Can existing reserves really preserve current levels of biological diversity? – An overview

Mai-He Li* and Norbert Kräuchi

WSL, Swiss Federal Institute for Forest, Snow and Landscape Research, Zuercherstrasse 111, CH-8903 Birmensdorf, Switzerland

*To whom correspondence should be addressed. E-mail: (M-H Li)

Abstract

Paleoecological evidence and paleoclimatic records indicate there was a plant poleward migration in latitude and upward shift in elevation with increased temperatures after the last glaciation (1-3). Four recent papers in Nature (4-7) have shown that global warming over the past 100 years has been having a noticeable effect on living systems. It is causing a poleward and upward shift in the range of many plants and animals (4-6). Moreover, climate change, in connection with other global changes, is threatening the survival of a wide range of species, from mammals to trees (5-7). This raises the question: can existing reserves really preserve current levels of biological diversity in the long term given the present rapid pace of climate change?

Findings from palaeoecological and palaeoclimatic research (1-3) and recent global studies (4-7) indicate that global warming has led to significant shifts in the range of many plants and animals in the past. Over the past 100 years, the global average temperature has increased by approximately 0.6°C and is projected to continue to rise at a rapid rate (8). Most scientists agree that average global temperatures could rise by 1.4 to 5.8°C over this century, with slight warming near the equator and substantial warming at high latitudes (8). Increasing temperatures will lead to corresponding changes in local, regional and global weather patterns, affecting wind velocity, the amount and type of precipitation, and the types and frequency of severe weather events (9). These in turn will result in changes in disturbance regimes, such as fire, drought, and insect outbreak. Climate change alone, and in combination with other global environmental changes, as mentioned above, will impact existing ecosystems (10). Many species may re-adapt to the changed and changing environmental conditions and survive for generations. And many other species may shift their ranges to track climate change. But if environmental conditions change faster than plants can move to more suitable habitats, they will become extinct.

Due to the cyclic changes in climate during the late Quaternary, C3 and C4 plants (11) were alternately dominant in southern India (12) and in the Chinese Loess Plateau (13). As climate warmed 16,000 - 10,000 years ago, tree species moved progressively northward in North America (1-2), and upward in the Northern Andes (14-15), in the wake of the retreating ice. During the warming period at the end of the last glaciation, plant migration rates ranged from 5 to 150 km per century (16). Regarding the human-induced rapid climate change observed recently, various studies have suggested that plants would require range shifts of up to 500 km within this century to keep pace with climate change (17). Theoretically, a rise of 1°C in mean annual temperature could cause a poleward shift of each vegetation zone of about 200 km or an altitudinal shift of about 180 m (18). If this is true, then most species will be outside their existing reserves by the end of this century, assuming temperatures do indeed rise by 1.4 to 5.8°C (8).

Two recent papers emphasise the unfortunate impacts of global climate change on plant migration. Parmesan and Yohe presented a meta-analysis of studies of more than 1,700 species (plants and animals), and found that there have been significant range shifts averaging 6.1 km per decade towards the poles (or 6.1 m per decade upwards) (4). In another meta-analysis of about 150 articles, Root and her co-authors found also that many species are shifting their ranges poleward in latitude and upward in elevation with increasing global temperatures (5). Recent ecological surveys have also found that the alpine timberline has moved upward worldwide during the past 100 years (19-20). However, range shifts of different species take place at different rates. Not all species of an ecosystem can move upward or poleward with the same speed or follow the same migration pattern given their different sensitivities, as a long-term observation study in the French Alps has shown (21).

On the other hand, in a world already transformed by humans, undisturbed habitats exist only as scattered islands surrounded by other forms of land use (e.g. cities, roads, and agricultural activities). All our nature reserves and park systems form a static, spatially fixed network, which cannot be very flexible in the face of global change. What will happen to the rare and unique species inhabiting these sites? Will these species be able to move to other suitable habitats, if these can be found, or are there impassable natural (e.g. mountain-ranges, lakes and oceans) and man-made (e.g. landscapes fragmented into urban and agricultural areas) barriers? Are species populations strong (e.g. population size) enough to launch migrations across largely hostile landscapes? More generally, can our existing nature reserves really preserve the current level of biological diversity under rapid climate change?

The suitable habitats for many rare and endangered plants and animals, such as the Giant Panda in southwest China, are restricted to very small areas isolated from each other by land used in different ways. According to the US Nature Conservancy, half of the endangered plant species in the U.S. are restricted to five or fewer populations (22). The present rate of global warming could mean that many plants and animals currently existing at lower elevations or at lower latitudes will progressively migrate to higher elevations and latitudes. In comparison with plants, the effects of climate change on animals may be even more drastic, as they depend on the availability of both migration route to new territories and on being able to obtain special food types (e.g. some specific species of bamboo for the Giant Panda) on the way to and then in their new “homes”.

Global climate change could drive species to extinction (7, 23). Together with habitat destruction and fragmentation, they could lead to the wholesale extinction of plants and animals trapped in inhospitable landscapes without egresses (7, 24-25). Thomas et al. calculated the rate of species extinctions for a variety of future climate scenarios, and estimated that more than 1 million species will be lost in the world by 2050 (7). In the scenario with a lower limit of 0.8ºC warming in the next 50 years, they claimed that roughly 20% of the 1,103 sampled plant and animal species would become extinct (7). Moreover, climate change and correspondingly changed disturbance regimes will induce the invader activities and facilitate the invasion of other species, as the original systems will be less stable and resistant (6, 23, 25-28). These could further negatively influence existing species through competition and replacement, and finally lead to massive losses in biological diversity on local, regional and global scales (23, 26, 29). For instance, Drayton and Primack reported changes in species composition between 1894 and 1993, in Middlesex Fells (West), an isolated, 400-ha conservation area in metropolitan Boston (30). The total number of plant species fell by 91 during the 100 year period. Out of 422 original plant species recorded in the first census in 1894, 155 species were no longer present in 1993, but 64 new species were recorded on the site in 1993, the majority (36 species; 56%) of which were exotic (30).

Global climate change in combination with other global change factors will cause species emigration from ecosystems and favour the invasion and replacement of non-native species. As a consequence, high rates of species extinction are to be expected in our small, static, spatially fixed and isolated conservation areas (25). This poses a major challenge to those scientists, conservation planners and policy-makers concerned with biodiversity conservation worldwide because, as discussed above, our existing reserve systems do not seem to be in a position to preserve many rare and endangered species in the long term under rapid rate of climate change. We recommend, therefore, expanding reserves towards the poles and/or towards higher altitudes, where possible. Biocorridors (31) or egresses must be planned and set up, regardless of any political boundaries, to link reserves, refuges and areas with a relatively large range of altitudinal and other geographical variation and thus to permit species to shift their ranges with less difficulty in the face of global change, so that a worldwide interconnected system of reserves can be established. This, we believe, would be a major contribution to ensuring the conservation of both species and genetic diversity.

References and Notes

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31. Biocorridors are habitat linkages – lands making a continuous connection between two or more larger land areas that form a corridor with vegetative cover suitable for facilitating the movement of animals and migration of plants.

32. We thank S. Dingwall, K. Novak and many colleagues for critical reading of the manuscript.

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