1Lecture 4 Characterizing the Vegetation, Part 3: Geographic Distribution of Plants and Phenology Instructor: Dennis Baldocchi Professor of Biometeorology Ecosystem Science Division Department of Environmental Science, Policy and Management 345 Hilgard Hall University of California, Berkeley Berkeley, CA 94720 August 31, 2012 This lecture will discuss: 1. Geographic distribution of plants 2. phenology, the timing of canopy characteristics such as leaf out and flowering. 3. impact of phenology on weather and climate Web Resources: Phenology Home page (http://www.uwm.edu/~mds/markph.html) Growing Degree Day Tracker http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/cdus/degree_days/ Check Noormets and Schwartz books.. L4.1 Phenology Phenology is a branch of science dealing with the relations between climate and the timing of biological phenomena, such as bud burst, leaf out and plant flowering. “Phenology: the study of the timing of recurring biological phases, the causes of their timing with regard to biotic and abiotic forces, and the interrelation among phases of the same or different species.” Many phenological relations exist in folklore. Jackson et al. (2001) cite the aphorism, “ seed should be sown when oak leaves are as big as sow’s ears”, for example. When living in Nebraska, I commonly heard that corn should be “knee high by the Fourth of July”.2A biometeorologist requires information on the timing of leaf out for it has drastic consequences on the direction and magnitude of carbon, water, heat fluxes, as well as the interception of radiation. The timing of spring leaf out has major implications on the status of the atmosphere, through variance biosphere-atmosphere feedbacks. Most obvious is a change of surface energy balance, as the new presence of leaves alters the surface albedo and its surface conductance. It will also perturb the regional carbon balance, as the surface will switch from losing to gaining carbon. The physical nature of the surface layer (as measured by its lapse rate and maximum temperature thickness) changes strongly in spring. The timing of leaf out also affects the humidification of the atmosphere through a triggering of transpiration (Schwartz, 1992; Schwartz and Crawford, 2001; Wilson and Baldocchi, 2000). A general sequence of events for annuals include: emergence, growth (early vegetated stage), late vegetated stage, flowering, fructification, senescence. To develop a phenological model observations of leaf development are needed. Five stages for phenological assessments of bud elongation are: b0: bud dormancy b1: bud swelling b2: first green leaf, beginning b3: real bud burst, young leaves protrude beyond scales b4: young leaves are free of bud scales The majority of phenology models in the literature are empirical. They tend to use concepts such as summation of heat units, chilling units (to avoid frost and to experience sufficient dormancy and photoperiod (day length). These triggers have some phyisological basis, as day length does affect certain hormonal signals that regulate plant metabolism. Heating units scale with the thermodynamics of the plant soil system and affect the delivery and availability of water and nutrients. Jackson et al. (2001) describe three elements that are contained in a phenology model. They include a period of: a) chilling during the autumn and winter; b) period of warming in the late winter and spring; c) and a photoperiod trigger. Hari and Hakkinen (1991) define five classes of phenology models for budburst: 1. critical time or day length 2. temperature sum model 3. model based on respiration 4. period unit model 5. model with feedback development3Many phenological models are based on the concept of Degree Day. A degree day is defined as the difference between the daily mean temperature and some base temperature. The daily mean temperature is generally computed as the average of the daily maximum and minimum temperature. Over the course of the year, daily heat units are summed. Empirical evidence shows that phenological events are often triggered when a critical sum is exceeded. Critical growing degree sums for native and non-native plants growing in Sardegna were recently reported by Spano et al (1999). In their study, they found that growing degree sums provided good indicators of Mediterranean species, which have adapted to the seasonal and sparse rainfall. Phenological development of non-natives, on the other hand, was severely affected by spring rain. Table 1 Cumulative heat units for bud break, flowering and ripening. Spano et al. 1999 Species Bud break flowering Full ripe fruitPistacia lentiscus, L 1102 1219 4490 Spartium junceum, L 1021 1296 2963 Olea europea,L 1008 1504 4808 Quercu ilex, L 1494 1598 4974 Myrtus communis, L 1426 2348 5011 Kramer (1995) discusses a two-stage model for a deciduous plant would include: 1. rest phase. bud dormant period. Chilling units are accumulated during this phase, SRchill chilltt0 2. quiescent period. buds fail to grow due to unfavorable conditions. Forcing units are accumulated during this period. Nizinski, J.J. and B. Saugier. (1988) counted cumulative mean temperature after March 1 and base of 0 C. They show that the heat sum required for bud burst is a decreasing function of day length (minutes). The required sum of temperature heat units is a decreasing function of day-length (d, minutes) Tdd00242000141 1.. The denominator can't be negative, so it sets the minimum date, 4.1 (983-D’) Kaduk and Heimann (1997) use an NPP-based model that initiates budburst of grass, tundra and tropical biomes (dNPP/dLAI >0). For other biomes they use a scheme that counts the number of growing degree days below 5oC. Bud burst occurs when the number of 5 degree growing degrees days exceeds a function of the number of days below 5 degrees:4 GDD a b ctC55exp( ) Preliminary data, from our research (in association with the FLUXNET project), is showing that leaf out is correlated with soil temperature equal to the mean annual temperature. One anecdotal observation of colleagues at Oak Ridge, was that leaf out occurred when the soil temperature was near 13 oC. Obviously the entire deciduous biome does not leaf out at this temperature as the soil of northern deciduous forests may not even reach this level. On the other hand, this value was suspiciously close to the annual air