High frequency root dynamics: sampling and interpretation using replicated robotic minirhizotrons.

Automating dynamic fine root data collection in the field is a longstanding challenge with multiple applications for co-interpretation and synthesis for ecosystem understanding. High frequency root data are only achievable with paired automated sampling and processing. However, automatic minirhizotron (root camera) instruments are still rare and data are often not collected in natural soils or analysed at high temporal resolution. Instruments must also be affordable for replication and robust under variable natural conditions. Here, we show a system built with off-the-shelf parts which samples at sub-daily resolution. We paired this with a neural network to analyse all images collected. We performed two mesocosm studies and two field trials alongside ancillary data collection (soil CO2 efflux, temperature, and moisture content, and 'PhenoCam'-derived above-ground dynamics). We produce robust and replicated daily time series of root dynamics under all conditions. Temporal root changes were a stronger driver than absolute biomass on soil CO2 efflux in the mesocosm. Proximal sensed above-ground dynamics and below-ground dynamics from minirhizotron data were not synchronized. Root properties extracted were sensitive to soil moisture and occasionally to time of day (potentially relating to soil moisture). This may only affect high frequency imagery and should be considered in interpreting such data.

Shrub encroachment and climate change increase the exposure to drought of Mediterranean wood-pastures.

Pastures and wood-pastures, livestock grazing systems where scattered trees and shrubs co-occur, are essential for global food supply. The grazing value of these systems, which is closely related to soil moisture, is increasingly threatened by changes in climate variability and vegetation structure, mainly by shrub encroachment. However, it remains relatively unexplored to what extent the concurrent effect of climate change and shrub encroachment will affect the exposure to drought stress of Mediterranean wood-pastures - defined as a period where soil water availability drops below 40%. Here we combined soil moisture measurements and a process-based water balance model to assess the effect of shrubs, a shallow- and a deep-rooted, on soil moisture under current (2009-2012) and future weather (i.e. RCP4.5 and RCP8.5). Soil moisture was measured and predicted in six sites, three for each type of shrub, where two adjacent plots were selected, a control and an encroached plot. During 2009-2012, encroached plots had more extended droughts (29 and 48 days longer in sites encroached with shallow- and deep-rooted shrubs, respectively) and higher usage of deep water (~30%) than control plots. Under future climatic projections, our results show a consistent increase in the duration, an earlier onset of drought and higher reliance on shallow water with time, particularly under the worst climatic scenario. Encroached plots showed higher inter-annual variability than control plots, particularly in plots encroached with the deep-rooted shrub. Our results indicate that the presence of shrubs magnify the effect of climate. This suggests a likely increase in the exposure of Mediterranean wood-pastures to drought if processes of shrub encroachment persist in a context of climatic changes where earlier and more prolonged droughts will become more frequent.

Correction: Pattern or process? Evaluating the peninsula effect as a determinant of species richness in coastal dune forests.

[This corrects the article DOI: 10.1371/journal.pone.0173694.].

Pattern or process? Evaluating the peninsula effect as a determinant of species richness in coastal dune forests.

The peninsula effect predicts that the number of species should decline from the base of a peninsula to the tip. However, evidence for the peninsula effect is ambiguous, as different analytical methods, study taxa, and variations in local habitat or regional climatic conditions influence conclusions on its presence. We address this uncertainty by using two analytical methods to investigate the peninsula effect in three taxa that occupy different trophic levels: trees, millipedes, and birds. We surveyed 81 tree quadrants, 102 millipede transects, and 152 bird points within 150 km of coastal dune forest that resemble a habitat peninsula along the northeast coast of South Africa. We then used spatial (trend surface analyses) and non-spatial regressions (generalized linear mixed models) to test for the presence of the peninsula effect in each of the three taxa. We also used linear mixed models to test if climate (temperature and precipitation) and/or local habitat conditions (water availability associated with topography and landscape structural variables) could explain gradients in species richness. Non-spatial models suggest that the peninsula effect was present in all three taxa. However, spatial models indicated that only bird species richness declined from the peninsula base to the peninsula tip. Millipede species richness increased near the centre of the peninsula, while tree species richness increased near the tip. Local habitat conditions explained species richness patterns of birds and trees, but not of millipedes, regardless of model type. Our study highlights the idiosyncrasies associated with the peninsula effect-conclusions on the presence of the peninsula effect depend on the analytical methods used and the taxon studied. The peninsula effect might therefore be better suited to describe a species richness pattern where the number of species decline from a broader habitat base to a narrow tip, rather than a process that drives species richness.