Is tree diversity an important driver for phosphorus and nitrogen acquisition of a young tropical plantation? Forest Ecology and Management,

a b s t r a c t Many tropical plantations in Central America are monocultures of fast growing, mostly exotic species such as a teak, eucalypts and pines. This has been perceived as a problem for ecosystem stability, pest control, local biodiversity and long-term nutrient availability. In our study, we followed the effects of increasing tree diversity (1, 3 and 6 native species) on aboveground nitrogen (N) and phosphorus (P) pools in a young experimental biodiversity plantation (central Panama) over two subsequent years. Our results show a positive but not consistent net effect of biodiversity on the N and P pools, mainly explained by the complementarity effect. N and P use efficiencies strongly varied among the investigated tree species and the species richness gradient. Anacardium excelsum and Luehea seemannii were associated with higher N and P use efficiencies while Hura crepitans and Tabebuia rosea were less efficient in aboveground biomass production per unit N or P. Tree species tended to have lower P use efficiencies in the intermediate diversity level compared to monocultures and six-species mixtures. Although the environmental conditions explained a large part of the variation in the N and P pools (58%) in our experiment, we argue that incorporating tree mixtures in the management can bring additional benefits and improve tree growth and nutrient uptake as compared to the monocultures

Ultrasonic acoustic emissions in drought-stressed trees - more than signals from cavitation?

Ultrasonic acoustic emission (UAE) in trees is often related to collapsing water columns in the flow path as a result of tensions that are too strong (cavitation). However, in a decibel (dB) range below that associated with cavitation, a close relationship was found between UAE intensities and stem radius changes. • UAE was continuously recorded on the stems of mature field-grown trees of Scots pine (Pinus sylvestris) and pubescent oak (Quercus pubescens) at a dry inner-Alpine site in Switzerland over two seasons. The averaged 20-Hz records were related to microclimatic conditions in air and soil, sap-flow rates and stem-radius fluctuations de-trended for growth (ΔW). • Within a low-dB range (27 ± 1 dB), UAE regularly increased and decreased in a diurnal rhythm in parallel with ΔW on cloudy days and at night. These low-dB emissions were interrupted by UAE abruptly switching between the low-dB range and a high-dB range (36 ± 1 dB) on clear, sunny days, corresponding to the widely supported interpretation of UAE as sound from cavitations. • It is hypothesized that the low-dB signals in drought-stressed trees are caused by respiration and/or cambial growth as these physiological activities are tissue water-content dependent and have been shown to produce courses of CO2 efflux similar to our courses of ΔW and low-dB UAE

Establishment success in a forest biodiversity and ecosystem functioning experiment in subtropical China (BEF-China)

Experimental forest plantations to study biodiversity–ecosystem functioning (BEF) relationships have recently been established in different regions of the world, but subtropical biomes have not been covered so far. Here, we report about the initial survivorship of 26 tree species in the first such experiment in subtropical China. In the context of the joint Sino–German–Swiss Research Unit “BEF-China,” 271 experimental forest plots were established using 24 naturally occurring tree species and two native commercial conifers. Based on the survival inventories carried out in November 2009 and June 2010, the overall survival rate was 87 % after the first 14 months. Generalized mixed-effects models showed that survival rates of seedlings were significantly affected by species richness, the species’ leaf habit (deciduous or evergreen), species identity, planting date, and altitude. In the first survey, seedling establishment success decreased with increasing richness levels, a tendency that disappeared in the second survey after replanting. Though evergreen species performed less well than deciduous species with establishment rates of 84 versus 93 % in the second survey, their planting success exceeded the general expectation for subtropical broad-leaved evergreen species. These results have important implications for establishing mixed-species plantations for diversity conservation and improvement of ecosystem functioning in the Chinese subtropics and elsewhere. Additional costs associated with mixed-species plantations as compared to conventional plantations also demonstrate the potential of upscaling BEF experiments to large-scale afforestation projects