Ecological Report Struwig Eco-Reserve by Wildlife & Ecological Investments: 2012 to 2015

Transcription

1 Ecological Report Struwig Eco-Reserve by Wildlife & Ecological Investments: 2012 to 2015 WILDLIFE AND ECOLOGICAL INVESTMENTS (Registered as an NPO under Act 71 of 1997) Unit 20, Fountain Square, 136 Main Rd, Somerset West, 7130 P.O. Box 3288, Somerset West, 7129 Tel: +27 (0) Fax: +27 (0)

2 Contents Introduction... 3 Study Area... 4 Methods... 4 Bird Surveys... 4 Habitat Assessment... 5 Grass surveys... 6 Results... 7 Summary... 7 Bird Surveys... 7 Habitat Assessments... 8 Grass surveys Discussion References List of Appendices

3 Introduction Wildlife and Ecological Investments (WEI) has conducted ecological surveys and biodiversity monitoring in the Struwig Eco-Reserve since Collection of data over an extended time periods allows for an opportunity to detect trends and patterns. To best understand the health of an ecosystem we need to 1) monitor the response of organisms to their environment, 2) examine the response of populations of a specific species to the environment and considering processes such as abundance and fluctuations and 3) investigate the composition and structure of communities within a defined area. With this information we are better able to further examine the processes occurring within an ecosystem. Ecosystems have a wide range of components each responding to their environment. Complete and holistic biodiversity monitoring is impossible due to the large taxa representation. It is for this reason that WEI surveys macro fauna and flora. By surveying key organisms within an ecosystem, we obtain clues into ecosystem functioning and processes. To date the data that has been collected covers a wide ecological range and consists of herbaceous, woody vegetation, bird, insects and mammal surveys. The data has been collected systematically and consistently using the same methods within the same sampling sites. Vegetation communities are a critical foundation for determining numerous factors about an ecosystem. The health of an ecosystem can be determined by the quality of the vegetation particularly in terms of its function to provide food, shelter and soil stabilising amongst others. Detecting changes in vegetation quantity and quality influences the available browse and graze for ungulates. When considering large mammals such as elephants then monitoring of vegetation becomes of high importance for management. For this reason WEI conducts habitat assessments by monitoring the impacts on woody vegetation by elephants specifically however other ungulates are taken into account. Although Struwig Eco-Reserve is an open system with the Kruger National Park, understanding the impacts of elephants on vegetation may provide insight into the role of elephants as drivers in an ecosystem. Similarly birds are influenced by vegetation structures thus it is necessary to monitor birds to assess biodiversity and as indicators of ecosystem health. When monitoring the different bird species we categorise them into feeding guilds (frugivore, carnivore etc.) as this provides more detailed insight into the ecosystem health and processes. Birds are relatively diverse, easy to identify in the field and have different habitat requirements depending on the feeding guild. By subdividing the bird community into feeding guilds, we compensate for yearly changes in populations. The reserve can make use of the data collected and analysed by WEI to review changes over time where management can gain insight into the functioning and health of the reserve. Furthermore, the baseline data can contribute towards future specialised research or management decisions. This report supplies information on the trends and data collected since For the purpose of this report we have analysed vegetation and bird data. The extent of mammal data collected from game transects and camera trapping require a separate analysis and report. A separate report will analyse the details of the changes at each site as we hope to examine in depth the 2016 data after the drought. 3

4 Study Area Struwig Eco- Reserve is approximately 3,800ha and falls within Balule Game Reserve. The Olifants River forms the northern border. Ecological surveying began in 2012 in 17 sample sites evenly distributed across the reserve. The 17 sample sites are each 1ha plots and are GPS geotagged for ease of relocating (Figure 1). The collection of data from 2012 to 2015 has allowed us to obtain benchmark information to detect trends and patterns. This is particularly relevant in the face of drought and climatic changes that may impact the reserve. The survey sites are intended to be representative of the Struwig Eco-Reserve and thus we can use this data to infer the trends and patterns throughout the reserve. Figure 1: The locations of the 17 sites where ecological surveying is conducted throughout the year. Methods Bird Surveys Bird Point Counts (BPC) were conducted at each of the sampling sites at dawn when bird activity is highest. All birds seen and heard were recorded, the birds behaviour (flying, perched in the canopy or mid-storey etc.), GPS geotagged the location and the environmental information recorded. Bird species richness and diversity were calculated between 2012 and 2015 in Struwig. For ease of analysis the bird species were divided into feeding guilds namely insectivore/invertebrates, omnivore, carnivore, frugivore, nectivore and granivore. The feeding guild of each species identified was verified in the Roberts Bird Guide (Chittenden 2009). To calculate the species richness we used the Menhinick s Index (IM n) which is a species richness indices (Menhinick 1964). This index is based on the total number of species and individuals in the sample: I Mn = S N 4

5 The index is based on the ratio of species in a guild (S) and the square root of the total number of individuals in the guild (N). The Shannon Index (H) was used to determine the heterogeneity indices of the bird groups. This index measures species richness and evenness (Mirzaie et al., 2013). We used the Shannon Index of Diversity to determine the species diversity between the guilds. S H = (pi)lnpi i=1 The Shannon Index (H) is scored between 0 and 1 where 0 means there is no diversity and 1 is highly diverse. Where S is the total number of species in the community (richness), pi the proportion of S made up of the i th species. To determine if there was a difference between the years we used the One-way ANOVA. To determine if there was a difference between the guilds we used a One-way ANOVA. For both between years and between guilds, we used the Tukey Test when a significant difference was found. Habitat Assessment At each of the 17 habitat assessment sites we recorded all woody vegetation over 1 metre tall. Other data recorded included species name, height class, basal stem diameter, average stem diameter (for multi-stemmed bushes), the width of the widest point of the canopy, and the extent of elephant and fire impact (fire data is not featured in this report). A qualitative and quantitative evaluation of elephant and other browser impact was graded according to the Walker scale (Walker 1976) as detailed below: TYPE: CODE: Pulled or kicked out A Pushed over and dead or apparently dead B Main trunk broken, is or appears to be dead C Main trunk broken but re-sprouting or likely to re-sprout D Pushed over but still alive E Main trunk tusk-slashed F Main trunk debarked (% of the circumference) *G Roots exposed and eaten (% of the circumference) *H Primary branches broken *J Secondary and/or smaller branches broken *K None: Z *Impact types G, H, J, K must be quantified according to the percentage classes given below. The percentage classes refer to the percentage of the total canopy volume (J & K) and are estimated. In the case of exposed roots and debarking of the main trunk (types G & H), the percentage of the root base or trunk's perimeter (i.e. a circle) affected must be estimated and coded accordingly. 1-10% 11-25% 26-50% 51-75% 76-90% % 5

6 For the purpose of this report we focused on the height categories and species of the woody vegetation. The One-way ANOVA was used to determine if there was an overall change between the years the woody vegetation was measured in terms of the species and height categories between the years. If a significant difference was found we used the Tukey Test to identify where the difference was. The impact of elephants on woody vegetation was analysed by generating an impact score (IS): % impacted = ( si Nti )x100 Where si is the number of trees of the species or height category impacted and N ti is the total number of trees impacted. % availability = ( s ) x 100 Nt Where s is the number of tree species or height category measured and N t is the total number of trees. IS = %impacted %availability We also used the Jacob s Index to identify if there was a preference for either a species or a height category: D = r p r+p 2rp Where r is the proportion of the impacted trees by elephants in a year and p is the proportional availability of each species given the total trees sampled. The resulting values range from +1 which is maximum preference and -1 which is maximum avoidance. Grass surveys The herbaceous layer was measured to monitor volume of grass available. Grasses were measured between 2012 and The data for 2015 was unavailable at the time of analysis. The volume of the grass was measured using a Disk Pasture Meter (DPM) which was calibrated according to the Kruger National Park measurements. We analysed the data using equations from Zambatis et al., (2006) for grasses (<26 cm) and (> 26 cm) as stipulated in studies conducted in the Kruger National Park. The equation used to measure the grass volume for grasses <26 cm: Where x is the mean DPM height of at a site. Kg/ha -1 = [ ( x )x ] 2 The equation used to measure the grass volume for grasses >26 cm: Where x is the mean DPM height of at a site. Kg/ha -1 = [ ( /x )x ] 2 We compared the grass height and DPM measurements between 2012 and 2014 using One-way ANOVA. If a significant difference was found we used the Tukey Test to identify where the difference was. 6

7 Shannon's Index Results Summary Table 1: A summary of the number of ecological sites surveyed between 2012 and Survey sites Bird surveys Woody vegetation Grasses Bird Surveys Approximately 300 bird species are known to occur in the OREC. Of these species all six (insectivore/invertebrates, omnivore, carnivore, frugivore, nectivore and granivore) of the feeding guilds were represented. We observed 269 of the bird species listed as occurring in the OREC region. There were two birds that were seen twice that were on the edge of their range, the Green-backed camaroptera and the Yellow-fronted tinker bird. Of the birds seen six are listed on the IUCN Redlist as Near Threatened and one listed as Vulnerable (Appendix I). The Menhinick s Index suggested that there was little difference in species richness between the years (mean ± SD; ± 1.71). The species richness between 2012 and 2015 was not significantly different (F 3,20 = 0.91, p > 0.05). Shannon s Index of Diversity was defined as even between the years (Figure 2). 0,40 0,35 0,30 0,25 0,20 0,15 0,10 0,05 0,00 Insectivore Omnivore Frugivore Granivore Carnivore Nectivore Figure 2: Shannon s Index of Diversity of bird feeding guilds in Struwig Eco-Reserve from 2012 to Within each year there was a significant difference between the guilds (F 5,18 = 9.76, p < 0.05). The Tukey Test indicated that the difference was with the insectivores. The insectivores were more highly represented than the other guilds. This was closely followed by the omnivores. 7

8 Number of trees Habitat Assessments The woody vegetation (N = 2019) was measured between 2012 and The available woody vegetation (Figure 3) and elephant impacted vegetation (Figure 4) was measured and compared. There was no significant difference in the available woody vegetation measured (F 3,16 = 0.77, p > 0.05) and the woody vegetation impacted (F 3,16 = 0.76, p > 0.05) by elephants between the years 2012 and Within the height categories, there was a significant difference between the available woody vegetation measured (F 5,18 = 456, p < 0.05 ) and the woody vegetation impacted (F 5,18 = 1999, p < 0.05). The height category with the greatest elephant impact was 4-6m (Figure 5). Of the woody vegetation sampled, when using the impact score for species, Acacia erubescens, Acacia nigrescens, Dichrostachys cinerea and Sclerocarya birrea had the highest impact score (> 1). According to the Jacob s Index there was a preference for Acacia erubescens (D= 0.65) and Acacia nigrescens (D = 0.85) in In 2012 to 2014 there was little preference indicated by the Jacob s Index for any species. When using the impact score for height classes, woody vegetation between 1 to 2m had a score >1 for all years sampled (Figure 6) > Figure 3: Number of trees measured in the Struwig Eco-Reserve between 2012 and 2015 according to height category. 8

9 Proportion of trees (%) Number of trees > Figure 4: Woody vegetation impacted by elephants in the Struwig Eco-Reserve between 2012 and Impacted Available >10 Figure 5: The proportion of trees available and impacted by elephants in the Struwig Eco-Reserve between 2012 and 2015 according to height categories. 9

10 Grass height (cm) Impact score 1,60 1,40 1,20 1,00 0,80 0,60 0,40 0,20 0, > Figure 6: Impact Score of elephants on woody vegetation on different height categories in Struwig Eco-Reserve from 2012 to Where >1 is selected and <1 is not selected. Grass surveys The average grass height in 2012 (x = 23.77) at all sites was below 26cm while in the average grass height at all sites in 2013 (x = 47.59) and 2014 (x = 58.40) was above 26cm. There was a difference in grass height (F 2,33 = 12.25, p < 0.05) between 2012 and 2014 (Figure 7). The Tukey Test suggests that 2012 was different from 2013 and There was a difference in the DPM measurements (F 3,35 = 5.26, p < 0.05) from 2012 to 2014 (Figure 8) which was made evident in the difference in the average kg/ha -1 in 2012 (x = 1433 kg/ha -1 ), 2013 (x = 2899 kg/ha -1 ) and 2014 (x = 2799 kg/ha -1 ) Figure 7: Height of grass at 17 sites measured in Struwig Eco-Reserve between 2012 and

11 kg/ha Figure 8: Disk Pasture Meter readings of grass measured at 17 sites in Struwig Eco-Reserve between 2012 and Discussion Savanna systems are generally defined as stable and resilient however dynamic climatic changes and management strategies can manifest in a cascade effect through the trophic levels. An ecosystem such as the savannah, has underlying variables that gradually push that ecosystem towards a threshold. When a dramatic event such as a drought occurs then habitats and organisms can become affected. By collecting data over a long term period will allow for detection of changes. Similarly by monitoring habitats and bird communities, WEI is better able to investigate the drivers and consequences. The results from the bird survey suggest that species richness in terms of feeding guilds has not changed significantly since Insectivores represent approximately 60% of the known bird species thus they are highly represented in Struwig likely because this group has the largest representation (Morse 1971). Species richness in an ecosystem is dependent on the resources available such as food and shelter as well as competition for these resources. The evenness of abundance describes the relative abundance of species in each guild that make up the bird community. Evenness of abundance is considered high when the different species have similar abundances (Cotgreave & Harvey 1994). Although the insectivores had the highest abundance, the data suggests that evenness was high between the years for all the guilds. Evenness of bird communities varies by habitat thus further analysis of where the different groups are located and their relationship with elephant impact on vegetation will need to be analysed. Similarly further analysis on the effects of the 2016 drought on the species richness and evenness as well as the changes in migrant and resident species will need to be conducted. The data from the habitat assessments indicated that there was little change in the amount of available woody vegetation and elephant impact from 2012 to However, within the height 11

12 categories there was a change in the available and impacted woody vegetation. Tress below 4m are high in abundance thus they were selected according to their availability. There was however, a preference for trees taller than 4m. This is likely due to the palatability of the preferred trees; Acacia erubescens, Acacia nigrescens, Dichrostachys cinerea and Sclerocarya birrea. Further analysis on the changes over time between sites in different habitats is needed. This would provide insight and supporting data into the role of elephants as drivers in an ecosystem. The herbaceous data collected at the sites do not estimate grass biomass as we cover much larger areas than standard Veld Condition Assessments. The changes detected in grass volume from 2012 to 2014 will need to be compared with rainfall patterns as well as the data from game counts to investigate what was the driver behind the variation. The data collected to date provides an opportunity for future analysis as we continue surveying over the long term for several years. We currently gather very little information from so few sites in such a small area. The lack of significance with the results is likely due to the lack of data from a larger survey area. From the data collected and the information provided thus far, we could significantly increase the number of survey sites throughout Balule Game Reserve so that we can start to develop species distribution maps for the wider area and map species diversity across the Reserve using predictive species distribution modelling. Furthermore, we could detect trends and patterns and monitor the health of a greater ecosystem. References Cotgreave, P. and Harvey, P.H Evenness of abundance in bird communities. Journal of Animal Ecology. 63: Menhinick, E.F A comparison of some species-individuals diversity indices applied to sample of field insects. Ecology. 45(4): Mirzaie, F.S., Ghorbani, R. and Montajami, S A comparative study of different biological indices sensitivity: A case study of macroinvertibrates of Gomishan Wetland, Iran. World Journal of Fish and Marine Sciences. 5(6): Morse, D.H The insectivorous birds as an adaptive strategy. Annual Review of Ecology and Systematics. 2: Zambatis, N., Zacharias, P.J.K., Morris, C.D. and Derry, J.F Re-evaluation of the disc pasture meter calibration for the Kruger National Park, South Africa. African Journal of Range & Forage Science. 23(2):

13 List of Appendices Appendix I: List of birds identified during surveys on Struwig Eco-Reserve from 2012 to 2015 and birds on the IUCN Redlist birds that are Near Threatened*, Vulnerable**, Endangered*** or Critically Endangered****. Acacia Pied Barbet African Barred Owlet African Darter African Dusky Flycather African Firefinch African Fish-Eagle African Goshawk African Green-Pigeon African Grey Hornbill African Hawk-Eagle African Hoopoe African Jacana African Spoonbill African Wattled Lapwing Alpine Swift Amethyst Sunbird Arrow-marked babbler Ashy Flycatcher Barn Swallow Barratt's Warbler Bar-throated Apalis Bateleur* Bearded Scrub-Robin Bearded Woodpecker Bennett's Woodpecker Black Cuckooshrike Black Sparrow Hawk Black-backed Puffback Black-collared Barbet Black-crowned Tchagra Black-headed Oriole Black-shouldered Kite Blacksmith Lapwing Black-winged Stilt Blue Waxbill Bronze Mannikin Brown Snake-Eagle Brown throated Martin Brown-crowned Tchagra Brown-Hooded Kingfisher Brubru Burchell's Coucal Burchell's Starling Cape Glossy Starling Cape Turtle-Dove Cape Vulture*** Cape White-Eye Cardinal Woodpecker Cattle Egret Chinspot Batis Chorister Robin-Chat Cinnamon-breasted Bunting Cloud Cisticola Collared Sunbird Common Scimitarbill Common Swift Common Waxbill Crested Barbet Crested Francolin Croaking Cisticola Crowned Lapwing Dark Chanting Goshawk Dark-capped Bulbul Diderick Cuckoo Double-banded Sandgrouse Dusky Flycatcher Egyptian Goose African Paradise- Flycatcher African Pied Wagtail Emerald-spotted Wood- Dove Eurasian Golden Oriole European Bee-eater European Nightjar Flappet Lark Fork-tailed Drongo Gabar Goshawk Giant Kingfisher Glossy Ibis Golden-breasted Bunting Golden-tailed Woodpecker Greater Blue-eared Starling Greater Honeyguide Greater Striped Swallow Green Wood-Hoopoe Green-backed Camaroptera Green-capped Eremomela Green-winged Pytilia Grey Go-away-bird Grey Heron Grey Penduline-Tit Grey Tit-Flycatcher Grey-backed Camaroptera Grey-headed Bush-Shrike Grey-headed Sparrow (Southern) Groundscraper Thrush Hadeda Ibis Hamerkop Helmeted Guineafowl 13

14 Hooded Vulture House Sparrow Icterine Warbler Jacobin Cuckoo Jameson's Firefinch Klaas's Cuckoo Kurrichane Thrush Laughing Dove Lesser Masked-Weaver Lesser Striped Swallow Levaillant's Cuckoo Lilac-breasted Roller Little Bee-eater Little Egret Little Rush-Warbler Little Swift Lizard Buzzard Long-billed Crombec Long-tailed Whydah Magpie Shrike Marico Sunbird Martial Eagle** Mocking Cliff-Chat Monotonous Lark Namaqua Dove Natal Spurfowl Neddicky Pel's Fishing-Owl Pied Crow Pied Kingfisher Purple Roller Rattling Cisticola Red-backed Shrike Red-billed Hornbill Red-billed Oxpecker Red-billed Quelea Red-crested Korhaan Red-eyed Dove Red-faced Cisticola Red-faced Mousebird Red-headed Weaver Reed Cormorant Retz's Helmet-Shrike Rufous-naped Lark Sabota Lark Scarlet-chested Sunbird Shelly's Fracolin Sombre Greenbul Southern Black Flycatcher Southern Black Tit Southern Boubou Southern Double-collared Sunbird Southern Grey-headed Sparrow Southern Ground-Hornbill Southern White-crowned Shrike Southern White-faced Scops-Owl Southern Yellow-billed Hornbill Speckled Mousebird Spectacled Weaver Stierling's Wren- Warbler Stripped Pipit Swainson's Spurfowl Swee Waxbill Tawny Eagle Three-banded Plover Violet-backed Starling White-bellied Sunbird Water Thick-knee White-breasted Cormorant White-backed Vulture**** Paradise- Orange-breasted Bush- Shrike Pearl-spotted Owlet Red-billed Buffalo- Weaver Red-billed Firefinch White-browed Scrub- Robin White-fronted Bee-eater Wood Sandpiper Yellow-billed Stork Yellow-breasted Apalis Yellow-fronted tinkerbird Yellow-throated Petronia Yellow-fronted Canary Zitting Cisticola 14

15 Appendix II: List of commonly found tree species that were measured in Struwig Eco-Reserve between 2012 and Acacia angilatum Acacia burkei Acacia caffra Acacia erubescens Acacia gerrardii Acacia grandicornuta Acacia karroo Acacia nigrescens Boscia albitrunca Cissus cornifolia Colophospermum mopane Combretum apiculatum Combretum hereoense Combretum imberbe Combretum mozbiquenes Commiphora africana Commiphora pyracanthiode Dichrostachys cinerea Euclea undulata Grewia bicolor Grewia caffra Grewia flava Grewia flavescens Grewia hexamita Grewia monticola Grewia villosa Lannea schweinfurthii Peltophorum africanum Philenoptera violacea Sclerocarya birrea Small-leaved Guarri Stink shepard Terminalia prunioides Ziziphus mucronata 15