for the National Park and the respective
d) Identification of lacks of knowledge and proposition of additional research activities for
supporting the future management of the National Park and its surrounding.
In addition, a summary of the research activities at the former cattle ranch of Mkwaja is given in annex A.
2. Study area
Physiographical situation: The proposed National Park is situated in the Pangani District (plus a minor strip in Handeni District), Tanga Region and in the Bagamoyo District, Pwani 2Region. The protected area encloses the former Saadani Game Reserve (209 km, Tobler 22001) the former cattle ranches of Mkwaja (462 km, Tobler 2001) and Razaba (about 200 22km) and Zaraninge Forest Reserve (178 km, Peter Sumbi, personal communication). In
addition, at Madete Ranger Station (Mkwaja South) a maritime reserve is foreseen.
2The future National Park will be part of the Saadani ecosystem, an area of about 2000 km of
relatively intact continuous forest-savanna-grassland mosaic (including the coastal forest of Zaraninge) on the northern coast of Tanzania, directly opposite to Zanzibar (Milewski 1993; Baldus et al. 2001). The area is in the centre of the historically rich triangle of Bagamoyo, Pangani and Zanzibar (Baldus et al. 2001) and the vegetation has been widely influenced for millennia by human occupation (Lind & Morrison 1974). Nowadays however, the area is relatively sparsely settled (mainly Swahili people) and one of the least developed in Tanzania.
Geology: The Saadani ecosystem is found on the Mesozoic-Quaternary marine, fluviatile and lacustrine sediments (Griffiths 1993) including much clay but little coral rag. Alluvial floodplains with recent deposits occur along the larger rivers and estuaries and the zone immediately adjacent to the coast is mainly made up of relatively new marine sediment such as coral sand and clay (Milewski 1993).
Topography: The main topography varies from flat (much of the former Saadani Game Reserve and the former Razaba Ranch) to undulating (much of Mkwaja Ranch). Rivers have extensive floodplains. The major part of the former Zaraninge Forest Reserve lies on a dissected plateau between lower Wami and Mligaji Rivers, being itself the source of a short seasonal river, the Mvave River, supplying water to Saadani village (Milewski 1993). The altitude varies between sea-level and 350 m a.s.l.
Soil: Heavy, black clay-rich mbuga or black cotton soils in valleys and areas of impeded
drainage are widespread. Even on sloping ground texture is rather fine, especially in the subsoil, leading to remarkably poor drainage. The lowest lying basins along the coast are of saline clay. Hilltops and ridges of escarpment are of deep, reddish loamy sand over clay (Milewski 1993).
Climate: As in many regions of East Africa near the equator rainfall is bimodal. There is a short rainy season from October to December during which monthly averages exceed 100 mm. January and February are usually rather dry. Rains start again in March and continue until the beginning of June followed by four dryer months (Tobler 2001). The dry seasons are not very severe since the relative humidity is quite high all over the year and no month is absolutely dry.
There is an increasing rainfall gradient from south to north and from east to west. At the former ranch headquarters in Mkwaja North a mean annual rainfall of 1035 mm has been recorded (25 years; 1955 – 1979, see Bloesch 2002). The variability of annual rainfall is 1particularly high with a coefficient of variation of 30 %. This high annual rainfall fluctuation
reflects the constantly varying impact of two rainfall systems in this area, i.e. the wetter northeast monsoon regime from Tanga and the drier southeast monsoon regime from Dar es Salaam (Walter & Lieth 1960). The rainfall patterns within the Saadani ecosystem are not only remarkably irregular in time but also in space and therefore quite unpredictable.
The mean annual temperature is 26 ?C with an annual range of 5 ?C and a daily range of 8 ?C (Milewski 1993). The climate type in the Köppen system is Aw (Köppen 1931).
3. The main ecosystems of Saadani, their conservation values and threats
The future national park will be the only protected area in Tanzania bordering the sea. It offers the unique combination of terrestrial and maritime ecosystems. It will include four main vegetation complexes:
- A heterogeneous forest-savanna-grassland mosaic;
- The ancient coastal forest on the Zaraninge Plateau;
- A shoreline with salt flats, coastal fringe forests, herbaceous dune vegetation and
- A maritime ecosystem (this ecosystem will not be further treated in this report).
In the following we give as a brief ecological description of the main natural terrestrial vegetation units (including some typical species), their conservation values and threats.
1 The coefficient of variation for the annual rainfall is defined as standard deviation expressed as a % of the mean.
Cultivated areas and fallow land will not be described in this report. A typical transect
through the main vegetation units is given in Fig. 1.
3.1 Forest-savanna-grassland mosaic
The major part of the Saadani ecosystem consists of a rich forest-savanna-grassland mosaic. Humid savannas with a highly variable woody cover largely dominate this savanna landscape, while small forest formations and grasslands are irregularly interspersed. For the nomenclature we widely follow the classification of Yangambi (Scientific Council for Africa South of the Sahara 1956). We recognise that the word “savanna” has been used in so many different ways and we are aware that some workers, especially in East Africa (Greenway 1943; Pratt et al. 1966; Lind & Morrison; White 1983) have therefore rejected its use. We nevertheless think that the term is a very appropriate one. Savannas do not represent an ecological intermediate case between forests and grasslands but they represent an own biome with typical floristic composition, structure and function (see Klötzli 2000; Bloesch 2002). The strong and complex interactions between the woody and herbaceous plants give this vegetation a character of its own (Scholes & Walker 1993). For our purpose we define the term savanna following Bourlière & Hadley (1970):
“Savanna is a tropical or subtropical formation: 1) where the grass stratum is continuous and important, occasionally interrupted by trees and shrubs; 2) where bush fires occur from time to time; and 3) where the main growth patterns are closely associated with alternating wet and dry seasons.”
Water and nutrient supply (depending on climate and soil type) are referred to as primary determinants of savannas, because they define and constrain the potential consequences of herbivory and fire (Scholes & Walker 1993). Geomorphology (relief) influences widely the significance and the interactions of these four main determinants (Bloesch 2002). Furthermore, termitaria may favour the growth of woody plants (see Bloesch 2002).
The savannas are very dynamic (physiognomy) whereby their woody cover (encroachment) mainly depends on fire, herbivory and cutting (see Fig. 2). The balance between grasses and woody plants in many savannas is a labile one, and bush encroachment due to inappropriate management techniques is a widespread phenomenon. Bush encroachment is mostly caused by overgrazing as well as sudden cessation of grazing or reduced browsing pressure, by fire exclusion and frequent low intense early dry season burning (see Bloesch 2002).
The main vegetation units of the Saadani ecosystem and their dynamics 9
GL TSGS GL GL SF TSAZ GF CF HDV
Impact of fire / highly variable moderately herbivory on highly variable woody cover quite woody variable physiognomy quite stable stable none stable quite stable stable none (bush encroachment) stable woody cover
Impact of transform. extensive cutting into open transformation transformation transform. into bush savanna none bush encroachment none none none open savanna none into dense thicket encroachm. into open savanna on physiognomy
Fig. 1. The woody cover of tree, shrub and grass savannas is highly variable depending on fire, herbivory and cutting. These formations are
susceptible to bush encroachment. On the other hand, savanna woodland is more stable; extensive cutting, however, provokes its transformation into shrub/grass savanna. The other vegetation types are quite inert to herbivory (at low browsing intensity) and occasional fires. Extensive cutting, however, will transform gallery forest and coastal fringe forest into open savanna susceptible to erosion. Extensive cutting in hilltop forest will lead to dense degraded thicket due to many resprouting species. The Zaraninge coastal forest is not shown on the transect.
SW: savanna woodland GL: grassland HF: hilltop forest TSGS: tree to grass savanna with interspersed thicket clumps GF: gallery forest TSAZ: natural tree savanna
with Acacia zanzibarica SF: salt flat CF: coastal fringe forest HDV: herbaceous dune vegetation
Fig. 2. Schematic diagram of main factors determining tree-grass ratio in a savanna
landscape (from Bloesch 2002). 1) In East Africa, however, communities at the low end of rainfall gradient are dominated by thorn- scrublands, not by grasslands.
2) Relatively few savanna trees are adapted to seasonal waterlogging (Acacia zanzibarica, Balanites
aegyptiaca, Hyphaene compressa).
3) Most savanna trees have a high capacity of spreading clonally (coppice shoots and/or root suckers).
Based on old aerial photographs we suppose that prior to 1952 the vegetation structure at the former Mkwaja Ranch (1952 – 1996/2000) was similar to that of the Saadani Game Reserve
with a large part of open savannas. Nowadays Mkwaja has a up to three times higher encroachment ratio than the Saadani Game Reserve, especially in the vicinity of former paddocks where cattle were kept at night (Klötzli 1980a; Tobler 2001). Most of the encroached savannas at Mkwaja are dense stands of Acacia zanzibarica. This very
competitive species can adapt to a wide range of soil conditions and has a high regeneration potential from remaining rootstocks and / or seedbanks after cutting (Johansson & Kaarakka 1992). But also the doum palm Hyphaene compressa and to a lesser degree Acacia nilotica, A.
mellifera, Dichrostachys cinerea and Harrisonia abyssinica are susceptible to encroachment.
The replacement of a diverse community of native herbivores comprised of grazers and browsers by a single grazing species at Mkwaja changed the type of herbivory; bushes became favoured what triggered the encroachment. Wild herbivores migrate as an adaptation to spatial and temporal variations in the vegetation, while domestic herbivores are more or less restricted in their movements (Tobler 2001). This led to frequent overgrazing around paddocks what did not only directly weaken the grass sward but it also indirectly induced cool burning which favoured the woody components especially by increased sprouting (Bloesch 2002). Furthermore, brush cutting and other measures to control woody plants were not successful and some measures even favoured further encroachment (see annex A).
Klötzli (1980a, 1980b) concluded that any kind of weakening the grass sward (overgrazing, brushcutter, chemical control methods) leads to bush encroachment, especially after drought periods (bushes have access to water in deeper layers). Moreover, the active control of bush fires on the former ranch has certainly contributed to the rapid bush encroachment in many areas (see also 4.2.2).
3.1.1 Savanna formations and grassland
We may distinguish between five naturally grass-dominated vegetation types (see Fig. 1): Woodland savanna, tree savanna, shrub savanna, grass savanna and grassland.
Westward, probably due to increasing rainfall tree density increases eventually leading to savanna woodland having some Miombo characteristics. However, the physiognomy is still savanna-like with a high proportion of Acacias and only a limited number of Caesalpiniaceae
(e.g., Brachystegia sp.). Typical Miombo woodland would be characterised by the
overwhelming importance of Caesalpiniaceae trees of the genera Brachystegia, Julbernardia
and Isoberlinia (Lind & Morrison 1974; White 1983). Miombo woodland occurs in areas with a single dry season (Ernst 1971).
Dominant trees within the savanna woodland are Acacia polyacantha, Acacia robusta, Albizia
sp., Lannea stuhlmannii and Pteleopsis myrtifolia. The continuous tall grass cover is mostly
composed of millet grasses (e.g., Panicum maximum). Oxisol is widespread within savanna
woodland. On smooth ridges mainly orthic Oxisol occurs while in soft depressions humic Oxisol and on slope acric or rhodic Oxisol prevail. The texture is reddish loamy sand over clay.
A vast area between the shoreline and the savanna woodland more inland is covered with different types of tree, shrub and grass savannas and grassland (less than 2% canopy cover)