Influência da massa de semente e da fertilidade do solo no desempenho de espécies arbóreas em restauração de área ripária

Abstract

Riparian zones have been widely altered by deforestation and fragmentation in the last five decades, often being required human intervention for the recovery of these areas through the introduction of tree species. Direct seeding can be an alternative to the introduction of seedlings, being simpler and cheaper to implement. This study sought to understand the influence of seed mass on emergence and of seed mass, average time of emergence, initial height and soil fertility on the performance of nine tree species, reintroduced through direct seeding in the restoration of a degraded riparian area. The experiment was divided in four time intervals (1 – from seeding to 114 days (beginning of first dry season), 2 – 114 to 377 days (beginning of the second year), 3 – 377 to 728 days (beginning of the third year) and 4 – 728 to 1125 days (ending of the third year). We evaluated the influence of seed mass on emergence (in both field and nursery experiments), on survival after three years and on height after three years. The influences of seed mass, average time of emergence and soil fertility on survival and on height were simultaneously evaluated for the first interval, using a structural model. For the three following intervals, structural models were assembled, simultaneously evaluating the influence of seed mass, initial height and soil fertility on survival and on relative growth rate. Larger seeded species had higher emergence rates in relation to the smaller seed species, both in the nursery and in the field, with the highest rates detected in the nursery. Seed mass positively influenced the probability of survival after three years, with most mortality occurring in the first 114 days for all species. Structural model analyses revealed that seed mass influenced survival directly in the first 114 days, and indirectly through initial height in the later periods. Larger seeds generated larger seedlings, which tended to survive longer in relation to smaller seedlings. Soil fertility influenced survival only indirectly, through initial height. Larger seed species exhibited greater initial size, but after three years this difference was not detected, indicating higher growth rates of smaller seed species. Seed mass strongly influenced height in the first 114 days, but in later periods seed mass influenced growth rates only through initial height. In the second and third years, soil fertility indirectly influenced growth rates, through initial height. The relationship between seed mass and survival found for these nine species after three years is probably due to a combination of the effects of cotyledon reserves and seedling size, with larger seeds emerging earlier and originating bigger seedlings, which survive better due to their larger initial size. This study showed that direct seeding could be a viable alternative in the recovery of pasture areas for the nine species evaluated.