Timo Penttilä

Changes in structural inequality in Norway spruce stands on peatland sites after water-level drawdown

Size structural dynamics of naturally established Norway spruce (Picea abies (L.) Karst.) stands growing on peatlands drained for forestry were investigated. The study was based on modelling of diameter at breast height (DBH) distributions of repeatedly measured stands in southern Finland. The Weibull function was used to parameterize the DBH distributions and mixed linear models were constructed to characterize the impacts of different ecological factors on stand dynamics. Initially, the positive skewness of the DBH distributions increased after drainage as a result of in- creases in stem numbers and a reduction in mean diameters. Simultaneously, the size inequality among trees increased. These changes were due to regeneration and (or) ingrowth and indicated only little competition from the larger trees. Subsequently, the DBH distributions changed from positively skewed to normal and finally to negatively skewed result- ing from tree growth and a reduction in the number of small DBH trees. This indicated increased asymmetric intertree competition. Size inequality did not change during this later stage in stand development, suggesting a concurrent com- ponent of symmetric competition. Thinnings had little impact on DBH distribution trends. The observed stand dynam- ics allow the allocation of growth resources to the desired crop component by appropriate silvicultural treatments.

Microbial ecology in a future climate: effects of temperature and moisture on microbial communities of two boreal fens

Impacts of warming with open-top chambers on microbial communities in wet conditions and in conditions resulting from moderate water-level drawdown (WLD) were studied across 0-50 cm depth in northern and southern boreal sedge fens. Warming alone decreased microbial biomass especially in the northern fen. Impact of warming on microbial PLFA and fungal ITS composition was more obvious in the northern fen and linked to moisture regime and sample depth. Fungal-specific PLFA increased in the surface peat in the drier regime and decreased in layers below 10 cm in the wet regime after warming. OTUs representing Tomentella and Lactarius were observed in drier regime and Mortierella in wet regime after warming in the northern fen. The ectomycorrhizal fungi responded only to WLD. Interestingly, warming together with WLD decreased archaeal 16S rRNA copy numbers in general, and fungal ITS copy numbers in the northern fen. Expectedly, many results indicated that microbial response on warming may be linked to the moisture regime. Results indicated that microbial community in the northern fen representing Arctic soils would be more sensitive to environmental changes. The response to future climate change clearly may vary even within a habitat type, exemplified here by boreal sedge fen.

Large contribution of boreal upland forest soils to a catchment‐scale CH4 balance in a wet year

Upland forest soils affect the atmospheric methane (CH4) balance, not only through the soil sink but also due to episodic high emissions in wet conditions. We measured methane fluxes and found that during a wet fall the forest soil turned from a CH4 sink into a large source for several months, while the CH4 emissions from a nearby wetland did not increase. When upscaled to the whole catchment area the contribution of forests amounted to 60% of the annual CH4 emission from the wetlands, while in a normal year the forest soil consumes 10% of the wetland emission. The period of high upland soil emission was also captured by the nearby atmospheric concentration measurement station. Since the land cover within the catchment is representative of larger regions, our findings imply that upland forests in the boreal zone constitute an important part in the global CH4 cycle not previously accounted for.

Whole-tree, stem-only, and stump harvesting impacts on site nutrient capital of a Norway spruce-dominated peatland forest

About 15 million hectares of peat soils have been drained for forestry in temperate and boreal zones. Increasing interest in wood biomass as a source of bioenergy has led to more intensive harvests also in peatland forests. These harvestings remove branches, needles, and stump/root systems that would earlier have remained on-site. However, in drained peatland forests, some key growth-limiting nutrients, such as potassium (K) and boron (B), are largely stored in the living tree biomass, while the stores in peat in tree rooting layer are small. A concern has thus been raised that bioenergy harvesting may induce nutrient insufficiency and decrease second rotation forest productivity. We studied the effect of whole-tree and stump harvesting on site nitrogen (N), phosphorus (P), K, and B capitals in final harvesting of a well-productive, Norway spruce-dominated peatland forest. Harvesting of stumps and above-ground harvest residues resulted in minor depletion of site N and P stores, but significant depletion of K and B. Maximizing harvest residue biomass recovery, but minimizing nutrient depletion, our results indicated that stump harvesting is a more feasible option than harvesting of above-ground residues. If above-ground harvest residues are to be harvested for bioenergy, K and B depletion may be decreased by letting the branches dry out somewhat and the needles fall down before branch harvesting. Combining our results with data on waterborne K losses suggested that K depletion may become a serious problem in second rotation forests on drained peatlands, even if harvest residues and stumps were left completely non-harvested.

Vähäpuustoisten ojitusaluemetsiköiden harvennuspuunkorjuun ja jäävän puuston kasvatuksen kannattavuus kolmessa esimerkkileimikossa

Tutkimuksessa simuloitiin harvennushakkuu, optimoitiin lähikuljetus sekä ennustettiin jäävän puuston kehitys kolmessa, puustorakenteeltaan erilaisessa esimerkkileimikossa erilaisilla metsänkasvatusvaihtoehdoilla. Esimerkkileimikot kuvasivat monille kunnostusojituskohteille tyypillisiä vähäpuustoisia tai puustorakenteeltaan ryhmittäisiä suon osa-alueita. Puunkorjuun kannattavuutta selvitettiin leimikoille simuloitujen korjuuvaihtoehtojen avulla. Simuloimalla jäävän puuston myöhempi kehitys arvioitiin ensiharvennusvaiheen toimenpiteiden vaikutuksia metsänkasvatuksen kannattavuuteen pitkällä aikavälillä. Tulokset osoittivat, että puuston harventaminen kunnostusojituksen yhteydessä ei aina ole edullisin ratkaisu. Harvennuksen myöhentäminen kunnostusojitusajankohdasta 15–25 vuodella lisäsi oleellisesti harvennuksen ainespuukertymää ja paransi pitkän aikavälin tuotosja taloustulosta. Mikäli harvennus kuitenkin tehtiin kunnostusojituksen yhteydessä, voimakas kertaharvennus oli sekä puunkorjuun että pitkän aikavälin tuoton kannalta paras ratkaisu. Harvennuskertymien suureneminen alensi korjuukustannuksia vajaalla 10 prosentilla korjuukelpoisen vähimmäiskertymän tuottavaan harvennusvaihtoehtoon verrattuna. Liian voimakkaissa harvennuksissa, jäävän puuston määrän laskiessa alle asetuksessa säädetyn minimivaatimuksen, kasvutappiot lisääntyivät selvästi ja myös pitkän aikavälin taloustulos heikentyi. Metsänkasvatusvaihtoehtojen väliset erot tuotosja taloustuloksissa olivat pienimmillään karuimman kasvupaikan esimerkkileimikossa.