Estimation of local forest attributes, utilizing two-phase sampling and auxiliary data

This thesis examines the feasibility of a forest inventory method based on two-phase sampling in estimating forest attributes at the stand or substand levels for forest management purposes. The method is based on multi-source forest inventory combining auxiliary data consisting of remote sensing imagery or other geographic information and field measurements. Auxiliary data are utilized as first-phase data for covering all inventory units. Various methods were examined for improving the accuracy of the forest estimates. Pre-processing of auxiliary data in the form of correcting the spectral properties of aerial imagery was examined (I), as was the selection of aerial image features for estimating forest attributes (II). Various spatial units were compared for extracting image features in a remote sensing aided forest inventory utilizing very high resolution imagery (III). A number of data sources were combined and different weighting procedures were tested in estimating forest attributes (IV, V). Correction of the spectral properties of aerial images proved to be a straightforward and advantageous method for improving the correlation between the image features and the measured forest attributes. Testing different image features that can be extracted from aerial photographs (and other very high resolution images) showed that the images contain a wealth of relevant information that can be extracted only by utilizing the spatial organization of the image pixel values. Furthermore, careful selection of image features for the inventory task generally gives better results than inputting all extractable features to the estimation procedure. When the spatial units for extracting very high resolution image features were examined, an approach based on image segmentation generally showed advantages compared with a traditional sample plot-based approach. Combining several data sources resulted in more accurate estimates than any of the individual data sources alone. The best combined estimate can be derived by weighting the estimates produced by the individual data sources by the inverse values of their mean square errors. Despite the fact that the plot-level estimation accuracy in two-phase sampling inventory can be improved in many ways, the accuracy of forest estimates based mainly on single-view satellite and aerial imagery is a relatively poor basis for making stand-level management decisions.

Soil hydrological properties and conditions, site preparation, and the long-term performance of planted Scots pine (Pinus sylvestris L.) on upland forest sites in Finnish Lapland

Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) forests dominate in Finnish Lapland. The need to study the effect of both soil factors and site preparation on the performance of planted Scots pine has increased due to the problems encountered in reforestation, especially on mesic and moist, formerly spruce-dominated sites. The present thesis examines soil hydrological properties and conditions, and effect of site preparation on them on 10 pine- and 10 spruce-dominated upland forest sites. Finally, the effects of both the site preparation and reforestation methods, and soil hydrology on the long-term performance of planted Scots pine are summarized. The results showed that pine and spruce sites differ significantly in their soil physical properties. Under field capacity or wetter soil moisture conditions, planted pines presumably suffer from excessive soil water and poor soil aeration on most of the originally spruce sites, but not on the pine sites. The results also suggested that site preparation affects the soil-water regime and thus prerequisites for forest growth over two decades after site preparation. High variation in the survival and mean height of planted pine was found. The study suggested that on spruce sites, pine survival is the lowest on sites that dry out slowly after rainfall events, and that height growth is the fastest on soils that reach favourable aeration conditions for root growth soon after saturation, and/or where the average air-filled porosity near field capacity is large enough for good root growth. Survival, but not mean height can be enhanced by employing intensive site preparation methods on spruce sites. On coarser-textured pine sites, site preparation methods don t affect survival, but methods affecting soil fertility, such as prescribed burning and ploughing, seem to enhance the height growth of planted Scots pines over several decades. The use of soil water content in situ as the sole criterion for sites suitable for pine reforestation was tested and found to be a relatively uncertain parameter. The thesis identified new potential soil variables, which should be tested using other data in the future.

Quality Assessment of a Forest Inventory Based on Airborne Laser Scanning

In this study, a quality assessment method based on sampling of primary laser inventory units (microsegments) was analysed. The accuracy of a laser inventory carried out in Kuhmo was analysed as a case study. Field sample plots were measured on the sampled microsegments in the Kuhmo inventory area. Two main questions were considered. Did the ALS based inventory meet the accuracy requirements set for the provider and how should a reliable, cost-efficient and independent quality assessment be undertaken. The agreement between control measurement and ALS based inventory was analysed in four ways: 1) The root mean squared errors (RMSEs) and bias were calculated. 2) Scatter plots with 95% confidence intervals were plotted and the placing of identity lines was checked. 3) Bland-Altman plots were drawn so that the mean difference of attributes between the control method and ALS-method was calculated and plotted against average value of attributes. 4) The tolerance limits were defined and combined with Bland-Altman plots. The RMSE values were compared to a reference study from which the accuracy requirements had been set to the service provider. The accuracy requirements in Kuhmo were achieved, however comparison of RMSE values proved to be difficult. Field control measurements are costly and time-consuming, but they are considered to be robust. However, control measurements might include errors, which are difficult to take into account. Using the Bland-Altman plots none of the compared methods are considered to be completely exact, so this offers a fair way to interpret results of assessment. The tolerance limits to be set on order combined with Bland-Altman plots were suggested to be taken in practise. In addition, bias should be calculated for total area. Some other approaches for quality control were briefly examined. No method was found to fulfil all the required demands of statistical reliability, cost-efficiency, time efficiency, simplicity and speed of implementation. Some benefits and shortcomings of the studied methods were discussed.

Diversity and abundance of fungivorous thrips (Thysanoptera) associated with leaf-litter and bark across forest types and two tree genera in subtropical Australia

Leaf-litter thrips were much more common and diverse in dry sclerophyll forest than in wetter forest types in subtropical southeast Queensland, Australia. In dry sclerophyll forest, the species composition of thrips in leaf-litter was strongly differentiated from the thrips fauna associated with bark of the trees Eucalyptus major and Acacia melanoxylon (4 of 34 species in common). The species composition of bark-dwelling thrips was similar across the two tree species and also across two eucalypts with different bark types, Eucalyptus major (flaky) and Eucalyptus siderophloia (rough). The diversity of thrips from the leaf-litter was not differentiated across all of these tree species. Virtually all thrips collected were Phlaeothripidae, subfamilies Idolothripinae and Phlaeothripinae. Idolothripinae were associated almost exclusively with leaf-litter, but Phlaeothripinae were in leaf-litter and bark. The association of fungal-feeding thrips with dry sclerophyll forest raises questions about their ecological requirements and the role they play in nutrient cycling. © 2012 Copyright Taylor and Francis Group, LLC.

The effect of long-term repeated burning and fire exclusion on above- and below-ground Blackbutt (Eucalyptus pilularis) forest vegetation assemblages

We used a long-term fire experiment in south-east Queensland, Australia, to determine the effects of frequent prescribed burning and fire exclusion on understorey vegetation (<7.5 m) richness and density in Eucalyptus pilularis forest. Our study provided a point in time assessment of the standing vegetation and soil-stored vegetation at two experimental sites with treatments of biennial burning, quadrennial burning since 19711972 and no burning since 1969. Vegetation composition, density and richness of certain plant groups in the standing and soil-stored vegetation were influenced by fire treatments. The density of resprouting plants <3 m in height was higher in the biennially burnt treatment than in the unburnt treatment, but resprouters 37.5 m in height were absent from the biennial burning treatment. Obligate seeder richness and density in the standing vegetation was not significantly influenced by the fire treatments, but richness of this plant group in the seed bank was higher in the quadrennial treatment at one site and in the long unburnt treatment at the other site. Long unburnt treatments had an understorey of rainforest species, while biennial burning at one site and quadrennial burning at the other site were associated with greater standing grass density relative to the unburnt treatment. This difference in vegetation composition due to fire regime potentially influences the flammability of the standing understorey vegetation. Significant interactions between fire regime and site, apparent in the standing and soil-stored vegetation, demonstrate the high degree of natural variability in vegetation community responses to fire regimes.

Resilience of a eucalypt forest woody understorey to long-term (34–55 years) repeated burning in subtropical Australia

We investigated the effects of annual burning since 1952, triennial burning since 1973, fire exclusion since 1946 and infrequent wildfire (one fire in 61 years) on woody understorey vegetation in a dry sclerophyll eucalypt forest, south-eastern Queensland, Australia. We determined the influence of these treatments, and other site variables (rainfall, understorey density, topsoil C : N ratio, tree basal area, distance to watercourse and burn coverage) on plant taxa density, richness and composition. The richness of woody understorey taxa 0–1 m in height was not affected by burning treatments, but richness of woody plants 1–7.5 m in height was lower in the annually burnt treatment than in the triennially burnt treatment from 1989 to 2007. Fire frequency and other site variables explained 34% of the variation in taxa composition (three taxon groups and 10 species), of which 33% of the explained variance was explained by fire treatment and 46% was explained by other site variables. Annual burning between 1974 and 1993 was associated with lower understorey densities mainly due to reduced densities of eucalypts 1–7.5 m in height. Triennial burning during the same period was associated with higher densities of eucalypts 0–7.5 m in height relative to the annually burnt and unburnt treatments. Most woody taxa persisted in the frequently burnt treatments through resprouting mechanisms (e.g. lignotuberous regeneration), and fire patchiness associated with low-intensity burning was also found to be important. Persistence of plants <1 m tall demonstrates the resilience of woody taxa to repeated burning in this ecosystem, although they mainly exist in a suppressed growth state under annual burning.

Effect of rodents on seed fate of five hornbill-dispersed tree species in a tropical forest in north-east India

Hornbills are important dispersers of a wide range of tree species. Many of these species bear fruits with large, lipid-rich seeds that could attract terrestrial rodents. Rodents have multiple effects on seed fates, many of which remain poorly understood in the Palaeotropics. The role of terrestrial rodents was investigated by tracking seed fate of five horn bill-dispersed tree species in a tropical forest in north-cast India. Seeds were marked inside and outside of exclosures below 6-12 parent fruiting trees (undispersed seed rain) and six hornbill nest trees (a post-dispersal site). Rodent visitors and seed removal ere monitored using camera traps. Our findings suggest that several rodent species. especially two species of porcupine were major on-site seed predators. Scatter-hoarding was rare (1.4%). Seeds at hornbill nest trees had lower survival compared with parent fruiting trees, indicating that clumped dispersal by hornbills may not necessarily improve seed survival. Seed survival in the presence and absence of rodents varied with tree species. Some species (e.g. Polyalthia simiarum) showed no difference, others (e.g. Dysoxylum binectariferum) experienced up to a 64%. decrease in survival in the presence of rodents. The differing magnitude of seed predation by rodents can have significant consequences at the seed establishment stage.

Responses of soil microbial communities to clonal variation of Norway spruce

In boreal forests, microorganisms have a pivotal role in nutrient and water supply of trees as well as in litter decomposition and nutrient cycling. This reinforces the link between above-ground and below-ground communities in the context of sustainable productivity of forest ecosystems. In northern boreal forests, the diversity of microbes associated with the trees is high compared to the number of distinct tree species. In this thesis, the aim was to study whether conspecific tree individuals harbour different soil microbes and whether the growth of the trees and the community structure of the associated microbes are connected. The study was performed in a clonal field trial of Norway spruce, which was established in a randomized block design in a clear-cut area. Since out-planting in 1994, the spruce clones showed two-fold growth differences. The fast-growing spruce clones were associated with a more diverse community of ectomycorrhizal fungi than the slow-growing spruce clones. These growth performance groups also differed with respect to other aspects of the associated soil microorganisms: the species composition of ectomycorrhizal fungi, in the amount of extraradical fungal mycelium, in the structure of bacterial community associated with the mycelium, and in the structure of microbial community in the organic layer. The communities of fungi colonizing needle litter of the spruce clones in the field did not differ and the loss of litter mass after two-years decomposition was equal. In vitro, needles of the slow-growing spruce clones were colonized by a more diverse community of endophytic fungi that were shown to be significant needle decomposers. This study showed a relationship between the growth of Norway spruce clones and the community structure of the associated soil microbes. Spatial heterogeneity in soil microbial community was connected with intraspecific variation of trees. The latter may therefore influence soil biodiversity in monospecific forests.

Long-term repeated burning reduces Lantana camara regeneration in a dry eucalypt forest

Previous short-term studies predict that the use of fire to manage lantana (Lantana camara) may promote its abundance. We tested this prediction by examining long-term recruitment patterns of lantana in a dry eucalypt forest in Australia from 1959 to 2007 in three fire frequency treatments: repeated annual burning, repeated triennial burning and long unburnt. The dataset was divided into two periods (1959–1972, 1974–2007) due to logging that occurred at the study site between 1972 and 1974 and the establishment of the triennial burn treatment in 1973. Our results showed that repeated burning decreased lantana regeneration under an annual burn regime in the pre- and post-logging periods and maintained low levels of regeneration in the triennial burn compartment during the post-logging period. In the absence of fire, lantana recruitment exhibited a dome-shaped response over time, with the total population peaking in 1982 before declining to 2007. In addition to fire regime, soil pH and carbon to nitrogen ratio, the density of taller conspecifics and the interaction between rainfall and fire regime were found to influence lantana regeneration change over time. The results suggest that the reported positive association between fire disturbance and abundance of lantana does not hold for all forest types and that fire should be considered as part of an integrated weed management strategy for lantana in more fire-tolerant ecosystems.

Jewish Planted Forest

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