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Yu K, Chen HYH, Gessler A, Pugh TAM, Searle EB, Allen RB, Pretzsch H, Ciais P, Phillips OL, Brienen RJW, Chu C, Xie S, Ballantyne AP. Forest demography and biomass accumulation rates are associated with transient mean tree size vs. density scaling relations. PNAS Nexus 2024; 3:pgae008. [PMID: 38390215 PMCID: PMC10883769 DOI: 10.1093/pnasnexus/pgae008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Accepted: 12/27/2023] [Indexed: 02/24/2024]
Abstract
Linking individual and stand-level dynamics during forest development reveals a scaling relationship between mean tree size and tree density in forest stands, which integrates forest structure and function. However, the nature of this so-called scaling law and its variation across broad spatial scales remain unquantified, and its linkage with forest demographic processes and carbon dynamics remains elusive. In this study, we develop a theoretical framework and compile a broad-scale dataset of long-term sample forest stands (n = 1,433) from largely undisturbed forests to examine the association of temporal mean tree size vs. density scaling trajectories (slopes) with biomass accumulation rates and the sensitivity of scaling slopes to environmental and demographic drivers. The results empirically demonstrate a large variation of scaling slopes, ranging from -4 to -0.2, across forest stands in tropical, temperate, and boreal forest biomes. Steeper scaling slopes are associated with higher rates of biomass accumulation, resulting from a lower offset of forest growth by biomass loss from mortality. In North America, scaling slopes are positively correlated with forest stand age and rainfall seasonality, thus suggesting a higher rate of biomass accumulation in younger forests with lower rainfall seasonality. These results demonstrate the strong association of the transient mean tree size vs. density scaling trajectories with forest demography and biomass accumulation rates, thus highlighting the potential of leveraging forest structure properties to predict forest demography, carbon fluxes, and dynamics at broad spatial scales.
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Affiliation(s)
- Kailiang Yu
- High Meadows Environmental Institute, Princeton University, Princeton, NJ 08544, USA
- Department of Ecosystem and Conservation Sciences, WA Franke College of Forestry and Conservation, University of Montana, Missoula, MT 59801, USA
| | - Han Y H Chen
- Faculty of Natural Resources Management, Lakehead University, Thunder Bay, ON P7B 5E1, Canada
| | - Arthur Gessler
- Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf CH-8903, Switzerland
| | - Thomas A M Pugh
- Department of Physical Geography and Ecosystem Science, Lund University, Lund S-223 62, Sweden
- School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
- Birmingham Institute of Forest Research, University of Birmingham, Birmingham B15 2TT, UK
| | - Eric B Searle
- Faculty of Natural Resources Management, Lakehead University, Thunder Bay, ON P7B 5E1, Canada
| | | | - Hans Pretzsch
- Chair for Forest Growth and Yield Science, Center of Life and Food Sciences Weihenstephan, Technical University of Munich, Freising 85354, Germany
- Sustainable Forest Management Research Institute iuFOR, University Valladolid, Valladolid 47002, Spain
| | - Philippe Ciais
- Le Laboratoire des Sciences du Climat et de l'Environnement, IPSL-LSCECEA/CNRS/UVSQ Saclay, Gif-sur-Yvette 91191, France
| | | | | | - Chengjin Chu
- State Key Laboratory of Biocontrol, School of Ecology, Shenzhen Campus of Sun Yat-sen University, Shenzhen 518000, China
| | - Shubin Xie
- State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
| | - Ashley P Ballantyne
- Department of Ecosystem and Conservation Sciences, WA Franke College of Forestry and Conservation, University of Montana, Missoula, MT 59801, USA
- Le Laboratoire des Sciences du Climat et de l'Environnement, IPSL-LSCECEA/CNRS/UVSQ Saclay, Gif-sur-Yvette 91191, France
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Pugh TAM, Seidl R, Liu D, Lindeskog M, Chini LP, Senf C. The anthropogenic imprint on temperate and boreal forest demography and carbon turnover. Glob Ecol Biogeogr 2024; 33:100-115. [PMID: 38516343 PMCID: PMC10952773 DOI: 10.1111/geb.13773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Revised: 08/25/2023] [Accepted: 09/28/2023] [Indexed: 03/23/2024]
Abstract
Aim The sweeping transformation of the biosphere by humans over the last millennia leaves only limited windows into its natural state. Much of the forests that dominated temperate and southern boreal regions have been lost and those that remain typically bear a strong imprint of forestry activities and past land-use change, which have changed forest age structure and composition. Here, we ask how would the dynamics, structure and function of temperate and boreal forests differ in the absence of forestry and the legacies of land-use change? Location Global. Time Period 2001-2014, integrating over the legacy of disturbance events from 1875 to 2014. Major Taxa Studied Trees. Methods We constructed an empirical model of natural disturbance probability as a function of community traits and climate, based on observed disturbance rate and form across 77 protected forest landscapes distributed across three continents. Coupling this within a dynamic vegetation model simulating forest composition and structure, we generated estimates of stand-replacing disturbance return intervals in the absence of forestry for northern hemisphere temperate and boreal forests. We then applied this model to calculate forest stand age structure and carbon turnover rates. Results Comparison with observed disturbance rates revealed human activities to have almost halved the median return interval of stand-replacing disturbances across temperate forest, with more moderate changes in the boreal region. The resulting forests are typically much younger, especially in northern Europe and south-eastern North America, resulting in a 32% reduction in vegetation carbon turnover time across temperate forests and a 7% reduction for boreal forests. Conclusions The current northern hemisphere temperate forest age structure is dramatically out of equilibrium with its natural disturbance regimes. Shifts towards more nature-based approaches to forest policy and management should more explicitly consider the current disturbance surplus, as it substantially impacts carbon dynamics and litter (including deadwood) stocks.
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Affiliation(s)
- Thomas A. M. Pugh
- Department of Physical Geography and Ecosystem ScienceLund UniversityLundSweden
- School of Geography, Earth and Environmental ScienceUniversity of BirminghamBirminghamUK
- Birmingham Institute of Forest ResearchUniversity of BirminghamBirminghamUK
| | - Rupert Seidl
- Ecosystem dynamics and forest management groupTechnical University of MunichFreisingGermany
- Berchtesgaden National ParkBerchtesgadenGermany
| | - Daijun Liu
- School of Geography, Earth and Environmental ScienceUniversity of BirminghamBirminghamUK
- Birmingham Institute of Forest ResearchUniversity of BirminghamBirminghamUK
- Department of Botany and Biodiversity ResearchUniversity of ViennaViennaAustria
| | - Mats Lindeskog
- Department of Physical Geography and Ecosystem ScienceLund UniversityLundSweden
| | - Louise P. Chini
- Department of Geographical SciencesUniversity of MarylandCollege ParkMarylandUSA
| | - Cornelius Senf
- Ecosystem dynamics and forest management groupTechnical University of MunichFreisingGermany
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Dearborn KD, Baltzer JL. Unexpected greening in a boreal permafrost peatland undergoing forest loss is partially attributable to tree species turnover. Glob Chang Biol 2021; 27:2867-2882. [PMID: 33742732 DOI: 10.1111/gcb.15608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Accepted: 03/07/2021] [Indexed: 06/12/2023]
Abstract
Time series of vegetation indices derived from satellite imagery are useful in measuring vegetation response to climate warming in remote northern regions. These indices show that productivity is generally declining in the boreal forest, but it is unclear which components of boreal vegetation are driving these trends. We aimed to compare trends in the normalized difference vegetation index (NDVI) to forest growth and demographic data taken from a 10 ha mapped plot located in a spruce-dominated boreal peatland. We used microcores to quantify recent growth trends and tree census data to characterize mortality and recruitment rates of the three dominant tree species. We then compared spatial patterns in growth and demography to patterns in Landsat-derived maximum NDVI trends (1984-2019) in 78 pixels that fell within the plot. We found that NDVI trends were predominantly positive (i.e., "greening") in spite of the ongoing loss of black spruce (the dominant species; 80% of stems) from the plot. The magnitude of these trends correlated positively with black spruce growth trends, but was also governed to a large extent by tree mortality and recruitment. Greening trends were weaker (lower slope) in areas with high larch mortality, and high turnover of spruce and birch, but stronger (higher slope) in areas with high larch recruitment. Larch dominance is currently low (~11% of stems), but it is increasing in abundance as permafrost thaw progresses and will likely have a substantial influence on future NDVI trends. Our results emphasize that NDVI trends in boreal peatlands can be positive even when the forest as a whole is in decline, and that the magnitude of trends can be strongly influenced by the demographics of uncommon species.
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Astigarraga J, Andivia E, Zavala MA, Gazol A, Cruz-Alonso V, Vicente-Serrano SM, Ruiz-Benito P. Evidence of non-stationary relationships between climate and forest responses: Increased sensitivity to climate change in Iberian forests. Glob Chang Biol 2020; 26:5063-5076. [PMID: 32479675 DOI: 10.1111/gcb.15198] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2019] [Revised: 04/27/2020] [Accepted: 05/16/2020] [Indexed: 06/11/2023]
Abstract
Climate and forest structure are considered major drivers of forest demography and productivity. However, recent evidence suggests that the relationships between climate and tree growth are generally non-stationary (i.e. non-time stable), and it remains uncertain whether the relationships between climate, forest structure, demography and productivity are stationary or are being altered by recent climatic and structural changes. Here we analysed three surveys from the Spanish Forest Inventory covering c. 30 years of information and we applied mixed and structural equation models to assess temporal trends in forest structure (stand density, basal area, tree size and tree size inequality), forest demography (ingrowth, growth and mortality) and above-ground forest productivity. We also quantified whether the interactive effects of climate and forest structure on forest demography and above-ground forest productivity were stationary over two consecutive time periods. Since the 1980s, density, basal area and tree size increased in Iberian forests, and tree size inequality decreased. In addition, we observed reductions in ingrowth and growth, and increases in mortality. Initial forest structure and water availability mainly modulated the temporal trends in forest structure and demography. The magnitude and direction of the interactive effects of climate and forest structure on forest demography changed over the two time periods analysed indicating non-stationary relationships between climate, forest structure and demography. Above-ground forest productivity increased due to a positive balance between ingrowth, growth and mortality. Despite increasing productivity over time, we observed an aggravation of the negative effects of climate change and increased competition on forest demography, reducing ingrowth and growth, and increasing mortality. Interestingly, our results suggest that the negative effects of climate change on forest demography could be ameliorated through forest management, which has profound implications for forest adaptation to climate change.
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Affiliation(s)
- Julen Astigarraga
- Forest Ecology and Restoration Group, Department of Life Sciences, University of Alcala, Alcalá de Henares, Spain
| | - Enrique Andivia
- Department of Biodiversity, Ecology & Evolution, Complutense University of Madrid, Madrid, Spain
| | - Miguel A Zavala
- Forest Ecology and Restoration Group, Department of Life Sciences, University of Alcala, Alcalá de Henares, Spain
- Franklin Institute, University of Alcala, Alcalá de Henares, Spain
| | - Antonio Gazol
- Instituto Pirenaico de Ecología (IPE-CSIC), Zaragoza, Spain
| | - Verónica Cruz-Alonso
- Forest Ecology and Restoration Group, Department of Life Sciences, University of Alcala, Alcalá de Henares, Spain
- CREAF, Centre de Recerca Ecològica i Aplicacions Forestals, Cerdanyola de Vallès, Spain
| | | | - Paloma Ruiz-Benito
- Forest Ecology and Restoration Group, Department of Life Sciences, University of Alcala, Alcalá de Henares, Spain
- Environmental Remote Sensing Group, Department of Geology, Geography and Environment, University of Alcala, Alcalá de Henares, Spain
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