Managing nutritional landscapes as the next frontier in forest ecology and conservation

A diverse landscape can support a more diverse range of species and allow for more complex community structures. In forested habitats, openings and changes in tree composition allow for a higher species richness due to the greater chance of niche occupancy. Knowledge about these relationships may be useful for adapting forest harvesting strategies to, for example, support bird diversity conservation and studies are required to understand how different harvesting strategies influence forest structure and bird diversity. Here, we used Autonomous Recording Units (ARU) to record dawn signalling of forest birds between two forest-harvesting treatment types (complete clear-cuts and hardwood-retention patches) vs control forest patches in the John Prince Research Forest, British Columbia, Canada. We compared Species Richness and Shannon diversity as detected through identifying species in audio recordings, across treatments. The observed Species Richness and Shannon diversity did differ between the Retention treatment and Forest controls when controlling for number of individuals sampled, but both had higher Species Richness and Shannon diversity of passerine species than the Clear-cut treatments. When comparing species composition, we found that forest-associated species were disproportionately detected in Forest controls compared to Clear-cut treatments but detected at intermediate levels in Retention treatments. Species associated with early-seral habitats, though, had disproportionate detection in Clear-cut treatments compared to Forest controls, but also showed expected detections in Retention treatments. These results suggest that partial harvesting and retention of non-commercial hardwoods, can help retain forest-associated species while also helping attract early-seral avian species; this can help increase the overall diversity of the landscape while still making logging profitable. Further research should be conducted to determine the value of this retained habitat at different spatial scales to understand the impacts that it may have for larger-scale deployment.

Understanding how vegetation structure influences invertebrate diversity is critical for tropical forest conservation because invertebrates play key roles in ecosystem functioning. This study investigates the role of vegetation and selected microhabitats in shaping harvestmen assemblages across primary and planted forests in the Amazon rainforest. Our findings challenge the traditional view that vegetation quantity alone drives invertebrate distribution, revealing that specific plant species play a key role in shaping harvestmen assemblages. Notably, Geaya sp. (Sclerosomatidae) was strongly associated with specific arboreal species, especially Tetragastris altissima and Attalea maripa, and was identified as a bioindicator of trees. Tree diversity provides critical habitats in primary forests, illustrating how changes in tree composition can disproportionately impact specialist species. Two species of harvestmen were also identified as bioindicators of forest quality. For instance, Geaya sp. was exclusively linked to primary forests, while the cosmetid Gryne sp. emerged as moderately associated with this type of forest with high structural complexity. By identifying the specific relationships between harvestmen and vegetation, this study demonstrates their potential for monitoring ecosystem health and emphasizes the importance of preserving keystone plant species to maintain ecological integrity in tropical forests.

Optical remote sensing permits modeling of variables related to forest biomass, which is a critical determinant of carbon (C) stocks and fluxes. Plant functional characteristics can be captured by (hyper)spectral data, but it remains unclear whether the links between spectral information and C content are driven largely by tree composition, tree diversity, or by forest attributes not commonly measured in field inventories (e.g., physical canopy structure). Here, we examine the relationship between hyperspectral reflectance and aboveground C content in forests, testing the relative importance of tree composition and diversity in mediating this relationship. We use hyperspectral imaging data from an airborne survey with precisely geo-located field data on canopy trees in two forests in southern Québec, Canada. Spectral data covering visible (VIS), near infrared (NIR) and short-wave infrared (SWIR) wavelengths were extracted for 2626 tree crowns within 64 field plots distributed along an elevational gradient. We applied a continuum removal to the spectra and subsequently performed a principal component analysis to reduce the spectral dimensionality. From the spectral principal components, for each plot we quantified (i) spectral composition (based on average reflectance per plot), and (ii) spectral diversity using the convex hull volume. From field data, we calculated variables characterizing the taxonomic, functional and phylogenetic composition and diversity of canopy trees. Carbon content was calculated using allometric equations based on tree size. We applied a structural equation model based on partial-least squares to test both indirect effects of spectral composition and diversity on C storage of trees (via on-the-ground tree composition or diversity), and also direct effects (reflecting forest characteristics unmeasured in field surveys). We found that spectral composition, particularly from the VIS, is related to C content largely indirectly, via changes in tree composition along the elevational gradient (a transition from deciduous to coniferous species with increasing elevation). Though spectral diversity was significantly related to tree species diversity, no direct or indirect effects on C content were detected. Overall, our findings support (i) the importance of tree composition (but not diversity) in mediating the link between hyperspectral data and forest C content, and (ii) the use of hyperspectral remote sensing as an effective surrogate of taxonomic, functional, and phylogenetic composition of tree communities with strong links to C storage.

QUESTIONS: Ungulates affect plant community structure and composition. Vegetation response to these effects are variable. Wild large herbivore populations are declining globally, but how tree communities respond to this change is not clear. We experimentally examined how tree communities respond to changes in ungulate abundance in a heterogeneous landscape. LOCATION: Lake Mburo National Park, Uganda. METHODS: We recorded tree species in nine replicate sites each with four treatment plots: fenced off‐mound (excluding ungulates), unfenced off‐mound, fenced and unfenced on‐mound. Each species was assessed for fruit type, leafing strategy, spinescence and bark thickness. We compared tree communities on‐ and off‐mound, with and without ungulates using PERMANOVA, and the effects of habitat, fencing and time on stem density and traits using generalized linear mixed effects model. RESULTS: Stem density increased by 88% off‐mound and 138% on‐mound (p = 0.005) with fencing, between 2006 and 2015. Whether tree communities occurred on‐ or off‐mound determined species composition, but fencing had little effect. Tree traits were not markedly altered by fencing on‐mound. Off‐mound, fencing was associated with a 38% increase in the proportion of fleshy‐fruited tree stems (p < 0.001), 18% decline in armed tree stems (p = 0.035) and a 44% reduction in mean bark thickness (p = 0.001). CONCLUSION: Our study highlights the important role mounds play in maintaining tree community composition with declining ungulate abundance. While ungulates influence tree communities off‐mounds they have little effect on tree composition and traits of mound‐borne trees. Thus, Macrotermes mounds support distinct tree communities that are robust to exclusion of ungulates.

Tree composition and diversity in relation to urban park history in Hong Kong, China

QuestionsLong‐term legacies of historical human activities in temperate forests are increasingly recognised as an important driver of vegetation diversity and composition. To uncover centuries‐old legacies, novel approaches are, however, needed. Here, we combine anthracology of historical charcoal kilns and long‐term vegetation resurveys. We asked whether the historical coppicing oriented on charcoal production affected tree‐species composition and how the forest understorey vegetation changed after the coppicing was abandoned.LocationTemperate broadleaved forests in the Slovak Karst National Park, central Europe.MethodsTo explore the historical forest structure and long‐term changes in tree composition, we sampled charcoal remains from 28 historical kilns, identified the burnt tree taxa and estimated the original diameter of the burnt wood. To analyse the vegetation changes over the last four decades, we resurveyed plant composition of 60 quasi‐permanent plots established in 1975.ResultsHistorical charcoal burning was associated with coppicing, which decreased Fagus sylvatica dominance and favoured Quercus spp. in the tree layer. Several decades after the abandonment of coppicing, we observed the decline of Quercus spp. and spread of shade‐casting tree species with nutrient‐rich litter. This probably triggered the identified demise of light‐demanding species, the spread of nitrophytes and taxonomic homogenisation of the forest understorey.ConclusionsThe shift from historical coppicing to current high‐forest management was likely a main driver of the observed taxonomic homogenisation and decline of light‐demanding plants, as in other European lowland forests. Long‐term data from charcoal kilns showed, however, that closed‐canopy forests dominated by beech were historically more common and observed changes in vegetation thus represent a natural process. Findings also suggest that coppicing taking place over centuries enhanced diversity of forest understorey vegetation. Our novel approach combining a vegetation resurvey and charcoal kiln anthracology thus uncovered otherwise hidden links between current biological processes and the historical human legacies, with consequent important implications for nature protection and management.

Changes in tree composition along disturbance in the Sungai-Wain Forest Reserve in East Kalimantan

Although proposed as a means of increasing structural diversity in managed forests, the impact of single-tree selection on the temporal dynamics of three-dimensional structure has not been previously evaluated. Forest structural development in Picea-dominated stands was contrasted over 15 years in stem-mapped randomized plots in southern Finland that underwent either low thinning (creating the even-sized (ES) structure of a bell-shaped diameter distribution) or single-tree selection (maintaining the uneven-sized (UES) structure of a reverse-J-shaped distribution) through multiple harvest entries. Structure was quantified with nonspatial stand attributes (e.g., density) and indices that quantify spatially explicit relationships among neighboring trees (e.g., structural complexity index (SCI)). Over time, three-dimensional structure reflected differential tree growth and mortality, resulting in minor changes in tree composition, spatial pattern, and tree size differentiation and somewhat greater changes in the SCI. The third harvest entry simplified the forest structure in both structure types. However, structural metrics such as the variability of tree diameters, tree size differentiation, and the SCI recovered to preharvest levels within 2–4 years in UES plots, whereas no recovery was seen in the ES structure type. Single-tree selection was demonstrated to perpetuate the uneven-sized structure associated with natural nonpyrogenic Picea-dominated forests.

Changes in tree composition and diversity of streetscapes and their impact on allergenic risk of pollen during urban expansion: a case study in Chengdu, China

The southern edge of the boreal forest in central Saskatchewan, Canada, has had its forest composition changed in the first decades of this century, primarily by logging and escaped fires from adjacent agricultural clearance. Three timber berths were established in 1884 within and immediately adjacent to the present southern half of Prince Albert National Park (established in 1927). These timber berths were selectively logged for saw timber between 1900 and 1918. Between 1907 and 1918, an average of 70 trees per hectare were removed by selective logging. Most of these trees were white spruce (Picea glauca (Moench) Voss). Since logging companies were required to remove all merchantable trees with a basal diameter greater than 25 cm, it is estimated that between 28 and 54% of the canopy trees were removed. Between 1883 and 1942, 81% of the timber berths were burned two or more times by crown fires that spread through the study area from adjacent agricultural clearances 30 km or more away. By 1945, agricultural clearance was largely complete and the clearance-caused fires stopped. The changes in tree composition were determined by transition probabilities between forest surveys taken in 1883 and 1994. Forests subjected to short-interval, clearance-caused fires but no logging were significantly reduced in their abundance of sexually reproducing trees such as white spruce, but increased in trees with either vegetative reproduction (i.e., underground stems, not just basal sprouts) or serotinous cones, such as aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.), respectively. Transition probabilities for forests experiencing both short-interval, clearance-caused fires and logging reveal an even more marked compositional change in this direction.

Interkingdom plant-microbial ecological networks under selective and clear cutting of tropical rainforest

Aquatic consumers exhibit many types of inducible phenotypic responses to variation in resource quantity and quality. Leaf litter constitutes a primary resource in freshwater systems, and variation in litter quality can alter the growth and development of aquatic consumers. It is therefore reasonable to hypothesize that variation in litter quality might also induce phenotypic changes in consumers. To test this hypothesis, we exposed two densities of wood frog (Lithobates sylvaticus [Rana sylvatica]) tadpoles to six chemically distinct species of leaf litter from temperate broadleaf and coniferous trees. After several weeks, we quantified development rate, growth rate, intestinal length, size of the oral disc, and five external dimensions of the tadpoles. In addition to substantial changes in growth and development rates, we found striking changes in all morphological responses among different leaf litter environments, including up to 14% longer intestines, 11% deeper tails, and 6% deeper tail muscles. In addition, we found strong relationships of total nitrogen content with all morphological features except growth rate. Our results indicate that differences in resource quality can induce phenotypic changes that are as large as or larger than changes induced by resource quantity. Our study also has substantial implications for the future of aquatic consumers living in forested wetlands given that these forests are currently experiencing widespread changes in tree composition.

Amazon droughts have impacted regional ecosystem functioning as well as global carbon cycling. The severe dry-season droughts in 2005 and 2010, driven by Atlantic sea surface temperature (SST) anomaly, have been widely investigated in terms of drought severity and impacts on ecosystems. Although the influence of Pacific SST anomaly on wet-season precipitation has been well recognized, it remains uncertain to what extent the droughts driven by Pacific SST anomaly could affect forest greenness and photosynthesis in the Amazon. Here, we examined the monthly and annual dynamics of forest greenness and photosynthetic capacity when Amazon ecosystems experienced an extreme drought in 2015/2016 driven by a strong El Niño event. We found that the drought during August 2015-July 2016 was one of the two most severe meteorological droughts since 1901. Due to the enhanced solar radiation during this drought, overall forest greenness showed a small increase, and 21.6% of forests even greened up (greenness index anomaly ≥1 standard deviation). In contrast, solar-induced chlorophyll fluorescence (SIF), an indicator of vegetation photosynthetic capacity, showed a significant decrease. Responses of forest greenness and photosynthesis decoupled during this drought, indicating that forest photosynthesis could still be suppressed regardless of the variation in canopy greenness. If future El Niño frequency increases as projected by earth system models, droughts would result in persistent reduction in Amazon forest productivity, substantial changes in tree composition, and considerable carbon emissions from Amazon.

IntroductionClimate change has led to rising atmospheric CO2 levels and temperatures, projected to double CO2 concentrations and increase temperatures by 2–5°C by the end of the 21st century. These environmental changes influence plant primary and secondary metabolism, potentially altering plant-insect interactions. Herbivore performance depends on the nutritional quality of host plants, which may decline with elevated CO2 due to an increased carbon-to-nitrogen (C:N) ratio. To explore these effects, the performance of spongy moth larvae (Lymantria dispar) was assessed on oak (Quercus robur) and spruce (Picea abies) seedlings grown under varying climatic conditions. This approach compares a preferred host with a non-preferred one in the case of L. dispar, providing insight into how host plant selection may be influenced under future climate scenarios. In addition, the nun moth (Lymantria monacha), a conifer-feeding species, was also studied on the experimental spruce seedlings to facilitate a comparison with a specialist herbivore.MethodsThree-year-old oak and spruce seedlings were reared for 1 year under four climate scenarios combining two CO2 levels (ambient: 410 ppm and elevated: 820 ppm) and two temperature regimes (20:15°C and 25:20°C). Seedlings were then processed into leaf powder diets for laboratory bioassays with larvae. Secondary metabolites in the seedlings were analyzed to assess climate-induced changes in tree composition and their effects on herbivores.ResultsElevated CO2 increased the C:N ratio in both tree species, with spruce showing a higher ratio than oak. Higher temperatures led to increased nitrogen content, particularly in oak seedlings. L. dispar performed better on oak despite higher secondary metabolite concentrations, while L. monacha exhibited minimal variation in performance on spruce across climate treatments.ConclusionThe combined effects of elevated CO2 levels and increased temperatures impacted plant quality; however, there were nearly no differences in the performance of Lymantria larvae. Despite the higher concentrations of secondary metabolites in the trees, the larvae were able to thrive effectively, demonstrating their resilience to environmental changes.

Characterizing millennial and multi-millennial variability in disturbance regimes will be crucial in improving knowledge within the context of a changing climate and the development of sustainable forest management practices in the eastern Canadian mixed boreal forest. The major biotic and abiotic disturbances in the mixed boreal forest are the spruce budworm, and fire, respectively. The ability to reconstruct the variability of these disturbance agents under different climate conditions over long time periods will help elucidate the interaction between the agents and their dynamics in the mixed boreal forest. The objective of this observational study was to reconstruct the frequency of large spruce budworm population (LSBP) and fire disturbance events, and describe their interaction in the mixed boreal forest over the course of the Holocene within the context of changing vegetation and climatic conditions. Lepidopteran scales and sedimentary charcoal were used to reconstruct the local/extra-local disturbance history from lake sediment along with pollen to reconstruct changes in tree species composition. Spruce budworm and fire disturbance events were determined using the CharAnalysis software. Regime shifts in disturbance event frequencies along with changes in tree composition were detected using Sequential T-test Analysis of Regime Shifts. Spearman’s correlation was used to determine the relationship between spruce budworm and fire event frequencies. Over the course of the Holocene, 57 LSBP events and 76 fire events were detected with event frequencies ranging between 0.75-6.30 events*kyr-1 and 1.71-10.5 events*kyr-1 respectively. Nine and 7 regime shifts in LSBP and fire event frequencies were detected respectively, along with 2 shifts in vegetation. A significant negative correlation was observed between LSBP and fire event frequencies from 6000-1000 BP suggestive of a linked disturbance interaction. The first local lake sediment multi-millennial disturbance regime reconstruction comprising both spruce budworm and fire in the mixed forest revealed a very peculiar oscillation in disturbance event frequencies. Each disturbance seemingly establishes a positive disturbance-vegetation feedback that favors itself and inhibits the occurrence of the other. Further, rapid climate change events may act as a key trigger in establishing the respective feedback loops resulting in the observed disturbance event frequency oscillation.