Forests (Earth's Natural Biomes) Download Epub Mobi Pdf Fb2
Imelda Rudloff
Currently, the temperate forest biome cools the earth's climate and dampens anthropogenic climate change. However, climate change will substantially alter forest dynamics in the future, affecting the climate regulation function of forests. Increasing natural disturbances can reduce carbon uptake and evaporative cooling, but at the same time increase the albedo of a landscape. Simultaneous changes in vegetation composition can mitigate disturbance impacts, but also influence climate regulation directly (e.g., via albedo changes). As a result of a number of interactive drivers (changes in climate, vegetation, and disturbance) and their simultaneous effects on climate-relevant processes (carbon exchange, albedo, latent heat flux) the future climate regulation function of forests remains highly uncertain. Here we address these complex interactions to assess the effect of future forest dynamics on the climate system. Our specific objectives were (1) to investigate the long-term interactions between changing vegetation composition and disturbance regimes under climate change, (2) to quantify the response of climate regulation to changes in forest dynamics, and (3) to identify the main drivers of the future influence of forests on the climate system. We investigated these issues using the individual-based forest landscape and disturbance model (iLand). Simulations were run over 200 yr for Kalkalpen National Park (Austria), assuming different future climate projections, and incorporating dynamically responding wind and bark beetle disturbances. To consistently assess the net effect on climate the simulated responses of carbon exchange, albedo, and latent heat flux were expressed as contributions to radiative forcing. We found that climate change increased disturbances (+27.7% over 200 yr) and specifically bark beetle activity during the 21st century. However, negative feedbacks from a simultaneously changing tree species composition (+28.0% broadleaved species) decreased disturbance activity in the long run (-10.1%), mainly by reducing the host trees available for bark beetles. Climate change and the resulting future forest dynamics significantly reduced the climate regulation function of the landscape, increasing radiative forcing by up to +10.2% on average over 200 yr. Overall, radiative forcing was most strongly driven by carbon exchange. We conclude that future changes in forest dynamics can cause amplifying climate feedbacks from temperate forest ecosystems.
Forests (Earth's Natural Biomes) download epub mobi pdf fb2
Download File - https://bytlly.com/2yU54q
Abstract:Brazil has a monitoring system to track annual forest conversion in the Amazon and most recently to monitor the Cerrado biome. However, there is still a gap of annual land use and land cover (LULC) information in all Brazilian biomes in the country. Existing countrywide efforts to map land use and land cover lack regularly updates and high spatial resolution time-series data to better understand historical land use and land cover dynamics, and the subsequent impacts in the country biomes. In this study, we described a novel approach and the results achieved by a multi-disciplinary network called MapBiomas to reconstruct annual land use and land cover information between 1985 and 2017 for Brazil, based on random forest applied to Landsat archive using Google Earth Engine. We mapped five major classes: forest, non-forest natural formation, farming, non-vegetated areas, and water. These classes were broken into two sub-classification levels leading to the most comprehensive and detailed mapping for the country at a 30 m pixel resolution. The average overall accuracy of the land use and land cover time-series, based on a stratified random sample of 75,000 pixel locations, was 89% ranging from 73 to 95% in the biomes. The 33 years of LULC change data series revealed that Brazil lost 71 Mha of natural vegetation, mostly to cattle ranching and agriculture activities. Pasture expanded by 46% from 1985 to 2017, and agriculture by 172%, mostly replacing old pasture fields. We also identified that 86 Mha of the converted native vegetation was undergoing some level of regrowth. Several applications of the MapBiomas dataset are underway, suggesting that reconstructing historical land use and land cover change maps is useful for advancing the science and to guide social, economic and environmental policy decision-making processes in Brazil.Keywords: land use; land cover change; Landsat; random forest; time-series; Brazilian biomes
Along with the accumulation of atmospheric greenhouse gases, particularly carbon dioxide, the loss of primary forests and other natural ecosystems is a major disruption of the Earth's system and is causing global concern. Quantifying planetary warming from carbon emissions, global climate models highlight natural forests' high carbon storage potential supporting conservation policies. However, some model outcomes effectively deprioritize conservation of boreal and temperate forests by suggesting that increased albedo upon deforestation could cool the planet. A potential conflict of global cooling vs. regional forest conservation could harm environmental policies. Here we present theoretical and observational evidence to demonstrate that, compared to the carbon-related warming, modeling skills for assessing climatic impacts of deforestation is low. We argue that estimates for deforestation-induced global cooling result from the models' limited capacity to account for the global effect of cooling from evapotranspiration of intact forests. Specifically, transpiration of trees can change the greenhouse effect via small modifications of the vertical temperature profile. However, due to their convective parameterization (which postulates a certain critical temperature profile), global climate models do not properly capture this effect. This may lead to an underestimation of warming from the loss of forest evapotranspiration in both high and low latitudes. As a result, conclusions about deforestation-induced global cooling are not robust and could result in action that immediately worsened global warming. To avoid deepening the environmental crisis, these conclusions should not inform policies of vegetation cover management, especially as studies from multiple fields are accumulating that better quantify the stabilizing impact of natural ecosystems evolved to maintain environmental homeostasis. Given the critical state and our limited understanding of both climate and ecosystems, an optimal policy with immediate benefits would be a global moratorium on the exploitation of all natural forests.
Citation: Makarieva AM, Nefiodov AV, Rammig A and Nobre AD (2023) Re-appraisal of the global climatic role of natural forests for improved climate projections and policies. Front. For. Glob. Change 6:1150191. doi: 10.3389/ffgc.2023.1150191
Figure 2. Map of sites included in this analysis. Symbols are colored according to the number of records at each site. Underlying map shows coverage of evergreen, deciduous, and mixed forests (shading differences; data from Jung et al 2006) and biomes (color differences). Distribution of sites, plots, and records among biomes is shown in the inset.
Notably, net carbon sequestration (\textNEP) exhibits an overall increase with age across the first 100 years of stand development, with more pronounced patterns in temperate than boreal forests (figure 7). This finding is consistent with previous studies showing an increase in \textNEP across relatively young stand ages (Baldocchi et al 2001, Pregitzer and Euskirchen 2004, Luyssaert et al 2008). However, \textNEP is theoretically expected to peak in intermediate-aged stands and thereafter decline, consistent with decelerating C accumulation as stands age (figure 9, Odum 1969), and such declines have been documented (Law et al 2003, Luyssaert et al 2008). The fact that \textNEP values estimated by our models for 100 year-old stands were not systematically different from those of mature stands (lower for temperate broadleaf, higher for temperate conifer, and equal for boreal; figure 9) may be driven by differences in geographical representation across age classes or by the fitting of an inappropriate functional form. Moreover, both biomass and non-living C stocks often continue to increase well beyond the 100 year threshold used here to delimit young and mature stands (Luyssaert et al 2008, Lichstein et al 2009, McGarvey et al 2014). Additional data, including on age trends of deadwood, the organic layer, and soil C will be important to parsing the timing and extend of an age-related \textNEP decrease across forest biomes.
In terms of stocks, our study reveals consistent increases in live biomass stocks with stand age, a pattern that is well-known and expected (e.g. Lichstein et al 2009, Yang et al 2011). This contrasts with more variable age trends in deadwood and the organic layer (figure 9), which depend strongly on the type of disturbance. Disturbances that remove most woody material (e.g. clearcut logging, agriculture) result in negligible deadwood in young stands, followed by a buildup over time (e.g. tropical stands in figures 8 and 9, Vargas et al 2008). In contrast, natural disturbances (e.g. fire, drought, typhoons/hurricanes) can produce large amounts of deadwood (mostly \textD\textW_\textstanding) that slowly decomposes as the stand recovers, resulting in declines across young stand ages (e.g. temperate and boreal stands in figures 8 and 9, Carmona et al 2002). Further study and synthesis of non-living C stocks across biomes, stand ages, and disturbance types will be valuable in giving a more comprehensive picture.
Importantly, ForC and the analyses presented here cover the forests that have received research attention, which are not a representative sample of the world's existing forests, either geographically or in terms of human impacts (Martin et al 2012). Geographically, all variables are poorly covered in Africa and Siberia (figure 2), a common problem in the carbon-cycle community (Schimel et al 2015, Xu and Shang 2016). In terms of human impacts, research efforts tend to focus on interior forest ecosystems (Martin et al 2012), often in permanently protected areas (e.g. Davies et al 2021). Studies of regrowth forests tend to focus on sites where recurring anthropogenic disturbance is not a confounding factor. Yet, fragmentation and degradation impact a large and growing proportion of Earth's forests (FAO and UNEP 2020). Fragmentation and the creation of edges strongly impact forest C cycling (e.g. Chaplin-Kramer et al 2015, Remy et al 2016, Reinmann and Hutyra 2017, Smith et al 2019, Ordway and Asner 2020, Reinmann et al 2020). Partial logging and other forms of non- stand clearing anthropogenic disturbance also alter forest C cycling (e.g. Huang and Asner 2010, Piponiot et al 2016), but are under-studied (Sist et al 2015) and excluded from this analysis. Fragmented and degraded forests do not fit the idealized conceptual framework around which this review is structured (figure 1), yet their representation in models, sustainability assessments, and C accounting systems is critical to accurate accounting of C cycling in Earth's forests (e.g. Huang and Asner 2010, Reinmann and Hutyra 2017, Piponiot et al 2019, Smith et al 2019). Finally, plantation forests account for approximately 3% of Earth's forests (FAO and UNEP 2020) but are not included in this analysis. While it is known that these tend to accumulate biomass faster than naturally regenerating forests (Anderson et al 2006, Bonner et al 2013), their global scale C cycling patterns remain less clearly understood (see Cook-Patton et al 2020). Additional research and synthesis are needed to fill these critical gaps in our understanding of forest C cycling.
aa06259810