Final answer:
The use of sealant on trimmed branches of woody saplings prevents evaporation and provides a barrier against pathogens. Sealed cuts lead to healthier plants due to the retention of moisture and reduced infections, aiding the plants in better growth and recovery.
Step-by-step explanation:
The question asks why newly cut ends of detonating cord (in a metaphorical sense, referring to woody saplings) should be sealed. Upon trimming branches of woody saplings, using sealant on the cuts can be beneficial. When the trimmed branches were covered with a sealant, it is observed that those plants with sealed cuts demonstrate better health after several weeks compared to the ones with unsealed cuts.
The likely reason for the better condition of the plants with sealed cuts is that the sealant provides multiple benefits. It likely stops evaporation of vital moisture from the plant, thus retaining more water which is essential for its health. Moreover, the sealant can protect the open cuts from being infected by pathogens that might otherwise enter through the wounds and cause disease or decay, compromising the plant's vitality and ability to grow.