Forest soil is crucial in climate change mitigation, food security, and biogeochemical nutrient cycling. Mixed Sal forests enhance soil organic matter, improve nutrient availability, and regulate pH dynamics. However, anthropogenic disturbances, including deforestation and land-use changes, significantly alter forest cover, leading to shifts in soil physicochemical and microbial properties. These impacts necessitate rigorous monitoring and comprehensive assessment. Therefore, we investigated the effects of contrasting conditions- closed (no human activities) and open (human interferences) mixed Sal Forest on the vertical and seasonal dynamics of microbial biomass carbon (SMBC). Results revealed that the closed mixed Sal Forest had significantly higher SMBC than the open mixed Sal Forest across the soil profile (D1-D5) with a strong seasonal effect. Closed mixed Sal Forest had 60% higher SMBC in D1 than open mixed Sal Forest while it reduced with depth and 17.1 to 56.7% higher SMBC in the subsurface to bottom-most soil profile (D2-D5). Moreover, SMBC was higher in the monsoon period in both forests. The SMBC reduced by 24.2 to 45.1% in the post-monsoon period while reduction was more intense in the pre-monsoon period (48.1 to 68.2%) compared to the monsoon period under closed mixed Sal Forest. Similarly, the decline was more intense in the open mixed Sal Forest, where SMBC declined 12.1 to 54% in the post-monsoon period and 56.1 to 76.2% in the pre-monsoon period compared to the monsoon period. The study indicates that human interference in mixed Sal forests leads to loss of forest cover, negatively affecting microbiological properties and reducing soil fertility, which weakens the forest's resilience to climate change. Additionally, SMBC exhibits seasonal variations, reflecting responses to environmental conditions. These results underline the need to reduce human disturbances and enhance forest conservation strategies to ensure soil sustainability and ecosystem stability.
Organic inputs from aboveground litter and underground roots are an important factor affecting nutrient cycling in forest ecosystems. However, we still know little about the seasonal effects of the interaction between aboveground and underground organic inputs on soil organic carbon, nutrients and microorganisms after vegetation restoration in degraded red soil. Therefore, we focused on a mixed forest dominated by Schima superba and Pinus massoniana that had been restored for 27 years on eroded and degraded red soil in a subtropical region. Five treatments were set as follows: retaining aboveground litter + retaining root + retaining mycorrhizae (LRM, control treatment), doubling aboveground litter + retaining root + retaining mycorrhizae (DLRM), removing aboveground litter + retaining root + retaining mycorrhizae (NRM), removing aboveground litter + removing root + retaining mycorrhizae (NNM), and removing aboveground litter + removing root + removing mycorrhizae (NNN). After more than three years of treatment, DLRM, NRM, NNM, and NNN treatments reduced soil moisture content by 32.0-56.8 % in the rainy season compared with the LRM treatment. Soil total nitrogen and ammonium nitrogen concentrations were the highest in the DLRM treatment. Soil ammonium concentration and pH were higher in the rainy season than those in the dry season, while soil nitrate concentration was higher in the dry season. Soil available phosphorus concentration in the dry season decreased by 64.5 % in the DLRM treatment, while they were 2.0-10.7 times of those in the LRM, NRM, NNM, and NNN treatments compared to the rainy season. Soil microbial communities were dominated by bacteria across treatments, accounting for 74.0-75.5 % of the total phospholipid fatty acid (PLFA) of soil microbes, and there was no significant difference among treatments. Except for fungi, the total PLFAs of soil microorganisms and the PLFA content of each microbial taxon were higher in the dry season than those in the rainy season. The F/B value in the rainy season was higher than that in the dry season. The PLFA contents of gram-positive bacteria and actinomyces in the DLRM and NRM treatments were higher than those in the NNM treatment, and PLFA contents of both in the dry season were 1.5 and 1.6 times of those in the rainy season, respectively. Soil total phosphorus and pH had the highest contribution to soil microbial community changes in rainy and dry seasons, respectively. Comprehensive evaluation showed that double aboveground litter addition was more conducive to soil quality improvement. In conclusion, litter, roots and mycorrhiza manipulations affected the PLFA contents of soil microorganisms through the regulation of soil physicochemical properties, rather than the proportions of each microbial taxon in the total PLFAs, which was related to the season. The results can provide a theoretical basis for soil quality improvement as driven by soil microorganisms during the restoration of degraded red soil.
Accurate knowledge of site conditions and their effects on regeneration establishment is important for selecting the most appropriate tree species and regeneration methods for a given regeneration site. This study examined the response of the first-year field performance of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.) and silver birch (Betula pendula Roth.) seedlings in boreal forests to variables available in open forest and natural resources datasets. Survival, height increment and damage of planted tree seedlings and the success of direct seeding of pine were analysed on a total of 284 plots (1000 m(2)) in 18 regeneration experiments established in 2020-2022 in southern and central Finland. The height increment of silver birch was higher than that of conifers, while the lowest mortality rate was found for spruce. In the generalised linear mixed models, topographic wetness index, soil texture, site type and growing stock at clearcut explained the species-specific survival and height increment of planted seedlings and the success of pine seeding. Low-cost, open geospatial data effectively provide useful details on the site conditions suitable for diversifying tree species composition in boreal forests instead of monocultures.
Purpose of ReviewInternational ambitions for massive afforestation and restoration are high. To make these investments sustainable and resilient under future climate change, science is calling for a shift from planting monocultures to mixed forests. But what is the scientific basis for promoting diverse plantations, and what is the feasibility of their establishment and management? As the largest global network of tree diversity experiments, TreeDivNet is uniquely positioned to answer these pressing questions. Building on 428 peer-reviewed TreeDivNet studies, combined with the results of a questionnaire completed by managers of 32 TreeDivNet sites, we aimed to answer the following questions: (i) How and where have TreeDivNet experiments enabled the relationship between tree diversity and tree performance (including productivity, survival, and pathogen damage) to be studied, and what has been learned? (ii) What are the remaining key knowledge gaps in our understanding of the relationship between tree diversity and tree performance? and (iii) What practical insights can be gained from the TreeDivNet experiments for operational, real-world forest plantations?Recent FindingsWe developed a conceptual framework that identifies the variety of pathways through which target tree performance is related to local neighbourhood diversity and mapped the research efforts for each of those pathways. Experimental research on forest mixtures has focused primarily on direct tree diversity effects on productivity, with generally positive effects of species and functional diversity on productivity. Fewer studies focused on indirect effects mediated via biotic growing conditions (e.g. soil microbes and herbivores) and resource availability and uptake. Most studies examining light uptake found positive effects of species diversity. For pests and diseases, the evidence points mostly towards lower levels of infection for target trees when growing in mixed plantations. Tree diversity effects on the abiotic growing conditions (e.g. microclimate, soil properties) and resource-use efficiency have been less well studied to date. The majority of tree diversity experiments are situated in temperate forests, while (sub)tropical forests, and boreal forests in particular, remain underrepresented.SummaryTreeDivNet provides evidence in favour of mixing tree species to increase tree productivity while identifying a variety of different processes that drive these diversity effects. The design, scale, age, and management of TreeDivNet experiments reflect their focus on fundamental research questions pertaining to tree diversity-ecosystem function relationships and this scientific focus complicates translation of findings into direct practical management guidelines. Future research could focus on (i) filling the knowledge gaps related to underlying processes of tree diversity effects to better design plantation schemes, (ii) identifying optimal species mixtures, and (iii) developing practical approaches to make experimental mixed plantings more management oriented.