The bioclimatic stratification of Myanmar highlights the climatic diversity in the country, from the Extremely Cold and Mesic zone, above the alpine treeline on the tallest mountains in the north of the country, to the Extremely Hot and Moist zone, until recently largely occupied by tropical lowland rainforest, in the south, and the Extremely Hot and Xeric zone, with remnant patches of savanna and deciduous forests, in the center of the country. Representation of the bioclimatic zones and strata in protected areas is currently very uneven, with >30% of the areas of four coolest zones being protected and <1% of the two driest. To a large extent this reflects human pressures within these zones, with the cool high mountains sparsely populated, while the drier areas have had dense populations for centuries. The hyperdiverse Extremely Hot and Moist zone in the south is also underrepresented in terms of percentage area (2%) and is now under threat from expanding plantations [25
]. The percentage of the total land area protected in Myanmar (<6%) is also small, by both regional and global standards, and well below both the 17% area target (Aichi target 11) agreed by the Convention on Biological Diversity for 2020 and the proposed 30% area target for 2030 [41
The three earth system models used in this study all project an acceleration of recent warming trends across the whole of Myanmar, but with a fairly large spread (<1.5 °C) among models in the amount of warming. This spread is even wider for rainfall, in terms of both the amount and the spatial pattern of increase and decreases. In most projections and over most of Myanmar, rainfall is projected to increase, but the projected increases are small relative to both current interannual variation and variability over the last 200 years [40
]. Changes in the bioclimatic stratification are therefore dominated by the increases in temperature, resulting in an upwards shift in average elevation for all zones and strata. The hottest zones increase in area while the cooler zones decline, with the coldest disappearing with two models. Changes in the strata are greater, reflecting their narrower bounds, but mostly model-dependent. Up to a third of Myanmar’s land area will change bioclimatic zone by 2070, depending on the model and RCP, while up to half will change stratum. Projected changes within the protected area system are similar to those in the country as a whole, but individual reserves are highly variable, with a complete switch of bioclimatic zone or stratum in some small reserves, as well as some larger ones with a low elevational range.
The consequences of these climatic changes for biodiversity depend on how effective the bioclimatic stratification is as a proxy for species and ecosystems, both now and in the future. Too little biodiversity data is available in Myanmar to validate this assumption for the present day, but there is support from studies in similar ecosystems in southwest China [31
] and the transboundary Kailash Sacred Landscape of China, India, and Nepal [42
], as well as studies in other parts of the world. Validation of future predictions is not possible, but theory, paleoecological evidence, and some observations of responses to recent climate change suggests that the populations of many well-dispersed species will track changes in climate across the landscape [14
]. However, poorly dispersed species and those with long life-cycles will not be able to keep up. In particular, most of the individual trees that will dominate Myanmar’s forests in 2050 and 2070 are already growing and cannot move, although a majority of 20 tree species studied in Natma Taung National Park had a higher proportion of juveniles at the upper end of their ranges, suggesting that their populations will eventually shift upslope [43
]. Failure to track rapid climate change creates ecosystems that are not in equilibrium with the climate of the time, with consequences that are currently unclear, but are likely to be include slower growth and increased vulnerability to pests and diseases [14
An additional complication comes from the increase in carbon dioxide concentrations, which is not only the largest single driver of climate change, but also has a direct impact on plant physiology and thus on plant growth, competition, and vegetation [44
]. This means that bioclimate alone cannot predict future vegetation structure and species composition, which will also depend on the CO2
concentration. In other words, future analogues of modern climates are not necessarily ecologically equivalent. Rising atmospheric CO2
does not impact animals directly, but they will be impacted indirectly through changes in vegetation structure and composition. A recent modeling study which simulated the impacts of climate change on vegetation in South Asia (including Myanmar), with and without increasing CO2
, found that simulations with increasing CO2
resulted in transitions from savanna into forest and deciduous forest into evergreen forest which did not occur in the absence of elevated CO2
]. The vegetation model used (aDGVM2) does not include nutrient limitation, so the impacts of elevated CO2
may be overestimated, but woody invasion of savannas in other parts of the world has been attributed, in part, to this mechanism [45
The disappearance from Myanmar of the coldest bioclimatic zone, Extremely Cold and Wet, will have little direct impact on biodiversity, since this represents the summit zone of Mt Khakaborazi, which is barren rock and ice. In contrast, the large declines in the areas of the next three coolest zones, in both the country as a whole and the protected area system, will substantially reduce the area available for species adapted to high-mountain forest and alpine habitats in Myanmar. Upward shifts of several hundreds meters in steep topography, where they represent horizontal movements of a kilometer or two, may be within the dispersal capacities of most plant and animal species, but the area available declines with altitude on most mountains, and reaches zero at the summit. On isolated high mountains, such as Mt Victoria (Natma Taung) (3074 m) in southwest Myanmar, endemic species found only near the summit face potential mountain-top extinction. At the other extreme, species occurring in protected areas with little or no elevational range, because of flat topography (such as Chatthin and Shwesettaw Wildlife Sanctuaries) or small size (such as Chungponkan Wildlife Sanctuary, Lawkanada Sanctuary, and Wetthikan Bird Sanctuary), are threatened by the total loss of the bioclimatic zones or strata to which they are adapted, as the entire protected area undergoes a shift. Species adapted to open forests and savanna, such as the endangered Eld’s deer (Rucervus eldi thamin) may be particularly vulnerable to woody encroachment and canopy closure, as a result of climate change and/or rising atmospheric CO2 (see above).
The use of climatic data as a surrogate for biodiversity is not ideal, since bioclimatic zones and strata are not, in themselves, targets for conservation. This approach was necessitated by the patchy availability of biodiversity data in Myanmar. As more such data becomes available, it should be possible to calibrate the bioclimatic stratification in a way that makes it more useful for conservation planning [46
]. Where biodiversity data is lacking, the addition of geological information would be an improvement on using just climate as a surrogate. Myanmar’s extensive karsts, for example, support numerous narrow-range endemic species whose presence could not be predicted from climate alone.
It would be possible to make recommendations for additional protected areas and the expansion of existing ones based on this study, although recommendations based on climate variables alone should only be a first step. The vulnerability of the existing protected areas depends not only on their exposure to climate change, as assessed here, but also on their resilience (indicated by size, isolation, topographic variability, etc.) and capacity for adaptation [47
]. Clearly, both the total area and the representativeness of the protected area system need to be increased, and connectivity across climatic gradients should be enhanced to permit species movements [11
]. Extensive restoration of degraded vegetation, both passively (by removing the causes of degradation) and actively (by planting), may be needed, particularly in some lowland and drier areas [48
]. Reintroduction of locally extirpated animal species may be practical where hunting can be controlled.
However, the protected area system in Myanmar is not currently limited by technical knowledge, but rather reflects, to a large extent, the legacies of decades of armed internal conflicts, some of which continue at a lower level, despite cease fires and peace agreements. These conflicts have limited the collection of biodiversity data and continue to make it very difficult to create new protected areas agreed by both the central and regional governments. As in many other countries, biodiversity protection in Myanmar is intimately linked with a variety of political, social, and economic issues, and progress in conservation will depend on progress in solving all these. Experience in some of these countries suggests that the best way forward is to take the technical knowledge—in this case, from climate change science—as a starting point and then to focus on policy, planning, and management issues in dialogue with major stakeholders [49
Finally, we focus in this paper on protected areas, but the same climatic changes will also impact agricultural and urban areas, both directly and through their impacts on the supply of water and other services from natural ecosystems. Biodiversity conservation is easier in remote, unpopulated, areas, but arguably most important near to where most people live. Natural and restored ecosystems can not only provide a reliable source of water, but also reduce the risk from floods, cyclones, and other extreme weather events, regulate local climates, and provide accessible recreational and tourism opportunities, and associated economic benefits for local people [50