
What makes a tree grow well?
Site species matching to a particular environment is a critical element for any forestry project to be successful in that the trees grown are not only suitable for the relevant market conditions but that the tree crops attain optimal growth. This means that trees planted are able to survive during the early stages of growth, are healthy and vigorous throughout their life and reach a marketable stage as quickly as possible.
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Date Posted:
April 6, 2022
An introduction to site species matching and forestry applications.
Site species matching to a particular environment is a critical element for any forestry project to be successful in that the trees grown are not only suitable for the relevant market conditions but that the tree crops attain optimal growth. This means that trees planted are able to survive during the early stages of growth, are healthy and vigorous throughout their life and reach a marketable stage as quickly as possible.
For this to happen the type of tree selected needs to be suitable for the site conditions where it is established. In other words, the site will determine how well the trees will grow, so the trees that will grow well in those conditions are the ones that need to be selected for that site.
What makes a tree grow well?
There are three major site factors that determine how plants will grow in a specific area. These are the temperatures experienced at a site, the moisture conditions prevalent there and the soils that make up the site (Smith 2021). These are discussed in more detail below.

Temperature
Temperature plays a pivotal role in the successful growth of a tree as it affects the rate of photosynthesis which is the process by which trees convert light energy into chemical energy.
In general, trees grow best within a certain temperature range, with optimal growth occurring at temperatures between 15°C and 25°C. At temperatures above or below this range, the rate of photosynthesis will slow down and therefore negatively impact the growth.
Higher temperatures may have a number of negative effects on tree growth, including:
- Increased water loss through transpiration, which can lead to water stress and reduce the tree’s ability to photosynthesize.
- Increased respiration, which can reduce the tree’s energy availability for growth.
- Increased risk of heat damage to leaves and foliage, which can reduce the tree’s ability to photosynthesize.
Low temperatures can also have a negative impact on tree growth, including:
- Reduced photosynthesis at low temperatures, which can slow down the tree’s growth.
- Increased risk of damage from frost, which can kill buds, flowers, and young shoots, and can cause bark damage to the tree.
- Increased risk of injury from cold winds, which can dry out the foliage, and cause damage to the tree.
It’s worth noting that different tree species have different temperature requirements and tolerance, and some species are adapted to grow in specific temperature ranges and climates, such as tropical, temperate or boreal forests. Additionally, trees can also be affected by variations in temperature within a year and over time, such as extreme heat waves or cold snaps, which can have detrimental effects on tree growth and survival.
Temperature triggers vegetation growth, with cooler temperatures slowing growth, and warmer temperatures increasing growth (with limits on both ends). As with all vegetation, trees are adapted to grow optimally under certain temperature ranges (i.e., a minimum and maximum range). Temperatures are usually classified into Mean Annual Temperature (MAT) classes.
This is often further defined into Temperature Zones consisting of 2-degree temperature classes (e.g., 14-16ºC) which take into account mean monthly minimum and mean monthly maximum temperatures, as well as frost risk and altitude (because there is a direct relationship between temperature and altitude – the higher the altitude, the cooler the temperature).

Moisture
Trees absorb water through their roots and use it to transport nutrients and sugars throughout the tree which is essential for tree growth,
Sufficient moisture is necessary for the tree to perform its functions such as:
- Photosynthesis, the process by which trees convert light energy into chemical energy.
- Transport of nutrients and sugars throughout the tree, which are necessary for growth and survival.
- Maintenance of turgor pressure, which helps the tree maintain its shape and rigidity.
A lack of moisture can have a number of negative effects on tree growth, including:
- Reduced photosynthesis, which can slow down the tree’s growth.
- Reduced turgor pressure, which can cause the tree to wilt and reduce its ability to photosynthesize.
- Increased risk of damage from pests and diseases, as a dry tree is more susceptible to attack.
Excessive moisture can lead to oxygen deprivation in the roots, and can promote the growth of pathogens and pests, which can damage the tree.
Individual tree species all have unique moisture requirements and tolerance with some species well adapted to growth in specific moisture conditions and climates, such as dry or wet forests. The availability of moisture may vary depending on the season, and a tree’s ability to cope with drought or flooding varies depending on the species and stage of growth. It’s important to note that to optimize the tree’s growth, the availability of moisture should be balanced with other environmental factors such as temperature, light, and nutrient availability.
A trigger for plant growth is moisture availability. Plants need water to grow, and the primary source of this is rainfall, often referred to as precipitation. It is classified into Mean Annual Precipitation (MAP) classes (for example, 900mm p.a.), which is the average total rainfall measured at a location. However, temperature plays a role in the amount of moisture that is available to a plant due to evaporation.
The higher the temperature the more the evaporation, which means that a plant requires a higher precipitation level in hotter areas than in cooler areas. For example, a plant that requires 800mm per year in an area with an MAT of 14ºC might require 1000mm per year in an area with an MAT of 16ºC to achieve the same level of growth. Therefore, a more accurate indicator of moisture demand for a species is provided by using Moist Availability Zones, which are derived from the ratio between MAP and Potential Evapotranspiration (ETp).
The higher the ratio the more humid an area is. Conversely the lower the ratio, the more arid the area. Climatic data such as MAT, MAP and ETp have been derived for the whole world using climatic models and are available for use in deriving site suitability maps. Examples of such datasets are the WorldClim dataset (Fick and Hijmans, 2017) and the Aridity Index dataset (Trabucco and Zomer 2018).

Soil
Soil provides the foundation for a tree’s root system supplying the tree with the necessary nutrients and water for growth. The quality of soil can be affected by outside factors such as erosion, compaction, and pollution, which can have negative impacts on tree growth and survival.
Soil affects tree growth by providing:
- Nutrients: Soil contains a variety of essential nutrients that trees need to grow, including nitrogen, phosphorus, and potassium.
- Water: Soil holds and releases water, which is necessary for tree growth and survival. Trees absorb water through their roots and use it to transport nutrients and sugars throughout the tree.
- Anchoring: Soil provides an anchor for the tree’s root system, which helps to support the tree and prevent it from falling over.
- Drainage: Good soil drainage is important for the tree to have proper aeration, which is necessary for the tree’s health and survival.
- Microorganisms: Soil contains a diverse community of microorganisms that play a critical role in the tree’s growth and health. Some of these microorganisms help the tree to absorb nutrients, while others help to protect the tree from pests and diseases.
Soil will influence how well a species will grow at a particular site. Soils affect tree growth depending on how well they retain moisture, as well as by the physical impediments they might have within their structure that aid or hinder root development. Factors such as soil depth, soil structure and texture, organic carbon content and waterlogging all influence a site’s ability to support specific species in terms of optimal growth.
Shallow soils hold less water than deep soils, while well-drained soils (for example, less strongly structured soils with good texture (good balance between sand and clay particles) tend to promote good growth as they retain moisture better while not hindering root development). Soils with good organic carbon content tend to hold better nutrition for plant growth than those with lower organic carbon content.
Tree species have individual soil requirements and tolerance with some species adapted to growing in very particular soil types and conditions, such as clay, sand, or acidic soils.
References
Fick S and Hijmans R (2017). WorldClim 2: New 1-km spatial resolution climate surfaces for global land areas. International Journal of Climatology 37: 4302 – 4315
Smith C W (2021) A preliminary forestry site classification of Tanzania based on climate and soils. Internal Company Report – Forestry Development Trust Tanzania
Trabucco A and Zomer RJ (2018). Global Aridity Index and Potential Evapo-transpiration (ET0) Climate Database v2. CGIAR Consortium for Spatial Information (CGIAR – CSI). Published online, available from CGIAR-CSI GeoPortal at https://cgiarcsi.community.
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Dr Mark Norris-Rogers (PhD) PrGIScP
Having originally trained as a Forester, and spending over 10 years in forest management, Mark subsequently specialized in GIS and Remote Sensing, and has over 25 years’ experience in this field. He has a keen interest in applying spatial technologies to provide integrated forest management information for the Forest Managers.
Mark has considerable experience in applying Remote Sensing technologies, such as optical, Radar and Lidar, into forest planning and management. This has included applying Lidar technology to Enhanced Forest Inventory systems which have greatly enhanced the effectiveness of clients’ management plans and operations. Mark provides specialist Remote Sensing and GIS skills to several South African, Canadian and UK companies involved in forestry and natural resources management.
Apart from his forestry qualifications (Diploma in Forestry; NHD Forestry), Mark has a BA Hons in GIS and a PhD in Environmental Science, where his research involved monitoring forestry operations using medium and high-resolution satellite imagery. He is a registered Professional G.I. Science Practitioner with the South African Geomatics Council. Mark has also co-authored several papers in international journals and presented papers at various international conferences.