ASSISTING, BUT NOT OVERRULING
Reading material chosen: Helping forests to help themselves-accelerating natural regeneration.
In 2000, an estimated 60% of the world’s tropical forest was classified as degraded forest, including secondary forests, degraded primary forests and degraded forest land (ITTO 2002). No doubt that large infrequent disturbances in nature, such as hurricanes, floods, volcanoes, and fire, have strong impacts on forest landscapes[i], human behavior is the main disturbance them. To some extent, human history is made up of the conflicts between human beings and the nature. Nature is the ultimate source of life, but it has been in danger ever since people entered the so-called “civilized era”. Nature does have the ability of self-regeneration, but when deprivation overwhelms reproduction, disasters came. Deforestation is among the most severe environmental crises and has a history of more than 20,000 years.[ii] From the perspective of both nature sustainability and human survival, forest restoration is an urgent problem, which is gaining more and more attention. Restoration has been practiced for centuries, taking place when the ecosystem fails to naturally recover from disturbances or when this process may take over centuries to occur.[iii]
Ever since restoration came into being, it went through a long way and has made great progress.[iv] One of the main approaches to carry out restoration is replanting indigenous trees. ANR is short for accelerated natural regeneration or assisted natural regeneration. Unlike traditional ways, ANR relies on existing natural processes, and requires less labor input than tree planting, thus being a very cheap way to restore forest ecosystems.[v]
ANR is a young science and is interesting because it makes regeneration without planting trees possible! It’s easy to get the logic of replanting—adding new individuals in the place of the disappeared old ones. But what if we just lend a hand and let forests help themselves? It’s really encouraging when you think about the idea that less human labor can achieve a better recovery. I think the fundamental point is “existing natural processes”. On one hand, the existing conditions provide the basic information of the region and prepare for the regeneration. On the other hand, the recovery is still on its way, making it possible for us to do something to accelerate the processes. It is like a car on the slope: the car has its own engine to drive it uphill, but will surely arrive at the top earlier if there is someone pushing it in the proper way. Having an engine is important, because it would be too hard if we want to push a car without engine to the top of a hill.
Then comes the question of how to identify the area suitable for ANR, that is, a car with an engine. The site assessment should determine the existing potential for natural forest regeneration and identify which factors might be limiting natural forest regeneration. The book How To Plant A Forest has also provided a chart to decide whether tree planting is needed in particular area.
Another interesting point is about the emphasis of tree stumps. In traditional regeneration, stumps are seen as the evidence of degradation. But ANR makes full use of them, stressing their function of food reserve and fire protection.
Weeding is a vital process of ANR for the reason that it ensures the survival of seedlings and samplings. Distinguishing between weed and main species is the first step, followed by remove of the weed. Hand-pull is the better that machine because of its avoidance of removing the wrong individuals. Clearing the invasive species can also be seen as a kind of weeding which enhance the survival of the remaining species.[vi]
As for labor consume, ANR has advantage over traditional approaches. The labor of planting is largely reduced. And practitioners have also come up with an idea to lower the workload of weeding. Wooden boards with semicircles on both ends are used, raising the efficiency of weeding. The flattened weeds act as good food reserve, just the same as leaf litters, which enhance the generation of secondary forests.[vii]
However, applying ANR does not mean that tree planting should be absolutely excluded. Rather, it is supposed to combine other means to achieve success of restoration. As is mentioned above, there is a step to decide whether tree planting is needed. For those areas that do not have proper premise for ANR, including sampling planting and direct seeding makes regeneration feasible. As the most important way to restore forest, tree planting has been practiced across the world, including Costa Rica[viii], Canada[ix], Singapore[x], Brazil[xi],[xii] and Panama[xiii]. When dealing with direct seeding, one should take micro-site environment into consideration[xiv], or the result may be affected due to sensitivity of seeds.
Animal-plant interaction also plays an important role in regeneration. Birds[xv], cattle, bats, elephants can all act as seed dispersers. Degraded or fragmented forest has difficulty dispersing seeds[xvi], so what we should do is to attract the dispersers to the site of regeneration and get the seed rain. How to bring the dispersers to the site and at the same time reduce their negative effects (such as trampling the samplings) to the greatest extent are two main challenges faced by regeneration practitioners.
As a young science, ANR still needs exploration.
One of the limitations is that strict ANR can only be conducted in particular areas. Practitioners have to identify the conditions of the area before taking measures, which limit the popularization of the approach. The problem related to this is the difficulty of deciding to what extent we should interfere or plant trees. For a site requiring tree planting, not enough planting may fail the effort of regeneration, but over planting in turn would be a waste of labor and resource. It’s not easy to strike a balance.
Besides, ANR is not supposed to be a separated process, but should be incorporated into forest management. Understanding physiological ecology[xvii]and succession processes[xviii] helps us connect different areas to get an overview. For example, in ANR, the existing plants found in disturbed area are mainly early succession (pioneer) species. Knowledge of succession tells us that some of the pioneers should be cleared to get old growth (climax) forest[xix],[xx]. So we should introduce different ecological guilds (if needed) at different stages of regeneration, and do some clear-out work at proper time.
In a word, ANR should not be limited to only assisting. Various means can be combined to get the most effective results. With the development of both theory and practice, regeneration is expected to deal with agricultural-abandoned area[xxi],[xxii] and even urban forest restoration[xxiii]. We hope to estanbilish a cycle of positive effects: enrich the animal species-enrich the plant species-abundant animal species-abundant plant species. And finally achieve a self-sustainable ecosystem.
References
[i] Turner MG, Baker WL, Peterson CJ & Peet RK (1998) Factors influencing succession: Lessons from large, infrequent natural disturbances. Ecosystems 1: 511–523.
[ii] Brown, K.S., Brown, G.G., 1992: Habitat alteration and species loss in Brazilian forests. In: Whitmore, T.C., Sayer, J.A. (Eds.), Tropical Deforestation and Species Extinction. Chapman & Hall, London, pp. 119–142.
[iii] Chazdon, R.L., 2003. Tropical forest recovery: legacies of human impact and natural disturbances. Perspectives in Plant Ecology Evolution and Systematics 6, 51–71.
[iv] Ricardo R. Rodrigues, Renato A.F. Lima, Sérgius Gandolfi, André G. Nave: On the restoration of high diversity forests: 30 years of experience in the Brazilian Atlantic Forest. Biological Conservation 142 (2009) 1242–1251.
[v] HOW TO PLANT A FOREST. Part 4: Helping forests to help themselves-accelerating natural regeneration. http://www.forru.org
[vi] S. Galatowitsch, D.M. Richardson: Riparian scrub recovery after clearing of invasive alien trees in headwater streams of the Western Cape, South Africa. Biological Conservation 122 (2005) 509–521.
[vii] Juan Manuel Dupuy , Robin L. Chazdon: Interacting effects of canopy gap, understory vegetation and leaf litter on tree seedling recruitment and composition in tropical secondary forests. Forest Ecology and Management 255 (2008) 3716–3725.
[viii] Nelida J. Carnevale, Florencia Montagnini: Facilitating regeneration of secondary forests with the use of mixed and pure plantations of indigenous tree species. Forest Ecology and Management 163(2002)217-227.
[ix] S.M. McLachlan, D.R. Bazely: Outcomes of longterm deciduous forest restoration in southwestern Ontario, Canada. Biological Conservation 113(2003 ) 159–169.
[x] Kenichi Shono, Stuart J. Davies, Chua Yen Kheng: Regeneration of native plant species in restored forests on degraded lands in Singapore. Forest Ecology and Management 237 (2006) 574–582.
[xi] Flaviana Maluf de Souza, Joa˜o Luı´s Ferreira Batista: Restoration of seasonal semideciduous forests in Brazil: influence of age and restoration design on forest structure. Forest Ecology and Management 191 (2004) 185–200.
[xii] John A. Parrotta, Oliver H. Knowles: Restoring tropical forests on lands mined for bauxite: Examples from the Brazilian Amazon. Ecological Engineering 17 (2001) 219–239.
[xiii] M.H. Wishnie, D.H. Dent, E. Mariscal, J. Deago, N. Ceden˜o, D. Ibarra, R. Condit, P.M.S. Ashton: Initial performance and reforestation potential of 24 tropical tree species planted across a precipitation gradient in the Republic of Panama. Forest Ecology and Management 243 (2007) 39–49.
[xiv] Susan J. Doust, Peter D. Erskine, David Lamb: Direct seeding to restore rainforest species: Microsite effects on the early establishment and growth of rainforest tree seedlings on degraded land in the wet tropics of Australia. Forest Ecology and Management 234 (2006) 333–343.
[xv] Wendy Neilan, Carla P. Catterall, John Kanowski, Stephen McKenna: Do frugivorous birds assist rainforest succession in weed dominated oldfield regrowth of subtropical Australia? Biological Conservation 129(2006)393-407.
[xvi] Jennifer M. Cramer, Rita C.G. Mesquita, G. Bruce Williamson: Forest fragmentation differentially affects seed dispersal of large and small-seeded tropical trees. Biological Conservation 137(2007)415-423.
[xvii] T. T. Kozlowski: Physiological ecology of natural regeneration of harvested and disturbed forest stands: implications for forest management. Forest Ecology and Management 158(2002)195-221.
[xviii] Mauricio Quesada, G. Arturo Sanchez-Azofeifa , Mariana Alvarez-An˜orve, Kathryn E. Stoner et al.: Succession and management of tropical dry forests in the Americas: Review and new perspectives. Forest Ecology and Management xxx (2009) xxx–xxx.
[xix] Ricardo Ribeiro Rodrigues, Sebastia˜o Venaˆncio Martins, Luiz Carlos de Barros: Tropical Rain Forest regeneration in an area degraded by mining in Mato Grosso State, Brazil. Forest Ecology and Management 190 (2004) 323–333.
[xx] Tina V. Boucher, Bert R. Mead: Vegetation change and forest regeneration on the Kenai Peninsula, Alaska following a spruce beetle outbreak, 1987–2000. Forest Ecology and Management 227 (2006) 233–246.
[xxi] Xiaojun Du, Canran Liu, Xingjun Yu, Keping Ma: Effects of shading on early growth of Cyclobalanopsis glauca (Fagaceae) in subtropical abandoned fields: Implications for vegetation restoration. ACTA OECOLOGICA 33(2008)154-161.
[xxii] Ariel E. Lugo, Eileen Helmer: Emerging forests on abandoned land: Puerto Rico’s new forests. Forest Ecology and Management 190 (2004) 145–161.
[xxiii] Marı´a C. Ruiz-Jae´n, T. Mitchell Aide: An integrated approach for measuring urban forest restoration success. Urban Forestry & Urban Greening 4 (2006) 55–68.
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