Riparian vegetation: degradation, alien plant invasions, and restoration prospects

Rivers are conduits for materials and energy; this, the frequent and intense disturbances that these systems experience, and their narrow, linear nature, create problems for conservation of biodiversity and ecosystem functioning in the face of increasing human influence. In most parts of the world, riparian zones are highly modified. Changes caused by alien plants — or environmental changes that facilitate shifts in dominance creating novel ecosystems — are often important agents of perturbation in these systems. Many restoration projects are underway. Objective frameworks based on an understanding of biogeographical processes at different spatial scales (reach, segment, catchment), the specific relationships between invasive plants and resilience and ecosystem functioning, and realistic endpoints are needed to guide sustainable restoration initiatives. This paper examines the biogeography and the determinants of composition and structure of riparian vegetation in temperate and subtropical regions and conceptualizes the components of resilience in these systems. We consider changes to structure and functioning caused by, or associated with, alien plant invasions, in particular those that lead to breached abiotic‐ or biotic thresholds. These pose challenges when formulating restoration programmes. Pervasive and escalating human‐mediated changes to multiple factors and at a range of scales in riparian environments demand innovative and pragmatic approaches to restoration. The application of a new framework accommodating such complexity is demonstrated with reference to a hypothetical riparian ecosystem under three scenarios: (1) system unaffected by invasive plants; (2) system initially uninvaded, but with flood‐generated incursion of alien plants and escalating invasion‐driven alteration; and (3) system affected by both invasions and engineering interventions. The scheme has been used to derive a decision‐making framework for restoring riparian zones in South Africa and could guide similar initiatives in other parts of the world.

[1]  D. Patten.  Riparian ecosytems of semi-arid North America: Diversity and human impacts , 1998, Wetlands.

[2]  W. C. Johnson.  Adjustment of riparian vegetation to river regulation in the Great Plains, USA , 1998, Wetlands.

[3]  Wolfgang Nentwig,et al.  Historical dynamics of Heracleum mantegazzianum invasion at regional and local scales. , 2007 .

[4]  David P. Braun,et al.  Effects of Groundwater Decline on Riparian Vegetation of Semiarid Regions : The San Pedro , Arizona , 2007 .

[5]  P. Pyšek,et al.  What is the impact of Impatiens glandulifera on species diversity of invaded riparian vegetation , 2006 .

[6]  J. Aronson,et al.  Motivations for the Restoration of Ecosystems , 2006, Conservation biology : the journal of the Society for Conservation Biology.

[7]  Ilkka Hanski,et al.  Slow response of plant species richness to habitat loss and fragmentation. , 2005, Ecology letters.

[8]  S. Rood,et al.  Riparia: Ecology, Conservation, and Management of Streamside Communities , 2006 .

[9]  K. Bagstad,et al.  VEGETATION, SOILS, AND HYDROGEOMORPHOLOGY OF RIPARIAN PATCH TYPES OF A DRYLAND RIVER , 2006 .

[10]  D. Richardson,et al.  Novel ecosystems: theoretical and management aspects of the new ecological world order , 2006 .

[11]  D. Richardson,et al.  A decision-making framework for restoring riparian zones degraded by invasive alien plants in South Africa , 2005 .

[12]  David A. Norton,et al.  Are systems with strong underlying abiotic regimes more likely to exhibit alternative stable states , 2005 .

[13]  M. Huston,et al.  A Hierarchical Perspective of Plant Diversity , 2005, The Quarterly Review of Biology.

[14]  Pamela L. Nagler,et al.  Comparative ecophysiology of Tamarix ramosissima and native trees in western U.S. riparian zones , 2005 .

[15]  Susan M. Galatowitsch,et al.  Riparian scrub recovery after clearing of invasive alien trees in headwater streams of the Western Cape, South Africa , 2005 .

[16]  P. Shafroth,et al.  Control of Tamarix in the Western United States: Implications for Water Salvage, Wildlife Use, and Riparian Restoration , 2005, Environmental management.

[17]  F. Chapin,et al.  EFFECTS OF BIODIVERSITY ON ECOSYSTEM FUNCTIONING: A CONSENSUS OF CURRENT KNOWLEDGE , 2005 .

[18]  A. MacDougall,et al.  ARE INVASIVE SPECIES THE DRIVERS OR PASSENGERS OF CHANGE IN DEGRADED ECOSYSTEMS , 2005 .

[19]  P. Shafroth,et al.  Dominance of non-native riparian trees in western USA , 2005, Biological Invasions.

[20]  J. Stromberg,et al.  Soil seed banks of two montane riparian areas: implications for restoration , 2005, Biodiversity & Conservation.

[21]  D. Richardson,et al.  A reference framework for the restoration of riparian vegetation in the Western Cape, South Africa, degraded by invasive Australian Acacias , 2004 .

[22]  Gary A. Lamberti,et al.  Restoring Stream Ecosystems: Lessons from a Midwestern State , 2004 .

[23]  D. Goodrich,et al.  Hydraulic redistribution by a dominant, warm‐desert phreatophyte: seasonal patterns and response to precipitation pulses , 2004 .

[24]  C. Scott Findlay,et al.  Effect of Invasive Plant Species on Temperate Wetland Plant Diversity , 2004 .

[25]  D. Richardson,et al.  Effects of Invasive Alien Plants on Fire Regimes , 2004 .

[26]  R. Naiman,et al.  Vulnerability of riparian zones to invasion by exotic vascular plants , 2000, Plant Ecology.

[27]  Steven Gerald Whisenant,et al.  Repairing Damaged Wildlands – a Process Orientated, Landscape-Scale Approach , 1999, Biodiversity & Conservation.

[28]  Mohan K. Wali,et al.  Ecological succession and the rehabilitation of disturbed terrestrial ecosystems , 1999, Plant and Soil.

[29]  T. Stohlgren,et al.  Riparian zones as havens for exotic plant species in the central grasslands , 1998, Plant Ecology.

[30]  M. Barrat-Segretain.  Strategies of reproduction, dispersion, and competition in river plants: A review , 1996, Vegetatio.

[31]  D. Dudgeon.  Endangered ecosystems: a review of the conservation status of tropical Asian rivers , 1992, Hydrobiologia.

[32]  Guy Pautou,et al.  Historical influence of man on the riparian dynamics of a fluvial landscape , 1988, Landscape Ecology.

[33]  C. Jarmain,et al.  Water use by black wattle (Acacia mearnsii): implications for the link between removal of invading trees and catchment streamflow response , 2004 .

[34]  Composition change and vegetation degradation of riparian forests in the altai plain, NW China , 2004, Plant Ecology.

[35]  K. Gross,et al.  Alternative states and positive feedbacks in restoration ecology. , 2004, Trends in ecology & evolution.

[36]  W. Erskine,et al.  A practical scientific approach to riparian vegetation rehabilitation in Australia. , 2003, Journal of environmental management.

[37]  M. Morrison,et al.  Flows for Floodplain Forests: A Successful Riparian Restoration , 2003 .

[38]  M. Murakami,et al.  Stream meanders increase insectivorous bird abundance in riparian deciduous forests , 2003 .

[39]  F. Lefèvre,et al.  Dispersal and gene flow of Populus nigra (Salicaceae) along a dynamic river system , 2003 .

[40]  Mark A. Davis.  Biotic Globalization: Does Competition from Introduced Species Threaten Biodiversity? , 2003 .

[41]  P. Nagler,et al.  Comparison of transpiration rates among saltcedar, cottonwood and willow trees by sap flow and canopy temperature methods , 2003 .

[42]  D. Cooper,et al.  Multiple pathways for woody plant establishment on floodplains at local to regional scales , 2003 .

[43]  C. Nilsson,et al.  Basic Principles and Ecological Consequences of Changing Water Regimes: Riparian Plant Communities , 2002, Environmental management.

[44]  Ellen Wohl,et al.  PROCESSES GOVERNING HYDROCHORY ALONG RIVERS: HYDRAULICS, HYDROLOGY, AND DISPERSAL PHENOLOGY , 2002 .

[45]  L. Santamaría,et al.  Waterbirds as endozoochorous dispersers of aquatic organisms: a review of experimental evidence , 2002 .

[46]  T. Yerkes,et al.  Riparian Forest Restoration: Increasing Success by Reducing Plant Competition and Herbivory , 2002 .

[47]  E. Kiviat,et al.  Functional assessment of a reference wetland set as a tool for science, management and restoration , 2002, Aquatic Sciences.

[48]  D. C. Le Maitre,et al.  Invasive alien trees and water resources in South Africa: case studies of the costs and benefits of management , 2002 .

[49]  A. Robertson,et al.  The effects of flooding and livestock on post‐dispersal seed predation in river red gum habitats , 2002 .

[50]  J. Cleverly,et al.  Evapotranspiration at the land/water interface in a semi‐arid drainage basin , 2002 .

[51]  Armando Apan,et al.  Mapping and analysis of changes in the riparian landscape structure of the Lockyer Valley catchment, Queensland, Australia , 2002 .

[52]  Patrick B. Shafroth,et al.  RIPARIAN VEGETATION RESPONSE TO ALTERED DISTURBANCE AND STRESS REGIMES , 2002 .

[53]  D. C. L. Maitrea,et al.  Invasive alien trees and water resources in South Africa : case studies of the costs and benefits of management , 2002 .

[54]  P. Ladd,et al.  Habitat preference and reproductive traits of a major Australian riparian tree species (Casuarina cunninghamiana) , 2001 .

[55]  S. Fisher,et al.  The influence of a riparian shrub on nitrogen cycling in a Sonoran Desert stream , 2001 .

[56]  I. Washitani.  Plant conservation ecology for management and restoration of riparian habitats of lowland Japan , 2001, Population Ecology.

[57]  A. Gurnell,et al.  Riparian seed banks: structure, process and implications for riparian management , 2001 .

[58]  J. Stromberg,et al.  Effects of flooding on native and exotic plant seedlings: implications for restoring south-western riparian forests by manipulating water and sediment flows , 2001 .

[59]  Mark A. Davis,et al.  Experimental support for a resource-based mechanistic model of invasibility , 2001 .

[60]  Diana H. Wall,et al.  Managing Critical Transition Zones , 2001, Ecosystems.

[61]  Harold A. Mooney,et al.  Review Eradication: What Can Go Wrong Viewing Invasive Species Removal in a Whole-ecosystem Context , 2022 .

[62]  R. M. Nally,et al.  Relationships between terrestrial vertebrate diversity, abundance and availability of coarse woody debris on south-eastern Australian floodplains , 2001 .

[63]  Petr Pyšek,et al.  The role of spontaneous vegetation succession in ecosystem restoration: A perspective , 2001 .

[64]  A. Grootjans,et al.  Ecological Restoration: State of the Art or State of the Science? , 2001 .

[65]  Richard J. Hobbs,et al.  Restoration Ecology: Repairing the Earth's Ecosystems in the New Millennium , 2001 .

[66]  David A. Harpman,et al.  A MANAGED FLOOD ON THE COLORADO RIVER: BACKGROUND, OBJECTIVES, DESIGN, AND IMPLEMENTATION , 2001 .

[67]  A. Gurnell,et al.  Riparian plant invasions: hydrogeomorphological control and ecological impacts , 2001 .

[68]  Richard E. Sparks,et al.  Wetland Restoration, Flood Pulsing, and Disturbance Dynamics , 2001 .

[69]  D. Padilla,et al.  Food and environmental cues trigger an inducible offence , 2001 .

[70]  L. Slobodkin.  The good, the bad and the reified , 2001 .

[71]  A. Sher,et al.  Competition between Native Populus deltoides and Invasive Tamarix ramosissima and the Implications for Reestablishing Flooding Disturbance , 2000, Conservation biology : the journal of the Society for Conservation Biology.

[72]  W. J. Shuttleworth,et al.  The water use of two dominant vegetation communities in a semiarid riparian ecosystem , 2000 .

[73]  F. Gelwick.  River Ecology and Management: Lessons from the Pacific Coastal Ecoregion , 2000 .

[74]  E. Tabacchi,et al.  Impacts of riparian vegetation on hydrological processes , 2000 .

[75]  J. Howell,et al.  Predicting potential impacts of environmental flows on weedy riparian vegetation of the Hawkesbury–Nepean River, south-eastern Australia , 2000 .

[76]  C. Nilsson,et al.  Alterations of Riparian Ecosystems Caused by River Regulation , 2000 .

[77]  S. Kariuki,et al.  Disturbances and species distribution of the riparian vegetation of a Rift Valley stream , 2000 .

[78]  K. Rogers,et al.  Riparian vegetation‐environment relationships: complimentarity of gradients versus patch hierarchy approaches , 2000 .

[79]  Mark A. Davis,et al.  Fluctuating resources in plant communities: a general theory of invasibility , 2000 .

[80]  Joan G. Ehrenfeld,et al.  Defining the Limits of Restoration: The Need for Realistic Goals , 2000 .

[81]  C. J. West,et al.  Naturalization and invasion of alien plants: concepts and definitions , 2000 .

[82]  C. Nilsson,et al.  Effects of river regulation on river-margin vegetation : A comparison of eight boreal rivers , 2000 .

[83]  Ruth J. Mitchell,et al.  Ecosystem stability and resilience: a review of their relevance for the conservation management of lowland heaths , 2000 .

[84]  P. Lesica,et al.  Russian olive invasion into cottonwood forests along a regulated river in north-central Montana , 1999 .

[85]  D. Richardson,et al.  Protocols for Restoration Based on Recruitment Dynamics, Community Structure, and Ecosystem Function: Perspectives from South African Fynbos , 1999 .

[86]  Thomas J. Stohlgren,et al.  EXOTIC PLANT SPECIES INVADE HOT SPOTS OF NATIVE PLANT DIVERSITY , 1999 .

[87]  R. Beschta,et al.  Restoration and management of riparian ecosystems: a catchment perspective , 1998 .

[88]  L. Henderson.  Invasive alien woody plants of the southern and southwestern Cape region, South Africa , 1998 .

[89]  M. Kentula.  A Step Toward a Landscape Approach in Riparian Restoration , 1997 .

[90]  M. Palmer,et al.  Ecological Theory and Community Restoration Ecology , 1997 .

[91]  R. Naiman,et al.  The Ecology of Interfaces: Riparian Zones , 1997 .

[92]  J. Friedman,et al.  FLOOD DEPENDENCY OF COTTONWOOD ESTABLISHMENT ALONG THE MISSOURI RIVER, MONTANA, USA , 1997 .

[93]  C. Hancock,et al.  Biodiversity and management of riparian vegetation in Western Australia , 1996 .

[94]  Christer Nilsson,et al.  Do rivers function as corridors for plant dispersal , 1996 .

[95]  Charles C. Coutant,et al.  A GENERAL PROTOCOL FOR RESTORATION OF REGULATED RIVERS , 1996 .

[96]  R. Naiman,et al.  Invasibility of species-rich communities in riparian zones , 1996 .

[97]  A. Large,et al.  Floodplain ecology and management , 1996 .

[98]  C. Hupp,et al.  Riparian vegetation and fluvial geomorphic processes , 1996 .

[99]  A. Large,et al.  Floodplain Ecology and Management: The Luznice River in the Trebon Biosphere Reserve, central Europe , 1996 .

[100]  Riparian buffers and potentially unstable ground , 1995 .

[101]  E. Tabacchi,et al.  Changes in the hydrological regime and invasions by plant species along riparian systems of the Adour River, France , 1995 .

[102]  Laura L. Jackson,et al.  Ecological Restoration: A Definition and Comments , 1995 .

[103]  F. Douglas Shields,et al.  Can Large Rivers Be Restored?Most restoration projects are only attempts to rehabilitate selected river sections to a predetermined structure and functio , 1995 .

[104]  Petr Pyšek,et al.  Invasion dynamics of Impatiens glandulifera - a century of spreading reconstructed. , 1995 .

[105]  Gregor T. Auble,et al.  Relating Riparian Vegetation to Present and Future Streamflows , 1994 .

[106]  Ian D. Moore,et al.  Role of buffer strips in management of waterway pollution: A review , 1994 .

[107]  D. Rosgen.  A classification of natural rivers , 1994 .

[108]  P. M. Wade,et al.  How important are rivers for supporting plant invasions. , 1994 .

[109]  Petr Pyšek,et al.  Plant invasions and the role of riparian habitats: a comparison of four species alien to central Europe. , 1993 .

[110]  R. Naiman,et al.  The Role of Riparian Corridors in Maintaining Regional Biodiversity. , 1993, Ecological applications : a publication of the Ecological Society of America.

[111]  B. Walker,et al.  Vegetation, hydrology and sedimentation processes as determinants of channel form and dynamics in the northeastern Okavango Delta, Botswana , 1993 .

[112]  I. Cowie,et al.  Alien plant species invasive in Kakadu National Park, tropical Northern Australia , 1993 .

[113]  Risto Kalliola,et al.  New site formation and colonizing vegetation in primary succession on the western Amazon floodplains. , 1991 .

[114]  Christer Nilsson,et al.  Importance of hydrochory in structuring plant communities along rivers , 1991 .

[115]  F. Swanson,et al.  An Ecosystem Perspective of Riparian ZonesFocus on links between land and water , 1991 .

[116]  Stanley D. Smith,et al.  Functional Responses of Riparian Vegetation to Streamflow Diversion in the Eastern Sierra Nevada. , 1991, Ecological applications : a publication of the Ecological Society of America.

[117]  Christophe Thébaud,et al.  Rapid invasion of Fraxinus ornus L. along the Herault River system in southern France: the importance of seed dispersal by water , 1991 .

[118]  T. Wells.  Directing ecological succession , 1991 .

[119]  Charles P. Hawkins,et al.  Role of refugia in recovery from disturbances: Modern fragmented and disconnected river systems , 1990 .

[120]  P. Manders.  Soil seed banks and post‐fire seed deposition across a forest ‐ fynbos ecotone in the Cape Province , 1990 .

[121]  S. Rood,et al.  Collapse of riparian poplar forests downstream from dams in western prairies: Probable causes and prospects for mitigation , 1990 .

[122]  H. Ellenberg,et al.  Vegetation Ecology of Central Europe. , 1989 .

[123]  P. Harcombe,et al.  Woody seedling dynamics in an east Texas floodplain forest. , 1989 .

[124]  M. A. Leck.  CHAPTER 13 – Wetland Seed Banks , 1989 .

[125]  G. Frame,et al.  The invasion of introduced species into nature reserves in tropical savannas and dry woodlands , 1988 .

[126]  J. Hoffmann,et al.  The invasive weed Sesbania punicea in South Africa and prospects for its biological control. , 1988 .

[127]  B. Davies,et al.  The river research programme , 1988 .

[128]  Rebecca L. Schneider,et al.  SEED BANK DYNAMICS IN A SOUTHEASTERN RIVERINE SWAMP , 1986 .

[129]  C. Frissell,et al.  A hierarchical framework for stream habitat classification: Viewing streams in a watershed context , 1986 .

[130]  K. Gross.  Effects of seed size and growth form on seedling establishment of six monocarpic perennial plants , 1984 .

[131]  F. Kruger,et al.  The effect of afforestation with Eucalyptus grandis Hill ex Maiden and Pinus patula Schlecht. et Cham. on streamflow from experimental catchments at Mokobulaan, Transvaal , 1980 .

[132]  T. A. Rabotnov,et al.  On plant invasions. , 1978 .