•Mediterranean pine plantations are increasingly exposed to mortality processes.•These effects can be aggravated by a lack of management.•Thinning could help trees to reduce dieback and tree ...mortality related to drought.•Ten-year basal area showed strong growth responses following thinning.•Thinning had a significant effect on drought vulnerability indices.•Growth models provide information on the long-term effectiveness of thinning.•High values of modelled resilience were found after thinning, with a time to recovery of between two and four years after drought.
Forest plantations are more vulnerable to the stress induced by biotic and abiotic factors than are naturally regenerated forests. These effects can be aggravated by a lack of management in large reforestation areas, and thinning could, therefore, help trees to reduce dieback and tree mortality related to drought. We address this question using a dendrochronology and modelling approach to improve the understanding of the growth response of high-density planted pine forests to thinning in drought-prone areas of Southern Spain. An experimental trial was, therefore, carried out with three species (Pinus halepensis, P. nigra, and P. sylvestris) and three thinning treatments (unthinned, moderate, and heavy thinning), after which growth-climate relationships and drought vulnerability indices were assessed. Three separate generalized linear mixed-effects models (GLMM), one for each species and location, were fitted using BAI as the response variable, and post-thinning growth trajectories and drought vulnerability indices were also simulated. Ten-year basal area showed strong growth responses following the thinning treatment (BAI10, 72% for P. halepensis and 50% for P. sylvestris as regards heavy thinning and 51% for P. nigra as regards moderate thinning), with different responses to precipitation and temperature according to species and thinning intensity. The significant effects of thinning on drought vulnerability indices indicated that the thinning treatments had a positive effect, irrespective of the pine species, although this was more evident in the case of P. sylvestris (recovery F = 28.10, p < 0.001, and resilience F = 35.21, p < 0.001 respectively) and P. halepensis (recovery F = 10.97, p < 0.001 and resilience F = 16.91, p < 0.001). The models also showed that climatic effect was greater for P. nigra than for P. sylvestris. The simulation also provides information on the long-term effectiveness of thinning; in P. sylvestris the effect of thinning tended to be attenuated after 20 years, but this was not the case of P. nigra and P. halepensis. High values of modelled resilience were found after thinning, with a time to recovery of between two and four years after drought depending on thinning intensity. Our findings showed the advantages of thinning for growth under different climatic constraints, particularly drought. This work is a new contribution that demonstrates the urgent need for forest managers to take steps in order to help drought-vulnerable Mediterranean pine plantations to adapt to the risks posed by climate change.
Afforestation programs as a strategy to address the climate crisis are on the rise worldwide. Although concerns exist about the effects of afforesting treeless habitats on their biodiversity and ...ecosystem services, potential impacts on areas beyond afforestation boundaries have been largely overlooked. Cork oak (Quercus suber) woodlands in southern Spain are regarded as a successful example of sustainability. However, the afforestation of their neighbouring treeless habitats may compromise their productivity through indirect effects that are not fully understood. Using a multi-method approach, we studied the effects of the afforestation of Mediterranean heathland (herriza) areas with pine tree species on the productivity of neighbouring cork oak woodlands downslope over a 37-year period. The differences in Normalized Difference Vegetation Index (NDVI) and Basal Area Increment (BAI) between cork oak woodlands below open herriza and below afforested herriza became apparent approximately ten years after pine afforestation. Specifically, NDVI was significantly reduced in cork oak stands below afforested herriza areas for the remaining years, while a substantial decrease in BAI of cork oak trees was also associated with afforested herriza areas upslope. Moreover, the NDVI and BAI trends of cork oak stands below afforested herriza reached the minimum levels of the time series following an extreme drought event. Our results reveal that the ecological impacts of afforestation of naturally treeless habitats can expand beyond the plantation area. We propose that the restoration of treeless habitats, such as the herriza, in areas where pine plantations are no longer productive, may enhance their ecological services, particularly in the context of climate change. Therefore, afforestation programs worldwide should carefully consider the trade-offs between carbon mitigation and other ecosystem services at the landscape scale.
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•Indirect effects of afforestation are often overlooked amid climate efforts.•Both NDVI and BAI declined in cork oak woodlands below afforested areas over time.•Pine afforestation impacts can extend beyond the plantation.•Implications for rethinking future afforestation initiatives.
Fires are a complex phenomenon that may generate a chain of responses and processes that affect each part of the ecosystem. Thus, it is important to understand the magnitude of the impacts of fire on ...soil properties and the response of plants to this disturbance. For the moment, few studies have examined the effects of prescribed fire on large plots in afforested pine plantations in Mediterranean ecosystems. To fill this gap, the effects of a prescribed fire on runoff, soil erosion, and water quality for approximately one year after burning have been evaluated in pine plantations in south-eastern Spain. We constructed six erosion plots in the control area and six erosion plots in the burned area that were 4 m long and 2 m wide, immediately after the prescribed fire. Runoff, soil erosion and runoff water quality were studied after each rainy event in all plots. Our results reveal that prescribed fire did not significantly affect runoff and soil erosion when low intensity precipitations occur at pine plantations. In relation to water quality, water turbidity, salinity, pH, organic matter content and ionic substances concentrations increased immediately after prescribed burn, nevertheless these changes disappeared over time. We can conclude that prescribed fire can be a useful tool for fuel reduction in Mediterranean pine plantations without wide and long-term impacts to soil losses, or water quality.
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•Prescribed fires do not significantly affect runoff at pine plantations.•Low intensity prescribed burns seems not to affect soil erosion at pine plantations.•Runoff water quality parameters were slightly affected by prescribed fire.•Rain intensity may modulate runoff generation and erosion at pine plantations.
Mongolian pine (Pinus sylvestris var. mongolica) plantations have ecological significance for desertification control and degraded land restoration in drought-induced regions. To date, knowledge ...about the dynamics of transpiration and canopy stomatal conductance (gs) of Mongolian pine in the semiarid deserts in Northern China is quite limited. Thus, better understanding its physical response to environmental factors and exploring the mechanisms of forest transpiration can offer a theoretical basis for a reasonable tree planting program in semi-arid regions. In this study, transpiration and gs changes in Mongolian pine plantations for a mature forest (MMPP), half-mature forest (HMPP), and young forest (YMPP) were obtained using sap flow observations, while simultaneously monitoring the atmospheric and soil moisture contents. The results showed that the canopy transpiration per unit leaf area (EL) averaged 0.97 mm d–1, 0.60 mm d–1, and 0.45 mm d–1 in MMPP, HMPP, and YMPP, respectively, and the EL of Mongolian pine could be attributed to evaporative demand, soil moisture status, and gs. EL was obviously affected by air temperature, photosynthetic active radiation (PAR), and vapor pressure deficit (VPD) with the highest determined coefficient. The low values measured for the dimensionless coefficient (Ω = 0.041, 0.15, and 0.18) indicated that the canopy and the atmosphere were highly coupled. gs had more control over EL, and thus gs was more limited by VPD than that PAR. The average gs was 105.27, 105.26, and 99.44 mmol m–2 s–1 for MMPP, HMPP, and YMPP, respectively; Both MMPP and YMPP had lower sensitivity for stomatal regulation than HMPP, and the maximum gs was found in trees with both small and large tree diameters at breast height. Therefore, MMPP and YMPP were suspected to vary based on environmental conditions and were more susceptible to decline under mega drought conditions.
•Vapor pressure deficit is the main driving factor that affects transpiration rates.•A canopy is well coupled to the atmosphere and transpiration rate.•Old and young trees showed lower stomatal regulation upon water loss.•Mature and young forests are more susceptible to decline under drought conditions.
Loblolly pine (Pinus taeda L.) plantations in the southeastern United States are among the world's most intensively managed forest plantations. Under intensive management, a common practice is ...fertilizing at establishment. The objective of this study was to investigate the effect of establishment fertilization on leaf area development of loblolly pine plantation stands (n = 3997) over 16 years compared to stands that did not receive nutrient additions at planting. Leaf area index (LAI) is a meaningful biophysical indicator of vigor and an important functional and structural element of a planted stand. The study area was stratified by plant hardiness zone to account for climatic differences and soil type (texture and drainage class), using the Cooperative Research in Forest Fertilization (CRIFF) groupings. LAI was estimated from Landsat imagery to create trajectories of mean stand LAI over 16 years. Establishment fertilization, on average, (1) increased stand LAI beginning at year two, with a peak at years six and seven, and (2) decreased the time required for a stand to reach a winter LAI of 1.5 by almost two years. Fertilization responses varied by climate zone and soil drainage class, where the warmest zones benefited the most, particularly in poorly drained soils. Past year 10, the differences in LAI between fertilized and unfertilized stands were not practically important. Using Landsat data in a cloud-computing environment, we demonstrated the benefits of establishment fertilization to stand LAI development using a large sample over the native range of loblolly pine.
•Landsat-derived LAI trajectories were assessed for nearly 4000 industrially owned and managed stands.•Establishment fertilization decreased the time needed to reach a winter LAI of 1.5 by almost two years.•Google Earth Engine enables regional assessments of the effects of forest management on stand growth.•Establishment fertilization effects vary by soil type and hardiness zone.
•SPB outbreak frequency has decline over the last 20years across the Southern U.S.•Concurrently, pine plantation area has increased by 20 times since the 1950s.•Variables such as weather or natural ...enemies fall short at explaining these trends.•Changes to silvicultural practices may be partly responsible for lower SPB activity.
The southern pine beetle has shown a dramatic decline in outbreak activity over much of the southeastern United States since the turn of the 21st century compared to previous decades. Concurrently, from the 1950s through the present day, a twenty-fold increase in pine plantation area has occurred across the region while trends in genetic tree improvement and pine silvicultural advances have seen a marked increase in application towards the end of the 20th century. We examine southern pine beetle outbreaks in the Piedmont and Coastal Plain physiographic provinces of the southeastern U.S. relative to this increase in pine plantation area and intensive management. While climate and natural enemy hypotheses are discussed, the substantial changes to the management and condition of the southern pine resource in the form of plantations that are genetically improved, younger, faster growing, less overstocked or more fragmented may provide a more robust explanation for regional declines in SPB outbreak activity.
•We found no differences in bulk soil C stocks across treatments.•More C found in mineral-associated organic matter with more intensive management.•Results suggest management intensification could ...increase soil C persistence.
Early thinning of loblolly pine plantations can potentially deliver sustainable feedstocks for biofuel/bioenergy. However, the management intensification for increased productivity and the removal of additional biomass from these plantations could reduce carbon (C) inputs belowground and therefore reduce overall ecosystem C storage. Increased fertilization could also affect C stocks, and their relative distribution between soil organic matter (SOM) fractions. We analyzed soil C stocks as a function of soil type and different pine plantation management systems across the Western Gulf region of the United States. Additionally, we analyzed SOM fractions with inherently different stabilization mechanisms and potential C persistence. We found no significant differences in bulk soil C stocks across management intensities or soil types. The early thinning treatment had no effect on the C distribution across each soil organic matter fraction. However, proportionally more C was found in mineral-associated organic matter and less in particulate organic matter in the more intensive management regime treatment, possibly due to higher below ground nutrient inputs and enhanced microbial activity. Our results suggest that management intensification to support biofuel production from loblolly pine plantations will not affect soil C stocks, but may increase their persistence. This study demonstrates that, from a soil C perspective, early thinning of intensively managed loblolly pine plantations has potential as a sustainable biofuel feedstock.
•Pine management practices impose variable hydrologic impacts across spatial scales.•Management practices cause greater relative water yield impact at smaller spatial scales.•Water yield increases ...with decreasing biomass (i.e., increased thinning).•Short rotation causes an intensity-dependent increase in water yield.•Landowners and managers have agency in managing local and regional water yield rates.
Changes in global bioenergy consumption have catalyzed the emergence of forest plantations as an important energy alternative. In the southeastern United States, land cover changes caused by increasing demands for pine trees as a bioenergy feedstock incite associated impacts on local ecosystem services (e.g., water yield). However, water yield impacts from pine plantation management strategies, such as thinning and short rotation, have yet to be simultaneously examined on multiple spatial scales. Here, we modeled the effects of thinning and clear-cut conditions on long term mean annual water yield across a 55-year time horizon at the watershed scale (watershed area ranging 696 – 7,374 km2) in northern Florida, southern Georgia, and southern Alabama. Additionally, we assessed the long term water yield effects of thinning, clear-cut, and short-rotation management at the pine plantation (i.e., plot) scale. We compared three plot-level evapotranspiration models as well as the watershed-level Water Supply Stress Index water balance model to simulate plot and watershed hydrologic responses from pine plantation management scenarios. Both methods showed that 10% thinning had the smallest increase in water yield (<6%), while clear-cut conditions imposed the greatest increase (up to 51% for plot scale and up to 25% for watershed scale simulations). Short-rotation management caused plot-level water yield increases ranging from 3% to 24%. Overall, greater water yield effects were seen in site simulations, rather than in watersheds, reinforcing the importance of scale when assessing water budget impacts given land cover changes. These results suggest that landowners have agency over the magnitude of water that is yielded from their plantations and that local water supply shortages can be mitigated by changing forestry biomass management strategies. The opportunity to supplement local water availability is especially valuable within the context of changing climate cycles that may bring about drier local conditions. The multi-scale approach presented here can support efforts from landowners and water managers to optimize profit as well as ecosystem service provision.
To date, it is unclear how differences in litter quality affect soil organic matter (SOM) decomposition through a phenomenon called 'priming effects' (PEs), especially for low-fertility forest soils ...under field conditions. Here, the effects of low- and high-quality leaf litter on PE and microbial metabolism of litter-derived carbon (C) were explored in a low-fertility pine (Pinus massoniana) plantation. A 185-day in situ incubation experiment was carried out by adding two 13C-labeled leaf litters to the pine soil—a low-quality (high lignin: nitrogen ratio) litter sourced from pine and a broadleaved species Schima superba produced high-quality (low lignin: nitrogen ratio) litter. To determine the key microbial groups contributing to PEs, the abundance of 13C-labeled litter enrichment in soil phospholipid fatty acids (13C-PLFAs) was quantified. We found that high-quality litter decomposed more rapidly than low-quality litter, with both litter-derived CO2 efflux reaching a plateaued level during the experimental period. Low-quality litter induced net positive PEs, while high-quality litter induced net negative PEs during the litter decomposition processes. The 13C-PLFAs results showed that bacterial groups governed the negative PEs induced by high-quality litter, whereas fungal communities targeted the positive PEs induced by low-quality litter. Random forest model and variation partitioning analysis demonstrated that the direction and magnitude of PEs were driven by litter-induced changes in key microbial groups rather than the structure of the microbial community. Our results demonstrate that microorganisms preferentially utilized litter-derived C in high-quality litter treatment and SOM in low-quality litter treatment, respectively. In contrast to low-quality litter, adding high-quality litter promoted the microbial metabolism of litter-derived C, reducing SOM decomposition (strong negative PEs). Taken together, this study provides isotope-based suggestions for the improvement of degraded pine forests—introducing tree species that produce high-quality litter may benefit soil C sequestration by reducing soil C losses due to PE in nutrient-poor pine forests.
•An in situ based real and apparent PEs were observed synchronously in a pine forest.•Pine litter stimulated a positive PE and promoted SOM metabolization by microbes.•Inputs of high-quality litter downregulate the PE of pine forest soil.•High-quality litter reduced the PE and enhanced microbial utilization of litter-derived C.•The direction and magnitude of PEs were driven by key microbial groups rather than microbial community structure.
In Mediterranean ecosystems an increasing demand for in situ trace gas exchange data is emerging to enhance the adaptation and mitigation strategies under forest degradation. Field-chamber ...green-house gas fluxes and site characteristics were analysed in two Mediterranean peri-urban pine forests showing degradation symptoms. We examined the effect of different thinning interventions on soil CO2, CH4 and N2O fluxes, addressing the relationships with the environmental variables and C and N contents along forest floor-soil layers.
Soil temperature resulted as the main driving variable for CO2 efflux and CH4 uptake. Soil moisture content and organic matter availability affected CO2 emission patterns in the two sites. N2O fluxes showed a positive correlation with soil moisture under wetter climatic conditions only. GHG fluxes showed significant correlations with C and N content of both forest floor and mineral soil, especially in the deepest layers, suggesting that it should be considered, together with environmental variables when accounting GHG fluxes in degraded forests.
Short-term effects of thinning on CO2 emissions were dependent on disturbance induced by logging operations and organic matter inputs. After thinning CH4 uptake increased significantly under selective treatment, independently from specific site-induced effects. N2O fluxes were characterized by low emissions in both sites and were not affected by treatments. Soil CO2 efflux was the largest component of global warming potential (GWP) from both sites (11,553 kg ha−1 y−1 on average). Although it has a large global warming potential, N2O contribution to GWP was about 131 kg CO2eq ha−1 y−1. The contribution of CH4-CO2 equivalent to total GWP showed a clear and significant CH4 sink behaviour under selective treatment (36 kg ha−1 y−1 on average). However, in the short-term both thinning approaches produced a weak effect on total GWP.
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•We analysed site-related GHG fluxes in two Mediterranean pine forests after thinning.•Soil moisture content and organic matter availability affected CO2 emission patterns.•Short-term CO2 emissions increased after disturbance induced by logging operations.•Small gaps created with selective thinning increased CH4 uptake.•Low N2O emissions were found in both sites and were not affected by thinning.
