Effects of Herbivory on woody plant functional traits, structural diversity and ecosystem services in a semiarid. Staline Kibet

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1 Effects of Herbivory on woody plant functional traits, structural diversity and ecosystem services in a semiarid savanna Staline Kibet

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3 Background 3000 yrs BP & Wardei Pastoralists occupied Laikipia Maa speakers arrive in Laikipia Rinderpest & Pleuro-pneumonia East African British Protectorate Lenana Treaties Marching deserts call/hardin s Establishment of CR Economic hardship to present (CR) to present (PR)

4 What are the issues Declining forage resource particularly among the Group ranch (GR) Increasing woody cover (up to 28%) in the last 50 years particularly in private ranch (PR) Declining wildlife population despite increase investment in their protection within PR Increasing shoats by 57% ( ) in GR Increasing camel by 15.4% ( ) in GR

5 Main Objective To generate knowledge on the impacts of Ungulates herbivory on vegetation dynamics and long term provisioning of ecosystem services in a semi-arid savanna.

6 Specific objectives To evaluate effects of woody plant herbivory on plants traits, taxonomic and functional diversity under different land use types. To investigate the effects of woody plant herbivory on structural diversity, composition and edible biomass production under different land use types. To evaluate land use types and habitat invasibility To assess transformation in the management of group ranch natural and social capital assets and potential effects on pastoral community s socio-ecological resilience.

7 Hypotheses There is no significant variation in taxonomic and functional diversity between communal and private ranch. There is no significant variation on structural diversity, species composition and biomass production between communal and private ranch There is no significant variation in habitat invasibility between communal and private ranch

8 Assumptions made The original vegetation type between Private and communal ranch were similar given that the two are adjacent each other The vegetation dynamics are better reflected by woody plants because they are long-lived and have been subjected to prolong herbivory compared to herbaceous. Climatic conditions prevailing in the two land use type is similar (sampling sites < 8 km apart).

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10 General Methods Vegetation sampling was based on a permanent large plot (0.5 x 3 km) in Mpala used to study long-term vegetation dynamics and a dumpy establish for comparison in Ilmotiok with similar size. Used three transects selected purposefully to minimize abiotic variation between the land use types Each transect had 75 plots (20 x 20 m) arrange systematically in alternating manner about the transect plane place at 40 m intervals

11 Vegetation sampling (20x20 m) plots Plots

12 Alternating (20 x 20 m) plots, Arrow showing the transect direction

13 Structural data measured Height of woody plants (m) Diameter at Knee Height - DKH (~ 50 cm above ground) (cm) only individuals with DKH of 1 cm were enumerated. Canopy depth (m) Canopy (crown) diameter (m) (a +b)/2

14 Functional traits & functional diversity Chose three dominant, highly palatable species based on reconnaissance survey, literature review and interview with local community Chose (3 species per site; Vachellia brevispica, V. etbaica and Senegalia mellifera for Mpala PR & V. tortilis, V. etbaica and S. mellifera for Ilmotiok GR Selected randomly one of the 3 transects used earlier and selected the target species after every 100 m (GR) and 60 m PR. (nearest target sp neighbour)

15 Vachellia drepanolobium woodland

16 Edible biomass Double sampling branches method (Foroughbakhch et al 2008) Individual adjacent to the plots in Mpala were used. Branch diameter at the base measured later harvested and all leaves and young shoots harvested, oven dried and weighed. Regression equation established based on diameter and biomass.

17 Functional Traits variable collected Specific leaf area (SLA) Leaf Area (LA) Leaf dry matter content (LDMC) Leaf Nitrogen content (LNC) Leaf phosphorous content (LPC) Height DKH Canopy diameter Stem numbers

18 Habitat invasibility This is the vulnerability of habitat to invasion (AIS and native species) Healthy ecosystem should be able to resist invasion (all ecological niche space are occupied)

19 Habitat invasibility variables Abiotic environment properties Percent slope Elevation Percent bare ground Biotic Intensity of browsing Intensity of grazing Species richness Species diversity Cover density Plant density

20 Sansevieria volkensii Ipomoea kituensis

21 Browser-woody plants interactions: Effects on traits, functional diversity and implications for semi-arid savanna management. Woody component of savanna is key in ecosystem function and stability Browser-woody plants interactions remains unclear Intense browsing causes decline in palatable species (overgrazing) Converse intense browsing causes increase in browsing tolerant palatable species Also intense grazing/browsing causes decline in functional diversity through species filtering meaning homogenization of traits Limited studies done to compare functional and taxonomic diversity

22 What dynamics occur in an intensely browsed site dominated by palatable species? How to these species survive repeated defoliation?

23 Hypotheses Taxonomic diversity between intensely and lightly browsed/grazed sites was similar given their close proximity and similarity in bioclimatic conditions. The persistence of palatable species in intensely browsed/grazed site were mediated by overabundance of browsing-tolerant and/or browsing-avoidance traits. Intensely browsed/grazed ranch has low traits FD due to filtering out of browse intolerant species causing traits homogenization

24 Method Followed Cornelissen et al 2003 protocol for traits collection, processing and analysing Dominant palatable species selected as stated earlier from each site Well exposed, fully exposed twigs with no obvious damages harvested and kept in sealable bags under low temperatures about 4 C. Later leaves picked and scan

25 Leafscan for SLA & LA dtermination Senegalia mellifera Binary Image

26 Data analysis

27 Species diversity

28 Results Table 5.0. Aggregated traits mean values for four dominant browse species in lightly browsed/grazed (PR) and intensely browsed/grazed (CR). Units; DKH (cm), Hc & CRWN (m), LNC & LPC (mg/g), LA (mm²), LDMC (mg/g) and SLA (mm²/mg)

29 Traits PR n GR n z p-value Vegetative traits CRWN 1.7(±133) (±1.4) *** DKH 3.8(±4) (±3.8) *** H c 2.1(±1.02) (±1.1) *** STM 5.2(±5.6) (±2.1) *** Spines 26(±11) 68 23(±6.7) Leaf traits LNC 0.64(±0.3) (±0.33) LPC 0.26(±0.07) (±0.02) *** LA 971 (±661) (±292) *** LDMC 416(±60) (±78) *** SLA 11.4(±3.9) (±5.1) Whitney U-test statistic and level of significance given as *p<0.05, **p<0.01, ***p<0.001, n is the number of samples used and z represent critical values.

30 Hc (m) Senegalia mellifera PR CR Land use type Hc (m) Vachellia etbaica PR CR Land use type CRWN (m) Senegalia mellifera PR CR Land use type CRWN (m) Vachellia etbaica PR CR Land use type Mean values for height (H c ) and crown diameter (CRWN) for two species (S. mellifera & V. etbaica) under PR and CR land use types (Data log transformed)

31 Linear regression for mean values of leaf dry matter content (LDMC) for three species (S. mellifera, V.etbaica and V. tortilis) against distance from high browsing sites sacrificial site (near homesteads) to moderately browse sites (2 km away) in GR. Data log-transformed for uniformity 2.81 LDMC 2.76 LDMC (mg/g) Distance (m)

32 Table 5.3 Functional diversity (Rao coefficient index) and species diversity (Simpson & Shannon index) for lightly browsed site (Mpala) and intensely browsed (Ilmotiok) using binary, categorical and quantitative data. Indices Data type Site p Value PR GR Rao index Binary Category Quantitative Simpson Index Quantitative Shannon index

33 Key findings Intense herbivory diminishes both taxonomic and traits functional diversity. Intense herbivory promotes investment in browsing-tolerant as well as defense traits amongst persistent dominant- palatable species. Intense herbivory causes traits homogenization Intense herbivory diminishes functional diversity and subsequently ecosystem functions

34 Discussions intense herbivory diminishes both taxonomic and traits functional diversity. This suggest that palatable and less palatable browse-sensitive species may have been suppressed and/or outcompeted by more tolerant species when subjected to similar level of disturbance Intense browsing/grazing promotes investment in browsing-tolerant as well as defense traits amongst persistent dominant- palatable species. Effects of herbivory on plants could be direct death coz of biomass removal or indirect defoliated species is made vulnerable to pests & diseases (finally die) or loses fitness decline reproduction ultimately disappear

35 Discussions: Herbivory vs species diversity low diversity could be associated with direct impacts such as death due to intense defoliation of biomass or increase competition from nonbrowsed individuals or through indirect effect such as increase susceptibility to pests and disease infestation or decline in fitness causing low seed production and finally low seedlings recruitment Species with high density abundance in the intensely browsed/grazed site except one were of medium to high palatability. This disaproves the notion that heavy grazing always promote growth of unpalatable specie

36 Browsing and traits Browsing lawn typified by wider crown canopies, and more multiple stems that facilitated browsing, compensatory photosynthesis and re-browsing within GR was observed particularly in S. mellifera and V. etbaica having opposite effect to browsing.

37 Herbivory & Fuctional Diversity Generally all traits recorded low FD except LA in intensely browsed/grazed site. Overgrazing reduces FD and ultimately ecosystem functions DKH, CRWN and H c traits were functionally more diverse in PR. This could be linked to trait homogenization in GR thro filtering out of browsing - sensitive species. Rates of water, nutrient, and energy cycling thro ecosystems are dependent on the horizontal and vertical structural features of primary producers.

38 Conclusions These study findings suggest that management of livestock browsing levels can be used to manipulate species diversity, and functional diversity. Low stocking rates may promote proliferation of unpalatable species such as Euclea divinorum Overstocking may result in decline and/or complete loss of some species which in turn may facilitate encroachment by invasive species e.g. Vachellia reficiens due to increase availability of niche ecological space Trait homogenization (decline FD) attributable to intense browsing/grazing makes habitats less suitable for diverse species of animals e.g. Bird nesting sites

39 Conclusions contd Conversely intense browsing may create browsing lawn and promote increase biomass production and repeat browsing, but such observation may only occur up to some limits beyond which species fitness decline and degradation occurs Intense browsing/grazing may affect nutrients cycling regime. High LDMC means high lignin material in leaves hence low decay rate.

40 Thank you