Metla Project 3233

The ecological base and predictability of natural seedling establishment

[  Suomeksi  |  Objectives  |  Results  |  Project leader  |  Researchers  |  Publications  |  Metla Research  ]

Duration: 1998-2003   Keywords: Forest regeneration, drained peatlands, germination, seed crop, seedbed properties, seedling emergence, seedling establishment

Objectives

The objectives of the project include to study the dependence of the germination, emergence and initial development of germlings on the site factors of the regeneration area and the variability of the seed crop, and to draw up prognosis models depicting them. Furthermore, we are involved in formulating practical recommendations on the available alternatives in natural regeneration of old drainage sites and upland forests, and on combining natural and artificial regeneration.

In regard to the subject of seed crops, we look into their temporal and local variations, and the factors affecting involved. Time series models are drawn up for pine and spruce with long-term litter trials as the basis. The foremost topics when studying the dependencies between regeneration fellings and seed crops are the development of the pine seed crop following regeneration felling, the effect on the seed crop of the number and quality of seed trees retained, and the distribution of seed from the adjoining forest to the regeneration site.

Results

Seed crop as basis of natural regeneration
In Southern and Central Finland pine has been observed to produce abundant seed crops 2-3 times per decade and spruce 3-4 times per decade. However, various pests damage an average of two of spruce’s seed crops. Birch produces abundant seed crops at intervals of 2-3 years. The average annual seed crop of a mature pine stand in Southern Finland is 2.5-5 kg/ha and that of spruce about 15 kg/ha. In peaks years the seed crop of spruce can amount to 120 kg/ha. Thinning and fertilisation add to the seed crop of pine.

The seed crop has been observed to increase as a function of the number of seed trees retained per hectare. This applies to the range of 25-100 trees per hectare. When aiming to achieve fast regeneration, a lot of seed trees should be retained (100-150 trees/ha). The seed crop increases again during the fourth growing season after the stand has been reduced to seed-tree density. Regeneration felling and site preparation should be timed to take place in the autumn preceding a good seed crop. Another approach is to conduct the regeneration felling in the winter and site preparation by the following May.

Natural regeneration of old drainage areas
The presence of a “ready-to-go” naturally-arisen understorey of pine and smaller pine restocking on nutritionally poor old drainage areas is modest and an abundant seed crop and favourable weather conditions immediately subsequent to regeneration measures are important factors. However, milling, which corresponds to disc trenching on upland forest soils, can produce fully-stocked pine stands. Mounding is another treatment alternative. The success of milling depends, however, on the dominant ground vegetation. Peat moss (Sphagnum spp) patches often become well restocked even when unprepared, which means that the effect of site preparation is most evident on those drainage sites, which have already lost their Sphagnum moss cover. However, preparation of peat moss communities can in some cases produce the most favourable site for seedling emergence; this is especially the case during dry summers. These surfaces are especially favourable to downy birch, which can become a major problem as it can prevent the further development of pine seedlings, particularly on Vaccinium vitis-idaea type of old drainage sites.

The weather conditions at the time of germling emergence have a powerful effect, along with the properties of the substrate, on the success of regeneration. The height of the groundwater level is another factor affecting restocking, and it has been noted to depend on the weather conditions, but the differences between various groundwater levels are insignificant from the point of view of practical regeneration objectives. According to the results of this study, raising the groundwater level for the duration of the restocking stage is not an adequate substitute for site preparation.

Scarified patches produced using an excavator became restocked best of all with the groundwater level at 30 cm. The effect of scarifying in relation to non-treatment was at its greatest on those drainage sites, which had already lost their mire vegetation and especially so when common hair moss (Polytrichum spp) was present. Scarification of sites with Sphagnum moss was less effective because these became restocked even when untreated.

Combining natural restocking and artificial regeneration
The results of studies indicate that in poor seed years sowing accelerated and secured the result of the natural regeneration, but in good seed years it has no effect. In the case of small regeneration sites on dry and dryish upland soils, the seeding effect of the adjacent stand has been noted to match the seeding effect of having 20-25 seed trees per hectare. Seed originating from the adjacent stand has a great supplementing role also in the case of fertile sites, but the year-to-year variation is considerable and the uneven distribution of wildlings over the regeneration site reduces the usefulness of this natural restocking material.

Project leader: Saarinen, Markku
The Finnish Forest Research Institute, Parkano Research Unit, Kaironiementie 54, 39700 Parkano
Phone: +358 10 211 4058 Telefax: +358 10 211 4001
E-mail: markku.saarinen@metla.fi

Other researchers: Hartman, Markus, VA (1999-2002), Hokkanen, Tatu, VA (1998-2002), Hotanen, Juha-Pekka, JO (2000), Kinnunen, Kaarlo, PA (1998-2003), Saksa, Timo, SU (1998,2002), Vanha-Majamaa, Ilkka, VA (1998-99)


Top of page

Updated 30.12.2006
Comments