The word canopy is derived from the Latin conopeum, describing a mosquito net over a bed. For canopy researchers in many tropical and temperate forests, this derivation is all too ﬁtting. Forest canopies are home to perhaps 50% of all living organisms, many of which are uniquely specialized for life in the treetops and seldom, if ever, venture to the ground below. The canopy is the photosynthetic powerhouse of forest productivity which fuels this spectacular diversity of species. Over 90% of photosynthesis occurs in just the upper 20% of tree crowns. Here, over 60% of the total organic carbon in forests is ﬁxed and stored, forming an important buffer in the global carbon cycle.
[...] Definition For much of the early development of canopy biology, the nature and limits of forest canopies have been poorly deﬁned. In a functional sense, the forest canopy includes all aboveground plant structures and the interstitial spaces between them, which collectively form the interface between the soil and the atmosphere. Historically, there was a tendency to use more subjective deﬁnitions of the canopy that only included arbitrary portions of the upper foliage of the tallest trees. In practice, however, it has always proven difﬁcult to objectively deﬁne vertical substrata within forests, from either a structural or functional point of view. [...]
[...] The VCL uses near- infrared wavelength laser pulses ﬁred at regular intervals at the earth's surface. The time displacement of the reﬂected laser signal to the VCL determines the height above ground, with an incredible 30 cm vertical resolution, while the magnitude of signal scatter determines the absolute volume of canopy biomass intercepted by the laser. Already the VCL has produced revolutionary new views of forest canopies that would have taken several lifetimes of ground-based measurements to compile. The measurement of canopy architecture has direct applications in a wide range of disciplines. [...]
[...] In coniferous forests in Chile, forest canopy structure is also an important determinant of precipitation inﬁltration into soils, with dense canopies decreasing erosion and increasing the return time for landslide-forming events by over 20%. In other ﬁelds, quantitative models of three- dimensional canopy structures are being utilized to predict (and optimize) the dispersal pattern of pheromones released in forests to control insect pests, and drag coefﬁcients and turbulence around canopy elements are being utilized to parameterize within-canopy atmospheric exchange models. [...]
[...] Another method to partition and integrate the role of forest canopies in NEE at the ecosystem level is to analyze the stable isotope ratios of carbon and oxygen in CO2, as these vary according to the source of CO2 exchange from different ecosystem compartments (for example, autotrophic versus heterotrophic respiration). However, canopy structure can inﬂuence the composition of stable isotopes in belowground and above-canopy compartments by modifying radiation interception and photosynthetic activity of ground vegetation, and by reducing turbulent upwelling of air from the ground and thus inhibiting the mixing of respired CO2 from the soil. [...]
[...] Combinations of these methods have proven useful in monitoring forest responses to environmental change, such as in the use of the Scanning LIDAR Imager of Canopies by Echo Recovery (SLICER) to validate SAR data in North American forest ecosystems. Selecting an appropriate method Simply getting into the forest canopy is often the easy part choosing the most appropriate method of access and deciding how to collect data once you are there is much more difﬁcult. It relies on a clear evaluation of the research objectives and the tools and skills available to implement them. [...]
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