Abstract
Direct seeding has been considered a forest restoration option for centuries. Over the past half century, the use of this practice has declined in developed countries as forest regeneration programs have advanced with the production of quality seedlings that can successfully establish restoration sites. Direct seeding is being reconsidered as a restoration option as the potential size of the worldwide forest restoration program has grown because of massive deforestation in third-world nations and due to global climate change. This review examines direct seeding from a number of perspectives. First, merits of using this practice in restoration programs are defined. Major merits of this option are that it can be done quickly, over hard to reach and large disturbed areas, and at a relatively low cost. Second, current research findings from restoration programs are discussed. The major finding is that seedling establishment rates are low (i.e. typically around 20% of seeds planted) due to site conditions, seed predation and vegetation competition, and field performance (i.e. survival and growth) is lower than planted seedlings. Third, operational practices for the application in restoration programs are reviewed. To successfully conduct direct seeding programs practitioners need to consider seedbed receptivity, seed distribution and seeding rate. Fourth, potential new practices are presented. Some of these new practices attempt to create a more effective means to disperse seed across the site, minimize seed predation or create a more favorable microsite environment. This review provides a synthesis of what is known about direct seeding, thereby allowing practitioners to make a rational decision of whether to apply this practice towards their forest restoration program.
Highlights
The use of direct seeding with tree species has been an ongoing silvicultural practice in forest restoration programs for centuries
The objective of this review is fivefold: 1) to examine the merits of direct seeding, 2) explore current research findings from a biological perspective across temperate and tropical forest species, 3) to evaluate responses to operational silvicultural practices, 4) to examine potential new application practices, and 5) to provide a synthesis of what is currently known about direct seeding practices so practitioners can make rational decisions on whether to apply this practice in their forest restoration program
Knowing which tree species have suitable characteristics for direct seeding is critical to the success of forest restoration projects that rely on direct seeding (Tunjai and Elliott 2011)
Summary
The use of direct seeding with tree species has been an ongoing silvicultural practice in forest restoration programs for centuries. There is an increasing interest in the use of direct seeding as an alternative to seedling planting This is because the amount of forest restoration required worldwide is overwhelming. The last Forest Resources Assessment (FAO 2015) reported a global net forest loss of 3.3 x 106 ha year-1 from 2010 to 2015 This has resulted in the need to restore up to two billion hectares of forest sites worldwide (Minnemayer et al 2011). There is a necessity to consider this practice as an option where the availability of seedlings is limited to address this very large forest restoration requirement and to provide a low cost option to shape degraded landscapes with desired tree species that creates a biodiverse forest ecosystem. The objective of this review is fivefold: 1) to examine the merits of direct seeding, 2) explore current research findings from a biological perspective across temperate and tropical forest species, 3) to evaluate responses to operational silvicultural practices, 4) to examine potential new application practices, and 5) to provide a synthesis of what is currently known about direct seeding practices so practitioners can make rational decisions on whether to apply this practice in their forest restoration program
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