| 1. |
- Gärtner, Antje, et al.
(författare)
-
Temperature and Tree Size Explain the Mean Time to Fall of Dead Standing Trees across Large Scales
- 2023
-
Ingår i: Forests. - : MDPI. - 1999-4907. ; 14:5
-
Tidskriftsartikel (refereegranskat)abstract
- AbstractDead standing trees (DSTs) generally decompose slower than wood in contact with the forest floor. In many regions, DSTs are being created at an increasing rate due to accelerating tree mortality caused by climate change. Therefore, factors determining DST fall are crucial for predicting dead wood turnover time but remain poorly constrained. Here, we conduct a re-analysis of published DST fall data to provide standardized information on the mean time to fall (MTF) of DSTs across biomes. We used multiple linear regression to test covariates considered important for DST fall, while controlling for mortality and management effects. DSTs of species killed by fire, insects and other causes stood on average for 48, 13 and 19 years, but MTF calculations were sensitive to how tree size was accounted for. Species’ MTFs differed significantly between DSTs killed by fire and other causes, between coniferous and broadleaved plant functional types (PFTs) and between managed and unmanaged sites, but management did not explain MTFs when we distinguished by mortality cause. Mean annual temperature (MAT) negatively affected MTFs, whereas larger tree size or being coniferous caused DSTs to stand longer. The most important explanatory variables were MAT and tree size, with minor contributions of management and plant functional type depending on mortality cause. Our results provide a basis to improve the representation of dead wood decomposition in carbon cycle assessments.
|
|
| 2. |
- Jaakkola, Erica, et al.
(författare)
-
Spruce bark beetles (Ips typographus) cause up to 700 times higher bark BVOC emission rates compared to healthy Norway spruce (Picea abies)
- 2023
-
Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4189. ; 20:4, s. 803-826
-
Tidskriftsartikel (refereegranskat)abstract
- Biogenic volatile organic compound (BVOC) emissions from trees subjected to biotic stress are higher compared to healthy trees, and they may also have a different compound composition. This in turn affects atmospheric chemistry and can lead to either positive or negative feedback to the climate. Climate change favors the abundance of the European spruce bark beetle (Ips typographus) which attacks the bark of Norway spruce (Picea abies) trees, causing induced BVOC emissions from the trees as a response to the insect stress. Here, results are reported from a study analyzing the difference in emission rates between healthy and bark-beetle-infested Norway spruce trees, changes in emission rates over time since the infestation started, and differences in emission rates from bark-beetle-drilled entry and exit holes.Bark chamber measurements on both healthy and infested trees were performed during the summer of 2019 at Hyltemossa and Norunda research stations in Sweden. The measurements showed that induced BVOC emissions following the bark beetle infestation were dominated by entry hole emissions in the early growing season and exit hole emissions in the later season. The results showed a significant difference in emission rates between healthy and infested trees during both seasons. The seasonal average standardized BVOC emission rate of healthy trees was 32 ± 52 µg m−2 h−1 (mean ± standard deviation), while the average standardized BVOC emission rates of infested trees were 6700 ± 6900 and 2000 ± 1300 µg m−2 h−1 during the early and late season respectively. BVOC emission rates were highest at the start of the infestation and decreased exponentially with time, showing induced emission rates for up to 1 year after which the emission rates were similar to those from healthy bark. Constitutive needle emission rates from healthy trees were found to be 11 times higher than bark emissions from healthy trees. However, when Norway spruce trees were infested, the bark emission rates were instead 6 to 20 times higher than the needle emissions, causing substantial increases in the total tree BVOC emission rate. This could lead to high impacts on atmospheric processes, specifically the formation of secondary organic aerosols, which have a higher yield from some monoterpene compounds, which increased from infested trees.
|
|
| 3. |
- Li, Zhao, et al.
(författare)
-
Minimum carbon uptake controls the interannual variability of ecosystem productivity in tropical evergreen forests
- 2020
-
Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181. ; 195
-
Tidskriftsartikel (refereegranskat)abstract
- Tropical evergreen forests contribute an important part to the interannual variability (IAV) of the global terrestrial gross primary productivity (GPP). Due to its year-round growing-season, high minimum carbon uptake (GPPmin) and dry season greening-up, the key processes driving the GPP variability across seasonal to interannual scale are still in debate. Here, we analyzed the time-series of FLUXCOM GPP (1980–2013), sun-induced fluorescence (SIF; 2001–2013) and site-level GPP measurements in three tropical evergreen forests regions (i.e., Amazon, Africa, and Southeast Asia). We decomposed the annual accumulated GPP into the basic and recurrent GPP, which represent the accumulated minimum and seasonal vegetation productivity, respectively. Then we quantified the proportion of each component and estimated the contribution to the IAV of GPP. We find that the basic GPP overwhelmed the recurrent GPP with the averaging ratio of 4.2:1 across the global tropical regions, and dominated the IAV of annual total GPP in 83.7% of the tropical evergreen forest areas. The high contribution of the basic GPP resulted from the great sensitivity of GPPmin to rainfall changes among years. The decomposition of the basic and recurrent GPP sheds new light on the understanding of tropical GPP variability in responding to climate change at seasonal and annual scale. Our study highlights the critical role of the GPPmin in shaping temporal dynamics of the annual GPP in tropical forests and emphasizes the importance of managing tropical forest of the shifting periods between wet-dry seasons in global tropical regions.
|
|
