Dendrocronologia de Hovenia dulcis, exótica e invasora nas florestas subtropicais brasileiras.

Abstract

Hovenia dulcis Thunberg (Rhamnaceae) is a tree species from Asia invading forest formations in south Brazil, where it competes with native tree species in early succession areas and forest canopy gaps. The blueberry-japan shades its leaves in winter, indicating a seasonal phenological behavior that would be related to the formation of wood growth rings. This anatomical xylem structures mark seasonal cambium activity cycles, thus informing about tree age and annual growth. The formation of annual rings in H. dulcis would allow the development of dendroecological studies, relevant to understand and manage its invasion process. This study investigates long-term growth patterns of H. dulcis and relationships to regional climate through tree-ring analyses. The study was carried our in three riparian forests within the Dos Sinos river catchment (29˚40”30’S; 50˚70”20’W), between 64 and 274 m asl. Fourty nine trees were cored with an increment borer to obtain transversal trunk wood samples for tree ring analysis. The wood cores were surfaced, measured, cross-dated and detrended to obtain a annual growth index time series per tree. Regional temperature and precipitation series were obtained from modeled grid data-set. Growth patterns among trees and relationships with climate were explored through ordination, correlation and regression analyses. Trees from different riparian forests showed a similar growth pattern, indicative of a regional growth signal. The regional signal strength variation among trees did not varied in function of age but was directly related to tree size controlling age, indicating fast growing trees were more sensitive to such regional signal, probably because slow growing trees would be more influenced to site factors. The regional mean growth series was positively related to precipitation during current spring and summer and to temperature of previous autumn. It means H. dulcis growth is sensitive to low water availability during the vegetation period and cold temperature in autumn restricts the duration of growth activity, reducing growth in the next season.