Impacts of bush encroachment on animal diversity in savanna rangelands

Transcription

1 Impacts of bush encroachment on animal diversity in savanna rangelands Niels Blaum, Arnim Marquart, Morgan Hauptfleisch, Dave Joubert, Robert Hering, Anna Hannappel, Vinte Mendes, Lars Goldbach, Michelle Rodgers & Maren Lönz

2 Bush encroachment is a global phenomenon and occurs mainly in savannas and grasslands Fig. 1: Locations and mean annual rainfall associated with studies of bush encroachment effects on vertebrate community structure worldwide, Stanton, Blaum et al. (in revision): Shrub encroachment and vertebrate diversity: a global meta-analysis, Global Ecology & Biogeography

3 Bush encroachment is a global phenomenon with regional, national and local implications Slow process ~ 10 years Map: CARE - Conversion And Resource Evaluation Ltd

4 Bush encroachment is a major form of land degradation Economic consequences e.g. Zika & Erb 2009, Ecological Economics 69 Reduction in rangeland productivity/ decrease in NPP

5 The National Rangeland Management Policy and Strategy of the Ministry of Agriculture, Water and Forestry states: The vast extent and economic implications of the bush encroachment problem are such that it could be regarded as a national disaster.

6 Ecological consequences...?

7 The 2 nd Biodiversity Strategy and Action Plan of the Ministry of Environment and Tourism states: the critical importance of biodiversity to the socioeconomic development of our country.

8 Part 1 Effects of bush encroachment on animal diversity in southern Kalahari rangelands Part 2 Feedbacks between bush encroachment, biodiversity and soil moisture

9 Study area 21st NRF Kaglagadi Transfrontier Park Botswana South Africa Askham

10 20 Study sites with different stocking rate + shrub cover 1 IKONOS Satellite N 1000 m study sites (250 ha) Stocking rate: 2.4 LSU/ 100 ha 6.2 LSU/ 100 ha +/ constant since 1995 (uncertain historical data) Mixed grazing (cattle, sheep, goat and game)

11 Data sampling within a decade of land use Vegetation surveys Trees, shrubs, grasses and herbs Spatial pattern Animal groups Arthropods Reptiles Rodents Carnivores Passive Tracking Index Blaum et al 2008, Wildlife Research 35

12 Livestock management affects vegetation cover Changes in shrub cover Low High Suggested LSU Within a decade of land use: No/ little changes in shrub cover at low stocking rates Significant shrub encroachment at high stocking rates Large Stock Units/ 100 ha

13 Livestock management affects vegetation cover Changes in shrub cover affect the diversity of the landscape Low High Suggested LSU Large Stock Units/ 100 ha Many different shrub sizes provide different types of shelter and nesting sites

14 Example: shrubs provideshelter against heat

15 Livestock management affects vegetation cover Changes in shrub cover affect the diversity of the landscape Low High Suggested LSU Many different shrub sizes provide different types of shelter and nesting sites

16 Animal diversity along a shrub cover gradient Reptiles Rodents Carnivores Arthropods Western sandveld lizard Hairy-footed gerbil Yellow mongoose Species Richness R² = 0.52, P < 0.01 Wasiolka et al. (2009) Acta Oecologica R² = 0.74, P < R² = 0.71, P < 0.05 R² = 0.69, P < 0.01 Blaum & Wichmann (2007) J Animal Ecology Blaum et al. (2007) Acta Oecologica Shrub cover (%) Shrub cover (%) RTU richness Blaum et al. (2009) Biodiversity & Conservation Species richness in shrub dominated habitats is low across animal groups But highest at intermediate shrub cover -> shrubs per se are not bad! Implications for de-bushing

17 Ok, but why does biodiversity matter for savanna rangeland management? Because of the little things that biodiversity can do for savanna rangelands

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19 Part 2 Feedbacks between shrub encroachment, biodiversity and soil moisture

20 OPTIMASS research sites in Namibia Kuzikus Lake Otjikoto Waterberg Kuzikus/ Ebenhaezer Ebenhaezer

21 Management affects geo-bio feedbacks Small mammals Insects Water Vegetation Soil Biodiversity

22 Management affects geo-bio feedbacks Small mammals Insects Water Vegetation Soil Biodiversity Macropores Macropores

23 Management affects geo-bio feedbacks Small mammals Evaporation Water Vegetation Insects Infiltration Soil Biodiversity Macropores Macropores

24 Management affects geo-bio feedbacks Small mammals Evaporation Water Vegetation Insects Infiltration Soil Biodiversity Macropores Macropores

25 Management affects geo-bio feedbacks Small mammals Evaporation Water Vegetation Insects Infiltration Soil Biodiversity Macropores Macropores

26 Field observation 1 Key question: What are the impacts of shrub encroachment on beetlediversityand soilmoisture Master Thesis Robert Hering, University of Potsdam Methods: Pitfall trapping, soil moisture measurements Results: 2329 individuals, 13 beetles families

27 Beetle diversity along shrub cover gradient 1.0 Beetle diversity Simpson index F (2,9) = 15.96, p < 0.001, R 2 = Shrub cover (%) 1: Platymetopus figuratus, 2: Zophosis sp. A, 3: Cypholoba gracilis 4: Zophosis sp. B, 5: Gymnopleurus sp., 6: Manticora sp. 7: Graphipterus sp., 8: Renatiella sp., 9: Atractonotus mulsanti

28 Soil moisture along shrub cover gradient Indicates feedback between shrub encroachment, beetle diversity and soil moisture Soil moisture (vol %) Simpson index Beetle diversity Soil moisture (10cm) F (2,9) = 15.96, p < 0.001, R 2 = 0.73 F (2,9) = 15.56, p < 0.001, R 2 = Shrub cover (%)

29 Please visitrobert s Poster

30 Field observation 2 Key question: Howdoes bush encroachment and management type affect macropore abundance? Methods Drone surveys to record macropores > 10 cm in diameter (small mammals) at a game and livestock farm Field surveys to record of macropores < 5 cm in diameter (insects) at shrubs, grass tussocks and along shrub cover gradient

31 Field surveys to quantify macropores < 5 cm Macropore area (mm²) Bare soil Grass Bush Number of macropores 0 1% 11% 22% Shrub cover Positive effect of single shrubs on macropore abundance At larger spatial scale (50m x 50m) negative effect of bush encroachment on macropore abundance PhD Thesis of Arnim Marquart, University of Potsdam

32 Drone surveys to estimate macropores > 10 cm Honours Thesis of Michelle Rodgers, NUST Drone Survey (Sensefly ebee drone) 100 ha, 4 cm resolution, visual + NIR cameras Survey in March 2016 Game farm with higher abundance of mammal burrows Burrow size class Game farm Livestock farm Small (8 < 14,9 cm) Medium (15 < 30,9 cm) Large (31 < 100 cm) Total Burrows Game Livestock

33 Visitposterof Michelle Rodgers Drone survey to identify small mammal burrows Camera trapping to estimate mammal diversity

34 Field experiment Key question: What are the effects of macropores for infiltration of rainfall into the soil Master thesis of Lars Goldbach, University of Potsdam Honours thesis of Vinte Mendes, Namibia University of Science and Technology PhD thesis of Arnim Marquart, University of Potsdam

35 Construction of rainfall simulator Rainfall simulator (50 x 50 cm) 14 x 14 injection cannula Tube pump -> rainfall intensity PhD Thesis Arnim Marquart

36 Rainfall simulation experiments Paired experiments: with and without macropores High rainfall intensity (40mm/h) Blue tracer to visualize infiltration Digging of 3 soil profiles (50 x 25cm) Master Thesis Lars Goldbach and PhD Thesis Arnim Marquart

37 Macropores < 5 cm affect infiltration 0 macropores + macropores Infiltration depth (cm) Deeper infiltration with macropores Master Thesis Lars Goldbach and PhD Thesis Arnim Marquart

38 Macropores < 5 cm affect infiltration 0 macropores + macropores Infiltration depth (cm) Calculation of tracer coverage 40 Deeper infiltration with macropores Master Thesis Lars Goldbach and PhD Thesis Arnim Marquart

39 Macropores < 5 cm affect infiltration 0 macropores + macropores Infiltration depth (cm) Calculation of tracer coverage 40 Deeper infiltration with macropores Higher tracer coverage Strongly increased infiltration amount macropores + macropores Master Thesis Lars Goldbach and PhD Thesis Arnim Marquart

40 Also large macropores > 5 cm infiltration Small mammal burrow Without burrow (30cm) With burrow (40cm) Though anecdotal, rainfall simulation could suggest that small mammals contribute to water retention in savanna rangelands and associated services Honours thesis Vinte Mendes, Namibia University of Science and Technology

41 German-Namibian Tandem thesis Small mammals as indicators for rangeland degradation and feedback mechanisms (bioturbation soil water infiltration) Tandem thesis Vinte Mendes (NUST) and Anna Hannappel (UP)

42 Poster Lars Goldbach Poster Maren Lönz

43 Summary Within a decade of land use: no/ little increase in shrub cover at low stocking rates but strong increase at high stocking rates Species richness in shrub dominated habitats is low across all animal groups; but highest at intermediate shrub cover Shrubs per se are not bad! Positive effect of single shrubs on macropore abundance; but negative effect of shrub encroachment at a large area Drone survey valuable tool to estimate burrow abundance Deeper infiltration and amount with macropores Implications for de-bushing Implications for after care and potential re-seeding

44 New project proposal Wanted! Farmers interested in after care of de-bushing and re-seeding New project proposal RESEED: Understanding ecohydrology for restoring degraded savanna rangelands: Aim: Development of a fully automated measuring network system for site specific reseeding of native savanna grasses based on eco-hydrological threshold analyses

45 Thank you for your attention, and thanks to Pieter Hugo, Willie and Anthia van Rensburg and all other farmers in the study areas, Ministry of Environment and Tourism Namibia, Northern Cape Nature Conservation South Africa, all contributing co-workers and field helpers and the funding agencies (BMBF and DAAD)