Browsing by Subject "allometry"

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  • Vuorinne, Ilja (Helsingin yliopisto, 2020)
    Biomass is an important parameter for crop monitoring and management, as well as for assessing carbon cycle. In the field, allometric models can be used for non-destructive biomass assessment, whereas remote sensing is a convenient method for upscaling the biomass estimations over large areas. This study assessed the dry leaf biomass of Agave sisalana (sisal), a perennial crop whose leaves are grown for fibre and biofuel production in tropical and subtropical regions. First, an allometric model was developed for predicting the leaf biomass. Then, Sentinel-2 multispectral satellite imagery was used to model the leaf biomass at 8851 ha plantation in South-Eastern Kenya. For the allometric model 38 leaves were sampled and measured. Plant height and leaf maximum diameter were combined into a volume approximation and the relation to biomass was formalised with linear regression. A strong log-log linear relation was found and leave-one-out cross-validation for the model showed good prediction accuracy (R2 = 0.96, RMSE = 7.69g). The model was used to predict biomass for 58 field plots, which constituted a sample for modelling the biomass with Sentinel-2 data. Generalised additive models were then used to explore how well biomass was explained by various spectral vegetation indices (VIs). The highest performance (D2 = 74%, RMSE = 4.96 Mg/ha) was achieved with VIs based on the red-edge (R740 and R783), near-infrared (R865) and green (R560) spectral bands. Highly heterogeneous growing conditions, mainly variation in the understory vegetation seemed to be the main factor limiting the model performance. The best performing VI (R740/R783) was used to predict the biomass at plantation level. The leaf biomass ranged from 0 to 45.1 Mg/ha, with mean at 9.9 Mg/ha. This research resulted a newly established allometric equation that can be used as an accurate tool for predicting the leaf biomass of sisal. Further research is required to account for other parts of the plant, such as the stem and the roots. The biomass-VI modelling results showed that multispectral data is suitable for assessing sisal leaf biomass over large areas, but the heterogeneity of the understory vegetation limits the model performance. Future research should address this by investigating the background effects of understory and by looking into complementary data sources. The carbon stored in the leaf biomass at the plantation corresponds to that in the woody aboveground biomass of natural bushlands in the area. Future research is needed on soil carbon sequestration and soil and plant carbon fluxes, to fully understand the carbon cycle at sisal plantation.
  • Kaitaniemi, Pekka; Lintunen, Anna (2021)
    In many cases, the traditional ground-based estimates of competition between trees are not directly applicable with modern aerial inventories, due to incompatible measurements. Moreover, many former studies of competition consider extreme stand densities, hence the effect of competition under the density range in managed stands remains less explored. Here we explored the utility of a simple tree height- and distance-based competition index that provides compatibility with data produced by modern inventory methods. The index was used for the prediction of structural tree attributes in three boreal tree species growing in low to moderate densities within mixed stands. In silver birch, allometric models predicting tree diameter, crown height, and branch length all showed improvement when the effect of between-tree competition was included. A similar but non-significant trend was also present in a proxy for branch biomass. In Siberian larch, only the prediction of branch length was affected. In Scots pine, there was no improvement. The results suggest that quantification of competitive interactions based on individual tree heights and locations alone has potential to improve the prediction of tree attributes, although the outcomes can be species-specific.
  • Neiro, Jakke (Helsingin yliopisto, 2019)
    In recent years, the two-spotted field cricket Gryllus bimaculatus has emerged as a central model for studies on insect development, regeneration and physiology. At the moment, G.bimaculatus has the most extensive molecular toolkit within the Exopterygota, making it the foremost model for evolutionary developmental biology and comparative physiology within the field of entomology. However, the postembryonic development of G. bimaculatus has received considerably less attention than embryonic development. In this thesis, I have studied the postembryonic development of G. bimaculatus to better understand the evolution and physiology of the understudied Exopterygota. My thesis encompasses five parts: postembryonic morphology, wing development, appendage regeneration, allometry, and growth. The postembryonic stages, the nymphal stages, have never been properly characterised in G. bimaculatus. By following postembryonic development daily at 30 C, 8 nymphal stages (instars) were identified. Size, coloration, sclerotisation of the thorax, and morphology of the wings, the hind tibia and the ovipositor were useful characters in distinguishing the stages. The Dpp/BMP signalling pathway patterns the wing venation in the endopterygotan insects Drosophila melanogaster and Athaliae rosae, but nothing is virtually known about wing development in exopterygotan insects. The wings and the wing venation pattern in different nymphal stages of G. bimaculatus were studied using the hydrogen peroxide clearing protocol along with both brightfield and fluorescence microscopy, while the role of the Dpp/BMP signalling pathway was studied using immunohistochemistry (IHC), in situ hybridisation (ISH), and RNA interference (RNAi). The longitudinal veins are patterned in the 3rd and 4th nymphal stages, while the secondary veins in the 8th stage. The IHC and ISH experiments displayed only non-specific staining, while the RNAi experiments did not produce any change in the phenotype, possibly because of molecular redundancy. The nymphal legs of G. bimaculatus are known to be highly regenerative, and the Dpp/BMP signalling pathway has been shown to provide positional information in leg regeneration. However, nothing is known about the regeneration of the other appendages in G. bimaculatus. Antennae and cerci were amputated in different nymphal stages, and the degree of final regeneration depended on the nymphal stage. RNAi experiments did not produce any change in the phenotype, possibly because of molecular redundancy. The interrelationship between static, ontogenetic and evolutionary allometry in insects is poorly understood. The allometry of hind femur length with respect to body length has been shown to be negative in Orthoptera (i.e. evolutionary allometry), but nothing is known about corresponding ontogenetic and static allometry. By measuring hind femur length and body length in G. bimaculatus in different nymphal stages, the ontogenetic allometry was determined to be slightly positive or isometric, while the static allometries of different stages tended to be negative but highly variable. This may indicate that allometric relationships constrain development in the microevolutionary perspective, but are nevertheless evolvable in a macroevolutionary perspective of millions of years. The growth conditions and rearing of crickets and other insects have been widely reported, but the shape of the growth curve itself has been less investigated. The exponential, the von Bertalanffy (VBGF), the West, Brown and Enquist (WBE), and the dynamic energy budget (DBE) models have been proposed as continuous models for insect growth. These models were t to growth data from G. bimaculatus and the DBE and was shown to be optimal with parameter values α=0 and pAm = 0.69. The insects have been thought to follow Dyar's law, i.e. that the growth ratio or moulting increment (MI) is constant throughout development, although numerous other competing moulting models have been devised for the crustaceans. By fitting different moulting models to head width data from G. bimaculatus, the log-linear model (Mauchline's model) turned out to explain the MI the best. Lastly, the oxygen-dependent induction of moulting (ODIM) model has been proposed to explain moulting patterns in insects, but the model has never been applied to exopterygotan taxa. By fitting the ODIM model to growth data from G. bimaculatus, the model could predict moulting mass but not instar durations, probably because of high postembryonic plasticity in G. bimaculatus.