Print PageAfforestation is a common land-use change across the Campos grasslands of Uruguay, northeast Argentina, and southern Brazil and Paraguay. In Uruguay alone, 1.5 million ha (9% of the total land base) have been impacted by afforestation, and another 1.8 million ha (10%) will be afforested in the future. Grasslands are planted with monocultures of fast growing woody species that are harvested in < 20 years. Livestock grazing, which was widespread before afforestation, continues in these plantations. We examined how this complex agroforestry management cycle affects vegetation composition and species richness. We focused on eucalyptus plantations and distinguished between five phases of the management cycle: grassland (never planted; long-term grazing), young forest (planted 6 months prior; grazing removed), mid-stage forest (complete canopy development; grazing present), old forest (partial canopy removal from thinning; grazing present), and post-harvest (harvested 6 months prior; grazing present). Three sites were sampled from each phase (n = 15 sites), 5 in the spring and 10 in the autumn. We recorded species presence in 40, 1 m2 plots per site and categorized species life form (graminoid, herb, woody, or fern) and life span (annual or perennial). Sampling season was included as a blocking term in all analyses.
Results/Conclusions
Total species richness (S) was similar between phases. Graminoid S was greatest in grasslands and young forests, and declined significantly in later phases. Fern S was greatest in old forests. Neither herb nor woody S differed among phases. Annual and perennial S did not differ among phases. Community composition within mid-stage forests was significantly different than that in other phases. Although composition differed between seasons, the trend in composition change across the management cycle was similar. Our results indicate that vegetation changes during the agroforestry management cycle, but there seems to be strong potential for post-harvest recovery of the vegetation in terms of species richness and composition. This recovery may be due to the presence of similar species (although in differing abundance) throughout the management cycle and to the fact that afforested areas are interspersed with remnant grassland patches which allow re-colonization of disturbed areas following harvest. Our preliminary research suggests that historically grazed vegetation of Uruguay may not be severely impacted by first rotation afforestation, although further research is needed to fully understand the effects of multiple rotations and of increasing fragmentation caused by land use change across the Campos ecoregion.
