Models of individual tree mortality for trembling aspen, lodgepole pine, hybrid spruce and subalpine fir in northwestern British Columbia

Density dependent mortality is an important process in forest succession. The overall predictive abilities of forest simulation models are closely related to their ability to predict mortality. Finding appropriate methods for modelling mortality have often proved to be a difficult challenge. The objective of this study was to test a method on adult trees, which was previously used for modelling density dependent mortality for saplings with good results. In the basic model mortality is predicted as a function of recent diameter growth. It was also tested if incorporating tree size into the mortality model improved it. Models were developed for four species: trembling aspen (Populus tremuloides Michx.), lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia), hybrid spruce (a complex of white spruce (Picea glauca (Moench) Voss) and Engelmann spruce (Picea engelmanii Parry ex Engelm.)) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.). The models were parameterized from field data using a maximum-likelihood method. Field data was gathered from 16 stands in the Sub-Boreal Spruce Zone in northwestern British Columbia and comprised of 337 live and 345 recently dead trees in total. The mortality models were tested by incorporating them into the individual tree, spatially explicit forest simulation model SORTIE-ND. SORTIE-ND simulations of single species even-aged stands were compared to simulations of a commonly used stand level simulation model. Furthermore, SORTIE-ND simulations of permanent sample plots in mixed species uneven-aged stands were compared to remeasurements of the plots. It was determined that incorporating tree size into the mortality models gave better fits to the field data. Tolerance to low growth decreases to a minimum at intermediate trees size for all species except for subalpine fir, where it decreases and remains low as trees growth larger. This is probably an effect of the ontogenetic characteristics of the individual species. Testing the mortality models in SORTIE-ND showed that they contribute to realistic thinning patterns in simulations of both pure even-aged stands and complex stands. However, it was evident that the performance of the mortality models is highly dependent on the underlying growth models as well as mortality models accounting for random mortality. Discrepancies in modelling results were linked to over- and underestimation of growth or inappropriate random mortality rates. Overall the tested method provides a straight forwards approach to parameterizing growth based mortality models from field data which is relatively easy to obtain.Naturlig avgång på grund av trängsel är en viktig process för den skogliga successionen. Generellt är förmågan hos modeller för skogssimulering att göra exakta prognoser nära relaterad till hur väl de hanterar självgallring. Att hitta en lämplig metod för att modellera självgallring har ofta visat sig vara en svår utmaning. Syftet med detta examensarbete var att testa en metod på vuxna träd (DBH > 5cm) som tidigare har använts för att modellera självgallring hos plantor med gott resultat. Basmodellen skattar sannolikheten för att ett enskilt träd ska dö på grund av självgallring som en funktion av de senaste årens diametertillväxt. Dessutom testades om självgallringsmodellerna potentiellt förbättrades genom att inkludera trädstorleken som oberoende variabel. Det utvecklades självgallringsmodeller för fyra olika trädslag: asp (Populus tremuloides Michx.), contortatall (Pinus contorta Dougl. ex Loud. var. latifolia), hybridgran (hybrider mellan vitgran (Picea glauca (Moench) Voss) och Engelmann-gran (Picea engelmanii Parry ex Engelm.)) och klippgran (Abies lasiocarpa (Hook.) Nutt.). Modellernas parametrar skattades med en maximum-likelihood metod från fältdata. Data insamlades i 16 bestånd i den sub-boreala gran zon i nordvästra British Columbia och består av totalt 337 levande och 345 nyligen döda träd. Självgallringsmodellerna testades i SORTIE-ND, en trädvis och avståndsberoende skogsproduktionsmodell. SORTIE-ND simuleringar av rena likåldriga bestånd jämfördes med simuleringar gjorda med en ofta använd beståndsbaserad skogsproduktionsmodell. Dessutom jämfördes SORTIE-ND simuleringar för permanenta provytor i olikåldriga blandbestånd med uppmätt utveckling på dessa provytor. Genom att inkludera individuell trädstorlek i basmodellen uppnåddes bättre anpassning till fältdata. Avgångsrisken vid låg tillväxt var minst för medelstora träd för alla trädslag förutom klippgran. För detta trädslag minskar avgångsrisken vid låg tillväxt kontinuerligt med ökad trädstorlek. Detta är en konsekvens av de enskilda trädslagens karakteristika. Självgallringsmodellerna bidrog till realistisk avgång i båda likåldriga och komplexa bestånd. Det är dock uppenbart att självgallringsmodellerna är väldigt beroende av de underliggande tillväxtmodellerna och modeller som uppskattar den stokastiska avgången i ett bestånd. Modellernas avvikelser är relaterade till över- eller underskattning av tillväxten och orealistiska nivåer på den stokastiska avgången. Den testade metoden är ett relativt enkelt sätt att härleda och estimera parametra till en tillväxtbaserad självgallringsmodell från fältdata. Dessutom är data relativt enkla att erhålla

Diabetic retinopathy as a potential marker of Parkinson's disease:a register-based cohort study

Neurodegeneration is an early event in the pathogenesis of diabetic retinopathy, and an association between diabetic retinopathy and Parkinson’s disease has been proposed. In this nationwide register-based cohort study, we investigated the prevalence and incidence of Parkinson’s disease among patients screened for diabetic retinopathy in a Danish population-based cohort. Cases (n = 173 568) above 50 years of age with diabetes included in the Danish Registry of Diabetic Retinopathy between 2013 and 2018 were matched 1:5 by gender and birth year with a control population without diabetes (n = 843 781). At index date, the prevalence of Parkinson’s disease was compared between cases and controls. To assess the longitudinal relationship between diabetic retinopathy and Parkinson’s disease, a multivariable Cox proportional hazard model was estimated. The prevalence of Parkinson’s disease was 0.28% and 0.44% among cases and controls, respectively. While diabetic retinopathy was not associated with present (adjusted odds ratio 0.93, 95% confidence interval 0.72–1.21) or incident Parkinson’s disease (adjusted hazard ratio 0.77, 95% confidence interval 0.56–1.05), cases with diabetes were in general less likely to have or to develop Parkinson’s disease compared to controls without diabetes (adjusted odds ratio 0.79, 95% confidence interval 0.71–0.87 and adjusted hazard ratio 0.88, 95% confidence interval 0.78–1.00). In a national cohort of more than 1 million persons, patients with diabetes were 21% and 12% were less likely to have prevalent and develop incident Parkinson’s disease, respectively, compared to an age- and gender-matched control population without diabetes. We found no indication for diabetic retinopathy as an independent risk factor for incident Parkinson’s disease

Replication of newly proposed TNM staging system for medullary thyroid carcinoma:a nationwide study

A recent study proposed new TNM groupings for better survival discrimination among stage groups for medullary thyroid carcinoma (MTC) and validated these groupings in a population-based cohort in the United States. However, it is unknown how well the groupings perform in populations outside the United States. Consequently, we conducted the first population-based study aiming to evaluate if the recently proposed TNM groupings provide better survival discrimination than the current American Joint Committee on Cancer (AJCC) TNM staging system (seventh and eighth edition) in a nationwide MTC cohort outside the United States. This retrospective cohort study included 191 patients identified from the nationwide Danish MTC cohort between 1997 and 2014. In multivariate analysis, hazard ratios for overall survival under the current AJCC TNM staging system vs the proposed TNM groupings with stage I as reference were 1.32 (95% CI: 0.38–4.57) vs 3.04 (95% CI: 1.38–6.67) for stage II, 2.06 (95% CI: 0.45–9.39) vs 3.59 (95% CI: 1.61–8.03) for stage III and 5.87 (95% CI: 2.02–17.01) vs 59.26 (20.53–171.02) for stage IV. The newly proposed TNM groupings appear to provide better survival discrimination in the nationwide Danish MTC cohort than the current AJCC TNM staging. Adaption of the proposed TNM groupings by the current AJCC TNM staging system may potentially improve accurateness in survival discrimination. However, before such an adaption further population-based studies securing external validity are needed

Incidence and prevalence of sporadic and hereditary MTC in Denmark 1960–2014: a nationwide study

Recent studies have shown a significant increase in the temporal trend of medullary thyroid carcinoma (MTC) incidence. However, it remains unknown to which extent sporadic medullary thyroid carcinoma (SMTC) and hereditary MTC (HMTC) affect the MTC incidence over time. We conducted a nationwide retrospective study using previously described RET and MTC cohorts combined with review of medical records, pedigree comparison and relevant nationwide registries. The study included 474 MTC patients diagnosed in Denmark between 1960 and 2014. In the nationwide period from 1997 to 2014, we recorded a mean age-standardized incidence of all MTC, SMTC and HMTC of 0.19, 0.13 and 0.06 per 100,000 per year, respectively. The average annual percentage change in incidence for all MTC, SMTC and HMTC were 1.0 (P = 0.542), 2.8 (P = 0.125) and −3.1 (P = 0.324), respectively. The corresponding figures for point prevalence at January 1, 2015 were 3.8, 2.5 and 1.3 per 100,000, respectively. The average annual percentage change in prevalence from 1998 to 2015 for all MTC, SMTC and HMTC was 2.8 (P < 0.001), 3.8 (P < 0.001) and 1.5 (P = 0.010), respectively. We found no significant change in the incidence of all MTC, SMTC and HMTC possibly due to our small sample size. However, due to an increasing trend in the incidence of all MTC and opposing trends of SMTC (increasing) and HMTC (decreasing) incidence, it seems plausible that an increase for all MTC seen by others may be driven by the SMTC group rather than the HMTC group