Biodiversity in Southern Africa

Namibia ISBNNamibia ISBN Germany ISBNGermany ISBN Biodiversity in

9 789991 6573019 789991 657301 9 783933 1174419 783933 117441 Southern Africa

Biodiversity is important for sustaining life on Earth yet it is threatened globally. The BIOTA V ol. 2 Southern Africa project analysed the causes, trends, and processes of change in biodiversity in 2 Namibia and western South Africa over nearly a full decade, from 2001 until 2010. This book, Patterns Patterns and Processes which is comprised of three volumes, offers a summary of the results9 783933 from the 1174589 many 783933 and 117458 diverse 9 789991 6573189 789991 657318 and subprojects during this fi rst period of long-term observation and related research, at both local Processes at Regional Scale and regional scales, and with a focus on sustainable land management options for the region. at Regional Scale

ISBN-Namibia ISBN-Germany PUBLISHERS KLAUS HESS

9 783933 117465 9 789991 6573259 789991 657325 9 783933 117465

9 783933 1174729 783933 117472 9 789991 6573329 789991 657332 © University of Hamburg 2010 All rights reserved

Klaus Hess Publishers www.k-hess-verlag.de

ISBN all volumes: 978-3-933117-44-1 (Germany), 978-99916-57-30-1 (Namibia) ISBN this volume: 978-3-933117-46-5 (Germany), 978-99916-57-32-5 (Namibia)

Printed in Germany

Suggestion for citations:

Volume: Schmiedel, U., Jürgens, N. (2010) (eds.): Biodiversity in southern Africa 2: Patterns and processes at regional scale. Göttingen & Windhoek: Klaus Hess Publishers.

Article (example): Petersen, A., Gröngröft, A., Mills, A., Miehlich, G. (2010): Soils along the BIOTA transect. – In: Schmiedel, U., Jürgens, N. (eds.): Biodiversity in southern Africa 2: Patterns and processes at regional scale: 84–92. Göttingen & Windhoek: Klaus Hess Publishers.

Corrections brought to our attention will be published at the following location: http://www.biota-africa.org/biotabook/

Cover photograph: Giraffes on the game farm Omatako Ranch (Observatory S04 Toggekry) in the Namibian Thornbush Savanna. Photo: Jürgen Deckert, Berlin/Germany. Cover Design: Ria Henning

IV Article III.3.4 – Author’s copy –

Please cite this article as follows:

Büdel, B., Deutschewitz, K., Dojani, S., Friedl, T., Darienko, T., Mohr, K. I., Weber, B. (2010): Biological soil crusts along the BIOTA Southern Africa transects. – In: Schmiedel, U., Jürgens, N. [Eds.]: Biodiversity in southern Africa. Volume 2: Patterns and processes at regional scale: pp. 93–99, Klaus Hess Publishers, Göttingen & Windhoek.

Biological soil crusts along the BIOTA Southern Africa transects

BURKHARD BÜDEL*, KIRSTIN DEUTSCHEWITZ, STEPHANIE DOJANI, THOMAS FRIEDL, TATYANA DARIENKO, KATRIN I. MOHR & BETTINA WEBER

tural composition of soils infl uences the Summary: Biological soil crusts (BSCs) were reported from six out of seven presence and diversity of BSCs. biomes along the BIOTA Southern Africa transects. Seven morphological BSC types were distinguished: three cyanobacteria-dominated crusts (types 1and 2), one with additional cyanolichens (type 3), one type with chlorolichens (4), and Material and methods BIOTA transects BIOTA one with bryophytes—either liverworts (type 5a) or mosses (type 5b). The hy- For a detailed description of material and polithic crust type (6) was restricted to quartz gravel pavements, and another methods see Büdel et al. (2009). one comprised the unique lichen fi elds of the Namib Desert (type 7). In total, at least 120 different species with 58 cyanobacteria, 29 green algae, one het- erokont algae, 12 cyanolichens, 14 chlorolichens, two genera of liverworts, Results and three genera of mosses were found, placing these BSCs among the most Classifi cation of biological diverse worldwide. They contribute considerably to the biodiversity of the arid soil crusts and semi-arid regions of south-western Africa. The taxonomic diversity of cy- Seven main BSC types were distinguished anobacteria was higher in the winter rainfall zone than in the summer rainfall in the 28 Observatories along the BIOTA zone (54 versus 32 species). Soil photosynthetic biomass, carbon content and transects (Figs. 1, 4–9). (1) Early succes- the number of BSCs revealed the same signifi cant distribution patterns. Rainfall sional crusts were brittle, less than three frequency and duration of dry periods rather than the precipitation amount seem millimetres thick, and could be recognised to be the main factors infl uencing BSC growth and succession. This article is with the naked eye by a slight and patchy discoloration of the soil surface (Fig. 4). mostly based on the publication of Büdel et al. (2009). They were composed of fi lamentous cy- anobacteria, e.g. Microcoleus and Lep- tolyngbya. (2) The intermediate succession Introduction that was later named the “hypolithon” crust was a well established cyanobacterial (Schlesinger et al. 2003). Cyanobacterial crust, up to 3.9 mm thick, and included ad- Biological soil crusts (BSCs) are an inte- soil crusts have been reported from the ditional cyanobacterial species. The soil gral component of dry lands on all con- Kalahari region in South Africa, where was not only stabilised by the presence of tinents. They are an assemblage of mi- they cover 11 to 95% of the Kalahari this crust type but also had a predominant- croorganisms including cyanobacteria, ground surface (Thomas & Dougill 2006, ly dark discoloration on its surface. When algae, microfungi, lichens, liverworts and 2007). undisturbed, this type could develop into mosses in different proportions, which In this investigation, we tested the fol- the late succession crust, which included stabilise the upper few millimetres of the lowing hypotheses: (1) the presence of (3) cyanobacterial lichens (Fig. 5), (4) soil (Belnap et al. 2001) Their signifi cant BSCs on the soils of arid and semi-arid chlorolichens or both (Fig. 6). Where pre- role within terrestrial ecosystems has biomes is the rule and not the exception; cipitation events like rain or dewfall were only been recognised since the mid 20th (2) BSCs contribute considerably to the frequent enough, (5a) liverworts (Fig. 7) or century (Halperin et al. 1976, Komáromy biodiversity of these biomes and are the (5b) mosses developed. Later on, type 5a 1976, Rogers et al. 1966, Shields et al. primary colonisers of bare soils after and 5b may have occurred without cyano- 1957, Skarpe & Henriksson 1987). disturbances of either natural or artifi - bacteria and lichens. (6) Hypolithic crusts Within the sub-Saharan region, the cial disturbances; (3) BSC biomass (as were restricted to the occurrence of trans- southern and south-western parts of the chlorophyll content) rises with increas- lucent quartz gravel on the ground (Fig. 8). African continent seem to be centres of ing species diversity; (4) the duration (7) Due to their structure and high green BSC development (Ullmann & Büdel of drought periods and the frequency of algal lichen diversity, the crusts of the Na- 2001). Vogel (1955) was one of the fi rst to rainfall events are the driving factors for mib Desert were considered as a unique describe cyanobacterial and algal crusts the presence and development of BSCs BSC type (Fig 9). underneath quartz gravels (= hypolithic) and their diversity rather than the total The effectiveness of the presented classi- of the desert pavement, a community amount of annual rainfall; (5) the struc- fi cation scheme was refl ected by signifi cant

PATTERNS AND DYNAMICS ALONG THE BIOTA TRANSECTS 93 BIOTA transects BIOTA

Fig. 1: Crust types occurring at the Observatories along the transects.

2 differences of several parameters between (type 3; 86.3 ± 31.62 mg chla/m , 135.8 The highest degree of coverage (up to 2 crust types. Crust thickness of the three BSC ± 46.5 mg chla+b/m ) successional stages. 70%) was observed in the Namib Desert types increased with crust development For both factors, signifi cant differences with crust types 6 and 7, a value close from the early (type 1; 2.7 ± 0.224 mm, between the groups were shown using a to those found by other authors of up

N = 4) to the intermediate (type 2; 3.4 ± one-way ANOVA (chla, p = 0.005, chla+b, to 87% of the soil surface (Lalley et al. 0.99 mm, N = 13) and the late (type 3; 4.4 p = 0.004), and posterior F statistics re- 2006, Schieferstein & Loris 1992). This ± 0.89 mm, N = 13) successional stages. vealed signifi cant differences between was followed by the Savanna ecosystems

In a one-way ANOVA, crust thickness was crusts of types 1 and 2 (chla, p = 0.026, (up to 60%) with mainly crust types 1–4

shown to be signifi cantly different between chla+b, p = 0.014) as well as types 1 and 3 and rarely 5, and the Succulent Karoo (up

the groups (p = 0.002, N = 3), and posterior (chla, p = 0.001, chla+b, p = 0.001). Besides to 35%), where all types of crusts were

F statistics revealed signifi cant differences that, we found that high chla values were present, except the lichen fi eld type 7. In between both types 1 and 3 (p = 0.002) and also associated with a high number of dif- the Nama Karoo, mostly the early succes- types 2 and 3 (p = 0.006). ferent BSC types (Pearson correlation co- sional stages of BSCs (type 1) were ob- Similarly, the biomass values in- effi cient 0.64). There was no correlation served, with a low coverage of less than creased with higher successional stage. between BSC characteristics and carbon 6%. Hypolithic crusts (type 6) were also

Chlorophylla and chlorophylla+b both or nitrogen content of the soil. scattered over the area. revealed a considerable increase from At the Zambesian dry forest Observa- an early succession crust stage (type Distribution patterns of BSC tories, mainly type 1 and rarely type 2 2 types and abiotic factors 1; 31.8 ± 14.97 mg chla/m , 49.3 ± BSCs with low-coverage values for both 2 along the transects 28.25 mg chla+b/m ) to the intermedi- (< 1%) were encountered and their pres- 2 ate (type 2; 67.9 ± 46.33 mg chla/m , BSCs of various types were found in all ence was restricted to recently burned 2 112.5 ± 80.89 mg chla+b/m ) and the late biomes except for the Fynbos biome. areas. The Woodland Savanna Biome

94 BIODIVERSITY IN SOUTHERN AFRICA 2 – PATTERNS AND PROCESSES AT REGIONAL SCALE BIOTA transects BIOTA

Fig. 2: Number of algal taxa at the different Observatories along the transects.

exhibited BSC types 1–4 and 6, which type 6 crusts were also common where ing, no crust formations were detected on grew underneath exposed, scattered a quartz gravel pavement was present. the soil surface. In the savanna and semi- quartz rocks, with type 2 and 4 BSCs Here, BSCs were found only at one BI- desert biomes, early succession crust being the most common. BSC coverage OTA Observatory (i.e. Niko North, Ob- types were often observed developing in was between 20–60%. Bryophyte crusts servatory S08, coverage up to 5%). the dripping zone of shrubs. were extremely rare in this biome. BSCs The Succulent Karoo Biome was com- The soils along the transects were gen- of the types 1–2 (very rarely type 4 and 5) monly inhabited by six types of BSCs, erally nitrogen depleted and exhibited often occurred underneath the canopy of with the large quartz fi elds of the Kners- values between 0.1 g/kg (Zambesian dry shrubs. In the Namib Desert, the especial- vlakte being characterised by a particu- forest) and 0.6 g/kg (dry Savanna, Suc- ly diverse BSC type 7 occurred within the larly high coverage and species diversity culent Karoo) total nitrogen per dry mat- spectacular lichen fi elds, but type 6 BSCs of type 6 BSCs (up to 25% of the soil ter. This resulted in high C:N values (e.g. were also common within the quartz surface). These hypolithic crusts of the above 100 in the Nama Karoo), indicat- gravel pavements. In the fog zone of the Knersvlakte comprised mean chloro- ing the limiting role of N in the soil. A 2 desert, type 7 crusts covered up to 70% of phyll values of 74.5 ± 37.11 mg chla/m positive correlation between the number 2 the total area investigated revealing chlo- and 107.3 ± 47.13 mg chla+b/m (N = 8). of BSC types and the proportion of silt rophyll values of 156.2 ± 64.68 mg chl a/ Biological soil crusts with cyanolichens and clay in the soil (Pearson correlation 2 2 m and 230.5 ± 98.33 mg chla+b/m (N and/or chlorolichens as well as liverworts coeffi cient 0.52, p = 0.04) was found. = 9). Although present in the Kalahari and/or mosses (type 5a and b) were well Highveld, type 1 BSC occurrence was developed within this Biome. The Ob- Diversity of species very scattered, patchy and of extremely servatory in the Fynbos biome showed BSCs were present in all biomes except low biomass. BSCs in the Nama Karoo some growth of pro- and eukaryotic algae the Fynbos and at most Observatories biome mainly belonged to type 1, but in the soil, but despite intensive search- along the transects (Fig. 2). In total, we

PATTERNS AND DYNAMICS ALONG THE BIOTA TRANSECTS 95 recorded 58 species of cyanobacteria, to the winter rainfall zone, while the dura- reported from BSCs of other continents. 29 green algae, one heterokontophyte, tion of drought was signifi cantly shorter As already described for cyanobacteria, 12 cyanolichens and 14 chlorolichens. in the winter rainfall zone. The mean chlo- the green algal diversity was highest in Many cyanobacteria taxa were only rophyll content in the winter rainfall zone the BSCs of the Savanna (20) and the 2 2 found at one or two Observatories. The (67 mg chla/m , 102 mg chla+b/m ; N = Succulent Karoo (29) biomes. No other majority of cyanobacteria occurred in 29) was signifi cantly higher than in the BSC reported so far has shown such a 2 Observatories of both major rainfall re- summer rainfall zone (39 mg chla/m and high species richness in eukaryotic algae. 2 gimes. For a list of species see the de- 68 mg chla+b/m ; n = 27). Maximum val- The pro- and eukaryotic algal α-diversity tailed Observatory descriptions in Part II ues in the winter rainfall zone were well of different BSC types seems to be cor- 2 of this book. The number of cyanobac- above 100 mg chla/m , and 200 mg chla+b/ related with a higher fi ne-grain fraction teria species was considerably higher in m2. Dry-matter-related biomass in terms in the soil. For lichens and bryophytes, the winter rainfall zone (54 species) than of carbon content was also signifi cantly we have not yet been able to show a clear in the summer rainfall zone (32 species). higher in the winter rainfall zone (1.9 ver- distribution pattern with regard to mac-

In the winter rainfall zone, the cyanobac- sus 1.1, U21, 21 = 135, p = 0.031) and the roclimatic factors. With regard to total BIOTA transects BIOTA teria reached their highest diversity in the number of BSC types per Observatory species richness of lichens and mosses, Succulent Karoo (49 species), whereas in was also signifi cantly higher (1.8 versus our random sampling showed its weak-

the summer rainfall zone the highest spe- 1.1; U27, 29 = 261.5, p = 0.028). nesses. Since most lichens (26 species cies diversity was recorded in the Thorn- in 14 genera) and also many bryophytes bush Savanna (22 species). Diversity, rainfall regime/ have patchy distributions, we in all like- The diversity of eukaryotic algae was frequency, and soil lihood failed to collect the complete di- similar in both rainfall regime types with Relating BSC characteristics to site char- versity. For comparison, in BSCs of the 23 species in the winter rainfall zone and acteristics along the transects (Fig. 3), Columbia Basin (USA) as many as 144 22 in the summer rainfall zone (Fig. 2). we found a positive correlation between lichen species were reported (McCune &

The highest species numbers were found the number of BSC types as well as chla Rosentreter 2007). Nevertheless, it ap- in the Succulent Karoo Observatories (19 content with winter rainfall frequency pears that their occurrence in BSCs de- species, winter rainfall) and the Observa- (Pearson correlation coeffi cient: 0.51, pends on longer periods between distur- tories of the dry savanna (16 species, p = 0.036, and 0.6, p = 0.01), and a nega- bances and more frequent rainfall events summer rainfall). Species numbers in the tive correlation between the number of with shorter drought periods in between other biomes were all below ten. Gener- BSC types with summer rainfall fre- (Belnap & Lange 2001). ally, the species-rich biotopes were lo- quency (Pearson correlation coeffi cient: Our results reveal a signifi cantly higher cated in the northern parts of the transect −0.54, p = 0.024). The winter rainfall cyanobacterial species richness of BSCs and along the coast. Among the eukaryo- zone was characterised by a signifi cantly in winter rainfall areas (summer versus tic algae, 15 species were found at least shorter annual dry period (89 days versus winter, 32:54 species). This fi nding part-

three times. Most of them were observed 153 days in the summer rainfall zone, U8, 9 ly confi rms the third hypothesis in that in both winter and summer rainfall zones, = 5.0, p = 0.003) with a more even distri- BSCs contribute to the biodiversity of with only four occurring exclusively in bution of rainfall events over the year (64 their biomes. An increasing diversity of the summer rainfall zone and none exclu- days in summer versus 80 days with rain cyanobacteria was found with an increas- sively in the winter rainfall zone. in the winter rain zone, not signifi cant) ing diversity of BSC types, which partly The initial stages of soil crusts were and a higher winter rainfall frequency confi rms our third and fi fth hypotheses. always composed exclusively of cyano- (number of rainy days during the winter An increase in cyanobacterial species bacteria. Eukaryotic algae were common period from April to September). numbers was found to be correlated with soil organisms and were also present in the a biomass increase, partly confi rming our BSCs reported here. However, they were fourth hypothesis. not observed to form BSCs themselves in Discussion the biomes along the transect. While the Biological soil crust presence, cyanobacterial diversity correlated signifi - Species richness diversity

cantly with the mean chla and chla+b content The cyanobacterial diversity recorded The successional progress starting from (Pearson correlation coeffi cients of 0.58 in this study is probably the highest re- BSC type 1 containing only cyanobacte- and 0.51), this was not the case for green ported so far for BSCs occurring in arid ria and ending with types 3, 4, and/or 5 algae. Of the 26 recovered lichen species and semi-arid regions around the world, illustrates the importance of cyanobacte- 12 were cyano- and 14 chlorolichens. with a total of 58 species of which 49 oc- rial sheaths for crust development and curred in the Succulent Karoo and 24 in soil consolidation, whereas lichens and Relevance of rainfall frequency the Namib Desert. bryophytes contribute mainly to the high and regime Many of the 31 eukaryotic algal species chlorophyll (biomass) values of BSCs. Total precipitation was signifi cantly high- detected in soil crusts along the Namibia– In the Acacia mellifera thorny shrubland er in the summer rainfall zone compared South Africa transect have already been of the Kalahari Desert, Botswana, an ex-

96 BIODIVERSITY IN SOUTHERN AFRICA 2 – PATTERNS AND PROCESSES AT REGIONAL SCALE BIOTA transects BIOTA

Fig. 3: Chlorophyll content of BSCs at the different Observatories along the transects.

tensive cyanobacterial crust was found, from the other BSC types along the BIO- Fynbos Biome. The recording of seven 3–4 mm thick and comparable to type 1 TA Southern Africa transects. In addition different BSC types confi rms our second and 2 of our study, that covered between to terricolous crustose lichens involved hypothesis. The lack of BSCs in the Fyn- 11 and 95% of the bare soils (Dougill in crust formation, foliose and fruticose bos Biome is puzzling, especially since & Thomas 2004, Thomas et al. 2002, lichens occurred. Chlorophyll values of free-living soil algae are known to be Thomas & Dougill 2006, 2007). the Namib Desert crusts represent the present. Until now, we have been unable The very specialised hypolithon highest ones measured along the transect, to explain this absence, but it is interest-

(type 6) is not only composed of a reaching mean values of 156.2 mg chla/ ing to note that within the Fynbos Biome 2 2 number of different cyanobacteria and m and 230.5 mg chla+b/m . In a Lecidel- the soil pH is always well below pH 4 green algae, but lichens and bryophytes la crystallina-dominated crust system, (Petersen 2008). While BSC type 1 is are also reported from their protecting Lange et al. (1994) determined as much always an early succession type, crusts 2 and moisture gathering habitat (Büdel as 508 mg chla+b/m , a chlorophyll con- of type 2 can either be intermediate suc- & Schultz 2003, Vogel 1955, Werger & tent amongst the highest values known cessional stages, eventually developing During 1989). While the hypolithic crust for BSCs worldwide (Lange 2001). They into types 3–4, or are the fi nal stage (“cli- (type 6) also occurs in other arid and have two unique features: the absence of max”) reached under the given circum- semi-arid parts of the world (Cockell & cyanolichens (O.L. Lange, personal com- stances. Biological soil crusts of types Stokes 2004, Schlesinger et al. 2003), the munication), and the apparent limitation 3 and 4 are late successional stages and lichen fi elds (type 7) are unique to the Na- of cyanobacteria to hypolithic habitats. may develop into type 5, but can also be mib Desert with their unrivalled but not From the above we can confi rm hy- climax stages. Biological soil crusts of yet fully known lichen diversity and their pothesis 1, that BSCs are a regular and types 6 and 7 always represent “climax” wide extent (Loris et al. 2009, Articles common part of the vegetation in south- crusts. III.3.6, III.3.7). They differ considerably western Africa, with the exception of the

PATTERNS AND DYNAMICS ALONG THE BIOTA TRANSECTS 97 BIOTA transects BIOTA Fig. 4: Early successional crust composed of cyanobacteria, Fig. 5: Intermediate to later successional crust with cyanobac- type 1, Otjiamongombe, savanna. teria and fi rst cyanolichens (Heppia sp., Collema sp.), type 3, Duruchaus, savanna.

Fig. 6: Late successional/climax crust with additional chlorolichens Fig. 7: Climax crust with the liverwort Riccia sp., type 5a, Soebats- (Psora decipiens), type 4, Soebatsfontein, dry savanna to semi- fontein. desert.

Fig. 8: Hypolithic crust with cyanobacteria, type 6, Karios near Fish Fig. 9: Climax crust: the unique lichen fi elds of the Namib Desert River Canyon, Desert Biome. (chlorolichens and a few cyanobacteria), type 7, Wlotzkasbaken, Desert Biome. L.c. = Lecidella crystallina, N. = Neofuscelia sp., T.c. = Teloschistes capensis, C. = Caloplaca sp.

98 BIODIVERSITY IN SOUTHERN AFRICA 2 – PATTERNS AND PROCESSES AT REGIONAL SCALE Climatic and edaphic factors Acknowledgements Loris, K., Pfi z, M., Erb, E., Küppers, M. (2009): Since BSC diversity and species rich- The authors’ general acknowledgements to the Lichen vegetation in the Central Namib as organisations and institutions, which supported infl uenced by geomorphological and edaphic ness, as well as biomass were correlated this work are provided in Volume 1. conditions, climate and wind erosion. – Bib- with a higher rainfall frequency and with liotheca Lichenologica 100: 369–388. shorter annual dry periods in the winter References McCune, B., Rosentreter, R. (2007): Biotic soil Belnap, J., Lange, O.L. (2001): Biological soil crust lichens of the Columbia Basin. – In: rainfall zone, it would appear that pre- crusts: structure, function, and management. – Ponzetti, J.M. (ed.): Monographs in North cipitation frequency rather than the total Ecological Studies 150. 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PATTERNS AND DYNAMICS ALONG THE BIOTA TRANSECTS 99