Den här avhandlingen belyser hur avverkning och markberedning påverkar markfloran i den svenska barrskogen. Dessutom utvärderas två inventeringsmetoder som används inom växtekologin. Vid arbetet har både rikstäckande inventeringsdata och fältförsök använts och de likartade resultaten tyder på att rikstäckande inventeringar är en underutnyttjad resurs i forskningen. Ju större andel av träden som avverkas desto större blir förändringen av markflorans sammansättning. Vissa arter, som lingon, ljung, etc., verkar dock inte påverkas i nämnvärd omfattning, medan andra, som blåbär, minskar i relation till hur mycket som avverkats. Gräs och mjölkört ökar efter avverkning, dock visar sig vissa gräs och mjölkört inte reagera om inte avverkningen överskrider ett tröskelvärde på ca 80 %. Avverkning har en liten, men signifikant, effekt på antalet arter, medan artomsättning, d.v.s. arters etablering på och/eller försvinnande från provytorna, framförallt påverkas av andel gran innan avverkning, markens produktionsförmåga och först därefter av hur stor andel av träden som avverkas. Det var också uppenbart att markberedning har en stark effekt som skiljer sig från avverkning. Framförallt gynnas björnmossor av markberedning men även vårfryle, kruståtel och mjölkört. Arter som missgynnas av markberedning var bl.a., en levermossa, lingon, väggmossa och kråkbär. I växtekologi är visuell täckningsbedömning, d.v.s. hur stor del av en provyta som täcks av en växtart, och registrering av förekomst/icke förekomst, d.v.s. finns en växtart på en provyta eller inte, de två vanligaste metoderna vid vegetationsinventering. Vid registrering av förekomst/icke förekomst missas upp till en tredjedel av förekomsterna, vanligaste orsaken till missade registreringar verkar vara att man inte upptäcker arten snarare än att den inte kan identifieras. Det var stora variationer mellan arter, där arter med få exemplar på provytan missas oftare. Både den visuella täckningsbedömningen och förekomst/icke förekomst visar sig ha personberoende fel, d.v.s. att olika personer genomgående ger högre eller lägre värden än andra. Trots det personberoende felet visar sig täckningsbedömningar ha ett större informationsvärde än registrering av förekomst/icke förekomst när det gäller att särskilja olika typer av vegetation. Erfarenhet har en förvånansvärt liten effekt på kvaliteten av täckningsbedömningar. / This thesis has two main focuses; first, the response of forest ground layer flora on forestry, mainly harvesting and secondly, the quality of the vegetation assessment methods, cover estimates by eye and presence/absence data. The effect of harvesting intensity was evaluated with survey data from permanent plots as well as vegetation data from a field trial fourteen years after harvesting. Both data sets confirmed that response of ground layer flora increased with increasing logging intensity. Thereby, indicating that survey data is possible to use in research. From the survey data set, existence of a time lag was evident for several species and also a threshold level was evident in cutting intensity needed to affect a number of species. Logging had a modest, but significant positive effect on the change in species number per plot. Species turnover was influenced by the proportion of Picea abies in the tree canopy; site productivity; and logging intensity. In the field trial scarification had a strong effect that was different from the one created by cutting. In plant ecology cover estimate by eye and presence/absence recording are the two most frequent methods used. The methods were evaluated with survey data and a field trial. In the first data set vegetation was recorded independently by two observers in 342 permanent 100-m2 plots. Overall, one third of each occurrence was missed by one of the two observers, but with large differences among species. Species occurring at low abundance tended to be frequently overlooked. Observer-explained variance in cover estimates was <10% in 15 of 17 species. In the second data set, 10 observers independently estimated cover in sixteen 100-m2 plots in two different vegetation types. The bias connected to observer varied substantially between species. The estimates of missing field and bottom layer had the highest bias, indicating that missing layers are problematic to use in analysis of change. Experience had a surprisingly small impact on the bias connected to observer. Analyses revealed that for the statistical power, cover estimates by eye carries a higher information value than do presence/absence data when distinguishing between vegetation types, differences between observers is negligible, and using more than one observer had little effect.

Segundo a Teoria da Transição Florestal, países menos desenvolvidos teriam altas taxas de desmatamento, pois a economia destes países é baseada no desenvolvimento e expansão agrícola. Com o avanço do desenvolvimento econômico a industrialização, urbanização e a modernização do uso da terra levariam ao abandono de terras menos adequadas à agricultura que seriam ativamente reflorestadas ou regenerariam. Visto que São Paulo vem apresentando ganhos de cobertura florestal nativa, este estudo teve como objetivo principal identificar os fatores relacionados ao processo de transição florestal no estado de São Paulo entre 1960 e 2006. Para isso, o Capítulo 1 avaliou as discrepâncias entre três estimativas de cobertura florestal nativa disponíveis para o estado de São Paulo (censo agropecuário e dois mapeamentos com resolução de 10m e 30m), em escala municipal, e as possíveis fontes de viés associadas aos métodos de coleta. O Capítulo 2 identificou os fatores socioeconômicos e biofísicos associados ao desmatamento e à recuperação das florestas nativas nos municípios do estado de São Paulo em quatro períodos consecutivos (1960-1970, 1970-1980, 1980-1996, 1996-2006). Os resultados do Capítulo 1mostraram que o censo agropecuário subestima a cobertura florestal quando há áreas protegidas nos municípios. Mapas com resolução de 30m também subestimam a cobertura florestal nativa em relação aos mapas com 10m de resolução, visto que não detectam pequenos fragmentos. As três fontes de dados são congruentes, porém os vieses relacionados aos métodos podem refletir nos resultados. Logo, a escolha dos dados deve ser feita de acordo com os objetivos do estudo a ser desenvolvido e considerando os métodos de coleta e possíveis fontes de viés de cada conjunto de dados. O Capítulo 2 mostrou que as perdas de florestas ocorreram principalmente em municípios com solos mais úmidos e/ou naqueles em que houve expansão de cultivos. Enquanto ganhos de florestas ocorreram principalmente em municípios com maior cobertura florestal, maior declividade média, que empregaram maior número de trabalhadores permanentes e usaram mais fertilizantes. Estes resultados mostram que, entre 1960 e 2006, a expansão do uso da terra levou a perdas de florestas em áreas mais adequadas à agricultura de São Paulo. Com o tempo, porém, fatores que aumentam a produtividade ou reduzem a conversão de áreas naturais levaram ao aumento de florestas, principalmente em terras menos adequadas à agricultura. Tais fatores, no entanto, foram influenciados por políticas governamentais para modernização da agricultura e proteção dos ecossistemas naturais, e pela pressão do mercado externo por certificação ambiental. Estes resultados enfatizam a necessidade de se considerar, em conjunto, desenvolvimento da agricultura e conservação do meio ambiente para o desenvolvimento de políticas de uso da terra mais eficientes / According to Forest Transition Theory, less developed countries or regions present high rates of deforestation because their economy is based on agricultural development and agriculture expansion. As the economy develops industrialization, urbanization and agriculture modernization lead to the abandonment of lands less suitable for agriculture which are reforested or regenerate spontaneously. Since forest cover of São Paulo has increased, this study aimed to identify the socioeconomic and biophysical factors related to forest transition in the state of São Paulo between 1960 and 2006. For this purpose, Chapter 1 evaluate the discrepancies among three free datasets of São Paulo\'s forest cover (agricultural census, maps at 10m and 30m resolution), in municipality-scale, and the possible sources of bias. Chapter 2 identified the factors related to deforestation and forest gains in São Paulo\'s municipalities during four consecutive intervals (1960-1970, 1970-1980, 1980-1996, 1996-2006). Chapter 1 showed that census underestimate forest cover when legally protected areas are present, reflecting the limitation of survey methods in rural properties. Maps at 30m resolution also underestimate forest cover in comparison to maps at 10m resolution, since 30m resolution cannot detect small and narrow patches. The three datasets are congruent, but the results indicate that bias related to methods can affect analysis results. Therefore, users should choose a dataset according to aims of the study and considering the sources of bias in the data. Chapter 2 showed that forest losses were greater in municipalities with moist soils and large tracts of agricultural lands, while forest gains were higher in municipalities with high forest cover and steep slopes, and that employed a large number of permanent workers and relied on high fertilizer input. Between 1960 and 2006, land use expansion led to forest losses in more suitable areas for agriculture in São Paulo. Over time, factors that increase productivity or reduce pressure on land development led to forest gains mainly in less suitable lands. These proximate factors, however, were driven by underlying factors as governmental policies to modernize agriculture and protect natural ecosystems, and by external market demands for environmental certification. These results highlight the need to jointly consider agricultural development and environmental conservation policies for the development of effective land use policies