Browsing by Subject "community ecology"

In this thesis, I study plant biodiversity and ecosystem functioning in Finnish heath forests. To improve the understanding of how terrestrial understory plant biodiversity affects forest ecosystem functioning, I use structural equation modelling with information from climate and landscape land cover, using study areas along a 800 km latitudinal gradient. In addition, I describe the characteristics of the studied plant communities from taxonomical and functional point of view together with related environmental variables. I conducted a field survey during summer 2022. Study area consisted of five regions, ranging from southern Finland to near Arctic Circle: Tvärminne, Helsinki Metropolitan Area, Evo, Konnevesi and Kuusamo. I sampled and identified terrestrial vascular plants, lichens and bryophytes by coverage from 80 vegetation plots of 1 m2 in each region. In total, data consists of 400 vegetation plots and total amount of species was 134. We measured environmental variables in the field or draw them from remote sensing databases. To model the causal pathways among climate, landscape land cover, forest ecosystem functioning measured as Normalized Difference Vegetation Index (NDVI) and terrestrial understory plant biodiversity, I constructed six structural equation models (SEM) with different combinations of taxonomical biodiversity metrics and landscape land cover variables. Based on previous studies I hypothesized that biodiversity is positively related to ecosystem functioning. Models explained 17 – 21 % of observed variation in ecosystem functioning. The most important explanatory variable was the number of growing degree days and the second most was the taxonomical understory biodiversity. To provide functional summary of the studied plant communities, I categorized plant species according to their functional group as well as Grime’s CSR Triangle Theory’s strategy classes. The three strategy classes places species according to their high or low tolerance to stress and disturbance. Three classes are competitors (C), stress-tolerators (S) and ruderals (R). S-strategy was most common in all areas but variation between regions was observed. This emphasizes the importance of functional and compositional dimensions of biodiversity in addition to taxonomical biodiversity since loss or shift in them can lead to lost or altered ecosystem functioning. There is now a broad scientific consensus that biodiversity influences ecosystem functioning and thus the ongoing biodiversity loss is an existential threat to humanity as we depend on functioning ecosystems and their ability to produce ecosystem services. This study is important since it provides indicative empirical evidence from complex real-world ecosystems that has been limited as most biodiversity-ecosystem functioning (BEF) -studies have been experimental. Biodiversity information data also creates benchmarks for future comparison and latitudinal gradients describe how biodiversity varies across space.

Lake ecosystems are shaped by water chemistry processes that affect the lake environment and the species communities within. Changes in the water chemistry thus have far-reaching consequences. Water colour is one variable that affects water chemistry and stems from humic substances in the water. Dark water reduces light availability and also affects nutrient and oxygen availability. A trend of brownification of freshwater systems has been observed in recent years and it is expected to influence species community’s diversity and composition. The aim of this thesis was to study whether brownification is an ongoing issue in the study lakes and whether it has had a negative effect on phytoplankton diversity and resulted in shifts in the phytoplankton composition. A data set including about a 100 lakes in Finland with measurements from 1965 up until now served as the study system which was analysed with statistical methods. The results indicated a brownification trend in the past decades. The brownification so far had a positive impact on species richness but a negative impact on beta diversity. Brownification also affected species composition. Flagellates and autotrophic species increased in darker waters but mixotrophic species that are known to dominate in dark water colour, did not show a clear increase with water colour. Other hydrological variables than water colour could have had a bigger impact on the phytoplankton community than water colour but future monitoring of the phytoplankton community is recommended to see if water colour will have a negative impact on species diversity in the future.