Is the climate really changing?

Tropical montane cloud forests are critical reservoirs of biodiversity, supporting 15% of the world’s species despite covering only half of 1% of the Earth’s land surface. However, this biodiversity is threatened by climate change as the temperature rises and the forest becomes drier. Climate change is predicted to reduce rainfall and fog input to the Andean forest biodiversity hotspot. In Peru, a large-scale experiment has been implemented that aims to understand how a reduction in rainfall and fog could affect these unique cloud forest ecosystems.

The Wayqecha climate change experiments.

In the forests close to the Wayqecha Cloud Forest Biological Station exist two climate change experiments. Across one patch of forest, a roof has been built to exclude rainfall from reaching the soil, whilst around another patch of forest exists a giant mesh curtain that excludes fog. Together these simulate potential future climates for the cloud forest. At the experiments, dramatic changes are starting to appear as trees shift their carbon allocation, leaf area and growth rates. These changes are clearly driven by the experiments, but how do they exactly relate to climate changes? In order to fully understand this, we first have to understand how the experiments have changed the climate of the forest.

I recently returned to the Wayqecha in May 2022 to install four weather stations across our research plots. These weather stations will provide important data on the presence of fog (measured by visibility sensors), temperature, relative humidity and solar radiation. These variables can all limit photosynthesis and productivity of cloud forests so are important variables for us to measure. As part of the weather stations, we also installed leaf wetness sensors to understand how the experiments were changing the length of time that leaves are wet. This data is also important because photosynthesis can be considerably reduced when leaves are wet.

Each weather station is composed of a pyranometer sensor that measures solar radiation, a temperature and relative humidity sensor that has a radiation shield to keep measurements stable, a visibility sensor that measures the presence of fog and two leaf wetness sensors that measure the length of time that leaves are wet. At each station a data logger records the data and a solar panel charges the battery. Photo copyright: David Bartholomew

In order to best understand the climate that trees are experiencing in our experiments, we had to install the sensors above the canopy. Whilst this seems logical, it imposes some complicated logistics on our fieldwork. Fortunately, Peruvians can be incredibly innovative and my field team managed to find a way to get the sensors 20-30 metres above the ground. This involved constructing large metal structures where the sensors could be attached that were then installed on canopy towers. By climbing the tower and creating an innovative pulley system, they were able to get these sensors high up and above the canopy. A truly remarkable feat!

Each weather station imposed its own challenges.

The climate above the canopy is not the only change that will have happened within the experiment. Instead, changes to soil moisture availability will also likely have taken place. This is particularly true in the rainfall exclusion experiment, but may also have changed in the fog exclusion experiment if less water is intercepted by the trees. It is still unknown whether fog interception acts as an important source of water for cloud forest soils. With this in mind, we also used the fieldwork to install several soil moisture sensors. These were installed at a range of depths to assess how moisture is changing throughout the vertical soil profile. A total of 24 soil moisture sensors were installed across our four plots to get as much spatial coverage as possible.

With the sensors now left in the forest to record data, we will get a complete picture of how exactly we have manipulated the climate. From this data, we will then be able to answer many important questions about how climate change may impact the world’s tropical montane cloud forests.

We were also joined by a team who measured root traits across the experiment.

There was also time for some bird watching. The Andean cloud forests are home to a rich diversity of hummingbirds.

The trip to Wayqecha was also used to repair the cloud curtain.
A big thank you to the whole team who helped make the weather stations a reality. Photo credit: Ruthmery Pillco Huarcaya.

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