Evidence review: how effective are alternatives to plastic tree shelters for establishing new native trees and woodland?
Abstract
1. In recent decades, plastic tree shelters have been used to great effect to provide protection to individual planted trees in created woodlands. However, at the end of their useful lives (3-5 years), these shelters are difficult to collect, rarely re-usable or recyclable and form a source of plastic pollution in the environment. This review assesses the evidence on the effectiveness of alternative tree protection methods, as well as their potential impact on the biodiversity of created woodlands. 2. Young trees can tolerate low intensity browsing, but few published studies directly compare non-intervention to active protection methods in woodland creation. Similarly, the effectiveness of herbivore culling compared with tree shelters has not been directly established. However, culling (e.g. deer) is not thought to be practical for small-scale woodland creation projects. Fencing can be an effective solution, especially in combination with active deer management, but the cost for widescale usage is prohibitive on large sites. 3. High density planting (HPD) and direct seeding can improve survival rates, cover or vigour of saplings, but their efficacy still depends on a measure of herbivore control via fencing or culling. Woodland creation via natural regeneration can rapidly increase vegetative cover but lacks experimental evidence to date. 4. Alternative-material tree shelters are in their infancy and do not present a realistic solution at this stage. There are small-scale schemes to collect and reuse plastic tree shelters, but this still ultimately presents an end-of-life issue. Anti-herbivore paint needs frequent re-application during establishment and is not practical or cost-effective on a large scale. 5. There is a lack of evidence that plastic tree shelters, or any of the other methods, affects the biodiversity value of created woodlands on a long-term basis. However, preliminary evidence suggests microplastics can impact the woodland soil ecosystem (e.g. earthworm ingestion). It is prudent, therefore, to continue research in alternative tree protection methods, as well as improving the re-use or recycling of existing plastic shelters. 6. Overall, widespread herbivore culling is likely to have the most benefit on a landscape scale, both as a tool for woodland creation and in ongoing management.