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Alexandre de Vicente Ferraz

Cooperative Program Coordinator on Silviculture and Management of the Institute of Research and Forest Studies - PTSM/IPEF


The impact of seedling quality in a forest plantation

Talking about evaluating the quality of seedlings in current times can be somewhat challenging. With the forestry market booming, the need to expand the planted area in a short period of time requires companies and service providers (for example third-party nurseries) to quickly meet the forestry demand.

For this reason and others, a certain amount of concern was raised in the forestry media not long ago with the scarcity of seedlings in the nursery market, which, until then, had suffered from lack of demand and rising production costs. The nurseries that survived this era of “skinny cows” today do their best to meet the high demand of their customers for seedlings, such as eucalyptus.

After a more in-depth analysis on the subject, via corporate assessment carried out by the Cooperative Program on Silviculture and Management of the Forest Research and Studies Institute , it became evident that this “shortage of seedlings on the market” is not necessarily linked to the lack of seedlings in quantity. The main challenge for forestry companies today is to meet their demand for seedlings with sufficient quality for planting.

In the specialized literature, there are a series of works that established evaluation criteria and classification of eucalyptus, pine and native species seedlings according to the methods of production, such as substrate types, container size, irrigation depth, etc. Since the publication of the book Production and quality control of forest seedlings, by Professor José Geraldo de Araújo Carneiro, the criteria used to assess the quality of seedlings have not changed much in relation to the present day. Among these evaluation criteria, we can highlight: minimum neck diameter; optimal height range; number of leaf pairs; leaf coloring; stem lignification; presence of active young roots; stem straightness; and aggregation of the substrate to the root system.

Although there are peculiarities attributed to the type of species, clone and seedling propagation method, we can say that a good quality eucalyptus seedling has the following morphological characteristics: stem diameter between 2 and 4 millimeters; height between 25 and 35 centimeters; 4 to 6 pairs of leaves; no bifurcation; stem straight and arranged at 90 degrees in relation to the transverse plane of the tube.

An attribute that most nurserymen have highlighted when evaluating the quality of seedlings is the presence of active roots, which are commonly identified by their whitish color when removing the root system of the seedlings from the tube, that is, when “untubeting” the seedling. These roots ensure the rapid expansion of the root system right after planting, providing adequate conditions for the seedling to access a greater volume of soil and, consequently, a greater volume of water and nutrients available for its absorption.

Most companies in the forest sector have well-established criteria for classifying seedlings, as well as a variety of groupings according to the company's operations and culture. For example, there are companies that classify seedlings into: A (ideal), B (intermediate), C (immature) and D (old or past), according to a series of criteria already mentioned. Gabriela Gonçalves Moreira, when assessing the survival rate and growth of eucalyptus trees based on the quality of the seedlings, observed a series of relevant results that could significantly impact the forestry business, such as:

1) the disposal of seedlings outside the adequate quality standard (example: type C seedlings) could reach 16% of the total production, that is, in a nursery with an annual production of 12 million seedlings, 1.9 million seedlings would be discarded changes per year;
2) the survival rate of type C or D seedlings, after planting, was a maximum of 92%, which ended up requiring the practice of replanting (considering a maximum mortality of 5%) and, with that, increased the cost of production by approximately 6%; It is
3) after 5 years of cultivation, a productivity loss of 9% was observed in the final volume of wood in plantations where “passed” seedlings (type D) were used.

It is worth mentioning that there are few studies on the quality of forest seedlings and their impact on plantations, mainly on productivity (cubic meters per hectare per year) at the end of the rotation. I leave here on record the importance of the work developed by the author Moreira, in 2020, and the stimulus for other works to persevere in long-term evaluations.

Given the due importance and merit of the scientific work conducted so far on the quality of forest seedlings, we must ask ourselves: who is the nursery's final or majority customer? Particularly, I believe to be the forestry or planting front. In this context, what do planting teams and supervisors consider a good quality seedling?

I would venture to say that they expect a rustic seedling, with a “firm” stem that can withstand the adverse conditions in the field, as well as a seedling with a substrate well adhered to the root system, preventing it from falling apart when the seedling is untubed and at planting; with rectilinear stems and with branches that are not very branched, so that the seedling does not become entangled in the rattle during planting; and, finally, a seedling that needs little post-planting irrigation until it is properly established in the field, thus reducing the number of forestry operations.

An attribute that is difficult to measure on the quality of seedlings and that can have disastrous consequences for forestry is the plant health of the seedlings at the time of their dispatch. This scenario is aggravated mainly if the forestry company is not self-sufficient in meeting its demand for seedlings, starting to depend on third-party nurseries, where the control of these pathogens is secondary. An example of this is the spread of Ralstonia throughout most of Brazil. Although the damage caused by this pathogen is still not fully understood, there is significant concern in the industry about it.

In the near future, nurserymen and forest companies will have to reassess a series of processes used in the production of seedlings, as well as the quality concepts for planting them in the field. And why? With the advent of mechanization, forestry already has at its disposal some machines dedicated to planting and some others in the test phase in Brazil. There are planters with single and triple heads, already in operational use in some forestry companies. On the other hand, there are other planters in the testing and adjustment phase for their adaptation and use in the different growing conditions in Brazil, with good approval prospects.

In several demonstrations and presentations on the performance and quality of operation of these forest planters, one aspect was very evident: the quality standard of the seedlings needed to supply these machines must strictly follow specific criteria, so that there is satisfactory operational performance, justifying the beneficial cost of the planting mechanization process. In summary, any of the “challenges” that traditional silviculture accepted regarding the lack of quality of the seedlings at the time of planting will no longer be accepted by mechanized silviculture. This will require predictability, planning and strict control of operational quality in forest nurseries and, primarily, the quality of seedlings desired by a more demanding customer, that is, by modern forestry.