The types of tree grown and the extent of a forestry plantation can have a bearing on the diversity of the birds, fish and animals that populate it. Even the shape of a plantation can have an influence on the forest dweller populations.
These are some of the initial findings by NUI Cork researchers who are participating in a four-year study worth almost £200,000 and funded by Coford and Coilte. Coford is the National Council for Forest Research and Development which is based at UCD. It supports a wide range of scientific research in support of Ireland's forestry industry, from silviculture and forest management to plant propagation, harvesting equipment and wood-processing techniques.
The Cork team under the direction of Prof Paul Giller of the Department of Zoology and Animal Ecology with Dr John O'Halloran is three years into a project to develop strategies to enhance forest biodiversity. In particular, bird and salmonid populations are being assessed in a range of forestry configurations to determine whether there is an "optimum" forest arrangement.
"The idea is that we will be able to predict what should be in the forests and give advice to the management side of the forestry industry," Prof Giller explained. There are "extensive" and "intensive" studies underway as elements of the work. The team has identified 180 forestry stands across Munster which are being studied for fish and bird populations, and an intensive study of a single stand, Kilworth Forest in Co Cork, also forms part of the work.
About 60 sites are selected at random each year. Bird populations including goldcrests, tits, robins, chaffinches, wrens and song thrushes are calculated by observation. Forest streams and rivers are "stop-netted" to assess populations of trout, salmon, eels, stone loach, minnows and other species.
These studies also include river water chemistry, invertebrate populations and "morphological" aspects, such as the degree of tree shading, river-edge vegetation, water depth and position of pools, that can influence fish numbers. "We are trying to pick out what characteristics control fish numbers," Prof Giller explained.
The study has already provided a great deal of information. For example, Prof Giller has established that forestry activity has not reduced the number of salmon on his Munster test sites. "There is no negative effect of forestry on fish in Munster," he declared.
While forests can alter water chemistry, the physical characteristics of the watercourse are much more important to fish numbers. This includes edge vegetation and shading, providing cover for the fish in the form of rocks or fallen tree limbs and the availability of pools.
The group has also found that low- to medium-intensity forestry at low to medium altitudes seems to have a positive effect on fish numbers. More extensive bird populations arise when the forest stand includes older and younger trees, a factor which could influence forest management practice when trees are ready for harvest.
The shape of a forest stand also influences bird populations and seems to be more important than the overall size of the stand. Birds congregate in greatest numbers at the edges of the forestry which means that the worst possible stand shape would be a circle. Irregular shapes encourage more birds to congregate and nest.
The research also points up "artificial" ways to promote wildlife diversity, for example, by mounting nesting boxes at forest edges or by digging pools, dropping large limbs or tree trunks into streams or planting suitable vegetation along stream edges.
The fundamental question - whether there is an optimum tree species mix to enhance biodiversity - is far more complex and will require further study. Prof Giller expects, however, that the research will provide forest managers with solid data about "where to plant, what to plant and the shape and size of the stands".
The biodiversity of freshwater lakes, rivers and streams, water chemistry and ecology and the impact of pollution will be under discussion at a major international conference which gets under way this morning at University College Dublin. Up to 1,250 delegates from around the world are expected to attend the Societas Internationales Limnologiae (SIL) Congress. Limnology is the scientific study of fresh water lakes, streams and rivers.