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I would like to thank Ray Monaghan for encouraging this debate. The following is a response to a letter Ray sent to Pro Silva Ireland via the Forest Network Newsletter.
The extracts below are taken from the Pro Silva Principles and explain why under certain circumstances exotic species may be necessary. It is acceptable to assume that Ireland qualifies under both these categories, particularly 2.4:
2.3 Devastated forests:
In forest regions where historical influences have weakened the genetic fitness of tree populations and where soils have been harmed by human activities, and where indigenous species under the given circumstances can not be reintroduced and the natural succession will not take place, an introduction of exotics might contribute to the restoration of such forests.
2.4 Denuded forest land:
In places where former forests have been totally destroyed, and where a forest climate no longer exists, and where indigenous species under the given circumstances can not be reintroduced at the present time and the natural succession will not take place, exotic species might play an important pioneer role.
With reference to the Pro Silva Principles you quoted:
4.2 An introduced species should not be so aggressive in its competitive behavior and its natural regeneration as to suppress indigenous tree species or eliminate other indigenous species.
This refers to forest ecosystems and it is not realistic to expect indigenous species found exclusively outside forests to continue to thrive after afforestation. Pro Silva Ireland would be against existing semi-native forestry being converted to Sitka Spruce plantation.
Certainly we will have to look closely at Sitka Spruces ability to regenerate. Unfortunately it is far more realistic to expect deer etc. to insure that Sitka Spruce survives where indigenous species do not. It is the control of deer that will often dictate the abundance of indigenous species in particular forest ecosystems.
4.3 An introduced species should be adapted to the local climate and soils. It must not impoverish soils, and its litter should decompose easily.
It is a lack of appropriate management in the form of sufficient thinning, which results in 'dark shade' on the forest flow. This prevents any other species from establishing themselves except the most shade tolerant, such as mosses, etc. Decomposition of litter is also to a great extent dependant on light, so that even Beech litter tends not to decompose as the Beech also causes a dark shade unless thinned.
4.6 An introduced species should become integrated into the indigenous vegetation in a modest way. It must be able to merge with, without excluding, the indigenous flora and fauna.
4.7 An introduced species should be able to regenerate naturally, together with indigenous tree species.
Again it is management policy and implementation that has thus far prevented mature and second rotation Sitka Spruce becoming integrated into the vegetation in a modest way. It should be remembered that seed sources for native forest species might not be close enough to allow regeneration in the short term.
1.4 states that; The introduction of exotic species should only be allowed after critical qualitative and quantitative tests.
Experimental plots of Sitka Spruce established by what became the Forest Service showed Sitka Spruces suitability to the Irish climate, particularly as afforestation crop. Certainly further research into the role Sitka Spruce has to play as a component of semi native woodlands would be very rewarding.
Is your interest in Irish forestry purely academic or are you involved on a practical level? Since you are also in Kerry, I would be very interested in visiting the forests you may have been involved in creating/managing. If this is not possible, I would be very interested to read your silvicultural alternatives for the poor degraded sites on which most Sitka Spruce is planted and your own proposals for Irish forestry in general. Certainly Birch and Alder have potential, but both these species still require Research and Development. Pro Silva Ireland fully supports such Research and Development.
Sitka Spruce has played an important and effective role in returning land to forestry that had been degraded to the point that it would take many generations for woodlands to return to these sites. Now we have an opportunity to manage the areas of afforestation in such a way as to establish forestry that can both meet economic potentials and ecological roles. What's more this will be more effectively achieved, than if we had invested the same resources (as was initially attempted) in afforesting with native species. The goal is a healthy and stable forest, which will be a sustainably profitable forest.
There is no doubt that Sitka Spruce has both limitation and drawbacks. So what would be Sitka Spruces main limitation? As I made clear in my previous letter Sitka Spruce 'if managed properly (see Pro Silva Principles) will improve the site conditions for a second or third generation forest with an ever increasing proportion of native & natural biodiversity'. Sitka Spruce can not replace our native diversity, but should be used to effectively prepare sites for woodland conditions.
Proper management of Sitka Spruce is as important as with any other species, particularly as Sitka Spruce usually grows in this country as a plantation with little or no horizontal or vertical structure. What I mean by this is simply that each tree is the same size as its neighbours. At the foundation of Pro Silva Principles is the diversity of structure; trees of every size can be found on any given area.
In your letter you refer to the 'catastrophic reduction of earthworms under Sitka Spruce'. I would be interested in reading you source for this information and I have no doubt this is correct under certain circumstances. I don't believe earthworms are very prevalent on typical Sitka Spruce, and I feel that in the long term the management of Sitka Spruce plantation toward Near to Nature Forestry as described in Pro Silva Principles will insure that earthworms will become more prevalent than prior to afforestation.
Perhaps you wonder what will happen to Sitka Spruce if all plantations are converted as I have described. I believe that Sitka Spruce would continue to play a role on suitable sites in mixture with native species. Its hardiness against deer, among other factors, insures that we will always be grateful that it will grow where other species have not or can not be provided with the correct environment in which to thrive. Sitka Spruce's role should be restricted to establishment and difficult sites with the long-term trend to wards a steady reduction.
Through the technique of selective thinning with little or no regard for the even distribution of selected stems clumpyness is caused. Trees are selected in a plantation on the basis of their negative characteristics, health and stem quality being the most important in that order. Once the stems begin to reach a target diameter the selection process targets the stems that have reached the target diameter, always choosing the least healthy and poorer quality stem fist. We now have a stand of Sitka Spruce that has grown quickly, with the most valuable stems remaining till last. Gaps have appeared and these have either been filled with natural regeneration or planing. This type of conversion carried with it a cost factor, as the most valuable stems are grown beyond a typical plantation rotation causing a delay in financial return. Furthermore better management and infrastructure (e.g. roads) are required. On the other hand the subsequent costs such as unprofitable thinning and planting will be reduced or prevented altogether.
You refer to Ireland's foremost experts on natural forest. There contribution to our better understanding of Irish Forest Ecosystems can not be underestimated. Both the titles you quote refer to conservation and therefore have limited relevance to sites where establishment of forest ecosystems is the objective rather than the conservation of the same. One objective is to maintain and the other is to recreate. Sitka Spruce is an effective tool in recreating a forest ecosystem. It should be in no way the final objective, but a step toward healthy sustainable and mainly native forests.
As for your impression that there is no appreciable difference between Pro Silva Ireland' philosophy on forestry and that of Coillte Teoranta and the Forest Service I am glad to learn that our message has already had such a profound influence. I expect that such changes in philosophy require time to implement both psychologically and in practical terms. Pro Silva Ireland is made up of members that are converted to this philosophy, while Coillte and Forest Service have to an extent had this philosophy imposed on them.
I think it is too early to judge that our reliance on Sitka Spruce has been catastrophic as you suggest. Certainly I am in agreement with you that there has been an overreliance on Sitka Spruce and it has been planted on sites for which it was unsuitable, because such sites could have supported other species in particular native species. I am reassured to read that you do recognise the important place exotic species have in Irish forestry.
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