Ecology of the past

Hello everyone,

My name is Majoi Nascimento, I just started a new job as a postdoc researcher at the University of Amsterdam working on an ERC project named ALPHA (Assessing Legacies of Past Human Activities in Amazonia with Crystal McMichael). The main focus of ALPHA is to investigate the role of human disturbance and recovery processes that have occurred over the past few millennia in Amazonia, and their effects on the biodiversity and carbon dynamics that are observed there today. To do a good job, it is important that we understand the concepts of disturbance and recovery, but also the processes that underlie forest resilience. That is the reason why we decided to read and discuss this work from Adolf et al. 2020 “Identifying drivers of forest resilience in long-term records from the Neotropics”, published in the journal Biology Letters, during one of our lab meetings.

Resilience can be defined as either the capacity a system has to absorb changes before shifting to an alternative state (ecological resilience) or to rebound after the shift (engineering resilience). The paper calculates the first, by measuring recovery rates from disturbance events that did not cause change in states using paleo pollen records from the Neotropics. Their aim was to test if resilience was associated with diversity or with location-specific abiotic factors over the last 13,000 calibrated years before present (cal yr BP).

The idea is that high species diversity affects resilience because more species mean higher chances of some of them to keep the ecosystem functioning, even if others can’t. Now, abiotic factors would affect resilience by providing stability. A big lake that helps maintaining air humidity, or a the shadow of a mountain that always protects a region from intense sun light, are examples of abiotic factors that could work against dissection.

Three steps were used to calculate resilience. First the authors identified disturbance events for each pollen sequence, based on the total pollen percentage of forest taxa. Than they calculated the rate in which forest recovered after those disturbances using the percentage increase of forest pollen abundance per year relative to the pre-disturbance level. And lastly, they investigated if the forests returned to a similar community assemblage as their pre-disturbance state, or if the recovered forest was a novel community. They calculated this using squared chord distance coefficients.

After finding out when disturbances happened on a system, how long that system took to recover, and if the recovery represents the system’s pre-disturbance state or a new one, the authors wanted to understand what is the probable driver of that recovery rate. They used a generalized linear model to test the relationship between pollen richness and recovery rates, and a linear regression model to test the relationship between the same recovery rates and spatial patterns in present-day vegetation persistence.

The authors found pre-disturbance taxonomic richness and faster recovery rates to be positively associated in the studied systems, and that forest biodiversity may be important factor to keep an ecosystem functioning in a changing world.

If you are interested on this paper, here is the reference and a link to it: 

Adolf, C., Tovar, C., Kühn, N., Behling, H., Berrío, J.C., Dominguez-Vázquez, G., Figueroa-Rangel, B., Gonzalez-Carranza, Z., Islebe, G.A., Hooghiemstra, H., Neff, H., Olvera-Vargas, M., Whitney, B., Wooller, M.J. & Willis, K.J. (2020) Identifying drivers of forest resilience in long-term records from the Neotropics. Biology Letters 16, 20200005. DOI: 10.1098/rsbl.2020.0005