Forest ecosystem is more stable then land ecosystem why
Answers
In terms of the species, and the relative abundances you see of them from year to year, forests are the most stable. Deserts, grassland, and forest represent a gradient of annual precipitation going from very low to high amounts of rain received each year. This is fairly obvious, but what is more interesting in this context is that with decreasing annual precipitation, you also get increasing variability in precipitation. That means, in a grassland, the amount of precipitation can vary considerably from year to year, with one year receiving 300mm rainfall, and the next 1200mm. Deserts precipitation, while lower, is even more variable, and forest precipitation, while it can vary by substantial amounts, does not vary much relative to its total average. For instance, if the average rainfall in a forest is 1500, and it varies from 1200–1800mm, that is still a lot of variability, but its coefficient of variation (CV, variance/mean) is small compared to the other types of ecosystems.
As such, the vegetation of these places is different. In deserts, you have an assembly of highly drought tolerant plants, paired with a selection of annuals that exist only as seeds until rainfall occurs, and then they appear and disappear within a few weeks. We could consider this a lack of stability in the ecosystem over time, if we want to think of it on a 2–10 year scale. In one year we would observe one set of species, and in the next we could observe an almost entirely different set. We could even observe this over parts of a single year.
In grasslands, you typically see greater stability in the plants you find, but their abundances can change considerably from year to year. For instance, you’ll see big bluestem and indiangrass every time you visit the tallgrass prairie of the central US, but how much of them you’ll see will go up and down. This is especially true of the less abundant species in the grassland. Some years they will be rare, and in other years there will be many more, but you will always be able to find them.
In forests, even though rainfall may not always be exactly the same every year, you can depend on them (at least relative to deserts and grasslands) to have consistently high rainfall. Because of this, you’ll find plants here that are adapted to resources that are predictably available. Long-lived species make up a large portion of these communities, and you’ll see not just the same species, but the same individuals from those species, year after year. Most trees live at least 50 years, and many live for hundreds, if not thousands of years.
This is not to say that variability does not exist in forests, or that stability does not exist in deserts (there are long-lived species in deserts too), but as you make repeated visits to deserts, you’ll easily notice how they change every year, but the forest will be far more familiar. Note also, a lot of this is just scratching the surface of the subject of stability. I’ve ignored the effects of natural and anthropogenic disturbance, and how they vary in severity and frequency, climate change, the effects of grazers and their different abundances, and a lot of other factors