FOREST MANAGEMENT IN THE IRISH CLIMATE CONTD..........

sites annual amounts increase by about 100-150 mm per 100 m rise in altitude. The most commonly planted tree species, Sitka spruce and Douglas fir, are well suited to high rainfall and attain very fast growth rates in this country.

GLOSSARY:

Dry spell:
15 or more consecutive days each with less than 1.0mm of rain.

Absolute Drought:
15 or more consecutive days each with less than 0.2mm of rain.

Partial Drought:
29 or more consecutive days for which the mean daily rainfall is 0.2mm or less.

The distribution of rainfall and evaporation during the year is important to tree growth. Shallow rooted seedlings arc prone to drought and irrigation is often necessary to ensure growth during the summer months, especially in eastern regions with relatively low annual rainfall. Drought can also be critical for new growth if it occurs during shoot extension in conifers. On the other hand in saturated soils, root respiration is hampered and species such as Sitka spruce develop very shallow roots on waterlogged soils. Met Eireann routinely calculates the soil moisture balance for a grass surface on a weekly basis and this provides a good approximation to conditions in forests.

Forest planting Forest planting is usually confined to the period from November to the end of April. Hard ground during winter frosts makes planting difficult. During the pole stage some species, especially pines, are vulnerable to snow damage. Snow occurs most frequently in northern counties such as Donegal and at high elevations in Wicklow. Species such as Douglas fir are best planted during March - April when harsh weather is less likely and the plants are better able to survive the shock of outplanting. Cold easterly and northerly winds and harsh weather during February and March often lead to scorching of needles and to plant losses, if persistent.

Weather and forest operations Rain affects many forestry operations such as delayed planting and harvesting and influences crop stability or spraying tasks. The latest Met Eireann forecast should be checked for wind and rain during sensitive forestry operations, e.g. rainfall immediately after spraying reduces the effectiveness of contact herbicides.

Windthrow Wind has many positive effects on forests (e.g. helping heat transfer, dissemination of pollen) but high wind causing windthrow is the most important hazard to forestry production. Factors contributing to wind damage are climate, elevation, topography, soil type and silviculture practices such as thinning. Each year about 250 ha of forest are windthrown in Ireland.