Projections Of Future Dynamics Research Articles

Parameter uncertainty dominates C-cycle forecast errors over most of Brazil for the 21st century

Abstract. Identification of terrestrial carbon (C) sources and sinks is critical for understanding the Earth system as well as mitigating and adapting to climate change resulting from greenhouse gas emissions. Predicting whether a given location will act as a C source or sink using terrestrial ecosystem models (TEMs) is challenging due to net flux being the difference between far larger, spatially and temporally variable fluxes with large uncertainties. Uncertainty in projections of future dynamics, critical for policy evaluation, has been determined using multi-TEM intercomparisons, for various emissions scenarios. This approach quantifies structural and forcing errors. However, the role of parameter error within models has not been determined. TEMs typically have defined parameters for specific plant functional types generated from the literature. To ascertain the importance of parameter error in forecasts, we present a Bayesian analysis that uses data on historical and current C cycling for Brazil to parameterise five TEMs of varied complexity with a retrieval of model error covariance at 1∘ spatial resolution. After evaluation against data from 2001–2017, the parameterised models are simulated to 2100 under four climate change scenarios spanning the likely range of climate projections. Using multiple models, each with per pixel parameter ensembles, we partition forecast uncertainties. Parameter uncertainty dominates across most of Brazil when simulating future stock changes in biomass C and dead organic matter (DOM). Uncertainty of simulated biomass change is most strongly correlated with net primary productivity allocation to wood (NPPwood) and mean residence time of wood (MRTwood). Uncertainty of simulated DOM change is most strongly correlated with MRTsoil and NPPwood. Due to the coupling between these variables and C stock dynamics being bi-directional, we argue that using repeat estimates of woody biomass will provide a valuable constraint needed to refine predictions of the future carbon cycle. Finally, evaluation of our multi-model analysis shows that wood litter contributes substantially to fire emissions, necessitating a greater understanding of wood litter C cycling than is typically considered in large-scale TEMs.

Intense grazing of calcareous grasslands has negative consequences for the threatened marsh fritillary butterfly

Grazing generally benefits grassland biodiversity as it prevents shrub and tree succession. However, too intense grazing may have negative effects for example many grassland insects. EU-subsidies for grazing of some habitats, aimed at promoting biodiversity, still require a relatively intense grazing, and could therefore have negative consequences for some species. We quantified how such grazing affects habitat quality for the marsh fritillary butterfly, and how this influence its colonization-extinction dynamics and persistence. Specifically, we studied a metapopulation on Gotland (Sweden), where the marsh fritillary occupies unfertilized calcareous grassland with a naturally slow succession. We quantified the difference in larvae autumn nests between grazed and ungrazed habitat, and used this difference to adjust the ‘effective area’ of 256 habitat patches in a 50km2 landscape. We then parameterized a metapopulation model based on the occurrence pattern of the adult butterfly, and simulated future population development under different grazing regimes. The results showed that ungrazed habitat harbored 4.8 times more nests than grazed habitat. Reducing the ‘effective area’ of grazed patches accordingly increased the local extinction probability and decreased colonization. Grazing all suitable habitat reduced the occupancy by over 80%, while no grazing increased the occupancy by up to 40%, based on projections of future dynamics. Current grazing is clearly too intense, and EU-subsidies are here, thus, a conservation measure with negative consequences for a threatened butterfly. To prevent this, subsidies for grazing need to be more flexible and better adapted to the prevailing soil conditions and requirements of the target species.

Development of secondary woodland decreases epiphyte metapopulation sizes in wooded grasslands

Abandoned management of wooded grasslands leads to development of secondary woodland. We investigated how this development affects the colonization–extinction dynamics and persistence of epiphytic lichens associated with old trees. We modelled colonization probability based on observed colonizations (turnover data) during four years of two old-oak-associated lichens on 1236 oaks. Persistence was assessed by projections of future dynamics. We also used the turnover models to validate models fitted to snapshot data (from one point in time). Epiphyte colonization probabilities were lower on trees in closed than in open conditions, and the probabilities increased with increasing connectivity to surrounding occupied trees. The additional four study species had too few colonizations to be modelled, and thus, very low colonization rates. Local extinctions occurred only deterministically through patch destruction processes. In projections of future metapopulation dynamics, when assuming that all trees were in closed conditions, the metapopulations decreased slowly; new equilibria had not been reached after 200years. In contrast, when assuming open conditions for all trees, to test for effects of clearing vegetation around oaks in closed conditions, the metapopulations increased comparatively fast. The turnover models and the snapshot models, gave similar projections of metapopulation sizes, when assuming that the present level of secondary woodland remained constant over time. Development of secondary woodland in wooded grassland has negative impacts on epiphyte metapopulations. However, the slow metapopulation declines suggest that restoration will be successful. High priority should be given to resumed grazing and clearing vegetation around old trees, in particular close to dispersal sources.