Concurrently to being hunted and otherwise severed from the wild, Przewalski horses were indirectly impacted by the progressive transformations of East Asian drylands throughout the Holocene period under the combined influence of various natural and anthropogenic factors, some of which are briefly discussed below.
Agricultural development and regional population growth
Domestication of most animals and plants took place between 10,000 to 5,000 years ago. Animal husbandry and cultivation were broadly adopted in Eurasia although greatly varied in time, space and intensity. On East Asian drylands (see above map), particularly grasslands where the horses lived, animal husbandry dominated agriculture over the past 5,000 years; the harsh climate and low soil fertility of such regions generally made cultivation difficult.
As population grew, so did agriculture, but contrasting trends in population growth resulted in different levels of agricultural intensification on the vast drylands.
By 3,000 BC, most drylands situated in regions that correspond to the present-day Chinese provinces of Xinjiang, Gansu, Ningxia and Inner Mongolia (see above map) were used as pasturelands for livestock grazing, and most of those suitable for cropping had been converted to arable land by 0 AD. Cultivation gradually intensified from this time and pressure on pastureland exacerbated from the 16th century following the exponential growth of the Chinese population. Significant although fairly stable between 37-60 millions from the Han dynasty (206 BC-220 AD) to the commencement of the Ming era (1368-1644), it swelled from the 16th century, most dramatically during the Manchus, i.e. the Qing reign (1644-1911), when it doubled from 177 to 358 millions between 1749 and 1811 alone.
Most of the population concentrated eastward along the Yellow River, Yangtze River or Zhu Jiang River basins, so drylands were never heavily populated. However, farming on the Chinese drylands to feed this giant population caused a loss of natural grasslands and forested lands through overgrazing already visible at least 300 years ago, and more recently land degradation and erosion.
On the territory corresponding to present-day Mongolia, most grasslands were used by pastoral nomads by 1,000 AD. However, it is not until the 18th-19th centuries that pastures started being saturated with livestock. Colonel Nicolai Przewalski, who visited the country around 1880, remarked that “all suitable agricultural lands were reclaimed and all grazing lands were overloaded by livestock”. Cropping remained low-intensive and spatially marginal on the few suitable parcels available, which were eventually converted to arable land during the 19th and 20th centuries.
A slow-growing Mongolian population coupled with the permanence of a transhumant pastoral system even under Manchu and communist ruling explain this unique land use evolution, which prevented heavy steppe degradation far into the 20th century.
Over the centuries, Przewalski horses thus witnessed the gradual advance of agriculture on increasingly larger portions of their historic range and their dryland habitat diminish in size and quality as a result. In addition to being intrusive, agricultural activities represent environmental stressors, even more so to fragile ecosystems like grasslands. When adequately managed (rotation, fallow, livestock numbers consistent with the carrying capacity of a given pasture, etc.) pasture and crop lands little suffer, and we can imagine that disturbance was minor for the equids under low-density land use. On the other hand, intensive cultivation and overgrazing cause soils to lose their nutrients, making them prone to wind and water erosion, eventually leading to desertification; in the process, unpalatable or poisonous plants may replace the original vegetation; in the end, the land is worthless to men and animals, which are left with fragmented natural habitats. This phenomenon occurred early on in various parts of the Chinese drylands, but only relatively recently in Mongolia, which may partly explain why Takhis survived longer there.
Despite such major changes brought to the land, the resilient equids subsisted in large numbers at least in parts of their historic range until the late 18th century and in fewer numbers on a restricted territory until the early 20th century, which suggests that agricultural development cannot be blamed alone for the horse’s demise.
Warfare and military activities
Political instability dominated continental East Asia during most of the past two millennia. Territorial borders were frequently redefined through a myriad of conflicts opposing the numerous cultural groups that populated this immense area, which ultimately entailed the constitution of two sovereign states, China and Mongolia. Various episodes from the history of East Asian drylands suggest that Przewalski horses were not immune to such disorders which brought additional disturbance to the steppe where battles often took place.
The following quote from The Secret History of the Mongols proves that Takhi territory often served as a setting for wars and the equids were even used as a military diversion during the reign of Genghis Khan (1206-1227) and its successors: “Throw-Into-Disorder Tactics: If the enemy was strong on the battlefield or sheltering in a fort, the Mongols would herd oxen and wild horses into the enemy lines to cause confusion”. The training of Mongol soldiers also took place on the steppe and involved local wildlife, possibly Przewalski horses, a then common species: “One unique training method that the Mongols used were huge hunting excursions organized annually on the steppe. Mongols would make a great circle and drive all manner of animals to the center. This way of learning dynamic maneuvers was highly useful on a battlefield, contributing to their success”.
Clashes between nomadic tribes for control over the vast Inner Mongolian belt, where Takhis probably lived during part of the Holocene, were frequent, especially before Genghis Khan united the Mongol tribes at the dawn of the 13th century (see above map). Geographically, the belt was a corridor for eastward invasions to the Yellow River basin, the cradle of the Chinese civilization, which prompted the edification of the Great China Wall by the successive Chinese rulers from 500 BC. The Wall was not one but various strips of fortifications which run along the fluctuating Chinese border. A recent study suggests that, all sections combined, the total length of the Great Wall comes close to 21,000 km, of which only 8.2% still stands today. From the Qin dynasty (221-206 BC) to the Jin reign (1125-1234 AD) sections of the barricade were built across large pans of the steppe in Inner Mongolia, Outer Mongolia and Gansu, including through the very heart of the Gobi Desert.
We can imagine how this regular human traffic across the eastern part of the steppe might have represented a stressor to the local wildlife, including the Przewalski horse. This would have been particularly significant in the Middle Ages, marked by the rapid expansion of the Mongol Empire, and during the Manchurian conquest of China and Outer Mongolia from the early 17th century.
These few examples evidence the frequent use of the East Asian steppe for military purposes throughout history, which suggests that warfare activities, concurrently to agricultural development and hunting, continuously shaped the horses’ existence on their native grasslands during the Holocene period.
It is believed that military activities of the 20th century impacted the horses for the worst. From 1921, Mongolia turned to communism thereby becoming the first foreign satellite state of the USSR. From this time and until 1991, the Mongolian steppe was continually used for the stationment and movement of Soviet military forces. The dedicated area was split into different zones all erected along the country’s border with China (see map) and accessible via a network of roads and railways developed by the Russians to that purpose. Some of these military zones were situated in the Khovd-Southern Altai region, which matches the known Mongolian range of the Pzewalski horse from the late 1890’s until extinction. World War II bombings also destroyed part of the captive Takhi stock built from wild individuals captured in Mongolia at the turn of the past century.
The Holocene period has been characterized by an overall relative climatic stability and it is not until the 20th century that evolution towards more aridity in East Asia has been effectively documented. These changes are attributed to both human activities and climate change and, among other mutations, encompass the frequent occurrence of usually exceptional climatic phenomena. This climatic instability is believed to have given the species the final blow at a time when Takhi bands were diminished and scattered across their last known range prior to extinction, the Gobi Desert. The harsh winters of 1945, 1956 and 1965 were listed as black winters in the history of Takhis.
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