Tree shelters facilitate brown oak seedling survival and establishment in a grazing‐dominant forest of Bhutan, Eastern Himalaya

Abstract

Brown oak (Quercus semecarpifolia) forest is essential for ecological and socioeconomic functions, mainly grazing in the Himalayas. The tree has failed to regenerate naturally and is a threatened species. Restoration of brown oaks is crucial to ensure sustainability while maintaining livestock grazing in these habitats. Achieving this requires cost-effective restoration techniques that are practicable and sympathetic to the multiple uses of the forest. We assessed the combined effect of grazing (control) and three tree shelters (Protex tubes, mesh wires, and wooden frames) on the field performance of oak seedlings in a forest with heavy grazing pressure. Seedling survival and morphological indicators, including seedling height, collar diameter, sturdiness quotient (SQ), and leaf mass per area (LMA) indices, were measured. More than 90% of control seedlings without protective shelters suffered severe browsing and demonstrated significantly lower survival rates compared to tree shelter seedlings, indicating that grazing was the primary factor governing regeneration success. Seedling survival in tree shelters was three times higher, while the height increase was two times higher than the control. Additionally, locally made mesh wire and wooden tree shelters were more effective than Protex and control in producing quality seedlings reflected by the SQ and LMA values. We suggest that tree shelter is a promising option to restore brown oaks due to its efficacy to defend grazing and support the local community's rights to forest grazing. Our finding is expected to support Bhutan's forest policy of incorporating grazing and tree regeneration into forest management.

Weed control and use of tree shelters: improving restoration success of degraded north Patagonian forests

“…Height of N. dombeyi seedlings was not affected by the use of tree shelters neither in the xeric site, and nor in the mesic site, at least until the second growing season (prior to the browsing effect). This result contrasted with those of several hardwood (Davies 1985;Tuley 1985;Gillespie et al 1996;Bendfeldt et al 2001;McCreary and Tecklin 2001;Dorji et al 2020) and conifer species (Ward et al 2000;Jacobs 2011), which had shown a pronounced positive impact on height with the use of tree shelters. It seems that our results agree with those of the authors who indicate that the net effect of tree shelters on plant growth appeared to be site-and/or species-dependent (Frearson and Weiss 1987;Potter 1988;Burger et al 1992;Buresti and Sestini 1994;Ward and Stephens 1995;West et al 1999;Ponder 2003;Famiani et al 2007;Puértolas et al 2010;Oliet and Jacobs 2007;Piñeiro et al 2013).…”

“…These responses have been attributed to modified microclimatic conditions within the shelter environment (Potter 1988;Peterson et al 1994;Dupraz 1997, 2000;Clatterbuck 1999;Oliet and Jacobs 2007). Sheltered seedlings presented higher survival rates for many broadleaved and conifer species (Tuley 1985;Ward and Stephens 1995;Jacobs and Steinbeck 2001;Oliet et al 2005;Puértolas et al 2010;Valenzuela et al 2018;Dorji et al 2020). However, the effects could vary over time (Oliet et al 2005) and due to the environmental conditions of the site (Oliet and Jacobs 2007).…”

“…Thus, it could be expected that the height achieved by this species at the mesic site would be somewhat greater, and even that some effect of the treatments applied could be 1 3 missed from the third growing season and onwards. Although preventing browsing damage was not the purpose of the use of tree shelters in this study, it has been such for other studies presenting positive effects of using taller devises for seedling browsing protection (Piñeiro et al 2013;Dorji et al 2020).…”

“…Several studies suggest that seedling growth and survival can be significantly increased with the protection given by tree shelters (Costello et al 1996;Dubois et al 2000;Weitkamp et al 2001;Jacobs and Steinbeck 2001;Sweeney et al 2002;Ponder 2003;Dorji et al 2020). These responses have been attributed to an improvement of microclimatic conditions within the shelter environment (Potter 1988;Zastrowd and Marty 1991;Kjelgren et al 1994;Peterson et al 1994;Dupraz 1997, 2000;Oliet and Jacobs 2007;Jacobs 2011).…”

Meta-analysis of livestock effects on tree regeneration in oak agroforestry systems

“…We relied on the authors’ definitions to differentiate between seedlings and saplings of the same species, acknowledging minor variations in this classification across studies. When the included studies involved multiple levels of grazing treatment (e.g., Rossetti and Begella, 2014; Dorji et al, 2020), we calculated an average where applicable. To compare the effects of livestock in different oak agroforestry systems, we categorized each case study into two groups: (1) oaks and (2) oaks with broadleaves and/or conifers.…”