Project 3

Investigation of experimental methods to enhance biodiversity in plantation forests.

Project 3




"The treatment of the open spaces is the single most important factor in the success or failure of nature conservation within plantations” (Peterken, 1996) .

The distribution, composition and management of open space within forests is a factor that is acknowledged to be important by the requirement under the Forestry Biodiversity Guidelines for 15% open space and retained habitats in new plantations. It is a factor that is amenable to intervention for biodiversity enhancement, both at the forest planning stage, and through the subsequent treatment of the open space during the forest cycle. Afforestation can affect the species composition of adjacent habitats of biodiversity importance (Cameron, 1994). Management of open space, following its incorporation into a forestry plantation, can affect its biodiversity (Humphrey & Patterson, 2000). Therefore, research on the biodiversity of open space in plantations would contribute significantly to biodiversity enhancement of plantation forests.

Aim and Objectives

To identify the optimum configuration and management of open space within plantation forests for enhancement of biodiversity.

·         Determine the effects of different shapes of open space on biodiversity within forested areas

·         Determine the effects of experimental manipulations regarding open space in forests

·         Make recommendations as to how management practices can positively affect biodiversity in forests.


The proposed work programme involves the following:

·         extensive surveys to examine the relationship between biodiversity and open space management; and

·         experimental manipulations to test the observed relationships between biodiversity and open space management.

Extensive Surveys

The extensive surveys were carried out on twelve different forests in two distinct geographical clusters. Five different open spaces were examined in each forest. The variables examined included the following:

·         Total percentage of open space.

·         Composition of open space (rides, glades, retained habitats, firebreaks, etc.).

·         Distribution of open space.

·         Management of open space.

To allow adequate replication, the survey sites were restricted to mature Sitka spruce. The survey design was based upon matched clusters of sites. Within each cluster, geographical location, soil type, altitude, etc. were as similar as possible and open space configuration varied.

Experimental Manipulations

For practical reasons the manipulations concentrated on internal forest road widths. At the planting stage of eight forests, designated stretches of road were made where the treeless width was the current standard of 15m, the other twice that at 30m. The manipulations were carried out in association with Coillte on reforestation sites in two clusters in Munster and Leinster. The planting season for this experiment was 2004/2005, and the field survey in 2005 will provide an initial assessment of any immediate effect on the biodiversity of the different widths used. These data will also form a baseline for the future monitoring of the experiment as the forest grows through the cycle described and investigated in Project 2.

Specific methodologies for recording flora and fauna


In this project both ground vegetation and epiphytes were sampled. On the ground sample plots were placed at intervals along a gradient from the middle of the open space into the closed forest. Plots were four square metres, and both vascular and non-vascular plants were recorded.

There was a focus on epiphytes for the floral surveys of the extensive part of this project. The ground flora of Sitka spruce forests is not diverse and a study of the epiphytes, including lichens, was innovative and informative. The ecological distribution of epiphyte species is governed by a complex of gradients, notably: (i) host tree species, (ii) position on host tree, (iii) stage of the forest cycle, (iv) rainfall and humidity regime, (v) air quality. 

Epiphytes were sampled on one tree at the open space edge and one in the interior forest at each site. Sampled trees were not adjacent to rows that were entirely removed during thinning where possible. The forest edge tree sampled directly adjoined the open space. The interior forest tree was located at distance from the edge greater than or equal to the height of the edge trees at that point.

Epiphytes were sampled in plots located on the trunk and branches using tree-climbing techniques. Sampling was carried out at 4 different height zones in the tree– tree base, lower, middle and upper. The tree base zone began at the point where the trunk emerges from the soil or needle litter and reached to 0.5m above this point. The lower zone was centred on 1.3m height, and the middle and upper zones was centred on 1/3 and 2/3 of the height of the tree, respectively. Fifty cm long trunk plots were located on the side of the trunk facing the open space and the opposite side (north and south side) at each of these heights. The width of the plots varied from a maximum of 25cm to that required to sample a half cylinder of the trunk.


The invertebrate sampling focused on hoverflies (Syrphidae) and spiders (Aranae), as in the other sub-projects. Malaise traps were used to sample hoverflies, and the results were interpreted using the Syrph The Net database (Speight et al., 2001) to determine (a) the relative contribution of various types of open space habitat components to the overall syrphid biodiversity and (b) the implications of the differences observed in the experimental manipulations . Pitfall traps were used to sample spiders. Plots of pitfall traps will be located in a range of open space microhabitats on a gradient from the forest interior to the centre of the space.


Birds were sampled using point counts.  The exact number of point counts varied depending on the size of the open space, but where practicable the rules governing the selection of points counts (after (Bibby et al., 2000) ) were followed.


Bibby, C., Hill, D., Burgess, N.D., & Mustoe, S. (2000) Bird Census Techniques. Poyser.

Cornelissen, J.H.C. & ter Steege, H. (1989) Distribution and ecology of epiphytic bryophytes and lichens in dry evergreen forest of Guyana. Journal of Tropical Ecology 5, 131-150.

Johannson, R. (1974) Ecology of vascular epiphytes in West African rain forest. Acta Phytogeographica Suecica 59, 1-129.

Speight, M.C.D., Castella, E., Obrdlik, P., & Ball, S., eds. (2001) Syrph the Net,  the database of European Syrphidae. Syrph the Net publications, Dublin.  

Results and Conclusions

The subject chosen as a focus of this study was open space within forests. In 2003 an extensive survey was conducted of 60 open spaces within 12 mature forests dominated by Sitka spruce. These spaces included glades, rides and roads. A special study was made of epiphytes. After the extensive survey was completed a manipulation experiment was designed to investigate the effect of different road widths on biodiversity. Roads of two different widths were established during the planting phase of eight forests. The surfaced width of road is the same in both: about 5m, but in the narrow treatment the total gap created was 15m, and in the wide treatment, 30m. Forests were Coillte-owned reforestation sites.

A presentation on the epiphytes recorded during the extensive survey was made by Linda Coote in 2005.

Photo of forest road

Photo of climbing to sample epiphytes

Results and conclusions of this project were presented in a substantial technical report available which will be available from COFORD in electronic format:

Iremonger, S., T. Gittings, G.F. Smith, M.W. Wilson, A. Oxbrough, L. Coote, J. Pithon, S. O'Donoghue, A.-M. McKee, J. O'Halloran, D.L. Kelly, P.S. Giller, A. O'Sullivan, P. Neville, F.J.G. Mitchell, V. O'Donnell, T.C. Kelly, and P. Dowding. 2006 Investigation of experimental methods to enhance biodiversity in plantation forests. BIOFOREST Project 3.1.3 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:

Wilson, M., T. Gittings, J. O'Halloran, T. Kelly, & J. Pithon, 2005 The distribution of Hen Harriers in Ireland in relation to land-use cover in general and forest cover in particular. Dublin: Report for COFORD and EPA.

Coote, L. (due to submit 2006). Epiphyte diversity in Irish plantation forests. Ph.D. Thesis, Trinity College, University of Dublin, Ireland.

See Outputs page for details of other outputs and presentations.


Project 1
Project 2
Project 3