Forest type and height are important in shaping the altitudinal change of radial growth response to climate change

Contrasting vegetation response to climate change between two monsoon regions in Southwest China: The roles of climate condition and vegetation height

Southwest China is an important biodiversity hotspot in the world and is controlled by the Pacific and Indian Ocean monsoon in the east and west part respectively. However, how abiotic and biotic factors affect the response of vegetation to climate change in different monsoon regions is still not clear. Here we used the annual change rate of growing-season normalized difference vegetation index (NDVI trend) during 1982-2015 to explore the vulnerability of vegetation (forests and shrubs) activity to climate change in southwest China. We examined NDVI trend in relation to: 1) climate change trends, i.e. annual change rate of water and energy availability, indicated by the Palmer Drought Index (PDSI) and potential evapotranspiration (PET), respectively; 2) climatic condition, i.e. mean PDSI and PET during 1982-2015; 3) vegetation height; 4) biome type; 5) monsoon region. The results showed that NDVI generally increased in the Pacific monsoon region, especially in the southern areas, probably because the vegetation under more productive climate were more resistant to climate change, and also because decreased temperature lead to lower evapotranspiration which alleviated the slight drought trend in this region. In contrast, NDVI generally decreased in the Indian Ocean monsoon region which showed more pronounced drought trend, especially in the tall subalpine and tropical forests of Southeast Tibetan Mountains, which supports the "hydraulic limitation hypothesis" that vegetation height interacted with climate change in affecting vegetation vulnerability. Our analysis highlighted the critical roles of different monsoon systems, climate condition and vegetation height in affecting ecosystem vulnerability. We suggest that the (sub)tropical forests in the Pacific monsoon region may have act as an important carbon sink during the past decades, while the tall forests in Southeast Tibetan mountains (a biodiversity center with high carbon stock) are highly vulnerable to climate change and should have priority in ecosystem protection.

Evaluating the impacts of land use/land cover changes across topography against land surface temperature in Cameron Highlands

The Cameron Highlands has experienced multiple land encroachment activities and repeated deforestation, leading to extensive land-use and land-cover change (LULCC) during the past six decades. This study aims to determine the LULCC against topography in Cameron Highlands between 2009 and 2019 by using geospatial techniques to analyze Landsat 7 (ETM+) and 8 (OLI/TIRS), ASTER GDEM and MODIS imaging sensors. The results showed a decline of 35.98 km² in primary forests over ten years across the Cameron Highlands, while agricultural lands and urban areas flourished by a rise of 51.61 km² and 11.00 km² respectively. It can be noted that the elevation most affected is between 1000 and 1500 m, across all classes. Further results showed the expansion of both agriculture and urban development onto slopes above 35°, leading to an instability of soil structure. In a comparison of the base years of 2009 with 2019, mean LST results have shown temperatures rising by 7.5°C, while an average between 3 and 4°C across the region is recorded. The results obtained provide new information for government bodies and land planners to coordinate their actions without further jeopardizing the environment of the Cameron Highlands.

Gains or Losses in Forest Productivity under Climate Change? The Uncertainty of CO2 Fertilization and Climate Effects

Global warming poses great challenges for forest managers regarding adaptation strategies and species choices. More frequent drought events and heat spells are expected to reduce growth and increase mortality. Extended growing seasons, warming and elevated CO2 (eCO2) can also positively affect forest productivity. We studied the growth, productivity and mortality of beech (Fagus sylvatica L.) and fir (Abies alba Mill.) in the Black Forest (Germany) under three climate change scenarios (representative concentration pathways (RCP): RCP2.6, RCP4.5, RCP8.5) using the detailed biogeochemical forest growth model GOTILWA+. Averaged over the entire simulation period, both species showed productivity losses in RCP2.6 (16–20%) and in RCP4.5 (6%), but productivity gains in RCP8.5 (11–17%). However, all three scenarios had a tipping point (between 2035–2060) when initial gains in net primary productivity (NPP) (6–29%) eventually turned into losses (1–26%). With eCO2 switched off, the losses in NPP were 26–51% in RCP2.6, 36–45% in RCP4.5 and 33–71% in RCP8.5. Improved water-use efficiency dampened drought effects on NPP between 4 and 5%. Tree mortality increased, but without notably affecting forest productivity. Concluding, cultivation of beech and fir may still be possible in the study region, although severe productivity losses can be expected in the coming decades, which will strongly depend on the dampening CO2 fertilization effect.

Growth Trends of Coniferous Species along Elevational Transects in the Central European Alps Indicate Decreasing Sensitivity to Climate Warming

Tree growth at high elevation in the Central European Alps (CEA) is strongly limited by low temperature during the growing season. We developed a tree ring series of co-occurring conifers (Swiss stone pine, Norway spruce, European larch) along elevational transects stretching from the subalpine zone to the krummholz limit (1630–2290 m asl; n = 503 trees) and evaluated whether trends in basal area increment (BAI) are in line with two phases of climate warming, which occurred from 1915–1953 and from 1975–2015. Unexpectedly, results revealed that at subalpine sites (i) intensified climate warming in recent decades did not lead to a corresponding increase in BAI and (ii) increase in summer temperature since 1915 primarily favored growth of larch and spruce, although Swiss stone pine dominates at high elevations in the Eastern CEA, and therefore was expected to mainly benefit from climate warming. At treeline, BAI increases in all species were above the level expected based on determined age trend, whereas at the krummholz limit only deciduous larch showed a minor growth increase. We explain missing adequate growth response to recent climate warming by strengthened competition for resources (nutrients, light, water) in increasingly denser stands at subalpine sites, and by frost desiccation injuries of evergreen tree species at the krummholz limit. To conclude, accurate forecasts of tree growth response to climate warming at high elevation must consider changes in stand density as well as species-specific sensitivity to climate variables beyond the growing season.