Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - ECOHERB (Drivers and impacts of invertebrate herbivores across forest ecosystems globally.)

Teaser

Forests currently slow global climate change by absorbing large amounts of atmospheric carbon dioxide. However, the future of this carbon sink is critically limited by the availability of nutrients important for plant growth. Therefore, to understand the pattern of future...

Summary

Forests currently slow global climate change by absorbing large amounts of atmospheric carbon dioxide. However, the future of this carbon sink is critically limited by the availability of nutrients important for plant growth. Therefore, to understand the pattern of future climate change, it is first necessary to understand the factors regulating forest nutrient cycling. Herbivores potentially alter forest nutrient cycling in a range of ways, but these have mostly only been recorded for various species of large mammals. By comparison, the impacts of the abundant invertebrates in forests have largely been ignored and are not included in current models of the global carbon cycle used to generate projections of the future climate so vital for designing governmental policies.

After sunlight and water, biologically-available nitrogen and phosphorus are the most important resources limiting productivity and carbon uptake by ecosystems at a global scale. The proposed project is using a pioneering new approach with the overall objective of providing the most complete picture yet available of the rates, underlying drivers and ultimate impacts of nitrogen and phosphorus inputs from invertebrate herbivores across forest ecosystems worldwide. Specifically, we are establishing a network of monitoring stations across all major forest types to provide the first coordinated global assessment of the rates and regulators of herbivore nutrient transfers, to generate more accurate predictions of forest carbon sequestration under future climate change. The specific questions addressed are:

1) How large are herbivore inputs of nitrogen and phosphorus to the soil in different forest types and compared to other major ecosystem sources?
2) How does climate and habitat disturbance affect herbivore nutrient fluxes?
3) How do herbivore nutrient fluxes change soil processes and how does this vary with climate?
4) How do herbivores shape forest responses to climate and what will this mean for future patterns of forest carbon sequestration?

Work performed

Work Performed

This first phase of the project focused on laying the ground work for the international monitoring network: selecting field sites, and coordinating field logistics with collaborators. Some of the initially planned field sites have not been pursued for a range of reasons (e.g.: changes in the location of key site collaborators, shifts in country political environment) but a significant number of new collaborations and sites have been established that were not envisaged in the original proposal. This means that the overall geographic coverage remains broadly the same and our ability to address the study questions remains the same or even better.
Over the last six months we have been transitioning to the second phase of the project, where most of the sites within the network have been established and are delivering data. There is a subset of remaining sites that we expect to be installed over the next six months, after this the final network will be broadly in place. The installed and functioning sites are as follows: Tropical forest: Peru (4 sites), Brazil (4 sites), Peru (4 sites), Malaysia (6 sites), Ghana (5 sites); Temperate forest: UK (4 sites), Sweden (2 sites), USA, (15 sites); Boreal/Arctic forest: Canada (5 sites), Sweden (8 sites). Soon to be installed sites are as follows: Tropical Forest: Hawaii (5 sites), Democratic Republic of Congo (6 sites), Australia (8 sites); Temperate forest: Argentina (2 sites), Poland (2 sites), New Zealand (4 sites); Boreal/Arctic forest: USA (4 sites), Russia (2 sites). We have expanded the scope and range of measurements in non-pristine forests across the gradient, in recognition of the predominance of secondary forests across the world and the importance of understanding disturbance factors for predicting future global change impacts. So we now have herbivory measurement sites running or soon to be established on two elevated CO2 experiments, three large-scale drought simulation experiments, four experimental fire treatments, three logging experiments examining forest processes under different types and intensities of tree extraction. These experiments are in many cases distributed across different biomes so we have an opportunity to examine how these disturbance factors impact herbivory and ecosystem biogeochemistry in different ways depending on the type of forest biome.
The work of establishing and running of these sites has been performed by two PhD students employed within the ECOHERB project and a wide network of local project collaborators and field assistants funded by the ECOHERB project as subcontractors. The activities follow a unified protocol covering the types of sampling equipment installed and the methods of sample processing and analysis, which will aid comparison among sites and interpretation of broad-scale patterns. In most cases, we have identified sites where the basic sampling equipment was already in place for other purposes (to record litter fall mass) so we have been able to add herbivory measurements at these sites with minimal additional effort. Further, since the work has usually been adding to ongoing established experiments and studies, permits for site access and sample collection have already been secured by the collaborators for their ongoing projects.

Main Results

At this stage in the project, with the PhD students driving the work just nine months into their first year, the focus is on completing the installation of the plot network and planning subsequent laboratory measurements with collected soil and herbivore deposits. So while some data is collated and analyzed for individual sites / clusters the main project results thus far involve logistical / organization achievements which should place us in a position to deliver solid scientific breakthroughs over the next few years. The achievements include:
1) Establishment of pristine forest sites in all major forest biomes on all continents except Antarctica. We now have sites runni

Final results

Progress Beyond State Of The Art

There is a large existing body of research about herbivores but broadly the state of the art in this field reflects (1) a focus on large bodied animal herbivores, (2) where invertebrate herbivores are studied, a focus on (i) outbreaks, (ii) impacts in temperate ecosystems and/or (iii) links between leaf-level damage and traits. The present project aims to, and is on track to, exceed this state of the art by looking at background rates of invertebrate herbivory across all major forest types and under various major forest disturbances. Further, we focus on the broad ecosystem-level impacts of this herbivory in terms of carbon, nitrogen and phosphorus cycling.

Expected Results

We expect that the network will produce a large number of outputs in various forms (scientific papers, conference presentations, workshops, media summaries) so of which contribute directly to the major overall study questions, but many will address lower-level questions addressing specific issues, site-specific patterns and experimental comparisons. The broader-level field results will be:

1) Estimates of carbon, nitrogen and phosphorus inputs from background invertebrate herbivory across all major forest biomes.
2) Estimates of the impacts of different major disturbance factors (elevated CO2, drought experiments, wildfire, logging intensity) on carbon, nitrogen and phosphorus inputs from background invertebrate herbivory.

These outcomes above are already partly generated via the measurements installed across the project network. In the remainder of the project, in addition to the primary measurements, we aim to incubate herbivore products collected from several different sites with soil within a laboratory mesocosm and integrate the laboratory and field data within a modeling environment to generate further broad results:

3) Improved estimates of the impacts of herbivore products (frass, bodies) on soil carbon and nutrient cycling.
4) Improved estimates of the interactions between invertebrate herbivores, large-bodied herbivores and plants – and the end consequences for ecosystem biogeochemistry under different climate scenarios – simulated within a large-scale computer model.

Website & more info

More info: https://www.nateko.lu.se/dan-metcalfe.