Woody-plant encroachment in grasslands: a review of mechanisms and aftereffects

doi:10.11686/cyxb2017233

Abstract

Abstract: Woody-plant encroachment in grasslands has been a much-studied topic in ecology and animal husbandry over the past few decades. This paper clarifes the causes and consequences of this encroachment by reviewing recent progress in the study of invasion stages, invasion mechanisms, the impacts of this encroachment on grassland ecosystems and their aftereffects. The means of woody-plant encroachment include both anthropophyte and natural invasion. In general, this encroachment divides into three stages: dispersal, colonizing and establishing and diffusing. The causes of encroachment have been identified as fire suppression, climate change, changes in nutrient availability and over grazing. These factors effect encroachment through changing plant coverage, soil water use efficiency and allelopathy. We conclude that woody-plant encroachment changes many interfaces in grassland ecosystems and influences the ecological and hydrological processes that lead to grassland degradation and desertification.

Key words: woody-plant encroachment, invasion mechanism, climate change, grazing, fire

WANG Ying-xin, CHEN Xian-jiang, LOU Shan-ning, HU An, REN Jin-fei, HU Jun-qi, ZHANG Jing, HOU Fu-jiang. Woody-plant encroachment in grasslands: a review of mechanisms and aftereffects[J]. Acta Prataculturae Sinica, 2018, 27(5): 219-227.

References

[1] Sala O E, Maestre F T.Grass-woodland transitions: determinants and consequences for ecosystem functioning and provisioning of services. Journal of Ecology, 2014, 102(6): 1357-1362.
[2] Auken O W V. Shrub invasions of North American semiarid grasslands. Annual Review of Ecology, Evolution,and Systematics, 2000, 31(1): 197-215.
[3] Knapp A K, Briggs J M, Collins S L, et al. Shrub encroachment in North American grasslands: shifts in growth form dominance rapidly alters control of ecosystem carbon inputs. Global Change Biology, 2008, 14(3): 615-623.
[4] Eldridge D J, Bowker M A, Maestre F T, et al. Impacts of shrub encroachment on ecosystem structure and functioning: towards a global synthesis. Ecology Letters, 2011, 14(7): 709-722.
[5] Robinson T P, Van Klinken R D, Metternicht G. Spatial and temporal rates and patterns of mesquite (Prosopis species) invasion in Western Australia. Journal of Arid Environments, 2008, 72(3): 175-188.
[6] Peng H Y, Li X Y, Li G Y, et al. Shrub encroachment with increasing anthropogenic disturbance in the semiarid Inner Mongolia grasslands of China. Catena, 2013, 109(5): 39-48.
[7] Chen L, Li H, Zhang P, et al. Climate and native grassland vegetation as drivers of the community structures of shrub-encroached grasslands in Inner Mongolia, China. Landscape Ecology, 2015, 30(9): 1627-1641.
[8] Brandt J S, Haynes M A, Kuemmerle T, et al. Regime shift on the roof of the world: Alpine meadows converting to shrublands in the southern Himalayas. Biological Conservation, 2013, 158(2): 116-127.
[9] Roques K G, O’connor T G, Watkinson A R.Dynamics of shrub encroachment in an African savanna: relative influences of fire, herbivory, rainfall and density dependence. Journal of Applied Ecology, 2001, 38(2): 268-280.
[10] Jackson R B, Banner J L, Jobbágy E G, et al. Ecosystem carbon loss with woody plant invasion of grasslands. Nature, 2002, 418(6898): 623-626.
[11] Heisler J L, Briggs J M, Knapp A K, et al. Direct and indirect effects of fire on shrub density and aboveground productivity in a mesic grassland. Ecology, 2004, 85(8): 2245-2257.
[12] Huxman T E, Wilcox B P, Breshears D D, et al. Ecohydrological implications of woody plant encroachment. Ecology, 2005, 86(2): 308-319.
[13] Tape K E N, Sturm M, Racine C. The evidence for shrub expansion in northern Alaska and the Pan-Arctic. Global Change Biology, 2006, 12(4): 686-702.
[14] Bond W J.What limits trees in C₄ grasslands and savannas. Annual Review of Ecology, Evolution, and Systematics, 2008, 39(1): 641-659.
[15] Tennesen M.Ecology. When juniper and woody plants invade, water may retreat. Science, 2008, 322(5908): 1630.
[16] Sankaran M, Ratnam J, Hanan N.Woody cover in African savannas: the role of resources, fire and herbivory. Global Ecology and Biogeography, 2008, 17(2): 236-245.
[17] D’Odorico P, Okin G S, Bestelmeyer B T. A synthetic review of feedbacks and drivers of shrub encroachment in arid grasslands. Ecohydrology, 2012, 5(5): 520-530.
[18] Kulmatiski A, Beard K H.Woody plant encroachment facilitated by increased precipitation intensity. Nature Climate Change, 2013, 3(9): 833-837.
[19] Anadón J D, Sala O E, Nd T B, et al. Effect of woody-plant encroachment on livestock production in north and south America. Proceedings of the National Academy of Sciences, 2014, 111(35): 12948-12953.
[20] Browning D M, Franklin J, Archer S R, et al. Spatial patterns of grassland-shrubland state transitions: a 74-year record on grazed and protected areas. Ecological Applications, 2014, 24(6): 1421-1433.
[21] Ratajczak Z, Nippert J B, Ocheltree T W.Abrupt transition of mesic grassland to shrubland: evidence for thresholds, alternative attractors, and regime shifts. Ecology, 2014, 95(9): 2633-2645.
[22] Scheiter S, Higgins S I, Beringer J, et al. Climate change and long-term fire management impacts on Australian savannas. New Phytologist, 2015, 205(3): 1211-1226.
[23] Gherardi L A, Sala O E.Enhanced precipitation variability decreases grass-and increases shrub-productivity. Proceedings of the National Academy of Sciences, 2015, 112(41): 12735-12740.
[24] Stevens N, Erasmus B F N, Archibald S, et al. Woody encroachment over 70 years in South African savannahs: overgrazing, global change or extinction aftershock. Philosophical Transactions of the Royal Society of London, 2016, 371(1703): 20150437.
[25] Archer S R.Rangeland conservation and shrub encroachment: new perspectives on an old problem//Wild rangelands: conserving wildlife while maintaining livestock in semi-arid ecosystems. Oxford, UK: Wiley-Blackwell Publishing, 2010: 53-97.
[26] Good S P, Caylor K K.Climatological determinants of woody cover in Africa. Proceedings of the National Academy of Sciences, 2011, 108(12): 4902-4907.
[27] Darrouzet-Nardi A, D’Antonio C M, Dawson T E. Depth of water acquisition by invading shrubs and resident herbs in a Sierra Nevada meadow. Plant and Soil, 2006, 285(1/2): 31-43.
[28] Sankaran M, Ratnam J, Hanan N P.Tree-grass coexistence in savannas revisited-insights from an examination of assumptions and mechanisms invoked in existing models. Ecological Letter, 2004, 7(6): 480-490.
[29] Suding K N, Stanley Harpole W, Fukami T, et al. Consequences of plant-soil feedbacks in invasion. Journal of Ecology, 2013, 101(2): 298-308.
[30] Putten W H, Bardgett R D, Bever J D, et al. Plant-soil feedbacks: the past, the present and future challenges. Journal of Ecology, 2013, 101(2): 265-276.
[31] Berlow E L, D’Antonio C M, Reynolds S A. Shrub expansion in montane meadows: The interaction of local-scale disturbance and site aridity. Ecological Applications, 2002, 12(4): 1103-1118.
[32] Scheiter S, Higgins S I.Impacts of climate change on the vegetation of Africa: an adaptive dynamic vegetation modelling approach. Global Change Biology, 2009, 15(9): 2224-2246.
[33] Holmgren M, Hirota M.Effects of inter annual climate variability on tropical tree cover. Nature Climate Change, 2013, 3(8): 755-758.
[34] Martínez-Vilalta J, Pockman W T.The vulnerability to freezing-induced xylem cavitation of Larrea tridentata (Zygophyllaceae) in the Chihuahuan desert. American Journal of Botany, 2002, 89(12): 1916-1924.
[35] Sekhwela M B, Yates D J.A phenological study of dominant acacia tree species in areas with different rainfall regimes in the Kalahari of Botswana. Journal of Arid Environments, 2007, 70(1): 1-7.
[36] Gordon C, Wynn J M, Woodin S J.Impacts of increased nitrogen supply on high Arctic heath: the importance of bryophytes and phosphorus availability. New Phytologist, 2001, 149(3): 461-471.
[37] Gassó N, Sol D, Pino J, et al. Exploring species attributes and site characteristics to assess plant invasions in Spain. Diversity & Distributions, 2009, 15(1): 50-58.
[38] González-Moreno P, Pino J, Gassó N, et al. Landscape context modulates alien plant invasion in Mediterranean forest edges. Biological Invasions, 2013, 15(3): 547-557.
[39] McCarron J K, Knapp A K. C₃ woody plant expansion in a C₄ grassland: are grasses and shrubs functionally distinct. American Journal of Botany, 2001, 88(10): 1818-1823.
[40] Bond W J, Midgley J J.Ecology of sprouting in woody plants: the persistence niche. Trends in Ecology & Evolution, 2001, 16(1): 45-51.
[41] Smith R, Tighe M, Reid N, et al. Effects of grazing, trenching and surface soil disturbance on ground cover in woody encroachment on the Cobar Pediplain, south-eastern Australia. Journal of Arid Environments, 2013, 96: 80-86.
[42] Hempson G P, Archibald S, Bond W J, et al. Ecology of grazing lawns in Africa. Biological Reviews, 2015, 90(3): 979-994.
[43] Fredrickson E L, Estell R E, Laliberte A, et al. Mesquite recruitment in the Chihuahuan Desert: historic and prehistoric patterns with long-term impacts. Journal of Arid Environments, 2006, 65(2): 285-295.
[44] Christensen L, Coughenour M B, Ellis J E.Sustainability of Inner Mongolian grasslands: Application of the Savanna model. Journal of Range Management, 2003, 56(4): 319-327.
[45] Allred B W, Fuhlendorf S D, Smeins F E, et al. Herbivore species and grazing intensity regulate community composition and an encroaching woody plant in semi-arid rangeland. Basic and Applied Ecology, 2012, 13(2): 149-158.
[46] Standish R J, Cramer V A, Wild S L, et al. Seed dispersal and recruitment limitation are barriers to native recolonization of old-fields in Western Australia. Journal of Applied Ecology, 2007, 44(2): 435-445.
[47] Tews J, Schurr F, Jeltsch F.Seed dispersal by cattle may cause shrub encroachment of Grewia flava on southern Kalahari rangelands. Applied Vegetation Science, 2004, 7(1): 89-102.
[48] Milton S J, Dean W R J. Plant invasions in arid areas: special problems and solutions: a South African perspective. Biological Invasions, 2010, 12(12): 3935-3948.
[49] Booysen P V D, Tainton N M. Ecological effects of fire in South African ecosystems. Journal of Ecology, 1984, 48.
[50] Abades S R, Gaxiola A, Marquet P A.Fire, percolation thresholds and the savanna forest transition: a neutral model approach. Journal of Ecology, 2014, 102(6): 1386-1393.
[51] Rossiter N A, Setterfield S A, Douglas M M, et al. Testing the grass-fire cycle: alien grass invasion in the tropical savannas of northern Australia. Diversity and Distributions, 2003, 9(3): 169-176.
[52] Govender N, Trollope W S, Van Wilgen B W. The effect of fire season, fire frequency, rainfall and management on fire intensity in savanna vegetation in South Africa. Journal of Applied Ecology, 2006, 43(4): 748-758.
[53] Paula S, Pausas J G.Burning seeds: germinative response to heat treatments in relation to resprouting ability. Journal of Ecology, 2008, 96(3): 543-552.
[54] Flematti G R, Merritt D J, Piggott M J, et al. Burning vegetation produces cyanohydrins that liberate cyanide and stimulate seed germination. Nature Communications, 2011, 2(2): 2555-2559.
[55] Sharp B R, Whittaker R J.The irreversible cattle-driven transformation of a seasonally flooded Australian savanna. Journal of Biogeography, 2003, 30(5): 783-802.
[56] Wiegand K, Saltz D, Ward D.A patch-dynamics approach to savanna dynamics and woody plant encroachment——Insights from an arid savanna. Perspectives in Plant Ecology, Evolution and Systematics, 2006, 7(4): 229-242.
[57] Veach A M, Dodds W K, Skibbe A.Fire and grazing influences on rates of riparian woody plant expansion along grassland streams. PloS One, 2014, 9(9): e106922.
[58] De Torres Curth M I, Ghermandi L, Biscayart C. Are Fabiana imbricata shrublands advancing over northwestern patagonian Grasslands. A population dynamics study involving fire and precipitation. Journal of Arid Environments, 2012, 83(83): 78-85.
[59] Ratajczak Z, Nippert J B, Briggs J M, et al. Fire dynamics distinguish grasslands, shrublands and woodlands as alternative attractors in the Central Great Plains of North America. Journal of Ecology, 2014, 102(6): 1374-1385.
[60] Smith S D, Huxman T E, Zitzer S F, et al. Elevated CO₂ increases productivity and invasive species success in an arid ecosystem. Nature, 2000, 408(6808): 79-82.
[61] Whitford W G, Anderson J, Rice P M.Stemflow contribution to the ‘fertile island’ effect in creosotebush, Larrea tridentata. Journal of Arid Environments, 1997, 35(3): 451-457.
[62] Baer S G, Church J M, Kwj W, et al. Changes in intrasystem N cycling from N₂-fixing shrub encroachment in grassland: multiple positive feedbacks. Agriculture Ecosystems & Environment, 2006, 115(1): 174-182.
[63] Collins C G, Carey C J, Aronson E L, et al. Direct and indirect effects of native range expansion on soil microbial community structure and function. Journal of Ecology, 2016, 104(5): 1271-1283.
[64] Schlesinger W H, Raikes J A, Hartley A E, et al. On the spatial pattern of soil nutrients in desert ecosystems. Ecology, 1996, 77(2): 364-374.
[65] Pugnaire F I, Haase P, Puigdefabregas J.Facilitation between higher plant species in a semiarid environment. Ecology, 1996, 77(5): 1420-1426.
[66] Eldridge D J, Wang L, Ruiz-Colmenero M.Shrub encroachment alters the spatial patterns of infiltration. Ecohydrology, 2015, 8(1): 83-93.
[67] Li Y L, Chen J, Cui J Y, et al. Nutrient resorption in Caragana microphylla along a chronosequence of plantations: implications for desertified land restoration in North China. Ecological Engineering, 2013, 53: 299-305.
[68] Myers-Smith I, Forbes B C, Wilmking M, et al. Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities. Environmental Research Letters, 2011, 6(4): 45509-45523.
[69] Parizek B, Rostagno C M, Sottini R.Soil erosion as affected by shrub encroachment in northeastern Patagonia. Journal of Range Management, 2002, 1: 43-48.
[70] Lett M S, Knapp A K.Consequences of shrub expansion in mesic grassland: resource alterations and graminoid responses. Journal of Vegetation Science, 2003, 14(4): 487-496.
[71] Li X Y, Zhang S Y, Peng H Y, et al. Soil water and temperature dynamics in shrub-encroached grasslands and climatic implications: Results from Inner Mongolia steppe ecosystem of North China. Agricultural & Forest Meteorology, 2013, 171(8): 20-30.
[72] Zavaleta E S, Kettley L S.Ecosystem change along a woody invasion chronosequence in a California grassland. Journal of Arid Environments, 2006, 66(2): 290-306.
[73] Brantley S T, Young D R.Linking light attenuation, sunflecks, and canopy architecture in mesic shrub thickets. Plant Ecology, 2010, 206(2): 225-236.
[74] Bekele A, Hudnall W H.Spatial variability of soil chemical properties of a prairie-forest transition in Louisiana. Plant and Soil, 2006, 280(1/2): 7-21.
[75] Daryanto S, Eldridge D J, Koen T B.Soil nutrients under shrub hummocks and debris mounds two decades after ploughing. Plant and Soil, 2012, 351(1/2): 405-419.
[76] Osoro K, Ferreira L M, García U, et al. Diet selection and performance of sheep and goats grazing on different heathland vegetation types. Small Ruminant Research, 2013, 109(2): 119-127.
[77] Russell-Smith J, Cook G D, Cooke P M, et al. Managing fire regimes in north Australian savannas: applying aboriginal approaches to contemporary global problems. Frontiers in Ecology & the Environment, 2013, 11(Supple 1): E55-E63.
[78] Ryan K C, Knapp E E, Varner J M.Prescribed fire in North American forests and woodlands: history, current practice, and challenges. Frontiers in Ecology & the Environment, 2013, 11(Supple 1): E15-E24.