Biology subjects

Meir, P.

Publications and source records attributed to Meir, P..

4 recordsLinked to original sources

bioRxiv2022

The Ecosystem Pressure-Volume Curve

The ecosystem pressure-volume curve (EPV) is the relationship between vegetation water content and a representative value of water potential applied on a ground-area basis. The EPV attempts to reconcile our detailed and physically rigorous understanding of small-scale field-measureable processes to the spatial scale applicable to ecosystem and climate science. Successfully bridging that gap in scale potentially allows us to use field measurements to interpret remote sensing data, and then remote sensing data to inform our understanding of vegetation-climate interactions. Here we clearly define the idea of the EPV, evaluate the limitations of applying values of water content and water potential to ecosystems on a ground area basis, and discuss practical ways to construct the EPV with existing data. We also present the first EPVs based on data from nine different plots, including tropical rainforest, savanna, temperate forest, and a long-term drought experiment in Amazonian rainforest (Caxiuana, State of Para, Brazil). The initial findings suggest high levels of consistency among sites. In particular, the ratio of water to biomass across ecosystems appears to be constrained to around 1:3. Seven of nine sites had closely converging relative maximum water storage (the proportion of total stored water than can be lost before an ecosystem succumbs to physiological damage) at 9.1% +/-1.8 standard deviation. Relative ecosystem capacitance may increase with site biomass (P = 0.091), but varied little across sites with a mean of 0.068 MPa-1 +/-0.029 standard deviation. These first estimates suggest that the EPV idea may reveal useful trends across ecosystems, potentially paving the way to increasing the ecophysiological significance of remote sensing data, and enabling an alternative method for modelling long-term ecosystem-climate feedbacks based on equilibrium thermodynamics.

ecology↗

bioRxiv2020

New insights into large tropical tree mass and structure from direct harvest and terrestrial lidar

A large portion of the terrestrial vegetation carbon stock is stored in the above-ground biomass (AGB) of tropical forests, but the exact amount remains uncertain, partly due to the lack of measurements. To date, accessible peer-reviewed data are available for just 10 large tropical trees in the Amazon that have been harvested and directly measured entirely via weighing. Here, we harvested four large tropical rainforest trees (stem diameter: 0.6-1.2m, height: 30-46m, AGB: 3960-18 584 kg) in intact old-growth forest in East Amazonia, and measured above-ground green mass, moisture content and woody tissue density. We first present rare ecological insights provided by these data, including unsystematic intra-tree variations in density, with both height and radius. We also found the majority of AGB was usually found in the crown, but varied from 42-62%. We then compare non-destructive approaches for estimating the AGB of these trees, using both classical allometry, and new lidar-based methods. Terrestrial lidar point clouds were collected pre-harvest, on which we fitted cylinders to model woody structure, enabling retrieval of volume-derived AGB. Estimates from this approach were more accurate than allometric counterparts (mean tree-scale relative error: 3% vs. 15%), and error decreased when up-scaling to the cumulative AGB of the four trees (1% vs. 15%). Further, whilst allometric error increased four-fold with tree size over the diameter range, lidar error remained constant. This suggests error in these lidar-derived estimates is random and additive. Were these results transferable across forest scenes, terrestrial lidar methods would reduce uncertainty in stand-scale AGB estimates, and therefore advance our understanding of the role of tropical forests in the global carbon cycle.

ecology↗

bioRxiv2020

Induced drought strongly affects richness and composition of ground-dwelling ants in the eastern Amazon

Environmental change scenarios caused by low precipitation forecast species loss in tropical regions. We use one year of data from a long-term rainwater exclusion experiment in primary Amazonian rainforest to test whether induced water stress and covarying changes in soil moisture, soil respiration, tree species richness, diversity, size, and total biomass affected species richness and composition (relative abundance) of ground-dwelling ants. Induced drought reduced ant richness, whereas increased soil moisture and variability in tree biomass increased it. Species composition differed between control and rainfall-excluded plots. Occurrence of many ant species was strongly reduced by induced drought, but some generalist groups of ants were favored by it. The expected loss of ant species and changes in ant species composition in tropical forests likely will lead to cascading effects on ecosystem processes and the services they mediate.

ecology↗

bioRxiv2020

Evolutionary heritage shapes tree distributions along an Amazon-to-Andes elevation gradient

Understanding how evolutionary constraints shape the elevational distributions of tree lineages provides valuable insight into the future of tropical montane forests under global change. With narrow elevational ranges, high taxonomic turnover, frequent habitat specialisation, and exceptional levels of endemism, tropical montane forests and trees are predicted to be highly sensitive to environmental change. Using plot census data from a gradient traversing >3000 m in elevation on the Amazonian flank of the Peruvian Andes, we employ phylogenetic approaches to assess the influence of evolutionary heritage on distribution trends of trees at the genus level. We find that closely related lineages tend to occur at similar mean elevations, with sister genera pairs occurring a mean 254 m in elevation closer to each other than the mean elevational difference for all genera pairs. We also demonstrate phylogenetic clustering both above and below 1750 m a.s.l, corresponding roughly to the cloud-base ecotone. Belying these general trends, some lineages occur across many different elevations. However, these highly plastic lineages are not phylogenetically clustered. Overall, our findings suggest that tropical montane forests are home to unique tree lineage diversity, constrained by their evolutionary heritage and vulnerable to substantial losses under environmental changes, such as rising temperatures or an upward shift of the cloud base.

ecology↗