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I live in the midwestern United States. I cycle to work, sometimes on heavily wooded roads, and I can't help but notice that in most places within the surrounding deciduous forests Pine and evergreen trees don't seem to be doing so well - the few that exist don't look too happy.

In some places, however, there are majestic stands of pines - often completely free of the "seasonal" variety of trees.

Why is this? What allows the slow growing pines to out-compete the other arboreal denizens of the forest? And generally in such particular areas?

Thanks, this is killin' me...

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  • $\begingroup$ A lot of forest is planted... I've heard that here in Sweden around 95% of forest is planted rather than natural forest, I've not got a source available for that though $\endgroup$ – rg255 Feb 3 '16 at 20:37
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Forest Succession 101

enter image description here

Pines are actually fast-growing, shade-intolerant, early-successional species. When land is allowed to lay fallow after being cleared by fire, wind storms, human land use or other major disturbance, the successional sequence will begin.

At first only herbs and grasses grow, but eventually these are shaded out by shrubs and tree seedlings. In this setting, the limiting factor is typically light. Because pines are fast growing in the sun, they usually take over a field and develop a relatively dense even-aged stand.

young pine stand

Because the seedlings grow so well and densely, they usually shade out and prevent most other trees and shade-intolerant plants from growing. The result: a dense stand of mostly pines:

Pine stand

I'll note here that early on in this process (before processes of self-thinning really get to take off), you can end up with what are sometimes called "dog hair" stands. Also, if you see clear rows in the pine stand, that's a good indication the pines were planted.

Eventually (80-120 years), most of these pines will die and fall out of the canopy (both due to "natural" causes and additional wind, ice, pest, or fire disturbance). As large pines fall and clear large enough canopy gaps, shade-tolerant sub-canopy hardwoods can take their place. Because pines are highly shade intolerant, pines do not regenerate again in that stand (without another major canopy-clearing disturbance). The result: a mostly hardwood-dominated forest (with perhaps a few remnant older pines):

transition stage

So...

  • The all-pine stands you're seeing are early on in the successional sequence.
  • The few pines (that "don't look too happy" because of age) mixed with hardwood ("seasonal variety") trees are in a mid-to-late successional stand.
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    $\begingroup$ Note: my answer addresses the description of your question -- it is due to succession that you see the forest stands you're observing. This example of secondary succession does not apply to all instances of pine existence (as your actual questions asks). That question would have a very complicated answer involving niche theory, succession, disturbance regimes, interspecific and intraspecific interactions, trait descriptions, etc. and would need to be addressed at numerous scales (biology, population dynamics, community interactions, meta-populations/meta-communities, landscape scales, etc.) $\endgroup$ – theforestecologist Feb 3 '16 at 19:52
  • $\begingroup$ What about non natural forest - most forest these days is managed and has commercial interests. If @user1833028 has an exact location we might be able to rule that out! $\endgroup$ – rg255 Feb 4 '16 at 6:58
  • $\begingroup$ @rg255 I've addressed that in my answer. You'll know it was planted if you see a conspicuous rows of trees. If there are no rows, then there's a pretty good chance those seeds arrived on their own (via wind) $\endgroup$ – theforestecologist Feb 27 '16 at 14:16
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In nature, species compete for resources like water, light, nutrients, etc. and need to find 'their place' in this struggle. According to niche theory, every species occupies a certain spot in the multidimensional niche space (the dimensions describe the number of environmental factors) where it performs better than any other species. If there would not be such a place, the species is doomed to extinction in free nature. Let's look at the pine (Kiefer) and the beech (Buche), a common european deciduous tree:

competition between pine (=Kiefer) and beech (=Buche)

You see that the beech outcompetes the pine under intermediately moist conditions, although these conditions are theoretically best suited for the pine (physiological optimum). However, the pine can outcompte the beech at the extremes of the gradient (ecological optimum).

Now imagine many environmental factors and many species. Under the predominant conditions in the midwest USA, deciduous tree species are favored over confifers because they are the better competitors. If conditions change towards the more extreme (very dry/moist, harsh climate,...), the pine gains the upper hand and forms large stands.

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  • $\begingroup$ So if pines compete better in drier areas, you might find that the soil around pine stands is sandier, and would drain better than the soil where pines don't do as well. If you want to research this, your state probably has a university extension program willing to do soil testing for a small fee, you might find something that distinguishes pine stand soil to non pine soil. $\endgroup$ – user137 Aug 22 '14 at 18:13
  • $\begingroup$ Also, sir, would these be local conditions, temporal conditions (ie, they became established for a period where they had the oppourtunity) or both? $\endgroup$ – user1833028 Aug 23 '14 at 5:16
  • $\begingroup$ Both is basically possible, especially if you take deliberate alteration of site conditions and competition into account (forestry). However, on the long run and under natural conditions the general site characteristics will dominate temporarily beneficial effects. In general, trees are better adapted to stable conditions, whereas other plants like annuals or biennials are specialized in colonizing very unstable habitats. Trees aren't that good in taking advantage of short-term fluctuations. $\endgroup$ – Hav0k Aug 23 '14 at 11:52
  • $\begingroup$ But note that in different conditions - for instance the mountains of the US West - evergreens (pine, fir, cedar &c) almost totally dominate the landscape. The only large deciduous tree is the aspen, and it's restricted to wet area such as meadows and along streams. The rest are basically shrubs. $\endgroup$ – jamesqf Nov 1 '18 at 2:59

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