Fire, as it is easily concluded from the preceding analysis, continues to be an important factor even in the modified now wildland ecosystem that dominates, particularly, in the lower Mediterranean zone of Greece.
Moreover, all activities developed today for restoration of the wildland vegetation and the reestablishment of the forest primarily for protection and recreation purposes (environmental forests), magnify the importance of the fire factor and render it, I might say, dominant in the environmental forest ecosystem, under, especially, the rapidly increasing tourist traffic and the demand for outdoor recreation.
Upon the basis of these facts and considerations lie our studies on prescribed burning, inspired and guided by the relative research and application work done in the USA.
We thought that burning might be a very valuable tool, and an unsubstituted servant in the management of Greece’s wildlands, if properly used and manipulated with understanding. After a thorough analysis of the problem, it was concluded that prescribed burning might be indicated and valuable in management of the following three distinctive ecosystems:
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A.
In the coniferous forests of Pinus halepensis and Pinus brutia.
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B.
In the maquis formation.
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C.
In the high mountain grasslands, dominated by hard bunchgrasses.
The specific problems in each of these three ecosystems, and the experimental work planned and undertaken arc presented in the following discussion.
Coniferous Forests
In the coniferous forests of aleppo or brutia pine, naturally existing or artificially created in their natural area by reforestation, two main categories of stands can be distinguished.
Forests on good site. Growth conditions allow here the development or the creation and maintenance of thick stands during at least the first half of their rotation time.
With the progress in age of the stand one can see:
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1.
A number of trees dying-off under the effect of the severe competition developed among trees (natural thinning) having no commercial value, and thus representing an actual loss for the forest business. For the same reason all understory vegetation is gradually dying-out too (Figure 6).
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2.
A continuous increase of dead branches of living trees remaining in place, decreasing thus the quality, and consequently the value of the timber produced, even if after several years that they may be broken, but always in a considerable distance from the tree-trunks (Figures 7 and 8). Under Mediterranean climate, and particularly in its lower part, natural pruning, that constitutes in classical silviculture one of the reasons justifying thick stands, seems to be an empty word. Decomposers, the main agent in natural pruning, can not be very active, because moisture is insufficient when temperatures are sufficiently high in summer time.
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3.
An accumulation on the ground of pine needles in thick undecomposed layers, and a storage of dead pine needles upon the dead branches of trees or upon understory woody vegetation (Figure 9). The decomposition of the litter is very, very slow for the same reason mentioned above.
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4.
A large volume of slash left upon the ground after each thinning of the stands, once the diametre of the trees reaches commercial value.
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5.
In the older stage during the second half of the rotation time the stands are thinned naturally, for they are constituted by light tolerant (light demanding we might say better) species. The density of the stands is decreasing as they approach the end of the rotation time. Under such relatively open stands a dense understory of woody and herbaceous vegetation grows (Figure 3), which in summer time is very flammable; its moisture content is then very low. This is one of the reasons for which P. halepensis and P. brutia stands are not thinned properly in early age stages with the result of a lower value of timber produced.
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6.
After the final cut of the stand at the end of the rotation time the understory vegetation grows extremely vigorous and dense in absence of any competition from pine trees. Under such conditions natural regeneration becomes uncertain, or it completely fails. On the other hand, artificial regeneration can be warranted only with high cost.
Forests on poor site. Here the stands grow more or less open from a very young age. Under such stands an understory brush and/or herbaceous vegetation is developed, and a heavy flammable fuel is stored on the ground, much the same way as that under aged stands growing on good sites, creating similar problems from the very beginning in each stand.
It is certainly clear after this brief analysis that the fire hazard in such coniferous forests of the lower Mediterranean climate is very big.
Obviously, the elimination of the accumulated on the ground highly flammable fuel, and furthermore the prevention of accumulation of new fuel on the forest floor is of paramount importance.
One way to do this is to take away from the forest any flammable matter every time its quantity exceeds the security limits. However, this creates heavy expenses, increasing, finally, very much the cost of the timber and/or gum produced, and the offered services of protection, recreation and landscape improvement as well.
Certainly, prescribed burning might be a suitable and extremely valuable tool, and a very good solution of the problem, under conditions we knew whether, how, when and where this technique could be applied in Greece. And furthermore, if following prescribed burning the establishment and maintenance of an understory vegetation of forage plants could be easy, then the practice of a proper grazing by livestock and/or wildlife animals could not only prevent the accumulation of fuel under the forest canopy, but it would, in addition, produce a considerable income instead of expenses. Besides, this would minimize the competition of the understory vegetation with trees, as far as soil moisture is concerned that constitutes the main limiting factor of plant growth in the Mediterranean zone, and thus greatly benefit the forest and consequently timber production. This would, perhaps, also encourage silviculturists to thin properly the stands for maximizing the value of the timber that can be produced in proportion to site potential, since they would not be annoyed by an undesirable understory vegetation. In addition, once the understory vegetation could be easily controlled even with benefit (grazing), the application of fertilizers for further increase of timber and forage production would be possible and economically justified.
With this in mind as the basic hypothesis, and in view of the facts and experience gained in the USA, a number of experiments were planned and have been put under way since 1968 in Pinus brutia stands. With this net of experiments it is hoped and expected to have valuable results, that properly analysed and interpreted, would answer the general problems created by the use of prescribed burning in forests of Pinus halepensis and Pinus brutia. More specifically it is expected to answer the questions which came out of the analysis of the problem made above, that constitute the general hypothesis of the study.
Up to date results. Although it is very early to have valuable conclusions, a number of data and observations could be of interest. The results of the compiled up-to-date data are as follows:
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1.
It is rather certain that Pinus halepensis and Pinus brutia endure quite well, prescribed burning of brush understory vegetation at an age of 30 years and thereafter. Their rhydidome is at that age thick enough to protect the cambium from the released heat (Figure 10).
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2.
The temperature of mineral soil under burnt brush and slash is hardly affected, when burning is applied in winter 2 or 3 days after a rain good enough to soak well under the litter humus. Measurements made showed 15 °C after fire ran over it, while air temperature was 16 °C. Thus soil was not affected at all.
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3.
Soil nitrogen was found to be higher in burnt than in unburnt plot the first year after burning. It was 0.189 percent and 0.126 percent respectively.
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4.
The establishment of seeded orchardgrass (Dactylis glomerata L.)—after burning in intensively thinned plot was satisfactory. Volunteers, among which were many legumes, colonised the soil after burning in satisfactory degree. Main volunteers: Festuca ovina L., Aristella bromides (L.) Bertol., Andropogon ischaemum L., Koeleria cristata Pers., Phleum spp., Trifolium purpurem Loisel., Trifolium angustifolium L., Trifolium arvense L., Vicea spp., and Poterium sanguisorba L.
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5.
In burnt plot, after three consecutive thinnings of the 30 year old stand, that lowered the tree number per hectare from 1100 to 450, total volume (standing and taken by thinnings) was equal to that of the plot treated according to conservative silvicultural rules (see Table 1 and Figure 11). Also the increment of standing trees after thinning was much higher in the intensively thinned and burnt plot (Figure 12).
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6.
Pine regeneration 2 years after last burning was very good. In the unburnt plots many seedlings were found from germinated seed during past fall, but almost none from germinated seeds in previous years. Table 2 shows the pine seedlings found in February 1973 in burnt and unburnt plots.
Evergreen Brushlands
Maquis brushlands are now used by browsing animals such as goats and deer mainly. Their value as browse-land is not very high. Liacos and Moulopoulos (1967) found that browse production of this land in good condition does not exceed for the area studied, 750 kg ha−1 air dry. Liacos (unpublished data, University of Thessaloniki, Greece) in a conversion study from brushland to grass by seeding Dactylis glomerata, Phalaris tuberosa L., and Trifolium hirtum All. after mechanical clearing of brush, found that grass forage production was about 500 kg ha−1 air dry.
With this in mind and the fact that wildfire hazard is very high in this vegetation type a comparative research study was started last year. Prescribed burning is used as the main tool of conversion, followed by planting of a mixture of seeds of Lolium multiflorum Lam. (used as the main competitor against brush sprouts), Dactylis glomerata, Phalaris tuberosa and Trifolium hirtum. On the other hand, brush vegetation in the remaining underbrush covered plots is improved by proper manipulation of brush individuals and the whole community as well, for reaching maximum browse production (Figure 13).
The purpose of this experiment is to find out:
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(a)
Whether brush conversion by prescribed burning constitutes an efficient technique.
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(b)
How to control brush sprouts after burning.
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(c)
What is the production of forage as compared to browse produced.
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(d)
Which is the technique to follow in order to insure a good establishment and maintenance of forage cover.
High Mountain Grasslands
Prescribed burning has been also used in a research study to improve forage production of high mountain rangelands, dominated by hard bunch-grasses, grazed for centuries only by sheep and goats.
Large quantities of undecomposed litter on the ground surface prevent the seedlings from rooting into the mineral soil, and are easily and regularly uprooted by grazing sheep.
The experiment has been established at an elevation of 100 m the fall of 1971 in Mount Phalacron in northern Greece, representing an area of more than 10 000 ha in this mountain and manyfold larger area all over upland Greece.
Burning was applied in fall and in spring immediately after snow melt in combination with and without chemical fertilization (Figure 14).
The first year results show that burning improved the quality of the forage; it was more tender and palatable. Its crude protein content was higher than in unburnt forage, while quantitatively no difference was found thus far.
Reprinted and condensed with permission from Liacos, L.G., 1974. Present studies and history of burning in Greece. Tall Timbers Fire Ecology Conference Proceedings 13: 65–95, by Tall Timbers Research Station, Tallahassee, Florida, USA.