We are all aware that Global Warming is impacting our world. We’re aware that with it comes more extreme weather cycles.

The average Kiwi is probably aware that warmer summers may lead to drought, which may impact our farmers, lead to increased fires and damage our ecosystems. Similarly, we’re probably aware that colder winters will have the opposite but equally damaging impacts.

But what are some of the practical impacts of Global warming on our native forests and ecosystems? After all, extreme weather cycles may be bad for our country, but are there impacts of global warming that we are seeing today?

Let’s take a look at a couple of alarming facts about Global Warming and New Zealand.

1. Disrupted Breeding Cycles: How Warmer Summers Affect Native Species

On the surface, warmer summers don’t seem like a bad thing.

After all, we experience several degrees of temperature variation across Aotearoa/New Zealand anyway. You could conceivably travel from a freezing southern Fiordland storm to a balmy 25-degree Northland day at the beach in one short flight. Why then would a few degrees variation matter?

Well, one of the impacts of warmer summers is that our native trees fruit earlier. A significant number of our native plants and trees do not fruit annually. Instead, they ‘mast’ every two to five years. Typically in years where the summer is warmer than the previous year.

Our native species have often evolved to experience population ‘booms’ during these periods. Perhaps the most famous example is the Kakapo, which only breeds when the fruit from the Rimu tree ripens.

One of the issues with this type of fruiting is that most summers now are warmer year on year. Meaning trees fruit more frequently, for longer and produce larger crops. Unfortunately, our native species have not evolved to be able to handle this increased frequency of breeding. Between 1981 - 2008, less than 50% of female Kakapo would participate in a given breeding season, typically those in the best condition and capable of doing so. Between 2009 and 2022, that number has risen to over 80%.

Disturbingly, there has been a sharp rise in female mortality. While it’s too early to say if there’s a direct correlation, we can confidently say warmer summers are indirectly leading to an increase in female mortality. We’re seeing a rise in deaths of females due to Aspergillosis and other unknown causes. Possibly linked to the stress of the increased frequency of breeding, the stress of higher chick survival rates, and weakened immune systems from unnaturally breeding more often.

Kakapo are being impacted by hotter summers

2. Pest Proliferation: Warming Climate Fuels Threats to Native Fauna

The problems don’t stop there, though. Unfortunately, many of the introduced pests in New Zealand have similarly adapted to boom-bust cycles, in their own native environments. Possums are particularly adept at rapid breeding in times of abundance, as are rats. Both species prey on native birds, damage the canopy and shift the balance of our fragile ecosystems.

Often in the years after a Mega Mast, Stoats will see a similar population boom. Stoats often hold off breeding until food supplies (such as rats and birds) become abundant. The following winter as populations of rats begin to stabilize, hungry stoats shift to our native bird populations. The results can be horrific, localised extinctions are common in the winters following a mega mast year. In recent years we’ve seen our Yellow and Orange fronted Parakeet populations across the mainland be decimated by stoat predation. Mōhua too now occupy just five percent of their former range in part due to the impacts of stoats.

More mega mast fruiting years will lead to less time for these species to bounce back, and an increased cycle of extinction across our native bird species.

Warmer Summers lead to explosions of stoat populations

3. Melting Glaciers, Vanishing Landscapes: The Southern Alps in Peril

Warmer Summers have a devastating impact on the fragile Alpine environment, particularly in the Southern Alps.

Between 1977 - 2014 a third of our permanent snow and ice across our mountain ranges vanished forever; moreover, there is clear evidence that the rate of loss has accelerated a lot over the last fifteen years. So rapid has this glacier melt been, that it’s estimated that critical glaciers will begin completely vanishing within ten years.

The impacts are already visible around the country. The Franz Josef Glacier, one of our premier tourist attractions, has retreated by 900 meters in less than a decade. The Brewster glacier lost an eighth of its total mass in just three years between 2016 and 2019, which amounted to more than thirteen million cubic meters of ice.

The Southern Alps are losing ice rapidly

4. Erosion, Extinction, and Beyond: The Ongoing Environmental Crisis

The onflow effects are wide-ranging. A warmer Alpine environment produces a higher spring and summer melt which leads to greater erosion and soil damage. Moreover, warmer springs lower mortality rates amongst introduced pests like Tahr, Chamois, and Red Deer. Upwards of 30% of Chamois die from the impacts of the cold in their first year of life. Warmer seasons would dramatically increase herd numbers.

Moreover, animals would venture higher in summers, feeding on fragile Alpine grasslands. These grasslands provide critical habitats to Rock Wren, Kea, and Takahe. Takahe are particularly vulnerable to competition from browsing animals. A boom of Red Deer in Fiordland in the 1970’s and 80’s reduced the Takahe Population from 400 birds to just 118. Moreover, it can take upwards of twenty years for damaged Alpine Grasslands to recover from browsing damage, rendering them permanently unsuitable for Takahe for generations.

Warmer Summers don’t just bring browsing animals, they also bring with them pests. A recent study of Rock Wren populations near the Gertrude Saddle in Fiordland found that 100% of nests were attacked by stoats in a given season. Previously, rats and possums avoided the remote damp high altitude regions of Fiordland and the Southern Alps. A 1974 study of the Esperance Valley found Kiore (The Pacific Rat) still present; typically, they become extinct in the presence of the larger Ship and Norwegian Rats. Their presence was a key indicator of the relative health of the ecosystem.

Takahe struggle to survive in the presence of Deer

5. Changing Predator Behaviours in Warmer Summers

Similarly, Sinbad Gully, and much of Fiordland remained free of possums until recently. A 2004 study of Sinbad Gully discovered mice, rats, and possums had shifted into regions previously occupied only by Stoats (and even then sparsely). The presence of Stoats had already eradicated Kakapo by the late 1980’s (or possibly early 1990s) from the Gully. But the Sinbad Skink, an ecologically distinct species of skink, remained. There are fears that warmer summers will lead to more conflict with Rats and Possums and the eventual extinction of the species.

The effects don’t stop there. Each new problem brings with it another. More rats in turn leads to more stoats and cats. This has become a major issue on the eastern side of the south island with Kea populations plummeting due to increased conflict with feral cats. These feral cats tend to stray into Keas ranges chasing rats. But prey on Kea if food supplies dwindle. Such is the impact of cat predation that the population of Kea in Nelson Lakes National Park had collapsed from 50 - 60, to five or six in just twenty years.

Sadly warmer summers and melting glaciers may lead to loss of not only our alpine habitats but the native animals that inhabit them.

Kea struggle in the face of rising Cat Predation

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