Principles of Natural Regeneration of Tropical Dry Forests for Restoration
Tropical dry forests are the most threatened tropical terrestrial ecosystem. However, few studies have been conducted on the natural regeneration necessary to restore these forests. We reviewed the ecology of regeneration of tropical dry forests as a tool to restore disturbed lands. Dry forests are characterized by a relatively high number of tree species with small, dry, wind-dispersed seeds. Over small scales, wind-dispersed seeds are better able to colonize degraded areas than vertebrate-dispersed plants. Small seeds and those with low water content are less susceptible to desiccation, which is a major barrier for establishment in open areas. Seeds are available in the soil in the early rainy season to maximize the time to grow. However, highly variable precipitation and frequent dry spells are important sources of mortality in seeds and seedlings. Collecting seeds at the end of the dry season and planting them when soil has sufficient moisture may increase seedling establishment and reduce the time they are exposed to seed predators. Germination and early establishment in the field are favored in shaded sites, which have milder environment and moister soil than open sites during low rainfall periods. Growth of established seedlings, however, is favored in open areas. Therefore, clipping plants around established seedlings may be a good management option to improve growth and survival. Although dry forests have species either resistant to fire or that benefit from it, frequent fires simplify community species composition. Resprouting ability is a noticeable mechanism of regeneration in dry forests and must be considered for restoration. The approach to dry-forest restoration should be tailored to this ecosystem instead of merely following approaches developed for moister forests.
Natural regeneration as a tool for large-scale forest restoration in the tropics: prospects and challenges
A major global effort to enable cost-effective natural regeneration is needed to achieve ambitious forest and landscape restoration goals. Natural forest regeneration can potentially play a major role in large-scale landscape restoration in tropical regions. Here, we focus on the conditions that favor natural regeneration within tropical forest landscapes. We illustrate cases where large-scale natural regeneration followed forest clearing and non-forest land use, and describe the social and ecological factors that drove these local forest transitions. The self-organizing processes that create naturally regenerating forests and natural regeneration in planted forests promote local genetic adaptation, foster native species with known traditional uses, create spatial and temporal heterogeneity, and sustain local biodiversity and biotic interactions. These features confer greater ecosystem resilience in the face of future shocks and disturbances. We discuss economic, social, and legal issues that challenge natural regeneration in tropical landscapes. We conclude by suggesting ways to enable natural regeneration to become an effective tool for implementing large-scale forest and landscape restoration. Major research and policy priorities include: identifying and modeling the ecological and economic conditions where natural regeneration is a viable and favorable land-use option, developing monitoring protocols for natural regeneration that can be carried out by local communities, and developing enabling incentives, governance structures, and regulatory conditions that promote the stewardship of naturally regenerating forests. Aligning restoration goals and practices with natural regeneration can achieve the best possible outcome for achieving multiple social and environmental benefits at minimal cost.
On the Causes of Failure of Natural Regeneration in British Oakwoods
In the light of the foregoing what measure of success in natural regeneration may we expect to be found in the different oakwood associations? The importance of certain animals in the economy of the woodland has been pointed out in connection with the disappearance of both the acorn and the seedling. The prevalence of certain of these animals is in large measure, of course, dependent on local circumstances, e.g. on the attitude assumed towards them by the proprietors of the various estates. Pheasants for example may to a greater or less extent be thus limited. But in the case of the rabbit, natural circumstances favour its increase on sandy soils, so that the damage done on soils of this kind is greater than on clay soils. From the data available mice do not seem to be restricted in this way, so we may assume their ravages to be fairly evenly distributed over the various types of soil. The importance of concealment to the survival of the acorn and the value of a humus layer in this connection are pointed out. The latter occurs more abundantly in the Damp Oakwood than in either the Dry Oakwood or Oakbirch-heath associations. The relation of germination to the type of seed bed provided is also discussed and it is pointed out that while generally no inherent difficulties are met with to prevent natural regeneration in the Damp Oakwood, seed beds of an unfavourable kind became more frequent as we pass from the Dry Oakwood to the Oak-birch-heath associations. The efficacy of the mildew in producing fatal effects on oak seedlings is shown to be greater on sandy soils than on clay, and the bracken, by its increasing frequency in the Dry Oakwood and Oak-birch-heath associations, by greatly diminishing the supply of light and impairing the vitality of the seedlings, materially assists the fungus in producing these effects. Summing up one can say that the chances of success decrease as we pass from the Damp Oakwood association to the Dry Oakwood and from the latter to the Oak-birch-heath–a fact to be taken into consideration by the forester when he contemplates the natural regeneration of his oakwoods.
Application of Assisted Natural Regeneration to Restore Degraded Tropical Forestlands
Assisted natural regeneration (ANR) is a simple, low-cost forest restoration method that can effectively convert deforested lands of degraded vegetation to more productive forests. The method aims to accelerate, rather than replace, natural successional processes by removing or reducing barriers to natural forest regeneration such as soil degradation, competition with weedy species, and recurring disturbances (e.g., fire, grazing, and wood harvesting). Compared to conventional reforestation methods involving planting of tree seedlings, ANR offers significant cost advantages because it reduces or eliminates the costs associated with propagating, raising, and planting seedlings. It is most effectively utilized at the landscape level in restoring the protective functions of forests such as watershed protection and soil conservation. ANR techniques are flexible and allow for the integration of various values such as timber production, biodiversity recovery, and cultivation of crops, fruit trees, and non-timber forest products in the restored forest. This paper describes the steps of applying ANR and conditions under which it will be most effective. It also discusses ANR’s comparative advantages as well as some of its constraints.
The natural regeneration of Eucalyptus regnans.
The main factors influencing the regeneration of E. regnans forests in Victoria and Tasmania, in association with their utilization, are studied in detail under the following main chapter heads: (1) The E. regnans forests, their distribution and the regeneration problem [cf. F.A. 20 No. 2912]; (2) Description of intensive-study areas; (3) Seed production and seed shed [cf. F.A. 19 No. 1501]; (4) The fate of the dispersed seed; (5) Laboratory studies of factors affecting germination and their relation to field conditions [cf. F.A. 19 No. 1645]; (6) Germination in the field, and plot studies; (7) Seedling survival, covering (8) the factors affecting seedling survival in general, (9) winter losses, including losses due to fungi and the effect of reduced light intensity, and (10) the effect on seedling establishment of browsing by wild animals and of competing vegetation after logging; (11) Pre-logging seedbed preparation; (12) Partial cutting to obtain regeneration; and (13) Summary of the factors controlling regeneration, and discussion of the silvicultural techniques considered as suitable modifications applicable to the present basic seed-tree system.
 Vieira, D.L. and Scariot, A., 2006. Principles of natural regeneration of tropical dry forests for restoration. Restoration ecology, 14(1), pp.11-20.
 Chazdon, R.L. and Guariguata, M.R., 2016. Natural regeneration as a tool for large‐scale forest restoration in the tropics: prospects and challenges. Biotropica, 48(6), pp.716-730.
 Watt, A.S., 1919. On the causes of failure of natural regeneration in British oakwoods. The Journal of Ecology, pp.173-203.
 Shono, K., Cadaweng, E.A. and Durst, P.B., 2007. Application of assisted natural regeneration to restore degraded tropical forestlands. Restoration Ecology, 15(4), pp.620-626.
 Cunningham, T.M., 1960. The natural regeneration of Eucalyptus regnans. Bull. Sch. For. Univ. Melb., (1).