The Classification of Native Woodlands in Ireland and its Application to Native Woodland Management Authors: John Cross, National Parks and Wildlife Service; Philip Perrin, BEC Consultants Ltd; and Declan Little, Woodlands of Ireland November 2010 Native Woodland Information Note No. 6 Native woodlands vary considerably with respect to Therefore, this Information Note is relevant to species composition, depending on climatic and site those with an interest in Ireland’s native woodlands, conditions, particularly soil and elevation. This gives particularly practitioners involved in their management. rise to different woodland assemblages or communities, some of which are very distinctive. The classification of The classification system presented is also highly native woodlands is not only an indicative guide to the relevant to landowners, foresters and ecologists variety and diversity of native woodland communities involved in projects under the NWS, as it replaces that exist in any given region, but can also be an the classification system set out in Appendix 7 of the essential tool in the management and expansion of Native Woodland Scheme Manual (Forest Service, 2008). native woodlands. In any native woodland management As such, native woodland plans developed under the project and during the application of the Forest Service NWS must utilise the classification system set out in this Native Woodland Scheme (NWS), woodland classification Information Note when identifying the native woodland is a critical component at the planning stage by type(s) to be promoted. Please note, the inclusion of any particular native woodland type within this updated • enabling the identification of the most appropriate classification system does not infer that it will be woodland community type(s) within an existing eligible for grant aid under the NWS. woodland, which can then be promoted through appropriate management; or The classification system set out in this Information • providing guidance regarding the most appropriate Note is based on the recently completed National Survey native woodland type(s) that should be established of Native Woodlands 2003-2008 (Perrin et al., 2008), on a greenfield site, subsequent to the verification of which is the first national survey of the native woodland on-site parameters, including soil type, topography, resource undertaken in Ireland. New information on altitude, aspect, local climate and current vegetation. the variety and types of native woodland that exist in Ireland is included. Sponsored by: INTRODUCTION Background to the revised native • to aid in the identification of the woodland classification system most appropriate native woodland The National Survey of Native type(s) to be promoted or reinstated Since the classification system outlined Woodlands undertaken between 2003 by management of a site, and and 2008 was the first survey of its kind in this Information Note is primarily based • to guide the selection of appropriate ever undertaken in Ireland. Over 1300 on the findings of the National Survey species and mixtures for planting sites throughout the country were of Native Woodlands, the nomenclature on a site in the absence of, or examined in detail. At each site, a suite used differs considerably from that used in conjunction with, natural of physical and biological parameters to date by practitioners in the development regeneration. were recorded, including the flora, of NWS plans (i.e. Cross, 2008). The woodland vegetation type and structure, previous system was based on limited management and soil. The classification and biased data from detailed studies Woodland structure system outlined in this note is largely in specific regions. Woodlands in other Woodlands are typically characterised based on the vegetation and soil data regions were virtually unknown at that by well-developed layers traditionally from over 1600 quadrats collected during time. The new classification, while not referred to as the tree or canopy layer, the course of this survey (Perrin et al, 2008). based on exhaustive sampling, is much the shrub layer, the dwarf shrub layer, As native woodland classification is an more comprehensive as data were the herb or field layer and the ground integral part of the planning phase of collected across the whole country or moss (bryophyte, i.e. nonvascular projects under the NWS, it is appropriate from stratified samples based on plants, including the mosses, liverworts, that the findings of this national survey predetermined criteria (“arbitrary but and hornworts) layer. These layers may are used to update the classification without preconceived bias”). It closely sometimes be sub-divided into additional requirements. follows the system used in the British layers, e.g. the field layer may have a tall National Vegetation Classification Scheme layer of bracken above a lower layer of The survey concluded that there are (e.g. Rodwell, 1991). The woodland types shorter herbs. Trees and shrubs may occur four principal native woodland types in are named using the best indicator species in several layers depending on their stage Ireland: oak woodlands, ash woodlands, from the tree layer and from characteristic of development, while lianes (climbers), alder woodlands and birch woodlands. species among the other vascular plants1. such as ivy (Hedera helix2), may form These are further divided into 22 sub- Sub-types are named using the two best an important part of the herb layer types. Some of these sub-types represent vascular indicator species. To facilitate but also extend into the canopy. variations in the soil or hydrological comparisons with the previous, and other, regime while others are a result of past classification systems, a table showing Woodland vegetation is traditionally and current management. The variation the relationships and affinities is given divided into two major groups: high between some of these sub-types is in Appendix 1. forest and scrub. The dividing line subtle and may be hard for the non- between these two categories is specialist to recognise. Specifically, The classification system in this frequently obscure, particularly as variation is typically observed in the Information Note is designed for use scrub is often a precursor to high ground flora and a detailed knowledge in the NWS during the development forest so that one may merge of the range of species that occurs here of the native woodland plan for both imperceptibly into the other. is required. In addition, two units not Element 1 (Conservation of existing native Traditionally, however, the height described in the National Survey and woodlands) and Element 2 (Establishment of the vegetation is used to separate three scrub types are included in the of new native woodlands on greenfield the two groups, with 5 m being taken revised classification. sites). Its purpose is: as the upper limit for scrub on dry sites, and 4 m for scrub on wet sites. 1 Vascular plants – plants that have a specialised conducting system consisting mostly of phloem (food-conducting tissue) and xylem (water-conducting tissue), collectively called vascular tissue. Ferns, gymnosperms, and flowering plants are all vascular plants). 2 For nomenclature see classification system description on page 4. 2 Factors affecting the woodland Many woodlands around former demesnes of the former vegetation or individual vegetation are characterised by an abundance of plants may remain under Sitka spruce sycamore (Acer pseudoplatanus) or beech (Picea sitchensis) and other heavy shade- A variety of factors can determine the (Fagus sylvatica), often with a variety of casting trees. woodland vegetation. These include non-native shrubs, some of which may environmental factors such as soil type be invasive, e.g. cherry laurel (Prunus Grazing can profoundly influence both and climate but also biotic factors and laurocerasus) and rhododendron the structure and species composition management history. Management can (Rhododendron ponticum) (see Table 1). of a wood. Overgrazing, for example, strongly influence both the structure Former old woodland sites that have been can prevent the regeneration of trees and composition of a woodland and the replaced or underplanted with conifers or and shrubs and lead to the absence nature of many stands may be a reflection non-native broadleaves often retain of a shrub layer and a monoculture of of a management regime which has elements of the former flora, thus giving certain herbs or grasses, e.g. woodrush long since been abandoned. Many oak an indication of the type of woodland (Luzula sylvatica) or ivy. Subsequent woodlands, for example, are the product which previously existed. In order to cessation of grazing can result in the of past coppicing in which oak was the identify these it will be necessary to look prolific regeneration and dominance preferred species, resulting in today’s for scattered trees and shrubs from the of a single species, e.g. holly (Ilex even-aged, mono-dominant stands. On earlier stand and to examine the field aquifolium). the other hand, the species composition layer, where it is still present. The amount of the tree layer can sometimes be purely of native vegetation which survives will Selection of tree species a matter of chance, being determined, for depend on the species planted: the native for planting example, by the occurrence of a seed year flora often persists more or less unchanged coinciding with clear-felling, windthrow The relatively small number of native under Scots pine (Pinus sylvestris) and larch or land abandonment. tree species in Ireland makes the selection (Larix spp.). In contrast, only fragments of the most appropriate species relatively easy once the soil type, altitude and other Table 1: Notes regarding beech and sycamore edaphic factors have been determined. Variations within the woodland types Both beech and sycamore are introduced species which have been widely are principally reflected in the relative planted in Ireland for several hundred years. They both regenerate freely and proportion of trees and shrubs and, in places they have become an integral part of our woodlands. However, because often more critically, in the herb layer.