As with many organisms, the environment has a major impact on how the grapevine grows. Since the vine is a perennial plant, it exists under a set of varying conditions and, in a vineyard setting, the plants experience variation through both space and passage of time. Growth and development of the vine (and thus composition of the fruit) is modified by environment.
In order better to discuss how the environment impacts grapevines, it is useful to classify it. However, it is important to remember that the environment is an integrated system without specific boundaries and, just because we split it up into different categories, it doesn’t exactly exist in that manner.
Climate has been split into three levels: macroclimate, mesoclimate and microclimate (Smart, 1982). Starting with the largest scale, macroclimate (also called regional climate) is defined as the general climate pattern as may be determined from a central recording station. A scale that could be associated with it is tens to hundreds of kilometres (Smart and Robinson, 1991).
The types of factors associated with macroclimate are (i) latitude (which influences sunlight hours, among other things); (ii) altitude; (iii) temperature and altitude versus latitude (e.g.for every increase in altitude of 180 m, there is a decrease in average temperature of 1°C); (iv) topography (large scale, such as mountains/landscapes); (v) length of growing season (time between the previous spring frost and the first frost of autumn); and (vi) quality of growing season (factors such as humidity, presence of relevant insects and diseases).
One step down from there is mesoclimate (also called topoclimate or site climate). Every factor that affects macroclimate also influences mesoclimate, but the scale being discussed is smaller, in the order of tens of metres to kilometres. Factors here include differences in elevation, slope, aspect or proximity to large bodies of water. These affect vineyard temperature, wind, rain, relative humidity (RH), frost-free period (down to 150 days, with 180 days preferred, Tukey and Clore, 1972), row orientation and slope (inclination and aspect), which can reduce frost risk, increase warmth and usually has faster-draining soils and increased air movement.
Soil type may also have an effect; for example, light-coloured soils contributing reflected light in an albedo effect.
The smallest scale of climate is microclimate, also known as canopy climate.
Like mesoclimate, microclimate is a subset of the larger scale climates above it, so every factor that affects macro and mesoclimates also influences microclimate.
More precisely, microclimate is the climate within and immediately surrounding a plant canopy, which means a scale of millimetres to metres.
Factors associated with microclimate include (i) bunch and leaf exposure and their temperatures; (ii) localized photosynthetic differences (e.g. sunflecks);
(iii) irrigation dripper zones; (iv) fertilizer patches; and (v) plant water supply necessary for cell expansion/growth and stomatal function. Much of what the viticulturist does to vines on a seasonal basis relates best to the microclimate.
Trying to quantify climate
Once we have classified climate to help us understand it, we could also use some method of measuring the effect climate has on the growth of grapevines.
A popular method of doing this is known as calculating the growing degree days (GDD) for a location.
Professor Bioletti of the University of California, USA was the first to use temperature and proximity to the ocean to divide California into six different growing regions for planting table and raisin grape vineyards in the early 1900s
(Winkler et al., 1974). Later researchers found that this was not precise enough for the production of wine grapes, and set about improving the methodology used to create the regions. Using heat summation as a basis, Amerine and Winkler (1944) performed an extensive study using temperatures in areas already successfully growing wine grapes and quality parameters of the wines being produced. As a result of this, they defined five growing regions within California depending on the number of GDD accumulated. Each region produced grapes with distinct properties, even when comparing the same cultivar (Winkler et al., 1974).
A GDD in this case is defined as the number of degrees the average temperature for a given day is above 10°C. This can be calculated on a daily basis and the results added to determine the number of GDD for a time period.
In some cases, there may not be access to daily temperature data, so monthly average temperatures can be used, e.g. the monthly average temperature in °C minus 10°C, multiplied by the number of days in that month, with this calculation for each month summed over the growing season.
The threshold of 10°C is used for grapevines because there is little biological activity in plants below this temperature. An example of calculating the GDD for the month of February: if the average temperature for the month was 19.6°C, then GDD = (19.6⫺10)*28 = 269. Note that negative values of GDD are not included in the growing season summation. For a cool climate season the data look like that presented in Table 3.3. Data are usually presented in relation to the growing season, or generally April through to October in the northern hemisphere and October to April in the southern hemisphere, though in areas with a longer growing season (time between killing frosts), such as the eastern coast of New Zealand, it is longer.
Table 3.3. Growing degree day (GDD) calculation for the 2005⫺2006 growing season, Lincoln, Canterbury, New Zealand. GDD calculated on a monthly and daily basis are presented for comparison.
Average Cumulative Cumulative
temperature Days/ GDD/ GDD GDD
Month (°C) month month (monthly) (daily)
September 9.5 30 0 0 29
October 11.1 31 34 34 81
November 12.7 30 81 115 174
December 17.9 31 245 360 379
January 16.5 31 202 562 580
February 16.4 28 179 741 760
March 12.6 31 81 821 844
April 13.6 30 108 929 953
May 9.2 31 0 929 966
Although access to monthly temperature averages is reasonably common, calculations done on a daily basis will better reflect what the vines experience and, similarly, those that integrate information on hourly, or even smaller, intervals are also available and are claimed to be the most accurate way of forecasting the suitability of a site for the production of a certain wine style (Smart, 2003). However, the availability of data with that sort of resolution is fairly limited, especially in a new region that is being evaluated for grape growing.
In comparing GDD calculations, we must know on what basis the data were calculated. For example, calculating the data on a daily basis gives a slightly different value for the same time period (see Table 3.3). In addition, because plants will begin to develop whenever temperatures are above the 10°C threshold, data from the months surrounding the traditionally defined growing season may be appropriate. In this case, for example, the cumulative GDD for the location given in Table 3.3 would be 29 plus 13 GDD higher, due to a few days in September and May (respectively) being warmer than 10°C. The late-season warm days can be important to those cultivars that are harvested at the very end of the season.
Gladstone (1992), in his book Viticulture and Environment, took a more detailed and physiological view of GDD and added several modifications to suit the grapevine, such as limiting the effect of very hot temperatures, as photosynthesis⫺and therefore vine productivity ⫺stops as the environment becomes too extreme.
While 10°C has been settled on as a standard, it is not necessarily the most appropriate threshold temperature to use (as discussed earlier). Moncur et al.
(1989) suggested that base temperatures for budbreak should be 4°C and for leaf appearance 7°C, based on studies with grapevine cuttings. However, for most uses, the base temperature of 10°C is adequate for the bulk of the season and, importantly, comparable with many of the data already available for many areas.
There are a number of other methods of estimating the suitability of an area for grape growing, including the mean temperature of the warmest month (MTWM) and the Latitude Temperature Index (LTI), developed by Jackson and Cherry (1988). Every method has its advantages and disadvantages, so it is important to know some of the limitations of whichever system is used.
Having an historical database of information related to the climate at any given site can be very useful when it comes to predicting when important phenological stages of grapevines (such as budbreak, flowering, bunch closure, etc.) will occur. Keeping records of these stages, along with seasonal weather information, can help to make better management decisions, saving money and time.