•Fuel treatments have lasting impacts on forest structure and drought resistance.•Thinning treatments effectively met and maintained structural objectives.•Positive relationship between snag basal ...area, time, and woody fuel loads.•Tree ring data indicates thinning treatments improve drought resistance.
Sierra Nevada mixed-conifer forests have undergone significant changes in structure and composition and are increasingly vulnerable to altered disturbance regimes and climate-related extreme events. Fuel reduction treatments, including thinning and follow-up surface fuel treatments, can reduce this vulnerability by creating forest structural and woody fuel conditions that not only allow forest stands to mitigate wildfire, but also alleviate individual tree stress. However, direct observations that quantify these longer-term effects are lacking. This study compares observed changes in forest structure, tree species composition, and downed woody fuel loads across three distinct time periods: pre-treatment, 1 yr post-treatment, and 10 yr post-treatment. Additionally, using tree ring data, we assessed whether treatments affected individual tree resistance to a severe statewide drought (2012–2015). Thinning treatments were able to effectively reduce tree density and basal area, increase the retention of both larger-sized and shade-intolerant trees, and mitigate tree mortality. Treatments were also associated with significantly lower coarse woody fuel and snag basal area. Snag basal area and time since treatment were related to the accumulation of fine and coarse woody surface fuel loads. Tree ring information indicated that treatments improved drought resistance as well, especially in units with lower residual live basal area. This study complements previous studies on fuel reduction thinning by demonstrating that these treatments have lasting effects on forest structure, which also confers a degree of drought resistance.
•Diffuse radiation decreases linearly as forest canopy cover and basal area increase.•Species richness and cover decrease linearly as diffuse radiation decrease.•Frequent species respond differently ...to available solar radiation under the canopy.•Forest structures allowing different levels of light may enhance plant community.
In Patagonia, Argentina, forest management in plantations with exotic pines usually focus on timber production, without considering the plant community of their understory. However, there is growing interest in conserving the biodiversity in these productive systems, due to the important role of biodiversity in the stability and functions of newly created ecosystems. Since solar radiation is one of the main limiting factors for vegetation development in forest plantations established in treeless steppes, we carried out this study with the objectives of analyzing and establishing relationships among variables of the forest structure, the solar radiation transmitted through different forest structures, and attributes of the plant community in ponderosa pine plantations in northwestern Patagonia. We selected three plantations located in the steppe that were managed traditionally and presented a wide range of forest structures. We assessed relationships between variables of the forest structure and variables of the light environment, as well as the relationship of variables of the forest structure and the light environment with the richness and cover of the plant community, using generalized linear mixed-effects models. We also assessed the relationship of diffuse radiation with the presence and cover of species grouped by their growth-form, nativity, and the most frequent species, using generalized linear mixed-effects models and Kendall correlations. Canopy cover and basal area were the forest structural variables that explained most of the diffuse radiation variability, which was the best variable characterizing the light environment. Diffuse radiation decreased linearly as canopy cover and basal area increased, and the understory plant community responded to that gradient, decreasing both total species richness and cover. Besides, different responses of the presence and cover of the most frequent species and species grouped by their growth-form and nativity in response to the available solar radiation in the understory were detected. Whereas some species or groups did not show a significant response, those that did were, in general, positively related to diffuse radiation, although to a different extent. These results indicate that ponderosa pine plantations in Patagonia affect their understory plant community. However, they also suggest that promoting forest management guidelines that lower basal area, raises canopy height and manages residual slash would enhance plant community attributes, balancing timber production and biodiversity conservation.
Aim
Forest understorey microclimates are often buffered against extreme heat or cold, with important implications for the organisms living in these environments. We quantified seasonal effects of ...understorey microclimate predictors describing canopy structure, canopy composition and topography (i.e., local factors) and the forest patch size and distance to the coast (i.e., landscape factors).
Location
Temperate forests in Europe.
Time period
2017–2018.
Major taxa studied
Woody plants.
Methods
We combined data from a microclimate sensor network with weather‐station records to calculate the difference, or offset, between temperatures measured inside and outside forests. We used regression analysis to study the effects of local and landscape factors on the seasonal offset of minimum, mean and maximum temperatures.
Results
The maximum temperature during the summer was on average cooler by 2.1 °C inside than outside forests, and the minimum temperatures during the winter and spring were 0.4 and 0.9 °C warmer. The local canopy cover was a strong nonlinear driver of the maximum temperature offset during summer, and we found increased cooling beneath tree species that cast the deepest shade. Seasonal offsets of minimum temperature were mainly regulated by landscape and topographic features, such as the distance to the coast and topographic position.
Main conclusions
Forest organisms experience less severe temperature extremes than suggested by currently available macroclimate data; therefore, climate–species relationships and the responses of species to anthropogenic global warming cannot be modelled accurately in forests using macroclimate data alone. Changes in canopy cover and composition will strongly modulate the warming of maximum temperatures in forest understories, with important implications for understanding the responses of forest biodiversity and functioning to the combined threats of land‐use change and climate change. Our predictive models are generally applicable across lowland temperate deciduous forests, providing ecologically important microclimate data for forest understories.
Understanding how Mediterranean forests respond to the increasing frequency of extreme droughts and forest densification is crucial for effective land management in the present context of climate ...change and land abandonment. We study the responses of Iberian holm oak (Quercus ilex L.) woodlands to recent extreme droughts during 2000–2019 along broad gradients of climate aridity and forest structure. To this purpose, we apply large-scale remote-sensing using MODIS EVI as a primary production proxy in 5274 Q. ilex sites distributed within a 100,000 km2 region in eastern Spain. These woodlands were extensively affected by two extreme drought events in 2005 and 2012. Resistance, assessed as the capacity of the ecosystems to maintain primary production during drought, was significantly lower for semi-arid than for sub-humid and dry-transition conditions. Holm oak woodlands located in semi-arid areas of the region showed also poorer resilience to drought, characterized by low capacity to fully recover to their pre-drought production levels. Further, drought intensity and both pre- and post-drought hydric conditions controlled the variations of resistance, recovery and resilience between the two analyzed extreme drought events. Drought effects were particularly negative for dense Q. ilex stands under semi-arid climate conditions, where strong competition for scarce water resources reduced drought resistance. The observed drought vulnerability of semi-arid holm oak woodlands may affect the long-term stability of these dry forests. Adaptive management strategies, such as selective forest thinning, may be useful for improving drought responses in these more vulnerable semi-arid woodlands. Conversely, natural rewilding may more appropriately guide management actions for more humid areas, where densely developed Q. ilex woodlands show in general a high ability to maintain ecosystem primary production during drought.
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•Large-scale remote sensing is used to study Quercus ilex forest response to drought.•Q. ilex forest response to drought is ruled by climate aridity and forest structure.•Drought intensity and both pre- and post-drought conditions affect drought responses.•Semi-arid Q. ilex woodlands show a low resistance and a poor resilience to drought.•Drought vulnerability is particularly high for dense semi-arid Q. ilex forest stands.
•SSCI of beech-dominated forests was highest in primary forests.•SSCI in thickets with shelterwood trees is nearly as high as in primary forests.•Lowest SSCI was found in National Parks with ...management ceased 30 yrs ago.•SSCI varied significantly across typical age classes in managed forests.
The high structural heterogeneity of primary forests is assumed to positively affect various ecosystem traits and functions, e.g. biodiversity, resilience and adaptability. Against this background, old-growth forest structures are emulated in many managed forests. To properly emulate such structures, quantitative reference values are required, through which primary forests are characterized. In this study, we used the stand structural complexity index (SSCI), derived from terrestrial laser scanning (TLS), to characterize and compare the structures in European beech (Fagus sylvatica L.) dominated forests along a management gradient, ranging from differently managed stands, over formerly managed but now unmanaged stands to primary forests, which have never been managed. The study objective was to quantify and compare the structural complexity of these forests to give insight into possible reference points for an improved prospective handling of managed forests. The highest stand structural complexity was found in primary forests. While there were no significant structural differences between the managed forests, they were more complex in structure than formerly managed forests that have been set aside as National Parks now. The results also showed that structural complexity significantly differed between the investigated stand age classes. Next to primary forests, thickets growing below sheltering overstory trees in managed forests resulted in high structural complexity values. The findings suggest that specific silvicultural management practices can increase the structural complexity in beech forests. This study may facilitate a ‘management for complexity’ in silvicultural practice and might lead the way towards a more precise promotion of three dimensional forest structures that are associated with specific forest functions as part of the stand management objectives.
•Kernel-based regression methods work well with hyperspectral data in the boreal zone.•GPR and SVR suit for boreal forest structure estimation; GPR slightly more accurate.•In boreal forest the ...benefit of hyperspectral data related to species information.•Model transferability between different scales of data problematic also for GPR & SVR.
Three-quarters of Finland’s land surface area is filled with forests, which compose a great part of the country’s biomass, carbon pools and carbon sinks. In order to acquire up-to-date information on the forests, optical remote sensing techniques are commonly used. Moreover, in the future hyperspectral satellite missions will start providing data to support the needs of natural resource management practices, such as forestry. It is, however, unclear what would be the additional value from using hyperspectral data compared to multispectral in quantifying forest variables of Finnish boreal forest. In this study, we used the remote sensing data by hyperspectral AISA imager (128 bands, 400–1000 nm, resolution 0.7 m) and Sentinel-2 (10 bands, resolution 10 m) to assess the possible benefits of higher spectral resolution. As reference data, we used a new nationwide forest resource dataset (stand-level data), which has a high potential in further remote sensing applications. In addition, we used a set of independent in situ measurements (plot-level data) for validation. We applied two kernel-based machine learning regression algorithms (Gaussian process and support vector regression) to relate boreal forest variables with the remote sensing data. The variables of interest were mean height, basal area, leaf area index (LAI), stem biomass and main tree species. The regression algorithms were trained with stand-level data and estimations were evaluated with stand- and plot-level holdout sets. The estimation accuracies were examined with absolute and relative root-mean-square errors. Successful variable estimations showed that kernel-based regression algorithms are suitable tools for forest structure estimation. Based on the results, the additional value of hyperspectral remote sensing data in forest variable estimation in Finnish boreal forest is mainly related to variables with species-specific information, such as main tree species and LAI. The more interesting variables for forestry industry, such as mean height, basal area and stem biomass, can also be estimated accurately with more traditional multispectral remote sensing data.
The link among the age of aboveground tree species, litter, soil quality and status in Mediterranean forests is not entirely comprehended (especially in Mediterranean forest sites). This study ...evaluates whether and by what extent tree stand composition and forest structure modify nutrient depository or alter physical, chemical and microbiological properties of soil and litter in a 120 years old pine forest chronosequence. In general, the enzymatic activity related to the phosphorous, carbon and nitrogen cycles were more developed in litter than in soil surface, while the sulphur enzymatic activity was not significantly different between the two analyzed systems. The higher dehydrogenase content measured in the litter may be an index of a higher extracellular microbial activity, compared to soil. A noticeable effect of forest age and structure on the majority of analyzed elements was detected, with nutrients and metals tending to accumulate in soil rather in the litter. Moreover, the contents of P and some metals and sulphur enzymatic activity in the litter are influenced by forest age and associated forest structure. Finally, since nutrient, metals and enzyme contents in the litter increase with forest age, forest management strategies targeted to increase the stand structure may be advisable in order to achieve higher soil functionality.
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•Nutrient, metal and enzyme contents in the litter increased with forest age.•Enzymatic activities were found to be more developed in litter than in soil.•Nutrients and metal tend to accumulate in soil rather in the litter.
Accurate estimation of aboveground forest biomass stocks is required to assess the impacts of land use changes such as deforestation and subsequent regrowth on concentrations of atmospheric CO2. The ...Global Ecosystem Dynamics Investigation (GEDI) is a lidar mission launched by NASA to the International Space Station in 2018. GEDI was specifically designed to retrieve vegetation structure within a novel, theoretical sampling design that explicitly quantifies biomass and its uncertainty across a variety of spatial scales. In this paper we provide the estimates of pan-tropical and temperate biomass derived from two years of GEDI observations. We present estimates of mean biomass densities at 1 km resolution, as well as estimates aggregated to the national level for every country GEDI observes, and at the sub-national level for the United States. For all estimates we provide the standard error of the mean biomass. These data serve as a baseline for current biomass stocks and their future changes, and the mission’s integrated use of formal statistical inference points the way towards the possibility of a new generation of powerful monitoring tools from space.
•Forest degradation significantly decrease carbon (C) stocks in live biomass.•Forest C loss in the open canopy is up to 45% higher than in the other canopies.•Forest C stocks are affected by stand ...basal area and deadwood C.•Soil C stock decrease s with depth and the highest stocks are in the closed canopy.•Humus C stocks are up to 95% lower in the open canopy than in the other canopies.
Tropical forests play a significant role in sequestrating and storing atmospheric carbon di-oxide (CO2) emissions. However, estimation of forest carbon (C) stocks in relation to changes in forest structure and disturbances are less studied. We estimated forest C stocks in live trees, saplings, lianas, deadwood, forest floor, and soil in Sitapahar natural forest reserve of Bangladesh based on field measurements and laboratory assessments. We categorized the 99 temporary sample plots into three canopy densities: closed, moderately closed, and open. According to the results, the forest C stocks were dominated by the soil C pool and forest C stocks in the closed canopy (91 Mg ha−1) differed significantly from that in the open canopy (50 Mg ha−1). Forest C stocks were also affected by basal area (BA) and deadwood C stocks. In the open canopy, the second highest contributor to forest C stock was deadwood, whereas it was above and below-ground live biomass in the closed and moderately closed canopies. In the open canopy, forest disturbances significantly decreased height and BA, and C stocks in live biomass were significantly lower compared to the other two canopy densities. In the open canopy, decreased tree density resulted in the lowest C stock in litterfall and humus, and they were up to 95% lower compared to the other two canopy densities. C stocks in humus were higher than those in litterfall in the closed and moderately closed canopies, which was opposite to that in the open canopy. The soil C stock decreased with soil depth and the highest C stocks across all depths were in the closed canopy, followed by the moderately closed and open canopy. This study also provided a stand-level estimation of C stocks that contribute to determining which tree species sequester more carbon, such as Swintonia floribunda, Lannea coromandelica, Anacardiaceae and Moraceae.
The global atmospheric nitrogen (N) deposition has intensified in recent years, resulting in a complex impact on forest ecosystems. This study investigated the effects of canopy (CAN) and understory ...additions of N (UAN) on leaf carbon (C) and N assimilations, as well as growth parameters of representative woody plant species in an evergreen broad-leaved forest, i.e. Castanea henryi, Schefflera heptaphylla, Blastus cochinchinensis, and Lasianthus chinensis. The results showed that leaf N assimilation key enzyme nitrate reductase (NR) activities of B. cochinchinensis and S. heptaphylla were significantly decreased by UAN, and were significantly decreased by CAN for C. henryi. CAN significantly decreased the nitrite reductase activity of C. henryi, while significantly increased that of L. chinensis. However, the Amax values of each woody species were not significantly different among control (CK), CAN, and UAN. Community surveys demonstrated that CAN and UAN inhibited the growth (diameter at breast height, height, or crown width) of the representative large tree, C. henryi, while promoting the growths of understory woody species (B. cochinchinensis and L. chinensis). Overall, N addition was found to change the physiological processes of N and C metabolisms of the dominant woody species in an evergreen broad-leaved forest. The community of subtropical evergreen broad-leaved forests may further decline and its C fixation capacity may be detrimentally changed under N deposition in the future.
•N addition changed Amax, NR and NiR activities of dominant woody plant in a forest.•DBH, height and crown width of plants were differentially changed by N addition.•Growth of large tree was inhibited while understory woody species were promoted.•Subtropical forest may decline and its C fixation may change under N deposition.
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