Forest Growth Rates Research Articles

The Bionomic Equilibrium Model for Balancing Forest Conservation and Economic Growth: Empirical Evidence from Indonesia

Abstract: The objective of this study is to balance forest conservation with economic growth while accounting for the rate of deforestation. The methodology employed in this research utilizes a mathematical modeling approach, specifically adopting the logistic model to represent forest growth rates. In addition, numerical analysis is applied to illustrate the impact of economic activities on forest areas. The data used in the study consist of deforestation rates in Indonesia from 2000 to 2021. The findings indicate that the rate of economic activity in forested areas is directly proportional to the reduction in forest area. If the rate of deforestation due to economic activity approaches the forest growth rate, the likelihood of forest area reduction increases, and forest depletion will occur if the two rates become equal. To resolve the dilemma between forest conservation and economic growth, this study proposes a solution consisting of three key steps: (1) establishing a minimum forest area that is strictly protected from economic exploitation; (2) setting the ratio between forest growth rates and economic activity rates as a primary foundation for ensuring sustainable forest conservation and economic development; and (3) calculating environmental costs, such as reforestation, based on the proportional relationship between deforestation rates and forest growth rates. Keywords: Deforestation, Environmental Cost, Economy, Forest, Growth Rate

Influence of Climatic Variables on the Stem Growth Rate in Trees of a Tropical Wet Forest

The growth of tropical wet forests has a significant relationship with the climate; aspects such as temperature and precipitation affect the species; however, few studies have characterized the stem growth rate of tropical tree species. This study’s objective was to characterize the effects of climatic variation on the interannual stem growth rate of eight species in tropical wet forest. Six trees per species were selected (n = 48 trees), and a dendrometer was installed to measure diametric growth bi-monthly between 2015 and 2018 (3 years), complemented with environmental measurements, to determine their growth equations from environmental variables and, finally, to define the relationship between the wood density and the stem growth rate. The results showed an average stem growth from 0.45 to 4.35 mm year−1, and 40 to 70% growth occurred in the months with the highest rainfall. Also, species with higher wood densities were found to have lower stem growth rates. Finally, the analysis of stem growth rate showed a significant relationship in all species between the variables of temperature and precipitation (R2 adj 0.88 to 0.96). Our results suggest that species with greater stem growth rates in wet tropical forests are more susceptible to climate changes, which may affect their dynamics in the face of potential drought scenarios and heat waves associated with climate change.

The Minimum Target Diameter and the Harvest Age of Oak Natural Secondary Forests in Different Sites Conditions: Case Study in Hunan Province, China

Maintaining permanent forest canopy cover and eventually harvesting timber by predetermined target diameter are often considered as a prototype for future management of the oak natural forest. However, target diameters and harvest age based on average forest growth rates from wide geographical areas often hamper improved management of oak forests. In this study, based on the sampling of 129 target trees from 51 oak natural secondary forest plots in Hunan Province, China, an individual-tree DBH (diameter at breast height) growth model of oak target trees was developed, and the site type (41 levels) was related to the model as random effects by a nonlinear mixed-effects approach. Moreover, the 41 site types were clustered into four site type groups (STG1, STG2, STG3, and STG4) by the K-means clustering algorithm to improve the model performance and practicality. With the help of the model, the five target diameters (including 24, 30, 40, 50, and 60 cm) were simulated in each of the four STGs, and the minimum target diameter was determined for each STG based on the theory of quantitative maturity. In the four STGs, the harvest age of the 24 cm diameter target ranged from 30 to 51 years; the harvest age of the 60 cm target diameter ranged from 131 to 220 years, with the oaks failing to reach 60 cm in the lowest-quality STG4; the minimum target diameter ranged from 21 cm to 29 cm. Results showed that lower-quality sites exclude higher target diameters from optimal harvesting strategies, in contrast to the higher target diameter as a more reasonable strategy in higher quality sites, and that the minimum target diameter is significantly influenced by site conditions. Therefore, it is necessary to develop a diverse target-diameter-harvesting strategy adapted for the complex site conditions of oak forests in Hunan Province towards site-specific timber management to improve the sustainability of timber production in oak forests.

Long-term and large-scale ecological restoration projects shaped the spatial heterogeneity in new forests

The implementation of long-term ecological restoration projects and policies over the past two decades has played a crucial role in advancing the achievement of Sustainable Development Goal 15. However, the resulting dynamics of new forests remain unclear. In this study, we initially examined the distribution and sources of new forests and subsequently investigated the gross primary productivity (GPP) variations within these forested regions. We discovered that new forests are mainly converted from previously cultivated land, which is primarily due to the Grain for Green Project. The new forests are mainly distributed in mid-low altitude areas and gentle slope regions, indicating that accessible areas are prone to damage but also easy to recover. Over approximately two decades of ecological restoration projects, the GPP of new forests has significantly increased trends and the growth rates of new forests vary significantly in different climatic zones. Moreover, the GPP and growth rates of new forests displayed spatial heterogeneity. Specifically, the GPP in the new forests was highest in the eastern region, followed by the central south region, while the northwest region had the lowest GPP. Meanwhile, the southwest region shows the highest GPP growth rate among new forests, while the northwest region has the slowest growth rate. Furthermore, the average GPP of new forests is lower than stable forests, but new forests in China grow faster (3.735 vs. 2.587), highlighting their substantial carbon potential. These findings indicate that it's crucial to account for variations in stand and forest change rates when modeling forest carbon sequestration potential.

Predicting net growth rates in boreal forests using Landsat time series and permanent sample plot data

Abstract Increasing temperature and changes in water dynamics are bringing uncertainty regarding the future productivity of boreal forests, even in the absence of stand-replacing disturbances. There is accumulating evidence that water deficits caused by warmer summer temperatures are linked to decreases in the growth rate of boreal tree species in some regions. In this context, it is essential to provide forest professionals with a means of monitoring net forest growth rates in undisturbed areas and at the scale of a management unit in order to determine where and when changes in growth are taking place. This is challenging using conventional forest inventory approaches. In this study, we use Landsat time series and data from permanent sample plots (PSP) to develop spatially explicit estimates of annual net basal area growth at a 30-m spatial resolution for a forest management unit in Canada. An ordinary least square regression model was developed using data from 120 PSPs and validated on an independent set of 60 PSPs, with R2 values of 0.61 and 0.58, respectively. Applying the model over a 586 607-ha study area revealed considerable temporal and spatial variability in the predicted growth rates and their evolution through time. There was an overall decline in predicted growth rates over time, with this trend corroborated by the PSP data and attributed to the ageing demographics of the forests in the study area. This variability was related to forest development stage, species composition, and structural attributes derived from light detection and ranging (LiDAR). The information generated by the suggested approach can help to improve yield predictions, optimize rotation lengths, and allow for the identification of target areas where silvicultural interventions aimed at maintaining or enhancing growth could be conducted.

Measuring Tree Diameter with Photogrammetry Using Mobile Phone Cameras

Tree inventories are a cornerstone of forest science and management. Inventories are essential for quantifying forest growth rates, determining biomass and carbon stock variation, assessing species diversity, and evaluating the impacts of both forest management and climate change. Recent advances in digital sensing technologies on mobile phones have the potential to improve traditional forest inventories through increased efficiency in measurement and transcription and potentially through increasing participation in data collection by non-experts. However, the degree to which digital sensing tools (e.g., camera-enabled smartphone applications) can accurately determine the tree parameters measured during forest inventories remains unclear. In this study, we assess the ability of a smartphone application to perform a user-assisted tree inventory and compare digital estimates of tree diameter to measurements made using traditional forestry field sampling approaches. The results suggest that digital sensing tools on mobile phones can accurately measure tree diameter (R2 = 0.95; RMSE = 2.71 cm compared to manual measurements) while saving time during both the data-collection stage and data-entry stage of field sampling. Importantly, we compare measurements of the same tree across users of the phone application in order to determine the per-user, per-tree, and per-species uncertainty associated with each form of measurement. Strong agreement between manual and digital measurements suggests that digital sensing technologies have the potential to facilitate the efficient collection of high-quality and auditable data collected by non-experts but with some important limitations compared to traditional tree measurement approaches. Most people in the world own a smartphone. Enabling accurate tree inventory data collection through mobile phones at scale can improve our understanding of tree growth and biomass accumulation and the key factors (e.g., climate change or management practices) that affect these processes, ultimately advancing forest science and management.

Middle-aged forests in the Eastern U.S. have significant climate mitigation potential

Middle-aged forests in the Eastern U.S. are broadly defined to consist of forests between the regeneration phase following harvest or disturbance, and an older phase with forests composed of large trees, complex structure, and increasing natural mortality. Study objectives were to develop new carbon accumulation curves based on recent inventory data that represent the actual growth rates of forests as they advance beyond middle age; quantify the projected carbon sink from reducing or increasing harvest of middle-aged forests; and disseminate credible estimates of future carbon stocks in ecosystems and harvested wood products to support policies designed to enhance the role of forests in removing carbon dioxide from the atmosphere and storing it securely. We found that middle-aged Eastern U.S. forests could continue to accumulate carbon for many decades or several centuries in the absence of harvesting, with relatively low risk of natural disturbances. Compared with a recent study that estimated a potential increase in biomass of only 22%, and some analyses that anticipate significant increases in risks from natural disturbances, our results indicate a potential increase of about 100% over current biomass stocks by 2100. Temperate Continental forests have greater potential to increase carbon stock over longer time periods than Subtropical Humid forests. Results from scenario analyses showed that in the near term of 20–40 years, reducing harvest will yield the greatest reduction in net greenhouse gas emissions compared with business as usual. Under an extreme “no-harvest” scenario, C sequestration could increase by about 20 TgC yr−1 in Temperate Continental forests by 2050, and by about 30 TgC yr−1 in Subtropical Humid forests over the same time period. In contrast, a scenario of tripling harvest would increase C emissions by 30 and 60 TgC yr−1 in the Temperate Continental and Subtropical Humid ecozones by 2050, respectively. In the longer term of 80 or so years, all scenarios and “business as usual” converge toward similar impacts on greenhouse gas emissions, nearing neutrality in the Subtropical Humid ecozone but separated by about 30 TgC yr−1 in the Temperate Continental ecozone. Our estimated annual emission reduction from stopping harvest over the 73 million ha of middle-aged forests amounts to 117 Mg CO2 per year in 2050, equivalent to about 7% of the emissions from using fossil energy in the two ecozones. Increasing harvest would have the opposite effect of increasing emissions by a similar magnitude in 2050. How middle-aged forests in the Eastern U.S. are managed can clearly affect their contribution to achieving net-zero GHG emissions by 2050 and beyond.

Assessing future climate trends and implications for managed forests across Canadian ecozones

Climate change interacts with ecological processes leading to changes in tree and forest growth rate, biome shifts and species composition, all of which are influenced by disturbances. This study explores future overarching climate trends of eight of Canada's ecozones containing managed forests. For the 2071 to 2100 period, climate projections indicate a warming trend of up to an additional 5.5 °C and an overall increase in annual precipitation. Future trends suggest marked contrast between coastal and interior forests and polarization between western and eastern forests. Warmer temperatures, accumulating degree-days above 5 °C and frost-free days suggest longer and drier growing seasons and greater risk of drought particularly in moisture-limited areas such as montane cordillera, taiga shield and boreal shield ecozones. Warmer temperatures and rising precipitation combined with less snow suggest shorter and wetter future winters. This indicates greater risk of rain-on-snow and freeze-thaw events, flooding and landslides particularly in coastal ecozones. We discuss how these projections are likely to result in shifts in dominant species and abundance, which when coupled with the cumulative effects of future disturbances, is likely to alter future forest dynamics and impact harvestable wood volumes for Canada's forestry industry.

Spatio-Temporal Changes in Forest Area and Its Ecosystem Service Value in Ganzi Prefecture, China, in the Period 1997–2017

It is possible to manage the forest ecosystem and promote sustainable development by keeping track of spatio-temporal fluctuation in the forest area and its ecosystem service value (ESV). The forest ecology of Ganzi Tibetan Autonomous Prefecture (Ganzi Prefecture), which is located in the northern Hengduan Mountains region, i.e., China’s most important ecological functional area, has seen significant alteration during the past 20 years. However, little is known about how the forest and its ESV evolve. We obtained data regarding Ganzi Prefecture’s forests using visual interpretation of remote sensing images derived from 1997, 2007, and 2017, and we evaluated the spatial–temporal changes in the forest ESV from 1997 to 2017 using global value coefficients and adjusted local value coefficients. The results revealed that (1) from 1997 to 2017, the forest area of Ganzi Prefecture increased by 6729.95 km2, and the forest growth rate was 336.50 km2/a, while (2) from 1997 to 2017, the forest ESV in Ganzi Prefecture experienced an overall increase of 257.59 × 108 yuan. The primary driver of the forest ESV increase was the implementation of forestry ecological engineering and protection policies. (3) Finally, the spatial distribution of the forest ESV revealed that the forest ESV density increased during this period, with the most significant increase occurring in Yajiang. The forest ESV was scattered with the highest density in Yajiang and the lowest density in Shiqu. This study emphasizes how crucial forest ecosystems are to Ganzi Prefecture’s mechanisms for maintaining life. It provided a scientific basis for the sustainable management of the forest ecosystem in the Hengduan Mountains.

The Effect of Forest Growth Rate on Climate Change Impacts of Logging Residue Utilization

Biofuel is encouraged because of its low impact on climate change. A new framework was developed to accurately assess the climate change impacts (CCI) of biofuel by integrating the atmospheric carbon cycle model and vegetation carbon dynamic models. Forests with different growth rates (fast, medium, slow) and three collection intensities (71%, 52%, 32%) of logging residues were presumed to test the performance of this framework. The CCI of biofuel was analyzed under two functional units: 1 GJ of biofuels and 1 ha of forests to supply biofuels. According to this study, increasing the forest growth rate could decrease the CCI in both functional units. Increasing the collection intensity could decrease the CCI of 1 GJ of biofuel but increase the CCI of 1 ha of forest land (unless the impacts were negative in fast-growth forests with high and medium collection intensities). Producing bioethanol resulted in a lower CCI (−3.1–67.7 kg CO2 eq/GJ) compared to bio-diesel (29.3–94.7 kg CO2 eq/GJ). Hence, collecting all available logging residues (without inhibiting forest regrowth) to produce low CCI biofuels such as bioethanol was found to be the optimal option for achieving high mitigation effects.

Patterns of regional site index across a North American boreal forest gradient

Forest structure—the height, cover, vertical complexity, and spatial patterns of trees—is a key indicator of productivity variation across forested extents. During the 2017 and 2019 growing seasons, NASA’s Arctic-Boreal Vulnerability Experiment collected full-waveform airborne LiDAR using the land, vegetation and imaging sensor, sampling boreal and tundra landscapes across a variety of ecological regions from central Canada westward through Alaska. Here, we compile and archive a geo-referenced gridded suite of these data that include vertical structure estimates and novel horizontal cover estimates of vegetation canopy cover derived from vegetation’s vertical LiDAR profile. We validate these gridded estimates with small footprint airborne LiDAR, and link >36 million of them with stand age estimates from a Landsat time-series of tree-canopy cover that we confirm with plot-level disturbance year data. We quantify the regional magnitude and variability in site index, the age-dependent rates of forest growth, across 15 boreal ecoregions in North America. With this open archive suite of forest structure data linked to stand age, we bound current forest productivity estimates across a boreal structure gradient whose response to key bioclimatic drivers may change with stand age. These results, derived from a reduction of a large archive of airborne LiDAR and a Landsat time series, quantify forest productivity bounds for input into forest and ecosystem growth models, to update forecasts of changes in North America’s boreal forests by improving the regional parametrization of forest growth rates.

Community Structure and Growth Rate of Korean Quercus mongolica Forests by Vegetation Climate Zone

Q. mongolica forests are representative forest types in Korea, belonging to the intermediate succession stage with the highest species diversity. Identifying the community structure and growth rate of Q. mongolica forests by the vegetation climate zone can help in planning efficient forest restoration strategies for each vegetation climate zone. The proportions of major communities based on the vegetation climate zones newly adjusted by the Korea National Arboretum in 2020 were determined. Major dominant species were identified in Quercus mongolica forests in which Q. mongolica dominates by more than 50% by analyzing the importance based on the basal area of the trees using data from the 7th National Forest Inventory Survey. The basal area growth rate was analyzed for permanent sample plots from the 5th to 7th National Forest Inventory Surveys. The analysis revealed statistically significant differences in the basal area growth rate by vegetation climate zone over a 10-year period. However, it should be noted that Q. mongolica forests with younger age classes were more abundant in the warm southern temperate zone; thus, it is likely that age class has a greater effect on the rate of basal area increase than the vegetation climate zone.

Forest Stand Composition of the Tapanuli Orangutan (Pongo tapanuliensis) Habitat in the Nature Reserves

The Forest areas of Dolok Sipirok Nature Reserve (DSNR) and Dolok Sibual-Buali Nature Reserve (DBNR) are part of Batang Toru forest landscape which is also the habitat of some protected and endangered wildlife such as Tapanuli orangutans (Pongo tapanuliensis). However, the forest has continued to experience widespread pressure and degradation or reduction, mainly due to forest conversion. Therefore, it is very notable to assess the composition of forest vegetation of DSNR and DBNR considering their very important role for the survival of the Tapanuli orangutan populations. The composition of forest vegetation in this research is known by vegetation analysis. The method vegetation analysis used is line transect. The length of the line transect is 1000 m which consists of 10 plots of each transect with a distance between plots of 100 m. Measurements are carried out on the growth rate of seedlings, saplings, poles and trees. Furthermore, the processing of vegetation analysis data is carried out to find out the Important Value Index (IVI), diversity index (H’), evenness (E) and richness (d) of vegetation species in the research area. The results showed that the composition of orangutan habitat vegetation in DSNR consisted of 107 species from 39 families, while DBNR forest consisted of 117 species from 45 families. Tree Syzygium sp1. species consistently have the highest IVI scores at all forest vegetation growth rates of both reserves. The diversity, evenness and richness of DBNR forest vegetation species tends to be higher than DSNR forest.

Fast-growing forest management to regulate the balance between wood production and water supply

Increasingly, fast-growing forest plantations are able to support the wood supply but may simultaneously reduce water availability. The trade-off between wood production and water supply is more evident in areas with low water availability, high seasonal variation, or high water demand from local communities. The management regime adopted in forest plantations can either increase or reduce this trade-off. Thus, we assess herein the water and wood supply under different fast-growing forest plantation management regimes to understand how forest management practices can balance the provision of these services. The study was conducted at two catchments with a predominance of fast-growing forest plantations, namely, the mosaic management catchment (MMC) and the intensive management catchment (IMC). Rainfall and streamflow were monitored for three water years. Hydrological indexes were calculated to assess the hydrological regime of both catchments, and make inventories of the forest to assess forest growth rates. MMC had streamflow coefficients, baseflow index and baseflow stability higher than those of IMC. Mean annual wood increment was 32.73 m3 ha-1 yr-1 in MMC, with a mean age of 15 years, and 44.40 m3 ha-1 yr-1 in IMC at coppice in the second year. MMC hydrological indexes remained stable over the period studied, while in IMC the hydrological indexes were affected by climatic variations, mainly in drier years. MMC showed potential for supplying both water and wood. However, in IMC there was a trade-off between wood supply at the expense of the water supply. Thus, the intensity of fast-growing management can be adjusted to achieve a balance between water and wood supply on a catchment scale.

Interannual variability of ozone fluxes in a broadleaf deciduous forest in Italy

Multiannual measurements of ozone (O3) fluxes were performed from 2012 to 2020 in a broadleaf deciduous forest of the Po Valley, Italy. Fluxes were measured with the eddy covariance technique on a 41-m high tower, 15 m above the forest canopy. Different partition methodologies, based on concomitant water and carbon dioxide measurements, were compared for the calculation of the stomatal and non-stomatal components of the O3 fluxes. Total O3 fluxes revealed a marked interannual variability that was mainly driven by the stomatal activity in summer. Therefore, those factors that influence stomatal conductance were responsible for the flux variability, with soil water content being the main physiological driver. Despite the variability of the total O3 fluxes, the annual mean of the stomatal fraction was similar in the different years, around 42% on a 24-h basis, with an average summer value of 52% and a maximum around 60% during the summer daylight hours. The non-stomatal deposition was mainly driven by air humidity, surface wetness, and chemical sinks such as reaction of O3 with nitric oxide. Wind speed, turbulence intensity, and surface temperature showed a negative relationship with the non-stomatal fraction, but this was probably the result of a temporal misalignment between the daily cycles of non-stomatal conductance and those of temperature, turbulence, and wind speed. During the 7 years of measurements, the forest experienced a phytotoxic O3 dose of 10.55 mmolO3 m−2, as annual average, with an estimated reduction of the forest growth rate around 3% yr−1 according to the dose–effect relationships of the United Nations Economic Commission for Europe for broadleaf deciduous forests. Besides their implication for the O3 risk assessment for vegetation, these long-term measurements could be useful to test the deposition models used to correctly assess the O3 budget in troposphere on a multiannual time span.

Costs of forest carbon sequestration in the presence of climate change impacts

Forests play a critical role in mitigating climate change, and, at the same time, are predicted to experience large-scale impacts of climate change that will affect the efficiency of forests in mitigation efforts. Projections of future carbon sequestration potential typically do not account for the changing economic costs of timber and agricultural production and land use change. We integrated a dynamic forward-looking economic optimization model of global land use with results from a dynamic global vegetation model and meta-analysis of climate impacts on crop yields to project future carbon sequestration in forests. We find that the direct impacts of climate change on forests, represented by changes in dieback and forest growth, and indirect effects due to lost crop productivity, together result in a net gain of 17 Gt C in aboveground forest carbon storage from 2000 to 2100. Increases in climate-driven forest growth rates will result in an 81%–99% reduction in costs of reaching a range of global forest carbon stock targets in 2100, while the increases in dieback rates are projected to raise the costs by 57%–132%. When combined, these two direct impacts are expected to reduce the global costs of climate change mitigation in forests by more than 70%. Inclusion of the third, indirect impact of climate change on forests through reduction in crop yields, and the resulting expansion of cropland, raises the costs by 11%–38% and widens the uncertainty range. While we cannot rule out the possibility of climate change increasing mitigation costs, the central outcomes of the simultaneous impacts of climate change on forests and agriculture are 64%–86% reductions in the mitigation costs. Overall, the results suggest that concerns about climate driven dieback in forests should not inhibit the ambitions of policy makers in expanding forest-based climate solutions.

A Carbon Sequestration Model for Better Forest Management and Future Environmental Protection

In recent years, with the economic development, people's demand for forest resources has increased, thus leading to a large increase in tree cutting. Forest resources have both ecological and economic values, and this paper will propose an innovative forest management model that is based on a model of forest carbon sequestration. We take a forest in the Daxinganling Mountains as an example. First, we use python to build a forest growth model, which is related to many factors including forest growth rate, mortality rate, natural harvesting rate, and distribution of populations by age. Then, based on this model, we calculate the ecological value of the forest by the carbon sequestration of the forest, and the economic value that the forest can provide to people by the carbon content of harvested trees, which is our carbon sequestration model. Finally, we use the TOPSIS analysis algorithm to determine the weights of ecological and economic benefits according to regions and to maximize the combined benefits of the forest. The innovation of this paper is to fully consider the population distribution, birth rate, and death rate of the forest, and build a forest model with a good fit for reality. Therefore, it is also possible to calculate the influence of human factors on the comprehensive benefits of the forest by changing factors such as cutting rate, so as to obtain the optimal solution of the forest management model within a certain range.

Lake Avlan drainage effects on radial tree growth at microecological level

Lake Avlan is a natural lake located in the mountainous areas in southwestern Turkey. The lake was drained towards the end of the 1970s. However, some serious socioeconomic impacts were felt in the region surrounding the lake basin. Because the increasing ecological problems were realized within 20 years, the lake was restored towards the end of the 1990s. The present study considers the effects of lake drying on the radial growth rate of cedar and juniper forests on the slopes adjacent to the lake basin, during the drained period. Dendrochronological methods were used in two stands, one from cedar and the other from juniper forests. Results showed that mean index values derived from annual growth rate for the drained period were 15% and 14% less than that of the average of pre- and post-drying periods of the lake for cedar and juniper sites, respectively. Microecological change, namely decreasing air humidity, due to drying the lake may be the main reason of differentiation in the index values. Natural lakes, like Avlan, on mountainous areas are an important component of forest ecosystems and should not be overlooked by natural resource planners in such regions.

See the forest not the trees! Ecosystem-based assessment of response, resilience, and scope for growth of global forests

Anthropogenic activities are degrading forest health globally. Detection of changes in forest growth rates is possible with field measures of total net primary productivity (tNpp), however, assessing forest adaptive capacity was historically challenging due to a scarcity of tNpp data, knowledge of carbon allocation to above- and belowground biomass, and inability to calculate forest productive potential. This study used a global data set of 307 published research studies to identify tNpp thresholds and site-level factors constraining growth for forests in boreal, temperate, and tropical biomes. This data makes it possible to: (i) calculate the ratio of measured tNpp to a theoretical maximum tNpp from variables external to the site, its “ecosystem fit,” (ii) identify environmental thresholds by scale and biogeography, and (iii) determine stand level conditions that limit growth. At the global scale, climatic variables explain most of the variance in tNpp whereas, at the biome scale different combinations of climatic/edaphic variables interact with phenological traits to explain productivity. For example, deciduous boreal forests were less resilient if precipitation increased, but deciduous tropical forests were less resilient if minimum annual temperature increased. At the biome scale, boreal forest mean tNpp (7.3 Mg ha−1 yr−1) was significantly lower than tropical forests (19.0 Mg ha−1 yr−1) but the mean tNpp of temperate forests tNpp (14.2 Mg ha−1 yr−1) did not significantly differ from boreal or tropical forests, representing a first-order latitudinal forcing of productivity. Comparison of ranked clusters of tNpp (low, medium, high) indicated that the tropics had a larger proportion of highly productive forests (20%) than temperate (12%) or boreal forests (14%). Tropical forests are highly adapted to small-scale environmental heterogeneity but their unique evolutionary trajectories make them more sensitive to land-use change, habitat fragmentation, and climate disruption. There was minimal overlap among the high tNpp groups between boreal forests (12.0–18.2 Mg ha−1 yr−1) and temperate forests (17.6–37.7 Mg ha−1 yr−1), and moderate overlap between temperate and tropical forests (26.8–45.9 Mg ha−1 yr−1), indicating increased adaptive capacity to environmental variability by climatic zone. All tropical forests had similar ecosystem fit, but Paleotropic forests growing on Inceptisol and Entisol soils were significantly more productive than Neotropical forests revealing similar adaptive capacity although there were less favorable growing conditions in the Neotropics. This study supports including site-level variations in edaphic and climatic factors to understand changes in primary productivity due to disturbance and proposes using Ecosystem fit to identify forest adaptive capacity in response to climate destabilization.

Responses of vegetation growth to climate change over the Tibetan Plateau from 1982 to 2018

The Tibetan Plateau (TP) plays a critical role in Earth’s climate system and is highly sensitive to global warming. However, comprehensive analysis of the interaction between various climatic factors and vegetation growth across the TP is still limited. Using daily normalized difference vegetation index (NDVI) series interpolated from the 16-day satellite measurements and climatic data during 1982–2018, we investigated the spatiotemporal changes in growing season NDVI (NDVIGS) and associated climatic drivers over the TP and analyzed the responses of NDVIGS to climatic drivers for different vegetation types. Our results show that NDVIGS of the TP as a whole exhibits a significant rising trend (0.0011 year−1; P < 0.01) from 1982 to 2018. However, trends in NDVIGS show apparent spatial heterogeneity over the TP with higher growth rates in forests (trend = 0.012 de−1; P < 0.01) and shrubs (trend = 0.009 de−1; P < 0.01) in the east and southeast than in alpine steppe (trend = 0.003 de−1; P < 0.01) and alpine meadow (trend = 0.006 de−1; P < 0.01) in the west and north. Air temperature, precipitation, and VPD serve as the dominant climatic factor affecting the NDVIGS trends in 62%, 19%, and 12% of the TP, respectively. Additionally, climatic factors show differential impacts on NDVIGS among different vegetation types. Air temperature has a predominantly positive correlation with NDVIGS for all vegetation types, while precipitation has a negative impact on plant growth in the eastern humid forest region but a generally positive impact in the other areas. Our results also highlight that the effect of VPD on NDVIGS varies among different vegetation types. These findings contribute to a systematic understanding of the possible mechanisms underlying the responses of vegetation growth to various climatic drivers across the TP.