Increasing temperatures associated with global climate change have resulted in subtle but noticeable changes in the way species act in both time and space. For example, spring flowering and budset for many plants has come earlier and earlier, birds migrate and nest earlier in the year, and insect outbreaks have become more severe. One area where climate change is predicted to have an especially dramatic impact is in tropical mountain cloudforests.
Unless you’ve spent a lot of time trekking around the Andes or retracing Alfred Wallace’s steps in Indonesia you have probably not noticed that most tropical mountain cloudforest trees are already responding to climate change. These ecosystems are highly diverse, unique ecosystems because the forest is constantly engulfed in clouds and fog, creating an eerie yet fascinating ecosystem where life is literally clinging to every surface.
Inside a tropical mountain cloudforest where every tree trunk and branch is covered in moss, orchids, and bromeliads.
On the eastern slope of the Andes this cloudforest is created when warm moist air moves westward across the lowland Amazonian jungle and runs into the very steep Andes. When this air hits the mountains it is forced upwards, cools, condenses and drops most of the moisture as precipitation or fog. Similarly, if you were to walk up this same mountain you would notice that temperatures decrease rather quickly as you ascend the mountain. What you may not notice is that the composition of the species present on the mountain also changes as you climb. Species turnover is so high because most species on these mountainsides are adapted to live within a narrow belt of temperature and precipitation, which is associated with a specific elevation. Moving just 300 vertical meters in the Andes can result in a complete change in the forest, from the species of trees to the birds and even down to fungus found in the soil.
As temperatures increase these species need to migrate upslope towards cooler, higher refugia because temperatures in their current range will quickly become too hot. This could lead to several scenarios where species shift their ranges in response to increasing temperatures. However, the most likely migration scenario is that species will slowly move upslope at the high elevation edge of their range but lose habitat at the lower edge of their range (Figure part D). This would lead to range contractions and elevated extinction risks in this hyper-diverse cloudforest ecosystem. In fact range contractions are already occurring on many tropical mountains including insects on Mt. Kinabalu in Borneo, lizards and snakes in Madagascar, and birds and trees in Peru.
The majority of tropical mountain cloudforest species are predicted to move upslope with changing climate. How they migrate upslope is important for the future conservation of this ecosystem. In scenario A the species range does not move upslope but the relative abundance of individuals within the range shifts upslope. An alternative is that the entire range, both the high elevation and low elevation edges shift upslope (B). One unlikely scenario is that the species high elevation edge shifts upslope and the low elevation edge remains the same (C). The most likely and most common scenario is that the high elevation edge of a species range does not shift upslope but the low elevation range does (D). Species will experience range contractions as the species continually lose area at the low elevation part of their ranges but do not gain elevation at the high end. Figure taken from Feeley, Rehm, Machovina. 2012. Frontiers in Biogeography.
As climate change biologists we are desperately trying to figure out how species will respond to increasing global temperatures so we can make informed conservation decisions yet our understanding of many ecosystems is so basic that we do not have much confidence in our ability to predict the future. Regardless of our predictions, we already see many species in the diverse tropical cloudforest systems suffering from increased regional and global temperatures. Unfortunately the pace of contemporary climate change far exceeds the capacity of most species to adapt to their environment and will result in major biodiversity losses in cloudforests and ecosystems worldwide.
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