Decline of Oak Forests

The decline of oak forests throughout much of the northeastern United States has become a great concern in the last decade. A number of factors play into the loss of this important forest type. A few of the primary reasons include: insects/wildlife, disease, and the nature in which an oak forest is managed.

Credit: - Dakota Durcho

Insects and wildlife are the main natural causes for this decline. Insect species such as gypsy moth, which prefer oak species, have wreaked havoc on this forest type for over 150 years. However, gypsy moth did not spread very far until the interstate systems were created in the 1950’s, which made it easier for their egg masses to be transported by cars. This species, in particular, consumes leaves during its larvae stage, which occurs from late spring into the summer. When infestations are large enough, these caterpillars can quickly and efficiently defoliate blocks of forest. If infestations last long enough or are very severe, trees can be quickly killed. Other more commonly noted wildlife, such as deer, can cause an equal amount of damage. Bucks, in particular, will frequently rub young trees, severely damaging their growth and future form. Seedlings are also consumed as they are a favored source of food, especially when other food sources are limited.

Disease also contributes to the mortality of oak forests. A few of the most notable diseases include oak anthracnose, bacterial leaf scorch, oak wilt, and root rot(s). By itself,Oak anthracnose does not typically kill oaks; however, it can greatly impede growth by severely damaging leaves, and over a period of time, can majorly setback trees. Bacterial leaf scorch also creates visible damage to leaves, as this bacterium restricts water uptake by the roots. Typically, bacterial leaf scorch will kill trees within a 2-5 year time span. Oak wilt, although not very common, is a more extreme disease. It is caused by fungal spores, which are disseminated over land, underground, and by insects. Once these spores come in contact with vulnerable trees, they can be dead in only a few weeks’ time. An array of root rots also exist. These diseases are often spread through the air or underground. They typically attack the root systems by cutting off water and nutrients that are key to the tree’s survival. Limited resources often lead to the demise of trees that are infected with root rot.

Management practice decisions are one of the greatest challenges to the oak species. This can be broken down into two distinct elements: overstocked stands, and changing forest type. An overstocked stand means that trees are growing in “tight” conditions with limited space. These conditions create greater competition for resources (sunlight, water, and nutrients) resulting in more stress on trees. This stress, overtime, can kill oaks, and is known as “oak decline. “ Oak decline is very apparent in immature sawtimber stands throughout the northeast. Changing forest type is the other threat to oak forests. As a forest ages, it transitions through successional phases. The oak forest type is a middle successional phase, and thus will eventually transition to a later phase. If oak forests are not continually managed to self-regenerate, they will eventually become beech, maple, or hemlock forest types (late successional). It is important to note that oak forests can also be diminished if improperly managed, transitioning them either forwards or backwards. Some timber cutting practices expedite the demise of the oak-dominated forest. Cuttings that remove only oaks can lead to the reduction in oak species in the next forest, especially if shade tolerant species are already established in the understory. Therefore, carefully planned silviculture should be implemented to maintain healthy oak forests, and their associated ecosystem.

Article by FCFCDB

Nature note for 6/13/20