Project 2

Assessment of biodiversity at different stages of the forest cycle

 

          

Introduction

This sub-project was the first in Ireland to investigate how biodiversity changes during the forest growth cycle. This project was a truly interdisciplinary one, where the fauna and flora were documented in in the same locations over the same periods of time, creating an invaluable database of information. The project was completed in 2004 and the final technical report will be officially released in October 2005. Publications in journals from individual disciplines involved have been made, and a number of presentations of the results have also been made at conferences (see Project 2 outputs). Two PhDs were awarded from this project, with their attendant publications.

Most plantation forests in Ireland are managed under a clearfelling regime, which means that they have very distinct stages of development from the planting stages up through thicket and pole stages to finally harvesting and re-planting, or "overmature" (where the forest is left to grow beyond the commercial optimum). There is very little information on biodiversity in plantation forests in Ireland, and even less on how this may change as the forest develops. As forests are dynamic systems, it is essential not only to have a picture of biodiversity that represents only one stage in the forest cycle, but a series of pictures that can be put together to provide a truer picture of biodiversity in the complete forest system as it changes with age.

Forest biodiversity is not only be affected by growth stage but by the forest type. Most of the plantation forest in Ireland is conifer, mainly Sitka spruce or lodgepole pine, and the biota of these forests differ both from each other and from other forest types, for example those dominated by broadleaves. These latter were very uncommonly planted in the past but are gaining in popularity due to changes in policy by the Forest Service. In addition to the differences between forests due to tree species dominance, there are differences due to variations in the environment, even within forests of a particular tree species type.


This project investigated the biodiversity in some different forest types over a range of growth stages. This project linked closely with sub-project 1: Biodiversity assessment of afforestation sites and sub-project 3: Investigation of experimental methods to enhance biodiversity in plantation forests. The approach to the assessment of biodiversity in the sites was similar in each project and this is outlined in the overall BIOFOREST project description. A combination of structural, functional and compositional indicators were used, the emphasis in this subproject being on the structural ones. The contribution of forest to the overall biodiversity of a predominantly agricultural landscape (in some cases, "pastoral forest") was given some attention during this study.

Objectives and targets

Main Objectives:

  • Assess the range of biodiversity in representative forests at key stages of the forest cycle

  • Review and recommend opportunities for enhancement of biodiversity in plantation forests

  • Assess the effectiveness of the Forest Service Guidelines for Forestry and Biodiversity

Targets:

  • Collect field data on particular components of biodiversity, including, for example, birds, hoverflies, spiders, and ground vegetation in relation to the forest cycle.

  • Develop appropriate indicators (either structural, compositional, functional) of plantation forest biodiversity

  • Produce digitised maps of sites with stages of forest cycle and including boundaries, internal and (outline) external habitat

  • Synthesise data and publish a report and papers on how biodiversity is affected by a variety of factors in the forest growth cycle.

Methods

The above objectives were achieved by studying a number of different forest sites, selected for their forest type and growth stage. Site selection was aided by querying the extensive Coillte and FIPS (Forest Inventory and Planning System of the Forest Service) databases, and covered as broad a geographical range as was allowed by the project logistics. See map for distribution of sites.

At the stand level, structural measures were made including size, shape, tree stand structural complexity, regeneration, gap distribution, dead wood (quality and amount), litter and the presence or absence of water courses. Compositional measures included the examination of plant, vertebrate and invertebrate taxa with particular attention to the species area requirement and similarity to potential natural vegetation. The functional key factors were also assessed, including the management regime.

Site maps were provided through Coillte and FIPS, and the boundaries of each study site were mapped and entered into a GIS. Habitat maps of the study sites, indicating sub-habitats and key biotopes, where relevant, were drafted in digital format.

Current Forest Service Guidelines for Forestry and Biodiversity were assessed in the light of the results from this project.

Results and Conclusions

This project was the first of the sub-projects to be completed. The final Project Report was launched at the BIOFOREST conference in October 2005 (see below). The project examined 44 sites around Ireland, focusing on plantations dominated by (a)Sitka spruce, (b)ash, and (c)Sitka spruce and ash in a non-intimate mix. Five different age categories of plantation were examined where possible (pre-thicket, thicket, mid-rotation, mature spruce (35-50 yr) and mature ash (>50 yr))..

Results showed that plantations can support diverse species assemblages over the forest cycle, but these contain a large proportion of generalist species and few species of conservation importance. However, mature stands develop a characteristic woodland flora and support forest specialist spiders and hoverflies. In terms of species richness a comparison of the ash and the spruce component of stands in a non-intimate mix found no overall difference in diversity between the two. However, each component supported different species assemblages, so on a plantation scale overall biodiversity was significantly increased by having ash as a component of a predominantly spruce forest. The results support many of the management recommendations in the Forest Service Forest Biodiversity Guidelines, including the choice of site location and design of open spaces and boundary habitats at the forest planning stage. Key issues for forestry management are the importance of thinning in opening up the forest canopy, the retention of standing and fallen dead trees, and the retention of scrub habitat.

This project generated huge amounts of information which have been built into an ArcGIS database to facilitate spatial analyses. Two PhDs were awarded from work on the project, and a number of presentations have been made on it. It is anticipated that more than five peer-reviewed articles will issue from the project.

Site photos - a selection.

Results and conclusions of this project were presented in a substantial technical report available in adobe acrobat form from COFORD (Final Report BIOFOREST 3.1.2 (1.22 Mb)). The reference for this is:

Smith, G.F., T. Gittings, M.W. Wilson, L. French, A. Oxbrough, S. O’Donoghue, J. Pithon, V. O’Donnell, A.-M. McKee, S. Iremonger, J. O’Halloran, D.L. Kelly, F.J.G. Mitchell, P.S. Giller and T. Kelly (2005). Assessment of biodiversity at different stages of the forest cycle. BIOFOREST Project 3.1.2 Final Report. Report prepared for COFORD and EPA.

In addition to this major final product, the project produced other reports and theses as shown below, and contributed to the BIOFOREST Project overall Synthesis Report and the major database product. The other products are:

French, L. (2005). Ground flora communities in Ireland's plantation forests: their diversity, structure and composition.   University of Dublin, Trinity College, Dublin244pp.

Oxbrough, A. (submitted March 2006) The effect of plantation forests on ground-dwelling spiders. PhD Thesis, University College, Cork, Ireland.

Oxbrough, A.G., T. Gittings, J. O’Halloran, and P.S. Giller (2005). Structural indicators of spider communities across the forest plantation cycle. Forest Ecology and Management 212 (1-3): 171-183.

Gittings, T., P.S. Giller and J. O’Halloran (2005). Notable hoverfly (Diptera: Syrphidae) records, 2001-2002. Irish Naturalists’ Journal 28 (3) 132-133.

Oxbrough, A. (in review). Distribution records of some uncommonly recorded spiders in Ireland including a new Irish record: Meioneta mollis (O.P. -Cambridge,1871) (Araneae: Linyphiidae). Irish Naturalists Journal.

Wilson, M.W., J. Pithon, T. Gittings, T.C Kelly, P.S. Giller and J. O'Halloran (in press). The effects of growth stage and tree species composition on breeding bird assemblages of plantation forests. Bird Study.

 

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