AT THE GLOBAL SCALE THE GREATEST UNCERTAINTY IN FOREST BIOMASS ESTIMATES (IN UNITS OF CARBON MASS PER LAND AREA) IS IN THE HIGHEST BIOMASS SYSTEMS. BECAUSE OF THE STRONG RELATIONSHIP OF TREE HEIGHT TO BIOMASS THESE HIGH BIOMASS SYSTEMS COINCIDE WITH TALL FOREST CANOPIES. TROPICAL FOREST BIOMASS ESTIMATES REPRESENT THE LARGEST UNCERTAINTY IN THE BIOTIC CARBON CYCLE WHICH IS MAKING FUTURE CLIMATE PREDICTION DIFFICULT. THE BIGGEST ERROR IN AMAZONIAN BIOMASS ESTIMATES IS IN TREE HEIGHT AND WOOD DENSITY. NEW TECHNOLOGIES ARE ENABLING THE DETECTION OF CANOPIES OF EXCEPTIONAL HEIGHT IN AMAZONIA AND IN MALAYSIA BUT THE RELATION OF THESE TALL FORESTS TO BIOMASS IS STILL UNCERTAIN. IN THE TEMPERATE ZONE TALL FORESTS ARE FOUND IN COASTAL ENVIRONMENTS WHERE TEMPERATURES ARE NOT EXTREME RAINFALL PLENTIFUL AND SOILS RELATIVELY FERTILE. PRIME EXAMPLES INCLUDE THE CONIFEROUS FORESTS OF WESTERN NORTH AMERICA. WE PROPOSE TO EVALUATE GEDI BIOMASS ESTIMATES IN EXCEPTIONALLY TALL FORESTS WHERE WE HAVE WORKED EXTENSIVELY AND HAVE DATA THAT CAN BE USED TO IMPROVE THESE ESTIMATES. ROBUST ALLOMETRIC EQUATIONS FOR SEQUOIA SEMPERVIRENS FORESTS HAVE BEEN DEVELOPED FOR ALL VASCULAR PLANT SPECIES IN THESE ECOSYSTEMS BASED ON INTENSIVE MEASUREMENTS OF STANDING TREES AND LIMITED DESTRUCTIVE SAMPLING IN BOTH TALL OLDGROWTH AND SHORTER REGENERATING FORESTS. A NETWORK OF FIXED AREA PLOTS HAS ESTABLISHED PLOTS THAT INCLUDES 5-YR RE-MEASUREMENTS OF ALL VEGETATION AND ANNUAL MORTALITY CHECKS TO QUANTIFY ABOVEGROUND BIOMASS LEAF AREA AND GROWTH INCREMENTS. HERE WE WILL LEVERAGE DETAILED GROUND-BASED STUDIES TO EVALUATE GEDI BIOMASS ESTIMATES AND IDENTIFY SOURCES OF ERROR. IN TROPICAL FORESTS WE HAVE DETAILED ESTIMATES OF TREE HEIGHT BIOMASS WOOD DENSITY FROM 180 1 HA PLOTS (35 WITH TRAITS AND SPECTRAL PROPERTIES) ACROSS THE KEY TROPICAL BIOMES OF AMAZONIA THE CONGO BASIN AND BORNEO. WE WILL USE GEDI OUR GROUND-BASED DATA TO IMPROVE ALLOMETRIC EQUATIONS AND BIOMASS PREDICTIONS AT THESE SITES. FURTHER WE WILL USE DESIS HYPERSPECTRAL DATA TO CREATE AN ALGORITHM PREDICTING WOOD DENSITY AT THESE SITES. IN PREVIOUS WORK WE HAVE DEMONSTRATED THE ABILITY OF HYPERSPECTRAL LEAF LEVEL REMOTE SENSING TO ACCURATELY PREDICT WOOD DENSITY IN BORNEO AND PERU. OVERALL OUR WORK WILL GREATLY IMPROVE GEDI PLOT-LEVEL BIOMASS PREDICTIONS IN THE REGIONS OF THE GREATEST UNCERTAINTY. WE WILL FURTHER EXPLORE AN EXCITING NOVEL HYPOTHESIS THAT CANOPY HEIGHT MAY HAVE CHANGED IN DIFFERENT FORESTED REGIONS IN RECENT DECADES BECAUSE OF THE BALANCE OF INFLUENCES BY RISING CO2 AND VPD. WITH RISING CO2 WATER USE EFFICIENCY (WUE CO2 ASSIMILATION PER UNIT WATER LOSS) HAS INCREASED OVER THE PAST 20 YEARS MAINLY THROUGH REDUCTIONS IN ET BY ~80 G H2O M2 HA2. IN THEORY INCREASED WUE MAY ALLOW THE TALLEST TREES TO GROW TALLER. IN REGIONS WHERE VAPOR PRESSURE DEFICIT (VPD) HAS INCREASED STRONGLY IN RECENT DECADES WATER STRESS MAY HAVE INCREASED IN TREETOPS AND CAUSED A REDUCTION OF CANOPY HEIGHT. WE PROPOSE TO IDENTIFY FORESTED REGIONS WHERE INCREASED WUE AND VPD SHOULD HAVE DRIVEN INCREASES OR DECREASES IN TREE HEIGHT BASED ON THEORETICAL CONSIDERATIONS AND THEN WE WILL COMPARE OUR ESTIMATES TO OBSERVATIONS OF CHANGE IN CANOPY STRUCTURE USING GLAS AND GEDI DATA. WE RECOGNIZE THAT BOTH GEDI AND GLAS HAVE LARGE VERTICAL UNCERTAINTIES IN TREE HEIGHT. HOWEVER WITH MILLIONS OF CANOPY HEIGHTS AVAILABLE A POWER ANALYSIS INDICATES THAT WE SHOULD BE ABLE TO SEE A STATISTICAL DIFFERENCE GIVEN MODERATE HEIGHT GROWTH (~20CM ACCORDING TO THE POWER ANALYSIS) AND THUS TEST WHETHER THE GROWTH MATCHES OUR THEORETICAL EXPECTATIONS. ALTHOUGH HEIGHT CHANGE ALONE IS INSUFFICIENT TO INFER SHORT-TERM BIOMASS CHANGE THIS ELEMENT OF OUR PROPOSED RESEARCH WILL ESTABLISH A FOUNDATION FOR LINKING REMOTELY SENSED CANOPY HEIGHT TO ENVIRONMENTAL DRIVERS OF FOREST STRUCTURE THAT ARE EXPECTED TO ALTER FOREST BIOMASS IN THE FUTURE.