Cross-site patterns in the response of Eucalyptus plantations to irrigation, climate and intra-annual weather variation

Abstract

Cross-site patterns for multiple sites tend to be more broadly applicable and more useful for constructing and constraining models. We examined cross-site patterns of Eucalyptus plantation response to water supply (including irrigation and 1/3 precipitation removal), mean annual temperature (MAT), vapor pressure deficit during the daytime (VPD), and nutrient addition in eight sites from the Brazil Eucalyptus Productivity Project (BEPP). Mean annual increment (MAI) for all treatments and sites varied from 12.7 to 37.3 Mg ha−1 yr−1 across a 1400 km latitudinal gradient where annual precipitation varied from 940 to 1430 mm yr−1. MAI varied with water added across all sites, with a near linear increase of 1.42 Mg ha−1 yr−1 per 100 mm yr−1 between 640 and 1800 mm yr−1, a MAI plateau of 30.8 Mg ha−1 yr−1 at ~2000 mm yr−1, then decreasing to MAI of 27.2 Mg ha−1 yr−1 at 3060 mm yr−1. Including MAT with the water response showed that MAI decreased at 1.23 Mg ha−1 yr−1 per °C. For the natural precipitation treatments, MAI decreased at 2.52 Mg ha−1 yr−1 per °C, comparable to that for the much broader TECHS Project (Binkley et al., 2020). MAI was not related to temperature for the irrigation treatments, suggesting that some or all of the response of MAI to temperature is related to water supply. The difference between the biomass of the irrigation treatments and that of natural precipitation treatment slowed its increase or stopped increasing at age 30–60 months for five of the eight sites, but increased through the study duration for the other three sites. The difference in biomass between the fertilization and no fertilization treatments increased throughout the study for two sites. Three- and six-month growth was generally unrelated prior 3–12 month weather. Age-related decline was observed for all of the treatments at four of the eight sites. These cross-site comparisons affirm that water supply is the key resource determining levels of plantation productivity in Brazil and that individual site studies are inadequate for understanding many key responses.