Patterns and drivers of post-fire vegetation in differently managed Central European Scots pine forests

In recent years, severe wildfires have burned large forest areas in Germany. However, fire ecology research is still underrepresented in Central Europe, but future scenarios predict an increased fire risk. To contribute to closing this knowledge gap, I have studied early post-fire vegetation in two differently burned Scots pine (Pinus sylvestris) forest stands in Brandenburg (NE Germany). First, I studied spatial initial recolonization patterns of post-fire vegetation. I started with post-fire tree regeneration patterns (Chapter 3). I analysed the effects of different post-fire forest management, distance to potential seed sources, fire severity and spatial position on the abundance of the four most frequent naturally regenerated tree species (Populus tremula, Betula pendula, Pinus sylvestris and Salix sp.). I revealed that densities of Pinus sylvestris and Betula pendula are distance limited, while the distance to the next potential seed source showed no effect on Populus tremula and Salix sp. Post-fire forest management was an important predictor of tree regeneration density, but was species specific. With a similar approach, I have studied the effects of post-fire forest management, fire severity and pre-fire land-use legacies on ground vegetation patterns (Chapter 4). On the one hand, I showed, that pre-fire land use legacies can still impact post-fire vegetation, for example by reduced colonization by the seed bank, but enhanced nutrient availability in older forests. On the other hand, soil disturbance by post-fire forest management activated the seed bank, but reduced the cover of bryophytes. Higher fire severity decreased the cover of seed bankers. Next, I focused on temporal patterns. For this, I have studied post-fire vegetation over the first six years after fire in differently managed burned forest sites (Chapter 5). I showed that vegetation on burned sites differed drastically from unburned controls and was characterized by open land species and indicators for nitrogen, reaction and light due to increased nutrient and light availability after the fire. Species composition was already shifting in the first post-fire years, as open land species started to decrease, while forest species increased. The effect of increased nutrient availability after the fire declined immediately, resulting in a decrease of nitrogen and reaction Ellenberg indicator values. Complete salvage logging resulted in slower recolonization and often different patterns. To enable precise estimation of post-fire vegetation biomass in our study area, I have adapted the aboveground allometric biomass estimation approach PhytoCalc for the most important species of Central European post-fire vegetation and extended the models for the estimation of belowground biomass (Chapter 6). For this, I have sampled aboveground and belowground biomass of the most important young tree, herb and grass species and aboveground biomass of dominant bryophyte species in our study area. A comparison with the original model, which was calibrated with samples from undisturbed forests and models calibrated for unburned clear-cuts, revealed that these models estimate post-fire vegetation biomass imprecisely, probably mainly due to increased irradiance and nutrient levels on burned sites, which affect tissue densities. In the last manuscript, I considered the effect of post-fire forest management on multiple components of post-fire ecosystems (Chapter 7). On the one hand, I could show, that intensive management such as complete salvage logging, leads to abiotic more extreme conditions, which resulted in higher microclimatic temperatures, enhanced heat and drought stress in the soil and lower nutrient availability. On the other hand, natural tree regeneration biomass was high on all sites. However, plant and saproxylic beetle diversity such as bryophyte biomass was clearly decreased by intensive management. In my thesis, I provide deep insights into the composition and dynamic of post-fire vegetation in Central European Scots pine forests. I could disentangle several factors, which affect initial spatial recolonization patterns and which are often dependent on the species traits such as the recolonization strategy or Ellenberg indicator values. I revealed that post-fire forest management is one main driver of spatial and temporal vegetation patterns. My thesis gives a comprehensive overview of the different effects of post-fire forest management and provides several management recommendations, which can be valuable for managing burned forests in the future.