Preserving the mammoth steppe

Question

During much of the Late Pleistocene stage, the world's most widespread biome was the so-called "mammoth steppe" - a cold, dry grassland which spanned eastward all the way from Spain to Canada. It was the favoured habitat of many iconic Pleistocene megafauna species.

Roughly 12,000 years ago, the mammoth steppe suddenly disappeared, replaced by tundra and boreal forest. Some put it down to humans killing off the local megafauna which were needed to maintain the grassland, but the prevailing hypothesis is that the climate became warmer, and therefore wetter, allowing shrubs, mosses and trees to move in.

For more information, see https://en.wikipedia.org/wiki/Mammoth_steppe.

In my world I want to have a ~10,000 square kilometre island, situated roughly here:

(Where the thick black dot is. Ignore the red arrow, that was in the original picture for some reason.)

And, more importantly, I'd like this island to contain a remnant of the mammoth steppe, and thus be a refugium for many extinct Beringian creatures. So, assuming that the Climatic Hypothesis is correct, how can I justify the mammoth steppe not being displaced by other biomes here?

Answer 1

Not much explanation is required. Several islands in that area were home to mammoths long after they became extinct on the mainland: Wrangel Island (7,600 sq km), the one on the top left of your map, had mammoths some 8000 years after the steppes disappeared. St. Paul Island is much smaller (100 sq km) and more southerly, but also hosted mammoths thousands of years after they had mostly disappeared.

Even today, it looks as though these islands have little in the way of vegetation larger than grass, much like mammoth steppes:

So if your hypothetical island existed, it would be quite reasonable for it to have a similar environment. With a little luck, megafauna might stick around even longer than they did on Wrangel.

Answer 2

By evolution. It may possible when there are only few predators and competitors for the primary food source of mammoth and also no drastic environmental changes. Maybe there was an earlier source of climate change that makes the environmental change smother but stretched duration. Mammoth may be altered because of fitting process. So maybe you could run an simulation of evolution to show that such scenario could be possible.

Answer 3

You need a glacier and abscence of rains. Best way to achive this - strategicaly placed high mountains on one side of an island - they would keep glacier and cast "wind shadow" with no-rain zone on (almoust) all the island. Mamonth steppes should be on sort of mesa in our warmer climate, so some traps would help.

Mamonth steppes formed between deserts and glaciers. When both gone (to simplify - glacer melted and weted deserts), steppes gone also.

Wrangel Island is not very good place - there is no tall grass for mammonths now (they need it a lot - tens of square kilometers of 1.5-2 meter grass per one mammonth). They gone extinct for a reason.