|The Atlantic rainforest harbour an outstandingly high biodiversirty. Many different environmental factors (climate, soil, geomorphology, ocean and etc) interact in a very large space creating complex ecosystems with high endemism. Altough, its richness, the Altnatic rainforest is highly endangered due to increasing human impact through the intensification of land-use and consequent broad landscape replacement. Many palaecological studies have been developed during the last decades providing important background of diverse location around Atlantic rainforest, however little is known about regional palaeoecological history and landscape dynamics. In this study, we present palynological analyses carried out in a compilation of several pollen records from Alantic rainforest ecosystems and surrounding regions that help to unveil patterns and processes in present and past vegetation change during the Late Quaternary.
A palaeoecological study of 3 time periods (3000 yrs BP, pre-colonization and modern) of 27 pollen records of Atlantic rainforest and associated ecosystems reveals marked vegetation changes as consequence of climate and human impacts during the Late Holocene. The samples concerning the pre-colonization period was used as standard for comparison once it represents the natural vegetation conditions once climate was similar to today and there was no human impact on it. Handling multivariate techniques associated to pollen abundaces threshold, the pre-colonization period was classified into 7 groups. Moreover, it was noticed a clear differentiation between grassland and forested vegetation and between tropical and subtropical vegetation types. The comparison of pre-colonization with the other two time slices revealed that using Poaceae threshold most of sites from 3,000 BP and modern assemblages maintained their classification. Furthermore, combining with other taxa abundance, the number of sites with the same classification became reduced. Using square chord dissimilarity as a quantitative of change indicator, the change prompted by human actions within 500 years of colonization and 3,000 years of natural changes were equivalent. Comparing pre-colonization with surface samples, it is noticed that modern pollen still able to represent important environmental gradients however, their use as modern analogue requires careful treatment.
Oonce fossil pollen are the best indicators to track past vegetation changes, we carried out a parallel analysis of 19 pollen records to unveil the regional vegetation history allowing inferences about synchronoicity. The accumulated probability distributions show potential synchronous vegetation at 8900, 5900, 2800, 1200 and 550 cal yrs BP. The southern sites experienced more cycles of changes than others, mainly during the late Holocene. The main variations on pollen spectra were captured by both PC and rate of change analysis, that well represented the main periods of change. In general, the early Holocene was a stable period, after the mid-Holocene the changes have started and intensified around 2800 cal yrs BP with other pulses later on agreeing with other researches carried out at other regions of South America indicating connections with continental climate patterns associated to South American monsoon.
The application of unconstrained cluster analysis and pollen abundance threshold to 16 pollen samples from southern andsoutheastern Brazil, revealed that although no large temporal pattern is noticed, the used of appropriate technique can give a broad perspective of vegetation type atspecific time. Moreover, the clear differentiation of vegetation among different times was successfully achived revealing the major variation of vegetation between open and forested landscapes.