Restoring forests: regeneration and ecosystem function for the future

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Anthropogenic activity has caused persistent and prominent losses of forest cover in dry tropical forests. Natural regeneration of forest trees in grazed areas often fails due to lack of seed sources and consumption by ungulates. To address this, the effective restoration of such sites often requires fencing and outplanting nursery-grown seedlings. In the degraded, dry forests of tropical Hawaii, USA, an additional challenge to restoration of native forest trees is the introduced kikuyu grass (Cenchrus clandestinus). This invasive, rapidly growing rhizomatous plant forms deep, dense mats. We studied the use of nursery cultural techniques to facilitate the establishment of koa (Acacia koa) seedlings outplanted amidst well-established kikuyu grass on a volcanic cinder cone on the dry, western side of Hawaii Island. Seedlings were grown four months in three container sizes (49, 164, 656 cm3) and with four rates (0, 4.8, 7.2, and 9.6 kg m−3) of 15–9–12 (NPK) controlled-release fertilizer incorporated into media prior to sowing. After 16 months in the field, seedling survival was > 80% for all treatments with two exceptions: the non-fertilized 49 cm3 (78%) and 164 cm3 (24%) containers. After 10 years, only these two treatments had significantly lower survival (35% and 10%, respectively) than the other treatments. One year following planting, none of the non-fertilized seedlings had transitioned to phyllodes from juvenile true leaves, regardless of container size. For the fertilized 656 cm3 container treatment, 78%–85% of seedlings had phyllodes, with mean values increasing by fertilizer rate. Phyllodes are known to confer greater drought resistance than true leaves in koa, which may help to explain the improved survival of fertilized trees on this relatively dry site. Overall, nursery fertilization was more influential on seedling height and diameter response than container size after outplanting. However, the largest container (656 cm3) with the addition of fertilizer, produced significantly larger trees than all other treatments during the early regeneration phase; early growth differences tended to fade at 10 years due to inter-tree canopy competition. Although koa is able to fix atmospheric nitrogen through rhizobium associations, our data confirm the importance of nursery fertilization in promoting regeneration establishment. Nursery cultural techniques may play an important role in forest restoration of dry tropical sites invaded by exotic vegetation.

Section: Discussionmentioning

confidence: 99%

Nursery Cultural Techniques Facilitate Restoration of Acacia koa Competing with Invasive Grass in a Dry Tropical Forest

Jacobs

Davis

Dumroese

et al. 2020

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“…However, there are few studies of impacts of deer browse on maritime forests [43]. While browse control techniques can be used (e.g., fencing and tree shelters), these are often logistically and economically prohibitive due to installation and maintenance costs [25,28,44].The Target Plant Concept provides a conceptual framework for forest restoration to increase the likelihood of outplanting success [45]. A component of the concept is to identify and overcome important limiting site factors using site preparation [46].…”

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confidence: 99%

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confidence: 99%

Herbivory and Competing Vegetation Interact as Site Limiting Factors in Maritime Forest Restoration

Thyroff

Burney

Jacobs

2019

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Herbivory and competition during the regeneration phase influence forest successional dynamics. We demonstrated the importance of using the Target Plant Concept to identify and overcome site limiting factors for subtropical maritime forest restoration associated with deer browsing and competition. Quercus virginiana Mill. (live oak) bareroot seedlings were planted into clearcuts along the US Southern Atlantic coast with different treatment combinations of herbivory control (fenced or non-fenced) against white-tailed deer (Odocoileus virginianus Zimm.) browsing and competing vegetation removal (none, one-year, or two-years). After three growing seasons, mean seedling survival was 61% with no significant treatment differences. Control of browse and vegetation interacted to facilitate growth of live oak; seedlings were significantly larger for all response parameters (diameter, height, crown width) when fenced and treated with vegetation control. Removal of vegetation improved seedling performance only in fenced plots, however, indicating a shift in pressure from herbivory to competition as the most limiting site factor when deer were excluded. After the second growing season, foliar nitrogen was greater in fenced plots than non-fenced plots and greater in two-year vegetation control subplots than non-vegetation control subplots. This result, however, was absent after the third growing season. Three years after clearcutting, there was no evidence of Q. virginiana natural regeneration in non-fenced plots. Even with artificial regeneration in non-fenced plots, Q. virginiana growth was slow, indicating that herbivory was a key limiting factor. Our findings illustrate the importance of accounting for site limiting factors and may aid in developing management prescriptions to promote semi-evergreen oak regeneration in ecosystems with high pressure from herbivory and competing vegetation.that simultaneous control of browsing and vegetative competition may synergistically improve seedling performance [13][14][15]. While there have been many studies on the individual effects of herbivory and competition, few previous studies have examined the interactive effects, with those that have showing varied results [16][17][18][19][20][21]. Competition between planted seedlings and neighboring vegetation limits the availability of soil nutrients, water, and light, impairing basic plant physiological processes [22]. In turn, competition restricts the ability of seedlings to establish, grow, and survive [23,24]. In clearcuts, light is notably increased, releasing competing vegetation from the seed bank and understory, while also providing habitat for recruitment of early successional competition via seed dispersal. Pioneer vegetation may acclimate quickly and take advantage of increased light and other resources in clearcuts, suppressing regeneration [25][26][27]. Controlling competition is therefore often deemed necessary following clearcutting. Under specific circumstances, however, a trade-off exists whereby competition may be bene...

“…The success of forest establishment program, including afforestation, reforestation, and forest restoration [1,2] mainly depends on the quality of Forest Reproductive Material (FRM), i.e., seedlings [3,4] and seeds [5]. FRM is often subjected to transfer and trade [6,7], emphasizing the genetic component of FRM quality regarding the seed source [8] and genetic diversity of seed lot used for production of seedlings in nursery or for direct seeding on the field [9].…”

Section: Introductionmentioning

confidence: 99%

Performance of Scots Pine Seedlings from Seeds Graded by Colour

Novikov

Соколов

Drapalyuk

et al. 2019

Research Highlights: One of the ways to improve the quality of a seedlot used in the forest nursery is the grading of seed by colour. Background and Objectives: The study is intended for forest’s engineers and owners because it offers an alternative solution for forest seeds improvement before sowing. The success of forest establishment program mainly depends on the quality of Forest Reproductive Material. At this time usual practices during the seed processing is seed grading on size. This causes a lot of controversy about the possible reduction of genetic diversity through directional selection. Materials and Methods: Aiming to study the effect of seed coat colour on seedling performance, a one-year old container seedlings of Pinus sylvestris L. were planted at the post-fire site. Seedlings were produced from three fractions, previously graded in the visible wavelength range on a standard optical separator, plus control obtained without separation by colour. Results: Seedlings from different seed fractions performed differently in the first growing season after planting on the field. Seedlings from light seed fraction grow better in height, but those from dark seed fraction resulted with the highest survival rate. Light-dark seeds, which constitute the largest group in the initial sample by absolute weight, resulted with seedlings of the lowest growth rates and survival. The good results showed by seedlings from the control, for both growth rates and survival, indicate the weak effect of seed colour grading on seedlings field performance, but also the need for the more comprehensive studies in the future.