Landscape history, time lags and drivers of change: urban natural grassland remnants in Potchefstroom, South Africa
- 474 Downloads
The history of the landscape directly affects biotic assemblages, resulting in time lags in species response to disturbances. In highly fragmented environments, this phenomenon often causes extinction debts. However, few studies have been carried out in urban settings.
To determine if there are time lags in the response of temperate natural grasslands to urbanization. Does it differ for indigenous species and for species indicative of disturbance and between woody and open grasslands? Do these time lags change over time? What are the potential landscape factors driving these changes? What are the corresponding vegetation changes?
In 1995 and 2012 vegetation sampling was carried out in 43 urban grassland sites. We calculated six urbanization and landscape measures in a 500 m buffer area surrounding each site for 1938, 1961, 1970, 1994, 1999, 2006, and 2010. We used generalized linear models and model selection to determine which time period best predicted the contemporary species richness patterns.
Woody grasslands showed time lags of 20–40 years. Contemporary open grassland communities were, generally, associated with more contemporary landscapes. Altitude and road network density of natural areas were the most frequent predictors of species richness. The importance of the predictors changed between the different models. Species richness, specifically, indigenous herbaceous species, declined from 1995 to 2012.
The history of urbanization affects contemporary urban vegetation assemblages. This indicates potential extinction debts, which have important consequences for biodiversity conservation planning and sustainable future scenarios.
KeywordsUrban ecology Urban landscape measures Temperate grasslands Indigenous species Exotic species Disturbance indicator species Extinction debt
We would like to thank the South African Weather Service for long-term climate data of Potchefstroom and the National Research Foundation (NRF) for financial assistance towards the studies of MJDT and incentive funding for SSC.
- Beyer HL (2006) Hawth’s analysis tools version 3.27Google Scholar
- Clarke KR, Gorley RN (2006) PRIMER v6: user manual/tutorial. PRIMER-E, PlymouthGoogle Scholar
- Davis MB (1986) Climatic instability, time lags, and community disequilibrium. In: Diamond J, Case TJ (eds) Community ecology. Harper & Row, New York, pp 269–284Google Scholar
- du Toit MJ (2009) Grassland ecology along an urban–rural gradient using GIS techniques in Klerksdorp, South Africa. North-West University, Potchefstroom. http://hdl.handle.net/10394/4197
- ESRI (2010) ArcGIS, version 10.0. Environmental Systems Research Institude, Redlands, CAGoogle Scholar
- Hamburg SP, Sanford RL Jr (1986) Disturbance, “Homo Sapiens,” and ecology. Bull Ecol Soc Am 67(2):169–171Google Scholar
- Jansen van Rensburg JP (2010) Investigation of the microbial diversity and functionality of soil in fragmented South African grasslands along an urbanization gradient. North-West University, PotchefstroomGoogle Scholar
- Kleijn D, Kohler F, Baldi A, Batary P, Concepcion ED, Clough Y, Diaz M, Gabriel D, Holzschuh A, Knop E, Kovacs A, Marshall EJ, Tscharntke T, Verhulst J (2009) On the relationship between farmland biodiversity and land-use intensity in Europe. Proc Biol Sci 276(1658):903–909CrossRefPubMedGoogle Scholar
- Krauss J, Bommarco R, Guardiola M, Heikkinen RK, Helm A, Kuussaari M, Lindborg R, Ockinger E, Partel M, Pino J, Poyry J, Raatikainen KM, Sang A, Stefanescu C, Teder T, Zobel M, Steffan-Dewenter I (2010) Habitat fragmentation causes immediate and time-delayed biodiversity loss at different trophic levels. Ecol Lett 13(5):597–605CrossRefPubMedPubMedCentralGoogle Scholar
- Louw WJ (1951) An ecological account of the vegetation of the Potchefstroom area. Memoirs of the botanical survey of South Africa, no. 24Google Scholar
- Mucina L, Rutherford MC (eds) (2006) The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, PretoriaGoogle Scholar
- Mueller-Dombois D, Ellenberg H (1974) Aims and methods of plant ecology. Wiley, New YorkGoogle Scholar
- Neser L (1967) Die Kleurlinge van Potchefstroom:’n algemene kultuurbeeld met besondere verwysing na gesinsgebruike. Potchefstroomse Universiteit vir Christelike Hoër OnderwysGoogle Scholar
- R Core Team (2013) R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna. http://R-project.org/
- Retief E, Herman PPJ (1997) Plants of the northern provinces of South Africa: keys and diagnostic characters. Strelitzia 6. South African National Biodiversity Institute, PretoriaGoogle Scholar
- Smit PA (1989) Die ekonomiese ontwikkeling van Potchefstroom vanaf 1902 tot 1945. Potchefstroom University for CHE, PotchefstroomGoogle Scholar
- Tlokwe City Council (2015) Business overview. http://www.potch.co.za/cdepstatment.htm. Accessed 25 April 2015
- van den Bergh G (1990) Voortrekker plaasbesetting op die Transvaalse Hoëveld: ‘n versteurde beeld. S Afr J Surv Mapp 20( Part 7):301–311Google Scholar
- van den Bergh G (1992) Die tweede Potchefstroom, opmeting en besetting 1841-60. S Afr J Surv Mapp 21(Part 4):167–178Google Scholar
- van der Walt L (2013) Landscape functionality and plant diversity of grassland fragments along an urban–rural gradient in the Tlokwe Municipal area, South Africa. North-West University, Potchefstroom. http://hdl.handle.net/10394/9732