Exclosure Field Manual
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Effects of herbivores and fire on riparian and upland savanna ecosystems Field Operations Manual for Herbivore & Fire Exclosures on the Sabie and Letaba Rivers in the Kruger National Park Compiled by Thomas O’Keefe and Glynn Alard December 2002 1 Contents Project Summary 3 Introduction 5 Project Background and History of Development 5 Guiding Research Questions 7 Vegetation Community and Disturbance Processes 7 Soil Ecology and Biogeochemistry 9 Additional areas of research interest 11 Exclosure Layout 12 Vegetation Sampling Protocol 13 Transects 13 Plots 14 Methods 16 Woody species 16 Herbaceous species 17 Alien plants 19 Instrumentation Protocol 19 Atmospheric Monitoring 19 Soil Monitoring 20 Ground water Monitoring 21 Fixed Point Photos 21 Fine scale 21 Coarse scale 21 2 Detailed Site Map Methodology 22 Aerial Photography 22 Management 23 Site Management 23 Patrolling & Maintenance 23 Data Management 24 Access 24 Rules and Safety 25 Contacts 27 References 27 Appendix Kruger Park Map Kruger Park 2000 Flood photos Sabie and Letaba River photos Schematic of Exclosure Layout Fencing Specifications Letaba Site, species list Sabie Site, species list Aerial view of Sabie sites showing basic vegetation associations Field Equipment List Elephant and Fire Impact assessment Aerial photo of Sabie pre and post flood Aerial photo of Letaba pre and post flood Channel detail of Sabie pre and post flood Sabie River site map Letaba River site map Data Sheets 3 Project Summary Recent (February 2000) floods on the eastern seaboard of Southern Africa inundated large areas of the Mozambique coastal plain. Rivers draining Kruger National Park (KNP) in South Africa experienced flows (c. 8,000 m3 s-1 for the Sabie River) with return intervals of approximately 1:50 years, causing widespread removal of riverine vegetation and extensive alterations to channel habitat. The floods caused widespread human suffering but also provided a unique research opportunity. For the first time in nearly a century we will be able to characterize the long-term development and recovery of riverine forests from a major disturbance. Savanna landscapes in South Africa are important reservoirs of biodiversity that are affected by expanding human populations and shifting patterns of land use. Within these landscapes, the riverine forests are important boundaries between aquatic and terrestrial systems that define the biodiversity and heterogeneity of these ecosystems. South African National Parks rates research along with ecosystem conservation as two of its core activities. Together with an international team of scientists we have constructed large exclosures to study the role of herbivory and fire in the alteration and determination of spatial and temporal heterogeneity patterns of vegetation. This research will directly benefit our ecosystem conservation planning. In their basic form, exclosures are fenced areas designed to keep out animals. At each locality, a pair of exclosures will limit the accessibility of herbivores; one being a “total” (electrified) exclosure, i.e. to exclude all herbivores (plant-eaters) from a hare upwards in size, and a “semi-exclosure”, consisting only of two cables and electric wiring at 1.8 m and 2.2 m above ground. The purpose of the semi-exclosure is to exclude elephant, and, by virtue of their size, giraffe, but will allow access to all other herbivores. Each exclosure will be divided in half, with one half allowed to burn should fire pass through, and the other kept unburned. These exclosures will extend from within the river channel to the crest, in order to enclose the full sequence of terrain morphological 4 features and their associated soils, vegetation, and smaller fauna. This will allow for the study of the relationships of habitats along the topographic gradient, from the crest to within the river channel. Funding for construction of the exclosures was provided by a grant from the U.S. National Science Foundation and funding from the Kruger Park Marathon Club. Kruger Park staff will maintain the exclosures while continuing to promote involvement with international scientists to conduct research at the sites. The placement of large herbivore exclosures in the Kruger National Park (KNP) is a fundamental research activity that provides solid evidence on which our whole management policy rests. A critical component of the current research initiative in the KNP concerns the effects of herbivores (especially elephant) and fire on the vegetation and biodiversity of the Park, with the ultimate objective of devising (or revising existing) scientifically based management policies. The rationale behind exclosures is that by excluding these two important modifiers of the ecosystem, their effects on the ecosystem can be determined over time. The proposed exclosures are thus designed to address these issues, as well as post-flood recovery of riparian vegetation which is thought to be heavily influenced by herbivory. As the nature of some ecological changes or processes are of a long-term nature, the exclosures will serve as long-term monitoring and research sites for at least 25 years. At that time, the objectives for the future use of the exclosures should be reviewed. These exclosures will thus provide extremely valuable long-term information on key ecological processes; information that would be nearly impossible to obtain. The exclosures along the Sabie are located across the river from Nkuhlu picnic site, in the area between the Sabie River and the Salitjie road. The Letaba exclosures are located approximately midway between the low-water bridge over the Letaba, and Mingerhout dam, and thus far from public view in a wilderness area. Special permission was obtained to locate the exclosure here and it may be subject to special research conditions. 5 Introduction Savanna landscapes in South Africa are important reservoirs of biodiversity, and are affected by expanding human populations and shifting patterns of land use. In order to understand and manage these landscapes, several concepts must be employed. Foremost is the application of a modern systems viewpoint (e.g., Likens 1992), which hypothesizes that spatial and temporal heterogeneity of savannas are key to their function (Rogers 1997). In these landscapes, large herbivores and fire are recognized to play an important role in determining these heterogeneous spatial and temporal patterns through their effects on vegetation and the physical landscape. Despite this general knowledge that herbivory and fire are important, careful long-term studies that rigorously document the changes in isolation and as interactions have yet to be conducted. Through the construction of large herbivore exclosures overlapping with fire treatments our primary research objective is to determine how herbivory and fire alter spatial and temporal heterogeneity patterns. These exclosures will extend from within the river channel to the crest, and encompass the riparian corridor representing a full sequence of geomorphological features and their associated soils, vegetation, and smaller fauna. Riparian corridors are perhaps the most obvious expression of boundaries in savanna regions, and these boundaries defining the heterogeneity of these ecosystems are of particular ecological interest. Project Background and History of Development This cooperative program builds on the extensive knowledge base generated by the many decades of research conducted by the Kruger National Park Scientific Services, and the decade-long Kruger National Park River Research Program and more recent River Savanna Boundaries Program in collaboration with several South African and American universities, government departments, and research agencies. The Kruger Park has a long history of interest in the possibility of erection of formal research exclosures (rather than the “incidental exclosures” which have become available because of for instance, enclosures being built to breed up rare antelope). This interest relates 6 particularly relating to fire and elephant effects. Fortunately this historical interest, and the more recent interest of other groups in riparian and riparian-upland issues in the Kruger Park, has provided an opportunity for unified structures dealing with all these interests, to be put in place. In February 2000 the Kruger National Park was presented with a unique opportunity to develop a long-term experiment designed to examine the effects of herbivory. The largest flood since 1925 for the Sabie (7,000 to 8,000 m3 s-1) and Letaba rivers removed most of the vegetation along these rivers, primary research sites in the park, resetting the system to bedrock and sand. The vegetation before the flood was a mature riparian forest including stately fig and other majestic riparian trees. The Sabie River catchment is 7,086 km2 with a river length of 230 km and a mean discharge of 633 million m3/a. The Letaba catchment is 13400 km2 with a length of 490 km and a mean discharge of 631 million m3/a. Construction of large exclosures subsequent to this major flood event will allow us to follow the successional development and pattern formation of vegetation along riparian zones. Riparian zones are recognized as “hotspots” of activity because they integrate terrestrial and aquatic systems (Naiman and Décamps 1997). We believe the research we are conducting (viewed across aquatic, riparian and upland zones) will generate a novel understanding of savannas as integrated yet heterogeneous ecological systems. The systems approach to