Restoring ecological function in temperate grassy woodlands: manipulating soil nutrients, exotic annuals and native perennial grasses through carbon supplements and spring burns

Summary 1Ecological invasions are often associated with persistent changes to underlying ecological processes. Restoration of invaded communities is dependent on manipulation of these processes to favour the target species composition and impart resistance to further invasion. We applied these principles to extensively degraded grassy woodlands in temperate agricultural regions of Australia, where widespread invasion by mediterranean annuals is related to altered ecological processes such as soil nutrient cycling. 2We investigated carbon supplementation and spring burns, in association with re-establishment of native perennial grasses, as potential management tools for manipulating nitrogen cycling, soil seed banks and establishment conditions in degraded woodland understoreys. Through these mechanisms we aimed to enhance native cover and increase resistance to invasion by exotic annuals. 3In two contrasting degraded remnants, repeated sucrose applications temporarily reduced soil nitrate to inferred pre-European levels, which dramatically reduced growth of exotic annuals and enhanced native perennial abundance. Repeated spring burns did not reduce soil nitrate but reduced exotic annual grasses through effects on soil seed banks and/or establishment conditions. 4Spring burns and carbon supplements both significantly enhanced establishment of Themeda australis, a dominant tussock grass prior to European settlement. Combinations of T. australis seed addition and either spring burning or carbon supplements enhanced native plant abundance more effectively than treatments without seed addition. 5Within 18 months of their establishment, T. australis seedlings significantly reduced soil nitrate in some treatments, providing a preliminary indication that re-establishment of a dense sward of this species may restore ecosystem function to a low-nitrate state that favours native perennials over exotic annuals. 6Synthesis and applications. Ecological restoration can be viewed as targeted intervention in species–environment interactions, whereby ecological conditions are manipulated to enhance establishment or vigour of key species, and these species in turn help restore ecological processes that favour the target species composition. In grassy ecosystems re-establishing a perennial sward of appropriate native tussock grasses may be critical for restoring pre-disturbance nitrogen cycles and improving resistance to invasion by exotic annuals. Carbon supplements and spring burns facilitate this process through complementary mechanisms.

[1]  Colin J. Yates,et al.  Woodland Restoration in the Western Australian Wheatbelt: A Conceptual Framework Using a State and Transition Model , 1997 .

[2]  F. N. David,et al.  Principles and procedures of statistics. , 1961 .

[3]  R. Marrs,et al.  Handbook of Ecological Restoration: Manipulating the chemical environment of the soil , 2002 .

[4]  Timothy R. Seastedt,et al.  Effects of Soil Nitrogen Reduction on Nonnative Plants in Restored Grasslands , 1999 .

[5]  M. Perrow,et al.  Handbook of ecological restoration , 2002 .

[6]  I. Lunt.  The soil seed bank of a long-grazed Themeda triandra grassland in Victoria. , 1990 .

[7]  D. Wheeler,et al.  Grasses of New South Wales , 1990 .

[8]  C. Moore.  The vegetation of the south-eastern Riverina, New South Wales. II. The disclimax communities , 1953 .

[9]  L. Russi,et al.  Seed bank dynamics in a Mediterranean grassland , 1992 .

[10]  P. Spooner,et al.  Is fencing enough? The short‐term effects of stock exclusion in remnant grassy woodlands in southern NSW , 2002 .

[11]  A. Sheppard,et al.  The comparative demography of the pasture weed Echium plantagineum between its native and invaded ranges , 2001 .

[12]  C. Rosen,et al.  Competitive control of invasive vegetation: a native wetland sedge suppresses Phalaris arundinacea in carbon-enriched soil , 2004 .

[13]  Terry McLendon,et al.  Original Articles: Nitrogen Availability and Old-Field Succession in a Shortgrass Steppe , 2000, Ecosystems.

[14]  M. Firestone,et al.  Plant and soil nitrogen dynamics in California annual grassland , 1988, Plant and Soil.

[15]  Richard J. Hobbs,et al.  Towards a Conceptual Framework for Restoration Ecology , 1996 .

[16]  C. Everson,et al.  A comparison of six methods of botanical analysis in the montane grasslands of Natal , 1987, Vegetatio.

[17]  S. Prober,et al.  Conservation of the grassy white box woodlands: relative contributions of size and disturbance to floristic composition and diversity of remnants. , 1995 .

[18]  W. Parton,et al.  Long- and short-term effects of fire on nitrogen cycling in tallgrass prairie , 1994 .

[19]  David Tilman,et al.  Plant Traits and Resource Reduction For Five Grasses Growing on a Nitrogen Gradient , 1991 .

[20]  S. Wilson,et al.  Using ecological restoration to constrain biological invasion , 2004 .

[21]  J. Hoopes.  A View from the South , 1993 .

[22]  Peter M. Vitousek,et al.  Nutrient Cycling and Nutrient Use Efficiency , 1982, The American Naturalist.

[23]  H. Heady.  Changes in a California Annual Plant Community Induced By Manipulation of Natural Mulch , 1956 .

[24]  Michael F. Allen,et al.  The effects of organic amendments on the restoration of a disturbed coastal sage scrub habitat , 1998 .

[25]  C. D’Antonio,et al.  Can Carbon Addition Increase Competitiveness of Native Grasses? A Case Study from California , 2004 .

[26]  James H. Torrie,et al.  Principles and procedures of statistics: a biometrical approach (2nd ed) , 1980 .

[27]  J. Morgan.  Patterns of invasion of an urban remnant of a species-rich grassland in southeastern Australia by non-native plant species , 1998 .

[28]  I. Lunt,et al.  Restoring Kangaroo Grass ( Themeda triandra ) to grassland and woodland understoreys: a review of establishment requirements and restoration exercises in south-east Australia , 2005 .

[29]  Richard J. Hobbs,et al.  Effects of landscape fragmentation on ecosystem processes in the Western Australian wheatbelt , 1993 .

[30]  G. E. Rayment,et al.  Australian laboratory handbook of soil and water chemical methods. , 1992 .

[31]  George Davey Smith,et al.  Meta-analysis: Principles and procedures , 1997, BMJ.

[32]  Colin J. Yates,et al.  Temperate eucalypt woodlands in Australia: biology, conservation, management and restoration. , 2000 .

[33]  J. Maron,et al.  Carbon Addition as a Countermeasure Against Biological Invasion by Plants , 2000, Biological Invasions.

[34]  A. Michelsen,et al.  Effects of carbohydrate amendments on nutrient partitioning, plant and microbial performance of a grassland-shrub ecosystem , 1996 .

[35]  B. Muller,et al.  Components of relative growth rate and sensitivity to nitrogen availability in annual and perennial species of Bromus , 1990, Oecologia.

[36]  R. J. Raison.  Modification of the soil environment by vegetation fires, with particular reference to nitrogen transformations: A review , 1979, Plant and Soil.

[37]  G. Harden,et al.  Flora of New South Wales Volume 2 , 2002 .

[38]  S. Prober,et al.  Spring burns control exotic annual grasses in a temperate grassy woodland , 2004 .

[39]  Christian Floret,et al.  Restoration and Rehabilitation of Degraded Ecosystems in Arid and Semi‐Arid Lands. I. A View from the South , 1993 .

[40]  T. Mclendon,et al.  Response of early and late semiarid seral species to nitrogen and phosphorus gradients , 1992, Plant and Soil.

[41]  S. Prober,et al.  Identifying ecological barriers to restoration in temperate grassy woodlands: soil changes associated with different degradation states , 2002 .

[42]  F. Bazzaz,et al.  RESPONSES OF PLANTS FROM THREE SUCCESSIONAL COMMUNITIES TO A NUTRIENT GRADIENT , 1982 .

[43]  N. Jordan,et al.  SOIL CARBON ADDITION CONTROLS WEEDS AND FACILITATES PRAIRIE RESTORATION , 2003 .

[44]  T. Mclendon,et al.  Effects of nitrogen limitation on species replacement dynamics during early secondary succession on a semiarid sagebrush site , 1992, Oecologia.

[45]  S. Prober,et al.  Determining reference conditions for management and restoration of temperate grassy woodlands: relationships among trees, topsoils and understorey flora in little-grazed remnants , 2002 .

[46]  K. Török,et al.  Immobilization of soil nitrogen as a possible method for the restoration of sandy grassland , 2000 .