Fungi have important roles as decomposers, mycorrhizal root symbionts and pathogens in forest ecosystems, but there is limited information about their diversity and composition at the landscape ...scale. This work aimed to disentangle the factors underlying fungal richness and composition along the landscape‐scale moisture, organic matter and productivity gradients. Using high‐throughput sequencing, we identified soil fungi from 54 low‐productivity Pinus sylvestris‐dominated plots across three study areas in Estonia and determined the main predictors of fungal richness based on edaphic, floristic and spatial variables. Fungal richness displayed unimodal relationship with organic matter and deduced soil moisture. Plant richness and productivity constituted the key predictors for taxonomic richness of functional guilds. Composition of fungi and the main ectomycorrhizal fungal lineages and hyphal exploration types was segregated by moisture availability and soil nitrogen. We conclude that plant productivity and diversity determine the richness and proportion of most functional groups of soil fungi in low‐productive pine forests on a landscape scale. Adjacent stands of pine forest may differ greatly in the dominance of functional guilds that have marked effects on soil carbon and nitrogen cycling in these forest ecosystems.
Forest canopy structural complexity (CSC), an emergent ecosystem property, plays a critical role in controlling ecosystem productivity, resource acquisition and resource use‐efficiency; yet is poorly ...characterized across broad geographic scales and is difficult to upscale from the plot to the landscape.
Here, we show that the relationship between canopy height and CSC can be explained using power laws by analysing lidar‐derived CSC data from 17 temperate forest sites spanning over 17 degrees of latitude. Across three plant functional types (deciduous broadleaf, evergreen needleleaf and mixed forests), CSC increases as an approximate power law of forest height. In evergreen needleleaf forests, increases in canopy height do not result in increases in complexity to the same magnitude as in other forest types.
We attribute differences in the slope of height:complexity relationships among forest types to: (a) the limited diversity of crown architectures among evergreen conifer trees relative to broadleaf species; (b) differences in how vertical forest layering develops with height; and (c) competitive exclusion by needleleaf species. We show support for these potential mechanisms with an analysis of 4,324 individual trees from across 18 National Ecological Observatory Network sites showing that crown geometry‐to‐tree height relationships differ consistently between broadleaf and needleleaf species.
Power law relationships between forest height and CSC have broad implications for modelling, scaling and mapping forest structural attributes. Our results suggest that forest research and management should consider the nonlinearity in scaling between forest height and CSC and that the nature of these relationships may differ by forest type.
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
The impact of shifting disturbance regimes on soil carbon (C) storage is a key uncertainty in global change research. Wildfires in coniferous forests are becoming more frequent in many regions, ...potentially causing large C emissions. Repeated low‐intensity prescribed fires can mitigate wildfire severity, but repeated combustion may decrease soil C unless compensatory responses stabilize soil organic matter. Here, we tested how 30 years of decadal prescribed burning affected C and nitrogen (N) in plants, detritus, and soils in coniferous forests in the Sierra Nevada mountains, USA. Tree basal area and litter stocks were resilient to fire, but fire reduced forest floor C by 77% (−36.4 Mg C/ha). In mineral soils, fire reduced C that was free from minerals by 41% (−4.4 Mg C/ha) but not C associated with minerals, and only in depths ≤ 5 cm. Fire also transformed the properties of remaining mineral soil organic matter by increasing the proportion of C in a pyrogenic form (from 3.2% to 7.5%) and associated with minerals (from 46% to 58%), suggesting the remaining soil C is more resistant to decomposition. Laboratory assays illustrated that fire reduced microbial CO2 respiration rates by 55% and the activity of eight extracellular enzymes that degrade cellulosic and aromatic compounds by 40–66%. Lower decomposition was correlated with lower inorganic N (−49%), especially ammonium, suggesting N availability is coupled with decomposition. The relative increase in forms of soil organic matter that are resistant to decay or stabilized onto mineral surfaces, and the associated decline in decomposition suggest that low‐intensity fires may promote mineral soil C storage in pools with long mean residence times in coniferous forests.
Fire changed the proportion of soil organic matter that is resistant to decay or stabilized onto mineral surfaces, which were coupled with declines in decomposition. This suggests that low‐intensity fires may promote mineral soil C storage in pools with long mean residence times in coniferous forests, presenting one benefit of prescribed burning to carbon storage in forests.
Abstract
The structural and functional traits of coniferous trees can reflect their growth states and adaptive strategies to a harsh environment. However, it is still unclear if and how hydraulic ...traits of subalpine conifers change with altitude.
Therefore, the changes in stem hydraulic characteristics of
Abies fabri
along an elevational gradient (2700–3700 m a.s.l.) were identified in a subalpine ecosystem in southwest China and linked to anatomical properties.
Xylem hydraulic efficiency decreased with increasing elevation. Surprisingly, higher hydraulic dysfunction and vulnerability to embolism occurred at higher altitudes. The trade‐off between hydraulic efficiency and safety was weak in
A. fabri
at higher elevations. Low temperature and superfluous precipitation may be the main constraints for hydraulic function and mechanical strength ((
t
/
b
)
2
)) in plants at high elevations (
p
< 0.05). The strongly limited hydraulic transport system reflected the severe growth constraint of
A. fabri
at high elevations. Although series of anatomical traits varied with elevation (e.g. smaller mean diameter of tracheid, mean hydraulic conduit diameter and mean pit aperture diameter at higher altitude) and revealed the adaptive strategies to enhance embolism resistance, thickness‐to‐span ratio ((
t
/
b
)
2
) played a dominant role in the trade‐off between hydraulic efficiency and safety. Thickness‐to‐span ratio was positively correlated with stem hydraulic conductivity but negatively correlated with percent loss of conductivity and water potential at 50% loss of conductivity, (
t
/
b
)
2
and specific leaf area. Therefore, plants with better hydraulic and growth states at low elevations could allocate more resources to building up solid mechanical supporting systems to cope with high wind load, while those at high elevations with impaired growth states and limited hydraulic functions had to invest more resources in leaves under the harsh environment. The weak trade‐off between hydraulic efficiency and safety (lower hydraulic efficiency and high risk of embolism) could limit the growth and distribution of
A. fabri
at timberlines; however, global warming trends may facilitate hydraulic transport and benefit plants' growth in the future.
Read the free
Plain Language Summary
for this article on the Journal blog.
Abstract
Defoliators cause extensive damage in boreal and temperate forests of the world. Considerable effort has been invested to understand their individual population dynamics, and despite ample ...theorising, there is little empirical evidence on factors causing spatial synchrony of pest eruptions at landscape scales.
We report on the landscape‐level effect of forest configuration and composition on the intensity of outbreaks of spruce budworm and forest tent caterpillar in a mixedwood boreal forest in northern Minnesota (USA) and adjacent Ontario (Canada), and how this is related to the degree of spatial synchrony in each species' outbreak cycling.
Using a large spatiotemporal tree‐ring reconstruction of outbreak impacts across these two systems, we evaluate two contrasting theories governing defoliator outbreaks: harmonic oscillation (a.k.a. ‘clockwork’) and relaxation oscillation (a.k.a. ‘catastrophe’), each with consequences linked to top‐down versus bottom‐up influences on outbreak behaviour in time and space.
We find synchrony varies temporally, among outbreak cycles and in direct proportion to cycle peak intensity; however, cycle peak intensities are distributed bimodally in time, and so, therefore, are synchrony coefficients. Spatially, the area where each pest species currently cycles with the greatest peak intensity and synchrony is where their preferred host trees are currently found in greatest proportion.
Despite overall synchrony in cycling, we found, in both systems, a persistent negative spatial correlation among successive eruptive pulses of defoliation. Many of these eruptions failed to spread spatially and to coalesce with other spot eruptions to form extensive area‐wide outbreaks. Eruptions often fail to spread at the hardwood‐conifer interface, resulting in outbreak pulses that systematically bounce back and forth between landscape types, particularly when systems were cycling at low amplitude. These over‐dispersed spatial patterns of pulse impact are consistent with a contagious theory of eruption and outbreak spread. They could be considered consistent with harmonic oscillation theory only for populations cycling at different frequencies, with cycling frequency determined by host forest landscape structure.
Synthesis
. We find that defoliator outbreak dynamics across systems include spatiotemporal signatures of each theoretical paradigm—suggesting a hybrid approach will better characterise outbreak behaviour. Host concentration influences which paradigm dominates the spatial dynamics in any given forest landscape context. Because of the synchronising effect of host concentration on forest insect spatial dynamics, mixedwoods appear to be less prone to intense, synchronised defoliator attack than forests of pure hardwood or pure conifer.
Temporal growth variability is an important indicator of ecosystem function under climate change. However, we still lack a unified understanding of how climate conditions, climate change (trends and ...variability), nitrogen (N) deposition, functional traits and stand factors together affect radial growth variability.
Using global conifer tree‐ring records (123 species from 1780 sites) during 1970–2010 to calculate growth variability, we assessed how abiotic and stand factors affect growth variability directly and indirectly via functional traits with boosted regression tree and structural equation models, and examined the differences among continents (North America, Asia and Europe).
We found: (a) growth variability was mainly affected by warm‐induced drought and increased at lower latitudes. Climate warming in winter could decrease growth variability, but this effect is by far not enough to offset the threat of hotter drought; (b) there existed a trade‐off between fast‐ and slow‐growing (drought tolerance) strategies for global conifer species, and abiotic and stand factors affected growth variability via functional traits. Contrary to common conjecture, species with higher drought tolerance revealed higher growth variability due to their occupation of more xeric sites, and may also because higher investment in drought tolerance leads to less investment remaining for growth; (c) older trees revealed higher growth variability due to their more conservative growth strategy, while at large scales, taller trees showed lower growth variability due to occupying more productive sites; and (d) moderate N deposition could reduce growth variability by leading conifers to adopt a more fast‐growing strategy (e.g. in Asia), but long‐term and excessive N deposition led to increased growth variability (e.g. in North America and Europe).
Synthesis. Our results suggest that coniferous forests in water‐limited regions should be more vulnerable to hotter drought, and the ‘fast–slow’ growth strategies may be key in regulating the effects of various abiotic and stand factors on ecosystem stability. Moreover, future hotter drought and N deposition will severely threaten conifer growth, especially for old trees and conifers at lower latitudes.
Temporal growth variability can provide new insights into forest response to climate change. Our results suggest warm‐induced drought as a major driver of the temporal growth variability and found that the ‘fast–slow’ growth strategies may be key in regulating the effects of various abiotic and stand factors on the ecosystem stability of coniferous forests. Future hotter drought and N deposition will severely threaten conifer growth, especially for old trees and conifers at lower latitudes.
The 137Cs content in mosses (Hylocomium splendens), lichens (Cladonia stellaris) and the needles of the Siberian pine (Pinus sibirica) and the common pine (Pinus sylvestris) along the transect from ...the north to the south of Western Siberia from N. 67.5° to N. 55° has been investigated. The appearance of 137Cs here is linked to the nuclear weapon tests at Novaya Zemlya. The measurements have shown that at all sampling points south of N. 59.6° there is a very sharp decrease in the 137Cs specific activity in all components of the ecosystem (in mosses and lichens by about 20 times, and in the needles of conifers by 100 times) instead of a smooth decrease. This fact can be explained by the existence of the global atmospheric circulation consisting of three circulation cells in the Northern hemisphere. It is just around N. 60° that the boundary between the Polar cell and the circulation cell of midle latitudes is drawn. At this boundary, the counter surface air flows of these cells (in our case, a contaminated flow from the north and a clean one from the south) collide and generate the upward air flows here that take 137Cs away. In addition, there is water vapor condensation in the upward flows resulting in snowfalls, rains and thunderstorms. And with these precipitation events, large amounts of 137Cs should have fallen out to the north of the Polar cell boundary during the Novaya Zemlya tests. The areas south around of N. 60° have been supposed to remain clean, which is what is being observed.
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•137Cs specific activities were measured in mosses, lichens and coniferous needles.•The appearance of 137Cs is linked to the nuclear weapon tests at Novaya Zemlya.•A very sharp decrease in the content of 137Cs was found to the south of N. 59.6°.•Main amounts of 137Cs fallen out to the north of the Polar cell boundary.
•The variation of canopy temperature was explained well by climatic variables.•A strong positive relationship was found between canopy and soil temperatures.•A weak negative relationship appeared ...between canopy temperatures and soil water.•Canopy temperatures were significantly related to afternoon-hour carbon exchange.•Canopy temperatures were more weakly related to latent heat fluxes.
Thermal infrared (TIR) techniques to collect thermal imagery have been useful for recording quasi-continuous plant surface temperatures. In this study, we applied a thermal camera to measure canopy skin temperatures in a mature ponderosa pine forest in central Oregon over one growing season from May to September 2014. This study had the following objectives: (1) to examine spatial and temporal variations of canopy temperature; (2) to explore the effects of climate and soil conditions on canopy temperature; and (3) to quantify the relationships of canopy temperatures to forest-atmosphere heat and carbon fluxes. The temporal variation of 30-min mean canopy temperature was large, and leaf temperatures ranged from −2.1 to 33.6°C during the study period. The temperature difference was small between the whole canopy and leaf regions, while tree stems had warmer temperatures than leaves, especially during the afternoon (12:00–19:59h). The canopy thermal regime was largely controlled by climatic conditions and related to the soil thermal states. Air temperature, relative humidity, longwave radiation, and soil temperature at 2-cm depth were tightly correlated with 30-min and daily/sub-daily mean canopy leaf temperatures (r≥0.6 or ≤−0.6, p<0.01). The daily/sub-daily mean canopy temperatures contained stronger relationships with the climatic and soil variables than the 30-min mean temperatures. During the afternoon, the mean leaf temperature was more closely related to net ecosystem exchange (r2=0.69) than air temperature, driven by the strong relationship between tissue temperature and photosynthesis and respiration. Our results show that canopy thermal conditions can be monitored almost continuously for extended time periods to better characterize how canopies respond to environmental conditions. Finally, thermal measurements show great promise for quantifying linkages to carbon exchange in forest ecosystems.
Leaf functional traits are widely used to detect and explain adaptations that enable plants to live under various environmental conditions. This study aims to determine the difference in leaf ...functional traits among four forest types of Pinus massoniana coniferous and broad‐leaved mixed forests by leaf morphological, nutrients, and stoichiometric traits in the subtropical mountain, Southeastern China. Our study indicated that the evergreen conifer species of P. massoniana had higher leaf dry matter content (LDMC), leaf C content, C/N and C/P ratios, while the three deciduous broad‐leaved species of L. formosana, Q. tissima, and P. strobilacea had higher specific leaf area (SLA), leaf N, leaf P nutrient contents, and N/P ratio in the three mixed forest types. The results showed that the species of P. massoniana has adapted to the nutrient‐poor environment by increasing their leaf dry matter for higher construction costs thereby reducing water loss and reflects a resource conservation strategy. In contrast, the three species of L. formosana, Q. tissima, and P. strobilacea exhibited an optimized resource acquisition strategy rather than resource conservation strategy in the subtropical mountain of southeastern China. Regarding the four forest types, the three mixed forest types displayed increased plant leaf nutrient contents when compared to the pure P. massoniana forest, especially the P. massoniana–L. formosana mixed forest type (PLM). Overall, variation in leaf functional traits among different forest types may play an adaptive role in the successful survival of plants under diverse environments because leaf functional traits can lead to significant effects on leaf function, especially for their acquisition of nutrients and use of light. The results of this study are beneficial to reveal the changes in plant leaf functional traits at the regional scale, which will provide a foundation for predicting changes in leaf traits and adaptation in the future environment.
This study aims to determine the difference in leaf functional traits among four forest types of Pinus massoniana coniferous and broad‐leaved mixed forests by leaf morphological, nutrients, and stoichiometric traits in the subtropical mountain, Southeastern China.
European forests are an important source for timber production, human welfare, income, protection and biodiversity. During the last two decades, Europe has experienced a number of droughts which have ...been exceptional within the last 500 years, both in terms of duration and intensity. These droughts seem to leave remarkable imprints on the mortality dynamics of European forests. However, systematic observations on tree decline, with emphasis on a single species, has been scarce so far so that our understanding of mortality dynamics and drought occurrence is still limited at a continental scale.
Here, we make use of the ICP Forest crown defoliation dataset, permitting us to retrospectively monitor tree mortality for all major conifers, major broadleaves, as well as a pooled dataset of minor tree species in Europe. In total, we analysed more than three million observations gathered during the last 25 years and employed a high‐resolution drought index which can assess soil moisture anomaly based on a hydrological water‐balance and runoff model.
We found overall and species‐specific increasing trends in mortality rates, accompanied by decreasing soil moisture. A generalized linear mixed model identified a previous‐year soil moisture anomaly as the most important driver of mortality patterns in conifers, but the response was not uniform across the numerous analysed plots.
We conclude that mortality patterns in European forests are currently reaching a concerning upward trend which could be further accelerated by global change‐type droughts in the near future.
European forests show consistent signals of drought‐induced dieback which can be partly explained by anomalies in soil moisture and the occurrence of global change‐type droughts during the last 25 years.
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