Effects of forests on water and climate at local, regional and continental scales through change in water and energy cycles. (1) Precipitation is recycled by forests and other forms of vegetation and ...transported across terrestrial surfaces to the other end of continents. (2) Upward fluxes of moisture, volatile organic compounds and microbes from plant surfaces (yellow dots) create precipitation triggers. (3) Forest-driven air pressure patterns may transport atmospheric moisture toward continental interiors. (4) Water fluxes cool temperatures and produce clouds that deflect additional radiation from terrestrial surfaces. (5) Fog and cloud interception by trees draws additional moisture out of the atmosphere. (6) Infiltration and groundwater recharge can be facilitated by trees. (7) All of the above processes naturally disperse water, thereby moderating floods.
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•We review the advantages of forests highlighted in the literature on forest, water and energy cycle interactions.•Forest, water and energy cycle interactions provide the foundation for achieving forest-based adaptation and mitigation goals.•Forests can be used, in particular, to mitigate problems related to water scarcity and global warming.•In addition to up- and downstream relationships, policy frameworks need to consider the transboundary nature of up- and downwind forest, water and energy cycle interactions.•Alongside the local level, regional and continental policy-making frameworks are necessary for adequate consideration of transboundary forest, water and energy cycle interactions.
Forest-driven water and energy cycles are poorly integrated into regional, national, continental and global decision-making on climate change adaptation, mitigation, land use and water management. This constrains humanity’s ability to protect our planet’s climate and life-sustaining functions. The substantial body of research we review reveals that forest, water and energy interactions provide the foundations for carbon storage, for cooling terrestrial surfaces and for distributing water resources. Forests and trees must be recognized as prime regulators within the water, energy and carbon cycles. If these functions are ignored, planners will be unable to assess, adapt to or mitigate the impacts of changing land cover and climate. Our call to action targets a reversal of paradigms, from a carbon-centric model to one that treats the hydrologic and climate-cooling effects of trees and forests as the first order of priority. For reasons of sustainability, carbon storage must remain a secondary, though valuable, by-product. The effects of tree cover on climate at local, regional and continental scales offer benefits that demand wider recognition. The forest- and tree-centered research insights we review and analyze provide a knowledge-base for improving plans, policies and actions. Our understanding of how trees and forests influence water, energy and carbon cycles has important implications, both for the structure of planning, management and governance institutions, as well as for how trees and forests might be used to improve sustainability, adaptation and mitigation efforts.
Abstract Secondary tropical forests are at the forefront of deforestation pressures. They store large amounts of carbon, which, if compensated for to avoid net emissions associated with conversion to ...non-forest uses, may help advance tropical forest conservation. We measured above- and below-ground carbon stocks down to 1 m soil depth across a secondary forest and in oil palm plantations in Malaysia. We calculated net carbon losses when converting secondary forests to oil palm plantations and estimated payments to avoid net emissions arising from land conversion to a 22-year oil palm rotation, based on land opportunity costs per hectare. We explored how estimates would vary between forests by also extracting carbon stock data for primary forest from the literature. When tree and soil carbon was accounted for, payments of US$18–51 tCO 2 –1 for secondary forests and US$14–40 tCO 2 –1 for primary forest would equal opportunity costs associated with oil palm plantations per hectare. If detailed assessments of soil carbon were not accounted for, payments to offset opportunity costs would need to be considerably higher for secondary forests (US$28–80 tCO 2 –1 ). These results show that assessment of carbon stocks down to 1 m soil depth in tropical forests can substantially influence the estimated value of avoided-emission payments.
•Linear mixed models provide appropriate framework for modeling forest growth data.•Supervised logging with climber cutting (SLC) reduces recovery time.•SLC reduces Macaranga establishment compared ...to conventional logging (CL).•Double growth rate for dipterocarps in SLC compared to CL.
To understand and predict the dynamics and productivity of the world’s tropical rainforests after logging is a major challenge for ecologists and forest managers. Realistic forest-dynamics models for this biome are largely lacking. Using linear mixed models, we analyse basal area development for the commercially valuable tree species of dipterocarps and the fast-growing pioneer Macaranga spp., following two selective logging methods; supervised logging (SL) and conventional logging (CL) combined with- or without pre-harvest climber cutting (SLC and SL, and CLC and CL, respectively). After logging there was an initial period of about five years before recovery started. During the 18-year study period, the average stand basal area growth rates of the dipterocarp group in the SLC treatment was double that in the CL treatment, revealing a faster recovery. Eighteen years after logging, SL and SLC treatments recovered 93% and 84%, respectively, of the initial standing dipterocarp basal area, compared to 73% and 72% recovery for the CL and CLC treatments. SLC treatments reduced the overall establishment of pioneer species (Macaranga spp.) by about 45% in contrast to CL and CLC treatments. Our study provides a framework for evaluating and comparing growth rates in tropical forests for different logging methods. The results suggest that a combination of directional felling, pre-aligned skid trails and pre-harvest climber cutting can improve future yields in tropical rainforests.
This study uses a 12-year time series (2001-2012) of eddy covariance measurements to investigate the long-term net ecosystem exchange (NEE) of carbon dioxide (CO2) and inter-annual variations in ...relation to abiotic drivers in a boreal fen in northern Sweden. The peatland was a sink for atmospheric CO2 in each of the twelve study years with a 12-year average (± standard deviation) NEE of −58 ± 21 g C m−2 yr−1. For ten out of twelve years, the cumulative annual NEE was within a range of −42 to −79 g C m−2 yr−1 suggesting a general state of resilience of NEE to moderate inter-annual climate variations. However, the annual NEE of −18 and −106 g C m−2 yr−1 in 2006 and 2008, respectively, diverged considerably from this common range. The lower annual CO2 uptake in 2006 was mainly due to late summer emissions related to an exceptional drop in water table level (WTL). A positive relationship (R 2 = 0.65) between pre-growing season (January to April) air temperature (Ta) and summer (June to July) gross ecosystem production (GEP) was observed. We suggest that enhanced GEP due to mild pre-growing season air temperature in combination with air temperature constraints on ecosystem respiration (ER) during the following cooler summer explained most of the greater net CO2 uptake in 2008. Differences in the annual and growing season means of other abiotic variables (e.g. radiation, vapor pressure deficit, precipitation) and growing season properties (i.e. start date, end date, length) were unable to explain the inter-annual variations of NEE. Overall, our findings suggest that this boreal fen acts as a persistent contemporary sink for atmospheric CO2 that is, however, susceptible to severe anomalies in WTL and pre-growing season air temperature associated with predicted changes in climate patterns for the boreal region.
The productivity of forests in sub-Saharan Africa is often summarized into large compartments or site classes. However, the classification of forest productivity levels based on the original site ...index model in Tanzania and the techniques applied to generate the model did not include the micro-toposequence variations within compartments. This may create false expectations of wood supply and hinder the estimation of sustainable harvesting processes. This study analyzed variations in forest productivity and the site index in P. patula stands in two forest plantations of Tanzania to assess the applicability and generality of the present site classification system. We used dominant height as a proxy for forest productivity in 48 plots at the Sao Hill forest plantation (SHFP) and 24 plots at the Shume forest plantation (SFP). We stratified the sampling plots in each site class along the soil catena and recorded the elevation, slope, and slope positions (summit, mid, and lower). Our results showed that the site classes did not generally match the previously assigned site classes and the productivity of a given site class varied between the two plantations. We found a consistently higher productivity than that implied by the original site index in SFP, while in SHFP, the productivity was both higher and lower than estimated in different compartments. Both elevations and slope significantly contributed to predicting the productivity variations within site classes. Overall, the results indicate that physiographic factors affect variations in forest productivity within the assigned site classes. We recommend a more comprehensive site productivity assessment that takes into account physiographic variations and hence provides more accurate information for sustainable forest plantation management in Tanzania and in the region at large.
Most climate change scenarios predict that the variability of weather conditions will increase in coming decades. Hence, the frequency and intensity of freeze-thaw cycles in high-latitude regions are ...likely to increase, with concomitant effect on soil carbon biogeochemistry and associated microbial processes. To address this issue we sampled riparian soil from a Swedish boreal forest and applied treatments with variations in four factors related to soil freezing (temperature, treatment duration, soil water content and frequency of freeze-thaw cycles), at three levels in a laboratory experiment, using a Central Composite Face-centred (CCF) experimental design. We then measured bacterial (leucine incorporation) and fungal (acetate in ergosterol incorporation) growth, basal respiration, soil microbial phospholipid fatty acid (PLFA) composition, and concentration of dissolved organic carbon (DOC). Fungal growth was higher in soil exposed to freeze-thawing perturbations and freezing temperatures of −6 °C and −12 °C, than under more constant conditions (steady 0 °C). The opposite pattern was found for bacteria, resulting in an increasing fungal-to-bacterial growth ratio following more intensive winter conditions. Soil respiration increased with water content, decreased with treatment duration and appeared to mainly be driven by treatment-induced changes in the DOC concentration. There was a clear shift in the PLFA composition at 0 °C, compared with the two lower temperatures, with PLFA markers associated with fungi as well as a number of unsaturated PLFAs being relatively more common at 0 °C. Shifts in the PLFA pattern were consistent with those expected for phenotypic plasticity of the cell membrane to low temperatures. There were small declines in PLFA concentrations after freeze-thawing and with longer durations. However, the number of freeze-thaw events had no effect on the microbiological variables. The findings suggest that the higher frequency of freeze-thaw events predicted to follow the global warming will likely have a limited impact on soil microorganisms.
► Study the effects of freezing-related factors on soil microbial activity/composition. ► Treatments including 3 levels of temperature, duration, moisture and freeze-thawing. ► Opposite responses of fungal and bacterial growth rates to soil frost intensity. ► Soil respiration mainly driven by frost-induced changes in dissolved organic carbon. ► No significant effect of freeze-thaw cycles on microbial growth and composition.
Tree planting in the tropics is conducted for a number of reasons including carbon sequestration, but often competes with increasingly scarce water resources. The basics of forest and water relations ...are frequently said to be well understood but there is a pressing need to better understand and predict the hydrological effects of land-use and climate change in the complex and dynamic landscapes of the tropics. This will remain elusive without the empirical data required to feed hydrological process models. It is argued that the current state of knowledge is confused by too broad a use of the terms 'forest' and '(af)forestation', as well as by a bias towards using data generated mostly outside the tropics and for nondegraded soil conditions. Definitions of forest, afforestation and reforestation as used in the climate change community and their application by land and water managers need to be reconciled.
As a result of canopy interception and transpiration, trees are often assumed to have negative effects on the local hydrological budget resulting in reduced soil and groundwater resources. However, ...it has also been shown that trees can have positive effects through reducing surface run-off and improving soil infiltrability and groundwater recharge, especially in many tropical ecosystems characterized by high rain intensity and degradation-prone soils. In this study, we used isotopic measurements of soil water to better understand the main processes by which trees influence local soil water dynamics within a tropical pasture with scattered tree cover in the Copan River catchment, Honduras. We also determined the stable isotope signature of xylem water in grasses and trees to assess potential competition for water sources during the wet and dry seasons. During the wet season, when soil water availability was not limiting, both grasses and trees primarily utilized soil water near the soil surface (i.e., 0–10 cm). In contrast, during the dry season, we observed niche partitioning for water resources where grasses primarily utilized soil moisture at deeper soil depth (i.e., 90–100 cm) while trees relied heavily on groundwater. Moreover, isotopic data of soil water suggest that trees reduce evaporative water losses from the soil surface, as indicated by the lack of correlation between soil water content and lc-excess (line condition excess) values of surface soil water under trees, and enhance preferential flow as suggested by less negative lc-excess values under trees compared to open areas during the dry season. Taken together, our findings provide further support that trees can have positive effects on the local water balance with implication for landscape management, promoting the inclusion of scattered trees to provide water ecosystem services in silvopastoral systems, adding to other ecosystem services like biodiversity or carbon sequestration.
While reforestation is gaining momentum to moderate climate change via carbon sequestration, there is also an opportunity to use tree planting to confront declining global biodiversity. Where tree ...species vary in support of diversity, selecting appropriate species for planting could increase conservation effectiveness. We used a common garden experiment in Borneo using 24 native tree species to examine how variation among tree species in their support of beetle diversity is predicted by plant traits associated with “acquisitive” and “conservative” resource acquisition strategies. We evaluate three hypotheses: (1) beetle communities show fidelity to host identity as indicated by variation in abundance and diversity among tree species, (2) the leaf economic spectrum partially explains this variation as shown by beetle preferences for plant species that are predicted by plant traits, and (3) a small number of selected tree species can capture higher beetle species richness than a random tree species community. We found high variation among tree species in supporting three highly intercorrelated metrics of beetle communities: abundance, richness, and Shannon diversity. Variation in support of beetle communities was predicted by plant traits and varied by plant functional groups; within the dipterocarp family, high beetle diversity was predicted by conservative traits such as high wood density and slow growth, and in non‐dipterocarps by the acquisitive traits of high foliar K and rapid growth. Using species accumulation curves and extrapolation to twice the original sample size, we show that 48 tree species were not enough to reach asymptote levels of beetle richness. Nevertheless, species accumulation curves of the six tree species with the highest richness had steeper slopes and supported 33% higher richness than a random community of tree species. Reforestation projects concerned about conservation can benefit by identifying tree species with a disproportional capacity to support biodiversity based on plant traits.
The functional relationship between plant diversity and diversity of organisms in higher trophic levels is a fundamental ecological question of what is important for understanding the contribution of restoration of plant communities for conservation. We show that tropical tree species vary in the level of diversity that they support and that this variation can be predicted by plant traits. We further illustrate how such variation can be utilized to increase the conservation value of plant diversity in restoration.
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