CHANGES IN ECOSYSTEM FUNCTION IN SAVANNAHS AND FIELDS INVADED BY CHROMOLAENA ODORATA IN CAMEROON

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1 CHANGES IN ECOSYSTEM FUNCTION IN SAVANNAHS AND FIELDS INVADED BY CHROMOLAENA ODORATA IN CAMEROON Lindsey Norgrove, University of Hohenheim & Interntionl Institute of Tropicl Agriculture, Cmeroon Juli Dux, Inst. Vegetble & Ornmentl Crops, Erfurt, Germny Prosper Fumbeng, Dept. Biodiversity & Lnd Rehbilittion, University of Hohenheim, Germny

2 Forest-svnnh trnsition Cmeroon Loj, Ecudor 1895 m sl World distribution of Chromolen odort. Are under lien infesttion in drk green nd ntive rnge in grey. (ISSG, 2004). Updted models of distributions (Kriticos et l 2005; Rimundo et l 2006)

3 C. odort in the forest-svnnh trnsition zone of Cmeroon colonises forest edges invdes svnnh (subject to nnul burning) $

4 C. odort in the forest-svnnh trnsition zone of Cmeroon Mjor weed in tree crop systems Mjor weed in food crop fields Colonises forest edges 3m-tll formidble fllow No lughing mtter Invdes grss fllows

5 Effects of C. odort on plnt community, North West Cmeroon Svnnh C. odort invded re Dominnt species Hyprrheni involucrt Chromolen odort Andropogon tectorum Pteridium quilinum Murdnni simplex Hyprrheni involucrt Dissotis erect Smilx krussin Sporobolus sp. Incresed biomss. Chnges in nutrient budgets AbG biomss (Mg h -1 ) # plnt spp Chnge in SPECIES species OUT composition SPECIES IN Afrmomom sp. Oldenlndi sp. Wht impct? Andropogon tectorum Smilx krussin Psplum polystchyum Stchyterphet cyennensis Murdnni simplex Agertum conyzoides smpling: 2 systems, 6 fields per system, 3 0.5*0.5m frmes per field (9m 2 totl) Nutrient concentrtions in C. odort compred with grsses N K (mg g -1 ) (mg g -1 ) C. odort leves C. odort stems 7 15 grsses Fumbeng MSc (2005)

6 Objective: Assess effects of C. odort invsion in svnnhs on ecosystem function EDAPHIC AND SOIL BIOTIC PROCESSES Soil biossys: plnt biomss production Residue decomposition rtes Soil enzyme ctivity Soil mcrofun: erthworm diversity

DM biomss per plnt g chlorophyll (SPAD units) 40 35 30 25 20 15 10 5 0 500 450 400 350 300 250 200 150 100 50 0 se=4.2 SPAD = 77soil N + 65 r 2 = 0.50 svnnh b se=6.0 ph 5.

odort, svnnh, forest soil 300 250 200 150 100 50 0 C cmol kg-1 3.88 Mg cmol kg-1 1.89 K cmol kg-1 0.17 b chlorophyll (SPAD) lef re cm2 forest C.

7 DM biomss per plnt g chlorophyll (SPAD units) se=4.2 SPAD = 77soil N + 65 r 2 = 0.50 svnnh b se=6.0 ph 5.50 c se=3.8 forest C. odort svnnh soil origin soil N concentrtion % 9.13 chlorophyll (SPAD units) Mehlich P (ppm) Biossys: mize grown on C. odort, svnnh, forest soil C cmol kg Mg cmol kg K cmol kg b chlorophyll (SPAD) lef re cm2 forest C. odort svnnh soil origin orgnic C (%) 1.97 c totl N (%) living lef re cm 2 C. odort-invded svnnh forest Norgrove, unpublished

Decomposition of stndrd mteril in 2mm mesh litterbgs on svnnh & C. odort invded svnnh soil, in- & ex-situ (n=3) 100 90 80 svnnh (in-situ) C.

odortinvded svnnh (morning) ir under cnopy soil t 20 mm depth b b % residue remining 70 60 50 40 30 0 5 10 15 weeks fter incubtion b c short dry seson long rin

8 Decomposition of stndrd mteril in 2mm mesh litterbgs on svnnh & C. odort invded svnnh soil, in- & ex-situ (n=3) svnnh (in-situ) C. odort invded re (in situ) svnnh soil (ex-situ) C. odort soil (ex-situ) Air nd soil temperture ( 0 C) under svnnh & C. odortinvded svnnh (morning) ir under cnopy soil t 20 mm depth b b % residue remining weeks fter incubtion b c short dry seson long rin seson soil t 60 mm depth soil wter content 50 mm depth svnnh (in-situ) C. odort invded site (in-situ) b o C Soil wter content (%) under svnnh & C. odort-invded svnnh Norgrove, unpublished

9 Soil enzyme ctivity (ß-glucosidse) in svnnh nd C.odort-invded svnnh from four pired sites in southern Cmeroon (n=4) ug Nitrophenol g-1 soil hr Activity in undisturbed forest b 0 Dux MSc (2005) svnnh C. odort invded svnnh

odort or grss residues (n=4) ug Nitrophenol g-1 soil hr-1 50 45 40 35 30 25 20 15 10

10 Soil enzyme ctivity (ß-glucosidse) in svnnh & C.odortinvded svnnh from four pired sites in southern Cmeroon: dding C. odort or grss residues (n=4) ug Nitrophenol g-1 soil hr in-situ soil soil plus grss 40 dys soil plus C. odort 40 dys,b c b,b c 0 Dux MSc 2005 svnnh C. odort invded svnnh

11 Erthworms Higher erthworm densities under C. odort invded site thn svnnh in North West Cmeroon (n=6). Erthworms smpled by expulsion method in three 0.25 m 2 internl reps per re. erthworm density ind. m Eudrilide gen.nov1. Eudrilide sp. Ocnerodrilus sp. Eudrilide gen.nov2 Enchytreide D.(Dt.) bolui Ocnerodrilus occidentlis 0 svnnh (34 ind. m-2) C. odort-invded site (58 ind. m-2) (Adpted from Norgrove, Fumbeng, Csuzdi 2007)

12 Humn Perspective In North West Cmeroon, for the frming Aghem people, C. odort is lest worst option. They prefer C. odort, to Impert cylindric or non-invded svnnh lnd. The use of biocontrol gent for C. odort in this zone would result in greter infesttion of I cylindric, & greter weeding drudgery. However, for their pstorlist trnshumnt neighbours (the Fulbe), relying on grzing svnnh lnd, C. odort negtively ffects their livelihood strtegy. Some hve become prt-time frmers (right), which hs resulted in ethnic conflicts with Aghem.

13 Conclusions In the context of lnd users in Cmeroon, C. odort invsion in svnnhs hs hd both negtive nd positive effects. C odort-invded res hve higher N sttus yet lower vilble P thn svnnh or grss-invded sites. Microclimtic conditions re ltered by C. odort invsion. This results in higher decomposition rtes. C. odort-invded res cn hve higher soil funl densities nd ctivity, higher soil enzyme ctivity thn svnnh, probbly due to the rich litter input, lthough both re lower thn djcent forest. Hence, frmers prefer this lnd for griculturl purposes. In species-poor svnnhs, C. odort invsion hs no significnt effect on plnt species richness, lthough cuses species shifts. Thus svnnhs re rendered less useful for grzing nd this negtively ffects pstorlists livelihoods. In forest res, however, species loss is likely.

14 Thnks to. you for listening Robert Bosch Foundtion, Germn Reserch Foundtion (DFG) Eiselen Foundtion (with Prosper Fumbeng) Tropische Agrrstiftung, Humboldt University (with Juli Dux) Project stff in Cmeroon Chiefs nd communities of Obo, Ngoungoumou, Wum, Essong, Nkometou III for permitting smpling

2007 Hypothesised recent boundry Distribution of svnnh

15 Au Cmeroun, l forêt équtorile ggne du terrin sur l svne In Cmeroon, the equtoril forest dvnces on the svnnh 17 Jnury 2007 Hypothesised recent boundry Distribution of svnnh tree cross the current forest grsslnd boundry (Gounes MSc 2006)

weed biomss (t h -1 ) 6 5 4 3 2 1 0 Plntin-timber groforestry systems in the forest zone of Cmeroon other weeds C.

odort incresing in dominnce Adpted from Norgrove, Huser, Weise (2000) Chnges in the exchngeble K pool by Y3 (Mg h -1 ) 0.50 Mg h-1 0.

16 weed biomss (t h -1 ) Plntin-timber groforestry systems in the forest zone of Cmeroon other weeds C. odort not burned burned not burned burned 1st weeding By Y6, no C. odort found in the understorey 2nd weeding Y1, C. odort incresing in dominnce Adpted from Norgrove, Huser, Weise (2000) Chnges in the exchngeble K pool by Y3 (Mg h -1 ) 0.50 Mg h Mg h -1 nnul erthworm csts plntin uptke, excluding bunches Norgrove, unpubl. C. odort 6 month growth nnul tree litterfll tree uptke Y tree uptke Y plntin bunches tree uptke Y

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