Response of riparian vegetation to clearing by Working for Water in the Kruger National Park

Transcription

1 Response of riparian vegetation to clearing by Working for Water in the Kruger National Park Taryn Morris 1, E.T.F. Witkowski 1, J.A. Coetzee 2 1 School of Animal, Plant and Environmental Sciences, WITS University, Private Bag 3, WITS 2050, South Africa; 2 Dept of Zoology and Entomology, P.O. Box 94, Rhodes University, Grahamstown 6140

2 Invasive alien plants (IAP) in Kruger National Park Kruger National Park IAS greatest threat to biodiversity 370spp. 121 invader status 30% alien infestation of riparian zones across park; isolated stands up to 90% Contradict the KNP mission statement: maintain biodiversity in all it s natural facets and fluxes Clearing of IAP become major priority (Foxcroft & Richardson 2003) 2

3 Working for Water 1997 Working for Water introduced into KNP Clearing IAP in major riparian areas Working for Water programme (1995): Conduct and co-ordinate alien plant management AIM: Secure water resources & alleviate poverty Photo L. Foxcroft 3

4 INTRODUCTION Impacts of IAP removal HOWEVER - cleared areas can experience: secondary problems reinvasion regrowth by indigenous vegetation is important for ecosystem recovery natural vs. active Working for Water sites left to recover naturally Rarely execute post clearance monitoring 4

5 RATIONALE 1. Assess efficacy of Working for Water teams 2. Assess effects of follow ups treatments Outside Kruger NP Initial clearance + max 3 follow-ups Beater et al. in prep. - without continuous follow-ups, sites returned to pre-clearance invasion levels Inside Kruger NP Continuous clearing over several years Current state of vegetation??? Smaller areas - well vs. Larger areas as best as possible 5

6 RATIONALE 3. Ecosystem Repair: National project initiated and funded by WfW several studies spanning various biomes AIMS: Assess current levels of repair Establish achievable targets for repair ID limiting factors of ecosystem recovery Develop protocols to incorporate into management programmes 6

7 OBJECTIVES 1. Assess density of IAP before and after clearing (efficacy of WfW) 2. Assess effects of IAP on vegetation community structure. 3. Investigate patterns of vegetation regrowth post removal of IAP 7

8 METHODS 8

9 Study site 12 sites Sabie River, Kruger National Park, South Africa. Three zones Data collections (Mar 06 & March 07) 1 2 Kruger National Park Sabie River 3 Mozambique 9

10 Rainfall Cumulative rainfaill (mm) '2005/6 Long term average '2006/7 Kruger National Park Sabie River Jul Aug Sep Oct Nov Dec Jan Feb Mar +70% -35% Created an enhanced response of IAP growth 10

11 Vegetation sampling 10m wide belt transects perpendicular to river Vegetation BSD >1cm - Identified - Counted (density) - Basal stem diameter - Height class - Growth form 11

12 Statistical Analyses Diversity measures Primer v5 Rarefied S (n=100) Simpson s diversity (1/D) Simpson s evenness (E1/D) SIMPER (Primer v5) Species contribution to dissimilarities before and after removal of IAP 12

13 RESULTS Mar 2006 Nov 2006 Mar

14 Objective 1: Alien densities Density (ha -1 ) Zone 1 Zone 2 Zone 3 Alien Indigenous B = Before clearing A = After clearing B A B A B A B A B A B A B A B A B A B A B A B A Transect number IAP density Before 3508 plants/ha vs. After 343 plants/ha Average reduction 80% in IAP density (P=0.0002) Zone 3 lowest alien densities (P=0.014) low propagule pressure 14

15 Objective 1: Alien Species Growth form Longevity Legal status Species 1 Densely invaded sites Herb Annual n/a Acanthospermum hispidum 9 3 Shrub Perennial DW1 Lantana camara 5 1 Shrub Annual n/a Senna obtusifolia Shrub Perennial n/a Senna occidentalis Herb Annual n/a Tagetes minuta Herb Annual DW1 Xanthium strumarium Total percentage density of abundant alien species Total percentage density of all invasive alien species Percentage of total alien density

16 Objective 1 Assess density of IAP before and after clearing Densities of IAP were significantly reduced after clearing. 16

17 Objective 2: IAP density effect on rs Rarefied species Richness R 2 = P = R 2 = P= Percent alien density Pre-clearance Post-clearance 17

18 Objective 2: IAP density effect on diversity Sim pson's diversity R 2 = P = Pre-clearance Post-clearance Poly. (Post-clearance) Poly. (Pre-clearance) R 2 = P = Percent alien density 18

19 Objective 2: IAP density effect on evenness Simpson's evenness R 2 = P= R 2 = P = Percent alien density Pre-clearance Post-clearance Expon. (Post-clearance) Expon. (Pre-clearance) 19

20 Objective 2 Assess effects of IAP on plant community structure Negative relationship - IAP density and diversity Major contribution of IAP densities annual /short-lived perennial spp. Often not a priority on management agendas BUT lower profile species in high abundance can have a negative impact on community diversity. 20

21 Objective 3: Response of indigenous veg. Indigenous Density (ha -1 ) Zone 1 Zone 2 Zone 3 B A B A B A B A B A B A B A B A B A B A B A B A Transect number B = Before clearing A = After clearing 21

22 Objective 3: Contribution of increaser spp. Percentage contribution % Alien density Zone 1 Zone 2 Zone Herbs Shrubs Trees Site

23 Objective 3 Patterns of veg. regrowth Herbaceous growth forms increased in response to removal of IAP in densely invaded sites. High levels of indigenous regrowth system shows resilience to disturbance by IAP. NB factor facilitates resilience ongoing clearing of IAP: - depletes alien seedbanks and maintains IAP at levels that are manageable. 23

24 CONCLUSIONS WfW teams are effective in short term clearing Levels of ecosystem recovery are high and no further intervention is needed in systems of higher integrity such as Kruger Repeated clearing maintains IAP at manageable levels - perhaps when acceptable control is sustainable in the long term - surplus resources can be rotated to other areas of need. 24

25 Thank you! Mellon Foundation National Research Foundation Working for Water KNP WfW managers SANparks & Kruger National Park Riparian Restoration team Andrew W. Mellon Foundation 25