The precommercial development of GE plants typically follows a series of steps, each accompanied by regulatory oversight (Figure S1). Confined field trials provide scientists with an essential experimental platform to further basic and applied scientific research through the evaluation of GE plants outside of the laboratory or greenhouse. Confined field trials also enable product developers to evaluate the performance of transgenic events and collect data to meet regulatory requirements.
The first ERA for a particular GE event is usually for a confined field trial. Regulatory permits to conduct confined field trials of a GE plant impose limits in time and space. These may include limits on the scale (e.g. area to be planted, number of locations and number of plants), the duration and the types of allowed activities (e.g. transportation, analytical and other experimental studies etc.). Permittees must apply control measures to ensure that the GE plants stay within these limits. As for GE crops, measures to confine GE trees may include spatial separation from the same or sexually compatible species, planting of border rows/pollen traps, and/or specific equipment cleaning, transport and disposal procedures.
ERAs for confined field trials primarily focus on the effectiveness of the risk control measures. Consequently, fewer data are needed to evaluate the risks posed by field trials than for commercial-scale environmental releases. Confined field trials of GE plants typically evaluate phenotypic characteristics and agronomic performance. The biology of the parent species, in particular, its reproductive capacity, and its potential for gene flow and long-distance dispersal, must be considered when determining the suitability and effectiveness of control measures. Details of the introduced gene(s)/genetic modification, the expected phenotype and any experience with the same or similar modifications in other species of plants may also be useful.
National information about the species and traits in confined field tests of GE trees is publicly available via the internet (Table 1). In some cases, a detailed description of the genetic modification and associated risk assessment are available. In the United States, risk assessments have been published for field trials of eucalypts, poplar, white spruce and sweetgum as well as nonforest trees including papaya, apple, walnut and plum (APHIS, 2012). Similarly, New Zealand has published detailed risk assessment and risk management decisions for field trials of GE trees (NZEPA, 2012). In Australia, while no GE forest trees have been approved for field trials, detailed risk assessment and risk management plans are available for several fruit trees and other long-lived perennials, including papaya, banana, grapevine and sugarcane, that are relevant for forest trees (OGTR, 2012b). In the European Union, Notification Reports are published that summarize potential environmental impacts and risk management measures (JRC, 2012). Notably, these reports specifically address forest trees as recipient or parental plants and describe factors affecting potential dissemination. Countries including Japan (J-BCH, 2012) and Brazil (CTNBio, 2013) provide information on the activities and procedures implemented to manage risk, while Canada publishes species-specific terms and conditions that must be met while conducting confined field trials (CFIA, 2012).
Key considerations for ERA of GE trees in confined field trials
For ERA of confined field trials of GE trees, a crucial aspect of the ERA is determining the effectiveness of confinement. The impact of the confined release of a GE tree on the environment will be minimized by the generally small scale of the release. Restricting access by wildlife or humans, and postharvest management and monitoring requirements, also contribute to minimizing potential environmental impacts. To determine the effectiveness of risk mitigation measures, a number of key aspects need to be considered: the reproductive biology of the host species; the biology of any sexually compatible species also present in or proximal to the receiving environment; potential for long-distance dispersal of propagules; and ecological interactions particularly if the interactions are with species of concern such as protected species or weeds. Information about the receiving environment including silvicultural practices may also be useful.
Reference biology documents, such as those published by the OECD and a number of individual countries, are available for many plant species including several trees (Craig et al., 2008; OECD, 2006). These simplify access to essential information about the reproductive biology of the host organism. Additionally, the possibility of dispersal of propagules by humans and animals is addressed. Tree species that are currently used for plantation forest production have been well studied, and extensive information exists that can contribute to proposing and assessing effective strategies for confining field trials of GE trees (Brunner et al., 2007; Byrne, 2008; Henry, 2011; OECD, 2012).
It is then important to consider how the introduced trait, both in its intended and potential unintended effects, might alter the biology of the tree with respect to the ability to achieve adequate confinement. Several sources of information can be used to inform the risk assessment. For example, observations of the tree's phenotype from laboratory or greenhouse studies will be available for use in the risk assessment, and experience with the same or similar genes introduced into crop plants can enhance a risk assessor's prediction of the potential effects (e.g. Nickson, 2008; Wolt et al., 2010). Additionally, the objectives for development of many GE trees involve the same traits as those sought through traditional breeding. The potential environmental impacts of these traits will be the same, or similar, to those introduced by conventional improvement programmes, and so risk assessments should be informed by experience with conventionally derived traits (NAS, 1987; NRC, 1989; OECD, 1993).
The proposed receiving environment for a confined GE tree release needs to be considered case by case, just as required for other GE plants. Consequently, the ERA should consider characteristics specific to the proposed site such as environmental conditions, silvicultural practices and the presence of sexually compatible species in so far as they relate to the confinement of the trial. The focus of the ERA for field trials should be assessment of the likelihood that the conditions of the trial will confine the genetically engineered trait. It should not be necessary, and indeed it may be impossible, to make precise predictions about what might happen should the transgenes escape confinement. The purpose of the field trial is to collect data to help make such predictions while minimizing the probability of escape. Lack of detail about ecological interactions between the GE tree and the environment ought not to prevent a field trial if confinement is reliable. Proximity of the proposed trial site to protected species is an issue that should be addressed and may be a legal requirement (e.g. Australia's Gene Technology Act 2000; US' 7 CFR 340 and 7 U.S.C. § 136, 16 U.S.C. § 1531 et seq., Canada's Part V, Seeds Regulations, Brazil's Normative Resolution No. 5).
The scale and duration of a field trial affects its confinement and should be driven by the need for data to test particular hypotheses. While most crop plants are annual or can be made to complete an annual reproductive cycle, forest tree species typically take years to attain sexual maturity. This prolonged juvenile phase may be advantageous for confinement; performance and some biosafety-related data may be collected without measures to prevent dissemination of propagules. However, repeated reproductive cycles at maturity and tree longevity suggest that dispersal of propagules must be managed in later stages of the trial. In this respect, trees and herbaceous perennial plants such as alfalfa present similar risk scenarios. The size and woody nature of trees may result in the need for measures for disposal of GE plant residue additional to the common practices of incorporation into the soil, burial or incineration that are applied to herbaceous GE plants.
If there is insufficient information about the parent tree species or about the phenotype and anticipated behaviour of an experimental GE tree in the environment, measures to reproductively isolate confined field trials of GE trees might be needed. These measures mimic those applied to crop plants and include removal of the developing inflorescences from any early flowering individual trees, or termination of the trial prior to flowering. Monitoring of the trial site after trial completion is also a standard management measure to ensure that the GE trees do not re-establish. For example, root suckering is typical for several tree species including aspen species (Fladung et al., 2003), and vegetative regeneration with sprouting and coppicing is a natural characteristic of birch (Koski and Rousi, 2005).
It is a common misunderstanding that confined field trials and commercial releases are subject to essentially the same risk assessment. The confinement of these trials (described above) blocks many of the potential pathways to harm. Therefore, an ERA for a field trial permit can be completed without the exhaustive data that are typically needed for an environmental release without confinement. This is important because the field data that may be required to assess the risks of an unconfined release are usually generated from confined field trials. Confusion between data requirements for confined and unconfined releases has been exacerbated by the Cartagena Protocol on Biosafety (SCBD, 2000) that does not differentiate these activities and, consequently, many national biosafety regulatory frameworks developed to implement the Biosafety Protocol do not either. GE tree development cannot advance past the laboratory stage unless biosafety regulatory systems are able to permit the field evaluation of GE plants of uncertain risk (McLean et al., 2012).