Landscape‐scale vegetation dynamics inferred from spatial patterns of soil δ13C in a subtropical savanna parkland

[1] Grasslands and savannas around the world have experienced woody plant encroachment during the past 100 years, but we know little regarding the manner in which woody plants spread across the landscape. We used soil δ 13 C, aerial photography, and geostatistics to quantify patterns of woody encroachment in a 160 x 100 m georeferenced grid subdivided into 10 × 10 m cells in a savanna parkland landscape in southern Texas. δ 13 C contour maps revealed that centers of closed contours coincided with centers of woody patches, and that larger woody patches developed from smaller woody plant clusters that spread laterally and coalesced. Areas where woody patches were expanding into grassland were characterized by low densities of soil δ 13 C contour lines, and indicated the direction and extent of woody encroachment. Conversely, areas with high contour densities represented grassland-woodland boundaries that were temporally stable. Indeed, aerial photos from 1930, 1941, 1982, and 2003 confirmed that woody patches with low spatial variability in δ 13 C corresponded to areas where woody plants had encroached during the past 30―75 years. While aerial photos can only record vegetation cover at the photo acquisition time, kriged maps of soil δ 13 C allowed us to accurately reconstruct long-term temporal dynamics of woody plant encroachment into grassland. This approach can reliably reconstruct landscape-scale vegetation changes in areas where historical aerial photography or satellite imagery are unavailable and provides a strong spatial context for studies aimed at understanding the functional consequences of vegetation change.

[1]  T. Boutton,et al.  Stable carbon isotope ratios of soil organic matter and their use as indicators of vegetation and climate change. , 1996 .

[2]  A. Rango,et al.  Object-oriented image analysis for mapping shrub encroachment from 1937 to 2003 in southern New Mexico , 2004 .

[3]  T. Dollery,et al.  Stable Isotopes , 1978, Palgrave Macmillan UK.

[4]  S. Archer,et al.  Simulated dynamics of succession in a North American subtropical Prosopis savanna , 1991 .

[5]  C. Scrimgeour,et al.  Spatial variability of soil total C and N and their stable isotopes in an upland Scottish grassland , 1997, Plant and Soil.

[6]  J. Derner,et al.  Grazing and Ecosystem Carbon Storage in the North American Great Plains , 2006, Plant and Soil.

[7]  Joanna Isobel House,et al.  Conundrums in mixed woody–herbaceous plant systems , 2003 .

[8]  R. Houghton,et al.  Changes in terrestrial carbon storage in the United States. 2: The role of fire and fire management , 2000 .

[9]  Roberta E. Martin,et al.  GRAZING SYSTEMS, ECOSYSTEM RESPONSES, AND GLOBAL CHANGE , 2004 .

[10]  Luiz Antonio Martinelli,et al.  Influence of soil texture on carbon dynamics and storage potential in tropical forest soils of Amazonia , 2003 .

[11]  C. Kessel,et al.  Carbon‐13 and Nitrogen‐15 Natural Abundance in Crop Residues and Soil Organic Matter , 1994 .

[12]  Vegetation dynamics in a Quercus-Juniperus savanna: An isotopic assessment , 2003 .

[13]  J. Skjemstad,et al.  Recent vegetation changes in central Queensland, Australia: Evidence from δ13C and 14C analyses of soil organic matter , 2005 .

[14]  Luca Ridolfi,et al.  On the spatial and temporal links between vegetation, climate, and soil moisture , 1999 .

[15]  B. Turner.  The Earth as Transformed by Human Action , 1988 .

[16]  S. Archer,et al.  TREES IN GRASSLANDS: BIOGEOCHEMICAL CONSEQUENCES OF WOODY PLANT EXPANSION , 2001 .

[17]  O. V. Auken.  Shrub Invasions of North American Semiarid Grasslands , 2000 .

[18]  Tyler B. Coplen,et al.  NEW GUIDELINES FOR REPORTING STABLE HYDROGEN, CARBON, AND OXYGEN ISOTOPE-RATIO DATA , 1996 .

[19]  R. Webb,et al.  δ13C values of soil organic matter in semiarid grassland with mesquite (Prosopis) encroachment in southeastern Arizona , 2002 .

[20]  P. Ciais,et al.  Consistent Land- and Atmosphere-Based U.S. Carbon Sink Estimates , 2001, Science.

[21]  M. C. Johnston.  Past and Present Grasslands of Southern Texas and Northeastern Mexico , 1963 .

[22]  Todd M. Scanlon,et al.  Determining land surface fractional cover from NDVI and rainfall time series for a savanna ecosystem , 2002 .

[23]  G. Gee,et al.  Particle-size Analysis , 2018, SSSA Book Series.

[24]  J. Jastrow,et al.  Organic matter turnover in soil physical fractions following woody plant invasion of grassland: Evidence from natural 13C and 15N , 2006 .

[25]  K. K. Aise.  Mineral surfaces and soil organic matter , 2003 .

[26]  André Mariotti,et al.  Natural 13C abundance as a tracer for studies of soil organic matter dynamics , 1987 .

[27]  L. Tieszen,et al.  Carbon Isotope Dynamics During Grass Decomposition and Soil Organic Matter Formation , 1995 .

[28]  C. Chenu,et al.  Organic carbon dynamics in soil particle‐size separates of sandy Spodosols when forest is cleared for maize cropping , 2003 .

[29]  Robert C. Maggio,et al.  Autogenic succession in a subtropical savanna: conversion of grassland to thorn woodland , 1988 .

[30]  J. McAuliffe.  Landscape Evolution, Soil Formation, and Ecological Patterns and Processes in Sonoran Desert Bajadas , 1994 .

[31]  David W. Peterson,et al.  FIRE SUPPRESSION AND ECOSYSTEM CARBON STORAGE , 2000 .

[32]  Nancy B. Grimm,et al.  SPATIAL HETEROGENEITY OF STREAM WATER NUTRIENT CONCENTRATIONS OVER SUCCESSIONAL TIME , 1999 .

[33]  J. A. Schell,et al.  Monitoring vegetation systems in the great plains with ERTS , 1973 .

[34]  S. Archer,et al.  δ13C values of soil organic carbon and their use in documenting vegetation change in a subtropical savanna ecosystem , 1998 .

[35]  Steven R. Archer,et al.  Scale-Dependent Influence of Topography-Based Hydrologic Features on Patterns of Woody Plant Encroachment in Savanna Landscapes , 2005, Landscape Ecology.

[36]  R. Scholes,et al.  Tree-grass interactions in Savannas , 1997 .

[37]  J. Rappole,et al.  Anthropogenic pressures and impacts on marginal, neotropical, semiarid ecosystems: The case of South Texas , 1986 .

[38]  John F. Richards,et al.  The Cambridge Encyclopedia of Human Evolution.@@@The Earth as Transformed by Human Action: Global and Regional Changes in the Biosphere Over the Past 300 Years. , 1993 .

[39]  R. Fensham,et al.  Assessing woody vegetation cover change in north-west Australian savanna using aerial photography , 2003 .

[40]  Steven Bray,et al.  Assessment of vegetation change and landscape variability by using stable carbon isotopes of soil organic matter , 2005 .

[41]  W. Horwath,et al.  Acid fumigation of soils to remove carbonates prior to total organic carbon or CARBON‐13 isotopic analysis , 2001 .

[42]  S. Archer,et al.  Stable isotopes in ecosystem science: structure, function and dynamics of a subtropical Savanna. , 1999, Rapid communications in mass spectrometry : RCM.

[43]  I. Kögel‐Knabner,et al.  Araucaria forest expansion on grassland in the southern Brazilian highlands as revealed by 14C and δ13C studies , 2008 .

[44]  Georg Cadisch,et al.  Carbon isotopic fractionation during decomposition of plant materials of different quality , 2003 .

[45]  S. Archer,et al.  Spatial variability in the potential for symbiotic N2 fixation by woody plants in a subtropical savanna ecosystem , 1996 .

[46]  Jean Pierre Henry Balbaud Ometto,et al.  RIVERINE ORGANIC MATTER COMPOSITION AS A FUNCTION OF LAND USE CHANGES, SOUTHWEST AMAZON , 2004 .

[47]  S. Archer,et al.  Tree-grass dynamics in a Prosopis-thornscrub savanna parkland: Reconstructing the past and predicting the future , 1995 .

[48]  Hj Norussis,et al.  SPSS for Windows , 1993 .

[49]  Eric R. Ziegel,et al.  Variowin: Software for Spatial Data Analysis , 1996 .

[50]  P. Martin.  Geoghronology of Pluvial Lake Cochise, Southern Arizona. II. Pollen Analysis of A 42‐Meter Core , 1963 .

[51]  Jessica Gurevitch,et al.  Ecography 25: 601 -- 615, 2002 , 2022 .

[52]  C. E. Fisher.  The Mesquite Problem in the Southwest. , 1950 .

[53]  X. Wu,et al.  Variation in woody plant δ13C along a topoedaphic gradient in a subtropical savanna parkland , 2008, Oecologia.

[54]  E. Perfect,et al.  Protection of organic carbon in soil microaggregates via restructuring of aggregate porosity and filling of pores with accumulating organic matter , 2008 .

[55]  Yvan Pannatier,et al.  Variowin: Software for Spatial Data Analysis in 2D , 1996 .

[56]  Michael S. Rosenberg,et al.  PASSaGE: Pattern Analysis, Spatial Statistics and Geographic Exegesis. Version 2 , 2011 .

[57]  M. Caldwell,et al.  Carbon isotope ratios of soil organic matter and their use in assessing community composition changes in Curlew Valley, Utah , 1985, Oecologia.