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Plant Ecology

, Volume 218, Issue 1, pp 1–6 | Cite as

The age of restoration: challenges presented by dryland systems

  • Lauren N. SvejcarEmail author
  • Olga A. Kildisheva
Article

Abstract

Intact drylands are highly evolved and complex ecosystems, which allow them to be productive despite harsh environmental conditions. However, drylands are particularly susceptible to degradation, even after minor disturbance events. Conditions for natural plant recruitment in dryland systems are spatially and temporally irregular, which can create challenges for restoration. Large-scale restoration and rehabilitation of dryland ecosystems have become a global concern, prompted by ever-increasing anthropogenic pressure and associated degradation of these natural systems worldwide. The success of plant reestablishment programs in these regions is closely linked to both ecological and socioeconomic opportunities and limitations. This special issue brings together papers that discuss the roles which ecological and socioeconomic factors play in influencing dryland ecosystem restoration outcomes. We aim to (1) highlight the current status of recovery efforts taking place across a range of dryland ecosystems, emphasize advances in the region-specific understanding of plant community development, and (2) provide comparisons between the primary drivers and limitations to restoration that exist across dryland systems.

Keywords

Arid lands Desert Ecosystem function Environmental economics Policy Rehabilitation Semiarid lands 

Introduction

Dryland ecosystems occur throughout the world and occupy nearly half of the Earth’s terrestrial surface (UNDP/UNSO 1997). They are defined as areas where the aridity index, or ratio of total annual precipitation to potential evapotranspiration, ranges between 0.05 and 0.65, and include arid, semiarid, and dry sub-humid regions (Reynolds and Stafford Smith 2002; UNCCD http://www.unccd.int). The global distribution of drylands is driven by atmospheric circulation patterns (Glenn et al. 1993) with the large majority of land areas occurring on the Asian and African continents, followed by the Americas, Australia, and Europe (Sivakumar 2007). These regions support in excess of two billion people and contain more than 30% of global biodiversity hotspots (James et al. 2013; Maestre et al. 2012; Reynolds et al. 2007; Verstraete et al. 2009). Current estimates of degradation and desertification extent vary based on the assessment method, and range from 20 million km2 (Mabbutt 1994) to 32.5 million km2 (Dregne 1983), representing between a third to more than half of dryland systems globally (UNDP/UNSO 1997).

In 2007, the United Nations recognized dryland degradation as one of the key ecological issues of the twenty-first century (Sivakumar 2007), largely due to the scale of disturbance and its impact on food security and environmental quality (MEA 2005; Ravi et al. 2010). The causes of dryland degradation are complex and typically are driven by a suite of interacting factors (e.g., changes in edaphic, climatic, and socioeconomic conditions) over many spatio-temporal scales (D’Odorico et al. 2013; Evans and Geerken 2004). Their interplay determines the extent of degradation and governs the methods necessary for subsequent ecosystem recovery (Boyd and Svejcar 2009; Hobbs and Norton 1996).

According to Hobbs and Norton (1996), the rationale for restoration can be largely broken into four general categories determined by the main drivers of restoration efforts. Specifically, according to the outlined framework, restoration can occur in order to (1) restore specific, highly degraded landscapes (e.g., mine sites, post-disturbance habitats), (2) enhance land-use productivity (e.g., increase grazing value, provide timber and non-timer products, reduce erosion), (3) improve the ecological/conservation value of protected areas (e.g., prevention of invasive species spread, exclusion of grazing, mitigation of pollution, and reduction in fragmentation), and (4) expand the ecological/conservation value of agro-silvo-pastoral landscapes (e.g., implementation of measures that improve habitat and enhance system biodiversity, structure, and function). This rationale thus drives the formation of the explicit restoration targets and desired ecosystem outcomes (Fig. 1). The restoration approach required is then delineated by the existing synergistic interactions between the region-specific degradation processes, environmental limitations, and socioeconomic factors.
Fig. 1

A conceptual diagram describing the steps involved in determining ecosystem restoration planning and project execution. The restoration rationale concept, adopted from Hobbs and Norton (1996), can be broken down into four goal categories: (1) to restore specific, highly degraded landscapes, (2) to enhance land-use productivity, (3) to improve the ecological/conservation value of protected areas, and (4) to expand the ecological/conservation value of agro-silvo-pastoral landscapes. The specific rationale thus determines the explicit restoration targets and desired ecosystem outcomes. The approach chosen to best achieve the set target is consequently guided by the existing synergistic interactions between the region-specific degradation processes, environmental limitations, and socioeconomic factors

Traditionally, ecological restoration targets and outcomes are guided by a reference system, wherein a particular ecosystem or vegetation composition forms the target of restoration projects (SERI 2004). Reference ecosystems are often intact systems nearby, or are based on evidence for historic conditions, though a full understanding of the composition, structure, and function of these systems is not always available and is relative to the spatio-temporal scales for which restoration efforts are being developed (Hobbs 2007; White and Walker 1997). Furthermore, in many dryland systems, the extent and scale of degradation may mean that many of these systems will not be able to be restored to their reference state or may lack a clear designation. In other cases, the original biotic and abiotic conditions have changed to such an extent that they are no longer capable of supporting the reference system without major intervention, including environmental and edaphic amendments (Hobbs 2007; Suding and Hobbs 2009).

Finally, more often than not, it is difficult to fully curtail factors contributing to the degradation process; thus, the reference state cannot always be a fixed one. For example, transition from novel ecosystem to neo-historic condition, such as reversing shrub encroachment and enabling the reinstatement of a historic grassland system (Ravi et al. 2010), may be cost-prohibitive, practically unattainable, and lack long-term resilience (Hobbs et al. 2011). In cases where classical intervention is not feasible, “alternate” stable states must be established (Suding et al. 2004). The structure, function, and composition of these alternate states will be determined by management objectives and the site conditions (both environmental and socioeconomic). The modes of attaining the established restoration targets rely on our understanding of the drivers involved and may require additional inputs to modify the site’s carrying capacity to allow new ecosystem development trajectories to emerge.

This special issue aims to explore the empirical and practical aspects of restoration in degraded dryland systems by (a) providing a snapshot of the current status of recovery efforts being carried out across a range of ecoregions, (b) highlighting advances in the region-specific understanding of plant ecology as it pertains to restoration practices and policy and (c) offering contrasts between key drivers of, and impediments to, restoration. In this context, we consider the term ‘restoration’ to follow the definition proposed by SERI (2004) as “the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed.” Further, because of the high level of degradation experienced by the dryland systems discussed in this special issue, our definition expands to include efforts that would sometimes be described as ‘rehabilitation,’ which are primarily focused on the reestablishment of ecosystem function (in regions severely altered by degradation where full ecological restoration to a reference state is not immediately possible), so long as rehabilitation efforts support the maintenance of biodiversity and aim to propel ecosystem processes toward recovery.

The papers included in this special issue reflect the complexity of these factors in restoration efforts across a suite of degradation drivers, ecoregions, socioeconomic conditions, and political borders. For the sake of clarity, the papers are grouped geographically into Africa, Middle East and North/Central America regions, and comprise a discussion of restoration efforts in six nations.

Paper summaries

Africa

In their paper, Bourne et al. (2017) detail the significant degradation of the highly diverse vegetation of South Africa’s Succulent Karoo as a result of decades of heavy grazing and fodder production. By combining two case studies, (1) outcomes of a local-scale restoration trial and (2) a cost–benefit assessment of regional-scale restoration efforts, the authors identify opportunities and challenges that face restoration in South Africa. Despite the high cost and low success rates reported, Bourne et al. suggest that a “holistic suite of land management actions” combining active management and oversight with investment in restoration efforts is paramount in ensuring that the ecological and socioeconomic stability of the region is maintained in the long-term.

Kimiti et al. (2017) describe the extensive degradation of the Ewaso ecosystem in North Central Kenya that has led to the increase of undesirable plant species cover and the expansion of barren lands. Together, this has resulted in the reduction of wildlife and grazing value, further exacerbated soil erosion rates, and reduced soil moisture content through decreased infiltration. Due to the nature of community-based land tenure, which supports both wildlife and nomadic pastoral use, effective land management of this system is challenging. The authors highlight the use of a three-pronged approach which combines (1) removing undesirable plant cover through mechanical means, (2) reseeding with native plant species, and (3) encouraging autogenic plant recovery (in a form of vegetation islands) through the reduction in grazing and trampling achieved using cattle enclosures. The results of these efforts, as well as recommendations for future objectives, are discussed.

Middle East

Kildisheva et al. (2017) describe drivers of forest degradation in Lebanon, highlighting that key historical barriers to reforestation success can be attributed to a lack of research-derived understanding of seedling morphophysiological development during nursery production, thus limiting the capacity to produce seedlings able to survive under harsh climatic and edaphic conditions. The authors provide recommendations for the use of tailored irrigation and nutrient application regimes to produce high-quality seedlings and demonstrate that the integration of locally and regionally based partnerships can result in the successful development of the necessary infrastructure, communication, and planning, and consequently improve long-term restoration outcomes.

Mayence et al. (2017) describe the synergistic influence of rapid urban expansion, the collapse of traditional grazing practices, changes in land tenure, and the increase in aridity on the ecological degradation of arid systems in Saudi Arabia. Recent efforts to mitigate degradation and create financial opportunities through tourism and recreation have resulted in the development of comprehensive plans aimed at establishing novel conservation and restoration programs, with the majority focused on Acacia woodland restoration.

The authors suggest that key ecological limitations to plant recruitment can be addressed by identifying optimal restoration microsites to extend the window of favorable conditions that support subsequent plant establishment and persistence.

North/Central America

Hruska et al. (2017) highlight the issue of extensive shrub encroachment in arid to semiarid grassland and savanna ecosystems along the US–Mexico border. Land management practices including excessive grazing, changes to fire regime, fragmentation, and the eradication of keystone animal species are considered to be the main drivers in the expansion of a shrub-dominated ecosystem state. Addressing these challenges in both the near and long-term requires a clear understanding of the social processes influencing land management, but this knowledge is currently lacking. In order to address this, the authors use the Chihuahuan Desert grasslands of the Janos Biosphere Reserve of Northern Mexico as a case study for elucidating the process of ecosystem change from a social–ecological perspective. Hruska et al. (2017) recommend addressing land degradation from both ecological and social perspectives and provide insights into how collaboration between researchers, land managers, federal and non-governmental organizations can be successful in engaging the local community to adopt novel management practices that improve the ecological value of these systems.

Finally, Svejcar et al. (2017) suggest that invasive exotic species and alterations in wildfire frequency are the two primary drivers of degradation in the Great Basin ecoregion of the Western United States. The authors discuss the environmental constraints to seedling recruitment, highlighting that plant establishment must occur before the onset of sub-zero winter temperatures or summer drought. To overcome these limitations, they argue that agronomic approaches, such as seed enhancement technologies, offer the potential to better match the time of seed germination and emergence with environmental conditions most likely to increase survival and persistence.

Conclusion

The discipline of restoration ecology has largely moved from an ad hoc site and situation-specific practice of the late 1980s and early 1990s (Hobbs and Norton 1996), to a more concerted theoretical and practical science addressing issues that impact entire regions (Aronson and Alexander 2013). However, due to the relative youth of the discipline (four decades), cohesion between restoration science and practice is often absent (Menz et al. 2013; Suding 2011). As such, there is an increasing need for the integration of empirically and practically based rationale to develop appropriate restoration modes and metrics required to ensure outcome success (Cabin 2007; Menz et al. 2013; Suding 2011). In addition, planning that acknowledges and accounts for the spatial and temporal time scales at which restoration practices are to be conducted is particularly critical (Hilderbrand et al. 2005).

The recognition of the need for a science-driven basis to support ecosystem restoration efforts is echoed through an increase in the publication of peer-reviewed scientific works that focus on the topic over the last decade (Appendix), although restoration in dryland systems comprises only a small portion of the total articles published (less than 5% over the past decade). This, in part, may be due to the lack of financial and institutional support, political stability, and biological understanding of ecosystem function in many of the world’s dryland regions. Given the scale and degree of degradation experienced, there is a substantial need to increase the extent of international multi-institutional dialogue and collaborative efforts to enhance scientific capacity and support restoration across borders.

Despite the ambitious target proposed by UNCCD at the Rio+20 summit of attaining a land degradation neutral world by 2030 (UN 2012), it has become increasingly clear that ecological restoration will play an important part in managing the problem of chronic degradation in dryland systems (Aronson and Alexander 2013). Thus, wide-ranging international interest lies in the development of cost-effective restoration methods that are capable of functioning across political boundaries (Aronson and Alexander 2013), but systematic modes of achieving this remain limited. The extent to which systems can be restored depends equally on the environmental and socioeconomic factors governing the geographic region. Future efforts to move global dryland restoration forward will rely on a clear understanding of the key limitations presented across these different environmental, socioeconomic, and political systems, and on identifying effective solutions capable of functioning on a landscape scale.

Notes

Acknowledgements

The authors would like to thank Erik Hamerlynck for his help with this Special Issue.

References

  1. Aronson J, Alexander S (2013) Ecosystem restoration is now a global priority: time to roll up our sleeves. Restor Ecol 21:293–296CrossRefGoogle Scholar
  2. Bourne A, Muller H, De Villiers A, Alam M, Hole D (2017) Assessing the efficiency and effectiveness of rangeland restoration in Namaqualand, South Africa. Plant Ecol 218:7–22. doi: 10.1007/s11258-016-0644-3 CrossRefGoogle Scholar
  3. Boyd CS, Svejcar TJ (2009) Managing complex problems in rangeland ecosystems. Range Ecol Manag 62:491–499CrossRefGoogle Scholar
  4. Cabin RJ (2007) Science-driven restoration: a square grid on a round earth? Restor Ecol 15:1–7CrossRefGoogle Scholar
  5. D’Odorico P, Bhattachan A, Davis KF, Ravi S, Runyan CW (2013) Global desertification: drivers and feedbacks. Adv Water Resour 51:326–344CrossRefGoogle Scholar
  6. Dregne HE (1983) Desertification of arid lands, vol 3. Harwood Academic Publishers, LondonGoogle Scholar
  7. Evans J, Geerken R (2004) Discrimination between climate and human-induced dryland degradation. J Arid Environ 57:535–554CrossRefGoogle Scholar
  8. Glenn E, Squires V, Olsen M, Frye R (1993) Potential for carbon sequestration in the drylands. In: Wisniewski J, Sampson RN (eds) Terrestrial biospheric carbon fluxes quantification of sinks and sources of CO2. Springer, Dordrecht, pp 341–355CrossRefGoogle Scholar
  9. Hilderbrand RH, Watts AC, Randle AM (2005) The myths of restoration ecology. Ecol Soc 10:19CrossRefGoogle Scholar
  10. Hobbs RJ (2007) Setting effective and realistic restoration goals: key directions for research. Restor Ecol 15:354–357CrossRefGoogle Scholar
  11. Hobbs RJ, Norton DA (1996) Towards a conceptual framework for restoration ecology. Restor Ecol 4:93–110CrossRefGoogle Scholar
  12. Hobbs RJ, Hallett LM, Ehrlich PR, Mooney HA (2011) Intervention ecology: applying ecological science in the twenty-first century. Bioscience 61:442–450CrossRefGoogle Scholar
  13. Hruska T, Toledo D, Sierra-Corona R, Solis-Gracia V (2017) Social-ecological dynamics of change and restoration attempts in the Chihuahuan Desert Grasslands of Janos Biosphere Reserve, Mexico. Plant Ecol 218:67–80. doi: 10.1007/s11258-016-0692-8 CrossRefGoogle Scholar
  14. James JJ, Sheley RL, Erickson T, Rollins KS, Taylor MH, Dixon KW (2013) A systems approach to restoring degraded drylands. J Appl Ecol 50:730–739CrossRefGoogle Scholar
  15. Kildisheva OA, Aghai MM, Bouazza K, Davis AS (2017) Improving restoration success through research driven initiatives: case studies targeting Pinus pinea reforestation stock development in Lebanon. Plant Ecol 218:39–53. doi: 10.1007/s11258-016-0632-7 CrossRefGoogle Scholar
  16. Kimiti DW, Hodge AMC, Herrick JE, Beh AW, Abbott LE (2017) Rehabilitation of community owned, mixed use rangelands: lessons from the Ewaso ecosystem in North-Central Kenya. Plant Ecol 218:23–37. doi: 10.1007/s11258-016-0691-9 CrossRefGoogle Scholar
  17. Mabbutt JA (1994) Climate change: some likely multiple impacts in Southern Africa. Food Policy 19:165–191CrossRefGoogle Scholar
  18. Maestre FT, Quero JL, Gotelli NJ, Escudero A, Ochoa V, Delgado-Baquerizo M et al (2012) Plant species richness and ecosystem multifunctionality in global drylands. Science 335:214–218CrossRefPubMedPubMedCentralGoogle Scholar
  19. Mayence CE, Stevens JC, Courtney P, Dixon KW (2017) Edaphic constraints on seed germination and emergence of three Acacia species for dryland restoration in Saudi Arabia. Plant Ecol 218:55–66. doi: 10.1007/s11258-016-0680-z CrossRefGoogle Scholar
  20. MEA (Millennium Ecosystem Assessment) (2005) Ecosystems and human well-being: desertification synthesis. World Resources Institute, Washington, DCGoogle Scholar
  21. Menz MH, Dixon KW, Hobbs RJ (2013) Hurdles and opportunities for landscape-scale restoration. Science 339:526–527CrossRefPubMedGoogle Scholar
  22. Ravi S, Breshears DD, Huxman TE, D’Odorico P (2010) Land degradation in drylands: interactions among hydrologic–aeolian erosion and vegetation dynamics. Geomorphology 116:236–245CrossRefGoogle Scholar
  23. Reynolds JF, Stafford Smith DM (2002) Do humans cause deserts? In: Reynolds JF, Stafford Smith DM (eds) Global desertification: do humans cause deserts? Dahlem University Press, Berlin, pp 1–21Google Scholar
  24. Reynolds JF, Maestre FT, Kemp PR, Stafford-Smith DM, Lambin E (2007) Natural and human dimensions of land degradation in drylands: causes and consequences. In: Canadell JG, Pataki DE, Pitelka LF (eds) Terrestrial ecosystems in a changing world. Springer, Berlin, pp 247–257CrossRefGoogle Scholar
  25. SERI (2004) The SER international primer on ecological restoration. Society for Ecological Restoration International, TucsonGoogle Scholar
  26. Sivakumar MVK (2007) Interactions between climate and desertification. Agric For Meteorol 142:143–155CrossRefGoogle Scholar
  27. Suding KN (2011) Toward an era of restoration in ecology: successes, failures, and opportunities ahead. Annu Rev Ecol Evol Syst 42:465CrossRefGoogle Scholar
  28. Suding KN, Hobbs RJ (2009) Threshold models in restoration and conservation: a developing framework. Trends Ecol Evol 24:271–279CrossRefPubMedGoogle Scholar
  29. Suding KN, Gross KL, Houseman GR (2004) Alternative states and positive feedbacks in restoration ecology. Trends Ecol Evol 19:46–53CrossRefPubMedGoogle Scholar
  30. Svejcar T, Boyd C, Davies K, Hamerlynck E, Svejcar L (2017) Challenges and limitations to native species restoration in the Great Basin, USA. Plant Ecol 218:81–94. doi: 10.1007/s11258-016-0648-z CrossRefGoogle Scholar
  31. UNDP/UNSO (1997) Aridity zones and dryland populations: an assessment of population levels in the world’s drylands with particular reference to Africa. UNDP Office to Combat Desertification and Drought (UNSO), New YorkGoogle Scholar
  32. UN-United Nations (2012) The future we want. Final document of the Rio+20 UN conference on sustainable development, New YorkGoogle Scholar
  33. Verstraete MM, Scholes RJ, Smith MS (2009) Climate and desertification: looking at an old problem through new lenses. Front Ecol Environ 7:421–428CrossRefGoogle Scholar
  34. White PS, Walker JL (1997) Approximating nature’s variation: selecting and using reference information in restoration ecology. Restor Ecol 5:338–349CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2017

Authors and Affiliations

  1. 1.Eastern Oregon Agricultural Research CenterOregon State UniversityBurnsUSA
  2. 2.University of Western AustraliaCrawleyAustralia
  3. 3.Chicago Botanic GardenGlencoeUSA
  4. 4.School of Veterinary and Life SciencesMurdoch UniversityMurdochAustralia
  5. 5.Biodiversity Conservation CenterKings Park and Botanic GardenKings ParkAustralia

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