Impacts of longleaf pine (Pinus palustris Mill.) on long-term hydrology at the watershed scale

Threats from climate change and growing populations require innovative solutions for restoring streamflow in many regions. In the arid western U.S., attempts to increase streamflow (Q) through forest management have had mixed results, but these approaches may be more successful in the eastern U.S. where greater precipitation (P) and lower evapotranspiration (ET) offer greater potential to increase Q by reducing ET. Longleaf pine (Pinus palustris Mill.) (LLP) woodlands, once the dominant land cover in the southeastern United States, often have lower ET than other forest types but it is unclear how longleaf pine cover impacts watershed-scale hydrology. To address this question, we analyzed 21 gaged rural watersheds. We estimated annual water balance ET (ETwb) as the difference between precipitation (P) and streamflow (Q) between 1989 and 2021 and quantified low flow rates (7Q10) among watersheds with high and low LLP cover. To control for climate variability among watersheds, we compared variation in hydrology metrics with biotic and abiotic variables using the Budyko equation (ETBudyko) to understand the differences between the two ET estimates (∆ET). Watersheds with 15-72 % LLP cover had 17 % greater mean annual Q, 7 % lower annual ETwb, and 92 % greater 7Q10 low flow rates than watersheds with <3 % LLP. LLP cover decreased ET and increased Q by 2.4 mm or 0.15 % Q/P per 1 % of watershed area, but only when LLP was managed as open woodlands. Our results demonstrate that ecological forest restoration in these systems, which entails mechanical thinning and re-introduction of low-intensity prescribed fire to maintain open woodlands, and enhance understory diversity, can contribute to decreases in ET and increases in Q in eastern forests.

Nature, smells, and human wellbeing

The link between nature and human wellbeing is well established. However, few studies go beyond considering the visual and auditory underpinnings of this relationship, even though engaging with nature is a multisensory experience. While research linking smell to wellbeing exists, it focuses predominantly on smells as a source of nuisance/offence. Smells clearly have a prominent influence, but a significant knowledge gap remains in the nexus of nature, smell, and wellbeing. Here, we examine how smells experienced in woodlands contribute to wellbeing across four seasons. We show that smells are associated with multiple wellbeing domains, both positively and negatively. They are linked to memories, and specific ecological characteristics and processes over space/time. By making the link between the spatiotemporal variability in biodiversity and wellbeing explicit, we unearth a new line of enquiry. Overall, the multisensory experience must be considered by researchers, practitioners, policy-makers and planners looking to improve wellbeing through nature.

Presentation of landscape-fuzzy approach of forest capability evaluation (LFAFCE) for degraded sites

Evaluation of forest sites capability (EFSC) is important for the restoration of degraded areas. The current costly EFSC approaches developed based on forest stand structure criteria is too costly for less developed countries (LDC) and not suitable for severely degraded lands. This paper describes an inexpensive Landscape-fuzzy approach for forest capability evaluation (LFAFCE) that can be used to restore degraded forest areas especially in LDC. Five physical criteria of slope, hillshade, altitude, precipitation, and geo formation were evaluated in the Zagros region of western Iran using the fuzzy membership functions, prioritized by analytic network process (ANP), and combined with GIS-based weighted linear combination. We then performed multi-criteria evaluation integrated by GIS. Given the positive correlation between the independent variable of EFSC and the dependent variable of the dominant tree height, the model results were validated based on the linear regression of the relationship between the two variables. The results of the validation showed that the linear regression model with appropriate coefficient of determination was significant. The results of EFSC by LFAFCE showed that most of the forest area was allocated to two classes: well (75%) and moderate (21.8%). In total, only 3.2% of the area belonged to the marginal (0.4%), high (0.1%), and unsuitable regions (2.7%) classes. Our results demonstrate that LFAFCE is valid for low-cost evaluation of degraded area in Zagros and for other similar areas, if calibrated, where normal forest mass parameters are not available.

Do ecosystem service frameworks represent people's values?

Since the Millennium Ecosystem Assessment was published, a plethora of ecosystem service frameworks have been developed to conceptualise the links between the natural environment and society. The intended geographic scales of application, the policy/practice context, and the scientific disciplines involved have driven variations in how the frameworks are constructed. However, the frameworks are homogenous in that they have been created predominately based on expert opinions and views of how ecosystem services are structured. Here, we use the Common International Classification of Ecosystem Services (CICES) to examine the extent to which frameworks capture people's values for British woodlands. Our findings reveal several disparities between how experts and the public conceptualise ecosystem services. The considerable refinement and specificity provided by CICES does not align with public values (e.g. some provisioning, and regulation and maintenance, services), which tend to be more generalised. We also demonstrate differences in values explained by social characteristics (e.g. ethnicity) that need to be accounted for in decision-making processes. Moving forwards, we need to consider how society views the services derived from nature and reflect this in frameworks to ensure ecosystem service approaches are effective, transparent and widely supported.

Sustainable woodland management and livelihood options in a charcoal producing region: An agent-based modelling approach

Woodland resources provide livelihoods for millions of people in Africa. Concerns about the impact of human utilization of woodlands have led to vigorous debates on woodland degradation. Ecological and socio-economic empirical data and understanding of the socio-ecological system have been synthesized in an agent-based model (ABM) to explore different woodland management options for a dynamic, semi-arid region in Kenya. In our simulations we accounted for the impacts of drought frequency, charcoal price changes, improved management practices and taxation of charcoal for a 20-year period to assess woodland changes in a spatially explicit way and evaluate the numbers of actors that can benefit from charcoal harvesting as a livelihood option. The model is based on an agent typology derived from 150 household interviews that focused on livelihood strategies and decision-making processes. Furthermore, the model integrates knowledge from vegetation plots and focus group meetings. From the model simulations we learn that favorable prices, improved management and taxation do not directly have the anticipated impact on woodland resources, as the improved conditions lead to fewer constraints on involvement in charcoal making. This reduces the positive impacts of these measures on the woodland quality but, at the same time, allows a larger number of actors to benefit from charcoal harvesting. Results show a very strong decrease in woodland area under the base scenario thereby reducing possibilities for households to supplement their incomes with charcoal making. Increased droughts and low prices for charcoal lead to early depletion of woodlands and reduction in livelihood options. Taxation stabilizes the number of charcoal producers but does not stop the depletion of woodland area. Woodland loss can only be prevented by controlling the number of charcoal makers and the amount of charcoal harvesting.

Land use and climate change impacts on runoff and soil erosion at the hillslope scale in the Brazilian Cerrado

Land use and climate change can influence runoff and soil erosion, threatening soil and water conservation in the Cerrado biome in Brazil. The adoption of a process-based model was necessary due to the lack of long-term observed data. Our goals were to calibrate the WEPP (Water Erosion Prediction Project) model for different land uses under subtropical conditions in the Cerrado biome; predict runoff and soil erosion for these different land uses; and simulate runoff and soil erosion considering climate change. We performed the model calibration using a 5-year dataset (2012-2016) of observed runoff and soil loss in four different land uses (wooded Cerrado, tilled fallow without plant cover, pasture, and sugarcane) in experimental plots. Selected soil and management parameters were optimized for each land use during the WEPP model calibration with the existing field data. The simulations were conducted using the calibrated WEPP model components with a 100-year climate dataset created with CLIGEN (weather generator) based on regional climate statistics. We obtained downscaled General Circulation Model (GCM) projections, and runoff and soil loss were predicted with WEPP using future climate scenarios for 2030, 2060, and 2090 considering different Representative Concentration Pathways (RCPs). The WEPP model had an acceptable performance for the subtropical conditions. Land use can influence runoff and soil loss rates in a significant way. Potential climate changes, which indicate the increase of rainfall intensities and depths, may increase the variability and rates of runoff and soil erosion. However, projected climate changes did not significantly affect the runoff and soil erosion for the four analyzed land uses at our location. Finally, the runoff behavior was distinct for each land use, but for soil loss we found similarities between pasture and wooded Cerrado, suggesting that the soil may attain a sustainable level when the land management follows conservation principles.

Why are there no C4 forests?

C₄ photosynthesis is absent from the arborescent life form, with the exception of seven Hawaiian Euphorbia species and a few desert shrubs that become arborescent with age. As a consequence, wherever C₃ trees can establish, their height advantage enables them to outcompete low stature C₄ vegetation. Had C₄ photosynthesis been able to evolve in an arborescent life form, forest cover (by C₄ trees) could have been much more extensive than today, with significant consequences for the biosphere. Here, we address why there are so few C₄ trees. Physiological explanations associated with low light performance of C₄ photosynthesis are not supported, because C₄ shade-tolerant species exhibit similar performance as shade-tolerant C₃ species in terms of quantum yield, steady-state photosynthetic and use of sunflecks. Hence, hypothetical C₄ trees could occur in the regeneration niche of forests. Constraints associated with the evolutionary history of the C₄ lineages are more plausible. Most C₄ species are grasses and sedges, which lack meristems needed for arborescence, while most C₄ eudicots are highly specialized for harsh (arid, saline, hot) or disturbed habitats where arborescence may be maladapted. Most C₄ eudicot clades are also young, and have not had sufficient time to radiate beyond the extreme environments where C₄ evolution is favored. In the case of the Hawaiian Euphorbia species, they belong to one of the oldest and most diverse C₄ lineages, which primed this group to evolve arborescence in a low-competition environment that appeared on the remote Hawaiian Islands.