Canopy Ecosystem Research Articles

Tapestry Thinking: An Interview with Dr. Nalini Nadkarni on an Unexpected Life in Science

In the ongoing series of Nova Interviews, Challenges Advisory Board member Alan C. Logan meets with thought leaders, scientists, scholars, healthcare professionals, artisans and visionaries concerned about health at the scales of persons, places, and the planet. In this interview, Dr. Nalini M. Nadkarni, of the University of Utah, responds to a set of questions posed by Nova for Challenges. For over forty years, Dr. Nadkarni has been studying the fragility and resiliency of rainforest ecosystems. During this time, Dr. Nadkarni has prioritized science communication with an emphasis on highlighting the interdisciplinary relevancy of research findings. Dr. Nadkarni has worked to promote an integrative way of thinking about the various branches of science and medicine, with an eye toward shifting public policy. Her research career has taken her where only a small minority of scientists have traveled—from remote cloud forests to segregated housing within prison facilities. Dr. Nadkarni successfully challenged the Mattel Corporation to update their globally-recognized toy, Barbie, with women in science in mind. Here, Dr. Nadkarni reflects on the early influences that shaped her career, updates Challenges on the latest directions of her work, and discusses the ways in which the canopy ecosystem can help us understand the complex interconnected challenges of our time.

Inter-annual Persistence of Canopy Fungi Driven by Abundance Despite High Spatial Turnover.

While it is now well established that fungal community composition varies spatially at a variety of scales, temporal turnover of fungi is less well understood. Here we studied inter-annual community compositional changes of fungi in a rainforest tree canopy environment. We tracked fungal community shifts over 3years in three substrate types (live bryophytes, dead bryophytes, and host tree bark) and compared these changes to amounts of community turnover seen at small spatial scales in the same system. The effect of substrate type on fungal community composition was stronger than that of sampling year, which was very small but significant. Although levels of temporal turnover varied among substrates, with greater turnover in live bryophytes than other substrates, the amount of turnover from year to year was comparable to what is seen at spatial distances between 5 and 9cm for the same substrate. Stability of communities was largely driven by a few fungi with high relative abundances. A majority of fungal occurrences were at low relative abundances (≤ 0.1%). These fungi tended to be short lived and persisted to following years ≤ 50% of the time, depending on substrate. Their presence and persistence are likely impacted by stochastic processes like dispersal limitation and disturbance. Most samples contained only one or a few fungi at high relative abundance (≥ 10%) that persisted half or more of the time. These more abundant and persistent fungi are expected to have sustained functional interactions within the canopy ecosystem.

Assessing Green Roof Contributions to Tree Canopy Ecosystem Services and Connectivity in a Highly Urbanized Area

Ecosystem services refer to the benefits provided to humans by the natural environment and healthy ecosystems. Green roofs can be used to enhance ecosystem services, which are reduced by urbanization. Moreover, green roofs can improve biodiversity by connecting green spaces. Therefore, it is necessary to examine the multi-dimensional contributions of green roofs to urban ecosystems. To this end, we used i-Tree Canopy to identify changes in land cover and tree canopy ecosystem services from 2003 to 2021 in Suwon City, Republic of Korea. Next, we simulated improved ecosystem service effects of tree canopies by green roofs. Graph theory was also used to analyze connectivity improvement at local and landscape scales. Tree area was found to decrease from 2003 to 2012, alongside the corresponding ecosystem services, which then showed a tendency to increase from 2012 to 2021. The tree area was expected to increase further in the green roof scenario than in 2003. Green roofs were found to improve tree canopy connectivity at the landscape scale more than the local scale, by acting as stepping stones in connecting fragmented forests and trees. Areas with improved connectivity at both scales should be prioritized for green roof development. These results will aid in the strategic planning of urban green infrastructure and provide support for decision-making processes to improve ecosystem services and connectivity using green roofs.

Influence and predictive capacity of climate anomalies on daily to decadal extremes in canopy photosynthesis

Significant advances have been made over the past decades in capabilities to simulate diurnal and seasonal variation of leaf-level and canopy-scale photosynthesis in temperate and boreal forests. However, long-term prediction of future forest productivity in a changing climate may be more dependent on how climate and biological anomalies influence extremes in interannual to decadal variability of canopy ecosystem carbon exchanges. These exchanges can differ markedly from leaf level responses, especially owing to the prevalence of long lags in nutrient and water cycling. Until recently, multiple long-term (10+ year) high temporal frequency (daily) observations of canopy exchange were not available to reliably assess this claim. An analysis of one of the longest running North American eddy covariance flux towers reveals that single climate variables do not adequately explain carbon exchange anomalies beyond the seasonal timescale. Daily to weekly lagged anomalies of photosynthesis positively autocorrelate with daily photosynthesis. This effect suggests a negative feedback in photosynthetic response to climate extremes, such as anomalies in evapotranspiration and maximum temperature. Moisture stress in the prior season did inhibit photosynthesis, but mechanisms are difficult to assess. A complex interplay of integrated and lagged productivity and moisture-limiting factors indicate a critical role of seasonal thresholds that limit growing season length and peak productivity. These results lead toward a new conceptual framework for improving earth system models with long-term flux tower observations.

Out on a limb: microarthropod and microclimate variation in coastal temperate rainforest canopies

Abstract Species richness of microarthropods in coastal temperate rainforests of western North America is enhanced by the presence of heterogeneous arboreal habitats (moss mats). We studied the relationship between species traits and microclimate as a structuring mechanism for understanding this high diversity. To examine whether community composition is associated with distinct microclimate zones we used Non‐metric Multidimensional Scaling ordination of environmental and community data. To link the traits of arboreal microarthropod species with observed environmental variables we used a trait‐based approach of RLQ and fourth‐corner analysis. Distinct microclimatic zones were observed in the canopy ecosystem stemming from gradients of moisture, temperature, and climatic stability associated with height in canopy and distance from trunk. Associated with these gradients is the growth and development of epiphytic bryophytes such as moss mats and suspended soils, which in turn, influence canopy microclimates. Microarthropod fauna displayed a community‐level response to microclimate gradients which was mediated and partially explained by a trait‐based analysis. A general decline in species richness was associated with harsher microclimate conditions. While many species possessed desiccation resistance traits under low‐moisture conditions, we posit that other species were able to persist by compensatory movements at very small spatial scales. In conclusion this study highlights the importance of environmental buffering associated with greater epiphytic biomass for preserving canopy microarthropod biodiversity, but also how developing an understanding of the species trait distributional shifts can enhance our understanding of communities under different environmental conditions, and for predicting future communities under global environmental change.

Examination of the extinction coefficient in the Beer–Lambert law for an accurate estimation of the forest canopy leaf area index

Leaf area index (LAI) is a crucial ecological parameter that represents canopy structure and controls many ecosystem functions and processes, but direct measurement and long-term monitoring of LAI are difficult, especially in forests. An indirect method to estimate the seasonal pattern of LAI in a given forest is to measure the attenuation of photosynthetically active radiation (PAR) by the canopy and then calculate LAI by the Beer–Lambert law. Use of this method requires an estimate of the PAR extinction coefficient (k), a parameter needed to calculate PAR attenuation. However, the determination of k itself requires direct measurement of LAI over seasons. Our goals were to determine (1) the best way to model k values that may vary seasonally in a forest, and (2) the sensitivity of estimates of canopy ecosystem functions to the errors in estimated LAI. We first analyzed the seasonal pattern of the “true” k (k p) under cloudy and sunny conditions in a Japanese deciduous broadleaved forest by using the inverted form of the Beer–Lambert law with the true LAI and PAR. We next calculated the errors of PAR-based LAIs estimated with an assumed constant k (LAIpred) and determined under what conditions we should expect k to be approximately constant during the growing period. Finally, we examined the effect of errors in LAIpred on estimates of gross primary production (GPP), net ecosystem production (NEP), and latent heat flux (LE) calculated with a land-surface model using LAIpred as an input parameter. During the growing period, cloudy k p varied from 0.47 to 1.12 and sunny k p from 0.45 to 1.59. Results suggest that the value of LAIpred was adequately estimated with the k p obtained under cloudy conditions during the fully-leaved period (0.53–0.57). However, LAIpred was overestimated by up to 0.6 m2 m–2 in May and November. The errors in LAIpred propagated to errors in modeled carbon and latent heat fluxes of –0.21 to 0.32 g C m–2 day–1 in GPP, –0.09 to 0.19 g C m–2 day–1 in NEP, and –3.2 to 3.9 W m–2 in LE, which is close to the measurement errors recognized in the tower flux measurement. LAIpred estimated with an assumed constant k can be useful for some ecosystem studies as a second-best alternative if k is equated to the value of k p measured under cloudy conditions especially during the fully-leaved period.

Arboreal Histosols in Old‐Growth Redwood Forest Canopies, Northern California

Within the canopy of old‐growth redwood (Sequoia sempervirens [D. Don] Endl.) forests, accumulations of plant debris in crotches and on massive limbs serve as parent materials for “arboreal soils” up to 1 m thick and over 50 m above the forest floor. These soils are important habitats and water sources for desiccation‐sensitive organisms in the forest canopy ecosystem. We investigated two of these arboreal soils to better understand how they form and function. The primary vascular epiphyte growing in these soils is leather‐leaf fern (Polypodium scouleri). Fern biomass and redwood leaves and bark are the main parent materials of the soils, which are entirely organic. The soils have distinct horizons and soil structure, and have been changed from their initial parent materials as a result of additions, losses, and transformations of organic matter. They are classified as Typic Udifolists. The soils become more decomposed with depth as fibrous components transition to sapric materials. They have low bulk densities (0.07–0.16 g cm−3) and lose most of their water at relatively high matric potentials. Field water contents and potentials of the arboreal soil materials taken near the end of the dry season indicate that water remains available for uptake by ferns. High base saturation values (>55%) suggest that nutrients are available for plant uptake. The soils are extremely acidic, with pH values around 3.0 in 0.01 M CaCl2 Decomposition may be hindered by the low soil pH and by relatively low soil moisture contents in surface horizons during the dry season.