From Your Forest Newsletter Vol. 2
Scheduling a harvest – Part 2
In a previous article, I discussed the fundamental timing of a harvest – when is the forest ready to be harvested? I discussed how measurements were made in the field and the data were interpreted with the help of a stocking guide to determine how crowded a forest is and how it compares to optimal growing conditions. Based on the conditions of the forest, a timber harvest schedule is developed. And as I mentioned in the previous article, that is the easy step of scheduling a harvest. Determining when to actually begin cutting and getting the job started are more complicated aspects.
Let’s assume a given forest is appropriately stocked for a timber sale and the management plan has scheduled a harvest for this year. Can, or should we start the operation tomorrow? Maybe we could, but maybe we shouldn’t. And in reality, we might not even be able to start tomorrow. There are a few logistical considerations. In most cases, the trees to be removed should be marked (with paint) prior to the operation starting. Although there are exceptions, the silvicultural treatment across the stand is much better if the trees are marked first. So the forester has to have the trees marked before the operation can start. Next, you need a logger – someone to cut, skid and truck the logs. Typically at any one time, a logger has several jobs lined up and he must fit you into his queue. This may mean waiting a few months to a year or more.
Having the trees marked and being on the logger’s queue are important steps toward scheduling a harvest but there are more fundamental aspects of timing related to when it is best to carry out a harvest to meet the forest management objectives and minimize the impact the operation has on the forest. Here are a few things a forester must consider.
- Availability of seeds – A main goal of most harvests is to create conditions that allow for the establishment of a new cohort, or group of trees – what will become the future canopy trees of the forest. Although some trees can arise from root and stump sprouting, many rely on seeds. Therefore, for a harvest to be successful at establishing new trees, seeds must be present. Some tree species produce seeds yearly, but many species produce every few years. Executing a harvest within a year of when target species produce seeds will increase the odds of establishing the new cohort.
- Ground disturbance – Related to the availability of seeds are the ground conditions that the seeds fall on. Each species has different demands for germination and establishing on a site. Some seed have the ability to germinate and root in a layer of forest humus (decomposing organic matter) but many are more successful on a patch of mineral soil that has been exposed when the humus has been pushed aside during the harvest. The process of forest floor disturbance is known as scarification and a timber harvest prescription can call for some scarification to occur in order to increase the germination rate. Snow and ice in the winter greatly reduce the disturbance to the forest floor, so in areas were regeneration of species that rely on scarification, such as oak, timber sales should be scheduled for the non-winter periods, unless these sites are sensitive, as described below.
- Season – Some sites have characteristics that make them more sensitive than others. Areas with seeps and wet ground, or forest that support rare herbaceous plants can potentially be seriously damaged by machinery. Executing the harvest in the winter protects the ground from most damage. Conversely, harvesting in the winter does not provide any scarification that aids in the establishment of new trees. Therefore, winter logging jobs should be saved for sensitive areas and those drier sites that would benefit from scarification should be carried out in the non-winter months.
- Impact on wildlife – A timber harvest typically involves big, loud machines and this can be disruptive to wildlife, especially for animals with smaller home ranges or during crucial parts of the year. Early summer is an important breeding and rearing time for many species, including birds, amphibians, and some mammals. Fall is another important window when many animals, such as bears, are seeking out food in preparation for winter.
- Weather – Weather and season may seem redundant, but weather is more specific to the present time. Although it is effectively impossible to predict what the weather will do during the course of a timber sale, the past weather trends can be taken into account. It might be best to delay a harvest if the previous few weeks have been very wet. This is especially true in the fall when rain, the end of the growing season and the oncoming winter can create pressure to produce in suboptimal conditions.
- Forest health – Even under the best conditions, a timber harvest is a disturbance to the forest and can cause stress to the remaining trees as well as to other plants, soil, and wildlife. For this reason, timber harvests should not be scheduled during a period when the forest is experiencing a serious disease or pest outbreak.
Southern Vermont recently experienced a three year forest tent caterpillar outbreak that caused widespread defoliation on many hardwoods, including defoliation of two flushes of leaves in one year in a few places. These defoliations depleted energy reserves and weakened trees. A harvest changes the dynamic of the forest including the nutrient dynamic in the soil and the light regime through the canopy which can shock the remaining trees. Coupling stress from a defoliation and a harvest can cause forest health decline. Add additional stresses, especially unpredictable ones such as drought and this can lead to tree mortality.
At the beginning I discussed human-related factors that influence the timing of a harvest. Next I listed some biological, climate and weather related factors. I will end with another human-related factor, one that is currently very pertinent – timber markets. Due to the economic slow-down, timber markets have been week for at least the last year and half. Fewer houses are being built or remodeled and people are buying fewer of just about everything. Demand for wood products had dropped considerably and along with it the price that mills are paying for the raw product. Selling timber in a down market can considerably reduce the financial return for the landowner, especially for higher grade logs. A difference in return to the landowner by up to 40% from a few years ago is not unrealistic. Luckily, for the most part, forests can’t “spoil” in a few years so a harvest can be delayed and the trees can simply be left to live until the markets rebound.
I have outlined many factors that influence the timing of a harvest. Unfortunately there are too many factors and they are too diverse so that a harvest is carried out at a time that best suits all of them. A conscientious forester will weigh all the factors and pick a time that best fits as many as possible, with the key being to minimize the impact of the disturbance on the forest.