In forest mensuration and tree growth curves:
Mean Annual Increment (MAI) is calculated as \(\text{MAI} = \frac{V_t}{t}\), where \(V_t\) is total standing volume at age \(t\). Since living trees always have some measurable positive biomass, MAI is never zero and can never be negative.
In contrast, Current Annual Increment (CAI) represents increment in a single year (\(V_t - V_{t-1}\)). In overmature, decadent, or diseased stands where wood rot and mortality exceed new annual growth, the net volume decreases, causing CAI to become negative.
वन क्षेत्र मापिकी (forest mensuration) में, माध्य वार्षिक वृद्धि (MAI = कुल आयतन / आयु) हमेशा धनात्मक रहती है और कभी भी शून्य या ऋणात्मक (Negative) नहीं हो सकती। जबकि चालू वार्षिक वृद्धि (CAI) पुराने व रोगग्रस्त वनों में क्षय होने पर ऋणात्मक हो सकती है।