Search

Old-growth studies commonly emphasize structural and age conditions, selecting proxy indicators of long-term ecological processes. Transition dynamics from mature to old-growth status reveal how natural legacies are progressively accumulated in forests after major disturbances, including human ones. In late-successional, multi-aged forests, the chronosequential ranking of developmental stages is a difficult task, as stand age provides little information, and time since last stand-replacing disturbance cannot be easily determined., Canopy age features, disturbance/suppression history and growth trajectories were reconstructed from ring-width series of canopy trees in a network of 19 old-growth and managed European beech forests in the eastern Alps and central Apennines. A set of tree-ring metrics able to describe the intensity and time distribution of biological and ecological processes (e.g. understorey suppression, canopy accession age) were used to describe the advancement of old-growth status and compared to established metrics of forest structure., Tree-ring metrics were site dependent, as biogeoclimate affects turnover rates and constrains the onset and recovery rate of old-growth attributes. Under the same environmental conditions (high-mountain, limestone-bedrock beech forests), values of the best indicators (number/duration of growth suppression phases; synchronicity of first release; maximum and range of canopy tree age; canopy accession age of the slowest-growing trees) increased monotonically (two to five times) from managed to secondary and primary old-growth forests. Trees in well-conserved primary old-growth forests experienced several and long suppressions, showing the highest complexity in recruitment history, canopy accession and growth trajectories. The best tree-ring metrics, condensed in a Naturalness Score to provide a synthetic functional ranking of forests, varied coherently with structural complexity, which represented stand dynamics more closely than biomass-related metrics., Synthesis and applications. We propose a synthetic ranking of forest functional naturalness based on the ecological processes experienced by trees. This ranking helps to overcome the limitations associated with the use of arbitrary size- or age-related thresholds of old-growth status and provides a functional approach to establish chronosequences in ecological studies. The quantitative description of complex processes underpinning the unique biological and ecological features (e.g. extreme tree longevity) found in primary old-growth forests enhances their irreplaceable value in nature conservation. The proposed framework of tree-ring indicators describes functional traits tightly related to forest naturalness and may thus become a tool to identify and protect old-growth forests, benchmark the impact of silvicultural practices, prescribe targets or evaluate the effectiveness of restoration programmes. [ABSTRACT FROM AUTHOR]

Two ecologically and economically important, and threatened Dipterocarp trees Sal ( Shorea robusta) and Garjan ( Dipterocarpus turbinatus) form mono-specific canopies in dry deciduous, moist deciduous, evergreen, and semievergreen forests across South Asia and continental parts of Southeast Asia. They provide valuable timber and play an important role in the economy of many Asian countries. However, both Dipterocarp trees are threatened by continuing forest clearing, habitat alteration, and global climate change. While climatic regimes in the Asian tropics are changing, research on climate change-driven shifts in the distribution of tropical Asian trees is limited. We applied a bioclimatic modeling approach to these two Dipterocarp trees Sal and Garjan. We used presence-only records for the tree species, five bioclimatic variables, and selected two climatic scenarios ( RCP4.5: an optimistic scenario and RCP8.5: a pessimistic scenario) and three global climate models ( GCMs) to encompass the full range of variation in the models. We modeled climate space suitability for both species, projected to 2070, using a climate envelope modeling tool 'MaxEnt' (the maximum entropy algorithm). Annual precipitation was the key bioclimatic variable in all GCMs for explaining the current and future distributions of Sal and Garjan (Sal: 49.97 ± 1.33; Garjan: 37.63 ± 1.19). Our models predict that suitable climate space for Sal will decline by 24% and 34% (the mean of the three GCMs) by 2070 under RCP4.5 and RCP8.5, respectively. In contrast, the consequences of imminent climate change appear less severe for Garjan, with a decline of 17% and 27% under RCP4.5 and RCP8.5, respectively. The findings of this study can be used to set conservation guidelines for Sal and Garjan by identifying vulnerable habitats in the region. In addition, the natural habitats of Sal and Garjan can be categorized as low to high risk under changing climates where artificial regeneration should be undertaken for forest restoration. [ABSTRACT FROM AUTHOR]

Background:Climate change is driving ecosystem shifts, which has implications for tropical forest system function and productivity. Aim:To investigate Amazon forest dynamics and test for compositional changes between 1985 and 2005 across different plant groups. Methods:Tree census data from 46 long-term RAINFOR forest plots in Amazonia for three climate-functional groups were used: dry-affiliate, climate-generalist and wet affiliate. Membership of each group was ascribed at genus level from the distribution of individuals across a wet–dry gradient in Amazonia, and then used to determine whether the proportions of these functional groups have changed over time, and the direction of any change. Results:In total, 91 genera, representing 59% of the stems and 18% of genera in the plots, were analysed. Wet-affiliates tended to move from a state of net basal area gain towards dynamic equilibrium, defined as where gain ≈ loss, governed by an increase in loss rather than a decrease in growth and mainly driven by plots in north-west Amazonia, the wettest part of the region. Dry-affiliates remained in a state of strong net basal area gain across western Amazonia and showed a strong increase in stem recruitment. Wet-affiliates and climate-generalists showed increases in stem mortality, and climate-generalists showed increased stem recruitment, resulting in overall equilibrium of stem numbers. Conclusions:While there were no significant shifts in most genera, the results suggest an overall shift in climate-functional forest composition in western Amazonia away from wet-affiliates, and potential for increased forest persistence under projected drier conditions in the future. [ABSTRACT FROM PUBLISHER]

The relationship between species richness and ecosystem function, as measured by productivity or biomass, is of long-standing theoretical and practical interest in ecology. This is especially true for forests, which represent a majority of global biomass, productivity and biodiversity., Here, we conduct an analysis of relationships between tree species richness, biomass and productivity in 25 forest plots of area 8-50 ha from across the world. The data were collected using standardized protocols, obviating the need to correct for methodological differences that plague many studies on this topic., We found that at very small spatial grains (0.04 ha) species richness was generally positively related to productivity and biomass within plots, with a doubling of species richness corresponding to an average 48% increase in productivity and 53% increase in biomass. At larger spatial grains (0.25 ha, 1 ha), results were mixed, with negative relationships becoming more common. The results were qualitatively similar but much weaker when we controlled for stem density: at the 0.04 ha spatial grain, a doubling of species richness corresponded to a 5% increase in productivity and 7% increase in biomass. Productivity and biomass were themselves almost always positively related at all spatial grains., Synthesis. This is the first cross-site study of the effect of tree species richness on forest biomass and productivity that systematically varies spatial grain within a controlled methodology. The scale-dependent results are consistent with theoretical models in which sampling effects and niche complementarity dominate at small scales, while environmental gradients drive patterns at large scales. Our study shows that the relationship of tree species richness with biomass and productivity changes qualitatively when moving from scales typical of forest surveys (0.04 ha) to slightly larger scales (0.25 and 1 ha). This needs to be recognized in forest conservation policy and management. [ABSTRACT FROM AUTHOR]

A typical way to quantify aboveground carbon in forests is to measure tree diameters and use species-specific allometric equations to estimate biomass and carbon stocks. Using "citizen scientists" to collect data that are usually time-consuming and labor-intensive can play a valuable role in ecological research. However, data validation, such as establishing the sampling error in volunteer measurements, is a crucial, but little studied, part of utilizing citizen science data. The aims of this study were to (1) evaluate the quality of tree diameter and height measurements carried out by volunteers compared to expert scientists and (2) estimate how sensitive carbon stock estimates are to these measurement sampling errors. Using all diameter data measured with a diameter tape, the volunteer mean sampling error (difference between repeated measurements of the same stem) was 9.9 mm, and the expert sampling error was 1.8 mm. Excluding those sampling errors >1 cm, the mean sampling errors were 2.3 mm (volunteers) and 1.4 mm (experts) (this excluded 14% [volunteer] and 3% [expert] of the data). The sampling error in diameter measurements had a small effect on the biomass estimates of the plots: a volunteer (expert) diameter sampling error of 2.3 mm (1.4 mm) translated into 1.7% (0.9%) change in the biomass estimates calculated from species-specific allometric equations based upon diameter. Height sampling error had a dependent relationship with tree height. Including height measurements in biomass calculations compounded the sampling error markedly; the impact of volunteer sampling error on biomass estimates was ±15%, and the expert range was ±9%. Using dendrometer bands, used to measure growth rates, we calculated that the volunteer (vs. expert) sampling error was 0.6 mm (vs. 0.3 mm), which is equivalent to a difference in carbon storage of ±0.011 kg C/yr (vs. ±0.002 kg C/yr) per stem. Using a citizen science model for monitoring carbon stocks not only has benefits in educating and engaging the public in science, but as demonstrated here, can also provide accurate estimates of biomass or forest carbon stocks. [ABSTRACT FROM AUTHOR]

Aim To test whether a direct relationship exists between the relative abundance of woody plant genera and precipitation regime along the north–south climate gradient of the western Amazon. Location Lowland rain forests in the western Amazon. Methods Floristic data on 91 woody plant genera, from 39 0.1-ha plots across the western Amazon, and precipitation data from a 0.5° global data set were used to test for correlations between plant relative abundance (defined as percentage number of stems ≥ 2.5 cm diameter at breast height for each woody plant genus per plot) and derived dry-season variables. Moisture preference was then assessed in terms of pioneer and shade-tolerant life-history strategy. Results There were significant associations between the distribution of plant relative abundances and seasonal precipitation variables in 34% of genera analysed. Significant differences were identified in size-class distribution between dry affiliates and generalists. Dry affiliates were not dominant in any size class in any plot type, whereas climate generalists dominated most of the size classes in the dry plots and the mid-range size classes in the wet plots. Dry-affiliate genera were a minority, even in dry forests. Wet-affiliate genera were correlated with shade tolerance, whereas genera with no rainfall affiliation were often pioneers. Main conclusions The results suggest that moisture variable seasonality influences community composition in a manner that can be related to the life-history trade-off between shade tolerance and pioneer ranking. One possible reason for higher diversity in wetter forests is that high rainfall amplifies the niche space available to shade-tolerant plants. Determining which plant groups are constrained by which environmental variables can contribute to our understanding of how forest composition may be changing now, and how it may change under future climate: if shade-tolerant trees are also drought-intolerant, community structure in wet forests may be more vulnerable to future increases in moisture stress. [ABSTRACT FROM AUTHOR]