Friday, August 12, 2011

Forest Under Stress

Typical roadway in The Woodlands with "dead" trees in August 2011
Remember 2009-2010? Our forestss came under attack by beetles. Specifically, the pine trees were stressed by drought, making them vulnerable to beetles. We lost many trees, large and small in The Woodlands Texas, as did the whole of southeast Texas.
Pine casualty of  2010 - remains standing
Today we are in the worse drought we have ever experienced on record. It is super hot, with the temperature breaking the century mark daily, and we have had very little relief from rainfall. This situation has become more harshly evident in our forests in recent days as the drought becomes more prolonged.
Forest floor in George Mitchell Preserve covered in falling leaves
Conditions and results have been evident by wilting, leaf browning, leaf falling and a notable decrease in wildlife occupants since May.  There were no birds singing in this area at mid-day and not one butterfly observation today. The pines are generally faring OK, but the hardwoods are really taking it on the chin, perhaps as a knockout blow!
Southern Red Oak in green belt appearing completely dead, easily identified

In one part of the green belt I investigated, nearly 1/2 of the hardwoods appeared dead. Are they? Maybe they are hibernating by premature sap withdrawal, essentially making Fall in July and August. I checked species and believe almost all of them are actually dead. It is difficult to believe they would survive one more month of high temperatures and drought. I could ascertain two different ways the leaves died - (1) wilting and then curling up, like being scorched with a blow torch, (2) Browning like in the fall, with the shape of the leaf retained.
Curling of leaves reveals the withering effect on this partly green Elm

It just depends on the species and the amount of water remaining in the soil. Everyone notices and most think that they understand, but the reality is not always obvious. It is hidden deep in the forest. After I gave this a bit of thought, I started seeking more understanding of the competitiveness of the various species in survival under these conditions. It looked like Darwin's theory of the survival of the fittest was taking place right before me. In some places, one species would be surviving. In others, it would not.
Mixed pines and hardwoods in dense underbrush

It is thought that the hardwoods generally win out in the forest over the conifers, but now the hardwoods appear to be not be able to compete in very severe droughts. The population density of the forest was about the same, size of the trees were large and mature, and the exposure to the western sun was about the same. There are many variables that need to be compared to understand the dynamics within the forest.  That includes the age of the tree, the soil, exposure to disease, the surrounding underbrush and the share of canopy. All of these variables are unknown to me,although I could have gathered some of it.  What is known is that all of the trees share soil proximity, similar companion brush, and similar floor cover. Most of the trees have trunks at varying angles to the ground further complicating the movement of water up from the root systems. There was no evidence of disease as evidenced by the bark being fully in tact on all specimens I noted. Fungal diseases of Oaks, such as the Red Oak, could be different in each individual.  The ground was not flat, so the small variations in altitude could affect water runoff and thereby availability of water, but I tried to correlate that with the dead trees and came up empty. I could find no one thing in common that could cause higher mortality.  
No dead trees at Lake Bedias nor in most locations in the preserve

In the lowlands near the creek, all the trees are doing much better than in the highlands just a mile or so away. The moist deep sands of the George Mitchell Preserve is significantly mitigating the effects of the drought. Although the drought is beginning to show its ugly head in parts of the forest, most of it remains alive. Wilt? yes! Die? mostly not, unless this extreme weather continues for another month or so.
American Beauty hanging on with fruit

The understory is faring much better than the canopy trees, but there is significant wilt to most of the plants, nearing death in some cases. I am amazed how well some of our plants endure this hardship. Yaupon is the toughest of all. Of all native plants, I revere this tree for its hardiness in recent winter and now summer environment extremes. American  Beauty plant has managed to produce berries this year, although not heartily as it usually does.
Palms normally living in coastal and forest wetlands are suffering
It is my belief that there is going to be substantial loss but let's cross our fingers and hope that we do not lose a high percentage of the hardwoods in our green belts. These trees are responsible for hiding our homes from the street and vice-a-versa, plus they help to absorb some of the street noise. These majestic trees are decades old and help provide us with the feeling of The Woodlands forests. After all, The Woodlands is absolutely nothing without its forests and inhabitants.

1 comment:

ChristineMM said...

I have learned some new to me information about the importance of fungi on the forest floor, they can help the trees access water and not die of drought. The book is very approachable, you may want to check it out. Mycophilia by Eugenia Bone.

Also, trees who receive fertilizer, and lawns, kill the beneficial fungi. Another reason to garden organically.